about summary refs log tree commit diff
path: root/src
diff options
context:
space:
mode:
Diffstat (limited to 'src')
-rw-r--r--src/build-remote/build-remote.cc13
-rw-r--r--src/cpptoml/cpptoml.h569
-rw-r--r--src/libexpr/common-eval-args.cc8
-rw-r--r--src/libexpr/eval.cc23
-rw-r--r--src/libexpr/eval.hh5
-rw-r--r--src/libexpr/get-drvs.cc2
-rw-r--r--src/libexpr/get-drvs.hh2
-rw-r--r--src/libexpr/local.mk2
-rw-r--r--src/libexpr/nix-expr.pc.in2
-rw-r--r--src/libexpr/parser.y28
-rw-r--r--src/libexpr/primops.cc112
-rw-r--r--src/libexpr/primops/context.cc187
-rw-r--r--src/libexpr/primops/fetchGit.cc8
-rw-r--r--src/libexpr/primops/fetchMercurial.cc15
-rw-r--r--src/libexpr/primops/fromTOML.cc13
-rw-r--r--src/libexpr/symbol-table.hh7
-rw-r--r--src/libmain/common-args.cc9
-rw-r--r--src/libmain/local.mk2
-rw-r--r--src/libmain/nix-main.pc.in2
-rw-r--r--src/libmain/shared.cc4
-rw-r--r--src/libstore/binary-cache-store.cc18
-rw-r--r--src/libstore/binary-cache-store.hh31
-rw-r--r--src/libstore/build.cc159
-rw-r--r--src/libstore/builtins/fetchurl.cc3
-rw-r--r--src/libstore/download.cc188
-rw-r--r--src/libstore/download.hh61
-rw-r--r--src/libstore/gc.cc126
-rw-r--r--src/libstore/globals.hh2
-rw-r--r--src/libstore/http-binary-cache-store.cc58
-rw-r--r--src/libstore/legacy-ssh-store.cc37
-rw-r--r--src/libstore/local-store.cc2
-rw-r--r--src/libstore/local-store.hh8
-rw-r--r--src/libstore/local.mk2
-rw-r--r--src/libstore/machines.cc9
-rw-r--r--src/libstore/nix-store.pc.in2
-rw-r--r--src/libstore/parsed-derivations.cc4
-rw-r--r--src/libstore/parsed-derivations.hh8
-rw-r--r--src/libstore/remote-store.cc4
-rw-r--r--src/libstore/remote-store.hh4
-rw-r--r--src/libstore/s3-binary-cache-store.cc1
-rw-r--r--src/libstore/ssh.cc3
-rw-r--r--src/libstore/store-api.cc114
-rw-r--r--src/libstore/store-api.hh50
-rw-r--r--src/libutil/archive.cc2
-rw-r--r--src/libutil/hash.cc34
-rw-r--r--src/libutil/hash.hh7
-rw-r--r--src/libutil/local.mk4
-rw-r--r--src/libutil/logging.cc3
-rw-r--r--src/libutil/logging.hh1
-rw-r--r--src/libutil/lru-cache.hh4
-rw-r--r--src/libutil/retry.hh38
-rw-r--r--src/libutil/serialise.cc2
-rw-r--r--src/libutil/types.hh2
-rw-r--r--src/libutil/util.cc40
-rw-r--r--src/libutil/util.hh24
-rwxr-xr-xsrc/nix-build/nix-build.cc16
-rwxr-xr-xsrc/nix-channel/nix-channel.cc23
-rw-r--r--src/nix-daemon/nix-daemon.cc16
-rw-r--r--src/nix-store/nix-store.cc35
-rw-r--r--src/nix/add-to-store.cc2
-rw-r--r--src/nix/edit.cc5
-rw-r--r--src/nix/hash.cc23
-rw-r--r--src/nix/local.mk2
-rw-r--r--src/nix/main.cc68
-rw-r--r--src/nix/progress-bar.cc78
-rw-r--r--src/nix/progress-bar.hh2
-rw-r--r--src/nix/repl.cc61
-rw-r--r--src/nix/run.cc4
-rw-r--r--src/nlohmann/json.hpp10830
-rw-r--r--src/resolve-system-dependencies/local.mk2
70 files changed, 9738 insertions, 3497 deletions
diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index abf3669b5b35..279ae62f69cc 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -38,6 +38,12 @@ static AutoCloseFD openSlotLock(const Machine & m, unsigned long long slot)
     return openLockFile(fmt("%s/%s-%d", currentLoad, escapeUri(m.storeUri), slot), true);
 }
 
+static bool allSupportedLocally(const std::set<std::string>& requiredFeatures) {
+    for (auto & feature : requiredFeatures)
+        if (!settings.systemFeatures.get().count(feature)) return false;
+    return true;
+}
+
 static int _main(int argc, char * * argv)
 {
     {
@@ -97,9 +103,10 @@ static int _main(int argc, char * * argv)
             source >> drvPath;
             auto requiredFeatures = readStrings<std::set<std::string>>(source);
 
-            auto canBuildLocally = amWilling
-                &&  (  neededSystem == settings.thisSystem
-                    || settings.extraPlatforms.get().count(neededSystem) > 0);
+             auto canBuildLocally = amWilling
+                 &&  (  neededSystem == settings.thisSystem
+                     || settings.extraPlatforms.get().count(neededSystem) > 0)
+                 &&  allSupportedLocally(requiredFeatures);
 
             /* Error ignored here, will be caught later */
             mkdir(currentLoad.c_str(), 0777);
diff --git a/src/cpptoml/cpptoml.h b/src/cpptoml/cpptoml.h
index 07de010b1520..5a00da3b4cda 100644
--- a/src/cpptoml/cpptoml.h
+++ b/src/cpptoml/cpptoml.h
@@ -4,8 +4,8 @@
  * @date May 2013
  */
 
-#ifndef _CPPTOML_H_
-#define _CPPTOML_H_
+#ifndef CPPTOML_H
+#define CPPTOML_H
 
 #include <algorithm>
 #include <cassert>
@@ -84,11 +84,12 @@ class option
         return &value_;
     }
 
-    const T& value_or(const T& alternative) const
+    template <class U>
+    T value_or(U&& alternative) const
     {
         if (!empty_)
             return value_;
-        return alternative;
+        return static_cast<T>(std::forward<U>(alternative));
     }
 
   private:
@@ -295,13 +296,12 @@ struct valid_value_or_string_convertible
 };
 
 template <class T>
-struct value_traits<T, typename std::
-                           enable_if<valid_value_or_string_convertible<T>::
-                                         value>::type>
+struct value_traits<T, typename std::enable_if<
+                           valid_value_or_string_convertible<T>::value>::type>
 {
-    using value_type = typename std::
-        conditional<valid_value<typename std::decay<T>::type>::value,
-                    typename std::decay<T>::type, std::string>::type;
+    using value_type = typename std::conditional<
+        valid_value<typename std::decay<T>::type>::value,
+        typename std::decay<T>::type, std::string>::type;
 
     using type = value<value_type>;
 
@@ -312,12 +312,11 @@ struct value_traits<T, typename std::
 };
 
 template <class T>
-struct value_traits<T,
-                    typename std::
-                        enable_if<!valid_value_or_string_convertible<T>::value
-                                  && std::is_floating_point<
-                                         typename std::decay<T>::type>::value>::
-                            type>
+struct value_traits<
+    T,
+    typename std::enable_if<
+        !valid_value_or_string_convertible<T>::value
+        && std::is_floating_point<typename std::decay<T>::type>::value>::type>
 {
     using value_type = typename std::decay<T>::type;
 
@@ -330,11 +329,11 @@ struct value_traits<T,
 };
 
 template <class T>
-struct value_traits<T,
-                    typename std::
-                        enable_if<!valid_value_or_string_convertible<T>::value
-                                  && std::is_signed<typename std::decay<T>::
-                                                        type>::value>::type>
+struct value_traits<
+    T, typename std::enable_if<
+           !valid_value_or_string_convertible<T>::value
+           && !std::is_floating_point<typename std::decay<T>::type>::value
+           && std::is_signed<typename std::decay<T>::type>::value>::type>
 {
     using value_type = int64_t;
 
@@ -356,11 +355,10 @@ struct value_traits<T,
 };
 
 template <class T>
-struct value_traits<T,
-                    typename std::
-                        enable_if<!valid_value_or_string_convertible<T>::value
-                                  && std::is_unsigned<typename std::decay<T>::
-                                                          type>::value>::type>
+struct value_traits<
+    T, typename std::enable_if<
+           !valid_value_or_string_convertible<T>::value
+           && std::is_unsigned<typename std::decay<T>::type>::value>::type>
 {
     using value_type = int64_t;
 
@@ -395,10 +393,15 @@ struct array_of_trait<array>
 template <class T>
 inline std::shared_ptr<typename value_traits<T>::type> make_value(T&& val);
 inline std::shared_ptr<array> make_array();
+
+namespace detail
+{
 template <class T>
 inline std::shared_ptr<T> make_element();
+}
+
 inline std::shared_ptr<table> make_table();
-inline std::shared_ptr<table_array> make_table_array();
+inline std::shared_ptr<table_array> make_table_array(bool is_inline = false);
 
 #if defined(CPPTOML_NO_RTTI)
 /// Base type used to store underlying data type explicitly if RTTI is disabled
@@ -576,7 +579,7 @@ class base : public std::enable_shared_from_this<base>
 #if defined(CPPTOML_NO_RTTI)
     base_type type() const
     {
-      return type_;
+        return type_;
     }
 
   protected:
@@ -698,7 +701,7 @@ inline std::shared_ptr<value<double>> base::as()
     if (type() == base_type::INT)
     {
         auto v = std::static_pointer_cast<value<int64_t>>(shared_from_this());
-        return make_value<double>(static_cast<double>(v->get()));;
+        return make_value<double>(static_cast<double>(v->get()));
     }
 #else
     if (auto v = std::dynamic_pointer_cast<value<double>>(shared_from_this()))
@@ -731,7 +734,8 @@ inline std::shared_ptr<const value<double>> base::as() const
 {
 #if defined(CPPTOML_NO_RTTI)
     if (type() == base_type::FLOAT)
-        return std::static_pointer_cast<const value<double>>(shared_from_this());
+        return std::static_pointer_cast<const value<double>>(
+            shared_from_this());
 
     if (type() == base_type::INT)
     {
@@ -1027,11 +1031,14 @@ inline std::shared_ptr<array> make_array()
     return std::make_shared<make_shared_enabler>();
 }
 
+namespace detail
+{
 template <>
 inline std::shared_ptr<array> make_element<array>()
 {
     return make_array();
 }
+} // namespace detail
 
 /**
  * Obtains a option<vector<T>>. The option will be empty if the array
@@ -1060,7 +1067,7 @@ class table;
 class table_array : public base
 {
     friend class table;
-    friend std::shared_ptr<table_array> make_table_array();
+    friend std::shared_ptr<table_array> make_table_array(bool);
 
   public:
     std::shared_ptr<base> clone() const override;
@@ -1152,14 +1159,25 @@ class table_array : public base
         array_.reserve(n);
     }
 
+    /**
+     * Whether or not the table array is declared inline. This mostly
+     * matters for parsing, where statically defined arrays cannot be
+     * appended to using the array-of-table syntax.
+     */
+    bool is_inline() const
+    {
+        return is_inline_;
+    }
+
   private:
 #if defined(CPPTOML_NO_RTTI)
-    table_array() : base(base_type::TABLE_ARRAY)
+    table_array(bool is_inline = false)
+        : base(base_type::TABLE_ARRAY), is_inline_(is_inline)
     {
         // nothing
     }
 #else
-    table_array()
+    table_array(bool is_inline = false) : is_inline_(is_inline)
     {
         // nothing
     }
@@ -1169,26 +1187,30 @@ class table_array : public base
     table_array& operator=(const table_array& rhs) = delete;
 
     std::vector<std::shared_ptr<table>> array_;
+    const bool is_inline_ = false;
 };
 
-inline std::shared_ptr<table_array> make_table_array()
+inline std::shared_ptr<table_array> make_table_array(bool is_inline)
 {
     struct make_shared_enabler : public table_array
     {
-        make_shared_enabler()
+        make_shared_enabler(bool mse_is_inline) : table_array(mse_is_inline)
         {
             // nothing
         }
     };
 
-    return std::make_shared<make_shared_enabler>();
+    return std::make_shared<make_shared_enabler>(is_inline);
 }
 
+namespace detail
+{
 template <>
 inline std::shared_ptr<table_array> make_element<table_array>()
 {
-    return make_table_array();
+    return make_table_array(true);
 }
+} // namespace detail
 
 // The below are overloads for fetching specific value types out of a value
 // where special casting behavior (like bounds checking) is desired
@@ -1679,11 +1701,14 @@ std::shared_ptr<table> make_table()
     return std::make_shared<make_shared_enabler>();
 }
 
+namespace detail
+{
 template <>
 inline std::shared_ptr<table> make_element<table>()
 {
     return make_table();
 }
+} // namespace detail
 
 template <class T>
 std::shared_ptr<base> value<T>::clone() const
@@ -1702,7 +1727,7 @@ inline std::shared_ptr<base> array::clone() const
 
 inline std::shared_ptr<base> table_array::clone() const
 {
-    auto result = make_table_array();
+    auto result = make_table_array(is_inline());
     result->reserve(array_.size());
     for (const auto& ptr : array_)
         result->array_.push_back(ptr->clone()->as_table());
@@ -1738,6 +1763,11 @@ inline bool is_number(char c)
     return c >= '0' && c <= '9';
 }
 
+inline bool is_hex(char c)
+{
+    return is_number(c) || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');
+}
+
 /**
  * Helper object for consuming expected characters.
  */
@@ -1766,6 +1796,13 @@ class consumer
                       [&](char c) { (*this)(c); });
     }
 
+    void eat_or(char a, char b)
+    {
+        if (it_ == end_ || (*it_ != a && *it_ != b))
+            on_error_();
+        ++it_;
+    }
+
     int eat_digits(int len)
     {
         int val = 0;
@@ -1830,7 +1867,7 @@ inline std::istream& getline(std::istream& input, std::string& line)
         line.push_back(static_cast<char>(c));
     }
 }
-}
+} // namespace detail
 
 /**
  * The parser class.
@@ -1914,21 +1951,25 @@ class parser
 
         std::string full_table_name;
         bool inserted = false;
-        while (it != end && *it != ']')
-        {
-            auto part = parse_key(it, end,
-                                  [](char c) { return c == '.' || c == ']'; });
 
+        auto key_end = [](char c) { return c == ']'; };
+
+        auto key_part_handler = [&](const std::string& part) {
             if (part.empty())
                 throw_parse_exception("Empty component of table name");
 
             if (!full_table_name.empty())
-                full_table_name += ".";
+                full_table_name += '.';
             full_table_name += part;
 
             if (curr_table->contains(part))
             {
+#if !defined(__PGI)
                 auto b = curr_table->get(part);
+#else
+                // Workaround for PGI compiler
+                std::shared_ptr<base> b = curr_table->get(part);
+#endif
                 if (b->is_table())
                     curr_table = static_cast<table*>(b.get());
                 else if (b->is_table_array())
@@ -1946,16 +1987,23 @@ class parser
                 curr_table->insert(part, make_table());
                 curr_table = static_cast<table*>(curr_table->get(part).get());
             }
-            consume_whitespace(it, end);
-            if (it != end && *it == '.')
-                ++it;
-            consume_whitespace(it, end);
-        }
+        };
+
+        key_part_handler(parse_key(it, end, key_end, key_part_handler));
 
         if (it == end)
             throw_parse_exception(
                 "Unterminated table declaration; did you forget a ']'?");
 
+        if (*it != ']')
+        {
+            std::string errmsg{"Unexpected character in table definition: "};
+            errmsg += '"';
+            errmsg += *it;
+            errmsg += '"';
+            throw_parse_exception(errmsg);
+        }
+
         // table already existed
         if (!inserted)
         {
@@ -1969,8 +2017,9 @@ class parser
             // since it has already been defined. If there aren't any
             // values, then it was implicitly created by something like
             // [a.b]
-            if (curr_table->empty() || std::any_of(curr_table->begin(),
-                                                   curr_table->end(), is_value))
+            if (curr_table->empty()
+                || std::any_of(curr_table->begin(), curr_table->end(),
+                               is_value))
             {
                 throw_parse_exception("Redefinition of table "
                                       + full_table_name);
@@ -1989,36 +2038,45 @@ class parser
         if (it == end || *it == ']')
             throw_parse_exception("Table array name cannot be empty");
 
-        std::string full_ta_name;
-        while (it != end && *it != ']')
-        {
-            auto part = parse_key(it, end,
-                                  [](char c) { return c == '.' || c == ']'; });
+        auto key_end = [](char c) { return c == ']'; };
 
+        std::string full_ta_name;
+        auto key_part_handler = [&](const std::string& part) {
             if (part.empty())
                 throw_parse_exception("Empty component of table array name");
 
             if (!full_ta_name.empty())
-                full_ta_name += ".";
+                full_ta_name += '.';
             full_ta_name += part;
 
-            consume_whitespace(it, end);
-            if (it != end && *it == '.')
-                ++it;
-            consume_whitespace(it, end);
-
             if (curr_table->contains(part))
             {
+#if !defined(__PGI)
                 auto b = curr_table->get(part);
+#else
+                // Workaround for PGI compiler
+                std::shared_ptr<base> b = curr_table->get(part);
+#endif
 
                 // if this is the end of the table array name, add an
-                // element to the table array that we just looked up
+                // element to the table array that we just looked up,
+                // provided it was not declared inline
                 if (it != end && *it == ']')
                 {
                     if (!b->is_table_array())
+                    {
                         throw_parse_exception("Key " + full_ta_name
                                               + " is not a table array");
+                    }
+
                     auto v = b->as_table_array();
+
+                    if (v->is_inline())
+                    {
+                        throw_parse_exception("Static array " + full_ta_name
+                                              + " cannot be appended to");
+                    }
+
                     v->get().push_back(make_table());
                     curr_table = v->get().back().get();
                 }
@@ -2059,15 +2117,16 @@ class parser
                         = static_cast<table*>(curr_table->get(part).get());
                 }
             }
-        }
+        };
+
+        key_part_handler(parse_key(it, end, key_end, key_part_handler));
 
         // consume the last "]]"
-        if (it == end)
-            throw_parse_exception("Unterminated table array name");
-        ++it;
-        if (it == end)
+        auto eat = make_consumer(it, end, [this]() {
             throw_parse_exception("Unterminated table array name");
-        ++it;
+        });
+        eat(']');
+        eat(']');
 
         consume_whitespace(it, end);
         eol_or_comment(it, end);
@@ -2076,7 +2135,35 @@ class parser
     void parse_key_value(std::string::iterator& it, std::string::iterator& end,
                          table* curr_table)
     {
-        auto key = parse_key(it, end, [](char c) { return c == '='; });
+        auto key_end = [](char c) { return c == '='; };
+
+        auto key_part_handler = [&](const std::string& part) {
+            // two cases: this key part exists already, in which case it must
+            // be a table, or it doesn't exist in which case we must create
+            // an implicitly defined table
+            if (curr_table->contains(part))
+            {
+                auto val = curr_table->get(part);
+                if (val->is_table())
+                {
+                    curr_table = static_cast<table*>(val.get());
+                }
+                else
+                {
+                    throw_parse_exception("Key " + part
+                                          + " already exists as a value");
+                }
+            }
+            else
+            {
+                auto newtable = make_table();
+                curr_table->insert(part, newtable);
+                curr_table = newtable.get();
+            }
+        };
+
+        auto key = parse_key(it, end, key_end, key_part_handler);
+
         if (curr_table->contains(key))
             throw_parse_exception("Key " + key + " already present");
         if (it == end || *it != '=')
@@ -2087,18 +2174,57 @@ class parser
         consume_whitespace(it, end);
     }
 
-    template <class Function>
-    std::string parse_key(std::string::iterator& it,
-                          const std::string::iterator& end, Function&& fun)
+    template <class KeyEndFinder, class KeyPartHandler>
+    std::string
+    parse_key(std::string::iterator& it, const std::string::iterator& end,
+              KeyEndFinder&& key_end, KeyPartHandler&& key_part_handler)
+    {
+        // parse the key as a series of one or more simple-keys joined with '.'
+        while (it != end && !key_end(*it))
+        {
+            auto part = parse_simple_key(it, end);
+            consume_whitespace(it, end);
+
+            if (it == end || key_end(*it))
+            {
+                return part;
+            }
+
+            if (*it != '.')
+            {
+                std::string errmsg{"Unexpected character in key: "};
+                errmsg += '"';
+                errmsg += *it;
+                errmsg += '"';
+                throw_parse_exception(errmsg);
+            }
+
+            key_part_handler(part);
+
+            // consume the dot
+            ++it;
+        }
+
+        throw_parse_exception("Unexpected end of key");
+    }
+
+    std::string parse_simple_key(std::string::iterator& it,
+                                 const std::string::iterator& end)
     {
         consume_whitespace(it, end);
-        if (*it == '"')
+
+        if (it == end)
+            throw_parse_exception("Unexpected end of key (blank key?)");
+
+        if (*it == '"' || *it == '\'')
         {
-            return parse_quoted_key(it, end);
+            return string_literal(it, end, *it);
         }
         else
         {
-            auto bke = std::find_if(it, end, std::forward<Function>(fun));
+            auto bke = std::find_if(it, end, [](char c) {
+                return c == '.' || c == '=' || c == ']';
+            });
             return parse_bare_key(it, bke);
         }
     }
@@ -2142,12 +2268,6 @@ class parser
         return key;
     }
 
-    std::string parse_quoted_key(std::string::iterator& it,
-                                 const std::string::iterator& end)
-    {
-        return string_literal(it, end, '"');
-    }
-
     enum class parse_type
     {
         STRING = 1,
@@ -2193,7 +2313,7 @@ class parser
     parse_type determine_value_type(const std::string::iterator& it,
                                     const std::string::iterator& end)
     {
-        if(it == end)
+        if (it == end)
         {
             throw_parse_exception("Failed to parse value type");
         }
@@ -2209,7 +2329,11 @@ class parser
         {
             return *dtype;
         }
-        else if (is_number(*it) || *it == '-' || *it == '+')
+        else if (is_number(*it) || *it == '-' || *it == '+'
+                 || (*it == 'i' && it + 1 != end && it[1] == 'n'
+                     && it + 2 != end && it[2] == 'f')
+                 || (*it == 'n' && it + 1 != end && it[1] == 'a'
+                     && it + 2 != end && it[2] == 'n'))
         {
             return determine_number_type(it, end);
         }
@@ -2235,6 +2359,13 @@ class parser
         auto check_it = it;
         if (*check_it == '-' || *check_it == '+')
             ++check_it;
+
+        if (check_it == end)
+            throw_parse_exception("Malformed number");
+
+        if (*check_it == 'i' || *check_it == 'n')
+            return parse_type::FLOAT;
+
         while (check_it != end && is_number(*check_it))
             ++check_it;
         if (check_it != end && *check_it == '.')
@@ -2283,57 +2414,56 @@ class parser
         bool consuming = false;
         std::shared_ptr<value<std::string>> ret;
 
-        auto handle_line
-            = [&](std::string::iterator& local_it,
-                  std::string::iterator& local_end) {
-                  if (consuming)
-                  {
-                      local_it = std::find_if_not(local_it, local_end, is_ws);
-
-                      // whole line is whitespace
-                      if (local_it == local_end)
-                          return;
-                  }
-
-                  consuming = false;
-
-                  while (local_it != local_end)
-                  {
-                      // handle escaped characters
-                      if (delim == '"' && *local_it == '\\')
-                      {
-                          auto check = local_it;
-                          // check if this is an actual escape sequence or a
-                          // whitespace escaping backslash
-                          ++check;
-                          consume_whitespace(check, local_end);
-                          if (check == local_end)
-                          {
-                              consuming = true;
-                              break;
-                          }
-
-                          ss << parse_escape_code(local_it, local_end);
-                          continue;
-                      }
-
-                      // if we can end the string
-                      if (std::distance(local_it, local_end) >= 3)
-                      {
-                          auto check = local_it;
-                          // check for """
-                          if (*check++ == delim && *check++ == delim
-                              && *check++ == delim)
-                          {
-                              local_it = check;
-                              ret = make_value<std::string>(ss.str());
-                              break;
-                          }
-                      }
-
-                      ss << *local_it++;
-                  }
-              };
+        auto handle_line = [&](std::string::iterator& local_it,
+                               std::string::iterator& local_end) {
+            if (consuming)
+            {
+                local_it = std::find_if_not(local_it, local_end, is_ws);
+
+                // whole line is whitespace
+                if (local_it == local_end)
+                    return;
+            }
+
+            consuming = false;
+
+            while (local_it != local_end)
+            {
+                // handle escaped characters
+                if (delim == '"' && *local_it == '\\')
+                {
+                    auto check = local_it;
+                    // check if this is an actual escape sequence or a
+                    // whitespace escaping backslash
+                    ++check;
+                    consume_whitespace(check, local_end);
+                    if (check == local_end)
+                    {
+                        consuming = true;
+                        break;
+                    }
+
+                    ss << parse_escape_code(local_it, local_end);
+                    continue;
+                }
+
+                // if we can end the string
+                if (std::distance(local_it, local_end) >= 3)
+                {
+                    auto check = local_it;
+                    // check for """
+                    if (*check++ == delim && *check++ == delim
+                        && *check++ == delim)
+                    {
+                        local_it = check;
+                        ret = make_value<std::string>(ss.str());
+                        break;
+                    }
+                }
+
+                ss << *local_it++;
+            }
+        };
 
         // handle the remainder of the current line
         handle_line(it, end);
@@ -2514,17 +2644,13 @@ class parser
         return value;
     }
 
-    bool is_hex(char c)
-    {
-        return is_number(c) || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');
-    }
-
     uint32_t hex_to_digit(char c)
     {
         if (is_number(c))
             return static_cast<uint32_t>(c - '0');
-        return 10 + static_cast<uint32_t>(
-                        c - ((c >= 'a' && c <= 'f') ? 'a' : 'A'));
+        return 10
+               + static_cast<uint32_t>(c
+                                       - ((c >= 'a' && c <= 'f') ? 'a' : 'A'));
     }
 
     std::shared_ptr<base> parse_number(std::string::iterator& it,
@@ -2538,17 +2664,23 @@ class parser
                 ++check_it;
         };
 
-        eat_sign();
+        auto check_no_leading_zero = [&]() {
+            if (check_it != end && *check_it == '0' && check_it + 1 != check_end
+                && check_it[1] != '.')
+            {
+                throw_parse_exception("Numbers may not have leading zeros");
+            }
+        };
 
-        auto eat_numbers = [&]() {
+        auto eat_digits = [&](bool (*check_char)(char)) {
             auto beg = check_it;
-            while (check_it != end && is_number(*check_it))
+            while (check_it != end && check_char(*check_it))
             {
                 ++check_it;
                 if (check_it != end && *check_it == '_')
                 {
                     ++check_it;
-                    if (check_it == end || !is_number(*check_it))
+                    if (check_it == end || !check_char(*check_it))
                         throw_parse_exception("Malformed number");
                 }
             }
@@ -2557,15 +2689,63 @@ class parser
                 throw_parse_exception("Malformed number");
         };
 
-        auto check_no_leading_zero = [&]() {
-            if (check_it != end && *check_it == '0' && check_it + 1 != check_end
-                && check_it[1] != '.')
+        auto eat_hex = [&]() { eat_digits(&is_hex); };
+
+        auto eat_numbers = [&]() { eat_digits(&is_number); };
+
+        if (check_it != end && *check_it == '0' && check_it + 1 != check_end
+            && (check_it[1] == 'x' || check_it[1] == 'o' || check_it[1] == 'b'))
+        {
+            ++check_it;
+            char base = *check_it;
+            ++check_it;
+            if (base == 'x')
             {
-                throw_parse_exception("Numbers may not have leading zeros");
+                eat_hex();
+                return parse_int(it, check_it, 16);
             }
-        };
+            else if (base == 'o')
+            {
+                auto start = check_it;
+                eat_numbers();
+                auto val = parse_int(start, check_it, 8, "0");
+                it = start;
+                return val;
+            }
+            else // if (base == 'b')
+            {
+                auto start = check_it;
+                eat_numbers();
+                auto val = parse_int(start, check_it, 2);
+                it = start;
+                return val;
+            }
+        }
 
+        eat_sign();
         check_no_leading_zero();
+
+        if (check_it != end && check_it + 1 != end && check_it + 2 != end)
+        {
+            if (check_it[0] == 'i' && check_it[1] == 'n' && check_it[2] == 'f')
+            {
+                auto val = std::numeric_limits<double>::infinity();
+                if (*it == '-')
+                    val = -val;
+                it = check_it + 3;
+                return make_value(val);
+            }
+            else if (check_it[0] == 'n' && check_it[1] == 'a'
+                     && check_it[2] == 'n')
+            {
+                auto val = std::numeric_limits<double>::quiet_NaN();
+                if (*it == '-')
+                    val = -val;
+                it = check_it + 3;
+                return make_value(val);
+            }
+        }
+
         eat_numbers();
 
         if (check_it != end
@@ -2604,14 +2784,17 @@ class parser
     }
 
     std::shared_ptr<value<int64_t>> parse_int(std::string::iterator& it,
-                                              const std::string::iterator& end)
+                                              const std::string::iterator& end,
+                                              int base = 10,
+                                              const char* prefix = "")
     {
         std::string v{it, end};
+        v = prefix + v;
         v.erase(std::remove(v.begin(), v.end(), '_'), v.end());
         it = end;
         try
         {
-            return make_value<int64_t>(std::stoll(v));
+            return make_value<int64_t>(std::stoll(v, nullptr, base));
         }
         catch (const std::invalid_argument& ex)
         {
@@ -2674,18 +2857,33 @@ class parser
     std::string::iterator find_end_of_number(std::string::iterator it,
                                              std::string::iterator end)
     {
-        return std::find_if(it, end, [](char c) {
+        auto ret = std::find_if(it, end, [](char c) {
             return !is_number(c) && c != '_' && c != '.' && c != 'e' && c != 'E'
-                   && c != '-' && c != '+';
+                   && c != '-' && c != '+' && c != 'x' && c != 'o' && c != 'b';
         });
+        if (ret != end && ret + 1 != end && ret + 2 != end)
+        {
+            if ((ret[0] == 'i' && ret[1] == 'n' && ret[2] == 'f')
+                || (ret[0] == 'n' && ret[1] == 'a' && ret[2] == 'n'))
+            {
+                ret = ret + 3;
+            }
+        }
+        return ret;
     }
 
     std::string::iterator find_end_of_date(std::string::iterator it,
                                            std::string::iterator end)
     {
-        return std::find_if(it, end, [](char c) {
-            return !is_number(c) && c != 'T' && c != 'Z' && c != ':' && c != '-'
-                   && c != '+' && c != '.';
+        auto end_of_date = std::find_if(it, end, [](char c) {
+            return !is_number(c) && c != '-';
+        });
+        if (end_of_date != end && *end_of_date == ' ' && end_of_date + 1 != end
+            && is_number(end_of_date[1]))
+            end_of_date++;
+        return std::find_if(end_of_date, end, [](char c) {
+            return !is_number(c) && c != 'T' && c != 'Z' && c != ':'
+                   && c != '-' && c != '+' && c != '.';
         });
     }
 
@@ -2754,7 +2952,7 @@ class parser
         if (it == date_end)
             return make_value(ldate);
 
-        eat('T');
+        eat.eat_or('T', ' ');
 
         local_datetime ldt;
         static_cast<local_date&>(ldt) = ldate;
@@ -2850,9 +3048,9 @@ class parser
         auto arr = make_array();
         while (it != end && *it != ']')
         {
-            auto value = parse_value(it, end);
-            if (auto v = value->as<Value>())
-                arr->get().push_back(value);
+            auto val = parse_value(it, end);
+            if (auto v = val->as<Value>())
+                arr->get().push_back(val);
             else
                 throw_parse_exception("Arrays must be homogeneous");
             skip_whitespace_and_comments(it, end);
@@ -2871,7 +3069,7 @@ class parser
                                                std::string::iterator& it,
                                                std::string::iterator& end)
     {
-        auto arr = make_element<Object>();
+        auto arr = detail::make_element<Object>();
 
         while (it != end && *it != ']')
         {
@@ -2881,7 +3079,7 @@ class parser
             arr->get().push_back(((*this).*fun)(it, end));
             skip_whitespace_and_comments(it, end);
 
-            if (*it != ',')
+            if (it == end || *it != ',')
                 break;
 
             ++it;
@@ -2906,8 +3104,11 @@ class parser
                 throw_parse_exception("Unterminated inline table");
 
             consume_whitespace(it, end);
-            parse_key_value(it, end, tbl.get());
-            consume_whitespace(it, end);
+            if (it != end && *it != '}')
+            {
+                parse_key_value(it, end, tbl.get());
+                consume_whitespace(it, end);
+            }
         } while (*it == ',');
 
         if (it == end || *it != '}')
@@ -2987,7 +3188,8 @@ class parser
         if (it[4] != '-' || it[7] != '-')
             return {};
 
-        if (len >= 19 && it[10] == 'T' && is_time(it + 11, date_end))
+        if (len >= 19 && (it[10] == 'T' || it[10] == ' ')
+            && is_time(it + 11, date_end))
         {
             // datetime type
             auto time_end = find_end_of_time(it + 11, date_end);
@@ -3243,7 +3445,7 @@ class toml_writer
             {
                 res += "\\\\";
             }
-            else if ((const uint32_t)*it <= 0x001f)
+            else if (static_cast<uint32_t>(*it) <= UINT32_C(0x001f))
             {
                 res += "\\u";
                 std::stringstream ss;
@@ -3274,12 +3476,21 @@ class toml_writer
      */
     void write(const value<double>& v)
     {
-        std::ios::fmtflags flags{stream_.flags()};
-
-        stream_ << std::showpoint;
-        write(v.get());
-
-        stream_.flags(flags);
+        std::stringstream ss;
+        ss << std::showpoint
+           << std::setprecision(std::numeric_limits<double>::max_digits10)
+           << v.get();
+
+        auto double_str = ss.str();
+        auto pos = double_str.find("e0");
+        if (pos != std::string::npos)
+            double_str.replace(pos, 2, "e");
+        pos = double_str.find("e-0");
+        if (pos != std::string::npos)
+            double_str.replace(pos, 3, "e-");
+
+        stream_ << double_str;
+        has_naked_endline_ = false;
     }
 
     /**
@@ -3287,9 +3498,9 @@ class toml_writer
      * offset_datetime.
      */
     template <class T>
-    typename std::enable_if<is_one_of<T, int64_t, local_date, local_time,
-                                      local_datetime,
-                                      offset_datetime>::value>::type
+    typename std::enable_if<
+        is_one_of<T, int64_t, local_date, local_time, local_datetime,
+                  offset_datetime>::value>::type
     write(const value<T>& v)
     {
         write(v.get());
@@ -3453,5 +3664,5 @@ inline std::ostream& operator<<(std::ostream& stream, const array& a)
     a.accept(writer);
     return stream;
 }
-}
-#endif
+} // namespace cpptoml
+#endif // CPPTOML_H
diff --git a/src/libexpr/common-eval-args.cc b/src/libexpr/common-eval-args.cc
index 3e0c78f280f7..13950ab8d169 100644
--- a/src/libexpr/common-eval-args.cc
+++ b/src/libexpr/common-eval-args.cc
@@ -45,9 +45,11 @@ Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
 
 Path lookupFileArg(EvalState & state, string s)
 {
-    if (isUri(s))
-        return getDownloader()->downloadCached(state.store, s, true);
-    else if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
+    if (isUri(s)) {
+        CachedDownloadRequest request(s);
+        request.unpack = true;
+        return getDownloader()->downloadCached(state.store, request).path;
+    } else if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
         Path p = s.substr(1, s.size() - 2);
         return state.findFile(p);
     } else
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index ab407e56907c..d8e10d9f20e1 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -130,6 +130,16 @@ std::ostream & operator << (std::ostream & str, const Value & v)
 }
 
 
+const Value *getPrimOp(const Value &v) {
+    const Value * primOp = &v;
+    while (primOp->type == tPrimOpApp) {
+        primOp = primOp->primOpApp.left;
+    }
+    assert(primOp->type == tPrimOp);
+    return primOp;
+}
+
+
 string showType(const Value & v)
 {
     switch (v.type) {
@@ -144,8 +154,10 @@ string showType(const Value & v)
         case tApp: return "a function application";
         case tLambda: return "a function";
         case tBlackhole: return "a black hole";
-        case tPrimOp: return "a built-in function";
-        case tPrimOpApp: return "a partially applied built-in function";
+        case tPrimOp:
+            return fmt("the built-in function '%s'", string(v.primOp->name));
+        case tPrimOpApp:
+            return fmt("the partially applied built-in function '%s'", string(getPrimOp(v)->primOp->name));
         case tExternal: return v.external->showType();
         case tFloat: return "a float";
     }
@@ -757,6 +769,7 @@ void EvalState::evalFile(const Path & path_, Value & v)
 void EvalState::resetFileCache()
 {
     fileEvalCache.clear();
+    fileParseCache.clear();
 }
 
 
@@ -1798,6 +1811,7 @@ void EvalState::printStats()
             gc.attr("totalBytes", totalBytes);
         }
 #endif
+
         if (countCalls) {
             {
                 auto obj = topObj.object("primops");
@@ -1833,6 +1847,11 @@ void EvalState::printStats()
                 }
             }
         }
+
+        if (getEnv("NIX_SHOW_SYMBOLS", "0") != "0") {
+            auto list = topObj.list("symbols");
+            symbols.dump([&](const std::string & s) { list.elem(s); });
+        }
     }
 }
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index d0f298e168e9..a314e01e0a71 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -81,7 +81,7 @@ public:
 
     /* The allowed filesystem paths in restricted or pure evaluation
        mode. */
-    std::experimental::optional<PathSet> allowedPaths;
+    std::optional<PathSet> allowedPaths;
 
     Value vEmptySet;
 
@@ -316,6 +316,9 @@ private:
 /* Return a string representing the type of the value `v'. */
 string showType(const Value & v);
 
+/* Decode a context string โ€˜!<name>!<path>โ€™ into a pair <path,
+   name>. */
+std::pair<string, string> decodeContext(const string & s);
 
 /* If `path' refers to a directory, then append "/default.nix". */
 Path resolveExprPath(Path path);
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index d38ed2df3b18..21a4d7917fce 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -295,7 +295,7 @@ static bool getDerivation(EvalState & state, Value & v,
 }
 
 
-std::experimental::optional<DrvInfo> getDerivation(EvalState & state, Value & v,
+std::optional<DrvInfo> getDerivation(EvalState & state, Value & v,
     bool ignoreAssertionFailures)
 {
     Done done;
diff --git a/src/libexpr/get-drvs.hh b/src/libexpr/get-drvs.hh
index daaa635fe1b1..d7860fc6a4bc 100644
--- a/src/libexpr/get-drvs.hh
+++ b/src/libexpr/get-drvs.hh
@@ -78,7 +78,7 @@ typedef list<DrvInfo> DrvInfos;
 
 /* If value `v' denotes a derivation, return a DrvInfo object
    describing it. Otherwise return nothing. */
-std::experimental::optional<DrvInfo> getDerivation(EvalState & state,
+std::optional<DrvInfo> getDerivation(EvalState & state,
     Value & v, bool ignoreAssertionFailures);
 
 void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index daa3258f0d3c..ccd5293e4e5e 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -6,7 +6,7 @@ libexpr_DIR := $(d)
 
 libexpr_SOURCES := $(wildcard $(d)/*.cc) $(wildcard $(d)/primops/*.cc) $(d)/lexer-tab.cc $(d)/parser-tab.cc
 
-libexpr_LIBS = libutil libstore libformat
+libexpr_LIBS = libutil libstore
 
 libexpr_LDFLAGS =
 ifneq ($(OS), FreeBSD)
diff --git a/src/libexpr/nix-expr.pc.in b/src/libexpr/nix-expr.pc.in
index 79f3e2f4506e..80f7a492b1a1 100644
--- a/src/libexpr/nix-expr.pc.in
+++ b/src/libexpr/nix-expr.pc.in
@@ -7,4 +7,4 @@ Description: Nix Package Manager
 Version: @PACKAGE_VERSION@
 Requires: nix-store bdw-gc
 Libs: -L${libdir} -lnixexpr
-Cflags: -I${includedir}/nix -std=c++14
+Cflags: -I${includedir}/nix -std=c++17
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index cbd576d7d126..967c88d9bc80 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -1,7 +1,7 @@
 %glr-parser
 %pure-parser
 %locations
-%error-verbose
+%define parse.error verbose
 %defines
 /* %no-lines */
 %parse-param { void * scanner }
@@ -81,6 +81,8 @@ static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
     AttrPath::iterator i;
     // All attrpaths have at least one attr
     assert(!attrPath.empty());
+    // Checking attrPath validity.
+    // ===========================
     for (i = attrPath.begin(); i + 1 < attrPath.end(); i++) {
         if (i->symbol.set()) {
             ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
@@ -102,11 +104,29 @@ static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
             attrs = nested;
         }
     }
+    // Expr insertion.
+    // ==========================
     if (i->symbol.set()) {
         ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
         if (j != attrs->attrs.end()) {
-            dupAttr(attrPath, pos, j->second.pos);
+            // This attr path is already defined. However, if both
+            // e and the expr pointed by the attr path are two attribute sets,
+            // we want to merge them.
+            // Otherwise, throw an error.
+            auto ae = dynamic_cast<ExprAttrs *>(e);
+            auto jAttrs = dynamic_cast<ExprAttrs *>(j->second.e);
+            if (jAttrs && ae) {
+                for (auto & ad : ae->attrs) {
+                    auto j2 = jAttrs->attrs.find(ad.first);
+                    if (j2 != jAttrs->attrs.end()) // Attr already defined in iAttrs, error.
+                        dupAttr(ad.first, j2->second.pos, ad.second.pos);
+                    jAttrs->attrs[ad.first] = ad.second;
+                }
+            } else {
+                dupAttr(attrPath, pos, j->second.pos);
+            }
         } else {
+            // This attr path is not defined. Let's create it.
             attrs->attrs[i->symbol] = ExprAttrs::AttrDef(e, pos);
             e->setName(i->symbol);
         }
@@ -657,7 +677,9 @@ std::pair<bool, std::string> EvalState::resolveSearchPathElem(const SearchPathEl
 
     if (isUri(elem.second)) {
         try {
-            res = { true, getDownloader()->downloadCached(store, elem.second, true) };
+            CachedDownloadRequest request(elem.second);
+            request.unpack = true;
+            res = { true, getDownloader()->downloadCached(store, request).path };
         } catch (DownloadError & e) {
             printError(format("warning: Nix search path entry '%1%' cannot be downloaded, ignoring") % elem.second);
             res = { false, "" };
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 7372134e2c9b..070e72f3a966 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -315,6 +315,12 @@ static void prim_isBool(EvalState & state, const Pos & pos, Value * * args, Valu
     mkBool(v, args[0]->type == tBool);
 }
 
+/* Determine whether the argument is a path. */
+static void prim_isPath(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tPath);
+}
 
 struct CompareValues
 {
@@ -555,7 +561,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
 
     PathSet context;
 
-    std::experimental::optional<std::string> outputHash;
+    std::optional<std::string> outputHash;
     std::string outputHashAlgo;
     bool outputHashRecursive = false;
 
@@ -687,21 +693,12 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             }
         }
 
-        /* See prim_unsafeDiscardOutputDependency. */
-        else if (path.at(0) == '~')
-            drv.inputSrcs.insert(string(path, 1));
-
         /* Handle derivation outputs of the form โ€˜!<name>!<path>โ€™. */
         else if (path.at(0) == '!') {
             std::pair<string, string> ctx = decodeContext(path);
             drv.inputDrvs[ctx.first].insert(ctx.second);
         }
 
-        /* Handle derivation contexts returned by
-           โ€˜builtins.storePathโ€™. */
-        else if (isDerivation(path))
-            drv.inputDrvs[path] = state.store->queryDerivationOutputNames(path);
-
         /* Otherwise it's a source file. */
         else
             drv.inputSrcs.insert(path);
@@ -724,16 +721,14 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         if (outputs.size() != 1 || *(outputs.begin()) != "out")
             throw Error(format("multiple outputs are not supported in fixed-output derivations, at %1%") % posDrvName);
 
-        HashType ht = parseHashType(outputHashAlgo);
-        if (ht == htUnknown)
-            throw EvalError(format("unknown hash algorithm '%1%', at %2%") % outputHashAlgo % posDrvName);
+        HashType ht = outputHashAlgo.empty() ? htUnknown : parseHashType(outputHashAlgo);
         Hash h(*outputHash, ht);
-        outputHash = h.to_string(Base16, false);
-        if (outputHashRecursive) outputHashAlgo = "r:" + outputHashAlgo;
 
         Path outPath = state.store->makeFixedOutputPath(outputHashRecursive, h, drvName);
         if (!jsonObject) drv.env["out"] = outPath;
-        drv.outputs["out"] = DerivationOutput(outPath, outputHashAlgo, *outputHash);
+        drv.outputs["out"] = DerivationOutput(outPath,
+            (outputHashRecursive ? "r:" : "") + printHashType(h.type),
+            h.to_string(Base16, false));
     }
 
     else {
@@ -928,6 +923,20 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
     mkPath(v, state.checkSourcePath(state.findFile(searchPath, path, pos)).c_str());
 }
 
+/* Return the cryptographic hash of a file in base-16. */
+static void prim_hashFile(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    string type = state.forceStringNoCtx(*args[0], pos);
+    HashType ht = parseHashType(type);
+    if (ht == htUnknown)
+      throw Error(format("unknown hash type '%1%', at %2%") % type % pos);
+
+    PathSet context; // discarded
+    Path p = state.coerceToPath(pos, *args[1], context);
+
+    mkString(v, hashFile(ht, state.checkSourcePath(p)).to_string(Base16, false), context);
+}
+
 /* Read a directory (without . or ..) */
 static void prim_readDir(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
@@ -1006,13 +1015,8 @@ static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Valu
     PathSet refs;
 
     for (auto path : context) {
-        if (path.at(0) == '=') path = string(path, 1);
-        if (isDerivation(path)) {
-            /* See prim_unsafeDiscardOutputDependency. */
-            if (path.at(0) != '~')
-                throw EvalError(format("in 'toFile': the file '%1%' cannot refer to derivation outputs, at %2%") % name % pos);
-            path = string(path, 1);
-        }
+        if (path.at(0) != '/')
+            throw EvalError(format("in 'toFile': the file '%1%' cannot refer to derivation outputs, at %2%") % name % pos);
         refs.insert(path);
     }
 
@@ -1796,41 +1800,6 @@ static void prim_stringLength(EvalState & state, const Pos & pos, Value * * args
 }
 
 
-static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
-{
-    PathSet context;
-    string s = state.coerceToString(pos, *args[0], context);
-    mkString(v, s, PathSet());
-}
-
-
-static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
-{
-    PathSet context;
-    state.forceString(*args[0], context, pos);
-    mkBool(v, !context.empty());
-}
-
-
-/* Sometimes we want to pass a derivation path (i.e. pkg.drvPath) to a
-   builder without causing the derivation to be built (for instance,
-   in the derivation that builds NARs in nix-push, when doing
-   source-only deployment).  This primop marks the string context so
-   that builtins.derivation adds the path to drv.inputSrcs rather than
-   drv.inputDrvs. */
-static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & pos, Value * * args, Value & v)
-{
-    PathSet context;
-    string s = state.coerceToString(pos, *args[0], context);
-
-    PathSet context2;
-    for (auto & p : context)
-        context2.insert(p.at(0) == '=' ? "~" + string(p, 1) : p);
-
-    mkString(v, s, context2);
-}
-
-
 /* Return the cryptographic hash of a string in base-16. */
 static void prim_hashString(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
@@ -2081,9 +2050,9 @@ static void prim_splitVersion(EvalState & state, const Pos & pos, Value * * args
 void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
     const string & who, bool unpack, const std::string & defaultName)
 {
-    string url;
-    Hash expectedHash;
-    string name = defaultName;
+    CachedDownloadRequest request("");
+    request.unpack = unpack;
+    request.name = defaultName;
 
     state.forceValue(*args[0]);
 
@@ -2094,27 +2063,27 @@ void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
         for (auto & attr : *args[0]->attrs) {
             string n(attr.name);
             if (n == "url")
-                url = state.forceStringNoCtx(*attr.value, *attr.pos);
+                request.uri = state.forceStringNoCtx(*attr.value, *attr.pos);
             else if (n == "sha256")
-                expectedHash = Hash(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA256);
+                request.expectedHash = Hash(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA256);
             else if (n == "name")
-                name = state.forceStringNoCtx(*attr.value, *attr.pos);
+                request.name = state.forceStringNoCtx(*attr.value, *attr.pos);
             else
                 throw EvalError(format("unsupported argument '%1%' to '%2%', at %3%") % attr.name % who % attr.pos);
         }
 
-        if (url.empty())
+        if (request.uri.empty())
             throw EvalError(format("'url' argument required, at %1%") % pos);
 
     } else
-        url = state.forceStringNoCtx(*args[0], pos);
+        request.uri = state.forceStringNoCtx(*args[0], pos);
 
-    state.checkURI(url);
+    state.checkURI(request.uri);
 
-    if (evalSettings.pureEval && !expectedHash)
+    if (evalSettings.pureEval && !request.expectedHash)
         throw Error("in pure evaluation mode, '%s' requires a 'sha256' argument", who);
 
-    Path res = getDownloader()->downloadCached(state.store, url, unpack, name, expectedHash);
+    Path res = getDownloader()->downloadCached(state.store, request).path;
 
     if (state.allowedPaths)
         state.allowedPaths->insert(res);
@@ -2220,6 +2189,7 @@ void EvalState::createBaseEnv()
     addPrimOp("__isInt", 1, prim_isInt);
     addPrimOp("__isFloat", 1, prim_isFloat);
     addPrimOp("__isBool", 1, prim_isBool);
+    addPrimOp("__isPath", 1, prim_isPath);
     addPrimOp("__genericClosure", 1, prim_genericClosure);
     addPrimOp("abort", 1, prim_abort);
     addPrimOp("__addErrorContext", 2, prim_addErrorContext);
@@ -2246,6 +2216,7 @@ void EvalState::createBaseEnv()
     addPrimOp("__readFile", 1, prim_readFile);
     addPrimOp("__readDir", 1, prim_readDir);
     addPrimOp("__findFile", 2, prim_findFile);
+    addPrimOp("__hashFile", 2, prim_hashFile);
 
     // Creating files
     addPrimOp("__toXML", 1, prim_toXML);
@@ -2301,9 +2272,6 @@ void EvalState::createBaseEnv()
     addPrimOp("toString", 1, prim_toString);
     addPrimOp("__substring", 3, prim_substring);
     addPrimOp("__stringLength", 1, prim_stringLength);
-    addPrimOp("__hasContext", 1, prim_hasContext);
-    addPrimOp("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
-    addPrimOp("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
     addPrimOp("__hashString", 2, prim_hashString);
     addPrimOp("__match", 2, prim_match);
     addPrimOp("__split", 2, prim_split);
diff --git a/src/libexpr/primops/context.cc b/src/libexpr/primops/context.cc
new file mode 100644
index 000000000000..2d79739ea047
--- /dev/null
+++ b/src/libexpr/primops/context.cc
@@ -0,0 +1,187 @@
+#include "primops.hh"
+#include "eval-inline.hh"
+#include "derivations.hh"
+
+namespace nix {
+
+static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    string s = state.coerceToString(pos, *args[0], context);
+    mkString(v, s, PathSet());
+}
+
+static RegisterPrimOp r1("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
+
+
+static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    state.forceString(*args[0], context, pos);
+    mkBool(v, !context.empty());
+}
+
+static RegisterPrimOp r2("__hasContext", 1, prim_hasContext);
+
+
+/* Sometimes we want to pass a derivation path (i.e. pkg.drvPath) to a
+   builder without causing the derivation to be built (for instance,
+   in the derivation that builds NARs in nix-push, when doing
+   source-only deployment).  This primop marks the string context so
+   that builtins.derivation adds the path to drv.inputSrcs rather than
+   drv.inputDrvs. */
+static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    string s = state.coerceToString(pos, *args[0], context);
+
+    PathSet context2;
+    for (auto & p : context)
+        context2.insert(p.at(0) == '=' ? string(p, 1) : p);
+
+    mkString(v, s, context2);
+}
+
+static RegisterPrimOp r3("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
+
+
+/* Extract the context of a string as a structured Nix value.
+
+   The context is represented as an attribute set whose keys are the
+   paths in the context set and whose values are attribute sets with
+   the following keys:
+     path: True if the relevant path is in the context as a plain store
+           path (i.e. the kind of context you get when interpolating
+           a Nix path (e.g. ./.) into a string). False if missing.
+     allOutputs: True if the relevant path is a derivation and it is
+                  in the context as a drv file with all of its outputs
+                  (i.e. the kind of context you get when referencing
+                  .drvPath of some derivation). False if missing.
+     outputs: If a non-empty list, the relevant path is a derivation
+              and the provided outputs are referenced in the context
+              (i.e. the kind of context you get when referencing
+              .outPath of some derivation). Empty list if missing.
+   Note that for a given path any combination of the above attributes
+   may be present.
+*/
+static void prim_getContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    struct ContextInfo {
+        bool path = false;
+        bool allOutputs = false;
+        Strings outputs;
+    };
+    PathSet context;
+    state.forceString(*args[0], context, pos);
+    auto contextInfos = std::map<Path, ContextInfo>();
+    for (const auto & p : context) {
+        Path drv;
+        string output;
+        const Path * path = &p;
+        if (p.at(0) == '=') {
+            drv = string(p, 1);
+            path = &drv;
+        } else if (p.at(0) == '!') {
+            std::pair<string, string> ctx = decodeContext(p);
+            drv = ctx.first;
+            output = ctx.second;
+            path = &drv;
+        }
+        auto isPath = drv.empty();
+        auto isAllOutputs = (!drv.empty()) && output.empty();
+
+        auto iter = contextInfos.find(*path);
+        if (iter == contextInfos.end()) {
+            contextInfos.emplace(*path, ContextInfo{isPath, isAllOutputs, output.empty() ? Strings{} : Strings{std::move(output)}});
+        } else {
+            if (isPath)
+                iter->second.path = true;
+            else if (isAllOutputs)
+                iter->second.allOutputs = true;
+            else
+                iter->second.outputs.emplace_back(std::move(output));
+        }
+    }
+
+    state.mkAttrs(v, contextInfos.size());
+
+    auto sPath = state.symbols.create("path");
+    auto sAllOutputs = state.symbols.create("allOutputs");
+    for (const auto & info : contextInfos) {
+        auto & infoVal = *state.allocAttr(v, state.symbols.create(info.first));
+        state.mkAttrs(infoVal, 3);
+        if (info.second.path)
+            mkBool(*state.allocAttr(infoVal, sPath), true);
+        if (info.second.allOutputs)
+            mkBool(*state.allocAttr(infoVal, sAllOutputs), true);
+        if (!info.second.outputs.empty()) {
+            auto & outputsVal = *state.allocAttr(infoVal, state.sOutputs);
+            state.mkList(outputsVal, info.second.outputs.size());
+            size_t i = 0;
+            for (const auto & output : info.second.outputs) {
+                mkString(*(outputsVal.listElems()[i++] = state.allocValue()), output);
+            }
+        }
+        infoVal.attrs->sort();
+    }
+    v.attrs->sort();
+}
+
+static RegisterPrimOp r4("__getContext", 1, prim_getContext);
+
+
+/* Append the given context to a given string.
+
+   See the commentary above unsafeGetContext for details of the
+   context representation.
+*/
+static void prim_appendContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    auto orig = state.forceString(*args[0], context, pos);
+
+    state.forceAttrs(*args[1], pos);
+
+    auto sPath = state.symbols.create("path");
+    auto sAllOutputs = state.symbols.create("allOutputs");
+    for (auto & i : *args[1]->attrs) {
+        if (!state.store->isStorePath(i.name))
+            throw EvalError("Context key '%s' is not a store path, at %s", i.name, i.pos);
+        if (!settings.readOnlyMode)
+            state.store->ensurePath(i.name);
+        state.forceAttrs(*i.value, *i.pos);
+        auto iter = i.value->attrs->find(sPath);
+        if (iter != i.value->attrs->end()) {
+            if (state.forceBool(*iter->value, *iter->pos))
+                context.insert(i.name);
+        }
+
+        iter = i.value->attrs->find(sAllOutputs);
+        if (iter != i.value->attrs->end()) {
+            if (state.forceBool(*iter->value, *iter->pos)) {
+                if (!isDerivation(i.name)) {
+                    throw EvalError("Tried to add all-outputs context of %s, which is not a derivation, to a string, at %s", i.name, i.pos);
+                }
+                context.insert("=" + string(i.name));
+            }
+        }
+
+        iter = i.value->attrs->find(state.sOutputs);
+        if (iter != i.value->attrs->end()) {
+            state.forceList(*iter->value, *iter->pos);
+            if (iter->value->listSize() && !isDerivation(i.name)) {
+                throw EvalError("Tried to add derivation output context of %s, which is not a derivation, to a string, at %s", i.name, i.pos);
+            }
+            for (unsigned int n = 0; n < iter->value->listSize(); ++n) {
+                auto name = state.forceStringNoCtx(*iter->value->listElems()[n], *iter->pos);
+                context.insert("!" + name + "!" + string(i.name));
+            }
+        }
+    }
+
+    mkString(v, orig, context);
+}
+
+static RegisterPrimOp r5("__appendContext", 2, prim_appendContext);
+
+}
diff --git a/src/libexpr/primops/fetchGit.cc b/src/libexpr/primops/fetchGit.cc
index 588b0fa4d53b..6229fef8d02e 100644
--- a/src/libexpr/primops/fetchGit.cc
+++ b/src/libexpr/primops/fetchGit.cc
@@ -26,7 +26,7 @@ struct GitInfo
 std::regex revRegex("^[0-9a-fA-F]{40}$");
 
 GitInfo exportGit(ref<Store> store, const std::string & uri,
-    std::experimental::optional<std::string> ref, std::string rev,
+    std::optional<std::string> ref, std::string rev,
     const std::string & name)
 {
     if (evalSettings.pureEval && rev == "")
@@ -120,7 +120,7 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
            git fetch to update the local ref to the remote ref. */
         struct stat st;
         doFetch = stat(localRefFile.c_str(), &st) != 0 ||
-            st.st_mtime + settings.tarballTtl <= now;
+            (uint64_t) st.st_mtime + settings.tarballTtl <= (uint64_t) now;
     }
     if (doFetch)
     {
@@ -194,7 +194,7 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
 static void prim_fetchGit(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     std::string url;
-    std::experimental::optional<std::string> ref;
+    std::optional<std::string> ref;
     std::string rev;
     std::string name = "source";
     PathSet context;
@@ -239,7 +239,7 @@ static void prim_fetchGit(EvalState & state, const Pos & pos, Value * * args, Va
     v.attrs->sort();
 
     if (state.allowedPaths)
-        state.allowedPaths->insert(gitInfo.storePath);
+        state.allowedPaths->insert(state.store->toRealPath(gitInfo.storePath));
 }
 
 static RegisterPrimOp r("fetchGit", 1, prim_fetchGit);
diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index 66f49f374321..a907d0e1cd82 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -80,7 +80,7 @@ HgInfo exportMercurial(ref<Store> store, const std::string & uri,
     time_t now = time(0);
     struct stat st;
     if (stat(stampFile.c_str(), &st) != 0 ||
-        st.st_mtime + settings.tarballTtl <= now)
+        (uint64_t) st.st_mtime + settings.tarballTtl <= (uint64_t) now)
     {
         /* Except that if this is a commit hash that we already have,
            we don't have to pull again. */
@@ -96,17 +96,14 @@ HgInfo exportMercurial(ref<Store> store, const std::string & uri,
                 try {
                     runProgram("hg", true, { "pull", "-R", cacheDir, "--", uri });
                 }
-                catch (ExecError & e){
+                catch (ExecError & e) {
                     string transJournal = cacheDir + "/.hg/store/journal";
                     /* hg throws "abandoned transaction" error only if this file exists */
-                    if (pathExists(transJournal))
-                    {
+                    if (pathExists(transJournal)) {
                         runProgram("hg", true, { "recover", "-R", cacheDir });
                         runProgram("hg", true, { "pull", "-R", cacheDir, "--", uri });
-                    }
-                    else 
-                    {
-                        throw ExecError(e.status, fmt("program hg '%1%' ", statusToString(e.status)));
+                    } else {
+                        throw ExecError(e.status, fmt("'hg pull' %s", statusToString(e.status)));
                     }
                 }
             } else {
@@ -214,7 +211,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
     v.attrs->sort();
 
     if (state.allowedPaths)
-        state.allowedPaths->insert(hgInfo.storePath);
+        state.allowedPaths->insert(state.store->toRealPath(hgInfo.storePath));
 }
 
 static RegisterPrimOp r("fetchMercurial", 1, prim_fetchMercurial);
diff --git a/src/libexpr/primops/fromTOML.cc b/src/libexpr/primops/fromTOML.cc
index 4128de05d0cf..a84e569e944d 100644
--- a/src/libexpr/primops/fromTOML.cc
+++ b/src/libexpr/primops/fromTOML.cc
@@ -49,6 +49,19 @@ static void prim_fromTOML(EvalState & state, const Pos & pos, Value * * args, Va
                 visit(*(v.listElems()[i] = state.allocValue()), t2->get()[i]);
         }
 
+        // Handle cases like 'a = [[{ a = true }]]', which IMHO should be
+        // parsed as a array containing an array containing a table,
+        // but instead are parsed as an array containing a table array
+        // containing a table.
+        else if (auto t2 = t->as_table_array()) {
+            size_t size = t2->get().size();
+
+            state.mkList(v, size);
+
+            for (size_t j = 0; j < size; ++j)
+                visit(*(v.listElems()[j] = state.allocValue()), t2->get()[j]);
+        }
+
         else if (t->is_value()) {
             if (auto val = t->as<int64_t>())
                 mkInt(v, val->get());
diff --git a/src/libexpr/symbol-table.hh b/src/libexpr/symbol-table.hh
index 44929f7eea06..91faea122ce1 100644
--- a/src/libexpr/symbol-table.hh
+++ b/src/libexpr/symbol-table.hh
@@ -75,6 +75,13 @@ public:
     }
 
     size_t totalSize() const;
+
+    template<typename T>
+    void dump(T callback)
+    {
+        for (auto & s : symbols)
+            callback(s);
+    }
 };
 
 }
diff --git a/src/libmain/common-args.cc b/src/libmain/common-args.cc
index 4c35a4199590..9e1d7cee60e6 100644
--- a/src/libmain/common-args.cc
+++ b/src/libmain/common-args.cc
@@ -35,6 +35,15 @@ MixCommonArgs::MixCommonArgs(const string & programName)
             }
         });
 
+    mkFlag()
+        .longName("max-jobs")
+        .shortName('j')
+        .label("jobs")
+        .description("maximum number of parallel builds")
+        .handler([=](std::string s) {
+            settings.set("max-jobs", s);
+        });
+
     std::string cat = "config";
     globalConfig.convertToArgs(*this, cat);
 
diff --git a/src/libmain/local.mk b/src/libmain/local.mk
index f1fd3eb72424..0c80f5a0a037 100644
--- a/src/libmain/local.mk
+++ b/src/libmain/local.mk
@@ -8,7 +8,7 @@ libmain_SOURCES := $(wildcard $(d)/*.cc)
 
 libmain_LDFLAGS = $(OPENSSL_LIBS)
 
-libmain_LIBS = libstore libutil libformat
+libmain_LIBS = libstore libutil
 
 libmain_ALLOW_UNDEFINED = 1
 
diff --git a/src/libmain/nix-main.pc.in b/src/libmain/nix-main.pc.in
index 38bc85c484eb..37b03dcd42c0 100644
--- a/src/libmain/nix-main.pc.in
+++ b/src/libmain/nix-main.pc.in
@@ -6,4 +6,4 @@ Name: Nix
 Description: Nix Package Manager
 Version: @PACKAGE_VERSION@
 Libs: -L${libdir} -lnixmain
-Cflags: -I${includedir}/nix -std=c++14
+Cflags: -I${includedir}/nix -std=c++17
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 4ed34e54dc55..cd752f4678a0 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -175,10 +175,6 @@ LegacyArgs::LegacyArgs(const std::string & programName,
         .description("build from source if substitution fails")
         .set(&(bool&) settings.tryFallback, true);
 
-    mkFlag1('j', "max-jobs", "jobs", "maximum number of parallel builds", [=](std::string s) {
-        settings.set("max-jobs", s);
-    });
-
     auto intSettingAlias = [&](char shortName, const std::string & longName,
         const std::string & description, const std::string & dest) {
         mkFlag<unsigned int>(shortName, longName, description, [=](unsigned int n) {
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 4527ee6ba660..8b736056e01d 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -10,6 +10,8 @@
 #include "nar-info-disk-cache.hh"
 #include "nar-accessor.hh"
 #include "json.hh"
+#include "retry.hh"
+#include "download.hh"
 
 #include <chrono>
 
@@ -79,13 +81,15 @@ void BinaryCacheStore::getFile(const std::string & path, Sink & sink)
 
 std::shared_ptr<std::string> BinaryCacheStore::getFile(const std::string & path)
 {
-    StringSink sink;
-    try {
-        getFile(path, sink);
-    } catch (NoSuchBinaryCacheFile &) {
-        return nullptr;
-    }
-    return sink.s;
+    return retry<std::shared_ptr<std::string>>(downloadSettings.tries, [&]() -> std::shared_ptr<std::string> {
+        StringSink sink;
+        try {
+            getFile(path, sink);
+        } catch (NoSuchBinaryCacheFile &) {
+            return nullptr;
+        }
+        return sink.s;
+    });
 }
 
 Path BinaryCacheStore::narInfoFileFor(const Path & storePath)
diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index 6bc83fc50ca1..953f3b90af46 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -72,24 +72,11 @@ public:
 
     bool isValidPathUncached(const Path & path) override;
 
-    PathSet queryAllValidPaths() override
-    { unsupported(); }
-
     void queryPathInfoUncached(const Path & path,
         Callback<std::shared_ptr<ValidPathInfo>> callback) override;
 
-    void queryReferrers(const Path & path,
-        PathSet & referrers) override
-    { unsupported(); }
-
-    PathSet queryDerivationOutputs(const Path & path) override
-    { unsupported(); }
-
-    StringSet queryDerivationOutputNames(const Path & path) override
-    { unsupported(); }
-
     Path queryPathFromHashPart(const string & hashPart) override
-    { unsupported(); }
+    { unsupported("queryPathFromHashPart"); }
 
     bool wantMassQuery() override { return wantMassQuery_; }
 
@@ -108,22 +95,10 @@ public:
 
     BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override
-    { unsupported(); }
+    { unsupported("buildDerivation"); }
 
     void ensurePath(const Path & path) override
-    { unsupported(); }
-
-    void addTempRoot(const Path & path) override
-    { unsupported(); }
-
-    void addIndirectRoot(const Path & path) override
-    { unsupported(); }
-
-    Roots findRoots() override
-    { unsupported(); }
-
-    void collectGarbage(const GCOptions & options, GCResults & results) override
-    { unsupported(); }
+    { unsupported("ensurePath"); }
 
     ref<FSAccessor> getFSAccessor() override;
 
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 59abae9b90db..5b38bcf3c5ec 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -12,6 +12,7 @@
 #include "json.hh"
 #include "nar-info.hh"
 #include "parsed-derivations.hh"
+#include "machines.hh"
 
 #include <algorithm>
 #include <iostream>
@@ -37,6 +38,7 @@
 #include <unistd.h>
 #include <errno.h>
 #include <cstring>
+#include <termios.h>
 
 #include <pwd.h>
 #include <grp.h>
@@ -460,6 +462,28 @@ static void commonChildInit(Pipe & logPipe)
     close(fdDevNull);
 }
 
+void handleDiffHook(uid_t uid, uid_t gid, Path tryA, Path tryB, Path drvPath, Path tmpDir)
+{
+    auto diffHook = settings.diffHook;
+    if (diffHook != "" && settings.runDiffHook) {
+        try {
+            RunOptions diffHookOptions(diffHook,{tryA, tryB, drvPath, tmpDir});
+            diffHookOptions.searchPath = true;
+            diffHookOptions.uid = uid;
+            diffHookOptions.gid = gid;
+            diffHookOptions.chdir = "/";
+
+            auto diffRes = runProgram(diffHookOptions);
+            if (!statusOk(diffRes.first))
+                throw ExecError(diffRes.first, fmt("diff-hook program '%1%' %2%", diffHook, statusToString(diffRes.first)));
+
+            if (diffRes.second != "")
+                printError(chomp(diffRes.second));
+        } catch (Error & error) {
+            printError("diff hook execution failed: %s", error.what());
+        }
+    }
+}
 
 //////////////////////////////////////////////////////////////////////
 
@@ -881,6 +905,9 @@ public:
         Worker & worker, BuildMode buildMode = bmNormal);
     ~DerivationGoal();
 
+    /* Whether we need to perform hash rewriting if there are valid output paths. */
+    bool needsHashRewrite();
+
     void timedOut() override;
 
     string key() override
@@ -1033,6 +1060,17 @@ DerivationGoal::~DerivationGoal()
 }
 
 
+inline bool DerivationGoal::needsHashRewrite()
+{
+#if __linux__
+    return !useChroot;
+#else
+    /* Darwin requires hash rewriting even when sandboxing is enabled. */
+    return true;
+#endif
+}
+
+
 void DerivationGoal::killChild()
 {
     if (pid != -1) {
@@ -1521,8 +1559,8 @@ void DerivationGoal::buildDone()
     if (hook) {
         hook->builderOut.readSide = -1;
         hook->fromHook.readSide = -1;
-    }
-    else builderOut.readSide = -1;
+    } else
+        builderOut.readSide = -1;
 
     /* Close the log file. */
     closeLogFile();
@@ -2072,7 +2110,7 @@ void DerivationGoal::startBuilder()
 #endif
     }
 
-    else {
+    if (needsHashRewrite()) {
 
         if (pathExists(homeDir))
             throw Error(format("directory '%1%' exists; please remove it") % homeDir);
@@ -2144,7 +2182,48 @@ void DerivationGoal::startBuilder()
     Path logFile = openLogFile();
 
     /* Create a pipe to get the output of the builder. */
-    builderOut.create();
+    //builderOut.create();
+
+    builderOut.readSide = posix_openpt(O_RDWR | O_NOCTTY);
+    if (!builderOut.readSide)
+        throw SysError("opening pseudoterminal master");
+
+    std::string slaveName(ptsname(builderOut.readSide.get()));
+
+    if (buildUser) {
+        if (chmod(slaveName.c_str(), 0600))
+            throw SysError("changing mode of pseudoterminal slave");
+
+        if (chown(slaveName.c_str(), buildUser->getUID(), 0))
+            throw SysError("changing owner of pseudoterminal slave");
+    } else {
+        if (grantpt(builderOut.readSide.get()))
+            throw SysError("granting access to pseudoterminal slave");
+    }
+
+    #if 0
+    // Mount the pt in the sandbox so that the "tty" command works.
+    // FIXME: this doesn't work with the new devpts in the sandbox.
+    if (useChroot)
+        dirsInChroot[slaveName] = {slaveName, false};
+    #endif
+
+    if (unlockpt(builderOut.readSide.get()))
+        throw SysError("unlocking pseudoterminal");
+
+    builderOut.writeSide = open(slaveName.c_str(), O_RDWR | O_NOCTTY);
+    if (!builderOut.writeSide)
+        throw SysError("opening pseudoterminal slave");
+
+    // Put the pt into raw mode to prevent \n -> \r\n translation.
+    struct termios term;
+    if (tcgetattr(builderOut.writeSide.get(), &term))
+        throw SysError("getting pseudoterminal attributes");
+
+    cfmakeraw(&term);
+
+    if (tcsetattr(builderOut.writeSide.get(), TCSANOW, &term))
+        throw SysError("putting pseudoterminal into raw mode");
 
     result.startTime = time(0);
 
@@ -2193,7 +2272,6 @@ void DerivationGoal::startBuilder()
         userNamespaceSync.create();
 
         options.allowVfork = false;
-        options.restoreMountNamespace = false;
 
         Pid helper = startProcess([&]() {
 
@@ -2260,7 +2338,6 @@ void DerivationGoal::startBuilder()
 #endif
     {
         options.allowVfork = !buildUser && !drv->isBuiltin();
-        options.restoreMountNamespace = false;
         pid = startProcess([&]() {
             runChild();
         }, options);
@@ -2371,6 +2448,9 @@ void DerivationGoal::initEnv()
        may change that in the future. So tell the builder which file
        descriptor to use for that. */
     env["NIX_LOG_FD"] = "2";
+
+    /* Trigger colored output in various tools. */
+    env["TERM"] = "xterm-256color";
 }
 
 
@@ -2415,7 +2495,7 @@ void DerivationGoal::writeStructuredAttrs()
        objects consisting entirely of those values. (So nested
        arrays or objects are not supported.) */
 
-    auto handleSimpleType = [](const nlohmann::json & value) -> std::experimental::optional<std::string> {
+    auto handleSimpleType = [](const nlohmann::json & value) -> std::optional<std::string> {
         if (value.is_string())
             return shellEscape(value);
 
@@ -2501,17 +2581,17 @@ void setupSeccomp()
         seccomp_release(ctx);
     });
 
-    if (settings.thisSystem == "x86_64-linux" &&
+    if (nativeSystem == "x86_64-linux" &&
         seccomp_arch_add(ctx, SCMP_ARCH_X86) != 0)
         throw SysError("unable to add 32-bit seccomp architecture");
 
-    if (settings.thisSystem == "x86_64-linux" &&
+    if (nativeSystem == "x86_64-linux" &&
         seccomp_arch_add(ctx, SCMP_ARCH_X32) != 0)
         throw SysError("unable to add X32 seccomp architecture");
 
-    if (settings.thisSystem == "aarch64-linux" &&
+    if (nativeSystem == "aarch64-linux" &&
         seccomp_arch_add(ctx, SCMP_ARCH_ARM) != 0)
-        printError("unsable to add ARM seccomp architecture; this may result in spurious build failures if running 32-bit ARM processes.");
+        printError("unable to add ARM seccomp architecture; this may result in spurious build failures if running 32-bit ARM processes");
 
     /* Prevent builders from creating setuid/setgid binaries. */
     for (int perm : { S_ISUID, S_ISGID }) {
@@ -2874,6 +2954,10 @@ void DerivationGoal::runChild()
                 for (auto & i : missingPaths) {
                     sandboxProfile += (format("\t(subpath \"%1%\")\n") % i.c_str()).str();
                 }
+                /* Also add redirected outputs to the chroot */
+                for (auto & i : redirectedOutputs) {
+                    sandboxProfile += (format("\t(subpath \"%1%\")\n") % i.second.c_str()).str();
+                }
                 sandboxProfile += ")\n";
 
                 /* Our inputs (transitive dependencies and any impurities computed above)
@@ -3026,8 +3110,7 @@ void DerivationGoal::registerOutputs()
     InodesSeen inodesSeen;
 
     Path checkSuffix = ".check";
-    bool runDiffHook = settings.runDiffHook;
-    bool keepPreviousRound = settings.keepFailed || runDiffHook;
+    bool keepPreviousRound = settings.keepFailed || settings.runDiffHook;
 
     std::exception_ptr delayedException;
 
