Fix length computation in Dart_StringToUTF8.

vm/dart_api_impl.cc

Index: vm/dart_api_impl.cc
===================================================================
--- vm/dart_api_impl.cc	(revision 14418)
+++ vm/dart_api_impl.cc	(working copy)
@@ -1669,7 +1669,7 @@
   if (str_obj.IsNull()) {
     RETURN_TYPE_ERROR(isolate, str, String);
   }
-  intptr_t str_len = str_obj.Length();
+  intptr_t str_len = Utf8::Length(str_obj);

[Bill Hesse, 2012/11/01 20:38:01]

There is still no way for the user to know the length of the encoding - I think
we have to expose Utf8::Length in the API.  Note that the maximum length is 3 *
length bytes, not 2 * length.

[siva, 2012/11/01 21:23:03]

I have changed the API to do a scope allocation inside here, so the caller does
not have to compute the length.

On 2012/11/01 20:38:01, Bill Hesse wrote:

   if (str_len > *length) {

[Bill Hesse, 2012/11/01 20:38:01]

I think this is not enough.  There is no way for the user to know the actual
desired size of the array - they have to overestimate at 3 * length.  I think
Utf8::Length has to be exposed in the API.  But StringToCString works well, and
its use should be encouraged.  Alternatively, you could convert up to the
available size, and report whether more space is needed.

[siva, 2012/11/01 21:23:03]

Check removed.

On 2012/11/01 20:38:01, Bill Hesse wrote:

     return Api::NewError("Input array is not large enough to hold the result");
   }