Gin: Consolidate all the Converter<Wrappable> subclasses.

gin/wrappable.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GIN_WRAPPABLE_H_
 #define GIN_WRAPPABLE_H_
 
+#include "base/template_util.h"
 #include "gin/converter.h"
 #include "gin/public/wrapper_info.h"
 
 namespace gin {
 
 // Wrappable is an abstract base class for C++ objects that have cooresponding
 // v8 wrapper objects. To retain a Wrappable object on the stack, use a
 // gin::Handle.
 class Wrappable {
  public:
@@ skipping 28 matching lines @@
   // Create function will enforce that clients actually create a wrapper for
   // the object. If clients fail to create a wrapper for a wrappable object,
   // the object will leak because we use the weak callback from the wrapper
   // as the signal to delete the wrapped object.
 
  protected:
   Wrappable();
   virtual ~Wrappable();
 
  private:
-  friend struct Converter<Wrappable*>;
-
   static void WeakCallback(
       const v8::WeakCallbackData<v8::Object, Wrappable>& data);
   v8::Handle<v8::Object> CreateWrapper(v8::Isolate* isolate);
 
   v8::Persistent<v8::Object> wrapper_;  // Weak
 
   DISALLOW_COPY_AND_ASSIGN(Wrappable);
 };
 
-template<>
-struct Converter<Wrappable*> {
-  static v8::Handle<v8::Value> ToV8(v8::Isolate* isolate,
-                                    Wrappable* val);
-  static bool FromV8(v8::Isolate* isolate, v8::Handle<v8::Value> val,
-                     Wrappable** out);
-};
+// This converter handles any subclass of Wrappable.
+template<typename T>
+struct Converter<T, typename base::enable_if<
+                      base::is_convertible<T, Wrappable*>::value>::type> {
+  static v8::Handle<v8::Value> ToV8(v8::Isolate* isolate, T val) {
+    return val->GetWrapper(isolate);
+  }
 
-template<typename T>
-struct WrappableConverter {
-  static v8::Handle<v8::Value> ToV8(v8::Isolate* isolate, T* val) {
-    return Converter<Wrappable*>::ToV8(isolate, val);
-  }
-  static bool FromV8(v8::Isolate* isolate, v8::Handle<v8::Value> val, T** out) {
-    Wrappable* wrappable = NULL;
-    if (!Converter<Wrappable*>::FromV8(isolate, val, &wrappable)
-        || wrappable->GetWrapperInfo() != &T::kWrapperInfo)

[abarth-chromium, 2013/12/06 01:50:55]

I think we're missing this security check.  You need some way of cross-checking
type T with the object.

+  static bool FromV8(v8::Isolate* isolate, v8::Handle<v8::Value> val, T* out) {
+    if (!val->IsObject())
       return false;
-    // Currently we require that you unwrap to the exact runtime type of the
-    // wrapped object.
-    // TODO(abarth): Support unwrapping to a base class.
-    *out = static_cast<T*>(wrappable);
+    v8::Handle<v8::Object> obj = v8::Handle<v8::Object>::Cast(val);
+    WrapperInfo* info = WrapperInfo::From(obj);
+    if (!info)
+      return false;
+    void* pointer = obj->GetAlignedPointerFromInternalField(kEncodedValueIndex);
+    T result = static_cast<T>(pointer);
+    CHECK(result->GetWrapperInfo() == info);  // Security check for cast above.
+    *out = result;
     return true;
   }
 };
 
 }  // namespace gin
 
 #endif  // GIN_WRAPPABLE_H_