@@ -3052,7 +3135,9 @@ void DerivationGoal::registerOutputs()
                         throw SysError(format("moving build output '%1%' from the sandbox to the Nix store") % path);
             }
             if (buildMode != bmCheck) actualPath = worker.store.toRealPath(path);
-        } else {
+        }
+
+        if (needsHashRewrite()) {
             Path redirected = redirectedOutputs[path];
             if (buildMode == bmRepair
                 && redirectedBadOutputs.find(path) != redirectedBadOutputs.end()
@@ -3170,11 +3255,17 @@ void DerivationGoal::registerOutputs()
             if (!worker.store.isValidPath(path)) continue;
             auto info = *worker.store.queryPathInfo(path);
             if (hash.first != info.narHash) {
-                if (settings.keepFailed) {
+                if (settings.runDiffHook || settings.keepFailed) {
                     Path dst = worker.store.toRealPath(path + checkSuffix);
                     deletePath(dst);
                     if (rename(actualPath.c_str(), dst.c_str()))
                         throw SysError(format("renaming '%1%' to '%2%'") % actualPath % dst);
+
+                    handleDiffHook(
+                        buildUser ? buildUser->getUID() : getuid(),
+                        buildUser ? buildUser->getGID() : getgid(),
+                        path, dst, drvPath, tmpDir);
+
                     throw Error(format("derivation '%1%' may not be deterministic: output '%2%' differs from '%3%'")
                         % drvPath % path % dst);
                 } else
@@ -3239,16 +3330,10 @@ void DerivationGoal::registerOutputs()
                     ? fmt("output '%1%' of '%2%' differs from '%3%' from previous round", i->second.path, drvPath, prev)
                     : fmt("output '%1%' of '%2%' differs from previous round", i->second.path, drvPath);
 
-                auto diffHook = settings.diffHook;
-                if (prevExists && diffHook != "" && runDiffHook) {
-                    try {
-                        auto diff = runProgram(diffHook, true, {prev, i->second.path});
-                        if (diff != "")
-                            printError(chomp(diff));
-                    } catch (Error & error) {
-                        printError("diff hook execution failed: %s", error.what());
-                    }
-                }
+                handleDiffHook(
+                    buildUser ? buildUser->getUID() : getuid(),
+                    buildUser ? buildUser->getGID() : getgid(),
+                    prev, i->second.path, drvPath, tmpDir);
 
                 if (settings.enforceDeterminism)
                     throw NotDeterministic(msg);
@@ -3313,8 +3398,8 @@ void DerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & outputs)
         struct Checks
         {
             bool ignoreSelfRefs = false;
-            std::experimental::optional<uint64_t> maxSize, maxClosureSize;
-            std::experimental::optional<Strings> allowedReferences, allowedRequisites, disallowedReferences, disallowedRequisites;
+            std::optional<uint64_t> maxSize, maxClosureSize;
+            std::optional<Strings> allowedReferences, allowedRequisites, disallowedReferences, disallowedRequisites;
         };
 
         /* Compute the closure and closure size of some output. This
@@ -3361,7 +3446,7 @@ void DerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & outputs)
                         info.path, closureSize, *checks.maxClosureSize);
             }
 
-            auto checkRefs = [&](const std::experimental::optional<Strings> & value, bool allowed, bool recursive)
+            auto checkRefs = [&](const std::optional<Strings> & value, bool allowed, bool recursive)
             {
                 if (!value) return;
 
@@ -3415,7 +3500,7 @@ void DerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & outputs)
                     if (maxClosureSize != output->end())
                         checks.maxClosureSize = maxClosureSize->get<uint64_t>();
 
-                    auto get = [&](const std::string & name) -> std::experimental::optional<Strings> {
+                    auto get = [&](const std::string & name) -> std::optional<Strings> {
                         auto i = output->find(name);
                         if (i != output->end()) {
                             Strings res;
@@ -4321,14 +4406,15 @@ void Worker::waitForInput()
         for (auto & k : fds2) {
             if (FD_ISSET(k, &fds)) {
                 ssize_t rd = read(k, buffer.data(), buffer.size());
-                if (rd == -1) {
-                    if (errno != EINTR)
-                        throw SysError(format("reading from %1%")
-                            % goal->getName());
-                } else if (rd == 0) {
+                // FIXME: is there a cleaner way to handle pt close
+                // than EIO? Is this even standard?
+                if (rd == 0 || (rd == -1 && errno == EIO)) {
                     debug(format("%1%: got EOF") % goal->getName());
                     goal->handleEOF(k);
                     j->fds.erase(k);
+                } else if (rd == -1) {
+                    if (errno != EINTR)
+                        throw SysError("%s: read failed", goal->getName());
                 } else {
                     printMsg(lvlVomit, format("%1%: read %2% bytes")
                         % goal->getName() % rd);
@@ -4413,6 +4499,11 @@ static void primeCache(Store & store, const PathSet & paths)
     PathSet willBuild, willSubstitute, unknown;
     unsigned long long downloadSize, narSize;
     store.queryMissing(paths, willBuild, willSubstitute, unknown, downloadSize, narSize);
+
+    if (!willBuild.empty() && 0 == settings.maxBuildJobs && getMachines().empty())
+        throw Error(
+            "%d derivations need to be built, but neither local builds ('--max-jobs') "
+            "nor remote builds ('--builders') are enabled", willBuild.size());
 }
 
 
diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc
index 92aec63a0379..b1af3b4fc316 100644
--- a/src/libstore/builtins/fetchurl.cc
+++ b/src/libstore/builtins/fetchurl.cc
@@ -64,7 +64,8 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
             try {
                 if (!hasSuffix(hashedMirror, "/")) hashedMirror += '/';
                 auto ht = parseHashType(getAttr("outputHashAlgo"));
-                fetch(hashedMirror + printHashType(ht) + "/" + Hash(getAttr("outputHash"), ht).to_string(Base16, false));
+                auto h = Hash(getAttr("outputHash"), ht);
+                fetch(hashedMirror + printHashType(h.type) + "/" + h.to_string(Base16, false));
                 return;
             } catch (Error & e) {
                 debug(e.what());
diff --git a/src/libstore/download.cc b/src/libstore/download.cc
index 467f570bbf05..0c5a73ea3c51 100644
--- a/src/libstore/download.cc
+++ b/src/libstore/download.cc
@@ -8,6 +8,7 @@
 #include "compression.hh"
 #include "pathlocks.hh"
 #include "finally.hh"
+#include "retry.hh"
 
 #ifdef ENABLE_S3
 #include <aws/core/client/ClientConfiguration.h>
@@ -19,34 +20,16 @@
 #include <curl/curl.h>
 
 #include <algorithm>
-#include <cmath>
 #include <cstring>
 #include <iostream>
 #include <queue>
-#include <random>
 #include <thread>
 
 using namespace std::string_literals;
 
 namespace nix {
 
-struct DownloadSettings : Config
-{
-    Setting<bool> enableHttp2{this, true, "http2",
-        "Whether to enable HTTP/2 support."};
-
-    Setting<std::string> userAgentSuffix{this, "", "user-agent-suffix",
-        "String appended to the user agent in HTTP requests."};
-
-    Setting<size_t> httpConnections{this, 25, "http-connections",
-        "Number of parallel HTTP connections.",
-        {"binary-caches-parallel-connections"}};
-
-    Setting<unsigned long> connectTimeout{this, 0, "connect-timeout",
-        "Timeout for connecting to servers during downloads. 0 means use curl's builtin default."};
-};
-
-static DownloadSettings downloadSettings;
+DownloadSettings downloadSettings;
 
 static GlobalConfig::Register r1(&downloadSettings);
 
@@ -62,9 +45,6 @@ struct CurlDownloader : public Downloader
 {
     CURLM * curlm = 0;
 
-    std::random_device rd;
-    std::mt19937 mt19937;
-
     struct DownloadItem : public std::enable_shared_from_this<DownloadItem>
     {
         CurlDownloader & downloader;
@@ -77,12 +57,6 @@ struct CurlDownloader : public Downloader
         bool active = false; // whether the handle has been added to the multi object
         std::string status;
 
-        unsigned int attempt = 0;
-
-        /* Don't start this download until the specified time point
-           has been reached. */
-        std::chrono::steady_clock::time_point embargo;
-
         struct curl_slist * requestHeaders = 0;
 
         std::string encoding;
@@ -270,6 +244,8 @@ struct CurlDownloader : public Downloader
             #if LIBCURL_VERSION_NUM >= 0x072f00
             if (downloadSettings.enableHttp2)
                 curl_easy_setopt(req, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
+            else
+                curl_easy_setopt(req, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
             #endif
             curl_easy_setopt(req, CURLOPT_WRITEFUNCTION, DownloadItem::writeCallbackWrapper);
             curl_easy_setopt(req, CURLOPT_WRITEDATA, this);
@@ -319,16 +295,21 @@ struct CurlDownloader : public Downloader
             long httpStatus = 0;
             curl_easy_getinfo(req, CURLINFO_RESPONSE_CODE, &httpStatus);
 
-            char * effectiveUrlCStr;
-            curl_easy_getinfo(req, CURLINFO_EFFECTIVE_URL, &effectiveUrlCStr);
-            if (effectiveUrlCStr)
-                result.effectiveUrl = effectiveUrlCStr;
+            char * effectiveUriCStr;
+            curl_easy_getinfo(req, CURLINFO_EFFECTIVE_URL, &effectiveUriCStr);
+            if (effectiveUriCStr)
+                result.effectiveUri = effectiveUriCStr;
 
             debug("finished %s of '%s'; curl status = %d, HTTP status = %d, body = %d bytes",
                 request.verb(), request.uri, code, httpStatus, result.bodySize);
 
-            if (decompressionSink)
-                decompressionSink->finish();
+            if (decompressionSink) {
+                try {
+                    decompressionSink->finish();
+                } catch (...) {
+                    writeException = std::current_exception();
+                }
+            }
 
             if (code == CURLE_WRITE_ERROR && result.etag == request.expectedETag) {
                 code = CURLE_OK;
@@ -396,9 +377,7 @@ struct CurlDownloader : public Downloader
                     }
                 }
 
-                attempt++;
-
-                auto exc =
+                fail(
                     code == CURLE_ABORTED_BY_CALLBACK && _isInterrupted
                     ? DownloadError(Interrupted, fmt("%s of '%s' was interrupted", request.verb(), request.uri))
                     : httpStatus != 0
@@ -409,31 +388,15 @@ struct CurlDownloader : public Downloader
                         )
                     : DownloadError(err,
                         fmt("unable to %s '%s': %s (%d)",
-                            request.verb(), request.uri, curl_easy_strerror(code), code));
-
-                /* If this is a transient error, then maybe retry the
-                   download after a while. */
-                if (err == Transient && attempt < request.tries) {
-                    int ms = request.baseRetryTimeMs * std::pow(2.0f, attempt - 1 + std::uniform_real_distribution<>(0.0, 0.5)(downloader.mt19937));
-                    printError(format("warning: %s; retrying in %d ms") % exc.what() % ms);
-                    embargo = std::chrono::steady_clock::now() + std::chrono::milliseconds(ms);
-                    downloader.enqueueItem(shared_from_this());
-                }
-                else
-                    fail(exc);
+                            request.verb(), request.uri, curl_easy_strerror(code), code)));
             }
         }
     };
 
     struct State
     {
-        struct EmbargoComparator {
-            bool operator() (const std::shared_ptr<DownloadItem> & i1, const std::shared_ptr<DownloadItem> & i2) {
-                return i1->embargo > i2->embargo;
-            }
-        };
         bool quit = false;
-        std::priority_queue<std::shared_ptr<DownloadItem>, std::vector<std::shared_ptr<DownloadItem>>, EmbargoComparator> incoming;
+        std::vector<std::shared_ptr<DownloadItem>> incoming;
     };
 
     Sync<State> state_;
@@ -446,7 +409,6 @@ struct CurlDownloader : public Downloader
     std::thread workerThread;
 
     CurlDownloader()
-        : mt19937(rd())
     {
         static std::once_flag globalInit;
         std::call_once(globalInit, curl_global_init, CURL_GLOBAL_ALL);
@@ -540,9 +502,7 @@ struct CurlDownloader : public Downloader
 
             nextWakeup = std::chrono::steady_clock::time_point();
 
-            /* Add new curl requests from the incoming requests queue,
-               except for requests that are embargoed (waiting for a
-               retry timeout to expire). */
+            /* Add new curl requests from the incoming requests queue. */
             if (extraFDs[0].revents & CURL_WAIT_POLLIN) {
                 char buf[1024];
                 auto res = read(extraFDs[0].fd, buf, sizeof(buf));
@@ -551,22 +511,9 @@ struct CurlDownloader : public Downloader
             }
 
             std::vector<std::shared_ptr<DownloadItem>> incoming;
-            auto now = std::chrono::steady_clock::now();
-
             {
                 auto state(state_.lock());
-                while (!state->incoming.empty()) {
-                    auto item = state->incoming.top();
-                    if (item->embargo <= now) {
-                        incoming.push_back(item);
-                        state->incoming.pop();
-                    } else {
-                        if (nextWakeup == std::chrono::steady_clock::time_point()
-                            || item->embargo < nextWakeup)
-                            nextWakeup = item->embargo;
-                        break;
-                    }
-                }
+                std::swap(state->incoming, incoming);
                 quit = state->quit;
             }
 
@@ -593,7 +540,7 @@ struct CurlDownloader : public Downloader
 
         {
             auto state(state_.lock());
-            while (!state->incoming.empty()) state->incoming.pop();
+            state->incoming.clear();
             state->quit = true;
         }
     }
@@ -609,11 +556,27 @@ struct CurlDownloader : public Downloader
             auto state(state_.lock());
             if (state->quit)
                 throw nix::Error("cannot enqueue download request because the download thread is shutting down");
-            state->incoming.push(item);
+            state->incoming.push_back(item);
         }
         writeFull(wakeupPipe.writeSide.get(), " ");
     }
 
+#ifdef ENABLE_S3
+    std::tuple<std::string, std::string, Store::Params> parseS3Uri(std::string uri)
+    {
+        auto [path, params] = splitUriAndParams(uri);
+
+        auto slash = path.find('/', 5); // 5 is the length of "s3://" prefix
+            if (slash == std::string::npos)
+                throw nix::Error("bad S3 URI '%s'", path);
+
+        std::string bucketName(path, 5, slash - 5);
+        std::string key(path, slash + 1);
+
+        return {bucketName, key, params};
+    }
+#endif
+
     void enqueueDownload(const DownloadRequest & request,
         Callback<DownloadResult> callback) override
     {
@@ -622,12 +585,15 @@ struct CurlDownloader : public Downloader
             // FIXME: do this on a worker thread
             try {
 #ifdef ENABLE_S3
-                S3Helper s3Helper("", Aws::Region::US_EAST_1, "", ""); // FIXME: make configurable
-                auto slash = request.uri.find('/', 5);
-                if (slash == std::string::npos)
-                    throw nix::Error("bad S3 URI '%s'", request.uri);
-                std::string bucketName(request.uri, 5, slash - 5);
-                std::string key(request.uri, slash + 1);
+                auto [bucketName, key, params] = parseS3Uri(request.uri);
+
+                std::string profile = get(params, "profile", "");
+                std::string region = get(params, "region", Aws::Region::US_EAST_1);
+                std::string scheme = get(params, "scheme", "");
+                std::string endpoint = get(params, "endpoint", "");
+
+                S3Helper s3Helper(profile, region, scheme, endpoint);
+
                 // FIXME: implement ETag
                 auto s3Res = s3Helper.getObject(bucketName, key);
                 DownloadResult res;
@@ -673,7 +639,9 @@ std::future<DownloadResult> Downloader::enqueueDownload(const DownloadRequest &
 
 DownloadResult Downloader::download(const DownloadRequest & request)
 {
-    return enqueueDownload(request).get();
+    return retry<DownloadResult>(request.tries, [&]() {
+        return enqueueDownload(request).get();
+    });
 }
 
 void Downloader::download(DownloadRequest && request, Sink & sink)
@@ -771,20 +739,26 @@ void Downloader::download(DownloadRequest && request, Sink & sink)
     }
 }
 
-Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpack, string name, const Hash & expectedHash, string * effectiveUrl, int ttl)
+CachedDownloadResult Downloader::downloadCached(
+    ref<Store> store, const CachedDownloadRequest & request)
 {
-    auto url = resolveUri(url_);
+    auto url = resolveUri(request.uri);
 
+    auto name = request.name;
     if (name == "") {
         auto p = url.rfind('/');
         if (p != string::npos) name = string(url, p + 1);
     }
 
     Path expectedStorePath;
-    if (expectedHash) {
-        expectedStorePath = store->makeFixedOutputPath(unpack, expectedHash, name);
-        if (store->isValidPath(expectedStorePath))
-            return store->toRealPath(expectedStorePath);
+    if (request.expectedHash) {
+        expectedStorePath = store->makeFixedOutputPath(request.unpack, request.expectedHash, name);
+        if (store->isValidPath(expectedStorePath)) {
+            CachedDownloadResult result;
+            result.storePath = expectedStorePath;
+            result.path = store->toRealPath(expectedStorePath);
+            return result;
+        }
     }
 
     Path cacheDir = getCacheDir() + "/nix/tarballs";
@@ -803,6 +777,8 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
 
     bool skip = false;
 
+    CachedDownloadResult result;
+
     if (pathExists(fileLink) && pathExists(dataFile)) {
         storePath = readLink(fileLink);
         store->addTempRoot(storePath);
@@ -810,10 +786,10 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
             auto ss = tokenizeString<vector<string>>(readFile(dataFile), "\n");
             if (ss.size() >= 3 && ss[0] == url) {
                 time_t lastChecked;
-                if (string2Int(ss[2], lastChecked) && lastChecked + ttl >= time(0)) {
+                if (string2Int(ss[2], lastChecked) && (uint64_t) lastChecked + request.ttl >= (uint64_t) time(0)) {
                     skip = true;
-                    if (effectiveUrl)
-                        *effectiveUrl = url_;
+                    result.effectiveUri = request.uri;
+                    result.etag = ss[1];
                 } else if (!ss[1].empty()) {
                     debug(format("verifying previous ETag '%1%'") % ss[1]);
                     expectedETag = ss[1];
@@ -826,17 +802,17 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
     if (!skip) {
 
         try {
-            DownloadRequest request(url);
-            request.expectedETag = expectedETag;
-            auto res = download(request);
-            if (effectiveUrl)
-                *effectiveUrl = res.effectiveUrl;
+            DownloadRequest request2(url);
+            request2.expectedETag = expectedETag;
+            auto res = download(request2);
+            result.effectiveUri = res.effectiveUri;
+            result.etag = res.etag;
 
             if (!res.cached) {
                 ValidPathInfo info;
                 StringSink sink;
                 dumpString(*res.data, sink);
-                Hash hash = hashString(expectedHash ? expectedHash.type : htSHA256, *res.data);
+                Hash hash = hashString(request.expectedHash ? request.expectedHash.type : htSHA256, *res.data);
                 info.path = store->makeFixedOutputPath(false, hash, name);
                 info.narHash = hashString(htSHA256, *sink.s);
                 info.narSize = sink.s->size();
@@ -851,11 +827,12 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
             writeFile(dataFile, url + "\n" + res.etag + "\n" + std::to_string(time(0)) + "\n");
         } catch (DownloadError & e) {
             if (storePath.empty()) throw;
-            printError(format("warning: %1%; using cached result") % e.msg());
+            warn("%s; using cached result", e.msg());
+            result.etag = expectedETag;
         }
     }
 
-    if (unpack) {
+    if (request.unpack) {
         Path unpackedLink = cacheDir + "/" + baseNameOf(storePath) + "-unpacked";
         PathLocks lock2({unpackedLink}, fmt("waiting for lock on '%1%'...", unpackedLink));
         Path unpackedStorePath;
@@ -878,14 +855,16 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
     }
 
     if (expectedStorePath != "" && storePath != expectedStorePath) {
-        Hash gotHash = unpack
-            ? hashPath(expectedHash.type, store->toRealPath(storePath)).first
-            : hashFile(expectedHash.type, store->toRealPath(storePath));
+        Hash gotHash = request.unpack
+            ? hashPath(request.expectedHash.type, store->toRealPath(storePath)).first
+            : hashFile(request.expectedHash.type, store->toRealPath(storePath));
         throw nix::Error("hash mismatch in file downloaded from '%s':\n  wanted: %s\n  got:    %s",
-            url, expectedHash.to_string(), gotHash.to_string());
+            url, request.expectedHash.to_string(), gotHash.to_string());
     }
 
-    return store->toRealPath(storePath);
+    result.storePath = storePath;
+    result.path = store->toRealPath(storePath);
+    return result;
 }
 
 
@@ -898,5 +877,4 @@ bool isUri(const string & s)
     return scheme == "http" || scheme == "https" || scheme == "file" || scheme == "channel" || scheme == "git" || scheme == "s3" || scheme == "ssh";
 }
 
-
 }
diff --git a/src/libstore/download.hh b/src/libstore/download.hh
index f0228f7d053a..9e965b506d0a 100644
--- a/src/libstore/download.hh
+++ b/src/libstore/download.hh
@@ -9,13 +9,34 @@
 
 namespace nix {
 
+struct DownloadSettings : Config
+{
+    Setting<bool> enableHttp2{this, true, "http2",
+        "Whether to enable HTTP/2 support."};
+
+    Setting<std::string> userAgentSuffix{this, "", "user-agent-suffix",
+        "String appended to the user agent in HTTP requests."};
+
+    Setting<size_t> httpConnections{this, 25, "http-connections",
+        "Number of parallel HTTP connections.",
+        {"binary-caches-parallel-connections"}};
+
+    Setting<unsigned long> connectTimeout{this, 0, "connect-timeout",
+        "Timeout for connecting to servers during downloads. 0 means use curl's builtin default."};
+
+    Setting<unsigned int> tries{this, 5, "download-attempts",
+        "How often Nix will attempt to download a file before giving up."};
+};
+
+extern DownloadSettings downloadSettings;
+
 struct DownloadRequest
 {
     std::string uri;
     std::string expectedETag;
     bool verifyTLS = true;
     bool head = false;
-    size_t tries = 5;
+    size_t tries = downloadSettings.tries;
     unsigned int baseRetryTimeMs = 250;
     ActivityId parentAct;
     bool decompress = true;
@@ -36,11 +57,33 @@ struct DownloadResult
 {
     bool cached = false;
     std::string etag;
-    std::string effectiveUrl;
+    std::string effectiveUri;
     std::shared_ptr<std::string> data;
     uint64_t bodySize = 0;
 };
 
+struct CachedDownloadRequest
+{
+    std::string uri;
+    bool unpack = false;
+    std::string name;
+    Hash expectedHash;
+    unsigned int ttl = settings.tarballTtl;
+
+    CachedDownloadRequest(const std::string & uri)
+        : uri(uri) { }
+};
+
+struct CachedDownloadResult
+{
+    // Note: 'storePath' may be different from 'path' when using a
+    // chroot store.
+    Path storePath;
+    Path path;
+    std::optional<std::string> etag;
+    std::string effectiveUri;
+};
+
 class Store;
 
 struct Downloader
@@ -53,19 +96,20 @@ struct Downloader
 
     std::future<DownloadResult> enqueueDownload(const DownloadRequest & request);
 
-    /* Synchronously download a file. */
+    /* Synchronously download a file. The request will be retried in
+       case of transient failures. */
     DownloadResult download(const DownloadRequest & request);
 
     /* Download a file, writing its data to a sink. The sink will be
-       invoked on the thread of the caller. */
+       invoked on the thread of the caller. The request will not be
+       retried in case of transient failures. */
     void download(DownloadRequest && request, Sink & sink);
 
     /* Check if the specified file is already in ~/.cache/nix/tarballs
        and is more recent than โ€˜tarball-ttlโ€™ seconds. Otherwise,
        use the recorded ETag to verify if the server has a more
        recent version, and if so, download it to the Nix store. */
-    Path downloadCached(ref<Store> store, const string & uri, bool unpack, string name = "",
-        const Hash & expectedHash = Hash(), string * effectiveUri = nullptr, int ttl = settings.tarballTtl);
+    CachedDownloadResult downloadCached(ref<Store> store, const CachedDownloadRequest & request);
 
     enum Error { NotFound, Forbidden, Misc, Transient, Interrupted };
 };
@@ -84,6 +128,11 @@ public:
     DownloadError(Downloader::Error error, const FormatOrString & fs)
         : Error(fs), error(error)
     { }
+
+    bool isTransient() override
+    {
+        return error == Downloader::Error::Transient;
+    }
 };
 
 bool isUri(const string & s);
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index b415d5421476..26e2b0dca7ca 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -129,8 +129,8 @@ Path LocalFSStore::addPermRoot(const Path & _storePath,
        check if the root is in a directory in or linked from the
        gcroots directory. */
     if (settings.checkRootReachability) {
-        Roots roots = findRoots();
-        if (roots.find(gcRoot) == roots.end())
+        Roots roots = findRoots(false);
+        if (roots[storePath].count(gcRoot) == 0)
             printError(
                 format(
                     "warning: '%1%' is not in a directory where the garbage collector looks for roots; "
@@ -197,10 +197,11 @@ void LocalStore::addTempRoot(const Path & path)
 }
 
 
-std::set<std::pair<pid_t, Path>> LocalStore::readTempRoots(FDs & fds)
-{
-    std::set<std::pair<pid_t, Path>> tempRoots;
+static std::string censored = "{censored}";
+
 
+void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots, bool censor)
+{
     /* Read the `temproots' directory for per-process temporary root
        files. */
     for (auto & i : readDirectory(tempRootsDir)) {
@@ -250,14 +251,12 @@ std::set<std::pair<pid_t, Path>> LocalStore::readTempRoots(FDs & fds)
             Path root(contents, pos, end - pos);
             debug("got temporary root '%s'", root);
             assertStorePath(root);
-            tempRoots.emplace(pid, root);
+            tempRoots[root].emplace(censor ? censored : fmt("{temp:%d}", pid));
             pos = end + 1;
         }
 
         fds.push_back(fd); /* keep open */
     }
-
-    return tempRoots;
 }
 
 
@@ -266,7 +265,7 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
     auto foundRoot = [&](const Path & path, const Path & target) {
         Path storePath = toStorePath(target);
         if (isStorePath(storePath) && isValidPath(storePath))
-            roots[path] = storePath;
+            roots[storePath].emplace(path);
         else
             printInfo(format("skipping invalid root from '%1%' to '%2%'") % path % storePath);
     };
@@ -306,7 +305,7 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
         else if (type == DT_REG) {
             Path storePath = storeDir + "/" + baseNameOf(path);
             if (isStorePath(storePath) && isValidPath(storePath))
-                roots[path] = storePath;
+                roots[storePath].emplace(path);
         }
 
     }
@@ -321,44 +320,31 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
 }
 
 
-Roots LocalStore::findRootsNoTemp()
+void LocalStore::findRootsNoTemp(Roots & roots, bool censor)
 {
-    Roots roots;
-
     /* Process direct roots in {gcroots,profiles}. */
     findRoots(stateDir + "/" + gcRootsDir, DT_UNKNOWN, roots);
     findRoots(stateDir + "/profiles", DT_UNKNOWN, roots);
 
-    /* Add additional roots returned by the program specified by the
-       NIX_ROOT_FINDER environment variable.  This is typically used
-       to add running programs to the set of roots (to prevent them
-       from being garbage collected). */
-    size_t n = 0;
-    for (auto & root : findRuntimeRoots())
-        roots[fmt("{memory:%d}", n++)] = root;
-
-    return roots;
+    /* Add additional roots returned by different platforms-specific
+       heuristics.  This is typically used to add running programs to
+       the set of roots (to prevent them from being garbage collected). */
+    findRuntimeRoots(roots, censor);
 }
 
 
-Roots LocalStore::findRoots()
+Roots LocalStore::findRoots(bool censor)
 {
-    Roots roots = findRootsNoTemp();
+    Roots roots;
+    findRootsNoTemp(roots, censor);
 
     FDs fds;
-    pid_t prev = -1;
-    size_t n = 0;
-    for (auto & root : readTempRoots(fds)) {
-        if (prev != root.first) n = 0;
-        prev = root.first;
-        roots[fmt("{temp:%d:%d}", root.first, n++)] = root.second;
-    }
+    findTempRoots(fds, roots, censor);
 
     return roots;
 }
 
-
-static void readProcLink(const string & file, StringSet & paths)
+static void readProcLink(const string & file, Roots & roots)
 {
     /* 64 is the starting buffer size gnu readlink uses... */
     auto bufsiz = ssize_t{64};
@@ -377,8 +363,8 @@ try_again:
         goto try_again;
     }
     if (res > 0 && buf[0] == '/')
-        paths.emplace(static_cast<char *>(buf), res);
-    return;
+        roots[std::string(static_cast<char *>(buf), res)]
+            .emplace(file);
 }
 
 static string quoteRegexChars(const string & raw)
@@ -387,20 +373,20 @@ static string quoteRegexChars(const string & raw)
     return std::regex_replace(raw, specialRegex, R"(\$&)");
 }
 
-static void readFileRoots(const char * path, StringSet & paths)
+static void readFileRoots(const char * path, Roots & roots)
 {
     try {
-        paths.emplace(readFile(path));
+        roots[readFile(path)].emplace(path);
     } catch (SysError & e) {
         if (e.errNo != ENOENT && e.errNo != EACCES)
             throw;
     }
 }
 
-PathSet LocalStore::findRuntimeRoots()
+void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 {
-    PathSet roots;
-    StringSet paths;
+    Roots unchecked;
+
     auto procDir = AutoCloseDir{opendir("/proc")};
     if (procDir) {
         struct dirent * ent;
@@ -410,10 +396,10 @@ PathSet LocalStore::findRuntimeRoots()
         while (errno = 0, ent = readdir(procDir.get())) {
             checkInterrupt();
             if (std::regex_match(ent->d_name, digitsRegex)) {
-                readProcLink((format("/proc/%1%/exe") % ent->d_name).str(), paths);
-                readProcLink((format("/proc/%1%/cwd") % ent->d_name).str(), paths);
+                readProcLink(fmt("/proc/%s/exe" ,ent->d_name), unchecked);
+                readProcLink(fmt("/proc/%s/cwd", ent->d_name), unchecked);
 
-                auto fdStr = (format("/proc/%1%/fd") % ent->d_name).str();
+                auto fdStr = fmt("/proc/%s/fd", ent->d_name);
                 auto fdDir = AutoCloseDir(opendir(fdStr.c_str()));
                 if (!fdDir) {
                     if (errno == ENOENT || errno == EACCES)
@@ -422,9 +408,8 @@ PathSet LocalStore::findRuntimeRoots()
                 }
                 struct dirent * fd_ent;
                 while (errno = 0, fd_ent = readdir(fdDir.get())) {
-                    if (fd_ent->d_name[0] != '.') {
-                        readProcLink((format("%1%/%2%") % fdStr % fd_ent->d_name).str(), paths);
-                    }
+                    if (fd_ent->d_name[0] != '.')
+                        readProcLink(fmt("%s/%s", fdStr, fd_ent->d_name), unchecked);
                 }
                 if (errno) {
                     if (errno == ESRCH)
@@ -434,18 +419,19 @@ PathSet LocalStore::findRuntimeRoots()
                 fdDir.reset();
 
                 try {
-                    auto mapLines =
-                        tokenizeString<std::vector<string>>(readFile((format("/proc/%1%/maps") % ent->d_name).str(), true), "\n");
-                    for (const auto& line : mapLines) {
+                    auto mapFile = fmt("/proc/%s/maps", ent->d_name);
+                    auto mapLines = tokenizeString<std::vector<string>>(readFile(mapFile, true), "\n");
+                    for (const auto & line : mapLines) {
                         auto match = std::smatch{};
                         if (std::regex_match(line, match, mapRegex))
-                            paths.emplace(match[1]);
+                            unchecked[match[1]].emplace(mapFile);
                     }
 
-                    auto envString = readFile((format("/proc/%1%/environ") % ent->d_name).str(), true);
+                    auto envFile = fmt("/proc/%s/environ", ent->d_name);
+                    auto envString = readFile(envFile, true);
                     auto env_end = std::sregex_iterator{};
                     for (auto i = std::sregex_iterator{envString.begin(), envString.end(), storePathRegex}; i != env_end; ++i)
-                        paths.emplace(i->str());
+                        unchecked[i->str()].emplace(envFile);
                 } catch (SysError & e) {
                     if (errno == ENOENT || errno == EACCES || errno == ESRCH)
                         continue;
@@ -465,7 +451,7 @@ PathSet LocalStore::findRuntimeRoots()
         for (const auto & line : lsofLines) {
             std::smatch match;
             if (std::regex_match(line, match, lsofRegex))
-                paths.emplace(match[1]);
+                unchecked[match[1]].emplace("{lsof}");
         }
     } catch (ExecError & e) {
         /* lsof not installed, lsof failed */
@@ -473,21 +459,23 @@ PathSet LocalStore::findRuntimeRoots()
 #endif
 
 #if defined(__linux__)
-    readFileRoots("/proc/sys/kernel/modprobe", paths);
-    readFileRoots("/proc/sys/kernel/fbsplash", paths);
-    readFileRoots("/proc/sys/kernel/poweroff_cmd", paths);
+    readFileRoots("/proc/sys/kernel/modprobe", unchecked);
+    readFileRoots("/proc/sys/kernel/fbsplash", unchecked);
+    readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
 #endif
 
-    for (auto & i : paths)
-        if (isInStore(i)) {
-            Path path = toStorePath(i);
-            if (roots.find(path) == roots.end() && isStorePath(path) && isValidPath(path)) {
+    for (auto & [target, links] : unchecked) {
+        if (isInStore(target)) {
+            Path path = toStorePath(target);
+            if (isStorePath(path) && isValidPath(path)) {
                 debug(format("got additional root '%1%'") % path);
-                roots.insert(path);
+                if (censor)
+                    roots[path].insert(censored);
+                else
+                    roots[path].insert(links.begin(), links.end());
             }
         }
-
-    return roots;
+    }
 }
 
 
@@ -754,16 +742,20 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     /* Find the roots.  Since we've grabbed the GC lock, the set of
        permanent roots cannot increase now. */
     printError(format("finding garbage collector roots..."));
-    Roots rootMap = options.ignoreLiveness ? Roots() : findRootsNoTemp();
+    Roots rootMap;
+    if (!options.ignoreLiveness)
+        findRootsNoTemp(rootMap, true);
 
-    for (auto & i : rootMap) state.roots.insert(i.second);
+    for (auto & i : rootMap) state.roots.insert(i.first);
 
     /* Read the temporary roots.  This acquires read locks on all
        per-process temporary root files.  So after this point no paths
        can be added to the set of temporary roots. */
     FDs fds;
-    for (auto & root : readTempRoots(fds))
-        state.tempRoots.insert(root.second);
+    Roots tempRoots;
+    findTempRoots(fds, tempRoots, true);
+    for (auto & root : tempRoots)
+        state.tempRoots.insert(root.first);
     state.roots.insert(state.tempRoots.begin(), state.tempRoots.end());
 
     /* After this point the set of roots or temporary roots cannot
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 53efc6a90fb6..0af8215d1fd8 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -255,7 +255,7 @@ public:
         "Secret keys with which to sign local builds."};
 
     Setting<unsigned int> tarballTtl{this, 60 * 60, "tarball-ttl",
-        "How soon to expire files fetched by builtins.fetchTarball and builtins.fetchurl."};
+        "How long downloaded files are considered up-to-date."};
 
     Setting<bool> requireSigs{this, true, "require-sigs",
         "Whether to check that any non-content-addressed path added to the "
diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index 8da0e2f9d82a..5633b4355d25 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -2,6 +2,7 @@
 #include "download.hh"
 #include "globals.hh"
 #include "nar-info-disk-cache.hh"
+#include "retry.hh"
 
 namespace nix {
 
@@ -84,7 +85,6 @@ protected:
         try {
             DownloadRequest request(cacheUri + "/" + path);
             request.head = true;
-            request.tries = 5;
             getDownloader()->download(request);
             return true;
         } catch (DownloadError & e) {
@@ -114,7 +114,6 @@ protected:
     DownloadRequest makeRequest(const std::string & path)
     {
         DownloadRequest request(cacheUri + "/" + path);
-        request.tries = 8;
         return request;
     }
 
@@ -137,21 +136,46 @@ protected:
     {
         checkEnabled();
 
-        auto request(makeRequest(path));
-
-        getDownloader()->enqueueDownload(request,
-            {[callback, this](std::future<DownloadResult> result) {
-                try {
-                    callback(result.get().data);
-                } catch (DownloadError & e) {
-                    if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
-                        return callback(std::shared_ptr<std::string>());
-                    maybeDisable();
-                    callback.rethrow();
-                } catch (...) {
-                    callback.rethrow();
-                }
-            }});
+        struct State
+        {
+            DownloadRequest request;
+            std::function<void()> tryDownload;
+            unsigned int attempt = 0;
+            State(DownloadRequest && request) : request(request) {}
+        };
+
+        auto state = std::make_shared<State>(makeRequest(path));
+
+        state->tryDownload = [callback, state, this]() {
+            getDownloader()->enqueueDownload(state->request,
+                {[callback, state, this](std::future<DownloadResult> result) {
+                    try {
+                        callback(result.get().data);
+                    } catch (DownloadError & e) {
+                        if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
+                            return callback(std::shared_ptr<std::string>());
+                        ++state->attempt;
+                        if (state->attempt < state->request.tries && e.isTransient()) {
+                            auto ms = retrySleepTime(state->attempt);
+                            warn("%s; retrying in %d ms", e.what(), ms);
+                            /* We can't sleep here because that would
+                               block the download thread. So use a
+                               separate thread for sleeping. */
+                            std::thread([state, ms]() {
+                                std::this_thread::sleep_for(std::chrono::milliseconds(ms));
+                                state->tryDownload();
+                            }).detach();
+                        } else {
+                            maybeDisable();
+                            callback.rethrow();
+                        }
+                    } catch (...) {
+                        callback.rethrow();
+                    }
+                }});
+        };
+
+        state->tryDownload();
     }
 
 };
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 26e1851981db..7c9bc2b68ba8 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -187,28 +187,17 @@ struct LegacySSHStore : public Store
         copyNAR(conn->from, sink);
     }
 
-    PathSet queryAllValidPaths() override { unsupported(); }
-
-    void queryReferrers(const Path & path, PathSet & referrers) override
-    { unsupported(); }
-
-    PathSet queryDerivationOutputs(const Path & path) override
-    { unsupported(); }
-
-    StringSet queryDerivationOutputNames(const Path & path) override
-    { unsupported(); }
-
     Path queryPathFromHashPart(const string & hashPart) override
-    { unsupported(); }
+    { unsupported("queryPathFromHashPart"); }
 
     Path addToStore(const string & name, const Path & srcPath,
         bool recursive, HashType hashAlgo,
         PathFilter & filter, RepairFlag repair) override
-    { unsupported(); }
+    { unsupported("addToStore"); }
 
     Path addTextToStore(const string & name, const string & s,
         const PathSet & references, RepairFlag repair) override
-    { unsupported(); }
+    { unsupported("addTextToStore"); }
 
     BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override
@@ -242,25 +231,7 @@ struct LegacySSHStore : public Store
     }
 
     void ensurePath(const Path & path) override
-    { unsupported(); }
-
-    void addTempRoot(const Path & path) override
-    { unsupported(); }
-
-    void addIndirectRoot(const Path & path) override
-    { unsupported(); }
-
-    Roots findRoots() override
-    { unsupported(); }
-
-    void collectGarbage(const GCOptions & options, GCResults & results) override
-    { unsupported(); }
-
-    ref<FSAccessor> getFSAccessor() override
-    { unsupported(); }
-
-    void addSignatures(const Path & storePath, const StringSet & sigs) override
-    { unsupported(); }
+    { unsupported("ensurePath"); }
 
     void computeFSClosure(const PathSet & paths,
         PathSet & out, bool flipDirection = false,
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 5b4e7ca4ca99..485fdd691932 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -366,8 +366,6 @@ void LocalStore::makeStoreWritable()
         throw SysError("getting info about the Nix store mount point");
 
     if (stat.f_flag & ST_RDONLY) {
-        saveMountNamespace();
-
         if (unshare(CLONE_NEWNS) == -1)
             throw SysError("setting up a private mount namespace");
 
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index fce963433a5e..6b655647b031 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -180,11 +180,11 @@ private:
     typedef std::shared_ptr<AutoCloseFD> FDPtr;
     typedef list<FDPtr> FDs;
 
-    std::set<std::pair<pid_t, Path>> readTempRoots(FDs & fds);
+    void findTempRoots(FDs & fds, Roots & roots, bool censor);
 
 public:
 
-    Roots findRoots() override;
+    Roots findRoots(bool censor) override;
 
     void collectGarbage(const GCOptions & options, GCResults & results) override;
 
@@ -267,9 +267,9 @@ private:
 
     void findRoots(const Path & path, unsigned char type, Roots & roots);
 
-    Roots findRootsNoTemp();
+    void findRootsNoTemp(Roots & roots, bool censor);
 
-    PathSet findRuntimeRoots();
+    void findRuntimeRoots(Roots & roots, bool censor);
 
     void removeUnusedLinks(const GCState & state);
 
diff --git a/src/libstore/local.mk b/src/libstore/local.mk
index 3799257f83ff..89fc918c30fd 100644
--- a/src/libstore/local.mk
+++ b/src/libstore/local.mk
@@ -6,7 +6,7 @@ libstore_DIR := $(d)
 
 libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc)
 
-libstore_LIBS = libutil libformat
+libstore_LIBS = libutil
 
 libstore_LDFLAGS = $(SQLITE3_LIBS) -lbz2 $(LIBCURL_LIBS) $(SODIUM_LIBS) -pthread
 ifneq ($(OS), FreeBSD)
diff --git a/src/libstore/machines.cc b/src/libstore/machines.cc
index edd03d147832..f848582dafd4 100644
--- a/src/libstore/machines.cc
+++ b/src/libstore/machines.cc
@@ -89,10 +89,11 @@ void parseMachines(const std::string & s, Machines & machines)
 
 Machines getMachines()
 {
-    Machines machines;
-
-    parseMachines(settings.builders, machines);
-
+    static auto machines = [&]() {
+        Machines machines;
+        parseMachines(settings.builders, machines);
+        return machines;
+    }();
     return machines;
 }
 
diff --git a/src/libstore/nix-store.pc.in b/src/libstore/nix-store.pc.in
index 5cf22faadcbe..6d67b1e03808 100644
--- a/src/libstore/nix-store.pc.in
+++ b/src/libstore/nix-store.pc.in
@@ -6,4 +6,4 @@ Name: Nix
 Description: Nix Package Manager
 Version: @PACKAGE_VERSION@
 Libs: -L${libdir} -lnixstore -lnixutil
-Cflags: -I${includedir}/nix -std=c++14
+Cflags: -I${includedir}/nix -std=c++17
diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index dc3286482736..17fde00a0167 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -16,7 +16,7 @@ ParsedDerivation::ParsedDerivation(const Path & drvPath, BasicDerivation & drv)
     }
 }
 
-std::experimental::optional<std::string> ParsedDerivation::getStringAttr(const std::string & name) const
+std::optional<std::string> ParsedDerivation::getStringAttr(const std::string & name) const
 {
     if (structuredAttrs) {
         auto i = structuredAttrs->find(name);
@@ -56,7 +56,7 @@ bool ParsedDerivation::getBoolAttr(const std::string & name, bool def) const
     }
 }
 
-std::experimental::optional<Strings> ParsedDerivation::getStringsAttr(const std::string & name) const
+std::optional<Strings> ParsedDerivation::getStringsAttr(const std::string & name) const
 {
     if (structuredAttrs) {
         auto i = structuredAttrs->find(name);
diff --git a/src/libstore/parsed-derivations.hh b/src/libstore/parsed-derivations.hh
index 0a82c146172b..ed07dc652e8d 100644
--- a/src/libstore/parsed-derivations.hh
+++ b/src/libstore/parsed-derivations.hh
@@ -8,22 +8,22 @@ class ParsedDerivation
 {
     Path drvPath;
     BasicDerivation & drv;
-    std::experimental::optional<nlohmann::json> structuredAttrs;
+    std::optional<nlohmann::json> structuredAttrs;
 
 public:
 
     ParsedDerivation(const Path & drvPath, BasicDerivation & drv);
 
-    const std::experimental::optional<nlohmann::json> & getStructuredAttrs() const
+    const std::optional<nlohmann::json> & getStructuredAttrs() const
     {
         return structuredAttrs;
     }
 
-    std::experimental::optional<std::string> getStringAttr(const std::string & name) const;
+    std::optional<std::string> getStringAttr(const std::string & name) const;
 
     bool getBoolAttr(const std::string & name, bool def = false) const;
 
-    std::experimental::optional<Strings> getStringsAttr(const std::string & name) const;
+    std::optional<Strings> getStringsAttr(const std::string & name) const;
 
     StringSet getRequiredSystemFeatures() const;
 
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index def140cfbe18..15faf78a526d 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -596,7 +596,7 @@ void RemoteStore::syncWithGC()
 }
 
 
-Roots RemoteStore::findRoots()
+Roots RemoteStore::findRoots(bool censor)
 {
     auto conn(getConnection());
     conn->to << wopFindRoots;
@@ -606,7 +606,7 @@ Roots RemoteStore::findRoots()
     while (count--) {
         Path link = readString(conn->from);
         Path target = readStorePath(*this, conn->from);
-        result[link] = target;
+        result[target].emplace(link);
     }
     return result;
 }
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 4f554b5980e8..80f18ab715d9 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -82,7 +82,7 @@ public:
 
     void syncWithGC() override;
 
-    Roots findRoots() override;
+    Roots findRoots(bool censor) override;
 
     void collectGarbage(const GCOptions & options, GCResults & results) override;
 
@@ -149,7 +149,7 @@ public:
 private:
 
     ref<RemoteStore::Connection> openConnection() override;
-    std::experimental::optional<std::string> path;
+    std::optional<std::string> path;
 };
 
 
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 51de89e0d92f..cd547a964850 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -126,6 +126,7 @@ ref<Aws::Client::ClientConfiguration> S3Helper::makeConfig(const string & region
         res->endpointOverride = endpoint;
     }
     res->requestTimeoutMs = 600 * 1000;
+    res->connectTimeoutMs = 5 * 1000;
     res->retryStrategy = std::make_shared<RetryStrategy>();
     res->caFile = settings.caFile;
     return res;
diff --git a/src/libstore/ssh.cc b/src/libstore/ssh.cc
index cf133b57cb20..5e0e44935cca 100644
--- a/src/libstore/ssh.cc
+++ b/src/libstore/ssh.cc
@@ -1,5 +1,4 @@
 #include "ssh.hh"
-#include "affinity.hh"
 
 namespace nix {
 
@@ -35,9 +34,7 @@ std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(const std::string
 
     auto conn = std::make_unique<Connection>();
     conn->sshPid = startProcess([&]() {
-        restoreAffinity();
         restoreSignals();
-        restoreMountNamespace();
 
         close(in.writeSide.get());
         close(out.readSide.get());
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index dc54c735fdb1..28ad7c019a94 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -6,10 +6,11 @@
 #include "thread-pool.hh"
 #include "json.hh"
 #include "derivations.hh"
+#include "retry.hh"
+#include "download.hh"
 
 #include <future>
 
-
 namespace nix {
 
 
@@ -562,64 +563,67 @@ void Store::buildPaths(const PathSet & paths, BuildMode buildMode)
 {
     for (auto & path : paths)
         if (isDerivation(path))
-            unsupported();
+            unsupported("buildPaths");
 
     if (queryValidPaths(paths).size() != paths.size())
-        unsupported();
+        unsupported("buildPaths");
 }
 
 
 void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
     const Path & storePath, RepairFlag repair, CheckSigsFlag checkSigs)
 {
-    auto srcUri = srcStore->getUri();
-    auto dstUri = dstStore->getUri();
-
-    Activity act(*logger, lvlInfo, actCopyPath,
-        srcUri == "local" || srcUri == "daemon"
-          ? fmt("copying path '%s' to '%s'", storePath, dstUri)
-          : dstUri == "local" || dstUri == "daemon"
-            ? fmt("copying path '%s' from '%s'", storePath, srcUri)
-            : fmt("copying path '%s' from '%s' to '%s'", storePath, srcUri, dstUri),
-        {storePath, srcUri, dstUri});
-    PushActivity pact(act.id);
-
-    auto info = srcStore->queryPathInfo(storePath);
-
-    uint64_t total = 0;
-
-    if (!info->narHash) {
-        StringSink sink;
-        srcStore->narFromPath({storePath}, sink);
-        auto info2 = make_ref<ValidPathInfo>(*info);
-        info2->narHash = hashString(htSHA256, *sink.s);
-        if (!info->narSize) info2->narSize = sink.s->size();
-        if (info->ultimate) info2->ultimate = false;
-        info = info2;
-
-        StringSource source(*sink.s);
-        dstStore->addToStore(*info, source, repair, checkSigs);
-        return;
-    }
+    retry<void>(downloadSettings.tries, [&]() {
 
-    if (info->ultimate) {
-        auto info2 = make_ref<ValidPathInfo>(*info);
-        info2->ultimate = false;
-        info = info2;
-    }
+        auto srcUri = srcStore->getUri();
+        auto dstUri = dstStore->getUri();
+
+        Activity act(*logger, lvlInfo, actCopyPath,
+            srcUri == "local" || srcUri == "daemon"
+              ? fmt("copying path '%s' to '%s'", storePath, dstUri)
+              : dstUri == "local" || dstUri == "daemon"
+                ? fmt("copying path '%s' from '%s'", storePath, srcUri)
+                : fmt("copying path '%s' from '%s' to '%s'", storePath, srcUri, dstUri),
+            {storePath, srcUri, dstUri});
+        PushActivity pact(act.id);
+
+        auto info = srcStore->queryPathInfo(storePath);
+
+        uint64_t total = 0;
+
+        if (!info->narHash) {
+            StringSink sink;
+            srcStore->narFromPath({storePath}, sink);
+            auto info2 = make_ref<ValidPathInfo>(*info);
+            info2->narHash = hashString(htSHA256, *sink.s);
+            if (!info->narSize) info2->narSize = sink.s->size();
+            if (info->ultimate) info2->ultimate = false;
+            info = info2;
+
+            StringSource source(*sink.s);
+            dstStore->addToStore(*info, source, repair, checkSigs);
+            return;
+        }
+
+        if (info->ultimate) {
+            auto info2 = make_ref<ValidPathInfo>(*info);
+            info2->ultimate = false;
+            info = info2;
+        }
 
-    auto source = sinkToSource([&](Sink & sink) {
-        LambdaSink wrapperSink([&](const unsigned char * data, size_t len) {
-            sink(data, len);
-            total += len;
-            act.progress(total, info->narSize);
+        auto source = sinkToSource([&](Sink & sink) {
+            LambdaSink wrapperSink([&](const unsigned char * data, size_t len) {
+                sink(data, len);
+                total += len;
+                act.progress(total, info->narSize);
+            });
+            srcStore->narFromPath({storePath}, wrapperSink);
+        }, [&]() {
+            throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", storePath, srcStore->getUri());
         });
-        srcStore->narFromPath({storePath}, wrapperSink);
-    }, [&]() {
-        throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", storePath, srcStore->getUri());
-    });
 
-    dstStore->addToStore(*info, *source, repair, checkSigs);
+        dstStore->addToStore(*info, *source, repair, checkSigs);
+    });
 }
 
 
@@ -842,12 +846,11 @@ namespace nix {
 
 RegisterStoreImplementation::Implementations * RegisterStoreImplementation::implementations = 0;
 
-
-ref<Store> openStore(const std::string & uri_,
-    const Store::Params & extraParams)
+/* Split URI into protocol+hierarchy part and its parameter set. */
+std::pair<std::string, Store::Params> splitUriAndParams(const std::string & uri_)
 {
     auto uri(uri_);
-    Store::Params params(extraParams);
+    Store::Params params;
     auto q = uri.find('?');
     if (q != std::string::npos) {
         for (auto s : tokenizeString<Strings>(uri.substr(q + 1), "&")) {
@@ -873,6 +876,15 @@ ref<Store> openStore(const std::string & uri_,
         }
         uri = uri_.substr(0, q);
     }
+    return {uri, params};
+}
+
+ref<Store> openStore(const std::string & uri_,
+    const Store::Params & extraParams)
+{
+    auto [uri, uriParams] = splitUriAndParams(uri_);
+    auto params = extraParams;
+    params.insert(uriParams.begin(), uriParams.end());
 
     for (auto fun : *RegisterStoreImplementation::implementations) {
         auto store = fun(uri, params);
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 106b2be5e6b2..59967737670d 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -11,6 +11,8 @@
 #include <atomic>
 #include <limits>
 #include <map>
+#include <unordered_map>
+#include <unordered_set>
 #include <memory>
 #include <string>
 
@@ -47,7 +49,7 @@ const size_t storePathHashLen = 32; // i.e. 160 bits
 const uint32_t exportMagic = 0x4558494e;
 
 
-typedef std::map<Path, Path> Roots;
+typedef std::unordered_map<Path, std::unordered_set<std::string>> Roots;
 
 
 struct GCOptions
@@ -349,7 +351,8 @@ public:
        (i.e. you'll get /nix/store/<hash> rather than
        /nix/store/<hash>-<name>). Use queryPathInfo() to obtain the
        full store path. */
-    virtual PathSet queryAllValidPaths() = 0;
+    virtual PathSet queryAllValidPaths()
+    { unsupported("queryAllValidPaths"); }
 
     /* Query information about a valid path. It is permitted to omit
        the name part of the store path. */
@@ -368,8 +371,8 @@ public:
 
     /* Queries the set of incoming FS references for a store path.
        The result is not cleared. */
-    virtual void queryReferrers(const Path & path,
-        PathSet & referrers) = 0;
+    virtual void queryReferrers(const Path & path, PathSet & referrers)
+    { unsupported("queryReferrers"); }
 
     /* Return all currently valid derivations that have `path' as an
        output.  (Note that the result of `queryDeriver()' is the
@@ -378,10 +381,12 @@ public:
     virtual PathSet queryValidDerivers(const Path & path) { return {}; };
 
     /* Query the outputs of the derivation denoted by `path'. */
-    virtual PathSet queryDerivationOutputs(const Path & path) = 0;
+    virtual PathSet queryDerivationOutputs(const Path & path)
+    { unsupported("queryDerivationOutputs"); }
 
     /* Query the output names of the derivation denoted by `path'. */
-    virtual StringSet queryDerivationOutputNames(const Path & path) = 0;
+    virtual StringSet queryDerivationOutputNames(const Path & path)
+    { unsupported("queryDerivationOutputNames"); }
 
     /* Query the full store path given the hash part of a valid store
        path, or "" if the path doesn't exist. */
@@ -447,14 +452,16 @@ public:
 
     /* Add a store path as a temporary root of the garbage collector.
        The root disappears as soon as we exit. */
-    virtual void addTempRoot(const Path & path) = 0;
+    virtual void addTempRoot(const Path & path)
+    { unsupported("addTempRoot"); }
 
     /* Add an indirect root, which is merely a symlink to `path' from
        /nix/var/nix/gcroots/auto/<hash of `path'>.  `path' is supposed
        to be a symlink to a store path.  The garbage collector will
        automatically remove the indirect root when it finds that
        `path' has disappeared. */
-    virtual void addIndirectRoot(const Path & path) = 0;
+    virtual void addIndirectRoot(const Path & path)
+    { unsupported("addIndirectRoot"); }
 
     /* Acquire the global GC lock, then immediately release it.  This
        function must be called after registering a new permanent root,
@@ -478,11 +485,15 @@ public:
 
     /* Find the roots of the garbage collector.  Each root is a pair
        (link, storepath) where `link' is the path of the symlink
-       outside of the Nix store that point to `storePath'.  */
-    virtual Roots findRoots() = 0;
+       outside of the Nix store that point to `storePath'. If
+       'censor' is true, privacy-sensitive information about roots
+       found in /proc is censored. */
+    virtual Roots findRoots(bool censor)
+    { unsupported("findRoots"); }
 
     /* Perform a garbage collection. */
-    virtual void collectGarbage(const GCOptions & options, GCResults & results) = 0;
+    virtual void collectGarbage(const GCOptions & options, GCResults & results)
+    { unsupported("collectGarbage"); }
 
     /* Return a string representing information about the path that
        can be loaded into the database using `nix-store --load-db' or
@@ -513,11 +524,13 @@ public:
     virtual bool verifyStore(bool checkContents, RepairFlag repair = NoRepair) { return false; };
 
     /* Return an object to access files in the Nix store. */
-    virtual ref<FSAccessor> getFSAccessor() = 0;
+    virtual ref<FSAccessor> getFSAccessor()
+    { unsupported("getFSAccessor"); }
 
     /* Add signatures to the specified store path. The signatures are
        not verified. */
-    virtual void addSignatures(const Path & storePath, const StringSet & sigs) = 0;
+    virtual void addSignatures(const Path & storePath, const StringSet & sigs)
+    { unsupported("addSignatures"); }
 
     /* Utility functions. */
 
@@ -620,9 +633,9 @@ protected:
     Stats stats;
 
     /* Unsupported methods. */
-    [[noreturn]] void unsupported()
+    [[noreturn]] void unsupported(const std::string & op)
     {
-        throw Unsupported("requested operation is not supported by store '%s'", getUri());
+        throw Unsupported("operation '%s' is not supported by store '%s'", op, getUri());
     }
 
 };
@@ -753,8 +766,7 @@ StoreType getStoreType(const std::string & uri = settings.storeUri.get(),
     const std::string & stateDir = settings.nixStateDir);
 
 /* Return the default substituter stores, defined by the
-   โ€˜substitutersโ€™ option and various legacy options like
-   โ€˜binary-cachesโ€™. */
+   โ€˜substitutersโ€™ option and various legacy options. */
 std::list<ref<Store>> getDefaultSubstituters();
 
 
@@ -789,4 +801,8 @@ ValidPathInfo decodeValidPathInfo(std::istream & str,
    for paths created by makeFixedOutputPath() / addToStore(). */
 std::string makeFixedOutputCA(bool recursive, const Hash & hash);
 
+
+/* Split URI into protocol+hierarchy part and its parameter set. */
+std::pair<std::string, Store::Params> splitUriAndParams(const std::string & uri);
+
 }
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index bb68e82886d0..3aa120270970 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -331,7 +331,7 @@ struct RestoreSink : ParseSink
                filesystem doesn't support preallocation (e.g. on
                OpenSolaris).  Since preallocation is just an
                optimisation, ignore it. */
-            if (errno && errno != EINVAL)
+            if (errno && errno != EINVAL && errno != EOPNOTSUPP && errno != ENOSYS)
                 throw SysError(format("preallocating file of %1% bytes") % len);
         }
 #endif
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 9d82f13a5e38..1c14ebb187cc 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -105,9 +105,9 @@ string printHash16or32(const Hash & hash)
 std::string Hash::to_string(Base base, bool includeType) const
 {
     std::string s;
-    if (includeType) {
+    if (base == SRI || includeType) {
         s += printHashType(type);
-        s += ':';
+        s += base == SRI ? '-' : ':';
     }
     switch (base) {
     case Base16:
@@ -117,6 +117,7 @@ std::string Hash::to_string(Base base, bool includeType) const
         s += printHash32(*this);
         break;
     case Base64:
+    case SRI:
         s += base64Encode(std::string((const char *) hash, hashSize));
         break;
     }
@@ -127,28 +128,33 @@ std::string Hash::to_string(Base base, bool includeType) const
 Hash::Hash(const std::string & s, HashType type)
     : type(type)
 {
-    auto colon = s.find(':');
-
     size_t pos = 0;
-
-    if (colon == string::npos) {
-        if (type == htUnknown)
+    bool isSRI = false;
+
+    auto sep = s.find(':');
+    if (sep == string::npos) {
+        sep = s.find('-');
+        if (sep != string::npos) {
+            isSRI = true;
+        } else if (type == htUnknown)
             throw BadHash("hash '%s' does not include a type", s);
-    } else {
-        string hts = string(s, 0, colon);
+    }
+
+    if (sep != string::npos) {
+        string hts = string(s, 0, sep);
         this->type = parseHashType(hts);
         if (this->type == htUnknown)
             throw BadHash("unknown hash type '%s'", hts);
         if (type != htUnknown && type != this->type)
             throw BadHash("hash '%s' should have type '%s'", s, printHashType(type));
-        pos = colon + 1;
+        pos = sep + 1;
     }
 
     init();
 
     size_t size = s.size() - pos;
 
-    if (size == base16Len()) {
+    if (!isSRI && size == base16Len()) {
 
         auto parseHexDigit = [&](char c) {
             if (c >= '0' && c <= '9') return c - '0';
@@ -164,7 +170,7 @@ Hash::Hash(const std::string & s, HashType type)
         }
     }
 
-    else if (size == base32Len()) {
+    else if (!isSRI && size == base32Len()) {
 
         for (unsigned int n = 0; n < size; ++n) {
             char c = s[pos + size - n - 1];
@@ -187,10 +193,10 @@ Hash::Hash(const std::string & s, HashType type)
         }
     }
 
-    else if (size == base64Len()) {
+    else if (isSRI || size == base64Len()) {
         auto d = base64Decode(std::string(s, pos));
         if (d.size() != hashSize)
-            throw BadHash("invalid base-64 hash '%s'", s);
+            throw BadHash("invalid %s hash '%s'", isSRI ? "SRI" : "base-64", s);
         assert(hashSize);
         memcpy(hash, d.data(), hashSize);
     }
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index fd7a61df8e46..2dbc3b630814 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -20,7 +20,7 @@ const int sha512HashSize = 64;
 
 extern const string base32Chars;
 
-enum Base : int { Base64, Base32, Base16 };
+enum Base : int { Base64, Base32, Base16, SRI };
 
 
 struct Hash
@@ -38,8 +38,9 @@ struct Hash
     Hash(HashType type) : type(type) { init(); };
 
     /* Initialize the hash from a string representation, in the format
-       "[<type>:]<base16|base32|base64>". If the 'type' argument is
-       htUnknown, then the hash type must be specified in the
+       "[<type>:]<base16|base32|base64>" or "<type>-<base64>" (a
+       Subresource Integrity hash expression). If the 'type' argument
+       is htUnknown, then the hash type must be specified in the
        string. */
     Hash(const std::string & s, HashType type = htUnknown);
 
diff --git a/src/libutil/local.mk b/src/libutil/local.mk
index 824f48fbfc9f..3ccc23fd5c1b 100644
--- a/src/libutil/local.mk
+++ b/src/libutil/local.mk
@@ -7,7 +7,3 @@ libutil_DIR := $(d)
 libutil_SOURCES := $(wildcard $(d)/*.cc)
 
 libutil_LDFLAGS = $(LIBLZMA_LIBS) -lbz2 -pthread $(OPENSSL_LIBS) $(LIBBROTLI_LIBS) -lboost_context
-
-libutil_LIBS = libformat
-
-libutil_CXXFLAGS = -DBROTLI=\"$(brotli)\"
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 799c6e1ae441..b379306f6ec0 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -21,7 +21,7 @@ Logger * logger = makeDefaultLogger();
 
 void Logger::warn(const std::string & msg)
 {
-    log(lvlInfo, ANSI_RED "warning:" ANSI_NORMAL " " + msg);
+    log(lvlWarn, ANSI_RED "warning:" ANSI_NORMAL " " + msg);
 }
 
 class SimpleLogger : public Logger
@@ -46,6 +46,7 @@ public:
             char c;
             switch (lvl) {
             case lvlError: c = '3'; break;
+            case lvlWarn: c = '4'; break;
             case lvlInfo: c = '5'; break;
             case lvlTalkative: case lvlChatty: c = '6'; break;
             default: c = '7';
diff --git a/src/libutil/logging.hh b/src/libutil/logging.hh
index 678703102e9b..5f221944594b 100644
--- a/src/libutil/logging.hh
+++ b/src/libutil/logging.hh
@@ -6,6 +6,7 @@ namespace nix {
 
 typedef enum {
     lvlError = 0,
+    lvlWarn,
     lvlInfo,
     lvlTalkative,
     lvlChatty,
diff --git a/src/libutil/lru-cache.hh b/src/libutil/lru-cache.hh
index 9b8290e634c9..8b83f842c324 100644
--- a/src/libutil/lru-cache.hh
+++ b/src/libutil/lru-cache.hh
@@ -2,7 +2,7 @@
 
 #include <map>
 #include <list>
-#include <experimental/optional>
+#include <optional>
 
 namespace nix {
 
@@ -64,7 +64,7 @@ public:
 
     /* Look up an item in the cache. If it exists, it becomes the most
        recently used item. */
-    std::experimental::optional<Value> get(const Key & key)
+    std::optional<Value> get(const Key & key)
     {
         auto i = data.find(key);
         if (i == data.end()) return {};
diff --git a/src/libutil/retry.hh b/src/libutil/retry.hh
new file mode 100644
index 000000000000..b45cb37f736b
--- /dev/null
+++ b/src/libutil/retry.hh
@@ -0,0 +1,38 @@
+#pragma once
+
+#include "logging.hh"
+
+#include <functional>
+#include <cmath>
+#include <random>
+#include <thread>
+
+namespace nix {
+
+inline unsigned int retrySleepTime(unsigned int attempt)
+{
+    std::random_device rd;
+    std::mt19937 mt19937;
+    return 250.0 * std::pow(2.0f,
+        attempt - 1 + std::uniform_real_distribution<>(0.0, 0.5)(mt19937));
+}
+
+template<typename C>
+C retry(unsigned int attempts, std::function<C()> && f)
+{
+    unsigned int attempt = 0;
+    while (true) {
+        try {
+            return f();
+        } catch (BaseError & e) {
+            ++attempt;
+            if (attempt >= attempts || !e.isTransient())
+                throw;
+            auto ms = retrySleepTime(attempt);
+            warn("%s; retrying in %d ms", e.what(), ms);
+            std::this_thread::sleep_for(std::chrono::milliseconds(ms));
+        }
+    }
+}
+
+}
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 0e75eeec2bfe..8201549fd7d0 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -171,7 +171,7 @@ std::unique_ptr<Source> sinkToSource(
 
         std::function<void(Sink &)> fun;
         std::function<void()> eof;
-        std::experimental::optional<coro_t::pull_type> coro;
+        std::optional<coro_t::pull_type> coro;
         bool started = false;
 
         SinkToSource(std::function<void(Sink &)> fun, std::function<void()> eof)
diff --git a/src/libutil/types.hh b/src/libutil/types.hh
index 92bf469b5c6f..88e3243f47a5 100644
--- a/src/libutil/types.hh
+++ b/src/libutil/types.hh
@@ -109,6 +109,8 @@ public:
     const string & msg() const { return err; }
     const string & prefix() const { return prefix_; }
     BaseError & addPrefix(const FormatOrString & fs);
+
+    virtual bool isTransient() { return false; }
 };
 
 #define MakeError(newClass, superClass) \
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index ce50334e1e62..17aee2d5c3d0 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -16,6 +16,7 @@
 #include <future>
 
 #include <fcntl.h>
+#include <grp.h>
 #include <limits.h>
 #include <pwd.h>
 #include <sys/ioctl.h>
@@ -38,6 +39,9 @@ extern char * * environ;
 namespace nix {
 
 
+const std::string nativeSystem = SYSTEM;
+
+
 BaseError & BaseError::addPrefix(const FormatOrString & fs)
 {
     prefix_ = fs.s + prefix_;
@@ -936,8 +940,6 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions & options)
                 throw SysError("setting death signal");
 #endif
             restoreAffinity();
-            if (options.restoreMountNamespace)
-                restoreMountNamespace();
             fun();
         } catch (std::exception & e) {
             try {
@@ -967,7 +969,7 @@ std::vector<char *> stringsToCharPtrs(const Strings & ss)
 
 
 string runProgram(Path program, bool searchPath, const Strings & args,
-    const std::experimental::optional<std::string> & input)
+    const std::optional<std::string> & input)
 {
     RunOptions opts(program, args);
     opts.searchPath = searchPath;
@@ -1024,6 +1026,16 @@ void runProgram2(const RunOptions & options)
         if (source && dup2(in.readSide.get(), STDIN_FILENO) == -1)
             throw SysError("dupping stdin");
 
+        if (options.chdir && chdir((*options.chdir).c_str()) == -1)
+            throw SysError("chdir failed");
+        if (options.gid && setgid(*options.gid) == -1)
+            throw SysError("setgid failed");
+        /* Drop all other groups if we're setgid. */
+        if (options.gid && setgroups(0, 0) == -1)
+            throw SysError("setgroups failed");
+        if (options.uid && setuid(*options.uid) == -1)
+            throw SysError("setuid failed");
+
         Strings args_(options.args);
         args_.push_front(options.program);
 
@@ -1506,26 +1518,4 @@ std::unique_ptr<InterruptCallback> createInterruptCallback(std::function<void()>
     return std::unique_ptr<InterruptCallback>(res.release());
 }
 
-static AutoCloseFD fdSavedMountNamespace;
-
-void saveMountNamespace()
-{
-#if __linux__
-    std::once_flag done;
-    std::call_once(done, []() {
-        fdSavedMountNamespace = open("/proc/self/ns/mnt", O_RDONLY);
-        if (!fdSavedMountNamespace)
-            throw SysError("saving parent mount namespace");
-    });
-#endif
-}
-
-void restoreMountNamespace()
-{
-#if __linux__
-    if (fdSavedMountNamespace && setns(fdSavedMountNamespace.get(), CLONE_NEWNS) == -1)
-        throw SysError("restoring parent mount namespace");
-#endif
-}
-
 }
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index d67bddc138c8..fce3cab8def5 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -14,7 +14,7 @@
 #include <cstdio>
 #include <map>
 #include <sstream>
-#include <experimental/optional>
+#include <optional>
 #include <future>
 
 #ifndef HAVE_STRUCT_DIRENT_D_TYPE
@@ -30,6 +30,10 @@ struct Sink;
 struct Source;
 
 
+/* The system for which Nix is compiled. */
+extern const std::string nativeSystem;
+
+
 /* Return an environment variable. */
 string getEnv(const string & key, const string & def = "");
 
@@ -250,7 +254,6 @@ struct ProcessOptions
     bool dieWithParent = true;
     bool runExitHandlers = false;
     bool allowVfork = true;
-    bool restoreMountNamespace = true;
 };
 
 pid_t startProcess(std::function<void()> fun, const ProcessOptions & options = ProcessOptions());
@@ -260,14 +263,17 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions & options = P
    shell backtick operator). */
 string runProgram(Path program, bool searchPath = false,
     const Strings & args = Strings(),
-    const std::experimental::optional<std::string> & input = {});
+    const std::optional<std::string> & input = {});
 
 struct RunOptions
 {
+    std::optional<uid_t> uid;
+    std::optional<uid_t> gid;
+    std::optional<Path> chdir;
     Path program;
     bool searchPath = true;
     Strings args;
-    std::experimental::optional<std::string> input;
+    std::optional<std::string> input;
     Source * standardIn = nullptr;
     Sink * standardOut = nullptr;
     bool _killStderr = false;
@@ -402,6 +408,7 @@ void ignoreException();
 /* Some ANSI escape sequences. */
 #define ANSI_NORMAL "\e[0m"
 #define ANSI_BOLD "\e[1m"
+#define ANSI_FAINT "\e[2m"
 #define ANSI_RED "\e[31;1m"
 #define ANSI_GREEN "\e[32;1m"
 #define ANSI_BLUE "\e[34;1m"
@@ -515,13 +522,4 @@ typedef std::function<bool(const Path & path)> PathFilter;
 extern PathFilter defaultPathFilter;
 
 
-/* Save the current mount namespace. Ignored if called more than
-   once. */
-void saveMountNamespace();
-
-/* Restore the mount namespace saved by saveMountNamespace(). Ignored
-   if saveMountNamespace() was never called. */
-void restoreMountNamespace();
-
-
 }
diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 11ea3b1f7ae1..c6a4d416648f 100755
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -274,19 +274,21 @@ static void _main(int argc, char * * argv)
         exprs = {state->parseStdin()};
     else
         for (auto i : left) {
-            auto absolute = i;
-            try {
-                absolute = canonPath(absPath(i), true);
-            } catch (Error e) {};
             if (fromArgs)
                 exprs.push_back(state->parseExprFromString(i, absPath(".")));
-            else if (store->isStorePath(absolute) && std::regex_match(absolute, std::regex(".*\\.drv(!.*)?")))
+            else {
+                auto absolute = i;
+                try {
+                    absolute = canonPath(absPath(i), true);
+                } catch (Error e) {};
+                if (store->isStorePath(absolute) && std::regex_match(absolute, std::regex(".*\\.drv(!.*)?")))
                 drvs.push_back(DrvInfo(*state, store, absolute));
             else
                 /* If we're in a #! script, interpret filenames
                    relative to the script. */
                 exprs.push_back(state->parseExprFromFile(resolveExprPath(state->checkSourcePath(lookupFileArg(*state,
                     inShebang && !packages ? absPath(i, absPath(dirOf(script))) : i)))));
+            }
         }
 
     /* Evaluate them into derivations. */
@@ -401,6 +403,8 @@ static void _main(int argc, char * * argv)
             } else
                 env[var.first] = var.second;
 
+        restoreAffinity();
+
         /* Run a shell using the derivation's environment.  For
            convenience, source $stdenv/setup to setup additional
            environment variables and shell functions.  Also don't
@@ -444,9 +448,7 @@ static void _main(int argc, char * * argv)
 
         auto argPtrs = stringsToCharPtrs(args);
 
-        restoreAffinity();
         restoreSignals();
-        restoreMountNamespace();
 
         execvp(shell.c_str(), argPtrs.data());
 
diff --git a/src/nix-channel/nix-channel.cc b/src/nix-channel/nix-channel.cc
index 8b66cc7e314e..06eb3d23ba83 100755
--- a/src/nix-channel/nix-channel.cc
+++ b/src/nix-channel/nix-channel.cc
@@ -86,10 +86,12 @@ static void update(const StringSet & channelNames)
         // We want to download the url to a file to see if it's a tarball while also checking if we
         // got redirected in the process, so that we can grab the various parts of a nix channel
         // definition from a consistent location if the redirect changes mid-download.
-        std::string effectiveUrl;
+        CachedDownloadRequest request(url);
+        request.ttl = 0;
         auto dl = getDownloader();
-        auto filename = dl->downloadCached(store, url, false, "", Hash(), &effectiveUrl, 0);
-        url = chomp(std::move(effectiveUrl));
+        auto result = dl->downloadCached(store, request);
+        auto filename = result.path;
+        url = chomp(result.effectiveUri);
 
         // If the URL contains a version number, append it to the name
         // attribute (so that "nix-env -q" on the channels profile
@@ -111,22 +113,11 @@ static void update(const StringSet & channelNames)
         }
 
         if (!unpacked) {
-            // The URL doesn't unpack directly, so let's try treating it like a full channel folder with files in it
-            // Check if the channel advertises a binary cache.
-            DownloadRequest request(url + "/binary-cache-url");
-            try {
-                auto dlRes = dl->download(request);
-                extraAttrs = "binaryCacheURL = \"" + *dlRes.data + "\";";
-            } catch (DownloadError & e) {
-            }
-
             // Download the channel tarball.
-            auto fullURL = url + "/nixexprs.tar.xz";
             try {
-                filename = dl->downloadCached(store, fullURL, false);
+                filename = dl->downloadCached(store, CachedDownloadRequest(url + "/nixexprs.tar.xz")).path;
             } catch (DownloadError & e) {
-                fullURL = url + "/nixexprs.tar.bz2";
-                filename = dl->downloadCached(store, fullURL, false);
+                filename = dl->downloadCached(store, CachedDownloadRequest(url + "/nixexprs.tar.bz2")).path;
             }
             chomp(filename);
         }
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index 8368c3266142..e88aaf636444 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -475,11 +475,19 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
 
     case wopFindRoots: {
         logger->startWork();
-        Roots roots = store->findRoots();
+        Roots roots = store->findRoots(!trusted);
         logger->stopWork();
-        to << roots.size();
+
+        size_t size = 0;
         for (auto & i : roots)
-            to << i.first << i.second;
+            size += i.second.size();
+
+        to << size;
+
+        for (auto & [target, links] : roots)
+            for (auto & link : links)
+                to << link << target;
+
         break;
     }
 
