1 files changed, 85 insertions, 0 deletions
diff --git a/third_party/nix/src/libutil/istringstream_nocopy.hh b/third_party/nix/src/libutil/istringstream_nocopy.hh
new file mode 100644
index 000000000000..31683d37c91b
--- /dev/null
+++ b/third_party/nix/src/libutil/istringstream_nocopy.hh
@@ -0,0 +1,85 @@
+/* This file provides a variant of std::istringstream that doesn't
+   copy 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. */
+
+#pragma once
+
+#include <iostream>
+#include <string>
+
+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:
+  using string_type = std::basic_string<CharT, Traits, Allocator>;
+
+  using off_type = typename std::basic_streambuf<CharT, Traits>::off_type;
+
+  using pos_type = typename std::basic_streambuf<CharT, Traits>::pos_type;
+
+  using int_type = typename std::basic_streambuf<CharT, Traits>::int_type;
+
+  using traits_type = typename std::basic_streambuf<CharT, Traits>::traits_type;
+
+ private:
+  const string_type& s;
+
+  off_type off;
+
+ public:
+  explicit 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> {
+  using buf_type = basic_istringbuf_nocopy<CharT, Traits, Allocator>;
+  buf_type buf;
+
+ public:
+  explicit basic_istringstream_nocopy(const typename buf_type::string_type& s)
+      : std::basic_iostream<CharT, Traits>(&buf), buf(s){};
+};
+
+using istringstream_nocopy = basic_istringstream_nocopy<char>;