Web MIDI API back-end (work-in-progress)

content/renderer/media/midi_message_filter.h

+// Copyright (c) 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 CONTENT_RENDERER_MEDIA_MIDI_MESSAGE_FILTER_H_
+#define CONTENT_RENDERER_MEDIA_MIDI_MESSAGE_FILTER_H_
+
+#include <map>
+#include <vector>
+
+#include "base/memory/scoped_ptr.h"
+#include "content/common/content_export.h"
+#include "ipc/ipc_channel_proxy.h"
+#include "media/midi/midi_port_info.h"
+#include "third_party/WebKit/public/platform/WebMIDIAccessor.h"
+#include "third_party/WebKit/public/platform/WebMIDIAccessorClient.h"
+
+namespace base {
+class MessageLoopProxy;
+}
+
+namespace content {
+
+// MessageFilter that handles MIDI messages.
+class CONTENT_EXPORT MIDIMessageFilter
+    : public IPC::ChannelProxy::MessageFilter {
+ public:
+  explicit MIDIMessageFilter(
+      const scoped_refptr<base::MessageLoopProxy>& io_message_loop);
+
+  // Each client registers for MIDI access here.
+  // If permission is granted, then the client's
+  // addInputPort() and addOutputPort() methods will be called,
+  // giving the client access to receive and send data.
+  void RequestAccess(WebKit::WebMIDIAccessorClient* client, int access);
+  void RemoveClient(WebKit::WebMIDIAccessorClient* client);
+
+  // A client will only be able to call this method if it has a suitable
+  // output port (from addOutputPort()).
+  void SendMIDIData(int port_index,
+                    const uint8* data,
+                    size_t length,
+                    double timestamp);
+
+  // IO message loop associated with this message filter.
+  scoped_refptr<base::MessageLoopProxy> io_message_loop() const {
+    return io_message_loop_;
+  }
+
+ protected:
+  virtual ~MIDIMessageFilter();
+
+ private:
+  // Sends an IPC message using |channel_|.
+  void Send(IPC::Message* message);
+
+  // IPC::ChannelProxy::MessageFilter override. Called on |io_message_loop|.
+  virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
+  virtual void OnFilterAdded(IPC::Channel* channel) OVERRIDE;
+  virtual void OnFilterRemoved() OVERRIDE;
+  virtual void OnChannelClosing() OVERRIDE;
+
+  // Called when the browser process has approved (or denied) access to
+  // MIDI hardware.
+  void OnAccessApproved(int client_id,
+                        int access,
+                        bool success,
+                        media::MIDIPortInfoList inputs,
+                        media::MIDIPortInfoList outputs);
+
+  // Called when the browser process has sent MIDI data containing one or
+  // more messages.
+  void OnDataReceived(int port,
+                      const std::vector<uint8>& data,
+                      double timestamp);
+
+  void HandleAccessApproved(int client_id,
+                            int access,
+                            bool success,
+                            media::MIDIPortInfoList inputs,
+                            media::MIDIPortInfoList outputs);
+
+  void HandleDataReceived(int port,
+                          const std::vector<uint8>& data,
+                          double timestamp);
+
+  WebKit::WebMIDIAccessorClient* GetClientFromId(int client_id);
+
+  // IPC channel for Send(); must only be accessed on |io_message_loop_|.
+  IPC::Channel* channel_;
+
+  // Message loop on which IPC calls are driven.
+  const scoped_refptr<base::MessageLoopProxy> io_message_loop_;
+
+  // Keeps track of all MIDI clients.
+  // We map client to "client id" used to track permission.
+  // When access has been approved, we add the input and output ports to
+  // the client, allowing it to actually receive and send MIDI data.
+  typedef std::map<WebKit::WebMIDIAccessorClient*, int> ClientsMap;
+  ClientsMap clients_;
+
+  // Dishes out client ids.
+  static int next_available_id_;

[piman, 2013/06/20 20:16:20]

nit: does this need to be static?

[Chris Rogers, 2013/06/21 23:04:11]

Done.

+
+  // Protects access to our clients.
+  base::Lock clients_lock_;

[piman, 2013/06/20 20:16:20]

I think you can do away with the lock:
channel_ is only accessed from the IO thread
io_message_loop_ is constant
clients_ is only accessed from the client thread
next_available_id_ is only accessed from the client thread
client_message_loop_ could be made constant if we took it in the constructor
(which happens on the main thread). Or you could even use
ChildThread::current()->message_loop().

[Chris Rogers, 2013/06/21 23:04:11]

Yes you're right - removed it.

+
+  // Will normally be the JS main thread.
+  scoped_refptr<base::MessageLoopProxy> client_message_loop_;
+
+  DISALLOW_COPY_AND_ASSIGN(MIDIMessageFilter);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_MIDI_MESSAGE_FILTER_H_