@@ -566,7 +574,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                 else if (setSubstituters(settings.extraSubstituters))
                     ;
                 else
-                    debug("ignoring untrusted setting '%s'", name);
+                    warn("ignoring the user-specified setting '%s', because it is a restricted setting and you are not a trusted user", name);
             } catch (UsageError & e) {
                 warn(e.what());
             }
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index a9ad14762e62..f324056bb3a1 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -427,10 +427,11 @@ static void opQuery(Strings opFlags, Strings opArgs)
                     maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise),
                     referrers, true, settings.gcKeepOutputs, settings.gcKeepDerivations);
             }
-            Roots roots = store->findRoots();
-            for (auto & i : roots)
-                if (referrers.find(i.second) != referrers.end())
-                    cout << format("%1%\n") % i.first;
+            Roots roots = store->findRoots(false);
+            for (auto & [target, links] : roots)
+                if (referrers.find(target) != referrers.end())
+                    for (auto & link : links)
+                        cout << format("%1% -> %2%\n") % link % target;
             break;
         }
 
@@ -485,11 +486,16 @@ static void opReadLog(Strings opFlags, Strings opArgs)
 static void opDumpDB(Strings opFlags, Strings opArgs)
 {
     if (!opFlags.empty()) throw UsageError("unknown flag");
-    if (!opArgs.empty())
-        throw UsageError("no arguments expected");
-    PathSet validPaths = store->queryAllValidPaths();
-    for (auto & i : validPaths)
-        cout << store->makeValidityRegistration({i}, true, true);
+    if (!opArgs.empty()) {
+        for (auto & i : opArgs)
+            i = store->followLinksToStorePath(i);
+        for (auto & i : opArgs)
+            cout << store->makeValidityRegistration({i}, true, true);
+    } else {
+        PathSet validPaths = store->queryAllValidPaths();
+        for (auto & i : validPaths)
+            cout << store->makeValidityRegistration({i}, true, true);
+    }
 }
 
 
@@ -585,9 +591,14 @@ static void opGC(Strings opFlags, Strings opArgs)
     if (!opArgs.empty()) throw UsageError("no arguments expected");
 
     if (printRoots) {
-        Roots roots = store->findRoots();
-        for (auto & i : roots)
-            cout << i.first << " -> " << i.second << std::endl;
+        Roots roots = store->findRoots(false);
+        std::set<std::pair<Path, Path>> roots2;
+        // Transpose and sort the roots.
+        for (auto & [target, links] : roots)
+            for (auto & link : links)
+                roots2.emplace(link, target);
+        for (auto & [link, target] : roots2)
+            std::cout << link << " -> " << target << "\n";
     }
 
     else {
diff --git a/src/nix/add-to-store.cc b/src/nix/add-to-store.cc
index d0003790d3b9..e86b96e3f3f2 100644
--- a/src/nix/add-to-store.cc
+++ b/src/nix/add-to-store.cc
@@ -8,7 +8,7 @@ using namespace nix;
 struct CmdAddToStore : MixDryRun, StoreCommand
 {
     Path path;
-    std::experimental::optional<std::string> namePart;
+    std::optional<std::string> namePart;
 
     CmdAddToStore()
     {
diff --git a/src/nix/edit.cc b/src/nix/edit.cc
index d8d5895bd867..c9671f76d0fa 100644
--- a/src/nix/edit.cc
+++ b/src/nix/edit.cc
@@ -3,7 +3,6 @@
 #include "eval.hh"
 #include "attr-path.hh"
 #include "progress-bar.hh"
-#include "affinity.hh"
 
 #include <unistd.h>
 
@@ -73,10 +72,6 @@ struct CmdEdit : InstallableCommand
 
         stopProgressBar();
 
-        restoreAffinity();
-        restoreSignals();
-        restoreMountNamespace();
-
         execvp(args.front().c_str(), stringsToCharPtrs(args).data());
 
         throw SysError("cannot run editor '%s'", editor);
diff --git a/src/nix/hash.cc b/src/nix/hash.cc
index 64062fb97955..af4105e28904 100644
--- a/src/nix/hash.cc
+++ b/src/nix/hash.cc
@@ -9,13 +9,14 @@ struct CmdHash : Command
 {
     enum Mode { mFile, mPath };
     Mode mode;
-    Base base = Base16;
+    Base base = SRI;
     bool truncate = false;
-    HashType ht = htSHA512;
+    HashType ht = htSHA256;
     std::vector<std::string> paths;
 
     CmdHash(Mode mode) : mode(mode)
     {
+        mkFlag(0, "sri", "print hash in SRI format", &base, SRI);
         mkFlag(0, "base64", "print hash in base-64", &base, Base64);
         mkFlag(0, "base32", "print hash in base-32 (Nix-specific)", &base, Base32);
         mkFlag(0, "base16", "print hash in base-16", &base, Base16);
@@ -43,7 +44,7 @@ struct CmdHash : Command
             Hash h = mode == mFile ? hashFile(ht, path) : hashPath(ht, path).first;
             if (truncate && h.hashSize > 20) h = compressHash(h, 20);
             std::cout << format("%1%\n") %
-                h.to_string(base, false);
+                h.to_string(base, base == SRI);
         }
     }
 };
@@ -54,7 +55,7 @@ static RegisterCommand r2(make_ref<CmdHash>(CmdHash::mPath));
 struct CmdToBase : Command
 {
     Base base;
-    HashType ht = htSHA512;
+    HashType ht = htUnknown;
     std::vector<std::string> args;
 
     CmdToBase(Base base) : base(base)
@@ -70,26 +71,30 @@ struct CmdToBase : Command
         return
             base == Base16 ? "to-base16" :
             base == Base32 ? "to-base32" :
-            "to-base64";
+            base == Base64 ? "to-base64" :
+            "to-sri";
     }
 
     std::string description() override
     {
-        return fmt("convert a hash to base-%d representation",
-            base == Base16 ? 16 :
-            base == Base32 ? 32 : 64);
+        return fmt("convert a hash to %s representation",
+            base == Base16 ? "base-16" :
+            base == Base32 ? "base-32" :
+            base == Base64 ? "base-64" :
+            "SRI");
     }
 
     void run() override
     {
         for (auto s : args)
-            std::cout << fmt("%s\n", Hash(s, ht).to_string(base, false));
+            std::cout << fmt("%s\n", Hash(s, ht).to_string(base, base == SRI));
     }
 };
 
 static RegisterCommand r3(make_ref<CmdToBase>(Base16));
 static RegisterCommand r4(make_ref<CmdToBase>(Base32));
 static RegisterCommand r5(make_ref<CmdToBase>(Base64));
+static RegisterCommand r6(make_ref<CmdToBase>(SRI));
 
 /* Legacy nix-hash command. */
 static int compatNixHash(int argc, char * * argv)
diff --git a/src/nix/local.mk b/src/nix/local.mk
index 40a0e8d6bde1..ca4604d566c3 100644
--- a/src/nix/local.mk
+++ b/src/nix/local.mk
@@ -15,7 +15,7 @@ nix_SOURCES := \
   $(wildcard src/nix-prefetch-url/*.cc) \
   $(wildcard src/nix-store/*.cc) \
 
-nix_LIBS = libexpr libmain libstore libutil libformat
+nix_LIBS = libexpr libmain libstore libutil
 
 nix_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS)
 
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 64c1dc35787c..a80fd0ea62fc 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -8,18 +8,53 @@
 #include "shared.hh"
 #include "store-api.hh"
 #include "progress-bar.hh"
+#include "download.hh"
 #include "finally.hh"
 
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <ifaddrs.h>
+#include <netdb.h>
+
 extern std::string chrootHelperName;
 
 void chrootHelper(int argc, char * * argv);
 
 namespace nix {
 
+/* Check if we have a non-loopback/link-local network interface. */
+static bool haveInternet()
+{
+    struct ifaddrs * addrs;
+
+    if (getifaddrs(&addrs))
+        return true;
+
+    Finally free([&]() { freeifaddrs(addrs); });
+
+    for (auto i = addrs; i; i = i->ifa_next) {
+        if (!i->ifa_addr) continue;
+        if (i->ifa_addr->sa_family == AF_INET) {
+            if (ntohl(((sockaddr_in *) i->ifa_addr)->sin_addr.s_addr) != INADDR_LOOPBACK) {
+                return true;
+            }
+        } else if (i->ifa_addr->sa_family == AF_INET6) {
+            if (!IN6_IS_ADDR_LOOPBACK(&((sockaddr_in6 *) i->ifa_addr)->sin6_addr) &&
+                !IN6_IS_ADDR_LINKLOCAL(&((sockaddr_in6 *) i->ifa_addr)->sin6_addr))
+                return true;
+        }
+    }
+
+    return false;
+}
+
 std::string programPath;
 
 struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
 {
+    bool printBuildLogs = false;
+    bool useNet = true;
+
     NixArgs() : MultiCommand(*RegisterCommand::commands), MixCommonArgs("nix")
     {
         mkFlag()
@@ -42,9 +77,20 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
             });
 
         mkFlag()
+            .longName("print-build-logs")
+            .shortName('L')
+            .description("print full build logs on stderr")
+            .set(&printBuildLogs, true);
+
+        mkFlag()
             .longName("version")
             .description("show version information")
             .handler([&]() { printVersion(programName); });
+
+        mkFlag()
+            .longName("no-net")
+            .description("disable substituters and consider all previously downloaded files up-to-date")
+            .handler([&]() { useNet = false; });
     }
 
     void printFlags(std::ostream & out) override
@@ -85,7 +131,7 @@ void mainWrapped(int argc, char * * argv)
         if (legacy) return legacy(argc, argv);
     }
 
-    verbosity = lvlError;
+    verbosity = lvlWarn;
     settings.verboseBuild = false;
 
     NixArgs args;
@@ -98,8 +144,24 @@ void mainWrapped(int argc, char * * argv)
 
     Finally f([]() { stopProgressBar(); });
 
-    if (isatty(STDERR_FILENO))
-        startProgressBar();
+    startProgressBar(args.printBuildLogs);
+
+    if (args.useNet && !haveInternet()) {
+        warn("you don't have Internet access; disabling some network-dependent features");
+        args.useNet = false;
+    }
+
+    if (!args.useNet) {
+        // FIXME: should check for command line overrides only.
+        if (!settings.useSubstitutes.overriden)
+            settings.useSubstitutes = false;
+        if (!settings.tarballTtl.overriden)
+            settings.tarballTtl = std::numeric_limits<unsigned int>::max();
+        if (!downloadSettings.tries.overriden)
+            downloadSettings.tries = 0;
+        if (!downloadSettings.connectTimeout.overriden)
+            downloadSettings.connectTimeout = 1;
+    }
 
     args.command->prepare();
     args.command->run();
diff --git a/src/nix/progress-bar.cc b/src/nix/progress-bar.cc
index 40b905ba3243..b1c1d87de1a2 100644
--- a/src/nix/progress-bar.cc
+++ b/src/nix/progress-bar.cc
@@ -2,6 +2,7 @@
 #include "util.hh"
 #include "sync.hh"
 #include "store-api.hh"
+#include "names.hh"
 
 #include <atomic>
 #include <map>
@@ -38,6 +39,7 @@ private:
         std::map<ActivityType, uint64_t> expectedByType;
         bool visible = true;
         ActivityId parent;
+        std::optional<std::string> name;
     };
 
     struct ActivitiesByType
@@ -60,6 +62,7 @@ private:
         uint64_t corruptedPaths = 0, untrustedPaths = 0;
 
         bool active = true;
+        bool haveUpdate = true;
     };
 
     Sync<State> state_;
@@ -68,14 +71,21 @@ private:
 
     std::condition_variable quitCV, updateCV;
 
+    bool printBuildLogs;
+    bool isTTY;
+
 public:
 
-    ProgressBar()
+    ProgressBar(bool printBuildLogs, bool isTTY)
+        : printBuildLogs(printBuildLogs)
+        , isTTY(isTTY)
     {
+        state_.lock()->active = isTTY;
         updateThread = std::thread([&]() {
             auto state(state_.lock());
             while (state->active) {
-                state.wait(updateCV);
+                if (!state->haveUpdate)
+                    state.wait(updateCV);
                 draw(*state);
                 state.wait_for(quitCV, std::chrono::milliseconds(50));
             }
@@ -109,8 +119,14 @@ public:
 
     void log(State & state, Verbosity lvl, const std::string & s)
     {
-        writeToStderr("\r\e[K" + s + ANSI_NORMAL "\n");
-        draw(state);
+        if (state.active) {
+            writeToStderr("\r\e[K" + s + ANSI_NORMAL "\n");
+            draw(state);
+        } else {
+            auto s2 = s + ANSI_NORMAL "\n";
+            if (!isTTY) s2 = filterANSIEscapes(s2, true);
+            writeToStderr(s2);
+        }
     }
 
     void startActivity(ActivityId act, Verbosity lvl, ActivityType type,
@@ -141,6 +157,7 @@ public:
             auto nrRounds = getI(fields, 3);
             if (nrRounds != 1)
                 i->s += fmt(" (round %d/%d)", curRound, nrRounds);
+            i->name = DrvName(name).name;
         }
 
         if (type == actSubstitute) {
@@ -163,7 +180,7 @@ public:
             || (type == actCopyPath && hasAncestor(*state, actSubstitute, parent)))
             i->visible = false;
 
-        update();
+        update(*state);
     }
 
     /* Check whether an activity has an ancestore with the specified
@@ -198,7 +215,7 @@ public:
             state->its.erase(i);
         }
 
-        update();
+        update(*state);
     }
 
     void result(ActivityId act, ResultType type, const std::vector<Field> & fields) override
@@ -208,7 +225,7 @@ public:
         if (type == resFileLinked) {
             state->filesLinked++;
             state->bytesLinked += getI(fields, 0);
-            update();
+            update(*state);
         }
 
         else if (type == resBuildLogLine) {
@@ -217,29 +234,33 @@ public:
                 auto i = state->its.find(act);
                 assert(i != state->its.end());
                 ActInfo info = *i->second;
-                state->activities.erase(i->second);
-                info.lastLine = lastLine;
-                state->activities.emplace_back(info);
-                i->second = std::prev(state->activities.end());
-                update();
+                if (printBuildLogs) {
+                    log(*state, lvlInfo, ANSI_FAINT + info.name.value_or("unnamed") + "> " + ANSI_NORMAL + lastLine);
+                } else {
+                    state->activities.erase(i->second);
+                    info.lastLine = lastLine;
+                    state->activities.emplace_back(info);
+                    i->second = std::prev(state->activities.end());
+                    update(*state);
+                }
             }
         }
 
         else if (type == resUntrustedPath) {
             state->untrustedPaths++;
-            update();
+            update(*state);
         }
 
         else if (type == resCorruptedPath) {
             state->corruptedPaths++;
-            update();
+            update(*state);
         }
 
         else if (type == resSetPhase) {
             auto i = state->its.find(act);
             assert(i != state->its.end());
             i->second->phase = getS(fields, 0);
-            update();
+            update(*state);
         }
 
         else if (type == resProgress) {
@@ -250,7 +271,7 @@ public:
             actInfo.expected = getI(fields, 1);
             actInfo.running = getI(fields, 2);
             actInfo.failed = getI(fields, 3);
-            update();
+            update(*state);
         }
 
         else if (type == resSetExpected) {
@@ -262,17 +283,19 @@ public:
             state->activitiesByType[type].expected -= j;
             j = getI(fields, 1);
             state->activitiesByType[type].expected += j;
-            update();
+            update(*state);
         }
     }
 
-    void update()
+    void update(State & state)
     {
+        state.haveUpdate = true;
         updateCV.notify_one();
     }
 
     void draw(State & state)
     {
+        state.haveUpdate = false;
         if (!state.active) return;
 
         std::string line;
@@ -333,11 +356,18 @@ public:
 
             if (running || done || expected || failed) {
                 if (running)
-                    s = fmt(ANSI_BLUE + numberFmt + ANSI_NORMAL "/" ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
-                        running / unit, done / unit, expected / unit);
+                    if (expected != 0)
+                        s = fmt(ANSI_BLUE + numberFmt + ANSI_NORMAL "/" ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
+                            running / unit, done / unit, expected / unit);
+                    else
+                        s = fmt(ANSI_BLUE + numberFmt + ANSI_NORMAL "/" ANSI_GREEN + numberFmt + ANSI_NORMAL,
+                            running / unit, done / unit);
                 else if (expected != done)
-                    s = fmt(ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
-                        done / unit, expected / unit);
+                    if (expected != 0)
+                        s = fmt(ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
+                            done / unit, expected / unit);
+                    else
+                        s = fmt(ANSI_GREEN + numberFmt + ANSI_NORMAL, done / unit);
                 else
                     s = fmt(done ? ANSI_GREEN + numberFmt + ANSI_NORMAL : numberFmt, done / unit);
                 s = fmt(itemFmt, s);
@@ -395,9 +425,9 @@ public:
     }
 };
 
-void startProgressBar()
+void startProgressBar(bool printBuildLogs)
 {
-    logger = new ProgressBar();
+    logger = new ProgressBar(printBuildLogs, isatty(STDERR_FILENO));
 }
 
 void stopProgressBar()
diff --git a/src/nix/progress-bar.hh b/src/nix/progress-bar.hh
index af8eda5a84fd..4d61175c24e4 100644
--- a/src/nix/progress-bar.hh
+++ b/src/nix/progress-bar.hh
@@ -4,7 +4,7 @@
 
 namespace nix {
 
-void startProgressBar();
+void startProgressBar(bool printBuildLogs = false);
 
 void stopProgressBar();
 
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
index d4806d74adb8..d8f812149069 100644
--- a/src/nix/repl.cc
+++ b/src/nix/repl.cc
@@ -192,6 +192,14 @@ static int listPossibleCallback(char *s, char ***avp) {
   return ac;
 }
 
+namespace {
+    // Used to communicate to NixRepl::getLine whether a signal occurred in ::readline.
+    volatile sig_atomic_t g_signal_received = 0;
+
+    void sigintHandler(int signo) {
+        g_signal_received = signo;
+    }
+}
 
 void NixRepl::mainLoop(const std::vector<std::string> & files)
 {
@@ -251,8 +259,40 @@ void NixRepl::mainLoop(const std::vector<std::string> & files)
 
 bool NixRepl::getLine(string & input, const std::string &prompt)
 {
+    struct sigaction act, old;
+    sigset_t savedSignalMask, set;
+
+    auto setupSignals = [&]() {
+        act.sa_handler = sigintHandler;
+        sigfillset(&act.sa_mask);
+        act.sa_flags = 0;
+        if (sigaction(SIGINT, &act, &old))
+            throw SysError("installing handler for SIGINT");
+
+        sigemptyset(&set);
+        sigaddset(&set, SIGINT);
+        if (sigprocmask(SIG_UNBLOCK, &set, &savedSignalMask))
+            throw SysError("unblocking SIGINT");
+    };
+    auto restoreSignals = [&]() {
+        if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr))
+            throw SysError("restoring signals");
+
+        if (sigaction(SIGINT, &old, 0))
+            throw SysError("restoring handler for SIGINT");
+    };
+
+    setupSignals();
     char * s = readline(prompt.c_str());
     Finally doFree([&]() { free(s); });
+    restoreSignals();
+
+    if (g_signal_received) {
+        g_signal_received = 0;
+        input.clear();
+        return true;
+    }
+
     if (!s)
       return false;
     input += s;
@@ -337,8 +377,6 @@ static int runProgram(const string & program, const Strings & args)
     if (pid == -1) throw SysError("forking");
     if (pid == 0) {
         restoreAffinity();
-        restoreSignals();
-        restoreMountNamespace();
         execvp(program.c_str(), stringsToCharPtrs(args2).data());
         _exit(1);
     }
@@ -643,30 +681,13 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
             for (auto & i : *v.attrs)
                 sorted[i.name] = i.value;
 
-            /* If this is a derivation, then don't show the
-               self-references ("all", "out", etc.). */
-            StringSet hidden;
-            if (isDrv) {
-                hidden.insert("all");
-                Bindings::iterator i = v.attrs->find(state.sOutputs);
-                if (i == v.attrs->end())
-                    hidden.insert("out");
-                else {
-                    state.forceList(*i->value);
-                    for (unsigned int j = 0; j < i->value->listSize(); ++j)
-                        hidden.insert(state.forceStringNoCtx(*i->value->listElems()[j]));
-                }
-            }
-
             for (auto & i : sorted) {
                 if (isVarName(i.first))
                     str << i.first;
                 else
                     printStringValue(str, i.first.c_str());
                 str << " = ";
-                if (hidden.find(i.first) != hidden.end())
-                    str << "ยซ...ยป";
-                else if (seen.find(i.second) != seen.end())
+                if (seen.find(i.second) != seen.end())
                     str << "ยซrepeatedยป";
                 else
                     try {
diff --git a/src/nix/run.cc b/src/nix/run.cc
index 1297072989b9..35b763345872 100644
--- a/src/nix/run.cc
+++ b/src/nix/run.cc
@@ -153,9 +153,9 @@ struct CmdRun : InstallablesCommand
 
         stopProgressBar();
 
-        restoreAffinity();
         restoreSignals();
-        restoreMountNamespace();
+
+        restoreAffinity();
 
         /* If this is a diverted store (i.e. its "logical" location
            (typically /nix/store) differs from its "physical" location
diff --git a/src/nlohmann/json.hpp b/src/nlohmann/json.hpp
index 5b0b0ea5b301..c9af0bed36d6 100644
--- a/src/nlohmann/json.hpp
+++ b/src/nlohmann/json.hpp
@@ -1,11 +1,12 @@
 /*
     __ _____ _____ _____
  __|  |   __|     |   | |  JSON for Modern C++
-|  |  |__   |  |  | | | |  version 3.0.1
+|  |  |__   |  |  | | | |  version 3.5.0
 |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 
 Licensed under the MIT License <http://opensource.org/licenses/MIT>.
-Copyright (c) 2013-2017 Niels Lohmann <http://nlohmann.me>.
+SPDX-License-Identifier: MIT
+Copyright (c) 2013-2018 Niels Lohmann <http://nlohmann.me>.
 
 Permission is hereby  granted, free of charge, to any  person obtaining a copy
 of this software and associated  documentation files (the "Software"), to deal
@@ -29,42 +30,104 @@ SOFTWARE.
 #ifndef NLOHMANN_JSON_HPP
 #define NLOHMANN_JSON_HPP
 
-#include <algorithm> // all_of, copy, fill, find, for_each, generate_n, none_of, remove, reverse, transform
-#include <array> // array
+#define NLOHMANN_JSON_VERSION_MAJOR 3
+#define NLOHMANN_JSON_VERSION_MINOR 5
+#define NLOHMANN_JSON_VERSION_PATCH 0
+
+#include <algorithm> // all_of, find, for_each
 #include <cassert> // assert
 #include <ciso646> // and, not, or
-#include <clocale> // lconv, localeconv
-#include <cmath> // isfinite, labs, ldexp, signbit
 #include <cstddef> // nullptr_t, ptrdiff_t, size_t
-#include <cstdint> // int64_t, uint64_t
-#include <cstdlib> // abort, strtod, strtof, strtold, strtoul, strtoll, strtoull
-#include <cstring> // memcpy, strlen
-#include <forward_list> // forward_list
-#include <functional> // function, hash, less
+#include <functional> // hash, less
 #include <initializer_list> // initializer_list
-#include <iomanip> // hex
-#include <iosfwd>   // istream, ostream
-#include <iterator> // advance, begin, back_inserter, bidirectional_iterator_tag, distance, end, inserter, iterator, iterator_traits, next, random_access_iterator_tag, reverse_iterator
-#include <limits> // numeric_limits
-#include <locale> // locale
-#include <map> // map
-#include <memory> // addressof, allocator, allocator_traits, unique_ptr
+#include <iosfwd> // istream, ostream
+#include <iterator> // random_access_iterator_tag
 #include <numeric> // accumulate
-#include <sstream> // stringstream
-#include <string> // getline, stoi, string, to_string
-#include <type_traits> // add_pointer, conditional, decay, enable_if, false_type, integral_constant, is_arithmetic, is_base_of, is_const, is_constructible, is_convertible, is_default_constructible, is_enum, is_floating_point, is_integral, is_nothrow_move_assignable, is_nothrow_move_constructible, is_pointer, is_reference, is_same, is_scalar, is_signed, remove_const, remove_cv, remove_pointer, remove_reference, true_type, underlying_type
-#include <utility> // declval, forward, make_pair, move, pair, swap
-#include <valarray> // valarray
+#include <string> // string, stoi, to_string
+#include <utility> // declval, forward, move, pair, swap
+
+// #include <nlohmann/json_fwd.hpp>
+#ifndef NLOHMANN_JSON_FWD_HPP
+#define NLOHMANN_JSON_FWD_HPP
+
+#include <cstdint> // int64_t, uint64_t
+#include <map> // map
+#include <memory> // allocator
+#include <string> // string
 #include <vector> // vector
 
+/*!
+@brief namespace for Niels Lohmann
+@see https://github.com/nlohmann
+@since version 1.0.0
+*/
+namespace nlohmann
+{
+/*!
+@brief default JSONSerializer template argument
+
+This serializer ignores the template arguments and uses ADL
+([argument-dependent lookup](https://en.cppreference.com/w/cpp/language/adl))
+for serialization.
+*/
+template<typename T = void, typename SFINAE = void>
+struct adl_serializer;
+
+template<template<typename U, typename V, typename... Args> class ObjectType =
+         std::map,
+         template<typename U, typename... Args> class ArrayType = std::vector,
+         class StringType = std::string, class BooleanType = bool,
+         class NumberIntegerType = std::int64_t,
+         class NumberUnsignedType = std::uint64_t,
+         class NumberFloatType = double,
+         template<typename U> class AllocatorType = std::allocator,
+         template<typename T, typename SFINAE = void> class JSONSerializer =
+         adl_serializer>
+class basic_json;
+
+/*!
+@brief JSON Pointer
+
+A JSON pointer defines a string syntax for identifying a specific value
+within a JSON document. It can be used with functions `at` and
+`operator[]`. Furthermore, JSON pointers are the base for JSON patches.
+
+@sa [RFC 6901](https://tools.ietf.org/html/rfc6901)
+
+@since version 2.0.0
+*/
+template<typename BasicJsonType>
+class json_pointer;
+
+/*!
+@brief default JSON class
+
+This type is the default specialization of the @ref basic_json class which
+uses the standard template types.
+
+@since version 1.0.0
+*/
+using json = basic_json<>;
+}  // namespace nlohmann
+
+#endif
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+
+// This file contains all internal macro definitions
+// You MUST include macro_unscope.hpp at the end of json.hpp to undef all of them
+
 // exclude unsupported compilers
-#if defined(__clang__)
-    #if (__clang_major__ * 10000 + __clang_minor__ * 100 + __clang_patchlevel__) < 30400
-        #error "unsupported Clang version - see https://github.com/nlohmann/json#supported-compilers"
-    #endif
-#elif defined(__GNUC__) && !(defined(__ICC) || defined(__INTEL_COMPILER))
-    #if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40900
-        #error "unsupported GCC version - see https://github.com/nlohmann/json#supported-compilers"
+#if !defined(JSON_SKIP_UNSUPPORTED_COMPILER_CHECK)
+    #if defined(__clang__)
+        #if (__clang_major__ * 10000 + __clang_minor__ * 100 + __clang_patchlevel__) < 30400
+            #error "unsupported Clang version - see https://github.com/nlohmann/json#supported-compilers"
+        #endif
+    #elif defined(__GNUC__) && !(defined(__ICC) || defined(__INTEL_COMPILER))
+        #if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40800
+            #error "unsupported GCC version - see https://github.com/nlohmann/json#supported-compilers"
+        #endif
     #endif
 #endif
 
@@ -90,14 +153,36 @@ SOFTWARE.
 #endif
 
 // allow to disable exceptions
-#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && not defined(JSON_NOEXCEPTION)
+#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && !defined(JSON_NOEXCEPTION)
     #define JSON_THROW(exception) throw exception
     #define JSON_TRY try
     #define JSON_CATCH(exception) catch(exception)
+    #define JSON_INTERNAL_CATCH(exception) catch(exception)
 #else
     #define JSON_THROW(exception) std::abort()
     #define JSON_TRY if(true)
     #define JSON_CATCH(exception) if(false)
+    #define JSON_INTERNAL_CATCH(exception) if(false)
+#endif
+
+// override exception macros
+#if defined(JSON_THROW_USER)
+    #undef JSON_THROW
+    #define JSON_THROW JSON_THROW_USER
+#endif
+#if defined(JSON_TRY_USER)
+    #undef JSON_TRY
+    #define JSON_TRY JSON_TRY_USER
+#endif
+#if defined(JSON_CATCH_USER)
+    #undef JSON_CATCH
+    #define JSON_CATCH JSON_CATCH_USER
+    #undef JSON_INTERNAL_CATCH
+    #define JSON_INTERNAL_CATCH JSON_CATCH_USER
+#endif
+#if defined(JSON_INTERNAL_CATCH_USER)
+    #undef JSON_INTERNAL_CATCH
+    #define JSON_INTERNAL_CATCH JSON_INTERNAL_CATCH_USER
 #endif
 
 // manual branch prediction
@@ -118,25 +203,35 @@ SOFTWARE.
 #endif
 
 /*!
-@brief namespace for Niels Lohmann
-@see https://github.com/nlohmann
-@since version 1.0.0
+@brief macro to briefly define a mapping between an enum and JSON
+@def NLOHMANN_JSON_SERIALIZE_ENUM
+@since version 3.4.0
 */
-namespace nlohmann
-{
-template<typename = void, typename = void>
-struct adl_serializer;
-
-// forward declaration of basic_json (required to split the class)
-template<template<typename, typename, typename...> class ObjectType = std::map,
-         template<typename, typename...> class ArrayType = std::vector,
-         class StringType = std::string, class BooleanType = bool,
-         class NumberIntegerType = std::int64_t,
-         class NumberUnsignedType = std::uint64_t,
-         class NumberFloatType = double,
-         template<typename> class AllocatorType = std::allocator,
-         template<typename, typename = void> class JSONSerializer = adl_serializer>
-class basic_json;
+#define NLOHMANN_JSON_SERIALIZE_ENUM(ENUM_TYPE, ...)                                           \
+    template<typename BasicJsonType>                                                           \
+    inline void to_json(BasicJsonType& j, const ENUM_TYPE& e)                                  \
+    {                                                                                          \
+        static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");         \
+        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                    \
+        auto it = std::find_if(std::begin(m), std::end(m),                                     \
+                               [e](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
+        {                                                                                      \
+            return ej_pair.first == e;                                                         \
+        });                                                                                    \
+        j = ((it != std::end(m)) ? it : std::begin(m))->second;                                \
+    }                                                                                          \
+    template<typename BasicJsonType>                                                           \
+    inline void from_json(const BasicJsonType& j, ENUM_TYPE& e)                                \
+    {                                                                                          \
+        static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");         \
+        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                    \
+        auto it = std::find_if(std::begin(m), std::end(m),                                     \
+                               [j](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
+        {                                                                                      \
+            return ej_pair.second == j;                                                        \
+        });                                                                                    \
+        e = ((it != std::end(m)) ? it : std::begin(m))->first;                                 \
+    }
 
 // Ugly macros to avoid uglier copy-paste when specializing basic_json. They
 // may be removed in the future once the class is split.
@@ -154,17 +249,590 @@ class basic_json;
     NumberIntegerType, NumberUnsignedType, NumberFloatType,                \
     AllocatorType, JSONSerializer>
 
+// #include <nlohmann/detail/meta/cpp_future.hpp>
+
+
+#include <ciso646> // not
+#include <cstddef> // size_t
+#include <type_traits> // conditional, enable_if, false_type, integral_constant, is_constructible, is_integral, is_same, remove_cv, remove_reference, true_type
+
+namespace nlohmann
+{
+namespace detail
+{
+// alias templates to reduce boilerplate
+template<bool B, typename T = void>
+using enable_if_t = typename std::enable_if<B, T>::type;
+
+template<typename T>
+using uncvref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
+
+// implementation of C++14 index_sequence and affiliates
+// source: https://stackoverflow.com/a/32223343
+template<std::size_t... Ints>
+struct index_sequence
+{
+    using type = index_sequence;
+    using value_type = std::size_t;
+    static constexpr std::size_t size() noexcept
+    {
+        return sizeof...(Ints);
+    }
+};
+
+template<class Sequence1, class Sequence2>
+struct merge_and_renumber;
+
+template<std::size_t... I1, std::size_t... I2>
+struct merge_and_renumber<index_sequence<I1...>, index_sequence<I2...>>
+        : index_sequence < I1..., (sizeof...(I1) + I2)... > {};
+
+template<std::size_t N>
+struct make_index_sequence
+    : merge_and_renumber < typename make_index_sequence < N / 2 >::type,
+      typename make_index_sequence < N - N / 2 >::type > {};
+
+template<> struct make_index_sequence<0> : index_sequence<> {};
+template<> struct make_index_sequence<1> : index_sequence<0> {};
+
+template<typename... Ts>
+using index_sequence_for = make_index_sequence<sizeof...(Ts)>;
+
+// dispatch utility (taken from ranges-v3)
+template<unsigned N> struct priority_tag : priority_tag < N - 1 > {};
+template<> struct priority_tag<0> {};
+
+// taken from ranges-v3
+template<typename T>
+struct static_const
+{
+    static constexpr T value{};
+};
+
+template<typename T>
+constexpr T static_const<T>::value;
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
+
+#include <ciso646> // not
+#include <limits> // numeric_limits
+#include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
+#include <utility> // declval
+
+// #include <nlohmann/json_fwd.hpp>
+
+// #include <nlohmann/detail/iterators/iterator_traits.hpp>
+
+
+#include <iterator> // random_access_iterator_tag
+
+// #include <nlohmann/detail/meta/void_t.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+template <typename ...Ts> struct make_void
+{
+    using type = void;
+};
+template <typename ...Ts> using void_t = typename make_void<Ts...>::type;
+} // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/meta/cpp_future.hpp>
+
 
+namespace nlohmann
+{
+namespace detail
+{
+template <typename It, typename = void>
+struct iterator_types {};
+
+template <typename It>
+struct iterator_types <
+    It,
+    void_t<typename It::difference_type, typename It::value_type, typename It::pointer,
+    typename It::reference, typename It::iterator_category >>
+{
+    using difference_type = typename It::difference_type;
+    using value_type = typename It::value_type;
+    using pointer = typename It::pointer;
+    using reference = typename It::reference;
+    using iterator_category = typename It::iterator_category;
+};
+
+// This is required as some compilers implement std::iterator_traits in a way that
+// doesn't work with SFINAE. See https://github.com/nlohmann/json/issues/1341.
+template <typename T, typename = void>
+struct iterator_traits
+{
+};
+
+template <typename T>
+struct iterator_traits < T, enable_if_t < !std::is_pointer<T>::value >>
+            : iterator_types<T>
+{
+};
+
+template <typename T>
+struct iterator_traits<T*, enable_if_t<std::is_object<T>::value>>
+{
+    using iterator_category = std::random_access_iterator_tag;
+    using value_type = T;
+    using difference_type = ptrdiff_t;
+    using pointer = T*;
+    using reference = T&;
+};
+}
+}
+
+// #include <nlohmann/detail/meta/cpp_future.hpp>
+
+// #include <nlohmann/detail/meta/detected.hpp>
+
+
+#include <type_traits>
+
+// #include <nlohmann/detail/meta/void_t.hpp>
+
+
+// http://en.cppreference.com/w/cpp/experimental/is_detected
+namespace nlohmann
+{
+namespace detail
+{
+struct nonesuch
+{
+    nonesuch() = delete;
+    ~nonesuch() = delete;
+    nonesuch(nonesuch const&) = delete;
+    void operator=(nonesuch const&) = delete;
+};
+
+template <class Default,
+          class AlwaysVoid,
+          template <class...> class Op,
+          class... Args>
+struct detector
+{
+    using value_t = std::false_type;
+    using type = Default;
+};
+
+template <class Default, template <class...> class Op, class... Args>
+struct detector<Default, void_t<Op<Args...>>, Op, Args...>
+{
+    using value_t = std::true_type;
+    using type = Op<Args...>;
+};
+
+template <template <class...> class Op, class... Args>
+using is_detected = typename detector<nonesuch, void, Op, Args...>::value_t;
+
+template <template <class...> class Op, class... Args>
+using detected_t = typename detector<nonesuch, void, Op, Args...>::type;
+
+template <class Default, template <class...> class Op, class... Args>
+using detected_or = detector<Default, void, Op, Args...>;
+
+template <class Default, template <class...> class Op, class... Args>
+using detected_or_t = typename detected_or<Default, Op, Args...>::type;
+
+template <class Expected, template <class...> class Op, class... Args>
+using is_detected_exact = std::is_same<Expected, detected_t<Op, Args...>>;
+
+template <class To, template <class...> class Op, class... Args>
+using is_detected_convertible =
+    std::is_convertible<detected_t<Op, Args...>, To>;
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+
+namespace nlohmann
+{
 /*!
-@brief unnamed namespace with internal helper functions
+@brief detail namespace with internal helper functions
 
-This namespace collects some functions that could not be defined inside the
-@ref basic_json class.
+This namespace collects functions that should not be exposed,
+implementations of some @ref basic_json methods, and meta-programming helpers.
 
 @since version 2.1.0
 */
 namespace detail
 {
+/////////////
+// helpers //
+/////////////
+
+// Note to maintainers:
+//
+// Every trait in this file expects a non CV-qualified type.
+// The only exceptions are in the 'aliases for detected' section
+// (i.e. those of the form: decltype(T::member_function(std::declval<T>())))
+//
+// In this case, T has to be properly CV-qualified to constraint the function arguments
+// (e.g. to_json(BasicJsonType&, const T&))
+
+template<typename> struct is_basic_json : std::false_type {};
+
+NLOHMANN_BASIC_JSON_TPL_DECLARATION
+struct is_basic_json<NLOHMANN_BASIC_JSON_TPL> : std::true_type {};
+
+//////////////////////////
+// aliases for detected //
+//////////////////////////
+
+template <typename T>
+using mapped_type_t = typename T::mapped_type;
+
+template <typename T>
+using key_type_t = typename T::key_type;
+
+template <typename T>
+using value_type_t = typename T::value_type;
+
+template <typename T>
+using difference_type_t = typename T::difference_type;
+
+template <typename T>
+using pointer_t = typename T::pointer;
+
+template <typename T>
+using reference_t = typename T::reference;
+
+template <typename T>
+using iterator_category_t = typename T::iterator_category;
+
+template <typename T>
+using iterator_t = typename T::iterator;
+
+template <typename T, typename... Args>
+using to_json_function = decltype(T::to_json(std::declval<Args>()...));
+
+template <typename T, typename... Args>
+using from_json_function = decltype(T::from_json(std::declval<Args>()...));
+
+template <typename T, typename U>
+using get_template_function = decltype(std::declval<T>().template get<U>());
+
+// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
+template <typename BasicJsonType, typename T, typename = void>
+struct has_from_json : std::false_type {};
+
+template <typename BasicJsonType, typename T>
+struct has_from_json<BasicJsonType, T,
+           enable_if_t<not is_basic_json<T>::value>>
+{
+    using serializer = typename BasicJsonType::template json_serializer<T, void>;
+
+    static constexpr bool value =
+        is_detected_exact<void, from_json_function, serializer,
+        const BasicJsonType&, T&>::value;
+};
+
+// This trait checks if JSONSerializer<T>::from_json(json const&) exists
+// this overload is used for non-default-constructible user-defined-types
+template <typename BasicJsonType, typename T, typename = void>
+struct has_non_default_from_json : std::false_type {};
+
+template<typename BasicJsonType, typename T>
+struct has_non_default_from_json<BasicJsonType, T, enable_if_t<not is_basic_json<T>::value>>
+{
+    using serializer = typename BasicJsonType::template json_serializer<T, void>;
+
+    static constexpr bool value =
+        is_detected_exact<T, from_json_function, serializer,
+        const BasicJsonType&>::value;
+};
+
+// This trait checks if BasicJsonType::json_serializer<T>::to_json exists
+// Do not evaluate the trait when T is a basic_json type, to avoid template instantiation infinite recursion.
+template <typename BasicJsonType, typename T, typename = void>
+struct has_to_json : std::false_type {};
+
+template <typename BasicJsonType, typename T>
+struct has_to_json<BasicJsonType, T, enable_if_t<not is_basic_json<T>::value>>
+{
+    using serializer = typename BasicJsonType::template json_serializer<T, void>;
+
+    static constexpr bool value =
+        is_detected_exact<void, to_json_function, serializer, BasicJsonType&,
+        T>::value;
+};
+
+
+///////////////////
+// is_ functions //
+///////////////////
+
+template <typename T, typename = void>
+struct is_iterator_traits : std::false_type {};
+
+template <typename T>
+struct is_iterator_traits<iterator_traits<T>>
+{
+  private:
+    using traits = iterator_traits<T>;
+
+  public:
+    static constexpr auto value =
+        is_detected<value_type_t, traits>::value &&
+        is_detected<difference_type_t, traits>::value &&
+        is_detected<pointer_t, traits>::value &&
+        is_detected<iterator_category_t, traits>::value &&
+        is_detected<reference_t, traits>::value;
+};
+
+// source: https://stackoverflow.com/a/37193089/4116453
+
+template <typename T, typename = void>
+struct is_complete_type : std::false_type {};
+
+template <typename T>
+struct is_complete_type<T, decltype(void(sizeof(T)))> : std::true_type {};
+
+template <typename BasicJsonType, typename CompatibleObjectType,
+          typename = void>
+struct is_compatible_object_type_impl : std::false_type {};
+
+template <typename BasicJsonType, typename CompatibleObjectType>
+struct is_compatible_object_type_impl <
+    BasicJsonType, CompatibleObjectType,
+    enable_if_t<is_detected<mapped_type_t, CompatibleObjectType>::value and
+    is_detected<key_type_t, CompatibleObjectType>::value >>
+{
+
+    using object_t = typename BasicJsonType::object_t;
+
+    // macOS's is_constructible does not play well with nonesuch...
+    static constexpr bool value =
+        std::is_constructible<typename object_t::key_type,
+        typename CompatibleObjectType::key_type>::value and
+        std::is_constructible<typename object_t::mapped_type,
+        typename CompatibleObjectType::mapped_type>::value;
+};
+
+template <typename BasicJsonType, typename CompatibleObjectType>
+struct is_compatible_object_type
+    : is_compatible_object_type_impl<BasicJsonType, CompatibleObjectType> {};
+
+template <typename BasicJsonType, typename ConstructibleObjectType,
+          typename = void>
+struct is_constructible_object_type_impl : std::false_type {};
+
+template <typename BasicJsonType, typename ConstructibleObjectType>
+struct is_constructible_object_type_impl <
+    BasicJsonType, ConstructibleObjectType,
+    enable_if_t<is_detected<mapped_type_t, ConstructibleObjectType>::value and
+    is_detected<key_type_t, ConstructibleObjectType>::value >>
+{
+    using object_t = typename BasicJsonType::object_t;
+
+    static constexpr bool value =
+        (std::is_constructible<typename ConstructibleObjectType::key_type, typename object_t::key_type>::value and
+         std::is_same<typename object_t::mapped_type, typename ConstructibleObjectType::mapped_type>::value) or
+        (has_from_json<BasicJsonType, typename ConstructibleObjectType::mapped_type>::value or
+         has_non_default_from_json<BasicJsonType, typename ConstructibleObjectType::mapped_type >::value);
+};
+
+template <typename BasicJsonType, typename ConstructibleObjectType>
+struct is_constructible_object_type
+    : is_constructible_object_type_impl<BasicJsonType,
+      ConstructibleObjectType> {};
+
+template <typename BasicJsonType, typename CompatibleStringType,
+          typename = void>
+struct is_compatible_string_type_impl : std::false_type {};
+
+template <typename BasicJsonType, typename CompatibleStringType>
+struct is_compatible_string_type_impl <
+    BasicJsonType, CompatibleStringType,
+    enable_if_t<is_detected_exact<typename BasicJsonType::string_t::value_type,
+    value_type_t, CompatibleStringType>::value >>
+{
+    static constexpr auto value =
+        std::is_constructible<typename BasicJsonType::string_t, CompatibleStringType>::value;
+};
+
+template <typename BasicJsonType, typename ConstructibleStringType>
+struct is_compatible_string_type
+    : is_compatible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
+
+template <typename BasicJsonType, typename ConstructibleStringType,
+          typename = void>
+struct is_constructible_string_type_impl : std::false_type {};
+
+template <typename BasicJsonType, typename ConstructibleStringType>
+struct is_constructible_string_type_impl <
+    BasicJsonType, ConstructibleStringType,
+    enable_if_t<is_detected_exact<typename BasicJsonType::string_t::value_type,
+    value_type_t, ConstructibleStringType>::value >>
+{
+    static constexpr auto value =
+        std::is_constructible<ConstructibleStringType,
+        typename BasicJsonType::string_t>::value;
+};
+
+template <typename BasicJsonType, typename ConstructibleStringType>
+struct is_constructible_string_type
+    : is_constructible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
+
+template <typename BasicJsonType, typename CompatibleArrayType, typename = void>
+struct is_compatible_array_type_impl : std::false_type {};
+
+template <typename BasicJsonType, typename CompatibleArrayType>
+struct is_compatible_array_type_impl <
+    BasicJsonType, CompatibleArrayType,
+    enable_if_t<is_detected<value_type_t, CompatibleArrayType>::value and
+    is_detected<iterator_t, CompatibleArrayType>::value and
+// This is needed because json_reverse_iterator has a ::iterator type...
+// Therefore it is detected as a CompatibleArrayType.
+// The real fix would be to have an Iterable concept.
+    not is_iterator_traits<
+    iterator_traits<CompatibleArrayType>>::value >>
+{
+    static constexpr bool value =
+        std::is_constructible<BasicJsonType,
+        typename CompatibleArrayType::value_type>::value;
+};
+
+template <typename BasicJsonType, typename CompatibleArrayType>
+struct is_compatible_array_type
+    : is_compatible_array_type_impl<BasicJsonType, CompatibleArrayType> {};
+
+template <typename BasicJsonType, typename ConstructibleArrayType, typename = void>
+struct is_constructible_array_type_impl : std::false_type {};
+
+template <typename BasicJsonType, typename ConstructibleArrayType>
+struct is_constructible_array_type_impl <
+    BasicJsonType, ConstructibleArrayType,
+    enable_if_t<std::is_same<ConstructibleArrayType,
+    typename BasicJsonType::value_type>::value >>
+            : std::true_type {};
+
+template <typename BasicJsonType, typename ConstructibleArrayType>
+struct is_constructible_array_type_impl <
+    BasicJsonType, ConstructibleArrayType,
+    enable_if_t<not std::is_same<ConstructibleArrayType,
+    typename BasicJsonType::value_type>::value and
+    is_detected<value_type_t, ConstructibleArrayType>::value and
+    is_detected<iterator_t, ConstructibleArrayType>::value and
+    is_complete_type<
+    detected_t<value_type_t, ConstructibleArrayType>>::value >>
+{
+    static constexpr bool value =
+        // This is needed because json_reverse_iterator has a ::iterator type,
+        // furthermore, std::back_insert_iterator (and other iterators) have a base class `iterator`...
+        // Therefore it is detected as a ConstructibleArrayType.
+        // The real fix would be to have an Iterable concept.
+        not is_iterator_traits <
+        iterator_traits<ConstructibleArrayType >>::value and
+
+        (std::is_same<typename ConstructibleArrayType::value_type, typename BasicJsonType::array_t::value_type>::value or
+         has_from_json<BasicJsonType,
+         typename ConstructibleArrayType::value_type>::value or
+         has_non_default_from_json <
+         BasicJsonType, typename ConstructibleArrayType::value_type >::value);
+};
+
+template <typename BasicJsonType, typename ConstructibleArrayType>
+struct is_constructible_array_type
+    : is_constructible_array_type_impl<BasicJsonType, ConstructibleArrayType> {};
+
+template <typename RealIntegerType, typename CompatibleNumberIntegerType,
+          typename = void>
+struct is_compatible_integer_type_impl : std::false_type {};
+
+template <typename RealIntegerType, typename CompatibleNumberIntegerType>
+struct is_compatible_integer_type_impl <
+    RealIntegerType, CompatibleNumberIntegerType,
+    enable_if_t<std::is_integral<RealIntegerType>::value and
+    std::is_integral<CompatibleNumberIntegerType>::value and
+    not std::is_same<bool, CompatibleNumberIntegerType>::value >>
+{
+    // is there an assert somewhere on overflows?
+    using RealLimits = std::numeric_limits<RealIntegerType>;
+    using CompatibleLimits = std::numeric_limits<CompatibleNumberIntegerType>;
+
+    static constexpr auto value =
+        std::is_constructible<RealIntegerType,
+        CompatibleNumberIntegerType>::value and
+        CompatibleLimits::is_integer and
+        RealLimits::is_signed == CompatibleLimits::is_signed;
+};
+
+template <typename RealIntegerType, typename CompatibleNumberIntegerType>
+struct is_compatible_integer_type
+    : is_compatible_integer_type_impl<RealIntegerType,
+      CompatibleNumberIntegerType> {};
+
+template <typename BasicJsonType, typename CompatibleType, typename = void>
+struct is_compatible_type_impl: std::false_type {};
+
+template <typename BasicJsonType, typename CompatibleType>
+struct is_compatible_type_impl <
+    BasicJsonType, CompatibleType,
+    enable_if_t<is_complete_type<CompatibleType>::value >>
+{
+    static constexpr bool value =
+        has_to_json<BasicJsonType, CompatibleType>::value;
+};
+
+template <typename BasicJsonType, typename CompatibleType>
+struct is_compatible_type
+    : is_compatible_type_impl<BasicJsonType, CompatibleType> {};
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+
+#include <exception> // exception
+#include <stdexcept> // runtime_error
+#include <string> // to_string
+
+// #include <nlohmann/detail/input/position_t.hpp>
+
+
+#include <cstddef> // size_t
+
+namespace nlohmann
+{
+namespace detail
+{
+/// struct to capture the start position of the current token
+struct position_t
+{
+    /// the total number of characters read
+    std::size_t chars_read_total = 0;
+    /// the number of characters read in the current line
+    std::size_t chars_read_current_line = 0;
+    /// the number of lines read
+    std::size_t lines_read = 0;
+
+    /// conversion to size_t to preserve SAX interface
+    constexpr operator size_t() const
+    {
+        return chars_read_total;
+    }
+};
+
+}
+}
+
+
+namespace nlohmann
+{
+namespace detail
+{
 ////////////////
 // exceptions //
 ////////////////
@@ -248,6 +916,7 @@ json.exception.parse_error.109 | parse error: array index 'one' is not a number
 json.exception.parse_error.110 | parse error at 1: cannot read 2 bytes from vector | When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
 json.exception.parse_error.112 | parse error at 1: error reading CBOR; last byte: 0xF8 | Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.
 json.exception.parse_error.113 | parse error at 2: expected a CBOR string; last byte: 0x98 | While parsing a map key, a value that is not a string has been read.
+json.exception.parse_error.114 | parse error: Unsupported BSON record type 0x0F | The parsing of the corresponding BSON record type is not implemented (yet).
 
 @note For an input with n bytes, 1 is the index of the first character and n+1
       is the index of the terminating null byte or the end of file. This also
@@ -271,15 +940,23 @@ class parse_error : public exception
     /*!
     @brief create a parse error exception
     @param[in] id_       the id of the exception
-    @param[in] byte_     the byte index where the error occurred (or 0 if the
-                         position cannot be determined)
+    @param[in] position  the position where the error occurred (or with
+                         chars_read_total=0 if the position cannot be
+                         determined)
     @param[in] what_arg  the explanatory string
     @return parse_error object
     */
+    static parse_error create(int id_, const position_t& pos, const std::string& what_arg)
+    {
+        std::string w = exception::name("parse_error", id_) + "parse error" +
+                        position_string(pos) + ": " + what_arg;
+        return parse_error(id_, pos.chars_read_total, w.c_str());
+    }
+
     static parse_error create(int id_, std::size_t byte_, const std::string& what_arg)
     {
         std::string w = exception::name("parse_error", id_) + "parse error" +
-                        (byte_ != 0 ? (" at " + std::to_string(byte_)) : "") +
+                        (byte_ != 0 ? (" at byte " + std::to_string(byte_)) : "") +
                         ": " + what_arg;
         return parse_error(id_, byte_, w.c_str());
     }
@@ -298,6 +975,12 @@ class parse_error : public exception
   private:
     parse_error(int id_, std::size_t byte_, const char* what_arg)
         : exception(id_, what_arg), byte(byte_) {}
+
+    static std::string position_string(const position_t& pos)
+    {
+        return " at line " + std::to_string(pos.lines_read + 1) +
+               ", column " + std::to_string(pos.chars_read_current_line);
+    }
 };
 
 /*!
@@ -377,6 +1060,7 @@ json.exception.type_error.313 | invalid value to unflatten | The @ref unflatten
 json.exception.type_error.314 | only objects can be unflattened | The @ref unflatten function only works for an object whose keys are JSON Pointers.
 json.exception.type_error.315 | values in object must be primitive | The @ref unflatten function only works for an object whose keys are JSON Pointers and whose values are primitive.
 json.exception.type_error.316 | invalid UTF-8 byte at index 10: 0x7E | The @ref dump function only works with UTF-8 encoded strings; that is, if you assign a `std::string` to a JSON value, make sure it is UTF-8 encoded. |
+json.exception.type_error.317 | JSON value cannot be serialized to requested format | The dynamic type of the object cannot be represented in the requested serialization format (e.g. a raw `true` or `null` JSON object cannot be serialized to BSON) |
 
 @liveexample{The following code shows how a `type_error` exception can be
 caught.,type_error}
@@ -419,6 +1103,9 @@ json.exception.out_of_range.403 | key 'foo' not found | The provided key was not
 json.exception.out_of_range.404 | unresolved reference token 'foo' | A reference token in a JSON Pointer could not be resolved.
 json.exception.out_of_range.405 | JSON pointer has no parent | The JSON Patch operations 'remove' and 'add' can not be applied to the root element of the JSON value.
 json.exception.out_of_range.406 | number overflow parsing '10E1000' | A parsed number could not be stored as without changing it to NaN or INF.
+json.exception.out_of_range.407 | number overflow serializing '9223372036854775808' | UBJSON and BSON only support integer numbers up to 9223372036854775807. |
+json.exception.out_of_range.408 | excessive array size: 8658170730974374167 | The size (following `#`) of an UBJSON array or object exceeds the maximal capacity. |
+json.exception.out_of_range.409 | BSON key cannot contain code point U+0000 (at byte 2) | Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string |
 
 @liveexample{The following code shows how an `out_of_range` exception can be
 caught.,out_of_range}
@@ -481,9 +1168,21 @@ class other_error : public exception
   private:
     other_error(int id_, const char* what_arg) : exception(id_, what_arg) {}
 };
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/value_t.hpp>
 
 
+#include <array> // array
+#include <ciso646> // and
+#include <cstddef> // size_t
+#include <cstdint> // uint8_t
 
+namespace nlohmann
+{
+namespace detail
+{
 ///////////////////////////
 // JSON type enumeration //
 ///////////////////////////
@@ -512,7 +1211,7 @@ value with the default value for a given type
 
 @since version 1.0.0
 */
-enum class value_t : uint8_t
+enum class value_t : std::uint8_t
 {
     null,             ///< null value
     object,           ///< object (unordered set of name/value pairs)
@@ -537,7 +1236,7 @@ Returns an ordering that is similar to Python:
 */
 inline bool operator<(const value_t lhs, const value_t rhs) noexcept
 {
-    static constexpr std::array<uint8_t, 8> order = {{
+    static constexpr std::array<std::uint8_t, 8> order = {{
             0 /* null */, 3 /* object */, 4 /* array */, 5 /* string */,
             1 /* boolean */, 2 /* integer */, 2 /* unsigned */, 2 /* float */
         }
@@ -547,80 +1246,573 @@ inline bool operator<(const value_t lhs, const value_t rhs) noexcept
     const auto r_index = static_cast<std::size_t>(rhs);
     return l_index < order.size() and r_index < order.size() and order[l_index] < order[r_index];
 }
+}  // namespace detail
+}  // namespace nlohmann
 
+// #include <nlohmann/detail/conversions/from_json.hpp>
 
-/////////////
-// helpers //
-/////////////
 
-template<typename> struct is_basic_json : std::false_type {};
+#include <algorithm> // transform
+#include <array> // array
+#include <ciso646> // and, not
+#include <forward_list> // forward_list
+#include <iterator> // inserter, front_inserter, end
+#include <map> // map
+#include <string> // string
+#include <tuple> // tuple, make_tuple
+#include <type_traits> // is_arithmetic, is_same, is_enum, underlying_type, is_convertible
+#include <unordered_map> // unordered_map
+#include <utility> // pair, declval
+#include <valarray> // valarray
 
-NLOHMANN_BASIC_JSON_TPL_DECLARATION
-struct is_basic_json<NLOHMANN_BASIC_JSON_TPL> : std::true_type {};
+// #include <nlohmann/detail/exceptions.hpp>
 
-// alias templates to reduce boilerplate
-template<bool B, typename T = void>
-using enable_if_t = typename std::enable_if<B, T>::type;
+// #include <nlohmann/detail/macro_scope.hpp>
 
-template<typename T>
-using uncvref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
+// #include <nlohmann/detail/meta/cpp_future.hpp>
 
-// implementation of C++14 index_sequence and affiliates
-// source: https://stackoverflow.com/a/32223343
-template<std::size_t... Ints>
-struct index_sequence
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
+// #include <nlohmann/detail/value_t.hpp>
+
+
+namespace nlohmann
 {
-    using type = index_sequence;
-    using value_type = std::size_t;
-    static constexpr std::size_t size() noexcept
+namespace detail
+{
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& j, typename std::nullptr_t& n)
+{
+    if (JSON_UNLIKELY(not j.is_null()))
     {
-        return sizeof...(Ints);
+        JSON_THROW(type_error::create(302, "type must be null, but is " + std::string(j.type_name())));
+    }
+    n = nullptr;
+}
+
+// overloads for basic_json template parameters
+template<typename BasicJsonType, typename ArithmeticType,
+         enable_if_t<std::is_arithmetic<ArithmeticType>::value and
+                     not std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
+                     int> = 0>
+void get_arithmetic_value(const BasicJsonType& j, ArithmeticType& val)
+{
+    switch (static_cast<value_t>(j))
+    {
+        case value_t::number_unsigned:
+        {
+            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>());
+            break;
+        }
+        case value_t::number_integer:
+        {
+            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_integer_t*>());
+            break;
+        }
+        case value_t::number_float:
+        {
+            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_float_t*>());
+            break;
+        }
+
+        default:
+            JSON_THROW(type_error::create(302, "type must be number, but is " + std::string(j.type_name())));
+    }
+}
+
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& j, typename BasicJsonType::boolean_t& b)
+{
+    if (JSON_UNLIKELY(not j.is_boolean()))
+    {
+        JSON_THROW(type_error::create(302, "type must be boolean, but is " + std::string(j.type_name())));
+    }
+    b = *j.template get_ptr<const typename BasicJsonType::boolean_t*>();
+}
+
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& j, typename BasicJsonType::string_t& s)
+{
+    if (JSON_UNLIKELY(not j.is_string()))
+    {
+        JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name())));
+    }
+    s = *j.template get_ptr<const typename BasicJsonType::string_t*>();
+}
+
+template <
+    typename BasicJsonType, typename ConstructibleStringType,
+    enable_if_t <
+        is_constructible_string_type<BasicJsonType, ConstructibleStringType>::value and
+        not std::is_same<typename BasicJsonType::string_t,
+                         ConstructibleStringType>::value,
+        int > = 0 >
+void from_json(const BasicJsonType& j, ConstructibleStringType& s)
+{
+    if (JSON_UNLIKELY(not j.is_string()))
+    {
+        JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name())));
+    }
+
+    s = *j.template get_ptr<const typename BasicJsonType::string_t*>();
+}
+
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& j, typename BasicJsonType::number_float_t& val)
+{
+    get_arithmetic_value(j, val);
+}
+
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& j, typename BasicJsonType::number_unsigned_t& val)
+{
+    get_arithmetic_value(j, val);
+}
+
+template<typename BasicJsonType>
+void from_json(const BasicJsonType& j, typename BasicJsonType::number_integer_t& val)
+{
+    get_arithmetic_value(j, val);
+}
+
+template<typename BasicJsonType, typename EnumType,
+         enable_if_t<std::is_enum<EnumType>::value, int> = 0>
+void from_json(const BasicJsonType& j, EnumType& e)
+{
+    typename std::underlying_type<EnumType>::type val;
+    get_arithmetic_value(j, val);
+    e = static_cast<EnumType>(val);
+}
+
+// forward_list doesn't have an insert method
+template<typename BasicJsonType, typename T, typename Allocator,
+         enable_if_t<std::is_convertible<BasicJsonType, T>::value, int> = 0>
+void from_json(const BasicJsonType& j, std::forward_list<T, Allocator>& l)
+{
+    if (JSON_UNLIKELY(not j.is_array()))
+    {
+        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
+    }
+    std::transform(j.rbegin(), j.rend(),
+                   std::front_inserter(l), [](const BasicJsonType & i)
+    {
+        return i.template get<T>();
+    });
+}
+
+// valarray doesn't have an insert method
+template<typename BasicJsonType, typename T,
+         enable_if_t<std::is_convertible<BasicJsonType, T>::value, int> = 0>
+void from_json(const BasicJsonType& j, std::valarray<T>& l)
+{
+    if (JSON_UNLIKELY(not j.is_array()))
+    {
+        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
+    }
+    l.resize(j.size());
+    std::copy(j.m_value.array->begin(), j.m_value.array->end(), std::begin(l));
+}
+
+template<typename BasicJsonType>
+void from_json_array_impl(const BasicJsonType& j, typename BasicJsonType::array_t& arr, priority_tag<3> /*unused*/)
+{
+    arr = *j.template get_ptr<const typename BasicJsonType::array_t*>();
+}
+
+template <typename BasicJsonType, typename T, std::size_t N>
+auto from_json_array_impl(const BasicJsonType& j, std::array<T, N>& arr,
+                          priority_tag<2> /*unused*/)
+-> decltype(j.template get<T>(), void())
+{
+    for (std::size_t i = 0; i < N; ++i)
+    {
+        arr[i] = j.at(i).template get<T>();
+    }
+}
+
+template<typename BasicJsonType, typename ConstructibleArrayType>
+auto from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr, priority_tag<1> /*unused*/)
+-> decltype(
+    arr.reserve(std::declval<typename ConstructibleArrayType::size_type>()),
+    j.template get<typename ConstructibleArrayType::value_type>(),
+    void())
+{
+    using std::end;
+
+    arr.reserve(j.size());
+    std::transform(j.begin(), j.end(),
+                   std::inserter(arr, end(arr)), [](const BasicJsonType & i)
+    {
+        // get<BasicJsonType>() returns *this, this won't call a from_json
+        // method when value_type is BasicJsonType
+        return i.template get<typename ConstructibleArrayType::value_type>();
+    });
+}
+
+template <typename BasicJsonType, typename ConstructibleArrayType>
+void from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr,
+                          priority_tag<0> /*unused*/)
+{
+    using std::end;
+
+    std::transform(
+        j.begin(), j.end(), std::inserter(arr, end(arr)),
+        [](const BasicJsonType & i)
+    {
+        // get<BasicJsonType>() returns *this, this won't call a from_json
+        // method when value_type is BasicJsonType
+        return i.template get<typename ConstructibleArrayType::value_type>();
+    });
+}
+
+template <typename BasicJsonType, typename ConstructibleArrayType,
+          enable_if_t <
+              is_constructible_array_type<BasicJsonType, ConstructibleArrayType>::value and
+              not is_constructible_object_type<BasicJsonType, ConstructibleArrayType>::value and
+              not is_constructible_string_type<BasicJsonType, ConstructibleArrayType>::value and
+              not is_basic_json<ConstructibleArrayType>::value,
+              int > = 0 >
+
+auto from_json(const BasicJsonType& j, ConstructibleArrayType& arr)
+-> decltype(from_json_array_impl(j, arr, priority_tag<3> {}),
+j.template get<typename ConstructibleArrayType::value_type>(),
+void())
+{
+    if (JSON_UNLIKELY(not j.is_array()))
+    {
+        JSON_THROW(type_error::create(302, "type must be array, but is " +
+                                      std::string(j.type_name())));
+    }
+
+    from_json_array_impl(j, arr, priority_tag<3> {});
+}
+
+template<typename BasicJsonType, typename ConstructibleObjectType,
+         enable_if_t<is_constructible_object_type<BasicJsonType, ConstructibleObjectType>::value, int> = 0>
+void from_json(const BasicJsonType& j, ConstructibleObjectType& obj)
+{
+    if (JSON_UNLIKELY(not j.is_object()))
+    {
+        JSON_THROW(type_error::create(302, "type must be object, but is " + std::string(j.type_name())));
+    }
+
+    auto inner_object = j.template get_ptr<const typename BasicJsonType::object_t*>();
+    using value_type = typename ConstructibleObjectType::value_type;
+    std::transform(
+        inner_object->begin(), inner_object->end(),
+        std::inserter(obj, obj.begin()),
+        [](typename BasicJsonType::object_t::value_type const & p)
+    {
+        return value_type(p.first, p.second.template get<typename ConstructibleObjectType::mapped_type>());
+    });
+}
+
+// overload for arithmetic types, not chosen for basic_json template arguments
+// (BooleanType, etc..); note: Is it really necessary to provide explicit
+// overloads for boolean_t etc. in case of a custom BooleanType which is not
+// an arithmetic type?
+template<typename BasicJsonType, typename ArithmeticType,
+         enable_if_t <
+             std::is_arithmetic<ArithmeticType>::value and
+             not std::is_same<ArithmeticType, typename BasicJsonType::number_unsigned_t>::value and
+             not std::is_same<ArithmeticType, typename BasicJsonType::number_integer_t>::value and
+             not std::is_same<ArithmeticType, typename BasicJsonType::number_float_t>::value and
+             not std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
+             int> = 0>
+void from_json(const BasicJsonType& j, ArithmeticType& val)
+{
+    switch (static_cast<value_t>(j))
+    {
+        case value_t::number_unsigned:
+        {
+            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>());
+            break;
+        }
+        case value_t::number_integer:
+        {
+            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_integer_t*>());
+            break;
+        }
+        case value_t::number_float:
+        {
+            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_float_t*>());
+            break;
+        }
+        case value_t::boolean:
+        {
+            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::boolean_t*>());
+            break;
+        }
+
+        default:
+            JSON_THROW(type_error::create(302, "type must be number, but is " + std::string(j.type_name())));
+    }
+}
+
+template<typename BasicJsonType, typename A1, typename A2>
+void from_json(const BasicJsonType& j, std::pair<A1, A2>& p)
+{
+    p = {j.at(0).template get<A1>(), j.at(1).template get<A2>()};
+}
+
+template<typename BasicJsonType, typename Tuple, std::size_t... Idx>
+void from_json_tuple_impl(const BasicJsonType& j, Tuple& t, index_sequence<Idx...> /*unused*/)
+{
+    t = std::make_tuple(j.at(Idx).template get<typename std::tuple_element<Idx, Tuple>::type>()...);
+}
+
+template<typename BasicJsonType, typename... Args>
+void from_json(const BasicJsonType& j, std::tuple<Args...>& t)
+{
+    from_json_tuple_impl(j, t, index_sequence_for<Args...> {});
+}
+
+template <typename BasicJsonType, typename Key, typename Value, typename Compare, typename Allocator,
+          typename = enable_if_t<not std::is_constructible<
+                                     typename BasicJsonType::string_t, Key>::value>>
+void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allocator>& m)
+{
+    if (JSON_UNLIKELY(not j.is_array()))
+    {
+        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
+    }
+    for (const auto& p : j)
+    {
+        if (JSON_UNLIKELY(not p.is_array()))
+        {
+            JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(p.type_name())));
+        }
+        m.emplace(p.at(0).template get<Key>(), p.at(1).template get<Value>());
+    }
+}
+
+template <typename BasicJsonType, typename Key, typename Value, typename Hash, typename KeyEqual, typename Allocator,
+          typename = enable_if_t<not std::is_constructible<
+                                     typename BasicJsonType::string_t, Key>::value>>
+void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyEqual, Allocator>& m)
+{
+    if (JSON_UNLIKELY(not j.is_array()))
+    {
+        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
+    }
+    for (const auto& p : j)
+    {
+        if (JSON_UNLIKELY(not p.is_array()))
+        {
+            JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(p.type_name())));
+        }
+        m.emplace(p.at(0).template get<Key>(), p.at(1).template get<Value>());
+    }
+}
+
+struct from_json_fn
+{
+    template<typename BasicJsonType, typename T>
+    auto operator()(const BasicJsonType& j, T& val) const
+    noexcept(noexcept(from_json(j, val)))
+    -> decltype(from_json(j, val), void())
+    {
+        return from_json(j, val);
     }
 };
+}  // namespace detail
 
-template<class Sequence1, class Sequence2>
-struct merge_and_renumber;
+/// namespace to hold default `from_json` function
+/// to see why this is required:
+/// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4381.html
+namespace
+{
+constexpr const auto& from_json = detail::static_const<detail::from_json_fn>::value;
+} // namespace
+}  // namespace nlohmann
 
-template<std::size_t... I1, std::size_t... I2>
-struct merge_and_renumber<index_sequence<I1...>, index_sequence<I2...>>
-        : index_sequence < I1..., (sizeof...(I1) + I2)... > {};
+// #include <nlohmann/detail/conversions/to_json.hpp>
 
-template<std::size_t N>
-struct make_index_sequence
-    : merge_and_renumber < typename make_index_sequence < N / 2 >::type,
-      typename make_index_sequence < N - N / 2 >::type > {};
 
-template<> struct make_index_sequence<0> : index_sequence<> {};
-template<> struct make_index_sequence<1> : index_sequence<0> {};
+#include <ciso646> // or, and, not
+#include <iterator> // begin, end
+#include <tuple> // tuple, get
+#include <type_traits> // is_same, is_constructible, is_floating_point, is_enum, underlying_type
+#include <utility> // move, forward, declval, pair
+#include <valarray> // valarray
+#include <vector> // vector
 
-template<typename... Ts>
-using index_sequence_for = make_index_sequence<sizeof...(Ts)>;
+// #include <nlohmann/detail/meta/cpp_future.hpp>
 
-/*
-Implementation of two C++17 constructs: conjunction, negation. This is needed
-to avoid evaluating all the traits in a condition
+// #include <nlohmann/detail/meta/type_traits.hpp>
 
-For example: not std::is_same<void, T>::value and has_value_type<T>::value
-will not compile when T = void (on MSVC at least). Whereas
-conjunction<negation<std::is_same<void, T>>, has_value_type<T>>::value will
-stop evaluating if negation<...>::value == false
+// #include <nlohmann/detail/value_t.hpp>
 
-Please note that those constructs must be used with caution, since symbols can
-become very long quickly (which can slow down compilation and cause MSVC
-internal compiler errors). Only use it when you have to (see example ahead).
-*/
-template<class...> struct conjunction : std::true_type {};
-template<class B1> struct conjunction<B1> : B1 {};
-template<class B1, class... Bn>
-struct conjunction<B1, Bn...> : std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type {};
+// #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 
-template<class B> struct negation : std::integral_constant<bool, not B::value> {};
 
-// dispatch utility (taken from ranges-v3)
-template<unsigned N> struct priority_tag : priority_tag < N - 1 > {};
-template<> struct priority_tag<0> {};
+#include <cstddef> // size_t
+#include <string> // string, to_string
+#include <iterator> // input_iterator_tag
+#include <tuple> // tuple_size, get, tuple_element
+
+// #include <nlohmann/detail/value_t.hpp>
+
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+template <typename IteratorType> class iteration_proxy_value
+{
+  public:
+    using difference_type = std::ptrdiff_t;
+    using value_type = iteration_proxy_value;
+    using pointer = value_type * ;
+    using reference = value_type & ;
+    using iterator_category = std::input_iterator_tag;
+
+  private:
+    /// the iterator
+    IteratorType anchor;
+    /// an index for arrays (used to create key names)
+    std::size_t array_index = 0;
+    /// last stringified array index
+    mutable std::size_t array_index_last = 0;
+    /// a string representation of the array index
+    mutable std::string array_index_str = "0";
+    /// an empty string (to return a reference for primitive values)
+    const std::string empty_str = "";
+
+  public:
+    explicit iteration_proxy_value(IteratorType it) noexcept : anchor(it) {}
+
+    /// dereference operator (needed for range-based for)
+    iteration_proxy_value& operator*()
+    {
+        return *this;
+    }
+
+    /// increment operator (needed for range-based for)
+    iteration_proxy_value& operator++()
+    {
+        ++anchor;
+        ++array_index;
+
+        return *this;
+    }
+
+    /// equality operator (needed for InputIterator)
+    bool operator==(const iteration_proxy_value& o) const noexcept
+    {
+        return anchor == o.anchor;
+    }
+
+    /// inequality operator (needed for range-based for)
+    bool operator!=(const iteration_proxy_value& o) const noexcept
+    {
+        return anchor != o.anchor;
+    }
+
+    /// return key of the iterator
+    const std::string& key() const
+    {
+        assert(anchor.m_object != nullptr);
+
+        switch (anchor.m_object->type())
+        {
+            // use integer array index as key
+            case value_t::array:
+            {
+                if (array_index != array_index_last)
+                {
+                    array_index_str = std::to_string(array_index);
+                    array_index_last = array_index;
+                }
+                return array_index_str;
+            }
+
+            // use key from the object
+            case value_t::object:
+                return anchor.key();
+
+            // use an empty key for all primitive types
+            default:
+                return empty_str;
+        }
+    }
+
+    /// return value of the iterator
+    typename IteratorType::reference value() const
+    {
+        return anchor.value();
+    }
+};
+
+/// proxy class for the items() function
+template<typename IteratorType> class iteration_proxy
+{
+  private:
+    /// the container to iterate
+    typename IteratorType::reference container;
+
+  public:
+    /// construct iteration proxy from a container
+    explicit iteration_proxy(typename IteratorType::reference cont) noexcept
+        : container(cont) {}
+
+    /// return iterator begin (needed for range-based for)
+    iteration_proxy_value<IteratorType> begin() noexcept
+    {
+        return iteration_proxy_value<IteratorType>(container.begin());
+    }
+
+    /// return iterator end (needed for range-based for)
+    iteration_proxy_value<IteratorType> end() noexcept
+    {
+        return iteration_proxy_value<IteratorType>(container.end());
+    }
+};
+// Structured Bindings Support
+// For further reference see https://blog.tartanllama.xyz/structured-bindings/
+// And see https://github.com/nlohmann/json/pull/1391
+template <std::size_t N, typename IteratorType, enable_if_t<N == 0, int> = 0>
+auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decltype(i.key())
+{
+    return i.key();
+}
+// Structured Bindings Support
+// For further reference see https://blog.tartanllama.xyz/structured-bindings/
+// And see https://github.com/nlohmann/json/pull/1391
+template <std::size_t N, typename IteratorType, enable_if_t<N == 1, int> = 0>
+auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decltype(i.value())
+{
+    return i.value();
+}
+}  // namespace detail
+}  // namespace nlohmann
 
