A proposal and implementation for an initial postMessage interface. These in...

webkit/plugins/ppapi/message_channel.h

+// Copyright (c) 2011 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 WEBKIT_PLUGINS_PPAPI_MESSAGE_CHANNEL_H_
+#define WEBKIT_PLUGINS_PPAPI_MESSAGE_CHANNEL_H_
+
+#include "third_party/npapi/bindings/npruntime.h"
+#include "webkit/plugins/ppapi/resource.h"
+
+struct PP_Var;
+
+namespace webkit {
+namespace ppapi {
+
+class PluginInstance;
+
+// MessageChannel implements bidirectional postMessage functionality, allowing
+// calls from JavaScript to plugins and vice-versa. See
+// PPB_Instance::PostMessage and PPP_Instance::HandleMessage for more
+// information.
+//
+// Currently, only 1 MessageChannel can exist, to implement postMessage
+// functionality for the instance interfaces.  In the future, when we create a
+// MessagePort type in PPAPI, those may be implemented here as well with some
+// refactoring.
+//   - Separate message ports won't require the passthrough object.
+//   - The message target won't be limited to instance, and should support
+//     either plugin-provided or JS objects.
+// TODO(dmichael):  Add support for separate MessagePorts.
+class MessageChannel {
+ public:
+  // MessageChannelNPObject is a simple struct that adds a pointer back to a
+  // MessageChannel instance.  This way, we can use an NPObject to allow
+  // JavaScript interactions without forcing MessageChannel to inherit from
+  // NPObject.
+  struct MessageChannelNPObject : public NPObject {
+    MessageChannelNPObject();
+    ~MessageChannelNPObject();
+
+    MessageChannel* message_channel;
+  };
+
+  explicit MessageChannel(PluginInstance* instance);
+  ~MessageChannel();
+
+  void PostMessageToJavaScript(PP_Var message_data);
+  void PostMessageToNative(PP_Var message_data);
+
+  // Return the NPObject* to which we should forward any calls which aren't
+  // related to postMessage.  Note that this can be NULL;  it only gets set if
+  // there is a scriptable 'InstanceObject' associated with this channel's
+  // instance.
+  NPObject* passthrough_object() {
+    return passthrough_object_;
+  }
+  void set_passthrough_object(NPObject* passthrough) {
+    passthrough_object_ = passthrough;
+  }
+
+  NPObject* np_object() { return np_object_; }
+
+  PluginInstance* instance() {
+    return instance_;
+  }
+
+ private:
+  PluginInstance* instance_;
+
+  // We pass all non-postMessage calls through to the passthrough_object_.
+  // This way, a plugin can use PPB_Class or PPP_Class_Deprecated and also
+  // postMessage.  This is necessary to support backwards-compatibility, and
+  // also trusted plugins for which we will continue to support synchronous
+  // scripting.
+  NPObject* passthrough_object_;
+
+  // The NPObject we use to expose postMessage to JavaScript.
+  MessageChannelNPObject* np_object_;
+
+  // An NPVariant referring to the JavaScript function we use to send a message
+  // to a JavaScript target.
+  NPVariant onmessage_invoker_;
+
+  bool EvaluateOnMessageInvoker();
+
+  DISALLOW_COPY_AND_ASSIGN(MessageChannel);
+};
+
+}  // namespace ppapi
+}  // namespace webkit
+
+#endif  // WEBKIT_PLUGINS_PPAPI_MESSAGE_CHANNEL_H_
+