Use official JSON encoding for stream

runtime/vm/json_stream.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/assert.h"
 
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/json_stream.h"
 #include "vm/message.h"
@@ skipping 804 matching lines @@
   intptr_t length = s.Length();
   ASSERT(offset >= 0);
   if (offset > length) {
     offset = length;
   }
   if (!Utils::RangeCheck(offset, count, length)) {
     count = length - offset;
   }
   intptr_t limit = offset + count;
   for (intptr_t i = offset; i < limit; i++) {
-    intptr_t code_unit = s.CharAt(i);
-    buffer_.EscapeAndAddCodeUnit(code_unit);
+    uint32_t code_unit = s.CharAt(i);
+    ASSERT(!Utf16::IsTrailSurrogate(code_unit));
+    if (Utf16::IsLeadSurrogate(code_unit)) {
+      uint32_t trail = s.CharAt(++i);

[rmacnak, 2016/06/21 16:56:56]

A Dart string may have unmatched surrogates, so this might read after the end of
a Dart string or remove a character from the string.

[cbernaschina, 2016/06/21 21:24:43]

Done.

+      buffer_.EscapeAndAddCodeUnit(Utf16::Decode(code_unit, trail));
+    } else {
+      buffer_.EscapeAndAddCodeUnit(code_unit);
+    }
   }
   // Return value indicates whether the string is truncated.
   return (offset > 0) || (limit < length);
 }
 
 
 JSONObject::JSONObject(const JSONArray* arr) : stream_(arr->stream_) {
   stream_->OpenObject();
 }
 
@@ skipping 108 matching lines @@
   ASSERT(len == len2);
   stream_->buffer_.AddChar('"');
   stream_->AddEscapedUTF8String(p);
   stream_->buffer_.AddChar('"');
   free(p);
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart