Preserve the contents of Dart strings with unmatched surrogate halfs by avoiding a UTF16 -> UTF8

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 199 matching lines @@
 
 
 void JSONStream::PrintValue(const char* s) {
   PrintCommaIfNeeded();
   buffer_.AddChar('"');
   AddEscapedUTF8String(s);
   buffer_.AddChar('"');
 }
 
 
-void JSONStream::PrintValue(const char* s, intptr_t len) {
+bool JSONStream::PrintValueStr(const String& s, intptr_t limit) {
   PrintCommaIfNeeded();
   buffer_.AddChar('"');
-  AddEscapedUTF8String(s, len);
+  bool did_truncate = AddDartString(s, limit);
   buffer_.AddChar('"');
+  return did_truncate;
 }
 
 
 void JSONStream::PrintValueNoEscape(const char* s) {
   PrintCommaIfNeeded();
   buffer_.Printf("%s", s);
 }
 
 
 void JSONStream::PrintfValue(const char* format, ...) {
@@ skipping 68 matching lines @@
   PrintValue(d);
 }
 
 
 void JSONStream::PrintProperty(const char* name, const char* s) {
   PrintPropertyName(name);
   PrintValue(s);
 }
 
 
-void JSONStream::PrintProperty(const char* name, const char* s, intptr_t len) {
+bool JSONStream::PrintPropertyStr(const char* name,
+                                  const String& s,
+                                  intptr_t limit) {
   PrintPropertyName(name);
-  PrintValue(s, len);
+  return PrintValueStr(s, limit);
 }
 
 
 void JSONStream::PrintPropertyNoEscape(const char* name, const char* s) {
   PrintPropertyName(name);
   PrintValueNoEscape(s);
 }
 
 
 void JSONStream::PrintProperty(const char* name, const DebuggerEvent* event) {
@@ skipping 108 matching lines @@
   if (s == NULL) {
     return;
   }
   const uint8_t* s8 = reinterpret_cast<const uint8_t*>(s);
   intptr_t i = 0;
   for (; i < len; ) {
     // Extract next UTF8 character.
     int32_t ch = 0;
     int32_t ch_len = Utf8::Decode(&s8[i], len - i, &ch);
     ASSERT(ch_len != 0);
-    buffer_.AddEscapedChar(ch);
+    buffer_.EscapeAndAddCodeUnit(ch);
     // Move i forward.
     i += ch_len;
   }
   ASSERT(i == len);
 }
 
 
+bool JSONStream::AddDartString(const String& s, intptr_t limit) {
+  bool did_truncate = false;
+  intptr_t length = s.Length();
+  if (limit == -1) {
+    limit = length;
+  }
+  if (length <= limit) {
+    limit = length;
+  } else {
+    did_truncate = true;
+  }
+
+  for (intptr_t i = 0; i < limit; i++) {
+    intptr_t code_unit = s.CharAt(i);
+    buffer_.EscapeAndAddCodeUnit(code_unit);
+  }
+  return did_truncate;
+}
+
+
 JSONObject::JSONObject(const JSONArray* arr) : stream_(arr->stream_) {
   stream_->OpenObject();
 }
 
 
 void JSONObject::AddPropertyF(const char* name,
                               const char* format, ...) const {
   stream_->PrintPropertyName(name);
   va_list args;
   va_start(args, format);
@@ skipping 22 matching lines @@
   intptr_t len2 = OS::VSNPrint(p, len+1, format, args);
   va_end(args);
   ASSERT(len == len2);
   stream_->buffer_.AddChar('"');
   stream_->AddEscapedUTF8String(p);
   stream_->buffer_.AddChar('"');
   free(p);
 }
 
 }  // namespace dart