+// The Addition to the STD Namespace is required to add
+// Structured Bindings Support to the iteration_proxy_value class
+// For further reference see https://blog.tartanllama.xyz/structured-bindings/
+// And see https://github.com/nlohmann/json/pull/1391
+namespace std
+{
+template <typename IteratorType>
+class tuple_size<::nlohmann::detail::iteration_proxy_value<IteratorType>>
+            : public std::integral_constant<std::size_t, 2> {};
 
+template <std::size_t N, typename IteratorType>
+class tuple_element<N, ::nlohmann::detail::iteration_proxy_value<IteratorType >>
+{
+  public:
+    using type = decltype(
+                     get<N>(std::declval <
+                            ::nlohmann::detail::iteration_proxy_value<IteratorType >> ()));
+};
+}
+
+namespace nlohmann
+{
+namespace detail
+{
 //////////////////
 // constructors //
 //////////////////
@@ -657,6 +1849,16 @@ struct external_constructor<value_t::string>
         j.m_value = std::move(s);
         j.assert_invariant();
     }
+
+    template<typename BasicJsonType, typename CompatibleStringType,
+             enable_if_t<not std::is_same<CompatibleStringType, typename BasicJsonType::string_t>::value,
+                         int> = 0>
+    static void construct(BasicJsonType& j, const CompatibleStringType& str)
+    {
+        j.m_type = value_t::string;
+        j.m_value.string = j.template create<typename BasicJsonType::string_t>(str);
+        j.assert_invariant();
+    }
 };
 
 template<>
@@ -783,159 +1985,6 @@ struct external_constructor<value_t::object>
     }
 };
 
-
-////////////////////////
-// has_/is_ functions //
-////////////////////////
-
-/*!
-@brief Helper to determine whether there's a key_type for T.
-
-This helper is used to tell associative containers apart from other containers
-such as sequence containers. For instance, `std::map` passes the test as it
-contains a `mapped_type`, whereas `std::vector` fails the test.
-
-@sa http://stackoverflow.com/a/7728728/266378
-@since version 1.0.0, overworked in version 2.0.6
-*/
-#define NLOHMANN_JSON_HAS_HELPER(type)                                        \
-    template<typename T> struct has_##type {                                  \
-    private:                                                                  \
-        template<typename U, typename = typename U::type>                     \
-        static int detect(U &&);                                              \
-        static void detect(...);                                              \
-    public:                                                                   \
-        static constexpr bool value =                                         \
-                std::is_integral<decltype(detect(std::declval<T>()))>::value; \
-    }
-
-NLOHMANN_JSON_HAS_HELPER(mapped_type);
-NLOHMANN_JSON_HAS_HELPER(key_type);
-NLOHMANN_JSON_HAS_HELPER(value_type);
-NLOHMANN_JSON_HAS_HELPER(iterator);
-
-#undef NLOHMANN_JSON_HAS_HELPER
-
-
-template<bool B, class RealType, class CompatibleObjectType>
-struct is_compatible_object_type_impl : std::false_type {};
-
-template<class RealType, class CompatibleObjectType>
-struct is_compatible_object_type_impl<true, RealType, CompatibleObjectType>
-{
-    static constexpr auto value =
-        std::is_constructible<typename RealType::key_type, typename CompatibleObjectType::key_type>::value and
-        std::is_constructible<typename RealType::mapped_type, typename CompatibleObjectType::mapped_type>::value;
-};
-
-template<class BasicJsonType, class CompatibleObjectType>
-struct is_compatible_object_type
-{
-    static auto constexpr value = is_compatible_object_type_impl <
-                                  conjunction<negation<std::is_same<void, CompatibleObjectType>>,
-                                  has_mapped_type<CompatibleObjectType>,
-                                  has_key_type<CompatibleObjectType>>::value,
-                                  typename BasicJsonType::object_t, CompatibleObjectType >::value;
-};
-
-template<typename BasicJsonType, typename T>
-struct is_basic_json_nested_type
-{
-    static auto constexpr value = std::is_same<T, typename BasicJsonType::iterator>::value or
-                                  std::is_same<T, typename BasicJsonType::const_iterator>::value or
-                                  std::is_same<T, typename BasicJsonType::reverse_iterator>::value or
-                                  std::is_same<T, typename BasicJsonType::const_reverse_iterator>::value;
-};
-
-template<class BasicJsonType, class CompatibleArrayType>
-struct is_compatible_array_type
-{
-    static auto constexpr value =
-        conjunction<negation<std::is_same<void, CompatibleArrayType>>,
-        negation<is_compatible_object_type<
-        BasicJsonType, CompatibleArrayType>>,
-        negation<std::is_constructible<typename BasicJsonType::string_t,
-        CompatibleArrayType>>,
-        negation<is_basic_json_nested_type<BasicJsonType, CompatibleArrayType>>,
-        has_value_type<CompatibleArrayType>,
-        has_iterator<CompatibleArrayType>>::value;
-};
-
-template<bool, typename, typename>
-struct is_compatible_integer_type_impl : std::false_type {};
-
-template<typename RealIntegerType, typename CompatibleNumberIntegerType>
-struct is_compatible_integer_type_impl<true, RealIntegerType, CompatibleNumberIntegerType>
-{
-    // is there an assert somewhere on overflows?
-    using RealLimits = std::numeric_limits<RealIntegerType>;
-    using CompatibleLimits = std::numeric_limits<CompatibleNumberIntegerType>;
-
-    static constexpr auto value =
-        std::is_constructible<RealIntegerType, CompatibleNumberIntegerType>::value and
-        CompatibleLimits::is_integer and
-        RealLimits::is_signed == CompatibleLimits::is_signed;
-};
-
-template<typename RealIntegerType, typename CompatibleNumberIntegerType>
-struct is_compatible_integer_type
-{
-    static constexpr auto value =
-        is_compatible_integer_type_impl <
-        std::is_integral<CompatibleNumberIntegerType>::value and
-        not std::is_same<bool, CompatibleNumberIntegerType>::value,
-        RealIntegerType, CompatibleNumberIntegerType >::value;
-};
-
-
-// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
-template<typename BasicJsonType, typename T>
-struct has_from_json
-{
-  private:
-    // also check the return type of from_json
-    template<typename U, typename = enable_if_t<std::is_same<void, decltype(uncvref_t<U>::from_json(
-                 std::declval<BasicJsonType>(), std::declval<T&>()))>::value>>
-    static int detect(U&&);
-    static void detect(...);
-
-  public:
-    static constexpr bool value = std::is_integral<decltype(
-                                      detect(std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
-};
-
-// This trait checks if JSONSerializer<T>::from_json(json const&) exists
-// this overload is used for non-default-constructible user-defined-types
-template<typename BasicJsonType, typename T>
-struct has_non_default_from_json
-{
-  private:
-    template<typename U, typename =
-             enable_if_t<std::is_same<T, decltype(uncvref_t<U>::from_json(std::declval<BasicJsonType>()))>::value>>
-    static int detect(U&&);
-    static void detect(...);
-
-  public:
-    static constexpr bool value = std::is_integral<decltype(detect(
-                                      std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
-};
-
-// This trait checks if BasicJsonType::json_serializer<T>::to_json exists
-template<typename BasicJsonType, typename T>
-struct has_to_json
-{
-  private:
-    template<typename U, typename = decltype(uncvref_t<U>::to_json(
-                 std::declval<BasicJsonType&>(), std::declval<T>()))>
-    static int detect(U&&);
-    static void detect(...);
-
-  public:
-    static constexpr bool value = std::is_integral<decltype(detect(
-                                      std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
-};
-
-
 /////////////
 // to_json //
 /////////////
@@ -995,10 +2044,14 @@ void to_json(BasicJsonType& j, const std::vector<bool>& e)
     external_constructor<value_t::array>::construct(j, e);
 }
 
-template<typename BasicJsonType, typename CompatibleArrayType,
-         enable_if_t<is_compatible_array_type<BasicJsonType, CompatibleArrayType>::value or
-                     std::is_same<typename BasicJsonType::array_t, CompatibleArrayType>::value,
-                     int> = 0>
+template <typename BasicJsonType, typename CompatibleArrayType,
+          enable_if_t<is_compatible_array_type<BasicJsonType,
+                      CompatibleArrayType>::value and
+                      not is_compatible_object_type<
+                          BasicJsonType, CompatibleArrayType>::value and
+                      not is_compatible_string_type<BasicJsonType, CompatibleArrayType>::value and
+                      not is_basic_json<CompatibleArrayType>::value,
+                      int> = 0>
 void to_json(BasicJsonType& j, const CompatibleArrayType& arr)
 {
     external_constructor<value_t::array>::construct(j, arr);
@@ -1006,7 +2059,7 @@ void to_json(BasicJsonType& j, const CompatibleArrayType& arr)
 
 template<typename BasicJsonType, typename T,
          enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
-void to_json(BasicJsonType& j, std::valarray<T> arr)
+void to_json(BasicJsonType& j, const std::valarray<T>& arr)
 {
     external_constructor<value_t::array>::construct(j, std::move(arr));
 }
@@ -1018,7 +2071,7 @@ void to_json(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
 }
 
 template<typename BasicJsonType, typename CompatibleObjectType,
-         enable_if_t<is_compatible_object_type<BasicJsonType, CompatibleObjectType>::value, int> = 0>
+         enable_if_t<is_compatible_object_type<BasicJsonType, CompatibleObjectType>::value and not is_basic_json<CompatibleObjectType>::value, int> = 0>
 void to_json(BasicJsonType& j, const CompatibleObjectType& obj)
 {
     external_constructor<value_t::object>::construct(j, obj);
@@ -1030,9 +2083,12 @@ void to_json(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
     external_constructor<value_t::object>::construct(j, std::move(obj));
 }
 
-template<typename BasicJsonType, typename T, std::size_t N,
-         enable_if_t<not std::is_constructible<typename BasicJsonType::string_t, T (&)[N]>::value, int> = 0>
-void to_json(BasicJsonType& j, T (&arr)[N])
+template <
+    typename BasicJsonType, typename T, std::size_t N,
+    enable_if_t<not std::is_constructible<typename BasicJsonType::string_t,
+                const T(&)[N]>::value,
+                int> = 0 >
+void to_json(BasicJsonType& j, const T(&arr)[N])
 {
     external_constructor<value_t::array>::construct(j, arr);
 }
@@ -1040,351 +2096,71 @@ void to_json(BasicJsonType& j, T (&arr)[N])
 template<typename BasicJsonType, typename... Args>
 void to_json(BasicJsonType& j, const std::pair<Args...>& p)
 {
-    j = {p.first, p.second};
-}
-
-template<typename BasicJsonType, typename Tuple, std::size_t... Idx>
-void to_json_tuple_impl(BasicJsonType& j, const Tuple& t, index_sequence<Idx...>)
-{
-    j = {std::get<Idx>(t)...};
-}
-
-template<typename BasicJsonType, typename... Args>
-void to_json(BasicJsonType& j, const std::tuple<Args...>& t)
-{
-    to_json_tuple_impl(j, t, index_sequence_for<Args...> {});
-}
-
-///////////////
-// from_json //
-///////////////
-
-// overloads for basic_json template parameters
-template<typename BasicJsonType, typename ArithmeticType,
-         enable_if_t<std::is_arithmetic<ArithmeticType>::value and
-                     not std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
-                     int> = 0>
-void get_arithmetic_value(const BasicJsonType& j, ArithmeticType& val)
-{
-    switch (static_cast<value_t>(j))
-    {
-        case value_t::number_unsigned:
-        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>());
-            break;
-        }
-        case value_t::number_integer:
-        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_integer_t*>());
-            break;
-        }
-        case value_t::number_float:
-        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_float_t*>());
-            break;
-        }
-
-        default:
-            JSON_THROW(type_error::create(302, "type must be number, but is " + std::string(j.type_name())));
-    }
-}
-
-template<typename BasicJsonType>
-void from_json(const BasicJsonType& j, typename BasicJsonType::boolean_t& b)
-{
-    if (JSON_UNLIKELY(not j.is_boolean()))
-    {
-        JSON_THROW(type_error::create(302, "type must be boolean, but is " + std::string(j.type_name())));
-    }
-    b = *j.template get_ptr<const typename BasicJsonType::boolean_t*>();
-}
-
-template<typename BasicJsonType>
-void from_json(const BasicJsonType& j, typename BasicJsonType::string_t& s)
-{
-    if (JSON_UNLIKELY(not j.is_string()))
-    {
-        JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name())));
-    }
-    s = *j.template get_ptr<const typename BasicJsonType::string_t*>();
-}
-
-template<typename BasicJsonType>
-void from_json(const BasicJsonType& j, typename BasicJsonType::number_float_t& val)
-{
-    get_arithmetic_value(j, val);
-}
-
-template<typename BasicJsonType>
-void from_json(const BasicJsonType& j, typename BasicJsonType::number_unsigned_t& val)
-{
-    get_arithmetic_value(j, val);
-}
-
-template<typename BasicJsonType>
-void from_json(const BasicJsonType& j, typename BasicJsonType::number_integer_t& val)
-{
-    get_arithmetic_value(j, val);
-}
-
-template<typename BasicJsonType, typename EnumType,
-         enable_if_t<std::is_enum<EnumType>::value, int> = 0>
-void from_json(const BasicJsonType& j, EnumType& e)
-{
-    typename std::underlying_type<EnumType>::type val;
-    get_arithmetic_value(j, val);
-    e = static_cast<EnumType>(val);
-}
-
-template<typename BasicJsonType>
-void from_json(const BasicJsonType& j, typename BasicJsonType::array_t& arr)
-{
-    if (JSON_UNLIKELY(not j.is_array()))
-    {
-        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
-    }
-    arr = *j.template get_ptr<const typename BasicJsonType::array_t*>();
-}
-
-// forward_list doesn't have an insert method
-template<typename BasicJsonType, typename T, typename Allocator,
-         enable_if_t<std::is_convertible<BasicJsonType, T>::value, int> = 0>
-void from_json(const BasicJsonType& j, std::forward_list<T, Allocator>& l)
-{
-    if (JSON_UNLIKELY(not j.is_array()))
-    {
-        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
-    }
-    std::transform(j.rbegin(), j.rend(),
-                   std::front_inserter(l), [](const BasicJsonType & i)
-    {
-        return i.template get<T>();
-    });
-}
-
-// valarray doesn't have an insert method
-template<typename BasicJsonType, typename T,
-         enable_if_t<std::is_convertible<BasicJsonType, T>::value, int> = 0>
-void from_json(const BasicJsonType& j, std::valarray<T>& l)
-{
-    if (JSON_UNLIKELY(not j.is_array()))
-    {
-        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
-    }
-    l.resize(j.size());
-    std::copy(j.m_value.array->begin(), j.m_value.array->end(), std::begin(l));
-}
-
-template<typename BasicJsonType, typename CompatibleArrayType>
-void from_json_array_impl(const BasicJsonType& j, CompatibleArrayType& arr, priority_tag<0> /*unused*/)
-{
-    using std::end;
-
-    std::transform(j.begin(), j.end(),
-                   std::inserter(arr, end(arr)), [](const BasicJsonType & i)
-    {
-        // get<BasicJsonType>() returns *this, this won't call a from_json
-        // method when value_type is BasicJsonType
-        return i.template get<typename CompatibleArrayType::value_type>();
-    });
-}
-
-template<typename BasicJsonType, typename CompatibleArrayType>
-auto from_json_array_impl(const BasicJsonType& j, CompatibleArrayType& arr, priority_tag<1> /*unused*/)
--> decltype(
-    arr.reserve(std::declval<typename CompatibleArrayType::size_type>()),
-    void())
-{
-    using std::end;
-
-    arr.reserve(j.size());
-    std::transform(j.begin(), j.end(),
-                   std::inserter(arr, end(arr)), [](const BasicJsonType & i)
-    {
-        // get<BasicJsonType>() returns *this, this won't call a from_json
-        // method when value_type is BasicJsonType
-        return i.template get<typename CompatibleArrayType::value_type>();
-    });
-}
-
-template<typename BasicJsonType, typename T, std::size_t N>
-void from_json_array_impl(const BasicJsonType& j, std::array<T, N>& arr, priority_tag<2> /*unused*/)
-{
-    for (std::size_t i = 0; i < N; ++i)
-    {
-        arr[i] = j.at(i).template get<T>();
-    }
-}
-
-template<typename BasicJsonType, typename CompatibleArrayType,
-         enable_if_t<is_compatible_array_type<BasicJsonType, CompatibleArrayType>::value and
-                     std::is_convertible<BasicJsonType, typename CompatibleArrayType::value_type>::value and
-                     not std::is_same<typename BasicJsonType::array_t, CompatibleArrayType>::value, int> = 0>
-void from_json(const BasicJsonType& j, CompatibleArrayType& arr)
-{
-    if (JSON_UNLIKELY(not j.is_array()))
-    {
-        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name())));
-    }
-
-    from_json_array_impl(j, arr, priority_tag<2> {});
-}
-
-template<typename BasicJsonType, typename CompatibleObjectType,
-         enable_if_t<is_compatible_object_type<BasicJsonType, CompatibleObjectType>::value, int> = 0>
-void from_json(const BasicJsonType& j, CompatibleObjectType& obj)
-{
-    if (JSON_UNLIKELY(not j.is_object()))
-    {
-        JSON_THROW(type_error::create(302, "type must be object, but is " + std::string(j.type_name())));
-    }
-
-    auto inner_object = j.template get_ptr<const typename BasicJsonType::object_t*>();
-    using value_type = typename CompatibleObjectType::value_type;
-    std::transform(
-        inner_object->begin(), inner_object->end(),
-        std::inserter(obj, obj.begin()),
-        [](typename BasicJsonType::object_t::value_type const & p)
-    {
-        return value_type(p.first, p.second.template get<typename CompatibleObjectType::mapped_type>());
-    });
-}
-
-// overload for arithmetic types, not chosen for basic_json template arguments
-// (BooleanType, etc..); note: Is it really necessary to provide explicit
-// overloads for boolean_t etc. in case of a custom BooleanType which is not
-// an arithmetic type?
-template<typename BasicJsonType, typename ArithmeticType,
-         enable_if_t <
-             std::is_arithmetic<ArithmeticType>::value and
-             not std::is_same<ArithmeticType, typename BasicJsonType::number_unsigned_t>::value and
-             not std::is_same<ArithmeticType, typename BasicJsonType::number_integer_t>::value and
-             not std::is_same<ArithmeticType, typename BasicJsonType::number_float_t>::value and
-             not std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
-             int> = 0>
-void from_json(const BasicJsonType& j, ArithmeticType& val)
-{
-    switch (static_cast<value_t>(j))
-    {
-        case value_t::number_unsigned:
-        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>());
-            break;
-        }
-        case value_t::number_integer:
-        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_integer_t*>());
-            break;
-        }
-        case value_t::number_float:
-        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_float_t*>());
-            break;
-        }
-        case value_t::boolean:
-        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::boolean_t*>());
-            break;
-        }
-
-        default:
-            JSON_THROW(type_error::create(302, "type must be number, but is " + std::string(j.type_name())));
-    }
+    j = { p.first, p.second };
 }
 
-template<typename BasicJsonType, typename A1, typename A2>
-void from_json(const BasicJsonType& j, std::pair<A1, A2>& p)
+// for https://github.com/nlohmann/json/pull/1134
+template < typename BasicJsonType, typename T,
+           enable_if_t<std::is_same<T, iteration_proxy_value<typename BasicJsonType::iterator>>::value, int> = 0>
+void to_json(BasicJsonType& j, const T& b)
 {
-    p = {j.at(0).template get<A1>(), j.at(1).template get<A2>()};
+    j = { {b.key(), b.value()} };
 }
 
 template<typename BasicJsonType, typename Tuple, std::size_t... Idx>
-void from_json_tuple_impl(const BasicJsonType& j, Tuple& t, index_sequence<Idx...>)
+void to_json_tuple_impl(BasicJsonType& j, const Tuple& t, index_sequence<Idx...> /*unused*/)
 {
-    t = std::make_tuple(j.at(Idx).template get<typename std::tuple_element<Idx, Tuple>::type>()...);
+    j = { std::get<Idx>(t)... };
 }
 
 template<typename BasicJsonType, typename... Args>
-void from_json(const BasicJsonType& j, std::tuple<Args...>& t)
+void to_json(BasicJsonType& j, const std::tuple<Args...>& t)
 {
-    from_json_tuple_impl(j, t, index_sequence_for<Args...> {});
+    to_json_tuple_impl(j, t, index_sequence_for<Args...> {});
 }
 
 struct to_json_fn
 {
-  private:
     template<typename BasicJsonType, typename T>
-    auto call(BasicJsonType& j, T&& val, priority_tag<1> /*unused*/) const noexcept(noexcept(to_json(j, std::forward<T>(val))))
+    auto operator()(BasicJsonType& j, T&& val) const noexcept(noexcept(to_json(j, std::forward<T>(val))))
     -> decltype(to_json(j, std::forward<T>(val)), void())
     {
         return to_json(j, std::forward<T>(val));
     }
+};
+}  // namespace detail
 
-    template<typename BasicJsonType, typename T>
-    void call(BasicJsonType& /*unused*/, T&& /*unused*/, priority_tag<0> /*unused*/) const noexcept
-    {
-        static_assert(sizeof(BasicJsonType) == 0,
-                      "could not find to_json() method in T's namespace");
+/// namespace to hold default `to_json` function
+namespace
+{
+constexpr const auto& to_json = detail::static_const<detail::to_json_fn>::value;
+} // namespace
+}  // namespace nlohmann
 
-#ifdef _MSC_VER
-        // MSVC does not show a stacktrace for the above assert
-        using decayed = uncvref_t<T>;
-        static_assert(sizeof(typename decayed::force_msvc_stacktrace) == 0,
-                      "forcing MSVC stacktrace to show which T we're talking about.");
-#endif
-    }
+// #include <nlohmann/detail/input/input_adapters.hpp>
 
-  public:
-    template<typename BasicJsonType, typename T>
-    void operator()(BasicJsonType& j, T&& val) const
-    noexcept(noexcept(std::declval<to_json_fn>().call(j, std::forward<T>(val), priority_tag<1> {})))
-    {
-        return call(j, std::forward<T>(val), priority_tag<1> {});
-    }
-};
 
-struct from_json_fn
-{
-  private:
-    template<typename BasicJsonType, typename T>
-    auto call(const BasicJsonType& j, T& val, priority_tag<1> /*unused*/) const
-    noexcept(noexcept(from_json(j, val)))
-    -> decltype(from_json(j, val), void())
-    {
-        return from_json(j, val);
-    }
+#include <cassert> // assert
+#include <cstddef> // size_t
+#include <cstring> // strlen
+#include <istream> // istream
+#include <iterator> // begin, end, iterator_traits, random_access_iterator_tag, distance, next
+#include <memory> // shared_ptr, make_shared, addressof
+#include <numeric> // accumulate
+#include <string> // string, char_traits
+#include <type_traits> // enable_if, is_base_of, is_pointer, is_integral, remove_pointer
+#include <utility> // pair, declval
+#include <cstdio> //FILE *
 
-    template<typename BasicJsonType, typename T>
-    void call(const BasicJsonType& /*unused*/, T& /*unused*/, priority_tag<0> /*unused*/) const noexcept
-    {
-        static_assert(sizeof(BasicJsonType) == 0,
-                      "could not find from_json() method in T's namespace");
-#ifdef _MSC_VER
-        // MSVC does not show a stacktrace for the above assert
-        using decayed = uncvref_t<T>;
-        static_assert(sizeof(typename decayed::force_msvc_stacktrace) == 0,
-                      "forcing MSVC stacktrace to show which T we're talking about.");
-#endif
-    }
+// #include <nlohmann/detail/macro_scope.hpp>
 
-  public:
-    template<typename BasicJsonType, typename T>
-    void operator()(const BasicJsonType& j, T& val) const
-    noexcept(noexcept(std::declval<from_json_fn>().call(j, val, priority_tag<1> {})))
-    {
-        return call(j, val, priority_tag<1> {});
-    }
-};
 
-// taken from ranges-v3
-template<typename T>
-struct static_const
+namespace nlohmann
 {
-    static constexpr T value{};
-};
-
-template<typename T>
-constexpr T static_const<T>::value;
+namespace detail
+{
+/// the supported input formats
+enum class input_format_t { json, cbor, msgpack, ubjson, bson };
 
 ////////////////////
 // input adapters //
@@ -1394,19 +2170,17 @@ constexpr T static_const<T>::value;
 @brief abstract input adapter interface
 
 Produces a stream of std::char_traits<char>::int_type characters from a
-std::istream, a buffer, or some other input type.  Accepts the return of exactly
-one non-EOF character for future input.  The int_type characters returned
-consist of all valid char values as positive values (typically unsigned char),
-plus an EOF value outside that range, specified by the value of the function
-std::char_traits<char>::eof().  This value is typically -1, but could be any
-arbitrary value which is not a valid char value.
+std::istream, a buffer, or some other input type. Accepts the return of
+exactly one non-EOF character for future input. The int_type characters
+returned consist of all valid char values as positive values (typically
+unsigned char), plus an EOF value outside that range, specified by the value
+of the function std::char_traits<char>::eof(). This value is typically -1, but
+could be any arbitrary value which is not a valid char value.
 */
 struct input_adapter_protocol
 {
     /// get a character [0,255] or std::char_traits<char>::eof().
     virtual std::char_traits<char>::int_type get_character() = 0;
-    /// restore the last non-eof() character to input
-    virtual void unget_character() = 0;
     virtual ~input_adapter_protocol() = default;
 };
 
@@ -1414,6 +2188,27 @@ struct input_adapter_protocol
 using input_adapter_t = std::shared_ptr<input_adapter_protocol>;
 
 /*!
+Input adapter for stdio file access. This adapter read only 1 byte and do not use any
+ buffer. This adapter is a very low level adapter.
+*/
+class file_input_adapter : public input_adapter_protocol
+{
+  public:
+    explicit file_input_adapter(std::FILE* f)  noexcept
+        : m_file(f)
+    {}
+
+    std::char_traits<char>::int_type get_character() noexcept override
+    {
+        return std::fgetc(m_file);
+    }
+  private:
+    /// the file pointer to read from
+    std::FILE* m_file;
+};
+
+
+/*!
 Input adapter for a (caching) istream. Ignores a UFT Byte Order Mark at
 beginning of input. Does not support changing the underlying std::streambuf
 in mid-input. Maintains underlying std::istream and std::streambuf to support
@@ -1428,56 +2223,32 @@ class input_stream_adapter : public input_adapter_protocol
     ~input_stream_adapter() override
     {
         // clear stream flags; we use underlying streambuf I/O, do not
-        // maintain ifstream flags
-        is.clear();
+        // maintain ifstream flags, except eof
+        is.clear(is.rdstate() & std::ios::eofbit);
     }
 
     explicit input_stream_adapter(std::istream& i)
         : is(i), sb(*i.rdbuf())
-    {
-        // skip byte order mark
-        std::char_traits<char>::int_type c;
-        if ((c = get_character()) == 0xEF)
-        {
-            if ((c = get_character()) == 0xBB)
-            {
-                if ((c = get_character()) == 0xBF)
-                {
-                    return; // Ignore BOM
-                }
-                else if (c != std::char_traits<char>::eof())
-                {
-                    is.unget();
-                }
-                is.putback('\xBB');
-            }
-            else if (c != std::char_traits<char>::eof())
-            {
-                is.unget();
-            }
-            is.putback('\xEF');
-        }
-        else if (c != std::char_traits<char>::eof())
-        {
-            is.unget(); // no byte order mark; process as usual
-        }
-    }
+    {}
 
     // delete because of pointer members
     input_stream_adapter(const input_stream_adapter&) = delete;
     input_stream_adapter& operator=(input_stream_adapter&) = delete;
+    input_stream_adapter(input_stream_adapter&&) = delete;
+    input_stream_adapter& operator=(input_stream_adapter&&) = delete;
 
     // std::istream/std::streambuf use std::char_traits<char>::to_int_type, to
     // ensure that std::char_traits<char>::eof() and the character 0xFF do not
     // end up as the same value, eg. 0xFFFFFFFF.
     std::char_traits<char>::int_type get_character() override
     {
-        return sb.sbumpc();
-    }
-
-    void unget_character() override
-    {
-        sb.sungetc();  // is.unget() avoided for performance
+        auto res = sb.sbumpc();
+        // set eof manually, as we don't use the istream interface.
+        if (res == EOF)
+        {
+            is.clear(is.rdstate() | std::ios::eofbit);
+        }
+        return res;
     }
 
   private:
@@ -1490,19 +2261,16 @@ class input_stream_adapter : public input_adapter_protocol
 class input_buffer_adapter : public input_adapter_protocol
 {
   public:
-    input_buffer_adapter(const char* b, const std::size_t l)
-        : cursor(b), limit(b + l), start(b)
-    {
-        // skip byte order mark
-        if (l >= 3 and b[0] == '\xEF' and b[1] == '\xBB' and b[2] == '\xBF')
-        {
-            cursor += 3;
-        }
-    }
+    input_buffer_adapter(const char* b, const std::size_t l) noexcept
+        : cursor(b), limit(b + l)
+    {}
 
     // delete because of pointer members
     input_buffer_adapter(const input_buffer_adapter&) = delete;
     input_buffer_adapter& operator=(input_buffer_adapter&) = delete;
+    input_buffer_adapter(input_buffer_adapter&&) = delete;
+    input_buffer_adapter& operator=(input_buffer_adapter&&) = delete;
+    ~input_buffer_adapter() override = default;
 
     std::char_traits<char>::int_type get_character() noexcept override
     {
@@ -1514,28 +2282,182 @@ class input_buffer_adapter : public input_adapter_protocol
         return std::char_traits<char>::eof();
     }
 
-    void unget_character() noexcept override
+  private:
+    /// pointer to the current character
+    const char* cursor;
+    /// pointer past the last character
+    const char* const limit;
+};
+
+template<typename WideStringType, size_t T>
+struct wide_string_input_helper
+{
+    // UTF-32
+    static void fill_buffer(const WideStringType& str, size_t& current_wchar, std::array<std::char_traits<char>::int_type, 4>& utf8_bytes, size_t& utf8_bytes_index, size_t& utf8_bytes_filled)
     {
-        if (JSON_LIKELY(cursor > start))
+        utf8_bytes_index = 0;
+
+        if (current_wchar == str.size())
         {
-            --cursor;
+            utf8_bytes[0] = std::char_traits<char>::eof();
+            utf8_bytes_filled = 1;
+        }
+        else
+        {
+            // get the current character
+            const auto wc = static_cast<int>(str[current_wchar++]);
+
+            // UTF-32 to UTF-8 encoding
+            if (wc < 0x80)
+            {
+                utf8_bytes[0] = wc;
+                utf8_bytes_filled = 1;
+            }
+            else if (wc <= 0x7FF)
+            {
+                utf8_bytes[0] = 0xC0 | ((wc >> 6) & 0x1F);
+                utf8_bytes[1] = 0x80 | (wc & 0x3F);
+                utf8_bytes_filled = 2;
+            }
+            else if (wc <= 0xFFFF)
+            {
+                utf8_bytes[0] = 0xE0 | ((wc >> 12) & 0x0F);
+                utf8_bytes[1] = 0x80 | ((wc >> 6) & 0x3F);
+                utf8_bytes[2] = 0x80 | (wc & 0x3F);
+                utf8_bytes_filled = 3;
+            }
+            else if (wc <= 0x10FFFF)
+            {
+                utf8_bytes[0] = 0xF0 | ((wc >> 18) & 0x07);
+                utf8_bytes[1] = 0x80 | ((wc >> 12) & 0x3F);
+                utf8_bytes[2] = 0x80 | ((wc >> 6) & 0x3F);
+                utf8_bytes[3] = 0x80 | (wc & 0x3F);
+                utf8_bytes_filled = 4;
+            }
+            else
+            {
+                // unknown character
+                utf8_bytes[0] = wc;
+                utf8_bytes_filled = 1;
+            }
         }
     }
+};
+
+template<typename WideStringType>
+struct wide_string_input_helper<WideStringType, 2>
+{
+    // UTF-16
+    static void fill_buffer(const WideStringType& str, size_t& current_wchar, std::array<std::char_traits<char>::int_type, 4>& utf8_bytes, size_t& utf8_bytes_index, size_t& utf8_bytes_filled)
+    {
+        utf8_bytes_index = 0;
+
+        if (current_wchar == str.size())
+        {
+            utf8_bytes[0] = std::char_traits<char>::eof();
+            utf8_bytes_filled = 1;
+        }
+        else
+        {
+            // get the current character
+            const auto wc = static_cast<int>(str[current_wchar++]);
+
+            // UTF-16 to UTF-8 encoding
+            if (wc < 0x80)
+            {
+                utf8_bytes[0] = wc;
+                utf8_bytes_filled = 1;
+            }
+            else if (wc <= 0x7FF)
+            {
+                utf8_bytes[0] = 0xC0 | ((wc >> 6));
+                utf8_bytes[1] = 0x80 | (wc & 0x3F);
+                utf8_bytes_filled = 2;
+            }
+            else if (0xD800 > wc or wc >= 0xE000)
+            {
+                utf8_bytes[0] = 0xE0 | ((wc >> 12));
+                utf8_bytes[1] = 0x80 | ((wc >> 6) & 0x3F);
+                utf8_bytes[2] = 0x80 | (wc & 0x3F);
+                utf8_bytes_filled = 3;
+            }
+            else
+            {
+                if (current_wchar < str.size())
+                {
+                    const auto wc2 = static_cast<int>(str[current_wchar++]);
+                    const int charcode = 0x10000 + (((wc & 0x3FF) << 10) | (wc2 & 0x3FF));
+                    utf8_bytes[0] = 0xf0 | (charcode >> 18);
+                    utf8_bytes[1] = 0x80 | ((charcode >> 12) & 0x3F);
+                    utf8_bytes[2] = 0x80 | ((charcode >> 6) & 0x3F);
+                    utf8_bytes[3] = 0x80 | (charcode & 0x3F);
+                    utf8_bytes_filled = 4;
+                }
+                else
+                {
+                    // unknown character
+                    ++current_wchar;
+                    utf8_bytes[0] = wc;
+                    utf8_bytes_filled = 1;
+                }
+            }
+        }
+    }
+};
+
+template<typename WideStringType>
+class wide_string_input_adapter : public input_adapter_protocol
+{
+  public:
+    explicit wide_string_input_adapter(const WideStringType& w)  noexcept
+        : str(w)
+    {}
+
+    std::char_traits<char>::int_type get_character() noexcept override
+    {
+        // check if buffer needs to be filled
+        if (utf8_bytes_index == utf8_bytes_filled)
+        {
+            fill_buffer<sizeof(typename WideStringType::value_type)>();
+
+            assert(utf8_bytes_filled > 0);
+            assert(utf8_bytes_index == 0);
+        }
+
+        // use buffer
+        assert(utf8_bytes_filled > 0);
+        assert(utf8_bytes_index < utf8_bytes_filled);
+        return utf8_bytes[utf8_bytes_index++];
+    }
 
   private:
-    /// pointer to the current character
-    const char* cursor;
-    /// pointer past the last character
-    const char* limit;
-    /// pointer to the first character
-    const char* start;
+    template<size_t T>
+    void fill_buffer()
+    {
+        wide_string_input_helper<WideStringType, T>::fill_buffer(str, current_wchar, utf8_bytes, utf8_bytes_index, utf8_bytes_filled);
+    }
+
+    /// the wstring to process
+    const WideStringType& str;
+
+    /// index of the current wchar in str
+    std::size_t current_wchar = 0;
+
+    /// a buffer for UTF-8 bytes
+    std::array<std::char_traits<char>::int_type, 4> utf8_bytes = {{0, 0, 0, 0}};
+
+    /// index to the utf8_codes array for the next valid byte
+    std::size_t utf8_bytes_index = 0;
+    /// number of valid bytes in the utf8_codes array
+    std::size_t utf8_bytes_filled = 0;
 };
 
 class input_adapter
 {
   public:
     // native support
-
+    input_adapter(std::FILE* file)
+        : ia(std::make_shared<file_input_adapter>(file)) {}
     /// input adapter for input stream
     input_adapter(std::istream& i)
         : ia(std::make_shared<input_stream_adapter>(i)) {}
@@ -1544,6 +2466,15 @@ class input_adapter
     input_adapter(std::istream&& i)
         : ia(std::make_shared<input_stream_adapter>(i)) {}
 
+    input_adapter(const std::wstring& ws)
+        : ia(std::make_shared<wide_string_input_adapter<std::wstring>>(ws)) {}
+
+    input_adapter(const std::u16string& ws)
+        : ia(std::make_shared<wide_string_input_adapter<std::u16string>>(ws)) {}
+
+    input_adapter(const std::u32string& ws)
+        : ia(std::make_shared<wide_string_input_adapter<std::u32string>>(ws)) {}
+
     /// input adapter for buffer
     template<typename CharT,
              typename std::enable_if<
@@ -1570,23 +2501,26 @@ class input_adapter
     /// input adapter for iterator range with contiguous storage
     template<class IteratorType,
              typename std::enable_if<
-                 std::is_same<typename std::iterator_traits<IteratorType>::iterator_category, std::random_access_iterator_tag>::value,
+                 std::is_same<typename iterator_traits<IteratorType>::iterator_category, std::random_access_iterator_tag>::value,
                  int>::type = 0>
     input_adapter(IteratorType first, IteratorType last)
     {
+#ifndef NDEBUG
         // assertion to check that the iterator range is indeed contiguous,
         // see http://stackoverflow.com/a/35008842/266378 for more discussion
-        assert(std::accumulate(
-                   first, last, std::pair<bool, int>(true, 0),
-                   [&first](std::pair<bool, int> res, decltype(*first) val)
+        const auto is_contiguous = std::accumulate(
+                                       first, last, std::pair<bool, int>(true, 0),
+                                       [&first](std::pair<bool, int> res, decltype(*first) val)
         {
             res.first &= (val == *(std::next(std::addressof(*first), res.second++)));
             return res;
-        }).first);
+        }).first;
+        assert(is_contiguous);
+#endif
 
         // assertion to check that each element is 1 byte long
         static_assert(
-            sizeof(typename std::iterator_traits<IteratorType>::value_type) == 1,
+            sizeof(typename iterator_traits<IteratorType>::value_type) == 1,
             "each element in the iterator range must have the size of 1 byte");
 
         const auto len = static_cast<size_t>(std::distance(first, last));
@@ -1610,7 +2544,7 @@ class input_adapter
     /// input adapter for contiguous container
     template<class ContiguousContainer, typename
              std::enable_if<not std::is_pointer<ContiguousContainer>::value and
-                            std::is_base_of<std::random_access_iterator_tag, typename std::iterator_traits<decltype(std::begin(std::declval<ContiguousContainer const>()))>::iterator_category>::value,
+                            std::is_base_of<std::random_access_iterator_tag, typename iterator_traits<decltype(std::begin(std::declval<ContiguousContainer const>()))>::iterator_category>::value,
                             int>::type = 0>
     input_adapter(const ContiguousContainer& c)
         : input_adapter(std::begin(c), std::end(c)) {}
@@ -1624,10 +2558,34 @@ class input_adapter
     /// the actual adapter
     input_adapter_t ia = nullptr;
 };
+}  // namespace detail
+}  // namespace nlohmann
 
-//////////////////////
-// lexer and parser //
-//////////////////////
+// #include <nlohmann/detail/input/lexer.hpp>
+
+
+#include <clocale> // localeconv
+#include <cstddef> // size_t
+#include <cstdlib> // strtof, strtod, strtold, strtoll, strtoull
+#include <cstdio> // snprintf
+#include <initializer_list> // initializer_list
+#include <string> // char_traits, string
+#include <vector> // vector
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+// #include <nlohmann/detail/input/input_adapters.hpp>
+
+// #include <nlohmann/detail/input/position_t.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+///////////
+// lexer //
+///////////
 
 /*!
 @brief lexical analysis
@@ -1640,6 +2598,7 @@ class lexer
     using number_integer_t = typename BasicJsonType::number_integer_t;
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
     using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
 
   public:
     /// token types for the parser
@@ -1701,17 +2660,22 @@ class lexer
                 return "end of input";
             case token_type::literal_or_value:
                 return "'[', '{', or a literal";
+            // LCOV_EXCL_START
             default: // catch non-enum values
-                return "unknown token"; // LCOV_EXCL_LINE
+                return "unknown token";
+                // LCOV_EXCL_STOP
         }
     }
 
-    explicit lexer(detail::input_adapter_t adapter)
+    explicit lexer(detail::input_adapter_t&& adapter)
         : ia(std::move(adapter)), decimal_point_char(get_decimal_point()) {}
 
     // delete because of pointer members
     lexer(const lexer&) = delete;
+    lexer(lexer&&) = delete;
     lexer& operator=(lexer&) = delete;
+    lexer& operator=(lexer&&) = delete;
+    ~lexer() = default;
 
   private:
     /////////////////////
@@ -1819,9 +2783,10 @@ class lexer
     @brief scan a string literal
 
     This function scans a string according to Sect. 7 of RFC 7159. While
-    scanning, bytes are escaped and copied into buffer yytext. Then the function
-    returns successfully, yytext is *not* null-terminated (as it may contain \0
-    bytes), and yytext.size() is the number of bytes in the string.
+    scanning, bytes are escaped and copied into buffer token_buffer. Then the
+    function returns successfully, token_buffer is *not* null-terminated (as it
+    may contain \0 bytes), and token_buffer.size() is the number of bytes in the
+    string.
 
     @return token_type::value_string if string could be successfully scanned,
             token_type::parse_error otherwise
@@ -1831,7 +2796,7 @@ class lexer
     */
     token_type scan_string()
     {
-        // reset yytext (ignore opening quote)
+        // reset token_buffer (ignore opening quote)
         reset();
 
         // we entered the function by reading an open quote
@@ -1999,39 +2964,194 @@ class lexer
 
                 // invalid control characters
                 case 0x00:
+                {
+                    error_message = "invalid string: control character U+0000 (NUL) must be escaped to \\u0000";
+                    return token_type::parse_error;
+                }
+
                 case 0x01:
+                {
+                    error_message = "invalid string: control character U+0001 (SOH) must be escaped to \\u0001";
+                    return token_type::parse_error;
+                }
+
                 case 0x02:
+                {
+                    error_message = "invalid string: control character U+0002 (STX) must be escaped to \\u0002";
+                    return token_type::parse_error;
+                }
+
                 case 0x03:
+                {
+                    error_message = "invalid string: control character U+0003 (ETX) must be escaped to \\u0003";
+                    return token_type::parse_error;
+                }
+
                 case 0x04:
+                {
+                    error_message = "invalid string: control character U+0004 (EOT) must be escaped to \\u0004";
+                    return token_type::parse_error;
+                }
+
                 case 0x05:
+                {
+                    error_message = "invalid string: control character U+0005 (ENQ) must be escaped to \\u0005";
+                    return token_type::parse_error;
+                }
+
                 case 0x06:
+                {
+                    error_message = "invalid string: control character U+0006 (ACK) must be escaped to \\u0006";
+                    return token_type::parse_error;
+                }
+
                 case 0x07:
+                {
+                    error_message = "invalid string: control character U+0007 (BEL) must be escaped to \\u0007";
+                    return token_type::parse_error;
+                }
+
                 case 0x08:
+                {
+                    error_message = "invalid string: control character U+0008 (BS) must be escaped to \\u0008 or \\b";
+                    return token_type::parse_error;
+                }
+
                 case 0x09:
+                {
+                    error_message = "invalid string: control character U+0009 (HT) must be escaped to \\u0009 or \\t";
+                    return token_type::parse_error;
+                }
+
                 case 0x0A:
+                {
+                    error_message = "invalid string: control character U+000A (LF) must be escaped to \\u000A or \\n";
+                    return token_type::parse_error;
+                }
+
                 case 0x0B:
+                {
+                    error_message = "invalid string: control character U+000B (VT) must be escaped to \\u000B";
+                    return token_type::parse_error;
+                }
+
                 case 0x0C:
+                {
+                    error_message = "invalid string: control character U+000C (FF) must be escaped to \\u000C or \\f";
+                    return token_type::parse_error;
+                }
+
                 case 0x0D:
+                {
+                    error_message = "invalid string: control character U+000D (CR) must be escaped to \\u000D or \\r";
+                    return token_type::parse_error;
+                }
+
                 case 0x0E:
+                {
+                    error_message = "invalid string: control character U+000E (SO) must be escaped to \\u000E";
+                    return token_type::parse_error;
+                }
+
                 case 0x0F:
+                {
+                    error_message = "invalid string: control character U+000F (SI) must be escaped to \\u000F";
+                    return token_type::parse_error;
+                }
+
                 case 0x10:
+                {
+                    error_message = "invalid string: control character U+0010 (DLE) must be escaped to \\u0010";
+                    return token_type::parse_error;
+                }
+
                 case 0x11:
+                {
+                    error_message = "invalid string: control character U+0011 (DC1) must be escaped to \\u0011";
+                    return token_type::parse_error;
+                }
+
                 case 0x12:
+                {
+                    error_message = "invalid string: control character U+0012 (DC2) must be escaped to \\u0012";
+                    return token_type::parse_error;
+                }
+
                 case 0x13:
+                {
+                    error_message = "invalid string: control character U+0013 (DC3) must be escaped to \\u0013";
+                    return token_type::parse_error;
+                }
+
                 case 0x14:
+                {
+                    error_message = "invalid string: control character U+0014 (DC4) must be escaped to \\u0014";
+                    return token_type::parse_error;
+                }
+
                 case 0x15:
+                {
+                    error_message = "invalid string: control character U+0015 (NAK) must be escaped to \\u0015";
+                    return token_type::parse_error;
+                }
+
                 case 0x16:
+                {
+                    error_message = "invalid string: control character U+0016 (SYN) must be escaped to \\u0016";
+                    return token_type::parse_error;
+                }
+
                 case 0x17:
+                {
+                    error_message = "invalid string: control character U+0017 (ETB) must be escaped to \\u0017";
+                    return token_type::parse_error;
+                }
+
                 case 0x18:
+                {
+                    error_message = "invalid string: control character U+0018 (CAN) must be escaped to \\u0018";
+                    return token_type::parse_error;
+                }
+
                 case 0x19:
+                {
+                    error_message = "invalid string: control character U+0019 (EM) must be escaped to \\u0019";
+                    return token_type::parse_error;
+                }
+
                 case 0x1A:
+                {
+                    error_message = "invalid string: control character U+001A (SUB) must be escaped to \\u001A";
+                    return token_type::parse_error;
+                }
+
                 case 0x1B:
+                {
+                    error_message = "invalid string: control character U+001B (ESC) must be escaped to \\u001B";
+                    return token_type::parse_error;
+                }
+
                 case 0x1C:
+                {
+                    error_message = "invalid string: control character U+001C (FS) must be escaped to \\u001C";
+                    return token_type::parse_error;
+                }
+
                 case 0x1D:
+                {
+                    error_message = "invalid string: control character U+001D (GS) must be escaped to \\u001D";
+                    return token_type::parse_error;
+                }
+
                 case 0x1E:
+                {
+                    error_message = "invalid string: control character U+001E (RS) must be escaped to \\u001E";
+                    return token_type::parse_error;
+                }
+
                 case 0x1F:
                 {
-                    error_message = "invalid string: control character must be escaped";
+                    error_message = "invalid string: control character U+001F (US) must be escaped to \\u001F";
                     return token_type::parse_error;
                 }
 
@@ -2303,7 +3423,7 @@ class lexer
     contains cycles, but any cycle can be left when EOF is read. Therefore,
     the function is guaranteed to terminate.
 
-    During scanning, the read bytes are stored in yytext. This string is
+    During scanning, the read bytes are stored in token_buffer. This string is
     then converted to a signed integer, an unsigned integer, or a
     floating-point number.
 
@@ -2315,9 +3435,9 @@ class lexer
           locale's decimal point is used instead of `.` to work with the
           locale-dependent converters.
     */
-    token_type scan_number()
+    token_type scan_number()  // lgtm [cpp/use-of-goto]
     {
-        // reset yytext to store the number's bytes
+        // reset token_buffer to store the number's bytes
         reset();
 
         // the type of the parsed number; initially set to unsigned; will be
@@ -2353,11 +3473,13 @@ class lexer
                 goto scan_number_any1;
             }
 
+            // LCOV_EXCL_START
             default:
             {
                 // all other characters are rejected outside scan_number()
-                assert(false); // LCOV_EXCL_LINE
+                assert(false);
             }
+                // LCOV_EXCL_STOP
         }
 
 scan_number_minus:
@@ -2601,10 +3723,10 @@ scan_number_done:
         // try to parse integers first and fall back to floats
         if (number_type == token_type::value_unsigned)
         {
-            const auto x = std::strtoull(yytext.data(), &endptr, 10);
+            const auto x = std::strtoull(token_buffer.data(), &endptr, 10);
 
             // we checked the number format before
-            assert(endptr == yytext.data() + yytext.size());
+            assert(endptr == token_buffer.data() + token_buffer.size());
 
             if (errno == 0)
             {
@@ -2617,10 +3739,10 @@ scan_number_done:
         }
         else if (number_type == token_type::value_integer)
         {
-            const auto x = std::strtoll(yytext.data(), &endptr, 10);
+            const auto x = std::strtoll(token_buffer.data(), &endptr, 10);
 
             // we checked the number format before
-            assert(endptr == yytext.data() + yytext.size());
+            assert(endptr == token_buffer.data() + token_buffer.size());
 
             if (errno == 0)
             {
@@ -2634,10 +3756,10 @@ scan_number_done:
 
         // this code is reached if we parse a floating-point number or if an
         // integer conversion above failed
-        strtof(value_float, yytext.data(), &endptr);
+        strtof(value_float, token_buffer.data(), &endptr);
 
         // we checked the number format before
-        assert(endptr == yytext.data() + yytext.size());
+        assert(endptr == token_buffer.data() + token_buffer.size());
 
         return token_type::value_float;
     }
@@ -2666,10 +3788,10 @@ scan_number_done:
     // input management
     /////////////////////
 
-    /// reset yytext; current character is beginning of token
+    /// reset token_buffer; current character is beginning of token
     void reset() noexcept
     {
-        yytext.clear();
+        token_buffer.clear();
         token_string.clear();
         token_string.push_back(std::char_traits<char>::to_char_type(current));
     }
@@ -2686,31 +3808,71 @@ scan_number_done:
     */
     std::char_traits<char>::int_type get()
     {
-        ++chars_read;
-        current = ia->get_character();
+        ++position.chars_read_total;
+        ++position.chars_read_current_line;
+
+        if (next_unget)
+        {
+            // just reset the next_unget variable and work with current
+            next_unget = false;
+        }
+        else
+        {
+            current = ia->get_character();
+        }
+
         if (JSON_LIKELY(current != std::char_traits<char>::eof()))
         {
             token_string.push_back(std::char_traits<char>::to_char_type(current));
         }
+
+        if (current == '\n')
+        {
+            ++position.lines_read;
+            ++position.chars_read_current_line = 0;
+        }
+
         return current;
     }
 
-    /// unget current character (return it again on next get)
+    /*!
+    @brief unget current character (read it again on next get)
+
+    We implement unget by setting variable next_unget to true. The input is not
+    changed - we just simulate ungetting by modifying chars_read_total,
+    chars_read_current_line, and token_string. The next call to get() will
+    behave as if the unget character is read again.
+    */
     void unget()
     {
-        --chars_read;
+        next_unget = true;
+
+        --position.chars_read_total;
+
+        // in case we "unget" a newline, we have to also decrement the lines_read
+        if (position.chars_read_current_line == 0)
+        {
+            if (position.lines_read > 0)
+            {
+                --position.lines_read;
+            }
+        }
+        else
+        {
+            --position.chars_read_current_line;
+        }
+
         if (JSON_LIKELY(current != std::char_traits<char>::eof()))
         {
-            ia->unget_character();
             assert(token_string.size() != 0);
             token_string.pop_back();
         }
     }
 
-    /// add a character to yytext
+    /// add a character to token_buffer
     void add(int c)
     {
-        yytext.push_back(std::char_traits<char>::to_char_type(c));
+        token_buffer.push_back(std::char_traits<char>::to_char_type(c));
     }
 
   public:
@@ -2737,9 +3899,9 @@ scan_number_done:
     }
 
     /// return current string value (implicitly resets the token; useful only once)
-    std::string move_string()
+    string_t& get_string()
     {
-        return std::move(yytext);
+        return token_buffer;
     }
 
     /////////////////////
@@ -2747,9 +3909,9 @@ scan_number_done:
     /////////////////////
 
     /// return position of last read token
-    constexpr std::size_t get_position() const noexcept
+    constexpr position_t get_position() const noexcept
     {
-        return chars_read;
+        return position;
     }
 
     /// return the last read token (for errors only).  Will never contain EOF
@@ -2764,10 +3926,9 @@ scan_number_done:
             if ('\x00' <= c and c <= '\x1F')
             {
                 // escape control characters
-                std::stringstream ss;
-                ss << "<U+" << std::setw(4) << std::uppercase << std::setfill('0')
-                   << std::hex << static_cast<int>(c) << ">";
-                result += ss.str();
+                char cs[9];
+                (std::snprintf)(cs, 9, "<U+%.4X>", static_cast<unsigned char>(c));
+                result += cs;
             }
             else
             {
@@ -2789,8 +3950,33 @@ scan_number_done:
     // actual scanner
     /////////////////////
 
+    /*!
+    @brief skip the UTF-8 byte order mark
+    @return true iff there is no BOM or the correct BOM has been skipped
+    */
+    bool skip_bom()
+    {
+        if (get() == 0xEF)
+        {
+            // check if we completely parse the BOM
+            return get() == 0xBB and get() == 0xBF;
+        }
+
+        // the first character is not the beginning of the BOM; unget it to
+        // process is later
+        unget();
+        return true;
+    }
+
     token_type scan()
     {
+        // initially, skip the BOM
+        if (position.chars_read_total == 0 and not skip_bom())
+        {
+            error_message = "invalid BOM; must be 0xEF 0xBB 0xBF if given";
+            return token_type::parse_error;
+        }
+
         // read next character and ignore whitespace
         do
         {
@@ -2860,14 +4046,17 @@ scan_number_done:
     /// the current character
     std::char_traits<char>::int_type current = std::char_traits<char>::eof();
 
-    /// the number of characters read
-    std::size_t chars_read = 0;
+    /// whether the next get() call should just return current
+    bool next_unget = false;
+
+    /// the start position of the current token
+    position_t position;
 
     /// raw input token string (for error messages)
     std::vector<char> token_string {};
 
     /// buffer for variable-length tokens (numbers, strings)
-    std::string yytext {};
+    string_t token_buffer {};
 
     /// a description of occurred lexer errors
     const char* error_message = "";
@@ -2880,6 +4069,887 @@ scan_number_done:
     /// the decimal point
     const char decimal_point_char = '.';
 };
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/input/parser.hpp>
+
+
+#include <cassert> // assert
+#include <cmath> // isfinite
+#include <cstdint> // uint8_t
+#include <functional> // function
+#include <string> // string
+#include <utility> // move
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+// #include <nlohmann/detail/meta/is_sax.hpp>
+
+
+#include <cstdint> // size_t
+#include <utility> // declval
+
+// #include <nlohmann/detail/meta/detected.hpp>
+
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+template <typename T>
+using null_function_t = decltype(std::declval<T&>().null());
+
+template <typename T>
+using boolean_function_t =
+    decltype(std::declval<T&>().boolean(std::declval<bool>()));
+
+template <typename T, typename Integer>
+using number_integer_function_t =
+    decltype(std::declval<T&>().number_integer(std::declval<Integer>()));
+
+template <typename T, typename Unsigned>
+using number_unsigned_function_t =
+    decltype(std::declval<T&>().number_unsigned(std::declval<Unsigned>()));
+
+template <typename T, typename Float, typename String>
+using number_float_function_t = decltype(std::declval<T&>().number_float(
+                                    std::declval<Float>(), std::declval<const String&>()));
+
+template <typename T, typename String>
+using string_function_t =
+    decltype(std::declval<T&>().string(std::declval<String&>()));
+
+template <typename T>
+using start_object_function_t =
+    decltype(std::declval<T&>().start_object(std::declval<std::size_t>()));
+
+template <typename T, typename String>
+using key_function_t =
+    decltype(std::declval<T&>().key(std::declval<String&>()));
+
+template <typename T>
+using end_object_function_t = decltype(std::declval<T&>().end_object());
+
+template <typename T>
+using start_array_function_t =
+    decltype(std::declval<T&>().start_array(std::declval<std::size_t>()));
+
+template <typename T>
+using end_array_function_t = decltype(std::declval<T&>().end_array());
+
+template <typename T, typename Exception>
+using parse_error_function_t = decltype(std::declval<T&>().parse_error(
+        std::declval<std::size_t>(), std::declval<const std::string&>(),
+        std::declval<const Exception&>()));
+
+template <typename SAX, typename BasicJsonType>
+struct is_sax
+{
+  private:
+    static_assert(is_basic_json<BasicJsonType>::value,
+                  "BasicJsonType must be of type basic_json<...>");
+
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using exception_t = typename BasicJsonType::exception;
+
+  public:
+    static constexpr bool value =
+        is_detected_exact<bool, null_function_t, SAX>::value &&
+        is_detected_exact<bool, boolean_function_t, SAX>::value &&
+        is_detected_exact<bool, number_integer_function_t, SAX,
+        number_integer_t>::value &&
+        is_detected_exact<bool, number_unsigned_function_t, SAX,
+        number_unsigned_t>::value &&
+        is_detected_exact<bool, number_float_function_t, SAX, number_float_t,
+        string_t>::value &&
+        is_detected_exact<bool, string_function_t, SAX, string_t>::value &&
+        is_detected_exact<bool, start_object_function_t, SAX>::value &&
+        is_detected_exact<bool, key_function_t, SAX, string_t>::value &&
+        is_detected_exact<bool, end_object_function_t, SAX>::value &&
+        is_detected_exact<bool, start_array_function_t, SAX>::value &&
+        is_detected_exact<bool, end_array_function_t, SAX>::value &&
+        is_detected_exact<bool, parse_error_function_t, SAX, exception_t>::value;
+};
+
+template <typename SAX, typename BasicJsonType>
+struct is_sax_static_asserts
+{
+  private:
+    static_assert(is_basic_json<BasicJsonType>::value,
+                  "BasicJsonType must be of type basic_json<...>");
+
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using exception_t = typename BasicJsonType::exception;
+
+  public:
+    static_assert(is_detected_exact<bool, null_function_t, SAX>::value,
+                  "Missing/invalid function: bool null()");
+    static_assert(is_detected_exact<bool, boolean_function_t, SAX>::value,
+                  "Missing/invalid function: bool boolean(bool)");
+    static_assert(is_detected_exact<bool, boolean_function_t, SAX>::value,
+                  "Missing/invalid function: bool boolean(bool)");
+    static_assert(
+        is_detected_exact<bool, number_integer_function_t, SAX,
+        number_integer_t>::value,
+        "Missing/invalid function: bool number_integer(number_integer_t)");
+    static_assert(
+        is_detected_exact<bool, number_unsigned_function_t, SAX,
+        number_unsigned_t>::value,
+        "Missing/invalid function: bool number_unsigned(number_unsigned_t)");
+    static_assert(is_detected_exact<bool, number_float_function_t, SAX,
+                  number_float_t, string_t>::value,
+                  "Missing/invalid function: bool number_float(number_float_t, const string_t&)");
+    static_assert(
+        is_detected_exact<bool, string_function_t, SAX, string_t>::value,
+        "Missing/invalid function: bool string(string_t&)");
+    static_assert(is_detected_exact<bool, start_object_function_t, SAX>::value,
+                  "Missing/invalid function: bool start_object(std::size_t)");
+    static_assert(is_detected_exact<bool, key_function_t, SAX, string_t>::value,
+                  "Missing/invalid function: bool key(string_t&)");
+    static_assert(is_detected_exact<bool, end_object_function_t, SAX>::value,
+                  "Missing/invalid function: bool end_object()");
+    static_assert(is_detected_exact<bool, start_array_function_t, SAX>::value,
+                  "Missing/invalid function: bool start_array(std::size_t)");
+    static_assert(is_detected_exact<bool, end_array_function_t, SAX>::value,
+                  "Missing/invalid function: bool end_array()");
+    static_assert(
+        is_detected_exact<bool, parse_error_function_t, SAX, exception_t>::value,
+        "Missing/invalid function: bool parse_error(std::size_t, const "
+        "std::string&, const exception&)");
+};
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/input/input_adapters.hpp>
+
+// #include <nlohmann/detail/input/json_sax.hpp>
+
+
+#include <cstddef>
+#include <string>
+#include <vector>
+
+// #include <nlohmann/detail/input/parser.hpp>
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+
+namespace nlohmann
+{
+
+/*!
+@brief SAX interface
+
+This class describes the SAX interface used by @ref nlohmann::json::sax_parse.
+Each function is called in different situations while the input is parsed. The
+boolean return value informs the parser whether to continue processing the
+input.
+*/
+template<typename BasicJsonType>
+struct json_sax
+{
+    /// type for (signed) integers
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    /// type for unsigned integers
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    /// type for floating-point numbers
+    using number_float_t = typename BasicJsonType::number_float_t;
+    /// type for strings
+    using string_t = typename BasicJsonType::string_t;
+
+    /*!
+    @brief a null value was read
+    @return whether parsing should proceed
+    */
+    virtual bool null() = 0;
+
+    /*!
+    @brief a boolean value was read
+    @param[in] val  boolean value
+    @return whether parsing should proceed
+    */
+    virtual bool boolean(bool val) = 0;
+
+    /*!
+    @brief an integer number was read
+    @param[in] val  integer value
+    @return whether parsing should proceed
+    */
+    virtual bool number_integer(number_integer_t val) = 0;
+
+    /*!
+    @brief an unsigned integer number was read
+    @param[in] val  unsigned integer value
+    @return whether parsing should proceed
+    */
+    virtual bool number_unsigned(number_unsigned_t val) = 0;
+
+    /*!
+    @brief an floating-point number was read
+    @param[in] val  floating-point value
+    @param[in] s    raw token value
+    @return whether parsing should proceed
+    */
+    virtual bool number_float(number_float_t val, const string_t& s) = 0;
+
+    /*!
+    @brief a string was read
+    @param[in] val  string value
+    @return whether parsing should proceed
+    @note It is safe to move the passed string.
+    */
+    virtual bool string(string_t& val) = 0;
+
+    /*!
+    @brief the beginning of an object was read
+    @param[in] elements  number of object elements or -1 if unknown
+    @return whether parsing should proceed
+    @note binary formats may report the number of elements
+    */
+    virtual bool start_object(std::size_t elements) = 0;
+
+    /*!
+    @brief an object key was read
+    @param[in] val  object key
+    @return whether parsing should proceed
+    @note It is safe to move the passed string.
+    */
+    virtual bool key(string_t& val) = 0;
+
+    /*!
+    @brief the end of an object was read
+    @return whether parsing should proceed
+    */
+    virtual bool end_object() = 0;
+
+    /*!
+    @brief the beginning of an array was read
+    @param[in] elements  number of array elements or -1 if unknown
+    @return whether parsing should proceed
+    @note binary formats may report the number of elements
+    */
+    virtual bool start_array(std::size_t elements) = 0;
+
+    /*!
+    @brief the end of an array was read
+    @return whether parsing should proceed
+    */
+    virtual bool end_array() = 0;
+
+    /*!
+    @brief a parse error occurred
+    @param[in] position    the position in the input where the error occurs
+    @param[in] last_token  the last read token
+    @param[in] ex          an exception object describing the error
+    @return whether parsing should proceed (must return false)
+    */
+    virtual bool parse_error(std::size_t position,
+                             const std::string& last_token,
+                             const detail::exception& ex) = 0;
+
+    virtual ~json_sax() = default;
+};
+
+
+namespace detail
+{
+/*!
+@brief SAX implementation to create a JSON value from SAX events
+
+This class implements the @ref json_sax interface and processes the SAX events
+to create a JSON value which makes it basically a DOM parser. The structure or
+hierarchy of the JSON value is managed by the stack `ref_stack` which contains
+a pointer to the respective array or object for each recursion depth.
+
+After successful parsing, the value that is passed by reference to the
+constructor contains the parsed value.
+
+@tparam BasicJsonType  the JSON type
+*/
+template<typename BasicJsonType>
+class json_sax_dom_parser
+{
+  public:
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+
+    /*!
+    @param[in, out] r  reference to a JSON value that is manipulated while
+                       parsing
+    @param[in] allow_exceptions_  whether parse errors yield exceptions
+    */
+    explicit json_sax_dom_parser(BasicJsonType& r, const bool allow_exceptions_ = true)
+        : root(r), allow_exceptions(allow_exceptions_)
+    {}
+
+    bool null()
+    {
+        handle_value(nullptr);
+        return true;
+    }
+
+    bool boolean(bool val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_integer(number_integer_t val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_unsigned(number_unsigned_t val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_float(number_float_t val, const string_t& /*unused*/)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool string(string_t& val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool start_object(std::size_t len)
+    {
+        ref_stack.push_back(handle_value(BasicJsonType::value_t::object));
+
+        if (JSON_UNLIKELY(len != std::size_t(-1) and len > ref_stack.back()->max_size()))
+        {
+            JSON_THROW(out_of_range::create(408,
+                                            "excessive object size: " + std::to_string(len)));
+        }
+
+        return true;
+    }
+
+    bool key(string_t& val)
+    {
+        // add null at given key and store the reference for later
+        object_element = &(ref_stack.back()->m_value.object->operator[](val));
+        return true;
+    }
+
+    bool end_object()
+    {
+        ref_stack.pop_back();
+        return true;
+    }
+
+    bool start_array(std::size_t len)
+    {
+        ref_stack.push_back(handle_value(BasicJsonType::value_t::array));
+
+        if (JSON_UNLIKELY(len != std::size_t(-1) and len > ref_stack.back()->max_size()))
+        {
+            JSON_THROW(out_of_range::create(408,
+                                            "excessive array size: " + std::to_string(len)));
+        }
+
+        return true;
+    }
+
+    bool end_array()
+    {
+        ref_stack.pop_back();
+        return true;
+    }
+
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
+                     const detail::exception& ex)
+    {
+        errored = true;
+        if (allow_exceptions)
+        {
+            // determine the proper exception type from the id
+            switch ((ex.id / 100) % 100)
+            {
+                case 1:
+                    JSON_THROW(*reinterpret_cast<const detail::parse_error*>(&ex));
+                case 4:
+                    JSON_THROW(*reinterpret_cast<const detail::out_of_range*>(&ex));
+                // LCOV_EXCL_START
+                case 2:
+                    JSON_THROW(*reinterpret_cast<const detail::invalid_iterator*>(&ex));
+                case 3:
+                    JSON_THROW(*reinterpret_cast<const detail::type_error*>(&ex));
+                case 5:
+                    JSON_THROW(*reinterpret_cast<const detail::other_error*>(&ex));
+                default:
+                    assert(false);
+                    // LCOV_EXCL_STOP
+            }
+        }
+        return false;
+    }
+
+    constexpr bool is_errored() const
+    {
+        return errored;
+    }
+
+  private:
+    /*!
+    @invariant If the ref stack is empty, then the passed value will be the new
+               root.
+    @invariant If the ref stack contains a value, then it is an array or an
+               object to which we can add elements
+    */
+    template<typename Value>
+    BasicJsonType* handle_value(Value&& v)
+    {
+        if (ref_stack.empty())
+        {
+            root = BasicJsonType(std::forward<Value>(v));
+            return &root;
+        }
+
+        assert(ref_stack.back()->is_array() or ref_stack.back()->is_object());
+
+        if (ref_stack.back()->is_array())
+        {
+            ref_stack.back()->m_value.array->emplace_back(std::forward<Value>(v));
+            return &(ref_stack.back()->m_value.array->back());
+        }
+        else
+        {
+            assert(object_element);
+            *object_element = BasicJsonType(std::forward<Value>(v));
+            return object_element;
+        }
+    }
+
+    /// the parsed JSON value
+    BasicJsonType& root;
+    /// stack to model hierarchy of values
+    std::vector<BasicJsonType*> ref_stack;
+    /// helper to hold the reference for the next object element
+    BasicJsonType* object_element = nullptr;
+    /// whether a syntax error occurred
+    bool errored = false;
+    /// whether to throw exceptions in case of errors
+    const bool allow_exceptions = true;
+};
+
+template<typename BasicJsonType>
+class json_sax_dom_callback_parser
+{
+  public:
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using parser_callback_t = typename BasicJsonType::parser_callback_t;
+    using parse_event_t = typename BasicJsonType::parse_event_t;
+
+    json_sax_dom_callback_parser(BasicJsonType& r,
+                                 const parser_callback_t cb,
+                                 const bool allow_exceptions_ = true)
+        : root(r), callback(cb), allow_exceptions(allow_exceptions_)
+    {
+        keep_stack.push_back(true);
+    }
+
+    bool null()
+    {
+        handle_value(nullptr);
+        return true;
+    }
+
+    bool boolean(bool val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_integer(number_integer_t val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_unsigned(number_unsigned_t val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool number_float(number_float_t val, const string_t& /*unused*/)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool string(string_t& val)
+    {
+        handle_value(val);
+        return true;
+    }
+
+    bool start_object(std::size_t len)
+    {
+        // check callback for object start
+        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::object_start, discarded);
+        keep_stack.push_back(keep);
+
+        auto val = handle_value(BasicJsonType::value_t::object, true);
+        ref_stack.push_back(val.second);
+
+        // check object limit
+        if (ref_stack.back())
+        {
+            if (JSON_UNLIKELY(len != std::size_t(-1) and len > ref_stack.back()->max_size()))
+            {
+                JSON_THROW(out_of_range::create(408,
+                                                "excessive object size: " + std::to_string(len)));
+            }
+        }
+
+        return true;
+    }
+
+    bool key(string_t& val)
+    {
+        BasicJsonType k = BasicJsonType(val);
+
+        // check callback for key
+        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::key, k);
+        key_keep_stack.push_back(keep);
+
+        // add discarded value at given key and store the reference for later
+        if (keep and ref_stack.back())
+        {
+            object_element = &(ref_stack.back()->m_value.object->operator[](val) = discarded);
+        }
+
+        return true;
+    }
+
+    bool end_object()
+    {
+        if (ref_stack.back())
+        {
+            if (not callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::object_end, *ref_stack.back()))
+            {
+                // discard object
+                *ref_stack.back() = discarded;
+            }
+        }
+
+        assert(not ref_stack.empty());
+        assert(not keep_stack.empty());
+        ref_stack.pop_back();
+        keep_stack.pop_back();
+
+        if (not ref_stack.empty() and ref_stack.back())
+        {
+            // remove discarded value
+            if (ref_stack.back()->is_object())
+            {
+                for (auto it = ref_stack.back()->begin(); it != ref_stack.back()->end(); ++it)
+                {
+                    if (it->is_discarded())
+                    {
+                        ref_stack.back()->erase(it);
+                        break;
+                    }
+                }
+            }
+        }
+
+        return true;
+    }
+
+    bool start_array(std::size_t len)
+    {
+        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::array_start, discarded);
+        keep_stack.push_back(keep);
+
+        auto val = handle_value(BasicJsonType::value_t::array, true);
+        ref_stack.push_back(val.second);
+
+        // check array limit
+        if (ref_stack.back())
+        {
+            if (JSON_UNLIKELY(len != std::size_t(-1) and len > ref_stack.back()->max_size()))
+            {
+                JSON_THROW(out_of_range::create(408,
+                                                "excessive array size: " + std::to_string(len)));
+            }
+        }
+
+        return true;
+    }
+
+    bool end_array()
+    {
+        bool keep = true;
+
+        if (ref_stack.back())
+        {
+            keep = callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::array_end, *ref_stack.back());
+            if (not keep)
+            {
+                // discard array
+                *ref_stack.back() = discarded;
+            }
+        }
+
+        assert(not ref_stack.empty());
+        assert(not keep_stack.empty());
+        ref_stack.pop_back();
+        keep_stack.pop_back();
+
+        // remove discarded value
+        if (not keep and not ref_stack.empty())
+        {
+            if (ref_stack.back()->is_array())
+            {
+                ref_stack.back()->m_value.array->pop_back();
+            }
+        }
+
+        return true;
+    }
+
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
+                     const detail::exception& ex)
+    {
+        errored = true;
+        if (allow_exceptions)
+        {
+            // determine the proper exception type from the id
+            switch ((ex.id / 100) % 100)
+            {
+                case 1:
+                    JSON_THROW(*reinterpret_cast<const detail::parse_error*>(&ex));
+                case 4:
+                    JSON_THROW(*reinterpret_cast<const detail::out_of_range*>(&ex));
+                // LCOV_EXCL_START
+                case 2:
+                    JSON_THROW(*reinterpret_cast<const detail::invalid_iterator*>(&ex));
+                case 3:
+                    JSON_THROW(*reinterpret_cast<const detail::type_error*>(&ex));
+                case 5:
+                    JSON_THROW(*reinterpret_cast<const detail::other_error*>(&ex));
+                default:
+                    assert(false);
+                    // LCOV_EXCL_STOP
+            }
+        }
+        return false;
+    }
+
+    constexpr bool is_errored() const
+    {
+        return errored;
+    }
+
+  private:
+    /*!
+    @param[in] v  value to add to the JSON value we build during parsing
+    @param[in] skip_callback  whether we should skip calling the callback
+               function; this is required after start_array() and
+               start_object() SAX events, because otherwise we would call the
+               callback function with an empty array or object, respectively.
+
+    @invariant If the ref stack is empty, then the passed value will be the new
+               root.
+    @invariant If the ref stack contains a value, then it is an array or an
+               object to which we can add elements
+
+    @return pair of boolean (whether value should be kept) and pointer (to the
+            passed value in the ref_stack hierarchy; nullptr if not kept)
+    */
+    template<typename Value>
+    std::pair<bool, BasicJsonType*> handle_value(Value&& v, const bool skip_callback = false)
+    {
+        assert(not keep_stack.empty());
+
+        // do not handle this value if we know it would be added to a discarded
+        // container
+        if (not keep_stack.back())
+        {
+            return {false, nullptr};
+        }
+
+        // create value
+        auto value = BasicJsonType(std::forward<Value>(v));
+
+        // check callback
+        const bool keep = skip_callback or callback(static_cast<int>(ref_stack.size()), parse_event_t::value, value);
+
+        // do not handle this value if we just learnt it shall be discarded
+        if (not keep)
+        {
+            return {false, nullptr};
+        }
+
+        if (ref_stack.empty())
+        {
+            root = std::move(value);
+            return {true, &root};
+        }
+
+        // skip this value if we already decided to skip the parent
+        // (https://github.com/nlohmann/json/issues/971#issuecomment-413678360)
+        if (not ref_stack.back())
+        {
+            return {false, nullptr};
+        }
+
+        // we now only expect arrays and objects
+        assert(ref_stack.back()->is_array() or ref_stack.back()->is_object());
+
+        if (ref_stack.back()->is_array())
+        {
+            ref_stack.back()->m_value.array->push_back(std::move(value));
+            return {true, &(ref_stack.back()->m_value.array->back())};
+        }
+        else
+        {
+            // check if we should store an element for the current key
+            assert(not key_keep_stack.empty());
+            const bool store_element = key_keep_stack.back();
+            key_keep_stack.pop_back();
+
+            if (not store_element)
+            {
+                return {false, nullptr};
+            }
+
+            assert(object_element);
+            *object_element = std::move(value);
+            return {true, object_element};
+        }
+    }
+
+    /// the parsed JSON value
+    BasicJsonType& root;
+    /// stack to model hierarchy of values
+    std::vector<BasicJsonType*> ref_stack;
+    /// stack to manage which values to keep
+    std::vector<bool> keep_stack;
+    /// stack to manage which object keys to keep
+    std::vector<bool> key_keep_stack;
+    /// helper to hold the reference for the next object element
+    BasicJsonType* object_element = nullptr;
+    /// whether a syntax error occurred
+    bool errored = false;
+    /// callback function
+    const parser_callback_t callback = nullptr;
+    /// whether to throw exceptions in case of errors
+    const bool allow_exceptions = true;
+    /// a discarded value for the callback
+    BasicJsonType discarded = BasicJsonType::value_t::discarded;
+};
+
+template<typename BasicJsonType>
+class json_sax_acceptor
+{
+  public:
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+
+    bool null()
+    {
+        return true;
+    }
+
+    bool boolean(bool /*unused*/)
+    {
+        return true;
+    }
+
+    bool number_integer(number_integer_t /*unused*/)
+    {
+        return true;
+    }
+
+    bool number_unsigned(number_unsigned_t /*unused*/)
+    {
+        return true;
+    }
+
+    bool number_float(number_float_t /*unused*/, const string_t& /*unused*/)
+    {
+        return true;
+    }
+
+    bool string(string_t& /*unused*/)
+    {
+        return true;
+    }
+
+    bool start_object(std::size_t  /*unused*/ = std::size_t(-1))
+    {
+        return true;
+    }
+
+    bool key(string_t& /*unused*/)
+    {
+        return true;
+    }
+
+    bool end_object()
+    {
+        return true;
+    }
+
+    bool start_array(std::size_t  /*unused*/ = std::size_t(-1))
+    {
+        return true;
+    }
+
+    bool end_array()
+    {
+        return true;
+    }
+
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const detail::exception& /*unused*/)
+    {
+        return false;
+    }
+};
+}  // namespace detail
+
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/input/lexer.hpp>
+
+// #include <nlohmann/detail/value_t.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+////////////
+// parser //
+////////////
 
 /*!
 @brief syntax analysis
@@ -2892,6 +4962,7 @@ class parser
     using number_integer_t = typename BasicJsonType::number_integer_t;
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
     using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
     using lexer_t = lexer<BasicJsonType>;
     using token_type = typename lexer_t::token_type;
 
@@ -2916,11 +4987,14 @@ class parser
         std::function<bool(int depth, parse_event_t event, BasicJsonType& parsed)>;
 
     /// a parser reading from an input adapter
-    explicit parser(detail::input_adapter_t adapter,
+    explicit parser(detail::input_adapter_t&& adapter,
                     const parser_callback_t cb = nullptr,
                     const bool allow_exceptions_ = true)
-        : callback(cb), m_lexer(adapter), allow_exceptions(allow_exceptions_)
-    {}
+        : callback(cb), m_lexer(std::move(adapter)), allow_exceptions(allow_exceptions_)
+    {
+        // read first token
+        get_token();
+    }
 
     /*!
     @brief public parser interface
@@ -2934,31 +5008,56 @@ class parser
     */
     void parse(const bool strict, BasicJsonType& result)
     {
-        // read first token
-        get_token();
+        if (callback)
+        {
+            json_sax_dom_callback_parser<BasicJsonType> sdp(result, callback, allow_exceptions);
+            sax_parse_internal(&sdp);
+            result.assert_invariant();
 
-        parse_internal(true, result);
-        result.assert_invariant();
+            // in strict mode, input must be completely read
+            if (strict and (get_token() != token_type::end_of_input))
+            {
+                sdp.parse_error(m_lexer.get_position(),
+                                m_lexer.get_token_string(),
+                                parse_error::create(101, m_lexer.get_position(),
+                                                    exception_message(token_type::end_of_input, "value")));
+            }
 
-        // in strict mode, input must be completely read
-        if (strict)
-        {
-            get_token();
-            expect(token_type::end_of_input);
-        }
+            // in case of an error, return discarded value
+            if (sdp.is_errored())
+            {
+                result = value_t::discarded;
+                return;
+            }
 
-        // in case of an error, return discarded value
-        if (errored)
-        {
-            result = value_t::discarded;
-            return;
+            // set top-level value to null if it was discarded by the callback
+            // function
+            if (result.is_discarded())
+            {
+                result = nullptr;
+            }
         }
-
-        // set top-level value to null if it was discarded by the callback
-        // function
-        if (result.is_discarded())
+        else
         {
-            result = nullptr;
+            json_sax_dom_parser<BasicJsonType> sdp(result, allow_exceptions);
+            sax_parse_internal(&sdp);
+            result.assert_invariant();
+
+            // in strict mode, input must be completely read
+            if (strict and (get_token() != token_type::end_of_input))
+            {
+                sdp.parse_error(m_lexer.get_position(),
+                                m_lexer.get_token_string(),
+                                parse_error::create(101, m_lexer.get_position(),
+                                                    exception_message(token_type::end_of_input, "value")));
+            }
+
+            // in case of an error, return discarded value
+            if (sdp.is_errored())
+            {
+                result = value_t::discarded;
+                return;
+            }
         }
     }
 
@@ -2970,413 +5069,317 @@ class parser
     */
     bool accept(const bool strict = true)
     {
-        // read first token
-        get_token();
+        json_sax_acceptor<BasicJsonType> sax_acceptor;
+        return sax_parse(&sax_acceptor, strict);
+    }
 
-        if (not accept_internal())
+    template <typename SAX>
+    bool sax_parse(SAX* sax, const bool strict = true)
+    {
+        (void)detail::is_sax_static_asserts<SAX, BasicJsonType> {};
+        const bool result = sax_parse_internal(sax);
+
+        // strict mode: next byte must be EOF
+        if (result and strict and (get_token() != token_type::end_of_input))
         {
-            return false;
+            return sax->parse_error(m_lexer.get_position(),
+                                    m_lexer.get_token_string(),
+                                    parse_error::create(101, m_lexer.get_position(),
+                                            exception_message(token_type::end_of_input, "value")));
         }
 
-        // strict => last token must be EOF
-        return not strict or (get_token() == token_type::end_of_input);
+        return result;
     }
 
   private:
-    /*!
-    @brief the actual parser
-    @throw parse_error.101 in case of an unexpected token
-    @throw parse_error.102 if to_unicode fails or surrogate error
-    @throw parse_error.103 if to_unicode fails
-    */
-    void parse_internal(bool keep, BasicJsonType& result)
+    template <typename SAX>
+    bool sax_parse_internal(SAX* sax)
     {
-        // never parse after a parse error was detected
-        assert(not errored);
+        // stack to remember the hierarchy of structured values we are parsing
+        // true = array; false = object
+        std::vector<bool> states;
+        // value to avoid a goto (see comment where set to true)
+        bool skip_to_state_evaluation = false;
 
-        // start with a discarded value
-        if (not result.is_discarded())
-        {
-            result.m_value.destroy(result.m_type);
-            result.m_type = value_t::discarded;
-        }
-
-        switch (last_token)
+        while (true)
         {
-            case token_type::begin_object:
+            if (not skip_to_state_evaluation)
             {
-                if (keep)
+                // invariant: get_token() was called before each iteration
+                switch (last_token)
                 {
-                    if (callback)
+                    case token_type::begin_object:
                     {
-                        keep = callback(depth++, parse_event_t::object_start, result);
-                    }
+                        if (JSON_UNLIKELY(not sax->start_object(std::size_t(-1))))
+                        {
+                            return false;
+                        }
 
-                    if (not callback or keep)
-                    {
-                        // explicitly set result to object to cope with {}
-                        result.m_type = value_t::object;
-                        result.m_value = value_t::object;
-                    }
-                }
+                        // closing } -> we are done
+                        if (get_token() == token_type::end_object)
+                        {
+                            if (JSON_UNLIKELY(not sax->end_object()))
+                            {
+                                return false;
+                            }
+                            break;
+                        }
 
-                // read next token
-                get_token();
+                        // parse key
+                        if (JSON_UNLIKELY(last_token != token_type::value_string))
+                        {
+                            return sax->parse_error(m_lexer.get_position(),
+                                                    m_lexer.get_token_string(),
+                                                    parse_error::create(101, m_lexer.get_position(),
+                                                            exception_message(token_type::value_string, "object key")));
+                        }
+                        if (JSON_UNLIKELY(not sax->key(m_lexer.get_string())))
+                        {
+                            return false;
+                        }
 
-                // closing } -> we are done
-                if (last_token == token_type::end_object)
-                {
-                    if (keep and callback and not callback(--depth, parse_event_t::object_end, result))
-                    {
-                        result.m_value.destroy(result.m_type);
-                        result.m_type = value_t::discarded;
-                    }
-                    break;
-                }
+                        // parse separator (:)
+                        if (JSON_UNLIKELY(get_token() != token_type::name_separator))
+                        {
+                            return sax->parse_error(m_lexer.get_position(),
+                                                    m_lexer.get_token_string(),
+                                                    parse_error::create(101, m_lexer.get_position(),
+                                                            exception_message(token_type::name_separator, "object separator")));
+                        }
 
-                // parse values
-                std::string key;
-                BasicJsonType value;
-                while (true)
-                {
-                    // store key
-                    if (not expect(token_type::value_string))
-                    {
-                        return;
+                        // remember we are now inside an object
+                        states.push_back(false);
+
+                        // parse values
+                        get_token();
+                        continue;
                     }
-                    key = m_lexer.move_string();
 
-                    bool keep_tag = false;
-                    if (keep)
+                    case token_type::begin_array:
                     {
-                        if (callback)
+                        if (JSON_UNLIKELY(not sax->start_array(std::size_t(-1))))
                         {
-                            BasicJsonType k(key);
-                            keep_tag = callback(depth, parse_event_t::key, k);
+                            return false;
                         }
-                        else
+
+                        // closing ] -> we are done
+                        if (get_token() == token_type::end_array)
                         {
-                            keep_tag = true;
+                            if (JSON_UNLIKELY(not sax->end_array()))
+                            {
+                                return false;
+                            }
+                            break;
                         }
-                    }
-
-                    // parse separator (:)
-                    get_token();
-                    if (not expect(token_type::name_separator))
-                    {
-                        return;
-                    }
 
-                    // parse and add value
-                    get_token();
-                    value.m_value.destroy(value.m_type);
-                    value.m_type = value_t::discarded;
-                    parse_internal(keep, value);
+                        // remember we are now inside an array
+                        states.push_back(true);
 
-                    if (JSON_UNLIKELY(errored))
-                    {
-                        return;
+                        // parse values (no need to call get_token)
+                        continue;
                     }
 
-                    if (keep and keep_tag and not value.is_discarded())
+                    case token_type::value_float:
                     {
-                        result.m_value.object->emplace(std::move(key), std::move(value));
-                    }
+                        const auto res = m_lexer.get_number_float();
 
-                    // comma -> next value
-                    get_token();
-                    if (last_token == token_type::value_separator)
-                    {
-                        get_token();
-                        continue;
+                        if (JSON_UNLIKELY(not std::isfinite(res)))
+                        {
+                            return sax->parse_error(m_lexer.get_position(),
+                                                    m_lexer.get_token_string(),
+                                                    out_of_range::create(406, "number overflow parsing '" + m_lexer.get_token_string() + "'"));
+                        }
+                        else
+                        {
+                            if (JSON_UNLIKELY(not sax->number_float(res, m_lexer.get_string())))
+                            {
+                                return false;
+                            }
+                            break;
+                        }
                     }
 
-                    // closing }
-                    if (not expect(token_type::end_object))
+                    case token_type::literal_false:
                     {
-                        return;
+                        if (JSON_UNLIKELY(not sax->boolean(false)))
+                        {
+                            return false;
+                        }
+                        break;
                     }
-                    break;
-                }
 
-                if (keep and callback and not callback(--depth, parse_event_t::object_end, result))
-                {
-                    result.m_value.destroy(result.m_type);
-                    result.m_type = value_t::discarded;
-                }
-                break;
-            }
-
-            case token_type::begin_array:
-            {
-                if (keep)
-                {
-                    if (callback)
+                    case token_type::literal_null:
                     {
-                        keep = callback(depth++, parse_event_t::array_start, result);
+                        if (JSON_UNLIKELY(not sax->null()))
+                        {
+                            return false;
+                        }
+                        break;
                     }
 
-                    if (not callback or keep)
+                    case token_type::literal_true:
                     {
-                        // explicitly set result to array to cope with []
-                        result.m_type = value_t::array;
-                        result.m_value = value_t::array;
+                        if (JSON_UNLIKELY(not sax->boolean(true)))
+                        {
+                            return false;
+                        }
+                        break;
                     }
-                }
-
-                // read next token
-                get_token();
 
-                // closing ] -> we are done
-                if (last_token == token_type::end_array)
-                {
-                    if (callback and not callback(--depth, parse_event_t::array_end, result))
+                    case token_type::value_integer:
                     {
-                        result.m_value.destroy(result.m_type);
-                        result.m_type = value_t::discarded;
+                        if (JSON_UNLIKELY(not sax->number_integer(m_lexer.get_number_integer())))
+                        {
+                            return false;
+                        }
+                        break;
                     }
-                    break;
-                }
 
-                // parse values
-                BasicJsonType value;
-                while (true)
-                {
-                    // parse value
-                    value.m_value.destroy(value.m_type);
-                    value.m_type = value_t::discarded;
-                    parse_internal(keep, value);
-
-                    if (JSON_UNLIKELY(errored))
+                    case token_type::value_string:
                     {
-                        return;
+                        if (JSON_UNLIKELY(not sax->string(m_lexer.get_string())))
+                        {
+                            return false;
+                        }
+                        break;
                     }
 
-                    if (keep and not value.is_discarded())
+                    case token_type::value_unsigned:
                     {
-                        result.m_value.array->push_back(std::move(value));
+                        if (JSON_UNLIKELY(not sax->number_unsigned(m_lexer.get_number_unsigned())))
+                        {
+                            return false;
+                        }
+                        break;
                     }
 
-                    // comma -> next value
-                    get_token();
-                    if (last_token == token_type::value_separator)
+                    case token_type::parse_error:
                     {
-                        get_token();
-                        continue;
+                        // using "uninitialized" to avoid "expected" message
+                        return sax->parse_error(m_lexer.get_position(),
+                                                m_lexer.get_token_string(),
+                                                parse_error::create(101, m_lexer.get_position(),
+                                                        exception_message(token_type::uninitialized, "value")));
                     }
 
-                    // closing ]
-                    if (not expect(token_type::end_array))
+                    default: // the last token was unexpected
                     {
-                        return;
+                        return sax->parse_error(m_lexer.get_position(),
+                                                m_lexer.get_token_string(),
+                                                parse_error::create(101, m_lexer.get_position(),
+                                                        exception_message(token_type::literal_or_value, "value")));
                     }
-                    break;
-                }
-
-                if (keep and callback and not callback(--depth, parse_event_t::array_end, result))
-                {
-                    result.m_value.destroy(result.m_type);
-                    result.m_type = value_t::discarded;
                 }
-                break;
-            }
-
-            case token_type::literal_null:
-            {
-                result.m_type = value_t::null;
-                break;
-            }
-
-            case token_type::value_string:
-            {
-                result.m_type = value_t::string;
-                result.m_value = m_lexer.move_string();
-                break;
-            }
-
-            case token_type::literal_true:
-            {
-                result.m_type = value_t::boolean;
-                result.m_value = true;
-                break;
-            }
-
-            case token_type::literal_false:
-            {
-                result.m_type = value_t::boolean;
-                result.m_value = false;
-                break;
             }
-
-            case token_type::value_unsigned:
+            else
             {
-                result.m_type = value_t::number_unsigned;
-                result.m_value = m_lexer.get_number_unsigned();
-                break;
+                skip_to_state_evaluation = false;
             }
 
-            case token_type::value_integer:
+            // we reached this line after we successfully parsed a value
+            if (states.empty())
             {
-                result.m_type = value_t::number_integer;
-                result.m_value = m_lexer.get_number_integer();
-                break;
+                // empty stack: we reached the end of the hierarchy: done
+                return true;
             }
-
-            case token_type::value_float:
+            else
             {
-                result.m_type = value_t::number_float;
-                result.m_value = m_lexer.get_number_float();
-
-                // throw in case of infinity or NAN
-                if (JSON_UNLIKELY(not std::isfinite(result.m_value.number_float)))
+                if (states.back())  // array
                 {
-                    if (allow_exceptions)
+                    // comma -> next value
+                    if (get_token() == token_type::value_separator)
                     {
-                        JSON_THROW(out_of_range::create(406, "number overflow parsing '" +
-                                                        m_lexer.get_token_string() + "'"));
+                        // parse a new value
+                        get_token();
+                        continue;
                     }
-                    expect(token_type::uninitialized);
-                }
-                break;
-            }
-
-            case token_type::parse_error:
-            {
-                // using "uninitialized" to avoid "expected" message
-                if (not expect(token_type::uninitialized))
-                {
-                    return;
-                }
-                break; // LCOV_EXCL_LINE
-            }
-
-            default:
-            {
-                // the last token was unexpected; we expected a value
-                if (not expect(token_type::literal_or_value))
-                {
-                    return;
-                }
-                break; // LCOV_EXCL_LINE
-            }
-        }
-
-        if (keep and callback and not callback(depth, parse_event_t::value, result))
-        {
-            result.m_type = value_t::discarded;
-        }
-    }
-
-    /*!
-    @brief the actual acceptor
-
-    @invariant 1. The last token is not yet processed. Therefore, the caller
-                  of this function must make sure a token has been read.
-               2. When this function returns, the last token is processed.
-                  That is, the last read character was already considered.
-
-    This invariant makes sure that no token needs to be "unput".
-    */
-    bool accept_internal()
-    {
-        switch (last_token)
-        {
-            case token_type::begin_object:
-            {
-                // read next token
-                get_token();
 
-                // closing } -> we are done
-                if (last_token == token_type::end_object)
-                {
-                    return true;
-                }
-
-                // parse values
-                while (true)
-                {
-                    // parse key
-                    if (last_token != token_type::value_string)
+                    // closing ]
+                    if (JSON_LIKELY(last_token == token_type::end_array))
                     {
-                        return false;
-                    }
+                        if (JSON_UNLIKELY(not sax->end_array()))
+                        {
+                            return false;
+                        }
 
-                    // parse separator (:)
-                    get_token();
-                    if (last_token != token_type::name_separator)
-                    {
-                        return false;
+                        // We are done with this array. Before we can parse a
+                        // new value, we need to evaluate the new state first.
+                        // By setting skip_to_state_evaluation to false, we
+                        // are effectively jumping to the beginning of this if.
+                        assert(not states.empty());
+                        states.pop_back();
+                        skip_to_state_evaluation = true;
+                        continue;
                     }
-
-                    // parse value
-                    get_token();
-                    if (not accept_internal())
+                    else
                     {
-                        return false;
+                        return sax->parse_error(m_lexer.get_position(),
+                                                m_lexer.get_token_string(),
+                                                parse_error::create(101, m_lexer.get_position(),
+                                                        exception_message(token_type::end_array, "array")));
                     }
-
+                }
+                else  // object
+                {
                     // comma -> next value
-                    get_token();
-                    if (last_token == token_type::value_separator)
+                    if (get_token() == token_type::value_separator)
                     {
+                        // parse key
+                        if (JSON_UNLIKELY(get_token() != token_type::value_string))
+                        {
+                            return sax->parse_error(m_lexer.get_position(),
+                                                    m_lexer.get_token_string(),
+                                                    parse_error::create(101, m_lexer.get_position(),
+                                                            exception_message(token_type::value_string, "object key")));
+                        }
+                        else
+                        {
+                            if (JSON_UNLIKELY(not sax->key(m_lexer.get_string())))
+                            {
+                                return false;
+                            }
+                        }
+
+                        // parse separator (:)
+                        if (JSON_UNLIKELY(get_token() != token_type::name_separator))
+                        {
+                            return sax->parse_error(m_lexer.get_position(),
+                                                    m_lexer.get_token_string(),
+                                                    parse_error::create(101, m_lexer.get_position(),
+                                                            exception_message(token_type::name_separator, "object separator")));
+                        }
+
+                        // parse values
                         get_token();
                         continue;
                     }
 
                     // closing }
-                    return (last_token == token_type::end_object);
-                }
-            }
-
-            case token_type::begin_array:
-            {
-                // read next token
-                get_token();
-
-                // closing ] -> we are done
-                if (last_token == token_type::end_array)
-                {
-                    return true;
-                }
-
-                // parse values
-                while (true)
-                {
-                    // parse value
-                    if (not accept_internal())
+                    if (JSON_LIKELY(last_token == token_type::end_object))
                     {
-                        return false;
-                    }
+                        if (JSON_UNLIKELY(not sax->end_object()))
+                        {
+                            return false;
+                        }
 
-                    // comma -> next value
-                    get_token();
-                    if (last_token == token_type::value_separator)
-                    {
-                        get_token();
+                        // We are done with this object. Before we can parse a
+                        // new value, we need to evaluate the new state first.
+                        // By setting skip_to_state_evaluation to false, we
+                        // are effectively jumping to the beginning of this if.
+                        assert(not states.empty());
+                        states.pop_back();
+                        skip_to_state_evaluation = true;
                         continue;
                     }
-
-                    // closing ]
-                    return (last_token == token_type::end_array);
+                    else
+                    {
+                        return sax->parse_error(m_lexer.get_position(),
+                                                m_lexer.get_token_string(),
+                                                parse_error::create(101, m_lexer.get_position(),
+                                                        exception_message(token_type::end_object, "object")));
+                    }
                 }
             }
-
-            case token_type::value_float:
-            {
-                // reject infinity or NAN
-                return std::isfinite(m_lexer.get_number_float());
-            }
-
-            case token_type::literal_false:
-            case token_type::literal_null:
-            case token_type::literal_true:
-            case token_type::value_integer:
-            case token_type::value_string:
-            case token_type::value_unsigned:
-                return true;
-
-            default: // the last token was unexpected
-                return false;
         }
     }
 
@@ -3386,31 +5389,17 @@ class parser
         return (last_token = m_lexer.scan());
     }
 
-    /*!
-    @throw parse_error.101 if expected token did not occur
-    */
-    bool expect(token_type t)
+    std::string exception_message(const token_type expected, const std::string& context)
     {
-        if (JSON_UNLIKELY(t != last_token))
+        std::string error_msg = "syntax error ";
+
+        if (not context.empty())
         {
-            errored = true;
-            expected = t;
-            if (allow_exceptions)
-            {
-                throw_exception();
-            }
-            else
-            {
-                return false;
-            }
+            error_msg += "while parsing " + context + " ";
         }
 
-        return true;
-    }
+        error_msg += "- ";
 
-    [[noreturn]] void throw_exception() const
-    {
-        std::string error_msg = "syntax error - ";
         if (last_token == token_type::parse_error)
         {
             error_msg += std::string(m_lexer.get_error_message()) + "; last read: '" +
@@ -3426,31 +5415,33 @@ class parser
             error_msg += "; expected " + std::string(lexer_t::token_type_name(expected));
         }
 
-        JSON_THROW(parse_error::create(101, m_lexer.get_position(), error_msg));
+        return error_msg;
     }
 
   private:
-    /// current level of recursion
-    int depth = 0;
     /// callback function
     const parser_callback_t callback = nullptr;
     /// the type of the last read token
     token_type last_token = token_type::uninitialized;
     /// the lexer
     lexer_t m_lexer;
-    /// whether a syntax error occurred
-    bool errored = false;
-    /// possible reason for the syntax error
-    token_type expected = token_type::uninitialized;
     /// whether to throw exceptions in case of errors
     const bool allow_exceptions = true;
 };
+}  // namespace detail
+}  // namespace nlohmann
 
-///////////////
-// iterators //
-///////////////
+// #include <nlohmann/detail/iterators/primitive_iterator.hpp>
 
-/*!
+
+#include <cstddef> // ptrdiff_t
+#include <limits>  // numeric_limits
+
+namespace nlohmann
+{
+namespace detail
+{
+/*
 @brief an iterator for primitive JSON types
 
 This class models an iterator for primitive JSON types (boolean, number,
@@ -3461,9 +5452,15 @@ end_value (`1`) models past the end.
 */
 class primitive_iterator_t
 {
-  public:
+  private:
     using difference_type = std::ptrdiff_t;
+    static constexpr difference_type begin_value = 0;
+    static constexpr difference_type end_value = begin_value + 1;
 
+    /// iterator as signed integer type
+    difference_type m_it = (std::numeric_limits<std::ptrdiff_t>::min)();
+
+  public:
     constexpr difference_type get_value() const noexcept
     {
         return m_it;
@@ -3503,10 +5500,10 @@ class primitive_iterator_t
         return lhs.m_it < rhs.m_it;
     }
 
-    primitive_iterator_t operator+(difference_type i)
+    primitive_iterator_t operator+(difference_type n) noexcept
     {
         auto result = *this;
-        result += i;
+        result += n;
         return result;
     }
 
@@ -3515,57 +5512,57 @@ class primitive_iterator_t
         return lhs.m_it - rhs.m_it;
     }
 
-    friend std::ostream& operator<<(std::ostream& os, primitive_iterator_t it)
-    {
-        return os << it.m_it;
-    }
-
-    primitive_iterator_t& operator++()
+    primitive_iterator_t& operator++() noexcept
     {
         ++m_it;
         return *this;
     }
 
-    primitive_iterator_t const operator++(int)
+    primitive_iterator_t const operator++(int) noexcept
     {
         auto result = *this;
-        m_it++;
+        ++m_it;
         return result;
     }
 
-    primitive_iterator_t& operator--()
+    primitive_iterator_t& operator--() noexcept
     {
         --m_it;
         return *this;
     }
 
-    primitive_iterator_t const operator--(int)
+    primitive_iterator_t const operator--(int) noexcept
     {
         auto result = *this;
-        m_it--;
+        --m_it;
         return result;
     }
 
-    primitive_iterator_t& operator+=(difference_type n)
+    primitive_iterator_t& operator+=(difference_type n) noexcept
     {
         m_it += n;
         return *this;
     }
 
-    primitive_iterator_t& operator-=(difference_type n)
+    primitive_iterator_t& operator-=(difference_type n) noexcept
     {
         m_it -= n;
         return *this;
     }
+};
+}  // namespace detail
+}  // namespace nlohmann
 
-  private:
-    static constexpr difference_type begin_value = 0;
-    static constexpr difference_type end_value = begin_value + 1;
+// #include <nlohmann/detail/iterators/internal_iterator.hpp>
+
+
+// #include <nlohmann/detail/iterators/primitive_iterator.hpp>
 
-    /// iterator as signed integer type
-    difference_type m_it = (std::numeric_limits<std::ptrdiff_t>::min)();
-};
 
+namespace nlohmann
+{
+namespace detail
+{
 /*!
 @brief an iterator value
 
@@ -3581,26 +5578,50 @@ template<typename BasicJsonType> struct internal_iterator
     /// generic iterator for all other types
     primitive_iterator_t primitive_iterator {};
 };
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/iterators/iter_impl.hpp>
+
+
+#include <ciso646> // not
+#include <iterator> // iterator, random_access_iterator_tag, bidirectional_iterator_tag, advance, next
+#include <type_traits> // conditional, is_const, remove_const
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+// #include <nlohmann/detail/iterators/internal_iterator.hpp>
 
+// #include <nlohmann/detail/iterators/primitive_iterator.hpp>
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+// #include <nlohmann/detail/meta/cpp_future.hpp>
+
+// #include <nlohmann/detail/value_t.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+// forward declare, to be able to friend it later on
 template<typename IteratorType> class iteration_proxy;
+template<typename IteratorType> class iteration_proxy_value;
 
 /*!
 @brief a template for a bidirectional iterator for the @ref basic_json class
-
 This class implements a both iterators (iterator and const_iterator) for the
 @ref basic_json class.
-
 @note An iterator is called *initialized* when a pointer to a JSON value has
       been set (e.g., by a constructor or a copy assignment). If the iterator is
       default-constructed, it is *uninitialized* and most methods are undefined.
       **The library uses assertions to detect calls on uninitialized iterators.**
-
 @requirement The class satisfies the following concept requirements:
 -
-[BidirectionalIterator](http://en.cppreference.com/w/cpp/concept/BidirectionalIterator):
+[BidirectionalIterator](https://en.cppreference.com/w/cpp/named_req/BidirectionalIterator):
   The iterator that can be moved can be moved in both directions (i.e.
   incremented and decremented).
-
 @since version 1.0.0, simplified in version 2.0.9, change to bidirectional
        iterators in version 3.0.0 (see https://github.com/nlohmann/json/issues/593)
 */
@@ -3611,6 +5632,7 @@ class iter_impl
     friend iter_impl<typename std::conditional<std::is_const<BasicJsonType>::value, typename std::remove_const<BasicJsonType>::type, const BasicJsonType>::type>;
     friend BasicJsonType;
     friend iteration_proxy<iter_impl>;
+    friend iteration_proxy_value<iter_impl>;
 
     using object_t = typename BasicJsonType::object_t;
     using array_t = typename BasicJsonType::array_t;
@@ -4149,7 +6171,7 @@ class iter_impl
     @brief  return the key of an object iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
-    typename object_t::key_type key() const
+    const typename object_t::key_type& key() const
     {
         assert(m_object != nullptr);
 
@@ -4174,94 +6196,26 @@ class iter_impl
     /// associated JSON instance
     pointer m_object = nullptr;
     /// the actual iterator of the associated instance
-    internal_iterator<typename std::remove_const<BasicJsonType>::type> m_it = {};
+    internal_iterator<typename std::remove_const<BasicJsonType>::type> m_it;
 };
+}  // namespace detail
+} // namespace nlohmann
+// #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 
-/// proxy class for the iterator_wrapper functions
-template<typename IteratorType> class iteration_proxy
-{
-  private:
-    /// helper class for iteration
-    class iteration_proxy_internal
-    {
-      private:
-        /// the iterator
-        IteratorType anchor;
-        /// an index for arrays (used to create key names)
-        std::size_t array_index = 0;
-
-      public:
-        explicit iteration_proxy_internal(IteratorType it) noexcept : anchor(it) {}
-
-        /// dereference operator (needed for range-based for)
-        iteration_proxy_internal& operator*()
-        {
-            return *this;
-        }
-
-        /// increment operator (needed for range-based for)
-        iteration_proxy_internal& operator++()
-        {
-            ++anchor;
-            ++array_index;
-
-            return *this;
-        }
-
-        /// inequality operator (needed for range-based for)
-        bool operator!=(const iteration_proxy_internal& o) const noexcept
-        {
-            return anchor != o.anchor;
-        }
-
-        /// return key of the iterator
-        std::string key() const
-        {
-            assert(anchor.m_object != nullptr);
-
-            switch (anchor.m_object->type())
-            {
-                // use integer array index as key
-                case value_t::array:
-                    return std::to_string(array_index);
-
-                // use key from the object
-                case value_t::object:
-                    return anchor.key();
-
-                // use an empty key for all primitive types
-                default:
-                    return "";
-            }
-        }
-
-        /// return value of the iterator
-        typename IteratorType::reference value() const
-        {
-            return anchor.value();
-        }
-    };
-
-    /// the container to iterate
-    typename IteratorType::reference container;
+// #include <nlohmann/detail/iterators/json_reverse_iterator.hpp>
 
-  public:
-    /// construct iteration proxy from a container
-    explicit iteration_proxy(typename IteratorType::reference cont)
-        : container(cont) {}
 
-    /// return iterator begin (needed for range-based for)
-    iteration_proxy_internal begin() noexcept
-    {
-        return iteration_proxy_internal(container.begin());
-    }
+#include <cstddef> // ptrdiff_t
+#include <iterator> // reverse_iterator
+#include <utility> // declval
 
-    /// return iterator end (needed for range-based for)
-    iteration_proxy_internal end() noexcept
-    {
-        return iteration_proxy_internal(container.end());
-    }
-};
+namespace nlohmann
+{
+namespace detail
+{
+//////////////////////
+// reverse_iterator //
+//////////////////////
 
 /*!
 @brief a template for a reverse iterator class
@@ -4272,10 +6226,10 @@ create @ref const_reverse_iterator).
 
 @requirement The class satisfies the following concept requirements:
 -
-[BidirectionalIterator](http://en.cppreference.com/w/cpp/concept/BidirectionalIterator):
+[BidirectionalIterator](https://en.cppreference.com/w/cpp/named_req/BidirectionalIterator):
   The iterator that can be moved can be moved in both directions (i.e.
   incremented and decremented).
-- [OutputIterator](http://en.cppreference.com/w/cpp/concept/OutputIterator):
+- [OutputIterator](https://en.cppreference.com/w/cpp/named_req/OutputIterator):
   It is possible to write to the pointed-to element (only if @a Base is
   @ref iterator).
 
@@ -4292,11 +6246,11 @@ class json_reverse_iterator : public std::reverse_iterator<Base>
     using reference = typename Base::reference;
 
     /// create reverse iterator from iterator
-    json_reverse_iterator(const typename base_iterator::iterator_type& it) noexcept
+    explicit json_reverse_iterator(const typename base_iterator::iterator_type& it) noexcept
         : base_iterator(it) {}
 
     /// create reverse iterator from base class
-    json_reverse_iterator(const base_iterator& it) noexcept : base_iterator(it) {}
+    explicit json_reverse_iterator(const base_iterator& it) noexcept : base_iterator(it) {}
 
     /// post-increment (it++)
     json_reverse_iterator const operator++(int)
@@ -4366,11 +6320,25 @@ class json_reverse_iterator : public std::reverse_iterator<Base>
         return it.operator * ();
     }
 };
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/output/output_adapters.hpp>
 
-/////////////////////
-// output adapters //
-/////////////////////
 
+#include <algorithm> // copy
+#include <cstddef> // size_t
+#include <ios> // streamsize
+#include <iterator> // back_inserter
+#include <memory> // shared_ptr, make_shared
+#include <ostream> // basic_ostream
+#include <string> // basic_string
+#include <vector> // vector
+
+namespace nlohmann
+{
+namespace detail
+{
 /// abstract output adapter interface
 template<typename CharType> struct output_adapter_protocol
 {
@@ -4388,7 +6356,9 @@ template<typename CharType>
 class output_vector_adapter : public output_adapter_protocol<CharType>
 {
   public:
-    explicit output_vector_adapter(std::vector<CharType>& vec) : v(vec) {}
+    explicit output_vector_adapter(std::vector<CharType>& vec) noexcept
+        : v(vec)
+    {}
 
     void write_character(CharType c) override
     {
@@ -4409,7 +6379,9 @@ template<typename CharType>
 class output_stream_adapter : public output_adapter_protocol<CharType>
 {
   public:
-    explicit output_stream_adapter(std::basic_ostream<CharType>& s) : stream(s) {}
+    explicit output_stream_adapter(std::basic_ostream<CharType>& s) noexcept
+        : stream(s)
+    {}
 
     void write_character(CharType c) override
     {
@@ -4426,11 +6398,13 @@ class output_stream_adapter : public output_adapter_protocol<CharType>
 };
 
 /// output adapter for basic_string
-template<typename CharType>
+template<typename CharType, typename StringType = std::basic_string<CharType>>
 class output_string_adapter : public output_adapter_protocol<CharType>
 {
   public:
-    explicit output_string_adapter(std::basic_string<CharType>& s) : str(s) {}
+    explicit output_string_adapter(StringType& s) noexcept
+        : str(s)
+    {}
 
     void write_character(CharType c) override
     {
@@ -4443,10 +6417,10 @@ class output_string_adapter : public output_adapter_protocol<CharType>
     }
 
   private:
-    std::basic_string<CharType>& str;
+    StringType& str;
 };
 
-template<typename CharType>
+template<typename CharType, typename StringType = std::basic_string<CharType>>
 class output_adapter
 {
   public:
@@ -4456,8 +6430,8 @@ class output_adapter
     output_adapter(std::basic_ostream<CharType>& s)
         : oa(std::make_shared<output_stream_adapter<CharType>>(s)) {}
 
-    output_adapter(std::basic_string<CharType>& s)
-        : oa(std::make_shared<output_string_adapter<CharType>>(s)) {}
+    output_adapter(StringType& s)
+        : oa(std::make_shared<output_string_adapter<CharType, StringType>>(s)) {}
 
     operator output_adapter_t<CharType>()
     {
@@ -4467,19 +6441,57 @@ class output_adapter
   private:
     output_adapter_t<CharType> oa = nullptr;
 };
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/input/binary_reader.hpp>
 
-//////////////////////////////
-// binary reader and writer //
-//////////////////////////////
+
+#include <algorithm> // generate_n
+#include <array> // array
+#include <cassert> // assert
+#include <cmath> // ldexp
+#include <cstddef> // size_t
+#include <cstdint> // uint8_t, uint16_t, uint32_t, uint64_t
+#include <cstdio> // snprintf
+#include <cstring> // memcpy
+#include <iterator> // back_inserter
+#include <limits> // numeric_limits
+#include <string> // char_traits, string
+#include <utility> // make_pair, move
+
+// #include <nlohmann/detail/input/input_adapters.hpp>
+
+// #include <nlohmann/detail/input/json_sax.hpp>
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+// #include <nlohmann/detail/meta/is_sax.hpp>
+
+// #include <nlohmann/detail/value_t.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+///////////////////
+// binary reader //
+///////////////////
 
 /*!
-@brief deserialization of CBOR and MessagePack values
+@brief deserialization of CBOR, MessagePack, and UBJSON values
 */
-template<typename BasicJsonType>
+template<typename BasicJsonType, typename SAX = json_sax_dom_parser<BasicJsonType>>
 class binary_reader
 {
     using number_integer_t = typename BasicJsonType::number_integer_t;
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using json_sax_t = SAX;
 
   public:
     /*!
@@ -4489,49 +6501,68 @@ class binary_reader
     */
     explicit binary_reader(input_adapter_t adapter) : ia(std::move(adapter))
     {
+        (void)detail::is_sax_static_asserts<SAX, BasicJsonType> {};
         assert(ia);
     }
 
     /*!
-    @brief create a JSON value from CBOR input
-
+    @param[in] format  the binary format to parse
+    @param[in] sax_    a SAX event processor
     @param[in] strict  whether to expect the input to be consumed completed
-    @return JSON value created from CBOR input
 
-    @throw parse_error.110 if input ended unexpectedly or the end of file was
-                           not reached when @a strict was set to true
-    @throw parse_error.112 if unsupported byte was read
+    @return
     */
-    BasicJsonType parse_cbor(const bool strict)
+    bool sax_parse(const input_format_t format,
+                   json_sax_t* sax_,
+                   const bool strict = true)
     {
-        const auto res = parse_cbor_internal();
-        if (strict)
+        sax = sax_;
+        bool result = false;
+
+        switch (format)
         {
-            get();
-            check_eof(true);
-        }
-        return res;
-    }
+            case input_format_t::bson:
+                result = parse_bson_internal();
+                break;
 
-    /*!
-    @brief create a JSON value from MessagePack input
+            case input_format_t::cbor:
+                result = parse_cbor_internal();
+                break;
 
-    @param[in] strict  whether to expect the input to be consumed completed
-    @return JSON value created from MessagePack input
+            case input_format_t::msgpack:
+                result = parse_msgpack_internal();
+                break;
 
-    @throw parse_error.110 if input ended unexpectedly or the end of file was
-                           not reached when @a strict was set to true
-    @throw parse_error.112 if unsupported byte was read
-    */
-    BasicJsonType parse_msgpack(const bool strict)
-    {
-        const auto res = parse_msgpack_internal();
-        if (strict)
+            case input_format_t::ubjson:
+                result = parse_ubjson_internal();
+                break;
+
+            // LCOV_EXCL_START
+            default:
+                assert(false);
+                // LCOV_EXCL_STOP
+        }
+
+        // strict mode: next byte must be EOF
+        if (result and strict)
         {
-            get();
-            check_eof(true);
+            if (format == input_format_t::ubjson)
+            {
+                get_ignore_noop();
+            }
+            else
+            {
+                get();
+            }
+
+            if (JSON_UNLIKELY(current != std::char_traits<char>::eof()))
+            {
+                return sax->parse_error(chars_read, get_token_string(),
+                                        parse_error::create(110, chars_read, exception_message(format, "expected end of input; last byte: 0x" + get_token_string(), "value")));
+            }
         }
-        return res;
+
+        return result;
     }
 
     /*!
@@ -4547,18 +6578,239 @@ class binary_reader
     }
 
   private:
+    //////////
+    // BSON //
+    //////////
+
+    /*!
+    @brief Reads in a BSON-object and passes it to the SAX-parser.
+    @return whether a valid BSON-value was passed to the SAX parser
+    */
+    bool parse_bson_internal()
+    {
+        std::int32_t document_size;
+        get_number<std::int32_t, true>(input_format_t::bson, document_size);
+
+        if (JSON_UNLIKELY(not sax->start_object(std::size_t(-1))))
+        {
+            return false;
+        }
+
+        if (JSON_UNLIKELY(not parse_bson_element_list(/*is_array*/false)))
+        {
+            return false;
+        }
+
+        return sax->end_object();
+    }
+
+    /*!
+    @brief Parses a C-style string from the BSON input.
+    @param[in, out] result  A reference to the string variable where the read
+                            string is to be stored.
+    @return `true` if the \x00-byte indicating the end of the string was
+             encountered before the EOF; false` indicates an unexpected EOF.
+    */
+    bool get_bson_cstr(string_t& result)
+    {
+        auto out = std::back_inserter(result);
+        while (true)
+        {
+            get();
+            if (JSON_UNLIKELY(not unexpect_eof(input_format_t::bson, "cstring")))
+            {
+                return false;
+            }
+            if (current == 0x00)
+            {
+                return true;
+            }
+            *out++ = static_cast<char>(current);
+        }
+
+        return true;
+    }
+
+    /*!
+    @brief Parses a zero-terminated string of length @a len from the BSON
+           input.
+    @param[in] len  The length (including the zero-byte at the end) of the
+                    string to be read.
+    @param[in, out] result  A reference to the string variable where the read
+                            string is to be stored.
+    @tparam NumberType The type of the length @a len
+    @pre len >= 1
+    @return `true` if the string was successfully parsed
+    */
+    template<typename NumberType>
+    bool get_bson_string(const NumberType len, string_t& result)
+    {
+        if (JSON_UNLIKELY(len < 1))
+        {
+            auto last_token = get_token_string();
+            return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::bson, "string length must be at least 1, is " + std::to_string(len), "string")));
+        }
+
+        return get_string(input_format_t::bson, len - static_cast<NumberType>(1), result) and get() != std::char_traits<char>::eof();
+    }
+
+    /*!
+    @brief Read a BSON document element of the given @a element_type.
+    @param[in] element_type The BSON element type, c.f. http://bsonspec.org/spec.html
+    @param[in] element_type_parse_position The position in the input stream,
+               where the `element_type` was read.
+    @warning Not all BSON element types are supported yet. An unsupported
+             @a element_type will give rise to a parse_error.114:
+             Unsupported BSON record type 0x...
+    @return whether a valid BSON-object/array was passed to the SAX parser
+    */
+    bool parse_bson_element_internal(const int element_type,
+                                     const std::size_t element_type_parse_position)
+    {
+        switch (element_type)
+        {
+            case 0x01: // double
+            {
+                double number;
+                return get_number<double, true>(input_format_t::bson, number) and sax->number_float(static_cast<number_float_t>(number), "");
+            }
+
+            case 0x02: // string
+            {
+                std::int32_t len;
+                string_t value;
+                return get_number<std::int32_t, true>(input_format_t::bson, len) and get_bson_string(len, value) and sax->string(value);
+            }
+
+            case 0x03: // object
+            {
+                return parse_bson_internal();
+            }
+
+            case 0x04: // array
+            {
+                return parse_bson_array();
+            }
+
+            case 0x08: // boolean
+            {
+                return sax->boolean(get() != 0);
+            }
+
+            case 0x0A: // null
+            {
+                return sax->null();
+            }
+
+            case 0x10: // int32
+            {
+                std::int32_t value;
+                return get_number<std::int32_t, true>(input_format_t::bson, value) and sax->number_integer(value);
+            }
+
+            case 0x12: // int64
+            {
+                std::int64_t value;
+                return get_number<std::int64_t, true>(input_format_t::bson, value) and sax->number_integer(value);
+            }
+
+            default: // anything else not supported (yet)
+            {
+                char cr[3];
+                (std::snprintf)(cr, sizeof(cr), "%.2hhX", static_cast<unsigned char>(element_type));
+                return sax->parse_error(element_type_parse_position, std::string(cr), parse_error::create(114, element_type_parse_position, "Unsupported BSON record type 0x" + std::string(cr)));
+            }
+        }
+    }
+
+    /*!
+    @brief Read a BSON element list (as specified in the BSON-spec)
+
+    The same binary layout is used for objects and arrays, hence it must be
+    indicated with the argument @a is_array which one is expected
+    (true --> array, false --> object).
+
+    @param[in] is_array Determines if the element list being read is to be
+                        treated as an object (@a is_array == false), or as an
+                        array (@a is_array == true).
+    @return whether a valid BSON-object/array was passed to the SAX parser
+    */
+    bool parse_bson_element_list(const bool is_array)
+    {
+        string_t key;
+        while (int element_type = get())
+        {
+            if (JSON_UNLIKELY(not unexpect_eof(input_format_t::bson, "element list")))
+            {
+                return false;
+            }
+
+            const std::size_t element_type_parse_position = chars_read;
+            if (JSON_UNLIKELY(not get_bson_cstr(key)))
+            {
+                return false;
+            }
+
+            if (not is_array)
+            {
+                if (not sax->key(key))
+                {
+                    return false;
+                }
+            }
+
+            if (JSON_UNLIKELY(not parse_bson_element_internal(element_type, element_type_parse_position)))
+            {
+                return false;
+            }
+
+            // get_bson_cstr only appends
+            key.clear();
+        }
+
+        return true;
+    }
+
+    /*!
+    @brief Reads an array from the BSON input and passes it to the SAX-parser.
+    @return whether a valid BSON-array was passed to the SAX parser
+    */
+    bool parse_bson_array()
+    {
+        std::int32_t document_size;
+        get_number<std::int32_t, true>(input_format_t::bson, document_size);
+
+        if (JSON_UNLIKELY(not sax->start_array(std::size_t(-1))))
+        {
+            return false;
+        }
+
+        if (JSON_UNLIKELY(not parse_bson_element_list(/*is_array*/true)))
+        {
+            return false;
+        }
+
+        return sax->end_array();
+    }
+
+    //////////
+    // CBOR //
+    //////////
+
     /*!
     @param[in] get_char  whether a new character should be retrieved from the
                          input (true, default) or whether the last read
                          character should be considered instead
+
+    @return whether a valid CBOR value was passed to the SAX parser
     */
-    BasicJsonType parse_cbor_internal(const bool get_char = true)
+    bool parse_cbor_internal(const bool get_char = true)
     {
         switch (get_char ? get() : current)
         {
             // EOF
             case std::char_traits<char>::eof():
-                JSON_THROW(parse_error::create(110, chars_read, "unexpected end of input"));
+                return unexpect_eof(input_format_t::cbor, "value");
 
             // Integer 0x00..0x17 (0..23)
             case 0x00:
@@ -4585,19 +6837,31 @@ class binary_reader
             case 0x15:
             case 0x16:
             case 0x17:
-                return static_cast<number_unsigned_t>(current);
+                return sax->number_unsigned(static_cast<number_unsigned_t>(current));
 
             case 0x18: // Unsigned integer (one-byte uint8_t follows)
-                return get_number<uint8_t>();
+            {
+                uint8_t number;
+                return get_number(input_format_t::cbor, number) and sax->number_unsigned(number);
+            }
 
             case 0x19: // Unsigned integer (two-byte uint16_t follows)
-                return get_number<uint16_t>();
+            {
+                uint16_t number;
+                return get_number(input_format_t::cbor, number) and sax->number_unsigned(number);
+            }
 
             case 0x1A: // Unsigned integer (four-byte uint32_t follows)
-                return get_number<uint32_t>();
+            {
+                uint32_t number;
+                return get_number(input_format_t::cbor, number) and sax->number_unsigned(number);
+            }
 
             case 0x1B: // Unsigned integer (eight-byte uint64_t follows)
-                return get_number<uint64_t>();
+            {
+                uint64_t number;
+                return get_number(input_format_t::cbor, number) and sax->number_unsigned(number);
+            }
 
             // Negative integer -1-0x00..-1-0x17 (-1..-24)
             case 0x20:
@@ -4624,28 +6888,31 @@ class binary_reader
             case 0x35:
             case 0x36:
             case 0x37:
-                return static_cast<int8_t>(0x20 - 1 - current);
+                return sax->number_integer(static_cast<int8_t>(0x20 - 1 - current));
 
             case 0x38: // Negative integer (one-byte uint8_t follows)
             {
-                // must be uint8_t !
-                return static_cast<number_integer_t>(-1) - get_number<uint8_t>();
+                uint8_t number;
+                return get_number(input_format_t::cbor, number) and sax->number_integer(static_cast<number_integer_t>(-1) - number);
             }
 
             case 0x39: // Negative integer -1-n (two-byte uint16_t follows)
             {
-                return static_cast<number_integer_t>(-1) - get_number<uint16_t>();
+                uint16_t number;
+                return get_number(input_format_t::cbor, number) and sax->number_integer(static_cast<number_integer_t>(-1) - number);
             }
 
             case 0x3A: // Negative integer -1-n (four-byte uint32_t follows)
             {
-                return static_cast<number_integer_t>(-1) - get_number<uint32_t>();
+                uint32_t number;
+                return get_number(input_format_t::cbor, number) and sax->number_integer(static_cast<number_integer_t>(-1) - number);
             }
 
             case 0x3B: // Negative integer -1-n (eight-byte uint64_t follows)
             {
-                return static_cast<number_integer_t>(-1) -
-                       static_cast<number_integer_t>(get_number<uint64_t>());
+                uint64_t number;
+                return get_number(input_format_t::cbor, number) and sax->number_integer(static_cast<number_integer_t>(-1)
+                        - static_cast<number_integer_t>(number));
             }
 
             // UTF-8 string (0x00..0x17 bytes follow)
@@ -4679,7 +6946,8 @@ class binary_reader
             case 0x7B: // UTF-8 string (eight-byte uint64_t for n follow)
             case 0x7F: // UTF-8 string (indefinite length)
             {
-                return get_cbor_string();
+                string_t s;
+                return get_cbor_string(s) and sax->string(s);
             }
 
             // array (0x00..0x17 data items follow)
@@ -4707,39 +6975,34 @@ class binary_reader
             case 0x95:
             case 0x96:
             case 0x97:
-            {
-                return get_cbor_array(current & 0x1F);
-            }
+                return get_cbor_array(static_cast<std::size_t>(current & 0x1F));
 
             case 0x98: // array (one-byte uint8_t for n follows)
             {
-                return get_cbor_array(get_number<uint8_t>());
+                uint8_t len;
+                return get_number(input_format_t::cbor, len) and get_cbor_array(static_cast<std::size_t>(len));
             }
 
             case 0x99: // array (two-byte uint16_t for n follow)
             {
-                return get_cbor_array(get_number<uint16_t>());
+                uint16_t len;
+                return get_number(input_format_t::cbor, len) and get_cbor_array(static_cast<std::size_t>(len));
             }
 
             case 0x9A: // array (four-byte uint32_t for n follow)
             {
-                return get_cbor_array(get_number<uint32_t>());
+                uint32_t len;
+                return get_number(input_format_t::cbor, len) and get_cbor_array(static_cast<std::size_t>(len));
             }
 
             case 0x9B: // array (eight-byte uint64_t for n follow)
             {
-                return get_cbor_array(get_number<uint64_t>());
+                uint64_t len;
+                return get_number(input_format_t::cbor, len) and get_cbor_array(static_cast<std::size_t>(len));
             }
 
             case 0x9F: // array (indefinite length)
-            {
-                BasicJsonType result = value_t::array;
-                while (get() != 0xFF)
-                {
-                    result.push_back(parse_cbor_internal(false));
-                }
-                return result;
-            }
+                return get_cbor_array(std::size_t(-1));
 
             // map (0x00..0x17 pairs of data items follow)
             case 0xA0:
@@ -4766,62 +7029,59 @@ class binary_reader
             case 0xB5:
             case 0xB6:
             case 0xB7:
-            {
-                return get_cbor_object(current & 0x1F);
-            }
+                return get_cbor_object(static_cast<std::size_t>(current & 0x1F));
 
             case 0xB8: // map (one-byte uint8_t for n follows)
             {
-                return get_cbor_object(get_number<uint8_t>());
+                uint8_t len;
+                return get_number(input_format_t::cbor, len) and get_cbor_object(static_cast<std::size_t>(len));
             }
 
             case 0xB9: // map (two-byte uint16_t for n follow)
             {
-                return get_cbor_object(get_number<uint16_t>());
+                uint16_t len;
+                return get_number(input_format_t::cbor, len) and get_cbor_object(static_cast<std::size_t>(len));
             }
 
             case 0xBA: // map (four-byte uint32_t for n follow)
             {
-                return get_cbor_object(get_number<uint32_t>());
+                uint32_t len;
+                return get_number(input_format_t::cbor, len) and get_cbor_object(static_cast<std::size_t>(len));
             }
 
             case 0xBB: // map (eight-byte uint64_t for n follow)
             {
-                return get_cbor_object(get_number<uint64_t>());
+                uint64_t len;
+                return get_number(input_format_t::cbor, len) and get_cbor_object(static_cast<std::size_t>(len));
             }
 
             case 0xBF: // map (indefinite length)
-            {
-                BasicJsonType result = value_t::object;
-                while (get() != 0xFF)
-                {
-                    auto key = get_cbor_string();
-                    result[key] = parse_cbor_internal();
-                }
-                return result;
-            }
+                return get_cbor_object(std::size_t(-1));
 
             case 0xF4: // false
-            {
-                return false;
-            }
+                return sax->boolean(false);
 
             case 0xF5: // true
-            {
-                return true;
-            }
+                return sax->boolean(true);
 
             case 0xF6: // null
-            {
-                return value_t::null;
-            }
+                return sax->null();
 
             case 0xF9: // Half-Precision Float (two-byte IEEE 754)
             {
-                const int byte1 = get();
-                check_eof();
-                const int byte2 = get();
-                check_eof();
+                const int byte1_raw = get();
+                if (JSON_UNLIKELY(not unexpect_eof(input_format_t::cbor, "number")))
+                {
+                    return false;
+                }
+                const int byte2_raw = get();
+                if (JSON_UNLIKELY(not unexpect_eof(input_format_t::cbor, "number")))
+                {
+                    return false;
+                }
+
+                const auto byte1 = static_cast<unsigned char>(byte1_raw);
+                const auto byte2 = static_cast<unsigned char>(byte2_raw);
 
                 // code from RFC 7049, Appendix D, Figure 3:
                 // As half-precision floating-point numbers were only added
@@ -4832,51 +7092,244 @@ class binary_reader
                 // half-precision floating-point numbers in the C language
                 // is shown in Fig. 3.
                 const int half = (byte1 << 8) + byte2;
-                const int exp = (half >> 10) & 0x1F;
-                const int mant = half & 0x3FF;
-                double val;
-                if (exp == 0)
-                {
-                    val = std::ldexp(mant, -24);
-                }
-                else if (exp != 31)
+                const double val = [&half]
                 {
-                    val = std::ldexp(mant + 1024, exp - 25);
-                }
-                else
-                {
-                    val = (mant == 0) ? std::numeric_limits<double>::infinity()
-                          : std::numeric_limits<double>::quiet_NaN();
-                }
-                return (half & 0x8000) != 0 ? -val : val;
+                    const int exp = (half >> 10) & 0x1F;
+                    const int mant = half & 0x3FF;
+                    assert(0 <= exp and exp <= 32);
+                    assert(0 <= mant and mant <= 1024);
+                    switch (exp)
+                    {
+                        case 0:
+                            return std::ldexp(mant, -24);
+                        case 31:
+                            return (mant == 0)
+                            ? std::numeric_limits<double>::infinity()
+                            : std::numeric_limits<double>::quiet_NaN();
+                        default:
+                            return std::ldexp(mant + 1024, exp - 25);
+                    }
+                }();
+                return sax->number_float((half & 0x8000) != 0
+                                         ? static_cast<number_float_t>(-val)
+                                         : static_cast<number_float_t>(val), "");
             }
 
             case 0xFA: // Single-Precision Float (four-byte IEEE 754)
             {
-                return get_number<float>();
+                float number;
+                return get_number(input_format_t::cbor, number) and sax->number_float(static_cast<number_float_t>(number), "");
             }
 
             case 0xFB: // Double-Precision Float (eight-byte IEEE 754)
             {
-                return get_number<double>();
+                double number;
+                return get_number(input_format_t::cbor, number) and sax->number_float(static_cast<number_float_t>(number), "");
             }
 
             default: // anything else (0xFF is handled inside the other types)
             {
-                std::stringstream ss;
-                ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << current;
-                JSON_THROW(parse_error::create(112, chars_read, "error reading CBOR; last byte: 0x" + ss.str()));
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::cbor, "invalid byte: 0x" + last_token, "value")));
             }
         }
     }
 
-    BasicJsonType parse_msgpack_internal()
+    /*!
+    @brief reads a CBOR string
+
+    This function first reads starting bytes to determine the expected
+    string length and then copies this number of bytes into a string.
+    Additionally, CBOR's strings with indefinite lengths are supported.
+
+    @param[out] result  created string
+
+    @return whether string creation completed
+    */
+    bool get_cbor_string(string_t& result)
+    {
+        if (JSON_UNLIKELY(not unexpect_eof(input_format_t::cbor, "string")))
+        {
+            return false;
+        }
+
+        switch (current)
+        {
+            // UTF-8 string (0x00..0x17 bytes follow)
+            case 0x60:
+            case 0x61:
+            case 0x62:
+            case 0x63:
+            case 0x64:
+            case 0x65:
+            case 0x66:
+            case 0x67:
+            case 0x68:
+            case 0x69:
+            case 0x6A:
+            case 0x6B:
+            case 0x6C:
+            case 0x6D:
+            case 0x6E:
+            case 0x6F:
+            case 0x70:
+            case 0x71:
+            case 0x72:
+            case 0x73:
+            case 0x74:
+            case 0x75:
+            case 0x76:
+            case 0x77:
+            {
+                return get_string(input_format_t::cbor, current & 0x1F, result);
+            }
+
+            case 0x78: // UTF-8 string (one-byte uint8_t for n follows)
+            {
+                uint8_t len;
+                return get_number(input_format_t::cbor, len) and get_string(input_format_t::cbor, len, result);
+            }
+
+            case 0x79: // UTF-8 string (two-byte uint16_t for n follow)
+            {
+                uint16_t len;
+                return get_number(input_format_t::cbor, len) and get_string(input_format_t::cbor, len, result);
+            }
+
+            case 0x7A: // UTF-8 string (four-byte uint32_t for n follow)
+            {
+                uint32_t len;
+                return get_number(input_format_t::cbor, len) and get_string(input_format_t::cbor, len, result);
+            }
+
+            case 0x7B: // UTF-8 string (eight-byte uint64_t for n follow)
+            {
+                uint64_t len;
+                return get_number(input_format_t::cbor, len) and get_string(input_format_t::cbor, len, result);
+            }
+
+            case 0x7F: // UTF-8 string (indefinite length)
+            {
+                while (get() != 0xFF)
+                {
+                    string_t chunk;
+                    if (not get_cbor_string(chunk))
+                    {
+                        return false;
+                    }
+                    result.append(chunk);
+                }
+                return true;
+            }
+
+            default:
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::cbor, "expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x" + last_token, "string")));
+            }
+        }
+    }
+
+    /*!
+    @param[in] len  the length of the array or std::size_t(-1) for an
+                    array of indefinite size
+    @return whether array creation completed
+    */
+    bool get_cbor_array(const std::size_t len)
+    {
+        if (JSON_UNLIKELY(not sax->start_array(len)))
+        {
+            return false;
+        }
+
+        if (len != std::size_t(-1))
+        {
+            for (std::size_t i = 0; i < len; ++i)
+            {
+                if (JSON_UNLIKELY(not parse_cbor_internal()))
+                {
+                    return false;
+                }
+            }
+        }
+        else
+        {
+            while (get() != 0xFF)
+            {
+                if (JSON_UNLIKELY(not parse_cbor_internal(false)))
+                {
+                    return false;
+                }
+            }
+        }
+
+        return sax->end_array();
+    }
+
+    /*!
+    @param[in] len  the length of the object or std::size_t(-1) for an
+                    object of indefinite size
+    @return whether object creation completed
+    */
+    bool get_cbor_object(const std::size_t len)
+    {
+        if (not JSON_UNLIKELY(sax->start_object(len)))
+        {
+            return false;
+        }
+
+        string_t key;
+        if (len != std::size_t(-1))
+        {
+            for (std::size_t i = 0; i < len; ++i)
+            {
+                get();
+                if (JSON_UNLIKELY(not get_cbor_string(key) or not sax->key(key)))
+                {
+                    return false;
+                }
+
+                if (JSON_UNLIKELY(not parse_cbor_internal()))
+                {
+                    return false;
+                }
+                key.clear();
+            }
+        }
+        else
+        {
+            while (get() != 0xFF)
+            {
+                if (JSON_UNLIKELY(not get_cbor_string(key) or not sax->key(key)))
+                {
+                    return false;
+                }
+
+                if (JSON_UNLIKELY(not parse_cbor_internal()))
+                {
+                    return false;
+                }
+                key.clear();
+            }
+        }
+
+        return sax->end_object();
+    }
+
+    /////////////
+    // MsgPack //
+    /////////////
+
+    /*!
+    @return whether a valid MessagePack value was passed to the SAX parser
+    */
+    bool parse_msgpack_internal()
     {
         switch (get())
         {
             // EOF
             case std::char_traits<char>::eof():
-                JSON_THROW(parse_error::create(110, chars_read, "unexpected end of input"));
+                return unexpect_eof(input_format_t::msgpack, "value");
 
             // positive fixint
             case 0x00:
@@ -5007,7 +7460,7 @@ class binary_reader
             case 0x7D:
             case 0x7E:
             case 0x7F:
-                return static_cast<number_unsigned_t>(current);
+                return sax->number_unsigned(static_cast<number_unsigned_t>(current));
 
             // fixmap
             case 0x80:
@@ -5026,9 +7479,7 @@ class binary_reader
             case 0x8D:
             case 0x8E:
             case 0x8F:
-            {
-                return get_msgpack_object(current & 0x0F);
-            }
+                return get_msgpack_object(static_cast<std::size_t>(current & 0x0F));
 
             // fixarray
             case 0x90:
@@ -5047,9 +7498,7 @@ class binary_reader
             case 0x9D:
             case 0x9E:
             case 0x9F:
-            {
-                return get_msgpack_array(current & 0x0F);
-            }
+                return get_msgpack_array(static_cast<std::size_t>(current & 0x0F));
 
             // fixstr
             case 0xA0:
@@ -5084,73 +7533,113 @@ class binary_reader
             case 0xBD:
             case 0xBE:
             case 0xBF:
-                return get_msgpack_string();
+            {
+                string_t s;
+                return get_msgpack_string(s) and sax->string(s);
+            }
 
             case 0xC0: // nil
-                return value_t::null;
+                return sax->null();
 
             case 0xC2: // false
-                return false;
+                return sax->boolean(false);
 
             case 0xC3: // true
-                return true;
+                return sax->boolean(true);
 
             case 0xCA: // float 32
-                return get_number<float>();
+            {
+                float number;
+                return get_number(input_format_t::msgpack, number) and sax->number_float(static_cast<number_float_t>(number), "");
+            }
 
             case 0xCB: // float 64
-                return get_number<double>();
+            {
+                double number;
+                return get_number(input_format_t::msgpack, number) and sax->number_float(static_cast<number_float_t>(number), "");
+            }
 
             case 0xCC: // uint 8
-                return get_number<uint8_t>();
+            {
+                uint8_t number;
+                return get_number(input_format_t::msgpack, number) and sax->number_unsigned(number);
+            }
 
             case 0xCD: // uint 16
-                return get_number<uint16_t>();
+            {
+                uint16_t number;
+                return get_number(input_format_t::msgpack, number) and sax->number_unsigned(number);
+            }
 
             case 0xCE: // uint 32
-                return get_number<uint32_t>();
+            {
+                uint32_t number;
+                return get_number(input_format_t::msgpack, number) and sax->number_unsigned(number);
+            }
 
             case 0xCF: // uint 64
-                return get_number<uint64_t>();
+            {
+                uint64_t number;
+                return get_number(input_format_t::msgpack, number) and sax->number_unsigned(number);
+            }
 
             case 0xD0: // int 8
-                return get_number<int8_t>();
+            {
+                int8_t number;
+                return get_number(input_format_t::msgpack, number) and sax->number_integer(number);
+            }
 
             case 0xD1: // int 16
-                return get_number<int16_t>();
+            {
+                int16_t number;
+                return get_number(input_format_t::msgpack, number) and sax->number_integer(number);
+            }
 
             case 0xD2: // int 32
-                return get_number<int32_t>();
+            {
+                int32_t number;
+                return get_number(input_format_t::msgpack, number) and sax->number_integer(number);
+            }
 
             case 0xD3: // int 64
-                return get_number<int64_t>();
+            {
+                int64_t number;
+                return get_number(input_format_t::msgpack, number) and sax->number_integer(number);
+            }
 
             case 0xD9: // str 8
             case 0xDA: // str 16
             case 0xDB: // str 32
-                return get_msgpack_string();
+            {
+                string_t s;
+                return get_msgpack_string(s) and sax->string(s);
+            }
 
             case 0xDC: // array 16
             {
-                return get_msgpack_array(get_number<uint16_t>());
+                uint16_t len;
+                return get_number(input_format_t::msgpack, len) and get_msgpack_array(static_cast<std::size_t>(len));
             }
 
             case 0xDD: // array 32
             {
-                return get_msgpack_array(get_number<uint32_t>());
+                uint32_t len;
+                return get_number(input_format_t::msgpack, len) and get_msgpack_array(static_cast<std::size_t>(len));
             }
 
             case 0xDE: // map 16
             {
-                return get_msgpack_object(get_number<uint16_t>());
+                uint16_t len;
+                return get_number(input_format_t::msgpack, len) and get_msgpack_object(static_cast<std::size_t>(len));
             }
 
             case 0xDF: // map 32
             {
-                return get_msgpack_object(get_number<uint32_t>());
+                uint32_t len;
+                return get_number(input_format_t::msgpack, len) and get_msgpack_object(static_cast<std::size_t>(len));
             }
 
-            // positive fixint
+            // negative fixint
             case 0xE0:
             case 0xE1:
             case 0xE2:
@@ -5183,338 +7672,749 @@ class binary_reader
             case 0xFD:
             case 0xFE:
             case 0xFF:
-                return static_cast<int8_t>(current);
+                return sax->number_integer(static_cast<int8_t>(current));
 
             default: // anything else
             {
-                std::stringstream ss;
-                ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << current;
-                JSON_THROW(parse_error::create(112, chars_read,
-                                               "error reading MessagePack; last byte: 0x" + ss.str()));
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::msgpack, "invalid byte: 0x" + last_token, "value")));
             }
         }
     }
 
     /*!
-    @brief get next character from the input
+    @brief reads a MessagePack string
 
-    This function provides the interface to the used input adapter. It does
-    not throw in case the input reached EOF, but returns a -'ve valued
-    `std::char_traits<char>::eof()` in that case.
+    This function first reads starting bytes to determine the expected
+    string length and then copies this number of bytes into a string.
 
-    @return character read from the input
+    @param[out] result  created string
+
+    @return whether string creation completed
     */
-    int get()
+    bool get_msgpack_string(string_t& result)
     {
-        ++chars_read;
-        return (current = ia->get_character());
-    }
+        if (JSON_UNLIKELY(not unexpect_eof(input_format_t::msgpack, "string")))
+        {
+            return false;
+        }
 
-    /*
-    @brief read a number from the input
+        switch (current)
+        {
+            // fixstr
+            case 0xA0:
+            case 0xA1:
+            case 0xA2:
+            case 0xA3:
+            case 0xA4:
+            case 0xA5:
+            case 0xA6:
+            case 0xA7:
+            case 0xA8:
+            case 0xA9:
+            case 0xAA:
+            case 0xAB:
+            case 0xAC:
+            case 0xAD:
+            case 0xAE:
+            case 0xAF:
+            case 0xB0:
+            case 0xB1:
+            case 0xB2:
+            case 0xB3:
+            case 0xB4:
+            case 0xB5:
+            case 0xB6:
+            case 0xB7:
+            case 0xB8:
+            case 0xB9:
+            case 0xBA:
+            case 0xBB:
+            case 0xBC:
+            case 0xBD:
+            case 0xBE:
+            case 0xBF:
+            {
+                return get_string(input_format_t::msgpack, current & 0x1F, result);
+            }
 
-    @tparam NumberType the type of the number
+            case 0xD9: // str 8
+            {
+                uint8_t len;
+                return get_number(input_format_t::msgpack, len) and get_string(input_format_t::msgpack, len, result);
+            }
 
-    @return number of type @a NumberType
+            case 0xDA: // str 16
+            {
+                uint16_t len;
+                return get_number(input_format_t::msgpack, len) and get_string(input_format_t::msgpack, len, result);
+            }
 
-    @note This function needs to respect the system's endianess, because
-          bytes in CBOR and MessagePack are stored in network order (big
-          endian) and therefore need reordering on little endian systems.
+            case 0xDB: // str 32
+            {
+                uint32_t len;
+                return get_number(input_format_t::msgpack, len) and get_string(input_format_t::msgpack, len, result);
+            }
+
+            default:
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::msgpack, "expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0x" + last_token, "string")));
+            }
+        }
+    }
 
-    @throw parse_error.110 if input has less than `sizeof(NumberType)` bytes
+    /*!
+    @param[in] len  the length of the array
+    @return whether array creation completed
     */
-    template<typename NumberType> NumberType get_number()
+    bool get_msgpack_array(const std::size_t len)
     {
-        // step 1: read input into array with system's byte order
-        std::array<uint8_t, sizeof(NumberType)> vec;
-        for (std::size_t i = 0; i < sizeof(NumberType); ++i)
+        if (JSON_UNLIKELY(not sax->start_array(len)))
         {
-            get();
-            check_eof();
+            return false;
+        }
 
-            // reverse byte order prior to conversion if necessary
-            if (is_little_endian)
-            {
-                vec[sizeof(NumberType) - i - 1] = static_cast<uint8_t>(current);
-            }
-            else
+        for (std::size_t i = 0; i < len; ++i)
+        {
+            if (JSON_UNLIKELY(not parse_msgpack_internal()))
             {
-                vec[i] = static_cast<uint8_t>(current); // LCOV_EXCL_LINE
+                return false;
             }
         }
 
-        // step 2: convert array into number of type T and return
-        NumberType result;
-        std::memcpy(&result, vec.data(), sizeof(NumberType));
-        return result;
+        return sax->end_array();
     }
 
     /*!
-    @brief create a string by reading characters from the input
+    @param[in] len  the length of the object
+    @return whether object creation completed
+    */
+    bool get_msgpack_object(const std::size_t len)
+    {
+        if (JSON_UNLIKELY(not sax->start_object(len)))
+        {
+            return false;
+        }
 
-    @param[in] len number of bytes to read
+        string_t key;
+        for (std::size_t i = 0; i < len; ++i)
+        {
+            get();
+            if (JSON_UNLIKELY(not get_msgpack_string(key) or not sax->key(key)))
+            {
+                return false;
+            }
 
-    @note We can not reserve @a len bytes for the result, because @a len
-          may be too large. Usually, @ref check_eof() detects the end of
-          the input before we run out of string memory.
+            if (JSON_UNLIKELY(not parse_msgpack_internal()))
+            {
+                return false;
+            }
+            key.clear();
+        }
 
-    @return string created by reading @a len bytes
+        return sax->end_object();
+    }
 
-    @throw parse_error.110 if input has less than @a len bytes
+    ////////////
+    // UBJSON //
+    ////////////
+
+    /*!
+    @param[in] get_char  whether a new character should be retrieved from the
+                         input (true, default) or whether the last read
+                         character should be considered instead
+
+    @return whether a valid UBJSON value was passed to the SAX parser
     */
-    template<typename NumberType>
-    std::string get_string(const NumberType len)
+    bool parse_ubjson_internal(const bool get_char = true)
     {
-        std::string result;
-        std::generate_n(std::back_inserter(result), len, [this]()
-        {
-            get();
-            check_eof();
-            return static_cast<char>(current);
-        });
-        return result;
+        return get_ubjson_value(get_char ? get_ignore_noop() : current);
     }
 
     /*!
-    @brief reads a CBOR string
+    @brief reads a UBJSON string
 
-    This function first reads starting bytes to determine the expected
-    string length and then copies this number of bytes into a string.
-    Additionally, CBOR's strings with indefinite lengths are supported.
+    This function is either called after reading the 'S' byte explicitly
+    indicating a string, or in case of an object key where the 'S' byte can be
+    left out.
 
