Fix crashing bug due to the fact that external one byte strings cannot be escaped

runtime/vm/object.cc

 // Copyright (c) 2012, 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 "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 13226 matching lines @@
       }
     }
   }
 }
 
 
 RawString* String::EscapeSpecialCharacters(const String& str) {
   if (str.IsOneByteString()) {
     return OneByteString::EscapeSpecialCharacters(str);
   }
-  ASSERT(str.IsTwoByteString());
-  return TwoByteString::EscapeSpecialCharacters(str);
+  if (str.IsTwoByteString()) {
+    return TwoByteString::EscapeSpecialCharacters(str);
+  }
+  if (str.IsExternalOneByteString()) {
+    return ExternalOneByteString::EscapeSpecialCharacters(str);
+  }
+  ASSERT(str.IsExternalTwoByteString());
+  // If EscapeSpecialCharacters is frequently called on external two byte
+  // strings, we should implement it directly on ExternalTwoByteString rather
+  // than first converting to a TwoByteString.
+  return TwoByteString::EscapeSpecialCharacters(
+      String::Handle(TwoByteString::New(str, Heap::kNew)));
 }
 
 
 RawString* String::NewFormatted(const char* format, ...) {
   va_list args;
   va_start(args, format);
   RawString* result = NewFormattedV(format, args);
   NoGCScope no_gc;
   va_end(args);
   return result;
@@ skipping 407 matching lines @@
       } else {
         *(CharAddr(dststr, index)) = *CharAddr(str, i);
         index += 1;
       }
     }
     return OneByteString::raw(dststr);
   }
   return OneByteString::null();
 }
 
+RawOneByteString* ExternalOneByteString::EscapeSpecialCharacters(
+    const String& str) {
+  intptr_t len = str.Length();
+  if (len > 0) {
+    intptr_t num_escapes = 0;
+    intptr_t index = 0;

[hausner, 2013/09/30 22:54:37]

declare index just before the loop below where it's used?

[Jacob, 2013/09/30 23:53:28]

Fixed that here and in the code this method was copied from modulo a couple
tweaks.

+    for (intptr_t i = 0; i < len; i++) {
+      if (IsSpecialCharacter(*CharAddr(str, i))) {
+        num_escapes += 1;
+      }
+    }
+    const String& dststr = String::Handle(
+        OneByteString::New(len + num_escapes, Heap::kNew));
+    for (intptr_t i = 0; i < len; i++) {
+      if (IsSpecialCharacter(*CharAddr(str, i))) {
+        *(OneByteString::CharAddr(dststr, index)) = '\\';
+        *(OneByteString::CharAddr(dststr, index + 1)) =
+        SpecialCharacter(*CharAddr(str, i));
+        index += 2;
+      } else {
+        *(OneByteString::CharAddr(dststr, index)) = *CharAddr(str, i);
+        index += 1;
+      }
+    }
+    return OneByteString::raw(dststr);
+  }
+  return OneByteString::null();

[hausner, 2013/09/30 22:54:37]

It it correct to return null when the input string is of length 0?

[Jacob, 2013/09/30 23:53:28]

That is what the existing code did but I agree it seems bad.  Added a test for
that case as well and fixed this code and the other corresponding code. 
Previously it was the case that 
escaping "" resulted in null which is definitely not what you want.

+}
+
 
 RawOneByteString* OneByteString::New(intptr_t len,
                                      Heap::Space space) {
   ASSERT(Isolate::Current() == Dart::vm_isolate() ||
          Isolate::Current()->object_store()->one_byte_string_class() !=
          Class::null());
   if (len < 0 || len > kMaxElements) {
     // This should be caught before we reach here.
     FATAL1("Fatal error in OneByteString::New: invalid len %" Pd "\n", len);
   }
@@ skipping 1494 matching lines @@
   return "_MirrorReference";
 }
 
 
 void MirrorReference::PrintToJSONStream(JSONStream* stream, bool ref) const {
   JSONObject jsobj(stream);
 }
 
 
 }  // namespace dart