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

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index f25f106c3a0ca8e11e0d3a6daef9e46e0c15172f..df62a758552e301c633970bb53914b00696a70b0 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -13244,8 +13244,18 @@ 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)));
 }
 
 
@@ -13673,6 +13683,35 @@ RawOneByteString* OneByteString::EscapeSpecialCharacters(const String& str) {
   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) {