-    @return string
+    @param[out] result   created string
+    @param[in] get_char  whether a new character should be retrieved from the
+                         input (true, default) or whether the last read
+                         character should be considered instead
 
-    @throw parse_error.110 if input ended
-    @throw parse_error.113 if an unexpected byte is read
+    @return whether string creation completed
     */
-    std::string get_cbor_string()
+    bool get_ubjson_string(string_t& result, const bool get_char = true)
     {
-        check_eof();
+        if (get_char)
+        {
+            get();  // TODO: may we ignore N here?
+        }
+
+        if (JSON_UNLIKELY(not unexpect_eof(input_format_t::ubjson, "value")))
+        {
+            return false;
+        }
 
         switch (current)
         {
-            // UTF-8 string (0x00..0x17 bytes follow)
-            case 0x60:
-            case 0x61:
-            case 0x62:
-            case 0x63:
-            case 0x64:
-            case 0x65:
-            case 0x66:
-            case 0x67:
-            case 0x68:
-            case 0x69:
-            case 0x6A:
-            case 0x6B:
-            case 0x6C:
-            case 0x6D:
-            case 0x6E:
-            case 0x6F:
-            case 0x70:
-            case 0x71:
-            case 0x72:
-            case 0x73:
-            case 0x74:
-            case 0x75:
-            case 0x76:
-            case 0x77:
+            case 'U':
             {
-                return get_string(current & 0x1F);
+                uint8_t len;
+                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
             }
 
-            case 0x78: // UTF-8 string (one-byte uint8_t for n follows)
+            case 'i':
             {
-                return get_string(get_number<uint8_t>());
+                int8_t len;
+                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
             }
 
-            case 0x79: // UTF-8 string (two-byte uint16_t for n follow)
+            case 'I':
             {
-                return get_string(get_number<uint16_t>());
+                int16_t len;
+                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
             }
 
-            case 0x7A: // UTF-8 string (four-byte uint32_t for n follow)
+            case 'l':
             {
-                return get_string(get_number<uint32_t>());
+                int32_t len;
+                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
             }
 
-            case 0x7B: // UTF-8 string (eight-byte uint64_t for n follow)
+            case 'L':
             {
-                return get_string(get_number<uint64_t>());
+                int64_t len;
+                return get_number(input_format_t::ubjson, len) and get_string(input_format_t::ubjson, len, result);
             }
 
-            case 0x7F: // UTF-8 string (indefinite length)
+            default:
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "expected length type specification (U, i, I, l, L); last byte: 0x" + last_token, "string")));
+        }
+    }
+
+    /*!
+    @param[out] result  determined size
+    @return whether size determination completed
+    */
+    bool get_ubjson_size_value(std::size_t& result)
+    {
+        switch (get_ignore_noop())
+        {
+            case 'U':
             {
-                std::string result;
-                while (get() != 0xFF)
+                uint8_t number;
+                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
+                {
+                    return false;
+                }
+                result = static_cast<std::size_t>(number);
+                return true;
+            }
+
+            case 'i':
+            {
+                int8_t number;
+                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
                 {
-                    check_eof();
-                    result.push_back(static_cast<char>(current));
+                    return false;
                 }
-                return result;
+                result = static_cast<std::size_t>(number);
+                return true;
+            }
+
+            case 'I':
+            {
+                int16_t number;
+                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
+                {
+                    return false;
+                }
+                result = static_cast<std::size_t>(number);
+                return true;
+            }
+
+            case 'l':
+            {
+                int32_t number;
+                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
+                {
+                    return false;
+                }
+                result = static_cast<std::size_t>(number);
+                return true;
+            }
+
+            case 'L':
+            {
+                int64_t number;
+                if (JSON_UNLIKELY(not get_number(input_format_t::ubjson, number)))
+                {
+                    return false;
+                }
+                result = static_cast<std::size_t>(number);
+                return true;
             }
 
             default:
             {
-                std::stringstream ss;
-                ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << current;
-                JSON_THROW(parse_error::create(113, chars_read, "expected a CBOR string; last byte: 0x" + ss.str()));
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "expected length type specification (U, i, I, l, L) after '#'; last byte: 0x" + last_token, "size")));
             }
         }
     }
 
-    template<typename NumberType>
-    BasicJsonType get_cbor_array(const NumberType len)
+    /*!
+    @brief determine the type and size for a container
+
+    In the optimized UBJSON format, a type and a size can be provided to allow
+    for a more compact representation.
+
+    @param[out] result  pair of the size and the type
+
+    @return whether pair creation completed
+    */
+    bool get_ubjson_size_type(std::pair<std::size_t, int>& result)
     {
-        BasicJsonType result = value_t::array;
-        std::generate_n(std::back_inserter(*result.m_value.array), len, [this]()
+        result.first = string_t::npos; // size
+        result.second = 0; // type
+
+        get_ignore_noop();
+
+        if (current == '$')
         {
-            return parse_cbor_internal();
-        });
-        return result;
-    }
+            result.second = get();  // must not ignore 'N', because 'N' maybe the type
+            if (JSON_UNLIKELY(not unexpect_eof(input_format_t::ubjson, "type")))
+            {
+                return false;
+            }
 
-    template<typename NumberType>
-    BasicJsonType get_cbor_object(const NumberType len)
-    {
-        BasicJsonType result = value_t::object;
-        std::generate_n(std::inserter(*result.m_value.object,
-                                      result.m_value.object->end()),
-                        len, [this]()
+            get_ignore_noop();
+            if (JSON_UNLIKELY(current != '#'))
+            {
+                if (JSON_UNLIKELY(not unexpect_eof(input_format_t::ubjson, "value")))
+                {
+                    return false;
+                }
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::ubjson, "expected '#' after type information; last byte: 0x" + last_token, "size")));
+            }
+
+            return get_ubjson_size_value(result.first);
+        }
+        else if (current == '#')
         {
-            get();
-            auto key = get_cbor_string();
-            auto val = parse_cbor_internal();
-            return std::make_pair(std::move(key), std::move(val));
-        });
-        return result;
+            return get_ubjson_size_value(result.first);
+        }
+        return true;
     }
 
     /*!
-    @brief reads a MessagePack string
+    @param prefix  the previously read or set type prefix
+    @return whether value creation completed
+    */
+    bool get_ubjson_value(const int prefix)
+    {
+        switch (prefix)
+        {
+            case std::char_traits<char>::eof():  // EOF
+                return unexpect_eof(input_format_t::ubjson, "value");
 
-    This function first reads starting bytes to determine the expected
-    string length and then copies this number of bytes into a string.
+            case 'T':  // true
+                return sax->boolean(true);
+            case 'F':  // false
+                return sax->boolean(false);
+
+            case 'Z':  // null
+                return sax->null();
 
-    @return string
+            case 'U':
+            {
+                uint8_t number;
+                return get_number(input_format_t::ubjson, number) and sax->number_unsigned(number);
+            }
+
+            case 'i':
+            {
+                int8_t number;
+                return get_number(input_format_t::ubjson, number) and sax->number_integer(number);
+            }
 
-    @throw parse_error.110 if input ended
-    @throw parse_error.113 if an unexpected byte is read
+            case 'I':
+            {
+                int16_t number;
+                return get_number(input_format_t::ubjson, number) and sax->number_integer(number);
+            }
+
+            case 'l':
+            {
+                int32_t number;
+                return get_number(input_format_t::ubjson, number) and sax->number_integer(number);
+            }
+
+            case 'L':
+            {
+                int64_t number;
+                return get_number(input_format_t::ubjson, number) and sax->number_integer(number);
+            }
+
+            case 'd':
+            {
+                float number;
+                return get_number(input_format_t::ubjson, number) and sax->number_float(static_cast<number_float_t>(number), "");
+            }
+
+            case 'D':
+            {
+                double number;
+                return get_number(input_format_t::ubjson, number) and sax->number_float(static_cast<number_float_t>(number), "");
+            }
+
+            case 'C':  // char
+            {
+                get();
+                if (JSON_UNLIKELY(not unexpect_eof(input_format_t::ubjson, "char")))
+                {
+                    return false;
+                }
+                if (JSON_UNLIKELY(current > 127))
+                {
+                    auto last_token = get_token_string();
+                    return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format_t::ubjson, "byte after 'C' must be in range 0x00..0x7F; last byte: 0x" + last_token, "char")));
+                }
+                string_t s(1, static_cast<char>(current));
+                return sax->string(s);
+            }
+
+            case 'S':  // string
+            {
+                string_t s;
+                return get_ubjson_string(s) and sax->string(s);
+            }
+
+            case '[':  // array
+                return get_ubjson_array();
+
+            case '{':  // object
+                return get_ubjson_object();
+
+            default: // anything else
+            {
+                auto last_token = get_token_string();
+                return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::ubjson, "invalid byte: 0x" + last_token, "value")));
+            }
+        }
+    }
+
+    /*!
+    @return whether array creation completed
     */
-    std::string get_msgpack_string()
+    bool get_ubjson_array()
     {
-        check_eof();
+        std::pair<std::size_t, int> size_and_type;
+        if (JSON_UNLIKELY(not get_ubjson_size_type(size_and_type)))
+        {
+            return false;
+        }
 
-        switch (current)
+        if (size_and_type.first != string_t::npos)
         {
-            // fixstr
-            case 0xA0:
-            case 0xA1:
-            case 0xA2:
-            case 0xA3:
-            case 0xA4:
-            case 0xA5:
-            case 0xA6:
-            case 0xA7:
-            case 0xA8:
-            case 0xA9:
-            case 0xAA:
-            case 0xAB:
-            case 0xAC:
-            case 0xAD:
-            case 0xAE:
-            case 0xAF:
-            case 0xB0:
-            case 0xB1:
-            case 0xB2:
-            case 0xB3:
-            case 0xB4:
-            case 0xB5:
-            case 0xB6:
-            case 0xB7:
-            case 0xB8:
-            case 0xB9:
-            case 0xBA:
-            case 0xBB:
-            case 0xBC:
-            case 0xBD:
-            case 0xBE:
-            case 0xBF:
+            if (JSON_UNLIKELY(not sax->start_array(size_and_type.first)))
             {
-                return get_string(current & 0x1F);
+                return false;
             }
 
-            case 0xD9: // str 8
+            if (size_and_type.second != 0)
             {
-                return get_string(get_number<uint8_t>());
+                if (size_and_type.second != 'N')
+                {
+                    for (std::size_t i = 0; i < size_and_type.first; ++i)
+                    {
+                        if (JSON_UNLIKELY(not get_ubjson_value(size_and_type.second)))
+                        {
+                            return false;
+                        }
+                    }
+                }
+            }
+            else
+            {
+                for (std::size_t i = 0; i < size_and_type.first; ++i)
+                {
+                    if (JSON_UNLIKELY(not parse_ubjson_internal()))
+                    {
+                        return false;
+                    }
+                }
+            }
+        }
+        else
+        {
+            if (JSON_UNLIKELY(not sax->start_array(std::size_t(-1))))
+            {
+                return false;
             }
 
-            case 0xDA: // str 16
+            while (current != ']')
             {
-                return get_string(get_number<uint16_t>());
+                if (JSON_UNLIKELY(not parse_ubjson_internal(false)))
+                {
+                    return false;
+                }
+                get_ignore_noop();
             }
+        }
 
-            case 0xDB: // str 32
+        return sax->end_array();
+    }
+
+    /*!
+    @return whether object creation completed
+    */
+    bool get_ubjson_object()
+    {
+        std::pair<std::size_t, int> size_and_type;
+        if (JSON_UNLIKELY(not get_ubjson_size_type(size_and_type)))
+        {
+            return false;
+        }
+
+        string_t key;
+        if (size_and_type.first != string_t::npos)
+        {
+            if (JSON_UNLIKELY(not sax->start_object(size_and_type.first)))
             {
-                return get_string(get_number<uint32_t>());
+                return false;
             }
 
-            default:
+            if (size_and_type.second != 0)
             {
-                std::stringstream ss;
-                ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << current;
-                JSON_THROW(parse_error::create(113, chars_read,
-                                               "expected a MessagePack string; last byte: 0x" + ss.str()));
+                for (std::size_t i = 0; i < size_and_type.first; ++i)
+                {
+                    if (JSON_UNLIKELY(not get_ubjson_string(key) or not sax->key(key)))
+                    {
+                        return false;
+                    }
+                    if (JSON_UNLIKELY(not get_ubjson_value(size_and_type.second)))
+                    {
+                        return false;
+                    }
+                    key.clear();
+                }
+            }
+            else
+            {
+                for (std::size_t i = 0; i < size_and_type.first; ++i)
+                {
+                    if (JSON_UNLIKELY(not get_ubjson_string(key) or not sax->key(key)))
+                    {
+                        return false;
+                    }
+                    if (JSON_UNLIKELY(not parse_ubjson_internal()))
+                    {
+                        return false;
+                    }
+                    key.clear();
+                }
+            }
+        }
+        else
+        {
+            if (JSON_UNLIKELY(not sax->start_object(std::size_t(-1))))
+            {
+                return false;
+            }
+
+            while (current != '}')
+            {
+                if (JSON_UNLIKELY(not get_ubjson_string(key, false) or not sax->key(key)))
+                {
+                    return false;
+                }
+                if (JSON_UNLIKELY(not parse_ubjson_internal()))
+                {
+                    return false;
+                }
+                get_ignore_noop();
+                key.clear();
             }
         }
+
+        return sax->end_object();
     }
 
-    template<typename NumberType>
-    BasicJsonType get_msgpack_array(const NumberType len)
+    ///////////////////////
+    // Utility functions //
+    ///////////////////////
+
+    /*!
+    @brief get next character from the input
+
+    This function provides the interface to the used input adapter. It does
+    not throw in case the input reached EOF, but returns a -'ve valued
+    `std::char_traits<char>::eof()` in that case.
+
+    @return character read from the input
+    */
+    int get()
     {
-        BasicJsonType result = value_t::array;
-        std::generate_n(std::back_inserter(*result.m_value.array), len, [this]()
-        {
-            return parse_msgpack_internal();
-        });
-        return result;
+        ++chars_read;
+        return (current = ia->get_character());
     }
 
-    template<typename NumberType>
-    BasicJsonType get_msgpack_object(const NumberType len)
+    /*!
+    @return character read from the input after ignoring all 'N' entries
+    */
+    int get_ignore_noop()
     {
-        BasicJsonType result = value_t::object;
-        std::generate_n(std::inserter(*result.m_value.object,
-                                      result.m_value.object->end()),
-                        len, [this]()
+        do
         {
             get();
-            auto key = get_msgpack_string();
-            auto val = parse_msgpack_internal();
-            return std::make_pair(std::move(key), std::move(val));
-        });
-        return result;
+        }
+        while (current == 'N');
+
+        return current;
     }
 
-    /*!
-    @brief check if input ended
-    @throw parse_error.110 if input ended
+    /*
+    @brief read a number from the input
+
+    @tparam NumberType the type of the number
+    @param[in] format   the current format (for diagnostics)
+    @param[out] result  number of type @a NumberType
+
+    @return whether conversion completed
+
+    @note This function needs to respect the system's endianess, because
+          bytes in CBOR, MessagePack, and UBJSON are stored in network order
+          (big endian) and therefore need reordering on little endian systems.
     */
-    void check_eof(const bool expect_eof = false) const
+    template<typename NumberType, bool InputIsLittleEndian = false>
+    bool get_number(const input_format_t format, NumberType& result)
     {
-        if (expect_eof)
+        // step 1: read input into array with system's byte order
+        std::array<uint8_t, sizeof(NumberType)> vec;
+        for (std::size_t i = 0; i < sizeof(NumberType); ++i)
         {
-            if (JSON_UNLIKELY(current != std::char_traits<char>::eof()))
+            get();
+            if (JSON_UNLIKELY(not unexpect_eof(format, "number")))
             {
-                JSON_THROW(parse_error::create(110, chars_read, "expected end of input"));
+                return false;
+            }
+
+            // reverse byte order prior to conversion if necessary
+            if (is_little_endian && !InputIsLittleEndian)
+            {
+                vec[sizeof(NumberType) - i - 1] = static_cast<uint8_t>(current);
+            }
+            else
+            {
+                vec[i] = static_cast<uint8_t>(current); // LCOV_EXCL_LINE
             }
         }
-        else
+
+        // step 2: convert array into number of type T and return
+        std::memcpy(&result, vec.data(), sizeof(NumberType));
+        return true;
+    }
+
+    /*!
+    @brief create a string by reading characters from the input
+
+    @tparam NumberType the type of the number
+    @param[in] format the current format (for diagnostics)
+    @param[in] len number of characters to read
+    @param[out] result string created by reading @a len bytes
+
+    @return whether string creation completed
+
+    @note We can not reserve @a len bytes for the result, because @a len
+          may be too large. Usually, @ref unexpect_eof() detects the end of
+          the input before we run out of string memory.
+    */
+    template<typename NumberType>
+    bool get_string(const input_format_t format,
+                    const NumberType len,
+                    string_t& result)
+    {
+        bool success = true;
+        std::generate_n(std::back_inserter(result), len, [this, &success, &format]()
         {
-            if (JSON_UNLIKELY(current == std::char_traits<char>::eof()))
+            get();
+            if (JSON_UNLIKELY(not unexpect_eof(format, "string")))
             {
-                JSON_THROW(parse_error::create(110, chars_read, "unexpected end of input"));
+                success = false;
             }
+            return static_cast<char>(current);
+        });
+        return success;
+    }
+
+    /*!
+    @param[in] format   the current format (for diagnostics)
+    @param[in] context  further context information (for diagnostics)
+    @return whether the last read character is not EOF
+    */
+    bool unexpect_eof(const input_format_t format, const char* context) const
+    {
+        if (JSON_UNLIKELY(current == std::char_traits<char>::eof()))
+        {
+            return sax->parse_error(chars_read, "<end of file>",
+                                    parse_error::create(110, chars_read, exception_message(format, "unexpected end of input", context)));
+        }
+        return true;
+    }
+
+    /*!
+    @return a string representation of the last read byte
+    */
+    std::string get_token_string() const
+    {
+        char cr[3];
+        (std::snprintf)(cr, 3, "%.2hhX", static_cast<unsigned char>(current));
+        return std::string{cr};
+    }
+
+    /*!
+    @param[in] format   the current format
+    @param[in] detail   a detailed error message
+    @param[in] context  further contect information
+    @return a message string to use in the parse_error exceptions
+    */
+    std::string exception_message(const input_format_t format,
+                                  const std::string& detail,
+                                  const std::string& context) const
+    {
+        std::string error_msg = "syntax error while parsing ";
+
+        switch (format)
+        {
+            case input_format_t::cbor:
+                error_msg += "CBOR";
+                break;
+
+            case input_format_t::msgpack:
+                error_msg += "MessagePack";
+                break;
+
+            case input_format_t::ubjson:
+                error_msg += "UBJSON";
+                break;
+
+            case input_format_t::bson:
+                error_msg += "BSON";
+                break;
+
+            // LCOV_EXCL_START
+            default:
+                assert(false);
+                // LCOV_EXCL_STOP
         }
+
+        return error_msg + " " + context + ": " + detail;
     }
 
   private:
@@ -5529,7 +8429,34 @@ class binary_reader
 
     /// whether we can assume little endianess
     const bool is_little_endian = little_endianess();
+
+    /// the SAX parser
+    json_sax_t* sax = nullptr;
 };
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/output/binary_writer.hpp>
+
+
+#include <algorithm> // reverse
+#include <array> // array
+#include <cstdint> // uint8_t, uint16_t, uint32_t, uint64_t
+#include <cstring> // memcpy
+#include <limits> // numeric_limits
+
+// #include <nlohmann/detail/input/binary_reader.hpp>
+
+// #include <nlohmann/detail/output/output_adapters.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+///////////////////
+// binary writer //
+///////////////////
 
 /*!
 @brief serialization to CBOR and MessagePack values
@@ -5537,6 +8464,8 @@ class binary_reader
 template<typename BasicJsonType, typename CharType>
 class binary_writer
 {
+    using string_t = typename BasicJsonType::string_t;
+
   public:
     /*!
     @brief create a binary writer
@@ -5549,7 +8478,28 @@ class binary_writer
     }
 
     /*!
-    @brief[in] j  JSON value to serialize
+    @param[in] j  JSON value to serialize
+    @pre       j.type() == value_t::object
+    */
+    void write_bson(const BasicJsonType& j)
+    {
+        switch (j.type())
+        {
+            case value_t::object:
+            {
+                write_bson_object(*j.m_value.object);
+                break;
+            }
+
+            default:
+            {
+                JSON_THROW(type_error::create(317, "to serialize to BSON, top-level type must be object, but is " + std::string(j.type_name())));
+            }
+        }
+    }
+
+    /*!
+    @param[in] j  JSON value to serialize
     */
     void write_cbor(const BasicJsonType& j)
     {
@@ -5557,15 +8507,15 @@ class binary_writer
         {
             case value_t::null:
             {
-                oa->write_character(static_cast<CharType>(0xF6));
+                oa->write_character(to_char_type(0xF6));
                 break;
             }
 
             case value_t::boolean:
             {
                 oa->write_character(j.m_value.boolean
-                                    ? static_cast<CharType>(0xF5)
-                                    : static_cast<CharType>(0xF4));
+                                    ? to_char_type(0xF5)
+                                    : to_char_type(0xF4));
                 break;
             }
 
@@ -5582,22 +8532,22 @@ class binary_writer
                     }
                     else if (j.m_value.number_integer <= (std::numeric_limits<uint8_t>::max)())
                     {
-                        oa->write_character(static_cast<CharType>(0x18));
+                        oa->write_character(to_char_type(0x18));
                         write_number(static_cast<uint8_t>(j.m_value.number_integer));
                     }
                     else if (j.m_value.number_integer <= (std::numeric_limits<uint16_t>::max)())
                     {
-                        oa->write_character(static_cast<CharType>(0x19));
+                        oa->write_character(to_char_type(0x19));
                         write_number(static_cast<uint16_t>(j.m_value.number_integer));
                     }
                     else if (j.m_value.number_integer <= (std::numeric_limits<uint32_t>::max)())
                     {
-                        oa->write_character(static_cast<CharType>(0x1A));
+                        oa->write_character(to_char_type(0x1A));
                         write_number(static_cast<uint32_t>(j.m_value.number_integer));
                     }
                     else
                     {
-                        oa->write_character(static_cast<CharType>(0x1B));
+                        oa->write_character(to_char_type(0x1B));
                         write_number(static_cast<uint64_t>(j.m_value.number_integer));
                     }
                 }
@@ -5612,22 +8562,22 @@ class binary_writer
                     }
                     else if (positive_number <= (std::numeric_limits<uint8_t>::max)())
                     {
-                        oa->write_character(static_cast<CharType>(0x38));
+                        oa->write_character(to_char_type(0x38));
                         write_number(static_cast<uint8_t>(positive_number));
                     }
                     else if (positive_number <= (std::numeric_limits<uint16_t>::max)())
                     {
-                        oa->write_character(static_cast<CharType>(0x39));
+                        oa->write_character(to_char_type(0x39));
                         write_number(static_cast<uint16_t>(positive_number));
                     }
                     else if (positive_number <= (std::numeric_limits<uint32_t>::max)())
                     {
-                        oa->write_character(static_cast<CharType>(0x3A));
+                        oa->write_character(to_char_type(0x3A));
                         write_number(static_cast<uint32_t>(positive_number));
                     }
                     else
                     {
-                        oa->write_character(static_cast<CharType>(0x3B));
+                        oa->write_character(to_char_type(0x3B));
                         write_number(static_cast<uint64_t>(positive_number));
                     }
                 }
@@ -5642,30 +8592,30 @@ class binary_writer
                 }
                 else if (j.m_value.number_unsigned <= (std::numeric_limits<uint8_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x18));
+                    oa->write_character(to_char_type(0x18));
                     write_number(static_cast<uint8_t>(j.m_value.number_unsigned));
                 }
                 else if (j.m_value.number_unsigned <= (std::numeric_limits<uint16_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x19));
+                    oa->write_character(to_char_type(0x19));
                     write_number(static_cast<uint16_t>(j.m_value.number_unsigned));
                 }
                 else if (j.m_value.number_unsigned <= (std::numeric_limits<uint32_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x1A));
+                    oa->write_character(to_char_type(0x1A));
                     write_number(static_cast<uint32_t>(j.m_value.number_unsigned));
                 }
                 else
                 {
-                    oa->write_character(static_cast<CharType>(0x1B));
+                    oa->write_character(to_char_type(0x1B));
                     write_number(static_cast<uint64_t>(j.m_value.number_unsigned));
                 }
                 break;
             }
 
-            case value_t::number_float: // Double-Precision Float
+            case value_t::number_float:
             {
-                oa->write_character(static_cast<CharType>(0xFB));
+                oa->write_character(get_cbor_float_prefix(j.m_value.number_float));
                 write_number(j.m_value.number_float);
                 break;
             }
@@ -5678,25 +8628,25 @@ class binary_writer
                 {
                     write_number(static_cast<uint8_t>(0x60 + N));
                 }
-                else if (N <= 0xFF)
+                else if (N <= (std::numeric_limits<uint8_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x78));
+                    oa->write_character(to_char_type(0x78));
                     write_number(static_cast<uint8_t>(N));
                 }
-                else if (N <= 0xFFFF)
+                else if (N <= (std::numeric_limits<uint16_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x79));
+                    oa->write_character(to_char_type(0x79));
                     write_number(static_cast<uint16_t>(N));
                 }
-                else if (N <= 0xFFFFFFFF)
+                else if (N <= (std::numeric_limits<uint32_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x7A));
+                    oa->write_character(to_char_type(0x7A));
                     write_number(static_cast<uint32_t>(N));
                 }
                 // LCOV_EXCL_START
-                else if (N <= 0xFFFFFFFFFFFFFFFF)
+                else if (N <= (std::numeric_limits<uint64_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x7B));
+                    oa->write_character(to_char_type(0x7B));
                     write_number(static_cast<uint64_t>(N));
                 }
                 // LCOV_EXCL_STOP
@@ -5716,25 +8666,25 @@ class binary_writer
                 {
                     write_number(static_cast<uint8_t>(0x80 + N));
                 }
-                else if (N <= 0xFF)
+                else if (N <= (std::numeric_limits<uint8_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x98));
+                    oa->write_character(to_char_type(0x98));
                     write_number(static_cast<uint8_t>(N));
                 }
-                else if (N <= 0xFFFF)
+                else if (N <= (std::numeric_limits<uint16_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x99));
+                    oa->write_character(to_char_type(0x99));
                     write_number(static_cast<uint16_t>(N));
                 }
-                else if (N <= 0xFFFFFFFF)
+                else if (N <= (std::numeric_limits<uint32_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x9A));
+                    oa->write_character(to_char_type(0x9A));
                     write_number(static_cast<uint32_t>(N));
                 }
                 // LCOV_EXCL_START
-                else if (N <= 0xFFFFFFFFFFFFFFFF)
+                else if (N <= (std::numeric_limits<uint64_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0x9B));
+                    oa->write_character(to_char_type(0x9B));
                     write_number(static_cast<uint64_t>(N));
                 }
                 // LCOV_EXCL_STOP
@@ -5755,25 +8705,25 @@ class binary_writer
                 {
                     write_number(static_cast<uint8_t>(0xA0 + N));
                 }
-                else if (N <= 0xFF)
+                else if (N <= (std::numeric_limits<uint8_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0xB8));
+                    oa->write_character(to_char_type(0xB8));
                     write_number(static_cast<uint8_t>(N));
                 }
-                else if (N <= 0xFFFF)
+                else if (N <= (std::numeric_limits<uint16_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0xB9));
+                    oa->write_character(to_char_type(0xB9));
                     write_number(static_cast<uint16_t>(N));
                 }
-                else if (N <= 0xFFFFFFFF)
+                else if (N <= (std::numeric_limits<uint32_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0xBA));
+                    oa->write_character(to_char_type(0xBA));
                     write_number(static_cast<uint32_t>(N));
                 }
                 // LCOV_EXCL_START
-                else if (N <= 0xFFFFFFFFFFFFFFFF)
+                else if (N <= (std::numeric_limits<uint64_t>::max)())
                 {
-                    oa->write_character(static_cast<CharType>(0xBB));
+                    oa->write_character(to_char_type(0xBB));
                     write_number(static_cast<uint64_t>(N));
                 }
                 // LCOV_EXCL_STOP
@@ -5793,7 +8743,7 @@ class binary_writer
     }
 
     /*!
-    @brief[in] j  JSON value to serialize
+    @param[in] j  JSON value to serialize
     */
     void write_msgpack(const BasicJsonType& j)
     {
@@ -5801,15 +8751,15 @@ class binary_writer
         {
             case value_t::null: // nil
             {
-                oa->write_character(static_cast<CharType>(0xC0));
+                oa->write_character(to_char_type(0xC0));
                 break;
             }
 
             case value_t::boolean: // true and false
             {
                 oa->write_character(j.m_value.boolean
-                                    ? static_cast<CharType>(0xC3)
-                                    : static_cast<CharType>(0xC2));
+                                    ? to_char_type(0xC3)
+                                    : to_char_type(0xC2));
                 break;
             }
 
@@ -5828,25 +8778,25 @@ class binary_writer
                     else if (j.m_value.number_unsigned <= (std::numeric_limits<uint8_t>::max)())
                     {
                         // uint 8
-                        oa->write_character(static_cast<CharType>(0xCC));
+                        oa->write_character(to_char_type(0xCC));
                         write_number(static_cast<uint8_t>(j.m_value.number_integer));
                     }
                     else if (j.m_value.number_unsigned <= (std::numeric_limits<uint16_t>::max)())
                     {
                         // uint 16
-                        oa->write_character(static_cast<CharType>(0xCD));
+                        oa->write_character(to_char_type(0xCD));
                         write_number(static_cast<uint16_t>(j.m_value.number_integer));
                     }
                     else if (j.m_value.number_unsigned <= (std::numeric_limits<uint32_t>::max)())
                     {
                         // uint 32
-                        oa->write_character(static_cast<CharType>(0xCE));
+                        oa->write_character(to_char_type(0xCE));
                         write_number(static_cast<uint32_t>(j.m_value.number_integer));
                     }
                     else if (j.m_value.number_unsigned <= (std::numeric_limits<uint64_t>::max)())
                     {
                         // uint 64
-                        oa->write_character(static_cast<CharType>(0xCF));
+                        oa->write_character(to_char_type(0xCF));
                         write_number(static_cast<uint64_t>(j.m_value.number_integer));
                     }
                 }
@@ -5861,28 +8811,28 @@ class binary_writer
                              j.m_value.number_integer <= (std::numeric_limits<int8_t>::max)())
                     {
                         // int 8
-                        oa->write_character(static_cast<CharType>(0xD0));
+                        oa->write_character(to_char_type(0xD0));
                         write_number(static_cast<int8_t>(j.m_value.number_integer));
                     }
                     else if (j.m_value.number_integer >= (std::numeric_limits<int16_t>::min)() and
                              j.m_value.number_integer <= (std::numeric_limits<int16_t>::max)())
                     {
                         // int 16
-                        oa->write_character(static_cast<CharType>(0xD1));
+                        oa->write_character(to_char_type(0xD1));
                         write_number(static_cast<int16_t>(j.m_value.number_integer));
                     }
                     else if (j.m_value.number_integer >= (std::numeric_limits<int32_t>::min)() and
                              j.m_value.number_integer <= (std::numeric_limits<int32_t>::max)())
                     {
                         // int 32
-                        oa->write_character(static_cast<CharType>(0xD2));
+                        oa->write_character(to_char_type(0xD2));
                         write_number(static_cast<int32_t>(j.m_value.number_integer));
                     }
                     else if (j.m_value.number_integer >= (std::numeric_limits<int64_t>::min)() and
                              j.m_value.number_integer <= (std::numeric_limits<int64_t>::max)())
                     {
                         // int 64
-                        oa->write_character(static_cast<CharType>(0xD3));
+                        oa->write_character(to_char_type(0xD3));
                         write_number(static_cast<int64_t>(j.m_value.number_integer));
                     }
                 }
@@ -5899,33 +8849,33 @@ class binary_writer
                 else if (j.m_value.number_unsigned <= (std::numeric_limits<uint8_t>::max)())
                 {
                     // uint 8
-                    oa->write_character(static_cast<CharType>(0xCC));
+                    oa->write_character(to_char_type(0xCC));
                     write_number(static_cast<uint8_t>(j.m_value.number_integer));
                 }
                 else if (j.m_value.number_unsigned <= (std::numeric_limits<uint16_t>::max)())
                 {
                     // uint 16
-                    oa->write_character(static_cast<CharType>(0xCD));
+                    oa->write_character(to_char_type(0xCD));
                     write_number(static_cast<uint16_t>(j.m_value.number_integer));
                 }
                 else if (j.m_value.number_unsigned <= (std::numeric_limits<uint32_t>::max)())
                 {
                     // uint 32
-                    oa->write_character(static_cast<CharType>(0xCE));
+                    oa->write_character(to_char_type(0xCE));
                     write_number(static_cast<uint32_t>(j.m_value.number_integer));
                 }
                 else if (j.m_value.number_unsigned <= (std::numeric_limits<uint64_t>::max)())
                 {
                     // uint 64
-                    oa->write_character(static_cast<CharType>(0xCF));
+                    oa->write_character(to_char_type(0xCF));
                     write_number(static_cast<uint64_t>(j.m_value.number_integer));
                 }
                 break;
             }
 
-            case value_t::number_float: // float 64
+            case value_t::number_float:
             {
-                oa->write_character(static_cast<CharType>(0xCB));
+                oa->write_character(get_msgpack_float_prefix(j.m_value.number_float));
                 write_number(j.m_value.number_float);
                 break;
             }
@@ -5939,22 +8889,22 @@ class binary_writer
                     // fixstr
                     write_number(static_cast<uint8_t>(0xA0 | N));
                 }
-                else if (N <= 255)
+                else if (N <= (std::numeric_limits<uint8_t>::max)())
                 {
                     // str 8
-                    oa->write_character(static_cast<CharType>(0xD9));
+                    oa->write_character(to_char_type(0xD9));
                     write_number(static_cast<uint8_t>(N));
                 }
-                else if (N <= 65535)
+                else if (N <= (std::numeric_limits<uint16_t>::max)())
                 {
                     // str 16
-                    oa->write_character(static_cast<CharType>(0xDA));
+                    oa->write_character(to_char_type(0xDA));
                     write_number(static_cast<uint16_t>(N));
                 }
-                else if (N <= 4294967295)
+                else if (N <= (std::numeric_limits<uint32_t>::max)())
                 {
                     // str 32
-                    oa->write_character(static_cast<CharType>(0xDB));
+                    oa->write_character(to_char_type(0xDB));
                     write_number(static_cast<uint32_t>(N));
                 }
 
@@ -5974,16 +8924,16 @@ class binary_writer
                     // fixarray
                     write_number(static_cast<uint8_t>(0x90 | N));
                 }
-                else if (N <= 0xFFFF)
+                else if (N <= (std::numeric_limits<uint16_t>::max)())
                 {
                     // array 16
-                    oa->write_character(static_cast<CharType>(0xDC));
+                    oa->write_character(to_char_type(0xDC));
                     write_number(static_cast<uint16_t>(N));
                 }
-                else if (N <= 0xFFFFFFFF)
+                else if (N <= (std::numeric_limits<uint32_t>::max)())
                 {
                     // array 32
-                    oa->write_character(static_cast<CharType>(0xDD));
+                    oa->write_character(to_char_type(0xDD));
                     write_number(static_cast<uint32_t>(N));
                 }
 
@@ -6004,16 +8954,16 @@ class binary_writer
                     // fixmap
                     write_number(static_cast<uint8_t>(0x80 | (N & 0xF)));
                 }
-                else if (N <= 65535)
+                else if (N <= (std::numeric_limits<uint16_t>::max)())
                 {
                     // map 16
-                    oa->write_character(static_cast<CharType>(0xDE));
+                    oa->write_character(to_char_type(0xDE));
                     write_number(static_cast<uint16_t>(N));
                 }
-                else if (N <= 4294967295)
+                else if (N <= (std::numeric_limits<uint32_t>::max)())
                 {
                     // map 32
-                    oa->write_character(static_cast<CharType>(0xDF));
+                    oa->write_character(to_char_type(0xDF));
                     write_number(static_cast<uint32_t>(N));
                 }
 
@@ -6031,25 +8981,745 @@ class binary_writer
         }
     }
 
+    /*!
+    @param[in] j  JSON value to serialize
+    @param[in] use_count   whether to use '#' prefixes (optimized format)
+    @param[in] use_type    whether to use '$' prefixes (optimized format)
+    @param[in] add_prefix  whether prefixes need to be used for this value
+    */
+    void write_ubjson(const BasicJsonType& j, const bool use_count,
+                      const bool use_type, const bool add_prefix = true)
+    {
+        switch (j.type())
+        {
+            case value_t::null:
+            {
+                if (add_prefix)
+                {
+                    oa->write_character(to_char_type('Z'));
+                }
+                break;
+            }
+
+            case value_t::boolean:
+            {
+                if (add_prefix)
+                {
+                    oa->write_character(j.m_value.boolean
+                                        ? to_char_type('T')
+                                        : to_char_type('F'));
+                }
+                break;
+            }
+
+            case value_t::number_integer:
+            {
+                write_number_with_ubjson_prefix(j.m_value.number_integer, add_prefix);
+                break;
+            }
+
+            case value_t::number_unsigned:
+            {
+                write_number_with_ubjson_prefix(j.m_value.number_unsigned, add_prefix);
+                break;
+            }
+
+            case value_t::number_float:
+            {
+                write_number_with_ubjson_prefix(j.m_value.number_float, add_prefix);
+                break;
+            }
+
+            case value_t::string:
+            {
+                if (add_prefix)
+                {
+                    oa->write_character(to_char_type('S'));
+                }
+                write_number_with_ubjson_prefix(j.m_value.string->size(), true);
+                oa->write_characters(
+                    reinterpret_cast<const CharType*>(j.m_value.string->c_str()),
+                    j.m_value.string->size());
+                break;
+            }
+
+            case value_t::array:
+            {
+                if (add_prefix)
+                {
+                    oa->write_character(to_char_type('['));
+                }
+
+                bool prefix_required = true;
+                if (use_type and not j.m_value.array->empty())
+                {
+                    assert(use_count);
+                    const CharType first_prefix = ubjson_prefix(j.front());
+                    const bool same_prefix = std::all_of(j.begin() + 1, j.end(),
+                                                         [this, first_prefix](const BasicJsonType & v)
+                    {
+                        return ubjson_prefix(v) == first_prefix;
+                    });
+
+                    if (same_prefix)
+                    {
+                        prefix_required = false;
+                        oa->write_character(to_char_type('$'));
+                        oa->write_character(first_prefix);
+                    }
+                }
+
+                if (use_count)
+                {
+                    oa->write_character(to_char_type('#'));
+                    write_number_with_ubjson_prefix(j.m_value.array->size(), true);
+                }
+
+                for (const auto& el : *j.m_value.array)
+                {
+                    write_ubjson(el, use_count, use_type, prefix_required);
+                }
+
+                if (not use_count)
+                {
+                    oa->write_character(to_char_type(']'));
+                }
+
+                break;
+            }
+
+            case value_t::object:
+            {
+                if (add_prefix)
+                {
+                    oa->write_character(to_char_type('{'));
+                }
+
+                bool prefix_required = true;
+                if (use_type and not j.m_value.object->empty())
+                {
+                    assert(use_count);
+                    const CharType first_prefix = ubjson_prefix(j.front());
+                    const bool same_prefix = std::all_of(j.begin(), j.end(),
+                                                         [this, first_prefix](const BasicJsonType & v)
+                    {
+                        return ubjson_prefix(v) == first_prefix;
+                    });
+
+                    if (same_prefix)
+                    {
+                        prefix_required = false;
+                        oa->write_character(to_char_type('$'));
+                        oa->write_character(first_prefix);
+                    }
+                }
+
+                if (use_count)
+                {
+                    oa->write_character(to_char_type('#'));
+                    write_number_with_ubjson_prefix(j.m_value.object->size(), true);
+                }
+
+                for (const auto& el : *j.m_value.object)
+                {
+                    write_number_with_ubjson_prefix(el.first.size(), true);
+                    oa->write_characters(
+                        reinterpret_cast<const CharType*>(el.first.c_str()),
+                        el.first.size());
+                    write_ubjson(el.second, use_count, use_type, prefix_required);
+                }
+
+                if (not use_count)
+                {
+                    oa->write_character(to_char_type('}'));
+                }
+
+                break;
+            }
+
+            default:
+                break;
+        }
+    }
+
   private:
+    //////////
+    // BSON //
+    //////////
+
+    /*!
+    @return The size of a BSON document entry header, including the id marker
+            and the entry name size (and its null-terminator).
+    */
+    static std::size_t calc_bson_entry_header_size(const string_t& name)
+    {
+        const auto it = name.find(static_cast<typename string_t::value_type>(0));
+        if (JSON_UNLIKELY(it != BasicJsonType::string_t::npos))
+        {
+            JSON_THROW(out_of_range::create(409,
+                                            "BSON key cannot contain code point U+0000 (at byte " + std::to_string(it) + ")"));
+        }
+
+        return /*id*/ 1ul + name.size() + /*zero-terminator*/1u;
+    }
+
+    /*!
+    @brief Writes the given @a element_type and @a name to the output adapter
+    */
+    void write_bson_entry_header(const string_t& name,
+                                 const std::uint8_t element_type)
+    {
+        oa->write_character(to_char_type(element_type)); // boolean
+        oa->write_characters(
+            reinterpret_cast<const CharType*>(name.c_str()),
+            name.size() + 1u);
+    }
+
+    /*!
+    @brief Writes a BSON element with key @a name and boolean value @a value
+    */
+    void write_bson_boolean(const string_t& name,
+                            const bool value)
+    {
+        write_bson_entry_header(name, 0x08);
+        oa->write_character(value ? to_char_type(0x01) : to_char_type(0x00));
+    }
+
+    /*!
+    @brief Writes a BSON element with key @a name and double value @a value
+    */
+    void write_bson_double(const string_t& name,
+                           const double value)
+    {
+        write_bson_entry_header(name, 0x01);
+        write_number<double, true>(value);
+    }
+
+    /*!
+    @return The size of the BSON-encoded string in @a value
+    */
+    static std::size_t calc_bson_string_size(const string_t& value)
+    {
+        return sizeof(std::int32_t) + value.size() + 1ul;
+    }
+
+    /*!
+    @brief Writes a BSON element with key @a name and string value @a value
+    */
+    void write_bson_string(const string_t& name,
+                           const string_t& value)
+    {
+        write_bson_entry_header(name, 0x02);
+
+        write_number<std::int32_t, true>(static_cast<std::int32_t>(value.size() + 1ul));
+        oa->write_characters(
+            reinterpret_cast<const CharType*>(value.c_str()),
+            value.size() + 1);
+    }
+
+    /*!
+    @brief Writes a BSON element with key @a name and null value
+    */
+    void write_bson_null(const string_t& name)
+    {
+        write_bson_entry_header(name, 0x0A);
+    }
+
+    /*!
+    @return The size of the BSON-encoded integer @a value
+    */
+    static std::size_t calc_bson_integer_size(const std::int64_t value)
+    {
+        if ((std::numeric_limits<std::int32_t>::min)() <= value and value <= (std::numeric_limits<std::int32_t>::max)())
+        {
+            return sizeof(std::int32_t);
+        }
+        else
+        {
+            return sizeof(std::int64_t);
+        }
+    }
+
+    /*!
+    @brief Writes a BSON element with key @a name and integer @a value
+    */
+    void write_bson_integer(const string_t& name,
+                            const std::int64_t value)
+    {
+        if ((std::numeric_limits<std::int32_t>::min)() <= value and value <= (std::numeric_limits<std::int32_t>::max)())
+        {
+            write_bson_entry_header(name, 0x10); // int32
+            write_number<std::int32_t, true>(static_cast<std::int32_t>(value));
+        }
+        else
+        {
+            write_bson_entry_header(name, 0x12); // int64
+            write_number<std::int64_t, true>(static_cast<std::int64_t>(value));
+        }
+    }
+
+    /*!
+    @return The size of the BSON-encoded unsigned integer in @a j
+    */
+    static constexpr std::size_t calc_bson_unsigned_size(const std::uint64_t value) noexcept
+    {
+        return (value <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
+               ? sizeof(std::int32_t)
+               : sizeof(std::int64_t);
+    }
+
+    /*!
+    @brief Writes a BSON element with key @a name and unsigned @a value
+    */
+    void write_bson_unsigned(const string_t& name,
+                             const std::uint64_t value)
+    {
+        if (value <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
+        {
+            write_bson_entry_header(name, 0x10 /* int32 */);
+            write_number<std::int32_t, true>(static_cast<std::int32_t>(value));
+        }
+        else if (value <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
+        {
+            write_bson_entry_header(name, 0x12 /* int64 */);
+            write_number<std::int64_t, true>(static_cast<std::int64_t>(value));
+        }
+        else
+        {
+            JSON_THROW(out_of_range::create(407, "integer number " + std::to_string(value) + " cannot be represented by BSON as it does not fit int64"));
+        }
+    }
+
+    /*!
+    @brief Writes a BSON element with key @a name and object @a value
+    */
+    void write_bson_object_entry(const string_t& name,
+                                 const typename BasicJsonType::object_t& value)
+    {
+        write_bson_entry_header(name, 0x03); // object
+        write_bson_object(value);
+    }
+
+    /*!
+    @return The size of the BSON-encoded array @a value
+    */
+    static std::size_t calc_bson_array_size(const typename BasicJsonType::array_t& value)
+    {
+        std::size_t embedded_document_size = 0ul;
+        std::size_t array_index = 0ul;
+
+        for (const auto& el : value)
+        {
+            embedded_document_size += calc_bson_element_size(std::to_string(array_index++), el);
+        }
+
+        return sizeof(std::int32_t) + embedded_document_size + 1ul;
+    }
+
+    /*!
+    @brief Writes a BSON element with key @a name and array @a value
+    */
+    void write_bson_array(const string_t& name,
+                          const typename BasicJsonType::array_t& value)
+    {
+        write_bson_entry_header(name, 0x04); // array
+        write_number<std::int32_t, true>(static_cast<std::int32_t>(calc_bson_array_size(value)));
+
+        std::size_t array_index = 0ul;
+
+        for (const auto& el : value)
+        {
+            write_bson_element(std::to_string(array_index++), el);
+        }
+
+        oa->write_character(to_char_type(0x00));
+    }
+
+    /*!
+    @brief Calculates the size necessary to serialize the JSON value @a j with its @a name
+    @return The calculated size for the BSON document entry for @a j with the given @a name.
+    */
+    static std::size_t calc_bson_element_size(const string_t& name,
+            const BasicJsonType& j)
+    {
+        const auto header_size = calc_bson_entry_header_size(name);
+        switch (j.type())
+        {
+            case value_t::object:
+                return header_size + calc_bson_object_size(*j.m_value.object);
+
+            case value_t::array:
+                return header_size + calc_bson_array_size(*j.m_value.array);
+
+            case value_t::boolean:
+                return header_size + 1ul;
+
+            case value_t::number_float:
+                return header_size + 8ul;
+
+            case value_t::number_integer:
+                return header_size + calc_bson_integer_size(j.m_value.number_integer);
+
+            case value_t::number_unsigned:
+                return header_size + calc_bson_unsigned_size(j.m_value.number_unsigned);
+
+            case value_t::string:
+                return header_size + calc_bson_string_size(*j.m_value.string);
+
+            case value_t::null:
+                return header_size + 0ul;
+
+            // LCOV_EXCL_START
+            default:
+                assert(false);
+                return 0ul;
+                // LCOV_EXCL_STOP
+        };
+    }
+
+    /*!
+    @brief Serializes the JSON value @a j to BSON and associates it with the
+           key @a name.
+    @param name The name to associate with the JSON entity @a j within the
+                current BSON document
+    @return The size of the BSON entry
+    */
+    void write_bson_element(const string_t& name,
+                            const BasicJsonType& j)
+    {
+        switch (j.type())
+        {
+            case value_t::object:
+                return write_bson_object_entry(name, *j.m_value.object);
+
+            case value_t::array:
+                return write_bson_array(name, *j.m_value.array);
+
+            case value_t::boolean:
+                return write_bson_boolean(name, j.m_value.boolean);
+
+            case value_t::number_float:
+                return write_bson_double(name, j.m_value.number_float);
+
+            case value_t::number_integer:
+                return write_bson_integer(name, j.m_value.number_integer);
+
+            case value_t::number_unsigned:
+                return write_bson_unsigned(name, j.m_value.number_unsigned);
+
+            case value_t::string:
+                return write_bson_string(name, *j.m_value.string);
+
+            case value_t::null:
+                return write_bson_null(name);
+
+            // LCOV_EXCL_START
+            default:
+                assert(false);
+                return;
+                // LCOV_EXCL_STOP
+        };
+    }
+
+    /*!
+    @brief Calculates the size of the BSON serialization of the given
+           JSON-object @a j.
+    @param[in] j  JSON value to serialize
+    @pre       j.type() == value_t::object
+    */
+    static std::size_t calc_bson_object_size(const typename BasicJsonType::object_t& value)
+    {
+        std::size_t document_size = std::accumulate(value.begin(), value.end(), 0ul,
+                                    [](size_t result, const typename BasicJsonType::object_t::value_type & el)
+        {
+            return result += calc_bson_element_size(el.first, el.second);
+        });
+
+        return sizeof(std::int32_t) + document_size + 1ul;
+    }
+
+    /*!
+    @param[in] j  JSON value to serialize
+    @pre       j.type() == value_t::object
+    */
+    void write_bson_object(const typename BasicJsonType::object_t& value)
+    {
+        write_number<std::int32_t, true>(static_cast<std::int32_t>(calc_bson_object_size(value)));
+
+        for (const auto& el : value)
+        {
+            write_bson_element(el.first, el.second);
+        }
+
+        oa->write_character(to_char_type(0x00));
+    }
+
+    //////////
+    // CBOR //
+    //////////
+
+    static constexpr CharType get_cbor_float_prefix(float /*unused*/)
+    {
+        return to_char_type(0xFA);  // Single-Precision Float
+    }
+
+    static constexpr CharType get_cbor_float_prefix(double /*unused*/)
+    {
+        return to_char_type(0xFB);  // Double-Precision Float
+    }
+
+    /////////////
+    // MsgPack //
+    /////////////
+
+    static constexpr CharType get_msgpack_float_prefix(float /*unused*/)
+    {
+        return to_char_type(0xCA);  // float 32
+    }
+
+    static constexpr CharType get_msgpack_float_prefix(double /*unused*/)
+    {
+        return to_char_type(0xCB);  // float 64
+    }
+
+    ////////////
+    // UBJSON //
+    ////////////
+
+    // UBJSON: write number (floating point)
+    template<typename NumberType, typename std::enable_if<
+                 std::is_floating_point<NumberType>::value, int>::type = 0>
+    void write_number_with_ubjson_prefix(const NumberType n,
+                                         const bool add_prefix)
+    {
+        if (add_prefix)
+        {
+            oa->write_character(get_ubjson_float_prefix(n));
+        }
+        write_number(n);
+    }
+
+    // UBJSON: write number (unsigned integer)
+    template<typename NumberType, typename std::enable_if<
+                 std::is_unsigned<NumberType>::value, int>::type = 0>
+    void write_number_with_ubjson_prefix(const NumberType n,
+                                         const bool add_prefix)
+    {
+        if (n <= static_cast<uint64_t>((std::numeric_limits<int8_t>::max)()))
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('i'));  // int8
+            }
+            write_number(static_cast<uint8_t>(n));
+        }
+        else if (n <= (std::numeric_limits<uint8_t>::max)())
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('U'));  // uint8
+            }
+            write_number(static_cast<uint8_t>(n));
+        }
+        else if (n <= static_cast<uint64_t>((std::numeric_limits<int16_t>::max)()))
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('I'));  // int16
+            }
+            write_number(static_cast<int16_t>(n));
+        }
+        else if (n <= static_cast<uint64_t>((std::numeric_limits<int32_t>::max)()))
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('l'));  // int32
+            }
+            write_number(static_cast<int32_t>(n));
+        }
+        else if (n <= static_cast<uint64_t>((std::numeric_limits<int64_t>::max)()))
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('L'));  // int64
+            }
+            write_number(static_cast<int64_t>(n));
+        }
+        else
+        {
+            JSON_THROW(out_of_range::create(407, "integer number " + std::to_string(n) + " cannot be represented by UBJSON as it does not fit int64"));
+        }
+    }
+
+    // UBJSON: write number (signed integer)
+    template<typename NumberType, typename std::enable_if<
+                 std::is_signed<NumberType>::value and
+                 not std::is_floating_point<NumberType>::value, int>::type = 0>
+    void write_number_with_ubjson_prefix(const NumberType n,
+                                         const bool add_prefix)
+    {
+        if ((std::numeric_limits<int8_t>::min)() <= n and n <= (std::numeric_limits<int8_t>::max)())
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('i'));  // int8
+            }
+            write_number(static_cast<int8_t>(n));
+        }
+        else if (static_cast<int64_t>((std::numeric_limits<uint8_t>::min)()) <= n and n <= static_cast<int64_t>((std::numeric_limits<uint8_t>::max)()))
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('U'));  // uint8
+            }
+            write_number(static_cast<uint8_t>(n));
+        }
+        else if ((std::numeric_limits<int16_t>::min)() <= n and n <= (std::numeric_limits<int16_t>::max)())
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('I'));  // int16
+            }
+            write_number(static_cast<int16_t>(n));
+        }
+        else if ((std::numeric_limits<int32_t>::min)() <= n and n <= (std::numeric_limits<int32_t>::max)())
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('l'));  // int32
+            }
+            write_number(static_cast<int32_t>(n));
+        }
+        else if ((std::numeric_limits<int64_t>::min)() <= n and n <= (std::numeric_limits<int64_t>::max)())
+        {
+            if (add_prefix)
+            {
+                oa->write_character(to_char_type('L'));  // int64
+            }
+            write_number(static_cast<int64_t>(n));
+        }
+        // LCOV_EXCL_START
+        else
+        {
+            JSON_THROW(out_of_range::create(407, "integer number " + std::to_string(n) + " cannot be represented by UBJSON as it does not fit int64"));
+        }
+        // LCOV_EXCL_STOP
+    }
+
+    /*!
+    @brief determine the type prefix of container values
+
+    @note This function does not need to be 100% accurate when it comes to
+          integer limits. In case a number exceeds the limits of int64_t,
+          this will be detected by a later call to function
+          write_number_with_ubjson_prefix. Therefore, we return 'L' for any
+          value that does not fit the previous limits.
+    */
+    CharType ubjson_prefix(const BasicJsonType& j) const noexcept
+    {
+        switch (j.type())
+        {
+            case value_t::null:
+                return 'Z';
+
+            case value_t::boolean:
+                return j.m_value.boolean ? 'T' : 'F';
+
+            case value_t::number_integer:
+            {
+                if ((std::numeric_limits<int8_t>::min)() <= j.m_value.number_integer and j.m_value.number_integer <= (std::numeric_limits<int8_t>::max)())
+                {
+                    return 'i';
+                }
+                if ((std::numeric_limits<uint8_t>::min)() <= j.m_value.number_integer and j.m_value.number_integer <= (std::numeric_limits<uint8_t>::max)())
+                {
+                    return 'U';
+                }
+                if ((std::numeric_limits<int16_t>::min)() <= j.m_value.number_integer and j.m_value.number_integer <= (std::numeric_limits<int16_t>::max)())
+                {
+                    return 'I';
+                }
+                if ((std::numeric_limits<int32_t>::min)() <= j.m_value.number_integer and j.m_value.number_integer <= (std::numeric_limits<int32_t>::max)())
+                {
+                    return 'l';
+                }
+                // no check and assume int64_t (see note above)
+                return 'L';
+            }
+
+            case value_t::number_unsigned:
+            {
+                if (j.m_value.number_unsigned <= (std::numeric_limits<int8_t>::max)())
+                {
+                    return 'i';
+                }
+                if (j.m_value.number_unsigned <= (std::numeric_limits<uint8_t>::max)())
+                {
+                    return 'U';
+                }
+                if (j.m_value.number_unsigned <= (std::numeric_limits<int16_t>::max)())
+                {
+                    return 'I';
+                }
+                if (j.m_value.number_unsigned <= (std::numeric_limits<int32_t>::max)())
+                {
+                    return 'l';
+                }
+                // no check and assume int64_t (see note above)
+                return 'L';
+            }
+
+            case value_t::number_float:
+                return get_ubjson_float_prefix(j.m_value.number_float);
+
+            case value_t::string:
+                return 'S';
+
+            case value_t::array:
+                return '[';
+
+            case value_t::object:
+                return '{';
+
+            default:  // discarded values
+                return 'N';
+        }
+    }
+
+    static constexpr CharType get_ubjson_float_prefix(float /*unused*/)
+    {
+        return 'd';  // float 32
+    }
+
+    static constexpr CharType get_ubjson_float_prefix(double /*unused*/)
+    {
+        return 'D';  // float 64
+    }
+
+    ///////////////////////
+    // Utility functions //
+    ///////////////////////
+
     /*
     @brief write a number to output input
-
     @param[in] n number of type @a NumberType
     @tparam NumberType the type of the number
+    @tparam OutputIsLittleEndian Set to true if output data is
+                                 required to be little endian
 
     @note This function needs to respect the system's endianess, because bytes
-          in CBOR and MessagePack are stored in network order (big endian) and
-          therefore need reordering on little endian systems.
+          in CBOR, MessagePack, and UBJSON are stored in network order (big
+          endian) and therefore need reordering on little endian systems.
     */
-    template<typename NumberType> void write_number(NumberType n)
+    template<typename NumberType, bool OutputIsLittleEndian = false>
+    void write_number(const NumberType n)
     {
         // step 1: write number to array of length NumberType
         std::array<CharType, sizeof(NumberType)> vec;
         std::memcpy(vec.data(), &n, sizeof(NumberType));
 
         // step 2: write array to output (with possible reordering)
-        if (is_little_endian)
+        if (is_little_endian and not OutputIsLittleEndian)
         {
             // reverse byte order prior to conversion if necessary
             std::reverse(vec.begin(), vec.end());
@@ -6058,6 +9728,47 @@ class binary_writer
         oa->write_characters(vec.data(), sizeof(NumberType));
     }
 
+  public:
+    // The following to_char_type functions are implement the conversion
+    // between uint8_t and CharType. In case CharType is not unsigned,
+    // such a conversion is required to allow values greater than 128.
+    // See <https://github.com/nlohmann/json/issues/1286> for a discussion.
+    template < typename C = CharType,
+               enable_if_t < std::is_signed<C>::value and std::is_signed<char>::value > * = nullptr >
+    static constexpr CharType to_char_type(std::uint8_t x) noexcept
+    {
+        return *reinterpret_cast<char*>(&x);
+    }
+
+    template < typename C = CharType,
+               enable_if_t < std::is_signed<C>::value and std::is_unsigned<char>::value > * = nullptr >
+    static CharType to_char_type(std::uint8_t x) noexcept
+    {
+        static_assert(sizeof(std::uint8_t) == sizeof(CharType), "size of CharType must be equal to std::uint8_t");
+        static_assert(std::is_pod<CharType>::value, "CharType must be POD");
+        CharType result;
+        std::memcpy(&result, &x, sizeof(x));
+        return result;
+    }
+
+    template<typename C = CharType,
+             enable_if_t<std::is_unsigned<C>::value>* = nullptr>
+    static constexpr CharType to_char_type(std::uint8_t x) noexcept
+    {
+        return x;
+    }
+
+    template < typename InputCharType, typename C = CharType,
+               enable_if_t <
+                   std::is_signed<C>::value and
+                   std::is_signed<char>::value and
+                   std::is_same<char, typename std::remove_cv<InputCharType>::type>::value
+                   > * = nullptr >
+    static constexpr CharType to_char_type(InputCharType x) noexcept
+    {
+        return x;
+    }
+
   private:
     /// whether we can assume little endianess
     const bool is_little_endian = binary_reader<BasicJsonType>::little_endianess();
@@ -6065,11 +9776,1150 @@ class binary_writer
     /// the output
     output_adapter_t<CharType> oa = nullptr;
 };
+}  // namespace detail
+}  // namespace nlohmann
 
