istringstream_nocopy: Implement in a standards-compliant way.

Fixes the problem mentioned in e6a61b8da788efbbbb0eb690c49434b6b5fc9741

See #1135

2 files changed, 88 insertions, 1 deletions

diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index f447c80c5d81..a8bbcf8c1754 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -104,7 +104,7 @@ Hash parseHash(HashType ht, const string & s)
         string s2(s, i * 2, 2);
         if (!isxdigit(s2[0]) || !isxdigit(s2[1]))
             throw BadHash(format("invalid hash ‘%1%’") % s);
-        std::istringstream str(s2);
+        istringstream_nocopy str(s2);
         int n;
         str >> std::hex >> n;
         hash.hash[i] = n;
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 2950f7daa5ec..7cb3e68b9ef1 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -449,4 +449,91 @@ struct ReceiveInterrupts
 };
 
 
+template <class CharT, class Traits = std::char_traits<CharT>, class Allocator = std::allocator<CharT>>
+class basic_istringbuf_nocopy : public std::basic_streambuf<CharT, Traits>
+{
+public:
+    typedef std::basic_string<CharT, Traits, Allocator> string_type;
+
+    typedef typename std::basic_streambuf<CharT, Traits>::off_type off_type;
+
+    typedef typename std::basic_streambuf<CharT, Traits>::pos_type pos_type;
+
+    typedef typename std::basic_streambuf<CharT, Traits>::int_type int_type;
+
+    typedef typename std::basic_streambuf<CharT, Traits>::traits_type traits_type;
+
+private:
+    const string_type & s;
+
+    off_type off;
+
+public:
+    basic_istringbuf_nocopy(const string_type & s) : s{s}, off{0}
+    {
+    }
+
+private:
+    pos_type seekoff(off_type off, std::ios_base::seekdir dir, std::ios_base::openmode which)
+    {
+        if (which & std::ios_base::in) {
+            this->off = dir == std::ios_base::beg
+                ? off
+                : (dir == std::ios_base::end
+                    ? s.size() + off
+                    : this->off + off);
+        }
+        return pos_type(this->off);
+    }
+
+    pos_type seekpos(pos_type pos, std::ios_base::openmode which)
+    {
+        return seekoff(pos, std::ios_base::beg, which);
+    }
+
+    std::streamsize showmanyc()
+    {
+        return s.size() - off;
+    }
+
+    int_type underflow()
+    {
+        if (typename string_type::size_type(off) == s.size())
+            return traits_type::eof();
+        return traits_type::to_int_type(s[off]);
+    }
+
+    int_type uflow()
+    {
+        if (typename string_type::size_type(off) == s.size())
+            return traits_type::eof();
+        return traits_type::to_int_type(s[off++]);
+    }
+
+    int_type pbackfail(int_type ch)
+    {
+        if (off == 0 || (ch != traits_type::eof() && ch != s[off - 1]))
+            return traits_type::eof();
+
+        return traits_type::to_int_type(s[--off]);
+    }
+
+};
+
+template <class CharT, class Traits = std::char_traits<CharT>, class Allocator = std::allocator<CharT>>
+class basic_istringstream_nocopy : public std::basic_iostream<CharT, Traits>
+{
+    typedef basic_istringbuf_nocopy<CharT, Traits, Allocator> buf_type;
+    buf_type buf;
+public:
+    basic_istringstream_nocopy(const typename buf_type::string_type & s) :
+        std::basic_iostream<CharT, Traits>(&buf), buf(s) {};
+};
+
+/* A variant of std::istringstream that doesn't its string
+   argument. This is useful for large strings. The caller must ensure
+   that the string object is not destroyed while it's referenced by
+   this object. */
+typedef basic_istringstream_nocopy<char> istringstream_nocopy;
+
 }