+// #include <nlohmann/detail/output/serializer.hpp>
+
+
+#include <algorithm> // reverse, remove, fill, find, none_of
+#include <array> // array
+#include <cassert> // assert
+#include <ciso646> // and, or
+#include <clocale> // localeconv, lconv
+#include <cmath> // labs, isfinite, isnan, signbit
+#include <cstddef> // size_t, ptrdiff_t
+#include <cstdint> // uint8_t
+#include <cstdio> // snprintf
+#include <limits> // numeric_limits
+#include <string> // string
+#include <type_traits> // is_same
+
+// #include <nlohmann/detail/exceptions.hpp>
+
+// #include <nlohmann/detail/conversions/to_chars.hpp>
+
+
+#include <cassert> // assert
+#include <ciso646> // or, and, not
+#include <cmath>   // signbit, isfinite
+#include <cstdint> // intN_t, uintN_t
+#include <cstring> // memcpy, memmove
+
+namespace nlohmann
+{
+namespace detail
+{
+
+/*!
+@brief implements the Grisu2 algorithm for binary to decimal floating-point
+conversion.
+
+This implementation is a slightly modified version of the reference
+implementation which may be obtained from
+http://florian.loitsch.com/publications (bench.tar.gz).
+
+The code is distributed under the MIT license, Copyright (c) 2009 Florian Loitsch.
+
+For a detailed description of the algorithm see:
+
+[1] Loitsch, "Printing Floating-Point Numbers Quickly and Accurately with
+    Integers", Proceedings of the ACM SIGPLAN 2010 Conference on Programming
+    Language Design and Implementation, PLDI 2010
+[2] Burger, Dybvig, "Printing Floating-Point Numbers Quickly and Accurately",
+    Proceedings of the ACM SIGPLAN 1996 Conference on Programming Language
+    Design and Implementation, PLDI 1996
+*/
+namespace dtoa_impl
+{
+
+template <typename Target, typename Source>
+Target reinterpret_bits(const Source source)
+{
+    static_assert(sizeof(Target) == sizeof(Source), "size mismatch");
+
+    Target target;
+    std::memcpy(&target, &source, sizeof(Source));
+    return target;
+}
+
+struct diyfp // f * 2^e
+{
+    static constexpr int kPrecision = 64; // = q
+
+    uint64_t f = 0;
+    int e = 0;
+
+    constexpr diyfp(uint64_t f_, int e_) noexcept : f(f_), e(e_) {}
+
+    /*!
+    @brief returns x - y
+    @pre x.e == y.e and x.f >= y.f
+    */
+    static diyfp sub(const diyfp& x, const diyfp& y) noexcept
+    {
+        assert(x.e == y.e);
+        assert(x.f >= y.f);
+
+        return {x.f - y.f, x.e};
+    }
+
+    /*!
+    @brief returns x * y
+    @note The result is rounded. (Only the upper q bits are returned.)
+    */
+    static diyfp mul(const diyfp& x, const diyfp& y) noexcept
+    {
+        static_assert(kPrecision == 64, "internal error");
+
+        // Computes:
+        //  f = round((x.f * y.f) / 2^q)
+        //  e = x.e + y.e + q
+
+        // Emulate the 64-bit * 64-bit multiplication:
+        //
+        // p = u * v
+        //   = (u_lo + 2^32 u_hi) (v_lo + 2^32 v_hi)
+        //   = (u_lo v_lo         ) + 2^32 ((u_lo v_hi         ) + (u_hi v_lo         )) + 2^64 (u_hi v_hi         )
+        //   = (p0                ) + 2^32 ((p1                ) + (p2                )) + 2^64 (p3                )
+        //   = (p0_lo + 2^32 p0_hi) + 2^32 ((p1_lo + 2^32 p1_hi) + (p2_lo + 2^32 p2_hi)) + 2^64 (p3                )
+        //   = (p0_lo             ) + 2^32 (p0_hi + p1_lo + p2_lo                      ) + 2^64 (p1_hi + p2_hi + p3)
+        //   = (p0_lo             ) + 2^32 (Q                                          ) + 2^64 (H                 )
+        //   = (p0_lo             ) + 2^32 (Q_lo + 2^32 Q_hi                           ) + 2^64 (H                 )
+        //
+        // (Since Q might be larger than 2^32 - 1)
+        //
+        //   = (p0_lo + 2^32 Q_lo) + 2^64 (Q_hi + H)
+        //
+        // (Q_hi + H does not overflow a 64-bit int)
+        //
+        //   = p_lo + 2^64 p_hi
+
+        const uint64_t u_lo = x.f & 0xFFFFFFFF;
+        const uint64_t u_hi = x.f >> 32;
+        const uint64_t v_lo = y.f & 0xFFFFFFFF;
+        const uint64_t v_hi = y.f >> 32;
+
+        const uint64_t p0 = u_lo * v_lo;
+        const uint64_t p1 = u_lo * v_hi;
+        const uint64_t p2 = u_hi * v_lo;
+        const uint64_t p3 = u_hi * v_hi;
+
+        const uint64_t p0_hi = p0 >> 32;
+        const uint64_t p1_lo = p1 & 0xFFFFFFFF;
+        const uint64_t p1_hi = p1 >> 32;
+        const uint64_t p2_lo = p2 & 0xFFFFFFFF;
+        const uint64_t p2_hi = p2 >> 32;
+
+        uint64_t Q = p0_hi + p1_lo + p2_lo;
+
+        // The full product might now be computed as
+        //
+        // p_hi = p3 + p2_hi + p1_hi + (Q >> 32)
+        // p_lo = p0_lo + (Q << 32)
+        //
+        // But in this particular case here, the full p_lo is not required.
+        // Effectively we only need to add the highest bit in p_lo to p_hi (and
+        // Q_hi + 1 does not overflow).
+
+        Q += uint64_t{1} << (64 - 32 - 1); // round, ties up
+
+        const uint64_t h = p3 + p2_hi + p1_hi + (Q >> 32);
+
+        return {h, x.e + y.e + 64};
+    }
+
+    /*!
+    @brief normalize x such that the significand is >= 2^(q-1)
+    @pre x.f != 0
+    */
+    static diyfp normalize(diyfp x) noexcept
+    {
+        assert(x.f != 0);
+
+        while ((x.f >> 63) == 0)
+        {
+            x.f <<= 1;
+            x.e--;
+        }
+
+        return x;
+    }
+
+    /*!
+    @brief normalize x such that the result has the exponent E
+    @pre e >= x.e and the upper e - x.e bits of x.f must be zero.
+    */
+    static diyfp normalize_to(const diyfp& x, const int target_exponent) noexcept
+    {
+        const int delta = x.e - target_exponent;
+
+        assert(delta >= 0);
+        assert(((x.f << delta) >> delta) == x.f);
+
+        return {x.f << delta, target_exponent};
+    }
+};
+
+struct boundaries
+{
+    diyfp w;
+    diyfp minus;
+    diyfp plus;
+};
+
+/*!
+Compute the (normalized) diyfp representing the input number 'value' and its
+boundaries.
+
+@pre value must be finite and positive
+*/
+template <typename FloatType>
+boundaries compute_boundaries(FloatType value)
+{
+    assert(std::isfinite(value));
+    assert(value > 0);
+
+    // Convert the IEEE representation into a diyfp.
+    //
+    // If v is denormal:
+    //      value = 0.F * 2^(1 - bias) = (          F) * 2^(1 - bias - (p-1))
+    // If v is normalized:
+    //      value = 1.F * 2^(E - bias) = (2^(p-1) + F) * 2^(E - bias - (p-1))
+
+    static_assert(std::numeric_limits<FloatType>::is_iec559,
+                  "internal error: dtoa_short requires an IEEE-754 floating-point implementation");
+
+    constexpr int      kPrecision = std::numeric_limits<FloatType>::digits; // = p (includes the hidden bit)
+    constexpr int      kBias      = std::numeric_limits<FloatType>::max_exponent - 1 + (kPrecision - 1);
+    constexpr int      kMinExp    = 1 - kBias;
+    constexpr uint64_t kHiddenBit = uint64_t{1} << (kPrecision - 1); // = 2^(p-1)
+
+    using bits_type = typename std::conditional< kPrecision == 24, uint32_t, uint64_t >::type;
+
+    const uint64_t bits = reinterpret_bits<bits_type>(value);
+    const uint64_t E = bits >> (kPrecision - 1);
+    const uint64_t F = bits & (kHiddenBit - 1);
+
+    const bool is_denormal = (E == 0);
+    const diyfp v = is_denormal
+                    ? diyfp(F, kMinExp)
+                    : diyfp(F + kHiddenBit, static_cast<int>(E) - kBias);
+
+    // Compute the boundaries m- and m+ of the floating-point value
+    // v = f * 2^e.
+    //
+    // Determine v- and v+, the floating-point predecessor and successor if v,
+    // respectively.
+    //
+    //      v- = v - 2^e        if f != 2^(p-1) or e == e_min                (A)
+    //         = v - 2^(e-1)    if f == 2^(p-1) and e > e_min                (B)
+    //
+    //      v+ = v + 2^e
+    //
+    // Let m- = (v- + v) / 2 and m+ = (v + v+) / 2. All real numbers _strictly_
+    // between m- and m+ round to v, regardless of how the input rounding
+    // algorithm breaks ties.
+    //
+    //      ---+-------------+-------------+-------------+-------------+---  (A)
+    //         v-            m-            v             m+            v+
+    //
+    //      -----------------+------+------+-------------+-------------+---  (B)
+    //                       v-     m-     v             m+            v+
+
+    const bool lower_boundary_is_closer = (F == 0 and E > 1);
+    const diyfp m_plus = diyfp(2 * v.f + 1, v.e - 1);
+    const diyfp m_minus = lower_boundary_is_closer
+                          ? diyfp(4 * v.f - 1, v.e - 2)  // (B)
+                          : diyfp(2 * v.f - 1, v.e - 1); // (A)
+
+    // Determine the normalized w+ = m+.
+    const diyfp w_plus = diyfp::normalize(m_plus);
+
+    // Determine w- = m- such that e_(w-) = e_(w+).
+    const diyfp w_minus = diyfp::normalize_to(m_minus, w_plus.e);
+
+    return {diyfp::normalize(v), w_minus, w_plus};
+}
+
+// Given normalized diyfp w, Grisu needs to find a (normalized) cached
+// power-of-ten c, such that the exponent of the product c * w = f * 2^e lies
+// within a certain range [alpha, gamma] (Definition 3.2 from [1])
+//
+//      alpha <= e = e_c + e_w + q <= gamma
+//
+// or
+//
+//      f_c * f_w * 2^alpha <= f_c 2^(e_c) * f_w 2^(e_w) * 2^q
+//                          <= f_c * f_w * 2^gamma
+//
+// Since c and w are normalized, i.e. 2^(q-1) <= f < 2^q, this implies
+//
+//      2^(q-1) * 2^(q-1) * 2^alpha <= c * w * 2^q < 2^q * 2^q * 2^gamma
+//
+// or
+//
+//      2^(q - 2 + alpha) <= c * w < 2^(q + gamma)
+//
+// The choice of (alpha,gamma) determines the size of the table and the form of
+// the digit generation procedure. Using (alpha,gamma)=(-60,-32) works out well
+// in practice:
+//
+// The idea is to cut the number c * w = f * 2^e into two parts, which can be
+// processed independently: An integral part p1, and a fractional part p2:
+//
+//      f * 2^e = ( (f div 2^-e) * 2^-e + (f mod 2^-e) ) * 2^e
+//              = (f div 2^-e) + (f mod 2^-e) * 2^e
+//              = p1 + p2 * 2^e
+//
+// The conversion of p1 into decimal form requires a series of divisions and
+// modulos by (a power of) 10. These operations are faster for 32-bit than for
+// 64-bit integers, so p1 should ideally fit into a 32-bit integer. This can be
+// achieved by choosing
+//
+//      -e >= 32   or   e <= -32 := gamma
+//
+// In order to convert the fractional part
+//
+//      p2 * 2^e = p2 / 2^-e = d[-1] / 10^1 + d[-2] / 10^2 + ...
+//
+// into decimal form, the fraction is repeatedly multiplied by 10 and the digits
+// d[-i] are extracted in order:
+//
+//      (10 * p2) div 2^-e = d[-1]
+//      (10 * p2) mod 2^-e = d[-2] / 10^1 + ...
+//
+// The multiplication by 10 must not overflow. It is sufficient to choose
+//
+//      10 * p2 < 16 * p2 = 2^4 * p2 <= 2^64.
+//
+// Since p2 = f mod 2^-e < 2^-e,
+//
+//      -e <= 60   or   e >= -60 := alpha
+
+constexpr int kAlpha = -60;
+constexpr int kGamma = -32;
+
+struct cached_power // c = f * 2^e ~= 10^k
+{
+    uint64_t f;
+    int e;
+    int k;
+};
+
+/*!
+For a normalized diyfp w = f * 2^e, this function returns a (normalized) cached
+power-of-ten c = f_c * 2^e_c, such that the exponent of the product w * c
+satisfies (Definition 3.2 from [1])
+
+     alpha <= e_c + e + q <= gamma.
+*/
+inline cached_power get_cached_power_for_binary_exponent(int e)
+{
+    // Now
+    //
+    //      alpha <= e_c + e + q <= gamma                                    (1)
+    //      ==> f_c * 2^alpha <= c * 2^e * 2^q
+    //
+    // and since the c's are normalized, 2^(q-1) <= f_c,
+    //
+    //      ==> 2^(q - 1 + alpha) <= c * 2^(e + q)
+    //      ==> 2^(alpha - e - 1) <= c
+    //
+    // If c were an exakt power of ten, i.e. c = 10^k, one may determine k as
+    //
+    //      k = ceil( log_10( 2^(alpha - e - 1) ) )
+    //        = ceil( (alpha - e - 1) * log_10(2) )
+    //
+    // From the paper:
+    // "In theory the result of the procedure could be wrong since c is rounded,
+    //  and the computation itself is approximated [...]. In practice, however,
+    //  this simple function is sufficient."
+    //
+    // For IEEE double precision floating-point numbers converted into
+    // normalized diyfp's w = f * 2^e, with q = 64,
+    //
+    //      e >= -1022      (min IEEE exponent)
+    //           -52        (p - 1)
+    //           -52        (p - 1, possibly normalize denormal IEEE numbers)
+    //           -11        (normalize the diyfp)
+    //         = -1137
+    //
+    // and
+    //
+    //      e <= +1023      (max IEEE exponent)
+    //           -52        (p - 1)
+    //           -11        (normalize the diyfp)
+    //         = 960
+    //
+    // This binary exponent range [-1137,960] results in a decimal exponent
+    // range [-307,324]. One does not need to store a cached power for each
+    // k in this range. For each such k it suffices to find a cached power
+    // such that the exponent of the product lies in [alpha,gamma].
+    // This implies that the difference of the decimal exponents of adjacent
+    // table entries must be less than or equal to
+    //
+    //      floor( (gamma - alpha) * log_10(2) ) = 8.
+    //
+    // (A smaller distance gamma-alpha would require a larger table.)
+
+    // NB:
+    // Actually this function returns c, such that -60 <= e_c + e + 64 <= -34.
+
+    constexpr int kCachedPowersSize = 79;
+    constexpr int kCachedPowersMinDecExp = -300;
+    constexpr int kCachedPowersDecStep = 8;
+
+    static constexpr cached_power kCachedPowers[] =
+    {
+        { 0xAB70FE17C79AC6CA, -1060, -300 },
+        { 0xFF77B1FCBEBCDC4F, -1034, -292 },
+        { 0xBE5691EF416BD60C, -1007, -284 },
+        { 0x8DD01FAD907FFC3C,  -980, -276 },
+        { 0xD3515C2831559A83,  -954, -268 },
+        { 0x9D71AC8FADA6C9B5,  -927, -260 },
+        { 0xEA9C227723EE8BCB,  -901, -252 },
+        { 0xAECC49914078536D,  -874, -244 },
+        { 0x823C12795DB6CE57,  -847, -236 },
+        { 0xC21094364DFB5637,  -821, -228 },
+        { 0x9096EA6F3848984F,  -794, -220 },
+        { 0xD77485CB25823AC7,  -768, -212 },
+        { 0xA086CFCD97BF97F4,  -741, -204 },
+        { 0xEF340A98172AACE5,  -715, -196 },
+        { 0xB23867FB2A35B28E,  -688, -188 },
+        { 0x84C8D4DFD2C63F3B,  -661, -180 },
+        { 0xC5DD44271AD3CDBA,  -635, -172 },
+        { 0x936B9FCEBB25C996,  -608, -164 },
+        { 0xDBAC6C247D62A584,  -582, -156 },
+        { 0xA3AB66580D5FDAF6,  -555, -148 },
+        { 0xF3E2F893DEC3F126,  -529, -140 },
+        { 0xB5B5ADA8AAFF80B8,  -502, -132 },
+        { 0x87625F056C7C4A8B,  -475, -124 },
+        { 0xC9BCFF6034C13053,  -449, -116 },
+        { 0x964E858C91BA2655,  -422, -108 },
+        { 0xDFF9772470297EBD,  -396, -100 },
+        { 0xA6DFBD9FB8E5B88F,  -369,  -92 },
+        { 0xF8A95FCF88747D94,  -343,  -84 },
+        { 0xB94470938FA89BCF,  -316,  -76 },
+        { 0x8A08F0F8BF0F156B,  -289,  -68 },
+        { 0xCDB02555653131B6,  -263,  -60 },
+        { 0x993FE2C6D07B7FAC,  -236,  -52 },
+        { 0xE45C10C42A2B3B06,  -210,  -44 },
+        { 0xAA242499697392D3,  -183,  -36 },
+        { 0xFD87B5F28300CA0E,  -157,  -28 },
+        { 0xBCE5086492111AEB,  -130,  -20 },
+        { 0x8CBCCC096F5088CC,  -103,  -12 },
+        { 0xD1B71758E219652C,   -77,   -4 },
+        { 0x9C40000000000000,   -50,    4 },
+        { 0xE8D4A51000000000,   -24,   12 },
+        { 0xAD78EBC5AC620000,     3,   20 },
+        { 0x813F3978F8940984,    30,   28 },
+        { 0xC097CE7BC90715B3,    56,   36 },
+        { 0x8F7E32CE7BEA5C70,    83,   44 },
+        { 0xD5D238A4ABE98068,   109,   52 },
+        { 0x9F4F2726179A2245,   136,   60 },
+        { 0xED63A231D4C4FB27,   162,   68 },
+        { 0xB0DE65388CC8ADA8,   189,   76 },
+        { 0x83C7088E1AAB65DB,   216,   84 },
+        { 0xC45D1DF942711D9A,   242,   92 },
+        { 0x924D692CA61BE758,   269,  100 },
+        { 0xDA01EE641A708DEA,   295,  108 },
+        { 0xA26DA3999AEF774A,   322,  116 },
+        { 0xF209787BB47D6B85,   348,  124 },
+        { 0xB454E4A179DD1877,   375,  132 },
+        { 0x865B86925B9BC5C2,   402,  140 },
+        { 0xC83553C5C8965D3D,   428,  148 },
+        { 0x952AB45CFA97A0B3,   455,  156 },
+        { 0xDE469FBD99A05FE3,   481,  164 },
+        { 0xA59BC234DB398C25,   508,  172 },
+        { 0xF6C69A72A3989F5C,   534,  180 },
+        { 0xB7DCBF5354E9BECE,   561,  188 },
+        { 0x88FCF317F22241E2,   588,  196 },
+        { 0xCC20CE9BD35C78A5,   614,  204 },
+        { 0x98165AF37B2153DF,   641,  212 },
+        { 0xE2A0B5DC971F303A,   667,  220 },
+        { 0xA8D9D1535CE3B396,   694,  228 },
+        { 0xFB9B7CD9A4A7443C,   720,  236 },
+        { 0xBB764C4CA7A44410,   747,  244 },
+        { 0x8BAB8EEFB6409C1A,   774,  252 },
+        { 0xD01FEF10A657842C,   800,  260 },
+        { 0x9B10A4E5E9913129,   827,  268 },
+        { 0xE7109BFBA19C0C9D,   853,  276 },
+        { 0xAC2820D9623BF429,   880,  284 },
+        { 0x80444B5E7AA7CF85,   907,  292 },
+        { 0xBF21E44003ACDD2D,   933,  300 },
+        { 0x8E679C2F5E44FF8F,   960,  308 },
+        { 0xD433179D9C8CB841,   986,  316 },
+        { 0x9E19DB92B4E31BA9,  1013,  324 },
+    };
+
+    // This computation gives exactly the same results for k as
+    //      k = ceil((kAlpha - e - 1) * 0.30102999566398114)
+    // for |e| <= 1500, but doesn't require floating-point operations.
+    // NB: log_10(2) ~= 78913 / 2^18
+    assert(e >= -1500);
+    assert(e <=  1500);
+    const int f = kAlpha - e - 1;
+    const int k = (f * 78913) / (1 << 18) + static_cast<int>(f > 0);
+
+    const int index = (-kCachedPowersMinDecExp + k + (kCachedPowersDecStep - 1)) / kCachedPowersDecStep;
+    assert(index >= 0);
+    assert(index < kCachedPowersSize);
+    static_cast<void>(kCachedPowersSize); // Fix warning.
+
+    const cached_power cached = kCachedPowers[index];
+    assert(kAlpha <= cached.e + e + 64);
+    assert(kGamma >= cached.e + e + 64);
+
+    return cached;
+}
+
+/*!
+For n != 0, returns k, such that pow10 := 10^(k-1) <= n < 10^k.
+For n == 0, returns 1 and sets pow10 := 1.
+*/
+inline int find_largest_pow10(const uint32_t n, uint32_t& pow10)
+{
+    // LCOV_EXCL_START
+    if (n >= 1000000000)
+    {
+        pow10 = 1000000000;
+        return 10;
+    }
+    // LCOV_EXCL_STOP
+    else if (n >= 100000000)
+    {
+        pow10 = 100000000;
+        return  9;
+    }
+    else if (n >= 10000000)
+    {
+        pow10 = 10000000;
+        return  8;
+    }
+    else if (n >= 1000000)
+    {
+        pow10 = 1000000;
+        return  7;
+    }
+    else if (n >= 100000)
+    {
+        pow10 = 100000;
+        return  6;
+    }
+    else if (n >= 10000)
+    {
+        pow10 = 10000;
+        return  5;
+    }
+    else if (n >= 1000)
+    {
+        pow10 = 1000;
+        return  4;
+    }
+    else if (n >= 100)
+    {
+        pow10 = 100;
+        return  3;
+    }
+    else if (n >= 10)
+    {
+        pow10 = 10;
+        return  2;
+    }
+    else
+    {
+        pow10 = 1;
+        return 1;
+    }
+}
+
+inline void grisu2_round(char* buf, int len, uint64_t dist, uint64_t delta,
+                         uint64_t rest, uint64_t ten_k)
+{
+    assert(len >= 1);
+    assert(dist <= delta);
+    assert(rest <= delta);
+    assert(ten_k > 0);
+
+    //               <--------------------------- delta ---->
+    //                                  <---- dist --------->
+    // --------------[------------------+-------------------]--------------
+    //               M-                 w                   M+
+    //
+    //                                  ten_k
+    //                                <------>
+    //                                       <---- rest ---->
+    // --------------[------------------+----+--------------]--------------
+    //                                  w    V
+    //                                       = buf * 10^k
+    //
+    // ten_k represents a unit-in-the-last-place in the decimal representation
+    // stored in buf.
+    // Decrement buf by ten_k while this takes buf closer to w.
+
+    // The tests are written in this order to avoid overflow in unsigned
+    // integer arithmetic.
+
+    while (rest < dist
+            and delta - rest >= ten_k
+            and (rest + ten_k < dist or dist - rest > rest + ten_k - dist))
+    {
+        assert(buf[len - 1] != '0');
+        buf[len - 1]--;
+        rest += ten_k;
+    }
+}
+
+/*!
+Generates V = buffer * 10^decimal_exponent, such that M- <= V <= M+.
+M- and M+ must be normalized and share the same exponent -60 <= e <= -32.
+*/
+inline void grisu2_digit_gen(char* buffer, int& length, int& decimal_exponent,
+                             diyfp M_minus, diyfp w, diyfp M_plus)
+{
+    static_assert(kAlpha >= -60, "internal error");
+    static_assert(kGamma <= -32, "internal error");
+
+    // Generates the digits (and the exponent) of a decimal floating-point
+    // number V = buffer * 10^decimal_exponent in the range [M-, M+]. The diyfp's
+    // w, M- and M+ share the same exponent e, which satisfies alpha <= e <= gamma.
+    //
+    //               <--------------------------- delta ---->
+    //                                  <---- dist --------->
+    // --------------[------------------+-------------------]--------------
+    //               M-                 w                   M+
+    //
+    // Grisu2 generates the digits of M+ from left to right and stops as soon as
+    // V is in [M-,M+].
+
+    assert(M_plus.e >= kAlpha);
+    assert(M_plus.e <= kGamma);
+
+    uint64_t delta = diyfp::sub(M_plus, M_minus).f; // (significand of (M+ - M-), implicit exponent is e)
+    uint64_t dist  = diyfp::sub(M_plus, w      ).f; // (significand of (M+ - w ), implicit exponent is e)
+
+    // Split M+ = f * 2^e into two parts p1 and p2 (note: e < 0):
+    //
+    //      M+ = f * 2^e
+    //         = ((f div 2^-e) * 2^-e + (f mod 2^-e)) * 2^e
+    //         = ((p1        ) * 2^-e + (p2        )) * 2^e
+    //         = p1 + p2 * 2^e
+
+    const diyfp one(uint64_t{1} << -M_plus.e, M_plus.e);
+
+    auto p1 = static_cast<uint32_t>(M_plus.f >> -one.e); // p1 = f div 2^-e (Since -e >= 32, p1 fits into a 32-bit int.)
+    uint64_t p2 = M_plus.f & (one.f - 1);                    // p2 = f mod 2^-e
+
+    // 1)
+    //
+    // Generate the digits of the integral part p1 = d[n-1]...d[1]d[0]
+
+    assert(p1 > 0);
+
+    uint32_t pow10;
+    const int k = find_largest_pow10(p1, pow10);
+
+    //      10^(k-1) <= p1 < 10^k, pow10 = 10^(k-1)
+    //
+    //      p1 = (p1 div 10^(k-1)) * 10^(k-1) + (p1 mod 10^(k-1))
+    //         = (d[k-1]         ) * 10^(k-1) + (p1 mod 10^(k-1))
+    //
+    //      M+ = p1                                             + p2 * 2^e
+    //         = d[k-1] * 10^(k-1) + (p1 mod 10^(k-1))          + p2 * 2^e
+    //         = d[k-1] * 10^(k-1) + ((p1 mod 10^(k-1)) * 2^-e + p2) * 2^e
+    //         = d[k-1] * 10^(k-1) + (                         rest) * 2^e
+    //
+    // Now generate the digits d[n] of p1 from left to right (n = k-1,...,0)
+    //
+    //      p1 = d[k-1]...d[n] * 10^n + d[n-1]...d[0]
+    //
+    // but stop as soon as
+    //
+    //      rest * 2^e = (d[n-1]...d[0] * 2^-e + p2) * 2^e <= delta * 2^e
+
+    int n = k;
+    while (n > 0)
+    {
+        // Invariants:
+        //      M+ = buffer * 10^n + (p1 + p2 * 2^e)    (buffer = 0 for n = k)
+        //      pow10 = 10^(n-1) <= p1 < 10^n
+        //
+        const uint32_t d = p1 / pow10;  // d = p1 div 10^(n-1)
+        const uint32_t r = p1 % pow10;  // r = p1 mod 10^(n-1)
+        //
+        //      M+ = buffer * 10^n + (d * 10^(n-1) + r) + p2 * 2^e
+        //         = (buffer * 10 + d) * 10^(n-1) + (r + p2 * 2^e)
+        //
+        assert(d <= 9);
+        buffer[length++] = static_cast<char>('0' + d); // buffer := buffer * 10 + d
+        //
+        //      M+ = buffer * 10^(n-1) + (r + p2 * 2^e)
+        //
+        p1 = r;
+        n--;
+        //
+        //      M+ = buffer * 10^n + (p1 + p2 * 2^e)
+        //      pow10 = 10^n
+        //
+
+        // Now check if enough digits have been generated.
+        // Compute
+        //
+        //      p1 + p2 * 2^e = (p1 * 2^-e + p2) * 2^e = rest * 2^e
+        //
+        // Note:
+        // Since rest and delta share the same exponent e, it suffices to
+        // compare the significands.
+        const uint64_t rest = (uint64_t{p1} << -one.e) + p2;
+        if (rest <= delta)
+        {
+            // V = buffer * 10^n, with M- <= V <= M+.
+
+            decimal_exponent += n;
+
+            // We may now just stop. But instead look if the buffer could be
+            // decremented to bring V closer to w.
+            //
+            // pow10 = 10^n is now 1 ulp in the decimal representation V.
+            // The rounding procedure works with diyfp's with an implicit
+            // exponent of e.
+            //
+            //      10^n = (10^n * 2^-e) * 2^e = ulp * 2^e
+            //
+            const uint64_t ten_n = uint64_t{pow10} << -one.e;
+            grisu2_round(buffer, length, dist, delta, rest, ten_n);
+
+            return;
+        }
+
+        pow10 /= 10;
+        //
+        //      pow10 = 10^(n-1) <= p1 < 10^n
+        // Invariants restored.
+    }
+
+    // 2)
+    //
+    // The digits of the integral part have been generated:
+    //
+    //      M+ = d[k-1]...d[1]d[0] + p2 * 2^e
+    //         = buffer            + p2 * 2^e
+    //
+    // Now generate the digits of the fractional part p2 * 2^e.
+    //
+    // Note:
+    // No decimal point is generated: the exponent is adjusted instead.
+    //
+    // p2 actually represents the fraction
+    //
+    //      p2 * 2^e
+    //          = p2 / 2^-e
+    //          = d[-1] / 10^1 + d[-2] / 10^2 + ...
+    //
+    // Now generate the digits d[-m] of p1 from left to right (m = 1,2,...)
+    //
+    //      p2 * 2^e = d[-1]d[-2]...d[-m] * 10^-m
+    //                      + 10^-m * (d[-m-1] / 10^1 + d[-m-2] / 10^2 + ...)
+    //
+    // using
+    //
+    //      10^m * p2 = ((10^m * p2) div 2^-e) * 2^-e + ((10^m * p2) mod 2^-e)
+    //                = (                   d) * 2^-e + (                   r)
+    //
+    // or
+    //      10^m * p2 * 2^e = d + r * 2^e
+    //
+    // i.e.
+    //
+    //      M+ = buffer + p2 * 2^e
+    //         = buffer + 10^-m * (d + r * 2^e)
+    //         = (buffer * 10^m + d) * 10^-m + 10^-m * r * 2^e
+    //
+    // and stop as soon as 10^-m * r * 2^e <= delta * 2^e
+
+    assert(p2 > delta);
+
+    int m = 0;
+    for (;;)
+    {
+        // Invariant:
+        //      M+ = buffer * 10^-m + 10^-m * (d[-m-1] / 10 + d[-m-2] / 10^2 + ...) * 2^e
+        //         = buffer * 10^-m + 10^-m * (p2                                 ) * 2^e
+        //         = buffer * 10^-m + 10^-m * (1/10 * (10 * p2)                   ) * 2^e
+        //         = buffer * 10^-m + 10^-m * (1/10 * ((10*p2 div 2^-e) * 2^-e + (10*p2 mod 2^-e)) * 2^e
+        //
+        assert(p2 <= UINT64_MAX / 10);
+        p2 *= 10;
+        const uint64_t d = p2 >> -one.e;     // d = (10 * p2) div 2^-e
+        const uint64_t r = p2 & (one.f - 1); // r = (10 * p2) mod 2^-e
+        //
+        //      M+ = buffer * 10^-m + 10^-m * (1/10 * (d * 2^-e + r) * 2^e
+        //         = buffer * 10^-m + 10^-m * (1/10 * (d + r * 2^e))
+        //         = (buffer * 10 + d) * 10^(-m-1) + 10^(-m-1) * r * 2^e
+        //
+        assert(d <= 9);
+        buffer[length++] = static_cast<char>('0' + d); // buffer := buffer * 10 + d
+        //
+        //      M+ = buffer * 10^(-m-1) + 10^(-m-1) * r * 2^e
+        //
+        p2 = r;
+        m++;
+        //
+        //      M+ = buffer * 10^-m + 10^-m * p2 * 2^e
+        // Invariant restored.
+
+        // Check if enough digits have been generated.
+        //
+        //      10^-m * p2 * 2^e <= delta * 2^e
+        //              p2 * 2^e <= 10^m * delta * 2^e
+        //                    p2 <= 10^m * delta
+        delta *= 10;
+        dist  *= 10;
+        if (p2 <= delta)
+        {
+            break;
+        }
+    }
+
+    // V = buffer * 10^-m, with M- <= V <= M+.
+
+    decimal_exponent -= m;
+
+    // 1 ulp in the decimal representation is now 10^-m.
+    // Since delta and dist are now scaled by 10^m, we need to do the
+    // same with ulp in order to keep the units in sync.
+    //
+    //      10^m * 10^-m = 1 = 2^-e * 2^e = ten_m * 2^e
+    //
+    const uint64_t ten_m = one.f;
+    grisu2_round(buffer, length, dist, delta, p2, ten_m);
+
+    // By construction this algorithm generates the shortest possible decimal
+    // number (Loitsch, Theorem 6.2) which rounds back to w.
+    // For an input number of precision p, at least
+    //
+    //      N = 1 + ceil(p * log_10(2))
+    //
+    // decimal digits are sufficient to identify all binary floating-point
+    // numbers (Matula, "In-and-Out conversions").
+    // This implies that the algorithm does not produce more than N decimal
+    // digits.
+    //
+    //      N = 17 for p = 53 (IEEE double precision)
+    //      N = 9  for p = 24 (IEEE single precision)
+}
+
+/*!
+v = buf * 10^decimal_exponent
+len is the length of the buffer (number of decimal digits)
+The buffer must be large enough, i.e. >= max_digits10.
+*/
+inline void grisu2(char* buf, int& len, int& decimal_exponent,
+                   diyfp m_minus, diyfp v, diyfp m_plus)
+{
+    assert(m_plus.e == m_minus.e);
+    assert(m_plus.e == v.e);
+
+    //  --------(-----------------------+-----------------------)--------    (A)
+    //          m-                      v                       m+
+    //
+    //  --------------------(-----------+-----------------------)--------    (B)
+    //                      m-          v                       m+
+    //
+    // First scale v (and m- and m+) such that the exponent is in the range
+    // [alpha, gamma].
+
+    const cached_power cached = get_cached_power_for_binary_exponent(m_plus.e);
+
+    const diyfp c_minus_k(cached.f, cached.e); // = c ~= 10^-k
+
+    // The exponent of the products is = v.e + c_minus_k.e + q and is in the range [alpha,gamma]
+    const diyfp w       = diyfp::mul(v,       c_minus_k);
+    const diyfp w_minus = diyfp::mul(m_minus, c_minus_k);
+    const diyfp w_plus  = diyfp::mul(m_plus,  c_minus_k);
+
+    //  ----(---+---)---------------(---+---)---------------(---+---)----
+    //          w-                      w                       w+
+    //          = c*m-                  = c*v                   = c*m+
+    //
+    // diyfp::mul rounds its result and c_minus_k is approximated too. w, w- and
+    // w+ are now off by a small amount.
+    // In fact:
+    //
+    //      w - v * 10^k < 1 ulp
+    //
+    // To account for this inaccuracy, add resp. subtract 1 ulp.
+    //
+    //  --------+---[---------------(---+---)---------------]---+--------
+    //          w-  M-                  w                   M+  w+
+    //
+    // Now any number in [M-, M+] (bounds included) will round to w when input,
+    // regardless of how the input rounding algorithm breaks ties.
+    //
+    // And digit_gen generates the shortest possible such number in [M-, M+].
+    // Note that this does not mean that Grisu2 always generates the shortest
+    // possible number in the interval (m-, m+).
+    const diyfp M_minus(w_minus.f + 1, w_minus.e);
+    const diyfp M_plus (w_plus.f  - 1, w_plus.e );
+
+    decimal_exponent = -cached.k; // = -(-k) = k
+
+    grisu2_digit_gen(buf, len, decimal_exponent, M_minus, w, M_plus);
+}
+
+/*!
+v = buf * 10^decimal_exponent
+len is the length of the buffer (number of decimal digits)
+The buffer must be large enough, i.e. >= max_digits10.
+*/
+template <typename FloatType>
+void grisu2(char* buf, int& len, int& decimal_exponent, FloatType value)
+{
+    static_assert(diyfp::kPrecision >= std::numeric_limits<FloatType>::digits + 3,
+                  "internal error: not enough precision");
+
+    assert(std::isfinite(value));
+    assert(value > 0);
+
+    // If the neighbors (and boundaries) of 'value' are always computed for double-precision
+    // numbers, all float's can be recovered using strtod (and strtof). However, the resulting
+    // decimal representations are not exactly "short".
+    //
+    // The documentation for 'std::to_chars' (https://en.cppreference.com/w/cpp/utility/to_chars)
+    // says "value is converted to a string as if by std::sprintf in the default ("C") locale"
+    // and since sprintf promotes float's to double's, I think this is exactly what 'std::to_chars'
+    // does.
+    // On the other hand, the documentation for 'std::to_chars' requires that "parsing the
+    // representation using the corresponding std::from_chars function recovers value exactly". That
+    // indicates that single precision floating-point numbers should be recovered using
+    // 'std::strtof'.
+    //
+    // NB: If the neighbors are computed for single-precision numbers, there is a single float
+    //     (7.0385307e-26f) which can't be recovered using strtod. The resulting double precision
+    //     value is off by 1 ulp.
+#if 0
+    const boundaries w = compute_boundaries(static_cast<double>(value));
+#else
+    const boundaries w = compute_boundaries(value);
+#endif
+
+    grisu2(buf, len, decimal_exponent, w.minus, w.w, w.plus);
+}
+
+/*!
+@brief appends a decimal representation of e to buf
+@return a pointer to the element following the exponent.
+@pre -1000 < e < 1000
+*/
+inline char* append_exponent(char* buf, int e)
+{
+    assert(e > -1000);
+    assert(e <  1000);
+
+    if (e < 0)
+    {
+        e = -e;
+        *buf++ = '-';
+    }
+    else
+    {
+        *buf++ = '+';
+    }
+
+    auto k = static_cast<uint32_t>(e);
+    if (k < 10)
+    {
+        // Always print at least two digits in the exponent.
+        // This is for compatibility with printf("%g").
+        *buf++ = '0';
+        *buf++ = static_cast<char>('0' + k);
+    }
+    else if (k < 100)
+    {
+        *buf++ = static_cast<char>('0' + k / 10);
+        k %= 10;
+        *buf++ = static_cast<char>('0' + k);
+    }
+    else
+    {
+        *buf++ = static_cast<char>('0' + k / 100);
+        k %= 100;
+        *buf++ = static_cast<char>('0' + k / 10);
+        k %= 10;
+        *buf++ = static_cast<char>('0' + k);
+    }
+
+    return buf;
+}
+
+/*!
+@brief prettify v = buf * 10^decimal_exponent
+
+If v is in the range [10^min_exp, 10^max_exp) it will be printed in fixed-point
+notation. Otherwise it will be printed in exponential notation.
+
+@pre min_exp < 0
+@pre max_exp > 0
+*/
+inline char* format_buffer(char* buf, int len, int decimal_exponent,
+                           int min_exp, int max_exp)
+{
+    assert(min_exp < 0);
+    assert(max_exp > 0);
+
+    const int k = len;
+    const int n = len + decimal_exponent;
+
+    // v = buf * 10^(n-k)
+    // k is the length of the buffer (number of decimal digits)
+    // n is the position of the decimal point relative to the start of the buffer.
+
+    if (k <= n and n <= max_exp)
+    {
+        // digits[000]
+        // len <= max_exp + 2
+
+        std::memset(buf + k, '0', static_cast<size_t>(n - k));
+        // Make it look like a floating-point number (#362, #378)
+        buf[n + 0] = '.';
+        buf[n + 1] = '0';
+        return buf + (n + 2);
+    }
+
+    if (0 < n and n <= max_exp)
+    {
+        // dig.its
+        // len <= max_digits10 + 1
+
+        assert(k > n);
+
+        std::memmove(buf + (n + 1), buf + n, static_cast<size_t>(k - n));
+        buf[n] = '.';
+        return buf + (k + 1);
+    }
+
+    if (min_exp < n and n <= 0)
+    {
+        // 0.[000]digits
+        // len <= 2 + (-min_exp - 1) + max_digits10
+
+        std::memmove(buf + (2 + -n), buf, static_cast<size_t>(k));
+        buf[0] = '0';
+        buf[1] = '.';
+        std::memset(buf + 2, '0', static_cast<size_t>(-n));
+        return buf + (2 + (-n) + k);
+    }
+
+    if (k == 1)
+    {
+        // dE+123
+        // len <= 1 + 5
+
+        buf += 1;
+    }
+    else
+    {
+        // d.igitsE+123
+        // len <= max_digits10 + 1 + 5
+
+        std::memmove(buf + 2, buf + 1, static_cast<size_t>(k - 1));
+        buf[1] = '.';
+        buf += 1 + k;
+    }
+
+    *buf++ = 'e';
+    return append_exponent(buf, n - 1);
+}
+
+} // namespace dtoa_impl
+
+/*!
+@brief generates a decimal representation of the floating-point number value in [first, last).
+
+The format of the resulting decimal representation is similar to printf's %g
+format. Returns an iterator pointing past-the-end of the decimal representation.
+
+@note The input number must be finite, i.e. NaN's and Inf's are not supported.
+@note The buffer must be large enough.
+@note The result is NOT null-terminated.
+*/
+template <typename FloatType>
+char* to_chars(char* first, const char* last, FloatType value)
+{
+    static_cast<void>(last); // maybe unused - fix warning
+    assert(std::isfinite(value));
+
+    // Use signbit(value) instead of (value < 0) since signbit works for -0.
+    if (std::signbit(value))
+    {
+        value = -value;
+        *first++ = '-';
+    }
+
+    if (value == 0) // +-0
+    {
+        *first++ = '0';
+        // Make it look like a floating-point number (#362, #378)
+        *first++ = '.';
+        *first++ = '0';
+        return first;
+    }
+
+    assert(last - first >= std::numeric_limits<FloatType>::max_digits10);
+
+    // Compute v = buffer * 10^decimal_exponent.
+    // The decimal digits are stored in the buffer, which needs to be interpreted
+    // as an unsigned decimal integer.
+    // len is the length of the buffer, i.e. the number of decimal digits.
+    int len = 0;
+    int decimal_exponent = 0;
+    dtoa_impl::grisu2(first, len, decimal_exponent, value);
+
+    assert(len <= std::numeric_limits<FloatType>::max_digits10);
+
+    // Format the buffer like printf("%.*g", prec, value)
+    constexpr int kMinExp = -4;
+    // Use digits10 here to increase compatibility with version 2.
+    constexpr int kMaxExp = std::numeric_limits<FloatType>::digits10;
+
+    assert(last - first >= kMaxExp + 2);
+    assert(last - first >= 2 + (-kMinExp - 1) + std::numeric_limits<FloatType>::max_digits10);
+    assert(last - first >= std::numeric_limits<FloatType>::max_digits10 + 6);
+
+    return dtoa_impl::format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
+}
+
+} // namespace detail
+} // namespace nlohmann
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+// #include <nlohmann/detail/meta/cpp_future.hpp>
+
+// #include <nlohmann/detail/output/binary_writer.hpp>
+
+// #include <nlohmann/detail/output/output_adapters.hpp>
+
+// #include <nlohmann/detail/value_t.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
 ///////////////////
 // serialization //
 ///////////////////
 
+/// how to treat decoding errors
+enum class error_handler_t
+{
+    strict,  ///< throw a type_error exception in case of invalid UTF-8
+    replace, ///< replace invalid UTF-8 sequences with U+FFFD
+    ignore   ///< ignore invalid UTF-8 sequences
+};
+
 template<typename BasicJsonType>
 class serializer
 {
@@ -6077,20 +10927,32 @@ class serializer
     using number_float_t = typename BasicJsonType::number_float_t;
     using number_integer_t = typename BasicJsonType::number_integer_t;
     using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    static constexpr uint8_t UTF8_ACCEPT = 0;
+    static constexpr uint8_t UTF8_REJECT = 1;
+
   public:
     /*!
     @param[in] s  output stream to serialize to
     @param[in] ichar  indentation character to use
+    @param[in] error_handler_  how to react on decoding errors
     */
-    serializer(output_adapter_t<char> s, const char ichar)
-        : o(std::move(s)), loc(std::localeconv()),
-          thousands_sep(loc->thousands_sep == nullptr ? '\0' : * (loc->thousands_sep)),
-          decimal_point(loc->decimal_point == nullptr ? '\0' : * (loc->decimal_point)),
-          indent_char(ichar), indent_string(512, indent_char) {}
+    serializer(output_adapter_t<char> s, const char ichar,
+               error_handler_t error_handler_ = error_handler_t::strict)
+        : o(std::move(s))
+        , loc(std::localeconv())
+        , thousands_sep(loc->thousands_sep == nullptr ? '\0' : * (loc->thousands_sep))
+        , decimal_point(loc->decimal_point == nullptr ? '\0' : * (loc->decimal_point))
+        , indent_char(ichar)
+        , indent_string(512, indent_char)
+        , error_handler(error_handler_)
+    {}
 
     // delete because of pointer members
     serializer(const serializer&) = delete;
     serializer& operator=(const serializer&) = delete;
+    serializer(serializer&&) = delete;
+    serializer& operator=(serializer&&) = delete;
+    ~serializer() = default;
 
     /*!
     @brief internal implementation of the serialization function
@@ -6303,323 +11165,249 @@ class serializer
 
   private:
     /*!
-    @brief returns the number of expected bytes following in UTF-8 string
-
-    @param[in]  u  the first byte of a UTF-8 string
-    @return  the number of expected bytes following
-    */
-    static constexpr std::size_t bytes_following(const uint8_t u)
-    {
-        return ((u <= 127) ? 0
-                : ((192 <= u and u <= 223) ? 1
-                   : ((224 <= u and u <= 239) ? 2
-                      : ((240 <= u and u <= 247) ? 3 : std::string::npos))));
-    }
+    @brief dump escaped string
 
-    /*!
-    @brief calculates the extra space to escape a JSON string
+    Escape a string by replacing certain special characters by a sequence of an
+    escape character (backslash) and another character and other control
+    characters by a sequence of "\u" followed by a four-digit hex
+    representation. The escaped string is written to output stream @a o.
 
     @param[in] s  the string to escape
     @param[in] ensure_ascii  whether to escape non-ASCII characters with
                              \uXXXX sequences
-    @return the number of characters required to escape string @a s
 
     @complexity Linear in the length of string @a s.
     */
-    static std::size_t extra_space(const string_t& s,
-                                   const bool ensure_ascii) noexcept
+    void dump_escaped(const string_t& s, const bool ensure_ascii)
     {
-        std::size_t res = 0;
+        uint32_t codepoint;
+        uint8_t state = UTF8_ACCEPT;
+        std::size_t bytes = 0;  // number of bytes written to string_buffer
+
+        // number of bytes written at the point of the last valid byte
+        std::size_t bytes_after_last_accept = 0;
+        std::size_t undumped_chars = 0;
 
         for (std::size_t i = 0; i < s.size(); ++i)
         {
-            switch (s[i])
-            {
-                // control characters that can be escaped with a backslash
-                case '"':
-                case '\\':
-                case '\b':
-                case '\f':
-                case '\n':
-                case '\r':
-                case '\t':
-                {
-                    // from c (1 byte) to \x (2 bytes)
-                    res += 1;
-                    break;
-                }
+            const auto byte = static_cast<uint8_t>(s[i]);
 
-                // control characters that need \uxxxx escaping
-                case 0x00:
-                case 0x01:
-                case 0x02:
-                case 0x03:
-                case 0x04:
-                case 0x05:
-                case 0x06:
-                case 0x07:
-                case 0x0B:
-                case 0x0E:
-                case 0x0F:
-                case 0x10:
-                case 0x11:
-                case 0x12:
-                case 0x13:
-                case 0x14:
-                case 0x15:
-                case 0x16:
-                case 0x17:
-                case 0x18:
-                case 0x19:
-                case 0x1A:
-                case 0x1B:
-                case 0x1C:
-                case 0x1D:
-                case 0x1E:
-                case 0x1F:
-                {
-                    // from c (1 byte) to \uxxxx (6 bytes)
-                    res += 5;
-                    break;
-                }
-
-                default:
+            switch (decode(state, codepoint, byte))
+            {
+                case UTF8_ACCEPT:  // decode found a new code point
                 {
-                    if (ensure_ascii and (s[i] & 0x80 or s[i] == 0x7F))
+                    switch (codepoint)
                     {
-                        const auto bytes = bytes_following(static_cast<uint8_t>(s[i]));
-                        // invalid characters will be detected by throw_if_invalid_utf8
-                        assert (bytes != std::string::npos);
-
-                        if (bytes == 3)
+                        case 0x08: // backspace
                         {
-                            // codepoints that need 4 bytes (i.e., 3 additional
-                            // bytes) in UTF-8 need a surrogate pair when \u
-                            // escaping is used: from 4 bytes to \uxxxx\uxxxx
-                            // (12 bytes)
-                            res += (12 - bytes - 1);
+                            string_buffer[bytes++] = '\\';
+                            string_buffer[bytes++] = 'b';
+                            break;
                         }
-                        else
+
+                        case 0x09: // horizontal tab
                         {
-                            // from x bytes to \uxxxx (6 bytes)
-                            res += (6 - bytes - 1);
+                            string_buffer[bytes++] = '\\';
+                            string_buffer[bytes++] = 't';
+                            break;
                         }
 
-                        // skip the additional bytes
-                        i += bytes;
-                    }
-                    break;
-                }
-            }
-        }
-
-        return res;
-    }
-
-    static void escape_codepoint(int codepoint, string_t& result, std::size_t& pos)
-    {
-        // expecting a proper codepoint
-        assert(0x00 <= codepoint and codepoint <= 0x10FFFF);
-
-        // the last written character was the backslash before the 'u'
-        assert(result[pos] == '\\');
-
-        // write the 'u'
-        result[++pos] = 'u';
-
-        // convert a number 0..15 to its hex representation (0..f)
-        static const std::array<char, 16> hexify =
-        {
-            {
-                '0', '1', '2', '3', '4', '5', '6', '7',
-                '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
-            }
-        };
-
-        if (codepoint < 0x10000)
-        {
-            // codepoints U+0000..U+FFFF can be represented as \uxxxx.
-            result[++pos] = hexify[(codepoint >> 12) & 0x0F];
-            result[++pos] = hexify[(codepoint >> 8) & 0x0F];
-            result[++pos] = hexify[(codepoint >> 4) & 0x0F];
-            result[++pos] = hexify[codepoint & 0x0F];
-        }
-        else
-        {
-            // codepoints U+10000..U+10FFFF need a surrogate pair to be
-            // represented as \uxxxx\uxxxx.
-            // http://www.unicode.org/faq/utf_bom.html#utf16-4
-            codepoint -= 0x10000;
-            const int high_surrogate = 0xD800 | ((codepoint >> 10) & 0x3FF);
-            const int low_surrogate = 0xDC00 | (codepoint & 0x3FF);
-            result[++pos] = hexify[(high_surrogate >> 12) & 0x0F];
-            result[++pos] = hexify[(high_surrogate >> 8) & 0x0F];
-            result[++pos] = hexify[(high_surrogate >> 4) & 0x0F];
-            result[++pos] = hexify[high_surrogate & 0x0F];
-            ++pos;  // backslash is already in output
-            result[++pos] = 'u';
-            result[++pos] = hexify[(low_surrogate >> 12) & 0x0F];
-            result[++pos] = hexify[(low_surrogate >> 8) & 0x0F];
-            result[++pos] = hexify[(low_surrogate >> 4) & 0x0F];
-            result[++pos] = hexify[low_surrogate & 0x0F];
-        }
-
-        ++pos;
-    }
+                        case 0x0A: // newline
+                        {
+                            string_buffer[bytes++] = '\\';
+                            string_buffer[bytes++] = 'n';
+                            break;
+                        }
 
-    /*!
-    @brief dump escaped string
+                        case 0x0C: // formfeed
+                        {
+                            string_buffer[bytes++] = '\\';
+                            string_buffer[bytes++] = 'f';
+                            break;
+                        }
 
-    Escape a string by replacing certain special characters by a sequence of an
-    escape character (backslash) and another character and other control
-    characters by a sequence of "\u" followed by a four-digit hex
-    representation. The escaped string is written to output stream @a o.
+                        case 0x0D: // carriage return
+                        {
+                            string_buffer[bytes++] = '\\';
+                            string_buffer[bytes++] = 'r';
+                            break;
+                        }
 
-    @param[in] s  the string to escape
-    @param[in] ensure_ascii  whether to escape non-ASCII characters with
-                             \uXXXX sequences
+                        case 0x22: // quotation mark
+                        {
+                            string_buffer[bytes++] = '\\';
+                            string_buffer[bytes++] = '\"';
+                            break;
+                        }
 
-    @complexity Linear in the length of string @a s.
-    */
-    void dump_escaped(const string_t& s, const bool ensure_ascii) const
-    {
-        throw_if_invalid_utf8(s);
+                        case 0x5C: // reverse solidus
+                        {
+                            string_buffer[bytes++] = '\\';
+                            string_buffer[bytes++] = '\\';
+                            break;
+                        }
 
-        const auto space = extra_space(s, ensure_ascii);
-        if (space == 0)
-        {
-            o->write_characters(s.c_str(), s.size());
-            return;
-        }
+                        default:
+                        {
+                            // escape control characters (0x00..0x1F) or, if
+                            // ensure_ascii parameter is used, non-ASCII characters
+                            if ((codepoint <= 0x1F) or (ensure_ascii and (codepoint >= 0x7F)))
+                            {
+                                if (codepoint <= 0xFFFF)
+                                {
+                                    (std::snprintf)(string_buffer.data() + bytes, 7, "\\u%04x",
+                                                    static_cast<uint16_t>(codepoint));
+                                    bytes += 6;
+                                }
+                                else
+                                {
+                                    (std::snprintf)(string_buffer.data() + bytes, 13, "\\u%04x\\u%04x",
+                                                    static_cast<uint16_t>(0xD7C0 + (codepoint >> 10)),
+                                                    static_cast<uint16_t>(0xDC00 + (codepoint & 0x3FF)));
+                                    bytes += 12;
+                                }
+                            }
+                            else
+                            {
+                                // copy byte to buffer (all previous bytes
+                                // been copied have in default case above)
+                                string_buffer[bytes++] = s[i];
+                            }
+                            break;
+                        }
+                    }
 
-        // create a result string of necessary size
-        string_t result(s.size() + space, '\\');
-        std::size_t pos = 0;
+                    // write buffer and reset index; there must be 13 bytes
+                    // left, as this is the maximal number of bytes to be
+                    // written ("\uxxxx\uxxxx\0") for one code point
+                    if (string_buffer.size() - bytes < 13)
+                    {
+                        o->write_characters(string_buffer.data(), bytes);
+                        bytes = 0;
+                    }
 
-        for (std::size_t i = 0; i < s.size(); ++i)
-        {
-            switch (s[i])
-            {
-                case '"': // quotation mark (0x22)
-                {
-                    result[pos + 1] = '"';
-                    pos += 2;
+                    // remember the byte position of this accept
+                    bytes_after_last_accept = bytes;
+                    undumped_chars = 0;
                     break;
                 }
 
-                case '\\': // reverse solidus (0x5C)
+                case UTF8_REJECT:  // decode found invalid UTF-8 byte
                 {
-                    // nothing to change
-                    pos += 2;
-                    break;
-                }
+                    switch (error_handler)
+                    {
+                        case error_handler_t::strict:
+                        {
+                            std::string sn(3, '\0');
+                            (std::snprintf)(&sn[0], sn.size(), "%.2X", byte);
+                            JSON_THROW(type_error::create(316, "invalid UTF-8 byte at index " + std::to_string(i) + ": 0x" + sn));
+                        }
 
-                case '\b': // backspace (0x08)
-                {
-                    result[pos + 1] = 'b';
-                    pos += 2;
-                    break;
-                }
+                        case error_handler_t::ignore:
+                        case error_handler_t::replace:
+                        {
+                            // in case we saw this character the first time, we
+                            // would like to read it again, because the byte
+                            // may be OK for itself, but just not OK for the
+                            // previous sequence
+                            if (undumped_chars > 0)
+                            {
+                                --i;
+                            }
 
-                case '\f': // formfeed (0x0C)
-                {
-                    result[pos + 1] = 'f';
-                    pos += 2;
+                            // reset length buffer to the last accepted index;
+                            // thus removing/ignoring the invalid characters
+                            bytes = bytes_after_last_accept;
+
+                            if (error_handler == error_handler_t::replace)
+                            {
+                                // add a replacement character
+                                if (ensure_ascii)
+                                {
+                                    string_buffer[bytes++] = '\\';
+                                    string_buffer[bytes++] = 'u';
+                                    string_buffer[bytes++] = 'f';
+                                    string_buffer[bytes++] = 'f';
+                                    string_buffer[bytes++] = 'f';
+                                    string_buffer[bytes++] = 'd';
+                                }
+                                else
+                                {
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xEF');
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBF');
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBD');
+                                }
+                                bytes_after_last_accept = bytes;
+                            }
+
+                            undumped_chars = 0;
+
+                            // continue processing the string
+                            state = UTF8_ACCEPT;
+                            break;
+                        }
+                    }
                     break;
                 }
 
-                case '\n': // newline (0x0A)
+                default:  // decode found yet incomplete multi-byte code point
                 {
-                    result[pos + 1] = 'n';
-                    pos += 2;
+                    if (not ensure_ascii)
+                    {
+                        // code point will not be escaped - copy byte to buffer
+                        string_buffer[bytes++] = s[i];
+                    }
+                    ++undumped_chars;
                     break;
                 }
+            }
+        }
 
-                case '\r': // carriage return (0x0D)
+        // we finished processing the string
+        if (JSON_LIKELY(state == UTF8_ACCEPT))
+        {
+            // write buffer
+            if (bytes > 0)
+            {
+                o->write_characters(string_buffer.data(), bytes);
+            }
+        }
+        else
+        {
+            // we finish reading, but do not accept: string was incomplete
+            switch (error_handler)
+            {
+                case error_handler_t::strict:
                 {
-                    result[pos + 1] = 'r';
-                    pos += 2;
-                    break;
+                    std::string sn(3, '\0');
+                    (std::snprintf)(&sn[0], sn.size(), "%.2X", static_cast<uint8_t>(s.back()));
+                    JSON_THROW(type_error::create(316, "incomplete UTF-8 string; last byte: 0x" + sn));
                 }
 
-                case '\t': // horizontal tab (0x09)
+                case error_handler_t::ignore:
                 {
-                    result[pos + 1] = 't';
-                    pos += 2;
+                    // write all accepted bytes
+                    o->write_characters(string_buffer.data(), bytes_after_last_accept);
                     break;
                 }
 
-                default:
+                case error_handler_t::replace:
                 {
-                    // escape control characters (0x00..0x1F) or, if
-                    // ensure_ascii parameter is used, non-ASCII characters
-                    if ((0x00 <= s[i] and s[i] <= 0x1F) or
-                            (ensure_ascii and (s[i] & 0x80 or s[i] == 0x7F)))
+                    // write all accepted bytes
+                    o->write_characters(string_buffer.data(), bytes_after_last_accept);
+                    // add a replacement character
+                    if (ensure_ascii)
                     {
-                        const auto bytes = bytes_following(static_cast<uint8_t>(s[i]));
-                        // invalid characters will be detected by throw_if_invalid_utf8
-                        assert (bytes != std::string::npos);
-
-                        // check that the additional bytes are present
-                        assert(i + bytes < s.size());
-
-                        // to use \uxxxx escaping, we first need to calculate
-                        // the codepoint from the UTF-8 bytes
-                        int codepoint = 0;
-
-                        // bytes is unsigned type:
-                        assert(bytes <= 3);
-                        switch (bytes)
-                        {
-                            case 0:
-                            {
-                                codepoint = s[i] & 0xFF;
-                                break;
-                            }
-
-                            case 1:
-                            {
-                                codepoint = ((s[i] & 0x3F) << 6)
-                                            + (s[i + 1] & 0x7F);
-                                break;
-                            }
-
-                            case 2:
-                            {
-                                codepoint = ((s[i] & 0x1F) << 12)
-                                            + ((s[i + 1] & 0x7F) << 6)
-                                            + (s[i + 2] & 0x7F);
-                                break;
-                            }
-
-                            case 3:
-                            {
-                                codepoint = ((s[i] & 0xF) << 18)
-                                            + ((s[i + 1] & 0x7F) << 12)
-                                            + ((s[i + 2] & 0x7F) << 6)
-                                            + (s[i + 3] & 0x7F);
-                                break;
-                            }
-
-                            default:
-                                break;  // LCOV_EXCL_LINE
-                        }
-
-                        escape_codepoint(codepoint, result, pos);
-                        i += bytes;
+                        o->write_characters("\\ufffd", 6);
                     }
                     else
                     {
-                        // all other characters are added as-is
-                        result[pos++] = s[i];
+                        o->write_characters("\xEF\xBF\xBD", 3);
                     }
                     break;
                 }
             }
         }
-
-        assert(pos == result.size());
-        o->write_characters(result.c_str(), result.size());
     }
 
     /*!
@@ -6644,7 +11432,7 @@ class serializer
             return;
         }
 
-        const bool is_negative = (x <= 0) and (x != 0);  // see issue #755
+        const bool is_negative = std::is_same<NumberType, number_integer_t>::value and not (x >= 0);  // see issue #755
         std::size_t i = 0;
 
         while (x != 0)
@@ -6679,17 +11467,39 @@ class serializer
     void dump_float(number_float_t x)
     {
         // NaN / inf
-        if (not std::isfinite(x) or std::isnan(x))
+        if (not std::isfinite(x))
         {
             o->write_characters("null", 4);
             return;
         }
 
-        // get number of digits for a text -> float -> text round-trip
-        static constexpr auto d = std::numeric_limits<number_float_t>::digits10;
+        // If number_float_t is an IEEE-754 single or double precision number,
+        // use the Grisu2 algorithm to produce short numbers which are
+        // guaranteed to round-trip, using strtof and strtod, resp.
+        //
+        // NB: The test below works if <long double> == <double>.
+        static constexpr bool is_ieee_single_or_double
+            = (std::numeric_limits<number_float_t>::is_iec559 and std::numeric_limits<number_float_t>::digits == 24 and std::numeric_limits<number_float_t>::max_exponent == 128) or
+              (std::numeric_limits<number_float_t>::is_iec559 and std::numeric_limits<number_float_t>::digits == 53 and std::numeric_limits<number_float_t>::max_exponent == 1024);
+
+        dump_float(x, std::integral_constant<bool, is_ieee_single_or_double>());
+    }
+
+    void dump_float(number_float_t x, std::true_type /*is_ieee_single_or_double*/)
+    {
+        char* begin = number_buffer.data();
+        char* end = ::nlohmann::detail::to_chars(begin, begin + number_buffer.size(), x);
+
+        o->write_characters(begin, static_cast<size_t>(end - begin));
+    }
+
+    void dump_float(number_float_t x, std::false_type /*is_ieee_single_or_double*/)
+    {
+        // get number of digits for a float -> text -> float round-trip
+        static constexpr auto d = std::numeric_limits<number_float_t>::max_digits10;
 
         // the actual conversion
-        std::ptrdiff_t len = snprintf(number_buffer.data(), number_buffer.size(), "%.*g", d, x);
+        std::ptrdiff_t len = (std::snprintf)(number_buffer.data(), number_buffer.size(), "%.*g", d, x);
 
         // negative value indicates an error
         assert(len > 0);
@@ -6744,15 +11554,16 @@ class serializer
     followed.
 
     @param[in,out] state  the state of the decoding
+    @param[in,out] codep  codepoint (valid only if resulting state is UTF8_ACCEPT)
     @param[in] byte       next byte to decode
+    @return               new state
 
-    @note The function has been edited: a std::array is used and the code
-          point is not calculated.
+    @note The function has been edited: a std::array is used.
 
     @copyright Copyright (c) 2008-2009 Bjoern Hoehrmann <bjoern@hoehrmann.de>
     @sa http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
     */
-    static void decode(uint8_t& state, const uint8_t byte)
+    static uint8_t decode(uint8_t& state, uint32_t& codep, const uint8_t byte) noexcept
     {
         static const std::array<uint8_t, 400> utf8d =
         {
@@ -6775,42 +11586,13 @@ class serializer
         };
 
         const uint8_t type = utf8d[byte];
-        state = utf8d[256u + state * 16u + type];
-    }
 
-    /*!
-    @brief throw an exception if a string is not UTF-8 encoded
-
-    @param[in] str  UTF-8 string to check
-    @throw type_error.316 if passed string is not UTF-8 encoded
+        codep = (state != UTF8_ACCEPT)
+                ? (byte & 0x3fu) | (codep << 6)
+                : static_cast<uint32_t>(0xff >> type) & (byte);
 
-    @since version 3.0.0
-    */
-    static void throw_if_invalid_utf8(const std::string& str)
-    {
-        // start with state 0 (= accept)
-        uint8_t state = 0;
-
-        for (size_t i = 0; i < str.size(); ++i)
-        {
-            const auto byte = static_cast<uint8_t>(str[i]);
-            decode(state, byte);
-            if (state == 1)
-            {
-                // state 1 means reject
-                std::stringstream ss;
-                ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << static_cast<int>(byte);
-                JSON_THROW(type_error::create(316, "invalid UTF-8 byte at index " + std::to_string(i) + ": 0x" + ss.str()));
-            }
-        }
-
-        if (state != 0)
-        {
-            // we finish reading, but do not accept: string was incomplete
-            std::stringstream ss;
-            ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << static_cast<int>(static_cast<uint8_t>(str.back()));
-            JSON_THROW(type_error::create(316, "incomplete UTF-8 string; last byte: 0x" + ss.str()));
-        }
+        state = utf8d[256u + state * 16u + type];
+        return state;
     }
 
   private:
@@ -6827,13 +11609,33 @@ class serializer
     /// the locale's decimal point character
     const char decimal_point = '\0';
 
+    /// string buffer
+    std::array<char, 512> string_buffer{{}};
+
     /// the indentation character
     const char indent_char;
-
     /// the indentation string
     string_t indent_string;
+
+    /// error_handler how to react on decoding errors
+    const error_handler_t error_handler;
 };
+}  // namespace detail
+}  // namespace nlohmann
+
+// #include <nlohmann/detail/json_ref.hpp>
 
+
+#include <initializer_list>
+#include <utility>
+
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
 template<typename BasicJsonType>
 class json_ref
 {
@@ -6852,15 +11654,19 @@ class json_ref
         : owned_value(init), value_ref(&owned_value), is_rvalue(true)
     {}
 
-    template<class... Args>
-    json_ref(Args&& ... args)
-        : owned_value(std::forward<Args>(args)...), value_ref(&owned_value), is_rvalue(true)
-    {}
+    template <
+        class... Args,
+        enable_if_t<std::is_constructible<value_type, Args...>::value, int> = 0 >
+    json_ref(Args && ... args)
+        : owned_value(std::forward<Args>(args)...), value_ref(&owned_value),
+          is_rvalue(true) {}
 
     // class should be movable only
     json_ref(json_ref&&) = default;
     json_ref(const json_ref&) = delete;
     json_ref& operator=(const json_ref&) = delete;
+    json_ref& operator=(json_ref&&) = delete;
+    ~json_ref() = default;
 
     value_type moved_or_copied() const
     {
@@ -6886,74 +11692,30 @@ class json_ref
     value_type* value_ref = nullptr;
     const bool is_rvalue;
 };
+}  // namespace detail
+}  // namespace nlohmann
 
-} // namespace detail
-
-/// namespace to hold default `to_json` / `from_json` functions
-namespace
-{
-constexpr const auto& to_json = detail::static_const<detail::to_json_fn>::value;
-constexpr const auto& from_json = detail::static_const<detail::from_json_fn>::value;
-}
-
-
-/*!
-@brief default JSONSerializer template argument
-
-This serializer ignores the template arguments and uses ADL
-([argument-dependent lookup](http://en.cppreference.com/w/cpp/language/adl))
-for serialization.
-*/
-template<typename, typename>
-struct adl_serializer
-{
-    /*!
-    @brief convert a JSON value to any value type
-
-    This function is usually called by the `get()` function of the
-    @ref basic_json class (either explicit or via conversion operators).
-
-    @param[in] j         JSON value to read from
-    @param[in,out] val  value to write to
-    */
-    template<typename BasicJsonType, typename ValueType>
-    static void from_json(BasicJsonType&& j, ValueType& val) noexcept(
-        noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val)))
-    {
-        ::nlohmann::from_json(std::forward<BasicJsonType>(j), val);
-    }
+// #include <nlohmann/detail/json_pointer.hpp>
 
-    /*!
-    @brief convert any value type to a JSON value
 
-    This function is usually called by the constructors of the @ref basic_json
-    class.
+#include <cassert> // assert
+#include <numeric> // accumulate
+#include <string> // string
+#include <vector> // vector
 
-    @param[in,out] j  JSON value to write to
-    @param[in] val     value to read from
-    */
-    template<typename BasicJsonType, typename ValueType>
-    static void to_json(BasicJsonType& j, ValueType&& val) noexcept(
-        noexcept(::nlohmann::to_json(j, std::forward<ValueType>(val))))
-    {
-        ::nlohmann::to_json(j, std::forward<ValueType>(val));
-    }
-};
+// #include <nlohmann/detail/macro_scope.hpp>
 
-/*!
-@brief JSON Pointer
+// #include <nlohmann/detail/exceptions.hpp>
 
-A JSON pointer defines a string syntax for identifying a specific value
-within a JSON document. It can be used with functions `at` and
-`operator[]`. Furthermore, JSON pointers are the base for JSON patches.
+// #include <nlohmann/detail/value_t.hpp>
 
-@sa [RFC 6901](https://tools.ietf.org/html/rfc6901)
 
-@since version 2.0.0
-*/
+namespace nlohmann
+{
+template<typename BasicJsonType>
 class json_pointer
 {
-    /// allow basic_json to access private members
+    // allow basic_json to access private members
     NLOHMANN_BASIC_JSON_TPL_DECLARATION
     friend class basic_json;
 
@@ -6967,19 +11729,21 @@ class json_pointer
     @param[in] s  string representing the JSON pointer; if omitted, the empty
                   string is assumed which references the whole JSON value
 
-    @throw parse_error.107 if the given JSON pointer @a s is nonempty and
-    does not begin with a slash (`/`); see example below
+    @throw parse_error.107 if the given JSON pointer @a s is nonempty and does
+                           not begin with a slash (`/`); see example below
 
-    @throw parse_error.108 if a tilde (`~`) in the given JSON pointer @a s
-    is not followed by `0` (representing `~`) or `1` (representing `/`);
-    see example below
+    @throw parse_error.108 if a tilde (`~`) in the given JSON pointer @a s is
+    not followed by `0` (representing `~`) or `1` (representing `/`); see
+    example below
 
-    @liveexample{The example shows the construction several valid JSON
-    pointers as well as the exceptional behavior.,json_pointer}
+    @liveexample{The example shows the construction several valid JSON pointers
+    as well as the exceptional behavior.,json_pointer}
 
     @since version 2.0.0
     */
-    explicit json_pointer(const std::string& s = "") : reference_tokens(split(s)) {}
+    explicit json_pointer(const std::string& s = "")
+        : reference_tokens(split(s))
+    {}
 
     /*!
     @brief return a string representation of the JSON pointer
@@ -6996,7 +11760,7 @@ class json_pointer
 
     @since version 2.0.0
     */
-    std::string to_string() const noexcept
+    std::string to_string() const
     {
         return std::accumulate(reference_tokens.begin(), reference_tokens.end(),
                                std::string{},
@@ -7021,7 +11785,7 @@ class json_pointer
     */
     static int array_index(const std::string& s)
     {
-        size_t processed_chars = 0;
+        std::size_t processed_chars = 0;
         const int res = std::stoi(s, &processed_chars);
 
         // check if the string was completely read
@@ -7051,7 +11815,7 @@ class json_pointer
     }
 
     /// return whether pointer points to the root document
-    bool is_root() const
+    bool is_root() const noexcept
     {
         return reference_tokens.empty();
     }
@@ -7076,8 +11840,66 @@ class json_pointer
     @throw parse_error.109 if array index is not a number
     @throw type_error.313 if value cannot be unflattened
     */
-    NLOHMANN_BASIC_JSON_TPL_DECLARATION
-    NLOHMANN_BASIC_JSON_TPL& get_and_create(NLOHMANN_BASIC_JSON_TPL& j) const;
+    BasicJsonType& get_and_create(BasicJsonType& j) const
+    {
+        using size_type = typename BasicJsonType::size_type;
+        auto result = &j;
+
+        // in case no reference tokens exist, return a reference to the JSON value
+        // j which will be overwritten by a primitive value
+        for (const auto& reference_token : reference_tokens)
+        {
+            switch (result->m_type)
+            {
+                case detail::value_t::null:
+                {
+                    if (reference_token == "0")
+                    {
+                        // start a new array if reference token is 0
+                        result = &result->operator[](0);
+                    }
+                    else
+                    {
+                        // start a new object otherwise
+                        result = &result->operator[](reference_token);
+                    }
+                    break;
+                }
+
+                case detail::value_t::object:
+                {
+                    // create an entry in the object
+                    result = &result->operator[](reference_token);
+                    break;
+                }
+
+                case detail::value_t::array:
+                {
+                    // create an entry in the array
+                    JSON_TRY
+                    {
+                        result = &result->operator[](static_cast<size_type>(array_index(reference_token)));
+                    }
+                    JSON_CATCH(std::invalid_argument&)
+                    {
+                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
+                    }
+                    break;
+                }
+
+                /*
+                The following code is only reached if there exists a reference
+                token _and_ the current value is primitive. In this case, we have
+                an error situation, because primitive values may only occur as
+                single value; that is, with an empty list of reference tokens.
+                */
+                default:
+                    JSON_THROW(detail::type_error::create(313, "invalid value to unflatten"));
+            }
+        }
+
+        return *result;
+    }
 
     /*!
     @brief return a reference to the pointed to value
@@ -7098,8 +11920,75 @@ class json_pointer
     @throw parse_error.109   if an array index was not a number
     @throw out_of_range.404  if the JSON pointer can not be resolved
     */
-    NLOHMANN_BASIC_JSON_TPL_DECLARATION
-    NLOHMANN_BASIC_JSON_TPL& get_unchecked(NLOHMANN_BASIC_JSON_TPL* ptr) const;
+    BasicJsonType& get_unchecked(BasicJsonType* ptr) const
+    {
+        using size_type = typename BasicJsonType::size_type;
+        for (const auto& reference_token : reference_tokens)
+        {
+            // convert null values to arrays or objects before continuing
+            if (ptr->m_type == detail::value_t::null)
+            {
+                // check if reference token is a number
+                const bool nums =
+                    std::all_of(reference_token.begin(), reference_token.end(),
+                                [](const char x)
+                {
+                    return (x >= '0' and x <= '9');
+                });
+
+                // change value to array for numbers or "-" or to object otherwise
+                *ptr = (nums or reference_token == "-")
+                       ? detail::value_t::array
+                       : detail::value_t::object;
+            }
+
+            switch (ptr->m_type)
+            {
+                case detail::value_t::object:
+                {
+                    // use unchecked object access
+                    ptr = &ptr->operator[](reference_token);
+                    break;
+                }
+
+                case detail::value_t::array:
+                {
+                    // error condition (cf. RFC 6901, Sect. 4)
+                    if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
+                    {
+                        JSON_THROW(detail::parse_error::create(106, 0,
+                                                               "array index '" + reference_token +
+                                                               "' must not begin with '0'"));
+                    }
+
+                    if (reference_token == "-")
+                    {
+                        // explicitly treat "-" as index beyond the end
+                        ptr = &ptr->operator[](ptr->m_value.array->size());
+                    }
+                    else
+                    {
+                        // convert array index to number; unchecked access
+                        JSON_TRY
+                        {
+                            ptr = &ptr->operator[](
+                                static_cast<size_type>(array_index(reference_token)));
+                        }
+                        JSON_CATCH(std::invalid_argument&)
+                        {
+                            JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
+                        }
+                    }
+                    break;
+                }
+
+                default:
+                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
+            }
+        }
+
+        return *ptr;
+    }
 
     /*!
     @throw parse_error.106   if an array index begins with '0'
@@ -7107,8 +11996,57 @@ class json_pointer
     @throw out_of_range.402  if the array index '-' is used
     @throw out_of_range.404  if the JSON pointer can not be resolved
     */
-    NLOHMANN_BASIC_JSON_TPL_DECLARATION
-    NLOHMANN_BASIC_JSON_TPL& get_checked(NLOHMANN_BASIC_JSON_TPL* ptr) const;
+    BasicJsonType& get_checked(BasicJsonType* ptr) const
+    {
+        using size_type = typename BasicJsonType::size_type;
+        for (const auto& reference_token : reference_tokens)
+        {
+            switch (ptr->m_type)
+            {
+                case detail::value_t::object:
+                {
+                    // note: at performs range check
+                    ptr = &ptr->at(reference_token);
+                    break;
+                }
+
+                case detail::value_t::array:
+                {
+                    if (JSON_UNLIKELY(reference_token == "-"))
+                    {
+                        // "-" always fails the range check
+                        JSON_THROW(detail::out_of_range::create(402,
+                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
+                                                                ") is out of range"));
+                    }
+
+                    // error condition (cf. RFC 6901, Sect. 4)
+                    if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
+                    {
+                        JSON_THROW(detail::parse_error::create(106, 0,
+                                                               "array index '" + reference_token +
+                                                               "' must not begin with '0'"));
+                    }
+
+                    // note: at performs range check
+                    JSON_TRY
+                    {
+                        ptr = &ptr->at(static_cast<size_type>(array_index(reference_token)));
+                    }
+                    JSON_CATCH(std::invalid_argument&)
+                    {
+                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
+                    }
+                    break;
+                }
+
+                default:
+                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
+            }
+        }
+
+        return *ptr;
+    }
 
     /*!
     @brief return a const reference to the pointed to value
@@ -7123,8 +12061,58 @@ class json_pointer
     @throw out_of_range.402  if the array index '-' is used
     @throw out_of_range.404  if the JSON pointer can not be resolved
     */
-    NLOHMANN_BASIC_JSON_TPL_DECLARATION
-    const NLOHMANN_BASIC_JSON_TPL& get_unchecked(const NLOHMANN_BASIC_JSON_TPL* ptr) const;
+    const BasicJsonType& get_unchecked(const BasicJsonType* ptr) const
+    {
+        using size_type = typename BasicJsonType::size_type;
+        for (const auto& reference_token : reference_tokens)
+        {
+            switch (ptr->m_type)
+            {
+                case detail::value_t::object:
+                {
+                    // use unchecked object access
+                    ptr = &ptr->operator[](reference_token);
+                    break;
+                }
+
+                case detail::value_t::array:
+                {
+                    if (JSON_UNLIKELY(reference_token == "-"))
+                    {
+                        // "-" cannot be used for const access
+                        JSON_THROW(detail::out_of_range::create(402,
+                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
+                                                                ") is out of range"));
+                    }
+
+                    // error condition (cf. RFC 6901, Sect. 4)
+                    if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
+                    {
+                        JSON_THROW(detail::parse_error::create(106, 0,
+                                                               "array index '" + reference_token +
+                                                               "' must not begin with '0'"));
+                    }
+
+                    // use unchecked array access
+                    JSON_TRY
+                    {
+                        ptr = &ptr->operator[](
+                            static_cast<size_type>(array_index(reference_token)));
+                    }
+                    JSON_CATCH(std::invalid_argument&)
+                    {
+                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
+                    }
+                    break;
+                }
+
+                default:
+                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
+            }
+        }
+
+        return *ptr;
+    }
 
     /*!
     @throw parse_error.106   if an array index begins with '0'
@@ -7132,8 +12120,57 @@ class json_pointer
     @throw out_of_range.402  if the array index '-' is used
     @throw out_of_range.404  if the JSON pointer can not be resolved
     */
-    NLOHMANN_BASIC_JSON_TPL_DECLARATION
-    const NLOHMANN_BASIC_JSON_TPL& get_checked(const NLOHMANN_BASIC_JSON_TPL* ptr) const;
+    const BasicJsonType& get_checked(const BasicJsonType* ptr) const
+    {
+        using size_type = typename BasicJsonType::size_type;
+        for (const auto& reference_token : reference_tokens)
+        {
+            switch (ptr->m_type)
+            {
+                case detail::value_t::object:
+                {
+                    // note: at performs range check
+                    ptr = &ptr->at(reference_token);
+                    break;
+                }
+
+                case detail::value_t::array:
+                {
+                    if (JSON_UNLIKELY(reference_token == "-"))
+                    {
+                        // "-" always fails the range check
+                        JSON_THROW(detail::out_of_range::create(402,
+                                                                "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
+                                                                ") is out of range"));
+                    }
+
+                    // error condition (cf. RFC 6901, Sect. 4)
+                    if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
+                    {
+                        JSON_THROW(detail::parse_error::create(106, 0,
+                                                               "array index '" + reference_token +
+                                                               "' must not begin with '0'"));
+                    }
+
+                    // note: at performs range check
+                    JSON_TRY
+                    {
+                        ptr = &ptr->at(static_cast<size_type>(array_index(reference_token)));
+                    }
+                    JSON_CATCH(std::invalid_argument&)
+                    {
+                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
+                    }
+                    break;
+                }
+
+                default:
+                    JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
+            }
+        }
+
+        return *ptr;
+    }
 
     /*!
     @brief split the string input to reference tokens
@@ -7170,11 +12207,11 @@ class json_pointer
             std::size_t slash = reference_string.find_first_of('/', 1),
             // set the beginning of the first reference token
             start = 1;
-            // we can stop if start == string::npos+1 = 0
+            // we can stop if start == 0 (if slash == std::string::npos)
             start != 0;
             // set the beginning of the next reference token
             // (will eventually be 0 if slash == std::string::npos)
-            start = slash + 1,
+            start = (slash == std::string::npos) ? 0 : slash + 1,
             // find next slash
             slash = reference_string.find_first_of('/', start))
         {
@@ -7230,7 +12267,7 @@ class json_pointer
         {}
     }
 
-    /// escape "~"" to "~0" and "/" to "~1"
+    /// escape "~" to "~0" and "/" to "~1"
     static std::string escape(std::string s)
     {
         replace_substring(s, "~", "~0");
@@ -7252,10 +12289,57 @@ class json_pointer
 
     @note Empty objects or arrays are flattened to `null`.
     */
-    NLOHMANN_BASIC_JSON_TPL_DECLARATION
     static void flatten(const std::string& reference_string,
-                        const NLOHMANN_BASIC_JSON_TPL& value,
-                        NLOHMANN_BASIC_JSON_TPL& result);
+                        const BasicJsonType& value,
+                        BasicJsonType& result)
+    {
+        switch (value.m_type)
+        {
+            case detail::value_t::array:
+            {
+                if (value.m_value.array->empty())
+                {
+                    // flatten empty array as null
+                    result[reference_string] = nullptr;
+                }
+                else
+                {
+                    // iterate array and use index as reference string
+                    for (std::size_t i = 0; i < value.m_value.array->size(); ++i)
+                    {
+                        flatten(reference_string + "/" + std::to_string(i),
+                                value.m_value.array->operator[](i), result);
+                    }
+                }
+                break;
+            }
+
+            case detail::value_t::object:
+            {
+                if (value.m_value.object->empty())
+                {
+                    // flatten empty object as null
+                    result[reference_string] = nullptr;
+                }
+                else
+                {
+                    // iterate object and use keys as reference string
+                    for (const auto& element : *value.m_value.object)
+                    {
+                        flatten(reference_string + "/" + escape(element.first), element.second, result);
+                    }
+                }
+                break;
+            }
+
+            default:
+            {
+                // add primitive value with its reference string
+                result[reference_string] = value;
+                break;
+            }
+        }
+    }
 
     /*!
     @param[in] value  flattened JSON
@@ -7267,19 +12351,112 @@ class json_pointer
     @throw type_error.315  if object values are not primitive
     @throw type_error.313  if value cannot be unflattened
     */
-    NLOHMANN_BASIC_JSON_TPL_DECLARATION
-    static NLOHMANN_BASIC_JSON_TPL
-    unflatten(const NLOHMANN_BASIC_JSON_TPL& value);
+    static BasicJsonType
+    unflatten(const BasicJsonType& value)
+    {
+        if (JSON_UNLIKELY(not value.is_object()))
+        {
+            JSON_THROW(detail::type_error::create(314, "only objects can be unflattened"));
+        }
+
+        BasicJsonType result;
+
+        // iterate the JSON object values
+        for (const auto& element : *value.m_value.object)
+        {
+            if (JSON_UNLIKELY(not element.second.is_primitive()))
+            {
+                JSON_THROW(detail::type_error::create(315, "values in object must be primitive"));
+            }
+
+            // assign value to reference pointed to by JSON pointer; Note that if
+            // the JSON pointer is "" (i.e., points to the whole value), function
+            // get_and_create returns a reference to result itself. An assignment
+            // will then create a primitive value.
+            json_pointer(element.first).get_and_create(result) = element.second;
+        }
+
+        return result;
+    }
 
     friend bool operator==(json_pointer const& lhs,
-                           json_pointer const& rhs) noexcept;
+                           json_pointer const& rhs) noexcept
+    {
+        return (lhs.reference_tokens == rhs.reference_tokens);
+    }
 
     friend bool operator!=(json_pointer const& lhs,
-                           json_pointer const& rhs) noexcept;
+                           json_pointer const& rhs) noexcept
+    {
+        return not (lhs == rhs);
+    }
 
     /// the reference tokens
     std::vector<std::string> reference_tokens;
 };
+}  // namespace nlohmann
+
+// #include <nlohmann/adl_serializer.hpp>
+
+
+#include <utility>
+
+// #include <nlohmann/detail/conversions/from_json.hpp>
+
+// #include <nlohmann/detail/conversions/to_json.hpp>
+
+
+namespace nlohmann
+{
+
+template<typename, typename>
+struct adl_serializer
+{
+    /*!
+    @brief convert a JSON value to any value type
+
+    This function is usually called by the `get()` function of the
+    @ref basic_json class (either explicit or via conversion operators).
+
+    @param[in] j        JSON value to read from
+    @param[in,out] val  value to write to
+    */
+    template<typename BasicJsonType, typename ValueType>
+    static auto from_json(BasicJsonType&& j, ValueType& val) noexcept(
+        noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val)))
+    -> decltype(::nlohmann::from_json(std::forward<BasicJsonType>(j), val), void())
+    {
+        ::nlohmann::from_json(std::forward<BasicJsonType>(j), val);
+    }
+
+    /*!
+    @brief convert any value type to a JSON value
+
+    This function is usually called by the constructors of the @ref basic_json
+    class.
+
+    @param[in,out] j  JSON value to write to
+    @param[in] val    value to read from
+    */
+    template <typename BasicJsonType, typename ValueType>
+    static auto to_json(BasicJsonType& j, ValueType&& val) noexcept(
+        noexcept(::nlohmann::to_json(j, std::forward<ValueType>(val))))
+    -> decltype(::nlohmann::to_json(j, std::forward<ValueType>(val)), void())
+    {
+        ::nlohmann::to_json(j, std::forward<ValueType>(val));
+    }
+};
+
+}  // namespace nlohmann
+
+
+/*!
+@brief namespace for Niels Lohmann
+@see https://github.com/nlohmann
+@since version 1.0.0
+*/
+namespace nlohmann
+{
 
 /*!
 @brief a class to store JSON values
@@ -7305,42 +12482,42 @@ and `from_json()` (@ref adl_serializer by default)
 
 @requirement The class satisfies the following concept requirements:
 - Basic
- - [DefaultConstructible](http://en.cppreference.com/w/cpp/concept/DefaultConstructible):
+ - [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible):
    JSON values can be default constructed. The result will be a JSON null
    value.
- - [MoveConstructible](http://en.cppreference.com/w/cpp/concept/MoveConstructible):
+ - [MoveConstructible](https://en.cppreference.com/w/cpp/named_req/MoveConstructible):
    A JSON value can be constructed from an rvalue argument.
- - [CopyConstructible](http://en.cppreference.com/w/cpp/concept/CopyConstructible):
+ - [CopyConstructible](https://en.cppreference.com/w/cpp/named_req/CopyConstructible):
    A JSON value can be copy-constructed from an lvalue expression.
- - [MoveAssignable](http://en.cppreference.com/w/cpp/concept/MoveAssignable):
+ - [MoveAssignable](https://en.cppreference.com/w/cpp/named_req/MoveAssignable):
    A JSON value van be assigned from an rvalue argument.
- - [CopyAssignable](http://en.cppreference.com/w/cpp/concept/CopyAssignable):
+ - [CopyAssignable](https://en.cppreference.com/w/cpp/named_req/CopyAssignable):
    A JSON value can be copy-assigned from an lvalue expression.
- - [Destructible](http://en.cppreference.com/w/cpp/concept/Destructible):
+ - [Destructible](https://en.cppreference.com/w/cpp/named_req/Destructible):
    JSON values can be destructed.
 - Layout
- - [StandardLayoutType](http://en.cppreference.com/w/cpp/concept/StandardLayoutType):
+ - [StandardLayoutType](https://en.cppreference.com/w/cpp/named_req/StandardLayoutType):
    JSON values have
-   [standard layout](http://en.cppreference.com/w/cpp/language/data_members#Standard_layout):
+   [standard layout](https://en.cppreference.com/w/cpp/language/data_members#Standard_layout):
    All non-static data members are private and standard layout types, the
    class has no virtual functions or (virtual) base classes.
 - Library-wide
- - [EqualityComparable](http://en.cppreference.com/w/cpp/concept/EqualityComparable):
+ - [EqualityComparable](https://en.cppreference.com/w/cpp/named_req/EqualityComparable):
    JSON values can be compared with `==`, see @ref
    operator==(const_reference,const_reference).
- - [LessThanComparable](http://en.cppreference.com/w/cpp/concept/LessThanComparable):
+ - [LessThanComparable](https://en.cppreference.com/w/cpp/named_req/LessThanComparable):
    JSON values can be compared with `<`, see @ref
    operator<(const_reference,const_reference).
- - [Swappable](http://en.cppreference.com/w/cpp/concept/Swappable):
+ - [Swappable](https://en.cppreference.com/w/cpp/named_req/Swappable):
    Any JSON lvalue or rvalue of can be swapped with any lvalue or rvalue of
    other compatible types, using unqualified function call @ref swap().
- - [NullablePointer](http://en.cppreference.com/w/cpp/concept/NullablePointer):
+ - [NullablePointer](https://en.cppreference.com/w/cpp/named_req/NullablePointer):
    JSON values can be compared against `std::nullptr_t` objects which are used
    to model the `null` value.
 - Container
- - [Container](http://en.cppreference.com/w/cpp/concept/Container):
+ - [Container](https://en.cppreference.com/w/cpp/named_req/Container):
    JSON values can be used like STL containers and provide iterator access.
- - [ReversibleContainer](http://en.cppreference.com/w/cpp/concept/ReversibleContainer);
+ - [ReversibleContainer](https://en.cppreference.com/w/cpp/named_req/ReversibleContainer);
    JSON values can be used like STL containers and provide reverse iterator
    access.
 
@@ -7367,15 +12544,19 @@ class basic_json
 {
   private:
     template<detail::value_t> friend struct detail::external_constructor;
-    friend ::nlohmann::json_pointer;
+    friend ::nlohmann::json_pointer<basic_json>;
     friend ::nlohmann::detail::parser<basic_json>;
     friend ::nlohmann::detail::serializer<basic_json>;
     template<typename BasicJsonType>
     friend class ::nlohmann::detail::iter_impl;
     template<typename BasicJsonType, typename CharType>
     friend class ::nlohmann::detail::binary_writer;
-    template<typename BasicJsonType>
+    template<typename BasicJsonType, typename SAX>
     friend class ::nlohmann::detail::binary_reader;
+    template<typename BasicJsonType>
+    friend class ::nlohmann::detail::json_sax_dom_parser;
+    template<typename BasicJsonType>
+    friend class ::nlohmann::detail::json_sax_dom_callback_parser;
 
     /// workaround type for MSVC
     using basic_json_t = NLOHMANN_BASIC_JSON_TPL;
@@ -7403,13 +12584,19 @@ class basic_json
 
   public:
     using value_t = detail::value_t;
-    /// @copydoc nlohmann::json_pointer
-    using json_pointer = ::nlohmann::json_pointer;
+    /// JSON Pointer, see @ref nlohmann::json_pointer
+    using json_pointer = ::nlohmann::json_pointer<basic_json>;
     template<typename T, typename SFINAE>
     using json_serializer = JSONSerializer<T, SFINAE>;
+    /// how to treat decoding errors
+    using error_handler_t = detail::error_handler_t;
     /// helper type for initializer lists of basic_json values
     using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
+    using input_format_t = detail::input_format_t;
+    /// SAX interface type, see @ref nlohmann::json_sax
+    using json_sax_t = json_sax<basic_json>;
+
     ////////////////
     // exceptions //
     ////////////////
@@ -7517,10 +12704,13 @@ class basic_json
         result["copyright"] = "(C) 2013-2017 Niels Lohmann";
         result["name"] = "JSON for Modern C++";
         result["url"] = "https://github.com/nlohmann/json";
-        result["version"] =
-        {
-            {"string", "3.0.1"}, {"major", 3}, {"minor", 0}, {"patch", 1}
-        };
+        result["version"]["string"] =
+            std::to_string(NLOHMANN_JSON_VERSION_MAJOR) + "." +
+            std::to_string(NLOHMANN_JSON_VERSION_MINOR) + "." +
+            std::to_string(NLOHMANN_JSON_VERSION_PATCH);
+        result["version"]["major"] = NLOHMANN_JSON_VERSION_MAJOR;
+        result["version"]["minor"] = NLOHMANN_JSON_VERSION_MINOR;
+        result["version"]["patch"] = NLOHMANN_JSON_VERSION_PATCH;
 
 #ifdef _WIN32
         result["platform"] = "win32";
@@ -7622,10 +12812,10 @@ class basic_json
     - When all names are unique, objects will be interoperable in the sense
       that all software implementations receiving that object will agree on
       the name-value mappings.
-    - When the names within an object are not unique, later stored name/value
-      pairs overwrite previously stored name/value pairs, leaving the used
-      names unique. For instance, `{"key": 1}` and `{"key": 2, "key": 1}` will
-      be treated as equal and both stored as `{"key": 1}`.
+    - When the names within an object are not unique, it is unspecified which
+      one of the values for a given key will be chosen. For instance,
+      `{"key": 2, "key": 1}` could be equal to either `{"key": 1}` or
+      `{"key": 2}`.
     - Internally, name/value pairs are stored in lexicographical order of the
       names. Objects will also be serialized (see @ref dump) in this order.
       For instance, `{"b": 1, "a": 2}` and `{"a": 2, "b": 1}` will be stored
@@ -8139,7 +13329,7 @@ class basic_json
                     object = nullptr;  // silence warning, see #821
                     if (JSON_UNLIKELY(t == value_t::null))
                     {
-                        JSON_THROW(other_error::create(500, "961c151d2e87f2686a955a9be24d316f1362bf21 3.0.1")); // LCOV_EXCL_LINE
+                        JSON_THROW(other_error::create(500, "961c151d2e87f2686a955a9be24d316f1362bf21 3.5.0")); // LCOV_EXCL_LINE
                     }
                     break;
                 }
@@ -8182,7 +13372,7 @@ class basic_json
             array = create<array_t>(std::move(value));
         }
 
-        void destroy(value_t t)
+        void destroy(value_t t) noexcept
         {
             switch (t)
             {
@@ -8227,7 +13417,7 @@ class basic_json
     value is changed, because the invariant expresses a relationship between
     @a m_type and @a m_value.
     */
-    void assert_invariant() const
+    void assert_invariant() const noexcept
     {
         assert(m_type != value_t::object or m_value.object != nullptr);
         assert(m_type != value_t::array or m_value.array != nullptr);
@@ -8307,7 +13497,6 @@ class basic_json
     */
     using parser_callback_t = typename parser::parser_callback_t;
 
-
     //////////////////
     // constructors //
     //////////////////
@@ -8409,6 +13598,7 @@ class basic_json
     - @a CompatibleType is not derived from `std::istream`,
     - @a CompatibleType is not @ref basic_json (to avoid hijacking copy/move
          constructors),
+    - @a CompatibleType is not a different @ref basic_json type (i.e. with different template arguments)
     - @a CompatibleType is not a @ref basic_json nested type (e.g.,
          @ref json_pointer, @ref iterator, etc ...)
     - @ref @ref json_serializer<U> has a
@@ -8432,21 +13622,91 @@ class basic_json
 
     @since version 2.1.0
     */
-    template<typename CompatibleType, typename U = detail::uncvref_t<CompatibleType>,
-             detail::enable_if_t<not std::is_base_of<std::istream, U>::value and
-                                 not std::is_same<U, basic_json_t>::value and
-                                 not detail::is_basic_json_nested_type<
-                                     basic_json_t, U>::value and
-                                 detail::has_to_json<basic_json, U>::value,
-                                 int> = 0>
-    basic_json(CompatibleType && val) noexcept(noexcept(JSONSerializer<U>::to_json(
-                std::declval<basic_json_t&>(), std::forward<CompatibleType>(val))))
+    template <typename CompatibleType,
+              typename U = detail::uncvref_t<CompatibleType>,
+              detail::enable_if_t<
+                  not detail::is_basic_json<U>::value and detail::is_compatible_type<basic_json_t, U>::value, int> = 0>
+    basic_json(CompatibleType && val) noexcept(noexcept(
+                JSONSerializer<U>::to_json(std::declval<basic_json_t&>(),
+                                           std::forward<CompatibleType>(val))))
     {
         JSONSerializer<U>::to_json(*this, std::forward<CompatibleType>(val));
         assert_invariant();
     }
 
     /*!
+    @brief create a JSON value from an existing one
+
+    This is a constructor for existing @ref basic_json types.
+    It does not hijack copy/move constructors, since the parameter has different
+    template arguments than the current ones.
+
+    The constructor tries to convert the internal @ref m_value of the parameter.
+
+    @tparam BasicJsonType a type such that:
+    - @a BasicJsonType is a @ref basic_json type.
+    - @a BasicJsonType has different template arguments than @ref basic_json_t.
+
+    @param[in] val the @ref basic_json value to be converted.
+
+    @complexity Usually linear in the size of the passed @a val, also
+                depending on the implementation of the called `to_json()`
+                method.
+
+    @exceptionsafety Depends on the called constructor. For types directly
+    supported by the library (i.e., all types for which no `to_json()` function
+    was provided), strong guarantee holds: if an exception is thrown, there are
+    no changes to any JSON value.
+
+    @since version 3.2.0
+    */
+    template <typename BasicJsonType,
+              detail::enable_if_t<
+                  detail::is_basic_json<BasicJsonType>::value and not std::is_same<basic_json, BasicJsonType>::value, int> = 0>
+    basic_json(const BasicJsonType& val)
+    {
+        using other_boolean_t = typename BasicJsonType::boolean_t;
+        using other_number_float_t = typename BasicJsonType::number_float_t;
+        using other_number_integer_t = typename BasicJsonType::number_integer_t;
+        using other_number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+        using other_string_t = typename BasicJsonType::string_t;
+        using other_object_t = typename BasicJsonType::object_t;
+        using other_array_t = typename BasicJsonType::array_t;
+
+        switch (val.type())
+        {
+            case value_t::boolean:
+                JSONSerializer<other_boolean_t>::to_json(*this, val.template get<other_boolean_t>());
+                break;
+            case value_t::number_float:
+                JSONSerializer<other_number_float_t>::to_json(*this, val.template get<other_number_float_t>());
+                break;
+            case value_t::number_integer:
+                JSONSerializer<other_number_integer_t>::to_json(*this, val.template get<other_number_integer_t>());
+                break;
+            case value_t::number_unsigned:
+                JSONSerializer<other_number_unsigned_t>::to_json(*this, val.template get<other_number_unsigned_t>());
+                break;
+            case value_t::string:
+                JSONSerializer<other_string_t>::to_json(*this, val.template get_ref<const other_string_t&>());
+                break;
+            case value_t::object:
+                JSONSerializer<other_object_t>::to_json(*this, val.template get_ref<const other_object_t&>());
+                break;
+            case value_t::array:
+                JSONSerializer<other_array_t>::to_json(*this, val.template get_ref<const other_array_t&>());
+                break;
+            case value_t::null:
+                *this = nullptr;
+                break;
+            case value_t::discarded:
+                m_type = value_t::discarded;
+                break;
+        }
+        assert_invariant();
+    }
+
+    /*!
     @brief create a container (array or object) from an initializer list
 
     Creates a JSON value of type array or object from the passed initializer
@@ -8718,7 +13978,7 @@ class basic_json
     @warning A precondition is enforced with a runtime assertion that will
              result in calling `std::abort` if this precondition is not met.
              Assertions can be disabled by defining `NDEBUG` at compile time.
-             See http://en.cppreference.com/w/cpp/error/assert for more
+             See https://en.cppreference.com/w/cpp/error/assert for more
              information.
 
     @throw invalid_iterator.201 if iterators @a first and @a last are not
@@ -8858,7 +14118,7 @@ class basic_json
     changes to any JSON value.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is linear.
     - As postcondition, it holds: `other == basic_json(other)`.
@@ -8943,7 +14203,7 @@ class basic_json
     exceptions.
 
     @requirement This function helps `basic_json` satisfying the
-    [MoveConstructible](http://en.cppreference.com/w/cpp/concept/MoveConstructible)
+    [MoveConstructible](https://en.cppreference.com/w/cpp/named_req/MoveConstructible)
     requirements.
 
     @liveexample{The code below shows the move constructor explicitly called
@@ -8977,7 +14237,7 @@ class basic_json
     @complexity Linear.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is linear.
 
@@ -8988,7 +14248,7 @@ class basic_json
 
     @since version 1.0.0
     */
-    reference& operator=(basic_json other) noexcept (
+    basic_json& operator=(basic_json other) noexcept (
         std::is_nothrow_move_constructible<value_t>::value and
         std::is_nothrow_move_assignable<value_t>::value and
         std::is_nothrow_move_constructible<json_value>::value and
@@ -9014,14 +14274,14 @@ class basic_json
     @complexity Linear.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is linear.
     - All stored elements are destroyed and all memory is freed.
 
     @since version 1.0.0
     */
-    ~basic_json()
+    ~basic_json() noexcept
     {
         assert_invariant();
         m_value.destroy(m_type);
@@ -9054,6 +14314,10 @@ class basic_json
     @param[in] ensure_ascii If @a ensure_ascii is true, all non-ASCII characters
     in the output are escaped with `\uXXXX` sequences, and the result consists
     of ASCII characters only.
+    @param[in] error_handler  how to react on decoding errors; there are three
+    possible values: `strict` (throws and exception in case a decoding error
+    occurs; default), `replace` (replace invalid UTF-8 sequences with U+FFFD),
+    and `ignore` (ignore invalid UTF-8 sequences during serialization).
 
     @return string containing the serialization of the JSON value
 
@@ -9072,13 +14336,16 @@ class basic_json
     @see https://docs.python.org/2/library/json.html#json.dump
 
     @since version 1.0.0; indentation character @a indent_char, option
-           @a ensure_ascii and exceptions added in version 3.0.0
+           @a ensure_ascii and exceptions added in version 3.0.0; error
+           handlers added in version 3.4.0.
     */
-    string_t dump(const int indent = -1, const char indent_char = ' ',
-                  const bool ensure_ascii = false) const
+    string_t dump(const int indent = -1,
+                  const char indent_char = ' ',
+                  const bool ensure_ascii = false,
+                  const error_handler_t error_handler = error_handler_t::strict) const
     {
         string_t result;
-        serializer s(detail::output_adapter<char>(result), indent_char);
+        serializer s(detail::output_adapter<char, string_t>(result), indent_char, error_handler);
 
         if (indent >= 0)
         {
@@ -9619,11 +14886,34 @@ class basic_json
     }
 
     /*!
+    @brief get special-case overload
+
+    This overloads converts the current @ref basic_json in a different
+    @ref basic_json type
+
+    @tparam BasicJsonType == @ref basic_json
+
+    @return a copy of *this, converted into @tparam BasicJsonType
+
+    @complexity Depending on the implementation of the called `from_json()`
+                method.
+
+    @since version 3.2.0
+    */
+    template<typename BasicJsonType, detail::enable_if_t<
+                 not std::is_same<BasicJsonType, basic_json>::value and
+                 detail::is_basic_json<BasicJsonType>::value, int> = 0>
+    BasicJsonType get() const
+    {
+        return *this;
+    }
+
+    /*!
     @brief get a value (explicit)
 
     Explicit type conversion between the JSON value and a compatible value
-    which is [CopyConstructible](http://en.cppreference.com/w/cpp/concept/CopyConstructible)
-    and [DefaultConstructible](http://en.cppreference.com/w/cpp/concept/DefaultConstructible).
+    which is [CopyConstructible](https://en.cppreference.com/w/cpp/named_req/CopyConstructible)
+    and [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible).
     The value is converted by calling the @ref json_serializer<ValueType>
     `from_json()` method.
 
@@ -9659,7 +14949,7 @@ class basic_json
     */
     template<typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>,
              detail::enable_if_t <
-                 not std::is_same<basic_json_t, ValueType>::value and
+                 not detail::is_basic_json<ValueType>::value and
                  detail::has_from_json<basic_json_t, ValueType>::value and
                  not detail::has_non_default_from_json<basic_json_t, ValueType>::value,
                  int> = 0>
@@ -9683,8 +14973,8 @@ class basic_json
     @brief get a value (explicit); special case
 
     Explicit type conversion between the JSON value and a compatible value
-    which is **not** [CopyConstructible](http://en.cppreference.com/w/cpp/concept/CopyConstructible)
-    and **not** [DefaultConstructible](http://en.cppreference.com/w/cpp/concept/DefaultConstructible).
+    which is **not** [CopyConstructible](https://en.cppreference.com/w/cpp/named_req/CopyConstructible)
+    and **not** [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible).
     The value is converted by calling the @ref json_serializer<ValueType>
     `from_json()` method.
 
@@ -9723,17 +15013,64 @@ class basic_json
     }
 
     /*!
-    @brief get a pointer value (explicit)
+    @brief get a value (explicit)
 
-    Explicit pointer access to the internally stored JSON value. No copies are
+    Explicit type conversion between the JSON value and a compatible value.
+    The value is filled into the input parameter by calling the @ref json_serializer<ValueType>
+    `from_json()` method.
+
+    The function is equivalent to executing
+    @code {.cpp}
+    ValueType v;
+    JSONSerializer<ValueType>::from_json(*this, v);
+    @endcode
+
+    This overloads is chosen if:
+    - @a ValueType is not @ref basic_json,
+    - @ref json_serializer<ValueType> has a `from_json()` method of the form
+      `void from_json(const basic_json&, ValueType&)`, and
+
+    @tparam ValueType the input parameter type.
+
+    @return the input parameter, allowing chaining calls.
+
+    @throw what @ref json_serializer<ValueType> `from_json()` method throws
+
+    @liveexample{The example below shows several conversions from JSON values
+    to other types. There a few things to note: (1) Floating-point numbers can
+    be converted to integers\, (2) A JSON array can be converted to a standard
+    `std::vector<short>`\, (3) A JSON object can be converted to C++
+    associative containers such as `std::unordered_map<std::string\,
+    json>`.,get_to}
+
+    @since version 3.3.0
+    */
+    template<typename ValueType,
+             detail::enable_if_t <
+                 not detail::is_basic_json<ValueType>::value and
+                 detail::has_from_json<basic_json_t, ValueType>::value,
+                 int> = 0>
+    ValueType & get_to(ValueType& v) const noexcept(noexcept(
+                JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), v)))
+    {
+        JSONSerializer<ValueType>::from_json(*this, v);
+        return v;
+    }
+
+
+    /*!
+    @brief get a pointer value (implicit)
+
+    Implicit pointer access to the internally stored JSON value. No copies are
     made.
 
-    @warning The pointer becomes invalid if the underlying JSON object
-    changes.
+    @warning Writing data to the pointee of the result yields an undefined
+    state.
 
     @tparam PointerType pointer type; must be a pointer to @ref array_t, @ref
     object_t, @ref string_t, @ref boolean_t, @ref number_integer_t,
-    @ref number_unsigned_t, or @ref number_float_t.
+    @ref number_unsigned_t, or @ref number_float_t. Enforced by a static
+    assertion.
 
     @return pointer to the internally stored JSON value if the requested
     pointer type @a PointerType fits to the JSON value; `nullptr` otherwise
@@ -9743,45 +15080,43 @@ class basic_json
     @liveexample{The example below shows how pointers to internal values of a
     JSON value can be requested. Note that no type conversions are made and a
     `nullptr` is returned if the value and the requested pointer type does not
-    match.,get__PointerType}
-
-    @sa @ref get_ptr() for explicit pointer-member access
+    match.,get_ptr}
 
     @since version 1.0.0
     */
     template<typename PointerType, typename std::enable_if<
                  std::is_pointer<PointerType>::value, int>::type = 0>
-    PointerType get() noexcept
+    auto get_ptr() noexcept -> decltype(std::declval<basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))
     {
-        // delegate the call to get_ptr
-        return get_ptr<PointerType>();
+        // delegate the call to get_impl_ptr<>()
+        return get_impl_ptr(static_cast<PointerType>(nullptr));
     }
 
     /*!
-    @brief get a pointer value (explicit)
-    @copydoc get()
+    @brief get a pointer value (implicit)
+    @copydoc get_ptr()
     */
     template<typename PointerType, typename std::enable_if<
-                 std::is_pointer<PointerType>::value, int>::type = 0>
-    constexpr const PointerType get() const noexcept
+                 std::is_pointer<PointerType>::value and
+                 std::is_const<typename std::remove_pointer<PointerType>::type>::value, int>::type = 0>
+    constexpr auto get_ptr() const noexcept -> decltype(std::declval<const basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))
     {
-        // delegate the call to get_ptr
-        return get_ptr<PointerType>();
+        // delegate the call to get_impl_ptr<>() const
+        return get_impl_ptr(static_cast<PointerType>(nullptr));
     }
 
     /*!
-    @brief get a pointer value (implicit)
+    @brief get a pointer value (explicit)
 
-    Implicit pointer access to the internally stored JSON value. No copies are
+    Explicit pointer access to the internally stored JSON value. No copies are
     made.
 
-    @warning Writing data to the pointee of the result yields an undefined
-    state.
+    @warning The pointer becomes invalid if the underlying JSON object
+    changes.
 
     @tparam PointerType pointer type; must be a pointer to @ref array_t, @ref
     object_t, @ref string_t, @ref boolean_t, @ref number_integer_t,
-    @ref number_unsigned_t, or @ref number_float_t. Enforced by a static
-    assertion.
+    @ref number_unsigned_t, or @ref number_float_t.
 
     @return pointer to the internally stored JSON value if the requested
     pointer type @a PointerType fits to the JSON value; `nullptr` otherwise
@@ -9791,59 +15126,30 @@ class basic_json
     @liveexample{The example below shows how pointers to internal values of a
     JSON value can be requested. Note that no type conversions are made and a
     `nullptr` is returned if the value and the requested pointer type does not
-    match.,get_ptr}
+    match.,get__PointerType}
+
+    @sa @ref get_ptr() for explicit pointer-member access
 
     @since version 1.0.0
     */
     template<typename PointerType, typename std::enable_if<
                  std::is_pointer<PointerType>::value, int>::type = 0>
-    PointerType get_ptr() noexcept
+    auto get() noexcept -> decltype(std::declval<basic_json_t&>().template get_ptr<PointerType>())
     {
-        // get the type of the PointerType (remove pointer and const)
-        using pointee_t = typename std::remove_const<typename
-                          std::remove_pointer<typename
-                          std::remove_const<PointerType>::type>::type>::type;
-        // make sure the type matches the allowed types
-        static_assert(
-            std::is_same<object_t, pointee_t>::value
-            or std::is_same<array_t, pointee_t>::value
-            or std::is_same<string_t, pointee_t>::value
-            or std::is_same<boolean_t, pointee_t>::value
-            or std::is_same<number_integer_t, pointee_t>::value
-            or std::is_same<number_unsigned_t, pointee_t>::value
-            or std::is_same<number_float_t, pointee_t>::value
-            , "incompatible pointer type");
-
-        // delegate the call to get_impl_ptr<>()
-        return get_impl_ptr(static_cast<PointerType>(nullptr));
+        // delegate the call to get_ptr
+        return get_ptr<PointerType>();
     }
 
     /*!
-    @brief get a pointer value (implicit)
-    @copydoc get_ptr()
+    @brief get a pointer value (explicit)
+    @copydoc get()
     */
     template<typename PointerType, typename std::enable_if<
-                 std::is_pointer<PointerType>::value and
-                 std::is_const<typename std::remove_pointer<PointerType>::type>::value, int>::type = 0>
-    constexpr const PointerType get_ptr() const noexcept
+                 std::is_pointer<PointerType>::value, int>::type = 0>
+    constexpr auto get() const noexcept -> decltype(std::declval<const basic_json_t&>().template get_ptr<PointerType>())
     {
-        // get the type of the PointerType (remove pointer and const)
-        using pointee_t = typename std::remove_const<typename
-                          std::remove_pointer<typename
-                          std::remove_const<PointerType>::type>::type>::type;
-        // make sure the type matches the allowed types
-        static_assert(
-            std::is_same<object_t, pointee_t>::value
-            or std::is_same<array_t, pointee_t>::value
-            or std::is_same<string_t, pointee_t>::value
-            or std::is_same<boolean_t, pointee_t>::value
-            or std::is_same<number_integer_t, pointee_t>::value
-            or std::is_same<number_unsigned_t, pointee_t>::value
-            or std::is_same<number_float_t, pointee_t>::value
-            , "incompatible pointer type");
-
-        // delegate the call to get_impl_ptr<>() const
-        return get_impl_ptr(static_cast<PointerType>(nullptr));
+        // delegate the call to get_ptr
+        return get_ptr<PointerType>();
     }
 
     /*!
@@ -9925,13 +15231,16 @@ class basic_json
     template < typename ValueType, typename std::enable_if <
                    not std::is_pointer<ValueType>::value and
                    not std::is_same<ValueType, detail::json_ref<basic_json>>::value and
-                   not std::is_same<ValueType, typename string_t::value_type>::value
+                   not std::is_same<ValueType, typename string_t::value_type>::value and
+                   not detail::is_basic_json<ValueType>::value
+
 #ifndef _MSC_VER  // fix for issue #167 operator<< ambiguity under VS2015
                    and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
-#endif
-#if defined(JSON_HAS_CPP_17)
+#if defined(JSON_HAS_CPP_17) && defined(_MSC_VER) and _MSC_VER <= 1914
                    and not std::is_same<ValueType, typename std::string_view>::value
 #endif
+#endif
+                   and detail::is_detected<detail::get_template_function, const basic_json_t&, ValueType>::value
                    , int >::type = 0 >
     operator ValueType() const
     {
@@ -10195,7 +15504,7 @@ class basic_json
             return m_value.array->operator[](idx);
         }
 
-        JSON_THROW(type_error::create(305, "cannot use operator[] with " + std::string(type_name())));
+        JSON_THROW(type_error::create(305, "cannot use operator[] with a numeric argument with " + std::string(type_name())));
     }
 
     /*!
@@ -10225,7 +15534,7 @@ class basic_json
             return m_value.array->operator[](idx);
         }
 
-        JSON_THROW(type_error::create(305, "cannot use operator[] with " + std::string(type_name())));
+        JSON_THROW(type_error::create(305, "cannot use operator[] with a numeric argument with " + std::string(type_name())));
     }
 
     /*!
@@ -10271,7 +15580,7 @@ class basic_json
             return m_value.object->operator[](key);
         }
 
-        JSON_THROW(type_error::create(305, "cannot use operator[] with " + std::string(type_name())));
+        JSON_THROW(type_error::create(305, "cannot use operator[] with a string argument with " + std::string(type_name())));
     }
 
     /*!
@@ -10313,7 +15622,7 @@ class basic_json
             return m_value.object->find(key)->second;
         }
 
-        JSON_THROW(type_error::create(305, "cannot use operator[] with " + std::string(type_name())));
+        JSON_THROW(type_error::create(305, "cannot use operator[] with a string argument with " + std::string(type_name())));
     }
 
     /*!
@@ -10360,7 +15669,7 @@ class basic_json
             return m_value.object->operator[](key);
         }
 
-        JSON_THROW(type_error::create(305, "cannot use operator[] with " + std::string(type_name())));
+        JSON_THROW(type_error::create(305, "cannot use operator[] with a string argument with " + std::string(type_name())));
     }
 
     /*!
@@ -10403,7 +15712,7 @@ class basic_json
             return m_value.object->find(key)->second;
         }
 
-        JSON_THROW(type_error::create(305, "cannot use operator[] with " + std::string(type_name())));
+        JSON_THROW(type_error::create(305, "cannot use operator[] with a string argument with " + std::string(type_name())));
     }
 
     /*!
@@ -10476,7 +15785,7 @@ class basic_json
 
     /*!
     @brief overload for a default value of type const char*
-    @copydoc basic_json::value(const typename object_t::key_type&, ValueType) const
+    @copydoc basic_json::value(const typename object_t::key_type&, const ValueType&) const
     */
     string_t value(const typename object_t::key_type& key, const char* default_value) const
     {
@@ -10512,7 +15821,7 @@ class basic_json
     @return copy of the element at key @a key or @a default_value if @a key
     is not found
 
-    @throw type_error.306 if the JSON value is not an objec; in that case,
+    @throw type_error.306 if the JSON value is not an object; in that case,
     using `value()` with a key makes no sense.
 
     @complexity Logarithmic in the size of the container.
@@ -10536,7 +15845,7 @@ class basic_json
             {
                 return ptr.get_checked(this);
             }
-            JSON_CATCH (out_of_range&)
+            JSON_INTERNAL_CATCH (out_of_range&)
             {
                 return default_value;
             }
@@ -11047,7 +16356,7 @@ class basic_json
     @complexity Constant.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is constant.
 
@@ -11086,7 +16395,7 @@ class basic_json
     @complexity Constant.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is constant.
     - Has the semantics of `const_cast<const basic_json&>(*this).begin()`.
@@ -11118,7 +16427,7 @@ class basic_json
     @complexity Constant.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is constant.
 
@@ -11157,7 +16466,7 @@ class basic_json
     @complexity Constant.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is constant.
     - Has the semantics of `const_cast<const basic_json&>(*this).end()`.
@@ -11187,7 +16496,7 @@ class basic_json
     @complexity Constant.
 
     @requirement This function helps `basic_json` satisfying the
-    [ReversibleContainer](http://en.cppreference.com/w/cpp/concept/ReversibleContainer)
+    [ReversibleContainer](https://en.cppreference.com/w/cpp/named_req/ReversibleContainer)
     requirements:
     - The complexity is constant.
     - Has the semantics of `reverse_iterator(end())`.
@@ -11224,7 +16533,7 @@ class basic_json
     @complexity Constant.
 
     @requirement This function helps `basic_json` satisfying the
-    [ReversibleContainer](http://en.cppreference.com/w/cpp/concept/ReversibleContainer)
+    [ReversibleContainer](https://en.cppreference.com/w/cpp/named_req/ReversibleContainer)
     requirements:
     - The complexity is constant.
     - Has the semantics of `reverse_iterator(begin())`.
@@ -11261,7 +16570,7 @@ class basic_json
     @complexity Constant.
 
     @requirement This function helps `basic_json` satisfying the
-    [ReversibleContainer](http://en.cppreference.com/w/cpp/concept/ReversibleContainer)
+    [ReversibleContainer](https://en.cppreference.com/w/cpp/named_req/ReversibleContainer)
     requirements:
     - The complexity is constant.
     - Has the semantics of `const_cast<const basic_json&>(*this).rbegin()`.
@@ -11290,7 +16599,7 @@ class basic_json
     @complexity Constant.
 
     @requirement This function helps `basic_json` satisfying the
-    [ReversibleContainer](http://en.cppreference.com/w/cpp/concept/ReversibleContainer)
+    [ReversibleContainer](https://en.cppreference.com/w/cpp/named_req/ReversibleContainer)
     requirements:
     - The complexity is constant.
     - Has the semantics of `const_cast<const basic_json&>(*this).rend()`.
@@ -11361,18 +16670,100 @@ class basic_json
 
     @note The name of this function is not yet final and may change in the
     future.
+
+    @deprecated This stream operator is deprecated and will be removed in
+                future 4.0.0 of the library. Please use @ref items() instead;
+                that is, replace `json::iterator_wrapper(j)` with `j.items()`.
     */
-    static iteration_proxy<iterator> iterator_wrapper(reference ref)
+    JSON_DEPRECATED
+    static iteration_proxy<iterator> iterator_wrapper(reference ref) noexcept
     {
-        return iteration_proxy<iterator>(ref);
+        return ref.items();
     }
 
     /*!
     @copydoc iterator_wrapper(reference)
     */
-    static iteration_proxy<const_iterator> iterator_wrapper(const_reference ref)
+    JSON_DEPRECATED
+    static iteration_proxy<const_iterator> iterator_wrapper(const_reference ref) noexcept
     {
-        return iteration_proxy<const_iterator>(ref);
+        return ref.items();
+    }
+
+    /*!
+    @brief helper to access iterator member functions in range-based for
+
+    This function allows to access @ref iterator::key() and @ref
+    iterator::value() during range-based for loops. In these loops, a
+    reference to the JSON values is returned, so there is no access to the
+    underlying iterator.
+
+    For loop without `items()` function:
+
+    @code{cpp}
+    for (auto it = j_object.begin(); it != j_object.end(); ++it)
+    {
+        std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
+    }
+    @endcode
+
+    Range-based for loop without `items()` function:
+
+    @code{cpp}
+    for (auto it : j_object)
+    {
+        // "it" is of type json::reference and has no key() member
+        std::cout << "value: " << it << '\n';
+    }
+    @endcode
+
+    Range-based for loop with `items()` function:
+
+    @code{cpp}
+    for (auto& el : j_object.items())
+    {
+        std::cout << "key: " << el.key() << ", value:" << el.value() << '\n';
+    }
+    @endcode
+
+    The `items()` function also allows to use
+    [structured bindings](https://en.cppreference.com/w/cpp/language/structured_binding)
+    (C++17):
+
+    @code{cpp}
+    for (auto& [key, val] : j_object.items())
+    {
+        std::cout << "key: " << key << ", value:" << val << '\n';
+    }
+    @endcode
+
+    @note When iterating over an array, `key()` will return the index of the
+          element as string (see example). For primitive types (e.g., numbers),
+          `key()` returns an empty string.
+
+    @return iteration proxy object wrapping @a ref with an interface to use in
+            range-based for loops
+
+    @liveexample{The following code shows how the function is used.,items}
+
+    @exceptionsafety Strong guarantee: if an exception is thrown, there are no
+    changes in the JSON value.
+
+    @complexity Constant.
+
+    @since version 3.1.0, structured bindings support since 3.5.0.
+    */
+    iteration_proxy<iterator> items() noexcept
+    {
+        return iteration_proxy<iterator>(*this);
+    }
+
+    /*!
+    @copydoc items()
+    */
+    iteration_proxy<const_iterator> items() const noexcept
+    {
+        return iteration_proxy<const_iterator>(*this);
     }
 
     /// @}
@@ -11417,7 +16808,7 @@ class basic_json
     false in the case of a string.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is constant.
     - Has the semantics of `begin() == end()`.
@@ -11488,7 +16879,7 @@ class basic_json
     the case of a string.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is constant.
     - Has the semantics of `std::distance(begin(), end())`.
@@ -11558,7 +16949,7 @@ class basic_json
     @exceptionsafety No-throw guarantee: this function never throws exceptions.
 
     @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
+    [Container](https://en.cppreference.com/w/cpp/named_req/Container)
     requirements:
     - The complexity is constant.
     - Has the semantics of returning `b.size()` where `b` is the largest
@@ -11970,6 +17361,26 @@ class basic_json
         return {it, res.second};
     }
 
+    /// Helper for insertion of an iterator
+    /// @note: This uses std::distance to support GCC 4.8,
+    ///        see https://github.com/nlohmann/json/pull/1257
+    template<typename... Args>
+    iterator insert_iterator(const_iterator pos, Args&& ... args)
+    {
+        iterator result(this);
+        assert(m_value.array != nullptr);
+
+        auto insert_pos = std::distance(m_value.array->begin(), pos.m_it.array_iterator);
+        m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
+        result.m_it.array_iterator = m_value.array->begin() + insert_pos;
+
+        // This could have been written as:
+        // result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, cnt, val);
+        // but the return value of insert is missing in GCC 4.8, so it is written this way instead.
+
+        return result;
+    }
+
     /*!
     @brief inserts element
 
@@ -12004,9 +17415,7 @@ class basic_json
             }
 
             // insert to array and return iterator
-            iterator result(this);
-            result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, val);
-            return result;
+            return insert_iterator(pos, val);
         }
 
         JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
@@ -12057,9 +17466,7 @@ class basic_json
             }
 
             // insert to array and return iterator
-            iterator result(this);
-            result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, cnt, val);
-            return result;
+            return insert_iterator(pos, cnt, val);
         }
 
         JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
@@ -12121,12 +17528,7 @@ class basic_json
         }
 
         // insert to array and return iterator
-        iterator result(this);
-        result.m_it.array_iterator = m_value.array->insert(
-                                         pos.m_it.array_iterator,
-                                         first.m_it.array_iterator,
-                                         last.m_it.array_iterator);
-        return result;
+        return insert_iterator(pos, first.m_it.array_iterator, last.m_it.array_iterator);
     }
 
     /*!
@@ -12168,9 +17570,7 @@ class basic_json
         }
 
         // insert to array and return iterator
-        iterator result(this);
-        result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, ilist.begin(), ilist.end());
-        return result;
+        return insert_iterator(pos, ilist.begin(), ilist.end());
     }
 
     /*!
@@ -12312,7 +17712,7 @@ class basic_json
 
         // passed iterators must belong to objects
         if (JSON_UNLIKELY(not first.m_object->is_object()
-                          or not first.m_object->is_object()))
+                          or not last.m_object->is_object()))
         {
             JSON_THROW(invalid_iterator::create(202, "iterators first and last must point to objects"));
         }
@@ -12943,8 +18343,8 @@ class basic_json
 
     /*!
     @brief serialize to stream
-    @deprecated This stream operator is deprecated and will be removed in a
-                future version of the library. Please use
+    @deprecated This stream operator is deprecated and will be removed in
+                future 4.0.0 of the library. Please use
                 @ref operator<<(std::ostream&, const basic_json&)
                 instead; that is, replace calls like `j >> o;` with `o << j;`.
     @since version 1.0.0; deprecated since version 3.0.0
@@ -12999,6 +18399,8 @@ class basic_json
     @param[in] cb  a parser callback function of type @ref parser_callback_t
     which is used to control the deserialization by filtering unwanted values
     (optional)
+    @param[in] allow_exceptions  whether to throw exceptions in case of a
+    parse error (optional, true by default)
 
     @return result of the deserialization
 
@@ -13027,19 +18429,7 @@ class basic_json
 
     @since version 2.0.3 (contiguous containers)
     */
-    static basic_json parse(detail::input_adapter i,
-                            const parser_callback_t cb = nullptr,
-                            const bool allow_exceptions = true)
-    {
-        basic_json result;
-        parser(i, cb, allow_exceptions).parse(true, result);
-        return result;
-    }
-
-    /*!
-    @copydoc basic_json parse(detail::input_adapter, const parser_callback_t)
-    */
-    static basic_json parse(detail::input_adapter& i,
+    static basic_json parse(detail::input_adapter&& i,
                             const parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true)
     {
@@ -13048,14 +18438,80 @@ class basic_json
         return result;
     }
 
-    static bool accept(detail::input_adapter i)
+    static bool accept(detail::input_adapter&& i)
     {
         return parser(i).accept(true);
     }
 
-    static bool accept(detail::input_adapter& i)
+    /*!
+    @brief generate SAX events
+
+    The SAX event lister must follow the interface of @ref json_sax.
+
+    This function reads from a compatible input. Examples are:
+    - an array of 1-byte values
+    - strings with character/literal type with size of 1 byte
+    - input streams
+    - container with contiguous storage of 1-byte values. Compatible container
+      types include `std::vector`, `std::string`, `std::array`,
+      `std::valarray`, and `std::initializer_list`. Furthermore, C-style
+      arrays can be used with `std::begin()`/`std::end()`. User-defined
+      containers can be used as long as they implement random-access iterators
+      and a contiguous storage.
+
+    @pre Each element of the container has a size of 1 byte. Violating this
+    precondition yields undefined behavior. **This precondition is enforced
+    with a static assertion.**
+
+    @pre The container storage is contiguous. Violating this precondition
+    yields undefined behavior. **This precondition is enforced with an
+    assertion.**
+    @pre Each element of the container has a size of 1 byte. Violating this
+    precondition yields undefined behavior. **This precondition is enforced
+    with a static assertion.**
+
+    @warning There is no way to enforce all preconditions at compile-time. If
+             the function is called with a noncompliant container and with
+             assertions switched off, the behavior is undefined and will most
+             likely yield segmentation violation.
+
+    @param[in] i  input to read from
+    @param[in,out] sax  SAX event listener
+    @param[in] format  the format to parse (JSON, CBOR, MessagePack, or UBJSON)
+    @param[in] strict  whether the input has to be consumed completely
+
+    @return return value of the last processed SAX event
+
+    @throw parse_error.101 if a parse error occurs; example: `""unexpected end
+    of input; expected string literal""`
+    @throw parse_error.102 if to_unicode fails or surrogate error
+    @throw parse_error.103 if to_unicode fails
+
+    @complexity Linear in the length of the input. The parser is a predictive
+    LL(1) parser. The complexity can be higher if the SAX consumer @a sax has
+    a super-linear complexity.
+
+    @note A UTF-8 byte order mark is silently ignored.
+
+    @liveexample{The example below demonstrates the `sax_parse()` function
+    reading from string and processing the events with a user-defined SAX
+    event consumer.,sax_parse}
+
+    @since version 3.2.0
+    */
+    template <typename SAX>
+    static bool sax_parse(detail::input_adapter&& i, SAX* sax,
+                          input_format_t format = input_format_t::json,
+                          const bool strict = true)
     {
-        return parser(i).accept(true);
+        assert(sax);
+        switch (format)
+        {
+            case input_format_t::json:
+                return parser(std::move(i)).sax_parse(sax, strict);
+            default:
+                return detail::binary_reader<basic_json, SAX>(std::move(i)).sax_parse(format, sax, strict);
+        }
     }
 
     /*!
@@ -13127,10 +18583,19 @@ class basic_json
         return parser(detail::input_adapter(first, last)).accept(true);
     }
 
+    template<class IteratorType, class SAX, typename std::enable_if<
+                 std::is_base_of<
+                     std::random_access_iterator_tag,
+                     typename std::iterator_traits<IteratorType>::iterator_category>::value, int>::type = 0>
+    static bool sax_parse(IteratorType first, IteratorType last, SAX* sax)
+    {
+        return parser(detail::input_adapter(first, last)).sax_parse(sax);
+    }
+
     /*!
     @brief deserialize from stream
-    @deprecated This stream operator is deprecated and will be removed in a
-                future version of the library. Please use
+    @deprecated This stream operator is deprecated and will be removed in
+                version 4.0.0 of the library. Please use
                 @ref operator>>(std::istream&, basic_json&)
                 instead; that is, replace calls like `j << i;` with `i >> j;`.
     @since version 1.0.0; deprecated since version 3.0.0
@@ -13331,9 +18796,11 @@ class basic_json
     vector in CBOR format.,to_cbor}
 
     @sa http://cbor.io
-    @sa @ref from_cbor(const std::vector<uint8_t>&, const size_t) for the
+    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool) for the
         analogous deserialization
     @sa @ref to_msgpack(const basic_json&) for the related MessagePack format
+    @sa @ref to_ubjson(const basic_json&, const bool, const bool) for the
+             related UBJSON format
 
     @since version 2.0.9
     */
@@ -13426,9 +18893,10 @@ class basic_json
     vector in MessagePack format.,to_msgpack}
 
     @sa http://msgpack.org
-    @sa @ref from_msgpack(const std::vector<uint8_t>&, const size_t) for the
-        analogous deserialization
+    @sa @ref from_msgpack for the analogous deserialization
     @sa @ref to_cbor(const basic_json& for the related CBOR format
+    @sa @ref to_ubjson(const basic_json&, const bool, const bool) for the
+             related UBJSON format
 
     @since version 2.0.9
     */
@@ -13450,6 +18918,192 @@ class basic_json
     }
 
     /*!
+    @brief create a UBJSON serialization of a given JSON value
+
+    Serializes a given JSON value @a j to a byte vector using the UBJSON
+    (Universal Binary JSON) serialization format. UBJSON aims to be more compact
+    than JSON itself, yet more efficient to parse.
+
+    The library uses the following mapping from JSON values types to
+    UBJSON types according to the UBJSON specification:
+
+    JSON value type | value/range                       | UBJSON type | marker
+    --------------- | --------------------------------- | ----------- | ------
+    null            | `null`                            | null        | `Z`
+    boolean         | `true`                            | true        | `T`
+    boolean         | `false`                           | false       | `F`
+    number_integer  | -9223372036854775808..-2147483649 | int64       | `L`
+    number_integer  | -2147483648..-32769               | int32       | `l`
+    number_integer  | -32768..-129                      | int16       | `I`
+    number_integer  | -128..127                         | int8        | `i`
+    number_integer  | 128..255                          | uint8       | `U`
+    number_integer  | 256..32767                        | int16       | `I`
+    number_integer  | 32768..2147483647                 | int32       | `l`
+    number_integer  | 2147483648..9223372036854775807   | int64       | `L`
+    number_unsigned | 0..127                            | int8        | `i`
+    number_unsigned | 128..255                          | uint8       | `U`
+    number_unsigned | 256..32767                        | int16       | `I`
+    number_unsigned | 32768..2147483647                 | int32       | `l`
+    number_unsigned | 2147483648..9223372036854775807   | int64       | `L`
+    number_float    | *any value*                       | float64     | `D`
+    string          | *with shortest length indicator*  | string      | `S`
+    array           | *see notes on optimized format*   | array       | `[`
+    object          | *see notes on optimized format*   | map         | `{`
+
+    @note The mapping is **complete** in the sense that any JSON value type
+          can be converted to a UBJSON value.
+
+    @note The following values can **not** be converted to a UBJSON value:
+          - strings with more than 9223372036854775807 bytes (theoretical)
+          - unsigned integer numbers above 9223372036854775807
+
+    @note The following markers are not used in the conversion:
+          - `Z`: no-op values are not created.
+          - `C`: single-byte strings are serialized with `S` markers.
+
+    @note Any UBJSON output created @ref to_ubjson can be successfully parsed
+          by @ref from_ubjson.
+
+    @note If NaN or Infinity are stored inside a JSON number, they are
+          serialized properly. This behavior differs from the @ref dump()
+          function which serializes NaN or Infinity to `null`.
+
+    @note The optimized formats for containers are supported: Parameter
+          @a use_size adds size information to the beginning of a container and
+          removes the closing marker. Parameter @a use_type further checks
+          whether all elements of a container have the same type and adds the
+          type marker to the beginning of the container. The @a use_type
+          parameter must only be used together with @a use_size = true. Note
+          that @a use_size = true alone may result in larger representations -
+          the benefit of this parameter is that the receiving side is
+          immediately informed on the number of elements of the container.
+
+    @param[in] j  JSON value to serialize
+    @param[in] use_size  whether to add size annotations to container types
+    @param[in] use_type  whether to add type annotations to container types
+                         (must be combined with @a use_size = true)
+    @return UBJSON serialization as byte vector
+
+    @complexity Linear in the size of the JSON value @a j.
+
+    @liveexample{The example shows the serialization of a JSON value to a byte
+    vector in UBJSON format.,to_ubjson}
+
+    @sa http://ubjson.org
+    @sa @ref from_ubjson(detail::input_adapter&&, const bool, const bool) for the
+        analogous deserialization
+    @sa @ref to_cbor(const basic_json& for the related CBOR format
+    @sa @ref to_msgpack(const basic_json&) for the related MessagePack format
+
+    @since version 3.1.0
+    */
+    static std::vector<uint8_t> to_ubjson(const basic_json& j,
+                                          const bool use_size = false,
+                                          const bool use_type = false)
+    {
+        std::vector<uint8_t> result;
+        to_ubjson(j, result, use_size, use_type);
+        return result;
+    }
+
+    static void to_ubjson(const basic_json& j, detail::output_adapter<uint8_t> o,
+                          const bool use_size = false, const bool use_type = false)
+    {
+        binary_writer<uint8_t>(o).write_ubjson(j, use_size, use_type);
+    }
+
+    static void to_ubjson(const basic_json& j, detail::output_adapter<char> o,
+                          const bool use_size = false, const bool use_type = false)
+    {
+        binary_writer<char>(o).write_ubjson(j, use_size, use_type);
+    }
+
+
+    /*!
+    @brief Serializes the given JSON object `j` to BSON and returns a vector
+           containing the corresponding BSON-representation.
+
+    BSON (Binary JSON) is a binary format in which zero or more ordered key/value pairs are
+    stored as a single entity (a so-called document).
+
+    The library uses the following mapping from JSON values types to BSON types:
+
+    JSON value type | value/range                       | BSON type   | marker
+    --------------- | --------------------------------- | ----------- | ------
+    null            | `null`                            | null        | 0x0A
+    boolean         | `true`, `false`                   | boolean     | 0x08
+    number_integer  | -9223372036854775808..-2147483649 | int64       | 0x12
+    number_integer  | -2147483648..2147483647           | int32       | 0x10
+    number_integer  | 2147483648..9223372036854775807   | int64       | 0x12
+    number_unsigned | 0..2147483647                     | int32       | 0x10
+    number_unsigned | 2147483648..9223372036854775807   | int64       | 0x12
+    number_unsigned | 9223372036854775808..18446744073709551615| --   | --
+    number_float    | *any value*                       | double      | 0x01
+    string          | *any value*                       | string      | 0x02
+    array           | *any value*                       | document    | 0x04
+    object          | *any value*                       | document    | 0x03
+
+    @warning The mapping is **incomplete**, since only JSON-objects (and things
+    contained therein) can be serialized to BSON.
+    Also, integers larger than 9223372036854775807 cannot be serialized to BSON,
+    and the keys may not contain U+0000, since they are serialized a
+    zero-terminated c-strings.
+
+    @throw out_of_range.407  if `j.is_number_unsigned() && j.get<std::uint64_t>() > 9223372036854775807`
+    @throw out_of_range.409  if a key in `j` contains a NULL (U+0000)
+    @throw type_error.317    if `!j.is_object()`
+
+    @pre The input `j` is required to be an object: `j.is_object() == true`.
+
+    @note Any BSON output created via @ref to_bson can be successfully parsed
+          by @ref from_bson.
+
+    @param[in] j  JSON value to serialize
+    @return BSON serialization as byte vector
+
+    @complexity Linear in the size of the JSON value @a j.
+
+    @liveexample{The example shows the serialization of a JSON value to a byte
+    vector in BSON format.,to_bson}
+
+    @sa http://bsonspec.org/spec.html
+    @sa @ref from_bson(detail::input_adapter&&, const bool strict) for the
+        analogous deserialization
+    @sa @ref to_ubjson(const basic_json&, const bool, const bool) for the
+             related UBJSON format
+    @sa @ref to_cbor(const basic_json&) for the related CBOR format
+    @sa @ref to_msgpack(const basic_json&) for the related MessagePack format
+    */
+    static std::vector<uint8_t> to_bson(const basic_json& j)
+    {
+        std::vector<uint8_t> result;
+        to_bson(j, result);
+        return result;
+    }
+
+    /*!
+    @brief Serializes the given JSON object `j` to BSON and forwards the
+           corresponding BSON-representation to the given output_adapter `o`.
+    @param j The JSON object to convert to BSON.
+    @param o The output adapter that receives the binary BSON representation.
+    @pre The input `j` shall be an object: `j.is_object() == true`
+    @sa @ref to_bson(const basic_json&)
+    */
+    static void to_bson(const basic_json& j, detail::output_adapter<uint8_t> o)
+    {
+        binary_writer<uint8_t>(o).write_bson(j);
+    }
+
+    /*!
+    @copydoc to_bson(const basic_json&, detail::output_adapter<uint8_t>)
+    */
+    static void to_bson(const basic_json& j, detail::output_adapter<char> o)
+    {
+        binary_writer<char>(o).write_bson(j);
+    }
+
+
+    /*!
     @brief create a JSON value from an input in CBOR format
 
     Deserializes a given input @a i to a JSON value using the CBOR (Concise
@@ -13490,7 +19144,7 @@ class basic_json
     map                    | object          | 0xBF
     False                  | `false`         | 0xF4
     True                   | `true`          | 0xF5
-    Nill                   | `null`          | 0xF6
+    Null                   | `null`          | 0xF6
     Half-Precision Float   | number_float    | 0xF9
     Single-Precision Float | number_float    | 0xFA
     Double-Precision Float | number_float    | 0xFB
@@ -13518,6 +19172,9 @@ class basic_json
     @param[in] i  an input in CBOR format convertible to an input adapter
     @param[in] strict  whether to expect the input to be consumed until EOF
                        (true by default)
+    @param[in] allow_exceptions  whether to throw exceptions in case of a
+    parse error (optional, true by default)
+
     @return deserialized JSON value
 
     @throw parse_error.110 if the given input ends prematurely or the end of
@@ -13533,27 +19190,39 @@ class basic_json
 
     @sa http://cbor.io
     @sa @ref to_cbor(const basic_json&) for the analogous serialization
-    @sa @ref from_msgpack(detail::input_adapter, const bool) for the
+    @sa @ref from_msgpack(detail::input_adapter&&, const bool, const bool) for the
         related MessagePack format
+    @sa @ref from_ubjson(detail::input_adapter&&, const bool, const bool) for the
+        related UBJSON format
 
     @since version 2.0.9; parameter @a start_index since 2.1.1; changed to
            consume input adapters, removed start_index parameter, and added
-           @a strict parameter since 3.0.0
+           @a strict parameter since 3.0.0; added @a allow_exceptions parameter
+           since 3.2.0
     */
-    static basic_json from_cbor(detail::input_adapter i,
-                                const bool strict = true)
+    static basic_json from_cbor(detail::input_adapter&& i,
+                                const bool strict = true,
+                                const bool allow_exceptions = true)
     {
-        return binary_reader(i).parse_cbor(strict);
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        const bool res = binary_reader(detail::input_adapter(i)).sax_parse(input_format_t::cbor, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
     }
 
     /*!
-    @copydoc from_cbor(detail::input_adapter, const bool)
+    @copydoc from_cbor(detail::input_adapter&&, const bool, const bool)
     */
     template<typename A1, typename A2,
              detail::enable_if_t<std::is_constructible<detail::input_adapter, A1, A2>::value, int> = 0>
-    static basic_json from_cbor(A1 && a1, A2 && a2, const bool strict = true)
+    static basic_json from_cbor(A1 && a1, A2 && a2,
+                                const bool strict = true,
+                                const bool allow_exceptions = true)
     {
-        return binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).parse_cbor(strict);
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        const bool res = binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).sax_parse(input_format_t::cbor, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
     }
 
     /*!
@@ -13606,6 +19275,10 @@ class basic_json
                   adapter
     @param[in] strict  whether to expect the input to be consumed until EOF
                        (true by default)
+    @param[in] allow_exceptions  whether to throw exceptions in case of a
+    parse error (optional, true by default)
+
+    @return deserialized JSON value
 
     @throw parse_error.110 if the given input ends prematurely or the end of
     file was not reached when @a strict was set to true
@@ -13620,29 +19293,212 @@ class basic_json
 
     @sa http://msgpack.org
     @sa @ref to_msgpack(const basic_json&) for the analogous serialization
-    @sa @ref from_cbor(detail::input_adapter, const bool) for the related CBOR
-        format
+    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool) for the
+        related CBOR format
+    @sa @ref from_ubjson(detail::input_adapter&&, const bool, const bool) for
+        the related UBJSON format
+    @sa @ref from_bson(detail::input_adapter&&, const bool, const bool) for
+        the related BSON format
 
     @since version 2.0.9; parameter @a start_index since 2.1.1; changed to
            consume input adapters, removed start_index parameter, and added
-           @a strict parameter since 3.0.0
+           @a strict parameter since 3.0.0; added @a allow_exceptions parameter
+           since 3.2.0
+    */
+    static basic_json from_msgpack(detail::input_adapter&& i,
+                                   const bool strict = true,
+                                   const bool allow_exceptions = true)
+    {
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        const bool res = binary_reader(detail::input_adapter(i)).sax_parse(input_format_t::msgpack, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
+    }
+
+    /*!
+    @copydoc from_msgpack(detail::input_adapter&&, const bool, const bool)
+    */
+    template<typename A1, typename A2,
+             detail::enable_if_t<std::is_constructible<detail::input_adapter, A1, A2>::value, int> = 0>
+    static basic_json from_msgpack(A1 && a1, A2 && a2,
+                                   const bool strict = true,
+                                   const bool allow_exceptions = true)
+    {
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        const bool res = binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).sax_parse(input_format_t::msgpack, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
+    }
+
+    /*!
+    @brief create a JSON value from an input in UBJSON format
+
+    Deserializes a given input @a i to a JSON value using the UBJSON (Universal
+    Binary JSON) serialization format.
+
+    The library maps UBJSON types to JSON value types as follows:
+
+    UBJSON type | JSON value type                         | marker
+    ----------- | --------------------------------------- | ------
+    no-op       | *no value, next value is read*          | `N`
+    null        | `null`                                  | `Z`
+    false       | `false`                                 | `F`
+    true        | `true`                                  | `T`
+    float32     | number_float                            | `d`
+    float64     | number_float                            | `D`
+    uint8       | number_unsigned                         | `U`
+    int8        | number_integer                          | `i`
+    int16       | number_integer                          | `I`
+    int32       | number_integer                          | `l`
+    int64       | number_integer                          | `L`
+    string      | string                                  | `S`
+    char        | string                                  | `C`
+    array       | array (optimized values are supported)  | `[`
+    object      | object (optimized values are supported) | `{`
+
+    @note The mapping is **complete** in the sense that any UBJSON value can
+          be converted to a JSON value.
+
+    @param[in] i  an input in UBJSON format convertible to an input adapter
+    @param[in] strict  whether to expect the input to be consumed until EOF
+                       (true by default)
+    @param[in] allow_exceptions  whether to throw exceptions in case of a
+    parse error (optional, true by default)
+
+    @return deserialized JSON value
+
+    @throw parse_error.110 if the given input ends prematurely or the end of
+    file was not reached when @a strict was set to true
+    @throw parse_error.112 if a parse error occurs
+    @throw parse_error.113 if a string could not be parsed successfully
+
+    @complexity Linear in the size of the input @a i.
+
+    @liveexample{The example shows the deserialization of a byte vector in
+    UBJSON format to a JSON value.,from_ubjson}
+
+    @sa http://ubjson.org
+    @sa @ref to_ubjson(const basic_json&, const bool, const bool) for the
+             analogous serialization
+    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool) for the
+        related CBOR format
+    @sa @ref from_msgpack(detail::input_adapter&&, const bool, const bool) for
+        the related MessagePack format
+    @sa @ref from_bson(detail::input_adapter&&, const bool, const bool) for
+        the related BSON format
+
+    @since version 3.1.0; added @a allow_exceptions parameter since 3.2.0
     */
-    static basic_json from_msgpack(detail::input_adapter i,
-                                   const bool strict = true)
+    static basic_json from_ubjson(detail::input_adapter&& i,
+                                  const bool strict = true,
+                                  const bool allow_exceptions = true)
     {
-        return binary_reader(i).parse_msgpack(strict);
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        const bool res = binary_reader(detail::input_adapter(i)).sax_parse(input_format_t::ubjson, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
     }
 
     /*!
-    @copydoc from_msgpack(detail::input_adapter, const bool)
+    @copydoc from_ubjson(detail::input_adapter&&, const bool, const bool)
     */
     template<typename A1, typename A2,
              detail::enable_if_t<std::is_constructible<detail::input_adapter, A1, A2>::value, int> = 0>
-    static basic_json from_msgpack(A1 && a1, A2 && a2, const bool strict = true)
+    static basic_json from_ubjson(A1 && a1, A2 && a2,
+                                  const bool strict = true,
+                                  const bool allow_exceptions = true)
     {
-        return binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).parse_msgpack(strict);
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        const bool res = binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).sax_parse(input_format_t::ubjson, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
     }
 
+    /*!
+    @brief Create a JSON value from an input in BSON format
+
+    Deserializes a given input @a i to a JSON value using the BSON (Binary JSON)
+    serialization format.
+
+    The library maps BSON record types to JSON value types as follows:
+
+    BSON type       | BSON marker byte | JSON value type
+    --------------- | ---------------- | ---------------------------
+    double          | 0x01             | number_float
+    string          | 0x02             | string
+    document        | 0x03             | object
+    array           | 0x04             | array
+    binary          | 0x05             | still unsupported
+    undefined       | 0x06             | still unsupported
+    ObjectId        | 0x07             | still unsupported
+    boolean         | 0x08             | boolean
+    UTC Date-Time   | 0x09             | still unsupported
+    null            | 0x0A             | null
+    Regular Expr.   | 0x0B             | still unsupported
+    DB Pointer      | 0x0C             | still unsupported
+    JavaScript Code | 0x0D             | still unsupported
+    Symbol          | 0x0E             | still unsupported
+    JavaScript Code | 0x0F             | still unsupported
+    int32           | 0x10             | number_integer
+    Timestamp       | 0x11             | still unsupported
+    128-bit decimal float | 0x13       | still unsupported
+    Max Key         | 0x7F             | still unsupported
+    Min Key         | 0xFF             | still unsupported
+
+    @warning The mapping is **incomplete**. The unsupported mappings
+             are indicated in the table above.
+
+    @param[in] i  an input in BSON format convertible to an input adapter
+    @param[in] strict  whether to expect the input to be consumed until EOF
+                       (true by default)
+    @param[in] allow_exceptions  whether to throw exceptions in case of a
+    parse error (optional, true by default)
+
+    @return deserialized JSON value
+
+    @throw parse_error.114 if an unsupported BSON record type is encountered
+
+    @complexity Linear in the size of the input @a i.
+
+    @liveexample{The example shows the deserialization of a byte vector in
+    BSON format to a JSON value.,from_bson}
+
+    @sa http://bsonspec.org/spec.html
+    @sa @ref to_bson(const basic_json&) for the analogous serialization
+    @sa @ref from_cbor(detail::input_adapter&&, const bool, const bool) for the
+        related CBOR format
+    @sa @ref from_msgpack(detail::input_adapter&&, const bool, const bool) for
+        the related MessagePack format
+    @sa @ref from_ubjson(detail::input_adapter&&, const bool, const bool) for the
+        related UBJSON format
+    */
+    static basic_json from_bson(detail::input_adapter&& i,
+                                const bool strict = true,
+                                const bool allow_exceptions = true)
+    {
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        const bool res = binary_reader(detail::input_adapter(i)).sax_parse(input_format_t::bson, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
+    }
+
+    /*!
+    @copydoc from_bson(detail::input_adapter&&, const bool, const bool)
+    */
+    template<typename A1, typename A2,
+             detail::enable_if_t<std::is_constructible<detail::input_adapter, A1, A2>::value, int> = 0>
+    static basic_json from_bson(A1 && a1, A2 && a2,
+                                const bool strict = true,
+                                const bool allow_exceptions = true)
+    {
+        basic_json result;
+        detail::json_sax_dom_parser<basic_json> sdp(result, allow_exceptions);
+        const bool res = binary_reader(detail::input_adapter(std::forward<A1>(a1), std::forward<A2>(a2))).sax_parse(input_format_t::bson, &sdp, strict);
+        return res ? result : basic_json(value_t::discarded);
+    }
+
+
+
     /// @}
 
     //////////////////////////
@@ -14008,20 +19864,20 @@ class basic_json
                                 // avoid undefined behavior
                                 JSON_THROW(out_of_range::create(401, "array index " + std::to_string(idx) + " is out of range"));
                             }
-                            else
-                            {
-                                // default case: insert add offset
-                                parent.insert(parent.begin() + static_cast<difference_type>(idx), val);
-                            }
+
+                            // default case: insert add offset
+                            parent.insert(parent.begin() + static_cast<difference_type>(idx), val);
                         }
                         break;
                     }
 
+                    // LCOV_EXCL_START
                     default:
                     {
                         // if there exists a parent it cannot be primitive
-                        assert(false);  // LCOV_EXCL_LINE
+                        assert(false);
                     }
+                        // LCOV_EXCL_STOP
                 }
             }
         };
@@ -14066,7 +19922,7 @@ class basic_json
             // wrapper to get a value for an operation
             const auto get_value = [&val](const std::string & op,
                                           const std::string & member,
-                                          bool string_type) -> basic_json&
+                                          bool string_type) -> basic_json &
             {
                 // find value
                 auto it = val.m_value.object->find(member);
@@ -14163,7 +20019,7 @@ class basic_json
                         // the "path" location must exist - use at()
                         success = (result.at(ptr) == get_value("test", "value", false));
                     }
-                    JSON_CATCH (out_of_range&)
+                    JSON_INTERNAL_CATCH (out_of_range&)
                     {
                         // ignore out of range errors: success remains false
                     }
@@ -14216,6 +20072,7 @@ class basic_json
     diff for two JSON values.,diff}
 
     @sa @ref patch -- apply a JSON patch
+    @sa @ref merge_patch -- apply a JSON Merge Patch
 
     @sa [RFC 6902 (JSON Patch)](https://tools.ietf.org/html/rfc6902)
 
@@ -14347,418 +20204,86 @@ class basic_json
     }
 
     /// @}
-};
 
-/////////////
-// presets //
-/////////////
+    ////////////////////////////////
+    // JSON Merge Patch functions //
+    ////////////////////////////////
 
-/*!
-@brief default JSON class
-
-This type is the default specialization of the @ref basic_json class which
-uses the standard template types.
-
-@since version 1.0.0
-*/
-using json = basic_json<>;
-
-//////////////////
-// json_pointer //
-//////////////////
-
-NLOHMANN_BASIC_JSON_TPL_DECLARATION
-NLOHMANN_BASIC_JSON_TPL&
-json_pointer::get_and_create(NLOHMANN_BASIC_JSON_TPL& j) const
-{
-    using size_type = typename NLOHMANN_BASIC_JSON_TPL::size_type;
-    auto result = &j;
-
-    // in case no reference tokens exist, return a reference to the JSON value
-    // j which will be overwritten by a primitive value
-    for (const auto& reference_token : reference_tokens)
-    {
-        switch (result->m_type)
-        {
-            case detail::value_t::null:
-            {
-                if (reference_token == "0")
-                {
-                    // start a new array if reference token is 0
-                    result = &result->operator[](0);
-                }
-                else
-                {
-                    // start a new object otherwise
-                    result = &result->operator[](reference_token);
-                }
-                break;
-            }
-
-            case detail::value_t::object:
-            {
-                // create an entry in the object
-                result = &result->operator[](reference_token);
-                break;
-            }
-
-            case detail::value_t::array:
-            {
-                // create an entry in the array
-                JSON_TRY
-                {
-                    result = &result->operator[](static_cast<size_type>(array_index(reference_token)));
-                }
-                JSON_CATCH(std::invalid_argument&)
-                {
-                    JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                }
-                break;
-            }
+    /// @name JSON Merge Patch functions
+    /// @{
 
-            /*
-            The following code is only reached if there exists a reference
-            token _and_ the current value is primitive. In this case, we have
-            an error situation, because primitive values may only occur as
-            single value; that is, with an empty list of reference tokens.
-            */
-            default:
-                JSON_THROW(detail::type_error::create(313, "invalid value to unflatten"));
-        }
-    }
+    /*!
+    @brief applies a JSON Merge Patch
+
+    The merge patch format is primarily intended for use with the HTTP PATCH
+    method as a means of describing a set of modifications to a target
+    resource's content. This function applies a merge patch to the current
+    JSON value.
+
+    The function implements the following algorithm from Section 2 of
+    [RFC 7396 (JSON Merge Patch)](https://tools.ietf.org/html/rfc7396):
+
+    ```
+    define MergePatch(Target, Patch):
+      if Patch is an Object:
+        if Target is not an Object:
+          Target = {} // Ignore the contents and set it to an empty Object
+        for each Name/Value pair in Patch:
+          if Value is null:
+            if Name exists in Target:
+              remove the Name/Value pair from Target
+          else:
+            Target[Name] = MergePatch(Target[Name], Value)
+        return Target
+      else:
+        return Patch
+    ```
+
+    Thereby, `Target` is the current object; that is, the patch is applied to
+    the current value.
+
+    @param[in] apply_patch  the patch to apply
+
+    @complexity Linear in the lengths of @a patch.
+
+    @liveexample{The following code shows how a JSON Merge Patch is applied to
+    a JSON document.,merge_patch}
 
-    return *result;
-}
+    @sa @ref patch -- apply a JSON patch
+    @sa [RFC 7396 (JSON Merge Patch)](https://tools.ietf.org/html/rfc7396)
 
-NLOHMANN_BASIC_JSON_TPL_DECLARATION
-NLOHMANN_BASIC_JSON_TPL&
-json_pointer::get_unchecked(NLOHMANN_BASIC_JSON_TPL* ptr) const
-{
-    using size_type = typename NLOHMANN_BASIC_JSON_TPL::size_type;
-    for (const auto& reference_token : reference_tokens)
+    @since version 3.0.0
+    */
+    void merge_patch(const basic_json& apply_patch)
     {
-        // convert null values to arrays or objects before continuing
-        if (ptr->m_type == detail::value_t::null)
-        {
-            // check if reference token is a number
-            const bool nums =
-                std::all_of(reference_token.begin(), reference_token.end(),
-                            [](const char x)
-            {
-                return (x >= '0' and x <= '9');
-            });
-
-            // change value to array for numbers or "-" or to object otherwise
-            *ptr = (nums or reference_token == "-")
-                   ? detail::value_t::array
-                   : detail::value_t::object;
-        }
-
-        switch (ptr->m_type)
+        if (apply_patch.is_object())
         {
-            case detail::value_t::object:
+            if (not is_object())
             {
-                // use unchecked object access
-                ptr = &ptr->operator[](reference_token);
-                break;
+                *this = object();
             }
-
-            case detail::value_t::array:
+            for (auto it = apply_patch.begin(); it != apply_patch.end(); ++it)
             {
-                // error condition (cf. RFC 6901, Sect. 4)
-                if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
-                {
-                    JSON_THROW(detail::parse_error::create(106, 0,
-                                                           "array index '" + reference_token +
-                                                           "' must not begin with '0'"));
-                }
-
-                if (reference_token == "-")
+                if (it.value().is_null())
                 {
-                    // explicitly treat "-" as index beyond the end
-                    ptr = &ptr->operator[](ptr->m_value.array->size());
+                    erase(it.key());
                 }
                 else
                 {
-                    // convert array index to number; unchecked access
-                    JSON_TRY
-                    {
-                        ptr = &ptr->operator[](
-                            static_cast<size_type>(array_index(reference_token)));
-                    }
-                    JSON_CATCH(std::invalid_argument&)
-                    {
-                        JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                    }
-                }
-                break;
-            }
-
-            default:
-                JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
-        }
-    }
-
-    return *ptr;
-}
-
-NLOHMANN_BASIC_JSON_TPL_DECLARATION
-NLOHMANN_BASIC_JSON_TPL&
-json_pointer::get_checked(NLOHMANN_BASIC_JSON_TPL* ptr) const
-{
-    using size_type = typename NLOHMANN_BASIC_JSON_TPL::size_type;
-    for (const auto& reference_token : reference_tokens)
-    {
-        switch (ptr->m_type)
-        {
-            case detail::value_t::object:
-            {
-                // note: at performs range check
-                ptr = &ptr->at(reference_token);
-                break;
-            }
-
-            case detail::value_t::array:
-            {
-                if (JSON_UNLIKELY(reference_token == "-"))
-                {
-                    // "-" always fails the range check
-                    JSON_THROW(detail::out_of_range::create(402,
-                                                            "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
-                                                            ") is out of range"));
-                }
-
-                // error condition (cf. RFC 6901, Sect. 4)
-                if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
-                {
-                    JSON_THROW(detail::parse_error::create(106, 0,
-                                                           "array index '" + reference_token +
-                                                           "' must not begin with '0'"));
-                }
-
-                // note: at performs range check
-                JSON_TRY
-                {
-                    ptr = &ptr->at(static_cast<size_type>(array_index(reference_token)));
+                    operator[](it.key()).merge_patch(it.value());
                 }
-                JSON_CATCH(std::invalid_argument&)
-                {
-                    JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                }
-                break;
             }
-
-            default:
-                JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
         }
-    }
-
-    return *ptr;
-}
-
-NLOHMANN_BASIC_JSON_TPL_DECLARATION
-const NLOHMANN_BASIC_JSON_TPL&
-json_pointer::get_unchecked(const NLOHMANN_BASIC_JSON_TPL* ptr) const
-{
-    using size_type = typename NLOHMANN_BASIC_JSON_TPL::size_type;
-    for (const auto& reference_token : reference_tokens)
-    {
-        switch (ptr->m_type)
-        {
-            case detail::value_t::object:
-            {
-                // use unchecked object access
-                ptr = &ptr->operator[](reference_token);
-                break;
-            }
-
-            case detail::value_t::array:
-            {
-                if (JSON_UNLIKELY(reference_token == "-"))
-                {
-                    // "-" cannot be used for const access
-                    JSON_THROW(detail::out_of_range::create(402,
-                                                            "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
-                                                            ") is out of range"));
-                }
-
-                // error condition (cf. RFC 6901, Sect. 4)
-                if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
-                {
-                    JSON_THROW(detail::parse_error::create(106, 0,
-                                                           "array index '" + reference_token +
-                                                           "' must not begin with '0'"));
-                }
-
-                // use unchecked array access
-                JSON_TRY
-                {
-                    ptr = &ptr->operator[](
-                        static_cast<size_type>(array_index(reference_token)));
-                }
-                JSON_CATCH(std::invalid_argument&)
-                {
-                    JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                }
-                break;
-            }
-
-            default:
-                JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
-        }
-    }
-
-    return *ptr;
-}
-
-NLOHMANN_BASIC_JSON_TPL_DECLARATION
-const NLOHMANN_BASIC_JSON_TPL&
-json_pointer::get_checked(const NLOHMANN_BASIC_JSON_TPL* ptr) const
-{
-    using size_type = typename NLOHMANN_BASIC_JSON_TPL::size_type;
-    for (const auto& reference_token : reference_tokens)
-    {
-        switch (ptr->m_type)
-        {
-            case detail::value_t::object:
-            {
-                // note: at performs range check
-                ptr = &ptr->at(reference_token);
-                break;
-            }
-
-            case detail::value_t::array:
-            {
-                if (JSON_UNLIKELY(reference_token == "-"))
-                {
-                    // "-" always fails the range check
-                    JSON_THROW(detail::out_of_range::create(402,
-                                                            "array index '-' (" + std::to_string(ptr->m_value.array->size()) +
-                                                            ") is out of range"));
-                }
-
-                // error condition (cf. RFC 6901, Sect. 4)
-                if (JSON_UNLIKELY(reference_token.size() > 1 and reference_token[0] == '0'))
-                {
-                    JSON_THROW(detail::parse_error::create(106, 0,
-                                                           "array index '" + reference_token +
-                                                           "' must not begin with '0'"));
-                }
-
-                // note: at performs range check
-                JSON_TRY
-                {
-                    ptr = &ptr->at(static_cast<size_type>(array_index(reference_token)));
-                }
-                JSON_CATCH(std::invalid_argument&)
-                {
-                    JSON_THROW(detail::parse_error::create(109, 0, "array index '" + reference_token + "' is not a number"));
-                }
-                break;
-            }
-
-            default:
-                JSON_THROW(detail::out_of_range::create(404, "unresolved reference token '" + reference_token + "'"));
-        }
-    }
-
-    return *ptr;
-}
-
-NLOHMANN_BASIC_JSON_TPL_DECLARATION
-void json_pointer::flatten(const std::string& reference_string,
-                           const NLOHMANN_BASIC_JSON_TPL& value,
-                           NLOHMANN_BASIC_JSON_TPL& result)
-{
-    switch (value.m_type)
-    {
-        case detail::value_t::array:
-        {
-            if (value.m_value.array->empty())
-            {
-                // flatten empty array as null
-                result[reference_string] = nullptr;
-            }
-            else
-            {
-                // iterate array and use index as reference string
-                for (std::size_t i = 0; i < value.m_value.array->size(); ++i)
-                {
-                    flatten(reference_string + "/" + std::to_string(i),
-                            value.m_value.array->operator[](i), result);
-                }
-            }
-            break;
-        }
-
-        case detail::value_t::object:
-        {
-            if (value.m_value.object->empty())
-            {
-                // flatten empty object as null
-                result[reference_string] = nullptr;
-            }
-            else
-            {
-                // iterate object and use keys as reference string
-                for (const auto& element : *value.m_value.object)
-                {
-                    flatten(reference_string + "/" + escape(element.first), element.second, result);
-                }
-            }
-            break;
-        }
-
-        default:
-        {
-            // add primitive value with its reference string
-            result[reference_string] = value;
-            break;
-        }
-    }
-}
-
-NLOHMANN_BASIC_JSON_TPL_DECLARATION
-NLOHMANN_BASIC_JSON_TPL
-json_pointer::unflatten(const NLOHMANN_BASIC_JSON_TPL& value)
-{
-    if (JSON_UNLIKELY(not value.is_object()))
-    {
-        JSON_THROW(detail::type_error::create(314, "only objects can be unflattened"));
-    }
-
-    NLOHMANN_BASIC_JSON_TPL result;
-
-    // iterate the JSON object values
-    for (const auto& element : *value.m_value.object)
-    {
-        if (JSON_UNLIKELY(not element.second.is_primitive()))
+        else
         {
-            JSON_THROW(detail::type_error::create(315, "values in object must be primitive"));
+            *this = apply_patch;
         }
-
-        // assign value to reference pointed to by JSON pointer; Note that if
-        // the JSON pointer is "" (i.e., points to the whole value), function
-        // get_and_create returns a reference to result itself. An assignment
-        // will then create a primitive value.
-        json_pointer(element.first).get_and_create(result) = element.second;
     }
 
-    return result;
-}
-
-inline bool operator==(json_pointer const& lhs, json_pointer const& rhs) noexcept
-{
-    return (lhs.reference_tokens == rhs.reference_tokens);
-}
-
-inline bool operator!=(json_pointer const& lhs, json_pointer const& rhs) noexcept
-{
-    return not (lhs == rhs);
-}
+    /// @}
+};
 } // namespace nlohmann
 
-
 ///////////////////////
 // nonmember support //
 ///////////////////////
@@ -14766,20 +20291,6 @@ inline bool operator!=(json_pointer const& lhs, json_pointer const& rhs) noexcep
 // specialization of std::swap, and std::hash
 namespace std
 {
-/*!
-@brief exchanges the values of two JSON objects
-
-@since version 1.0.0
-*/
-template<>
-inline void swap(nlohmann::json& j1,
-                 nlohmann::json& j2) noexcept(
-                     is_nothrow_move_constructible<nlohmann::json>::value and
-                     is_nothrow_move_assignable<nlohmann::json>::value
-                 )
-{
-    j1.swap(j2);
-}
 
 /// hash value for JSON objects
 template<>
@@ -14815,6 +20326,20 @@ struct less< ::nlohmann::detail::value_t>
     }
 };
 
+/*!
+@brief exchanges the values of two JSON objects
+
+@since version 1.0.0
+*/
+template<>
+inline void swap<nlohmann::json>(nlohmann::json& j1, nlohmann::json& j2) noexcept(
+    is_nothrow_move_constructible<nlohmann::json>::value and
+    is_nothrow_move_assignable<nlohmann::json>::value
+)
+{
+    j1.swap(j2);
+}
+
 } // namespace std
 
 /*!
@@ -14853,6 +20378,9 @@ inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std
     return nlohmann::json::json_pointer(std::string(s, n));
 }
 
+// #include <nlohmann/detail/macro_unscope.hpp>
+
+
 // restore GCC/clang diagnostic settings
 #if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
     #pragma GCC diagnostic pop
@@ -14862,13 +20390,17 @@ inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std
 #endif
 
 // clean up
+#undef JSON_INTERNAL_CATCH
 #undef JSON_CATCH
 #undef JSON_THROW
 #undef JSON_TRY
 #undef JSON_LIKELY
 #undef JSON_UNLIKELY
 #undef JSON_DEPRECATED
+#undef JSON_HAS_CPP_14
+#undef JSON_HAS_CPP_17
 #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
 #undef NLOHMANN_BASIC_JSON_TPL
 
+
 #endif
diff --git a/src/resolve-system-dependencies/local.mk b/src/resolve-system-dependencies/local.mk
index 8792a4a252fa..f9db16268be0 100644
--- a/src/resolve-system-dependencies/local.mk
+++ b/src/resolve-system-dependencies/local.mk
@@ -6,6 +6,6 @@ resolve-system-dependencies_DIR := $(d)
 
 resolve-system-dependencies_INSTALL_DIR := $(libexecdir)/nix
 
-resolve-system-dependencies_LIBS := libstore libmain libutil libformat
+resolve-system-dependencies_LIBS := libstore libmain libutil
 
 resolve-system-dependencies_SOURCES := $(d)/resolve-system-dependencies.cc