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

content/renderer/media/midi_message_filter.cc

+// 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.
+
+#include "content/renderer/media/midi_message_filter.h"
+
+#include "base/bind.h"
+#include "base/debug/trace_event.h"
+#include "base/message_loop/message_loop_proxy.h"
+#include "base/strings/utf_string_conversions.h"
+#include "content/common/media/midi_messages.h"
+#include "content/renderer/render_thread_impl.h"
+#include "ipc/ipc_logging.h"
+
+using media::MIDIPortInfoList;
+using base::AutoLock;
+
+namespace content {
+
+MIDIMessageFilter::MIDIMessageFilter(
+    const scoped_refptr<base::MessageLoopProxy>& io_message_loop)
+    : channel_(NULL),
+      io_message_loop_(io_message_loop),
+      next_available_id_(0) {
+}
+
+MIDIMessageFilter::~MIDIMessageFilter() {}
+
+void MIDIMessageFilter::Send(IPC::Message* message) {
+  DCHECK(io_message_loop_->BelongsToCurrentThread());
+  if (!channel_) {
+    delete message;
+  } else {
+    channel_->Send(message);
+  }
+}
+
+bool MIDIMessageFilter::OnMessageReceived(const IPC::Message& message) {
+  DCHECK(io_message_loop_->BelongsToCurrentThread());
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP(MIDIMessageFilter, message)
+    IPC_MESSAGE_HANDLER(MIDIMsg_AccessApproved, OnAccessApproved)
+    IPC_MESSAGE_HANDLER(MIDIMsg_DataReceived, OnDataReceived)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+  return handled;
+}
+
+void MIDIMessageFilter::OnFilterAdded(IPC::Channel* channel) {
+  DCHECK(io_message_loop_->BelongsToCurrentThread());
+  channel_ = channel;
+}
+
+void MIDIMessageFilter::OnFilterRemoved() {
+  DCHECK(io_message_loop_->BelongsToCurrentThread());
+
+  // Once removed, a filter will not be used again.  At this time all
+  // delegates must be notified so they release their reference.
+  OnChannelClosing();
+}
+
+void MIDIMessageFilter::OnChannelClosing() {
+  DCHECK(io_message_loop_->BelongsToCurrentThread());
+  channel_ = NULL;
+}
+
+void MIDIMessageFilter::RequestAccess(
+    WebKit::WebMIDIAccessorClient* client, int access) {
+  // Get the main thread message loop.
+  if (!client_message_loop_)
+    client_message_loop_ = base::MessageLoopProxy::current();

[piman, 2013/06/21 23:16:13]

Do you mind moving this to the constructor?
As is it looks racy because it's set on the main thread and used on the IO
thread (OnAccessApproved).
If you set it in the constructor, it's easy to convince oneself that it's safe.

+  else
+    CHECK(client_message_loop_ == base::MessageLoopProxy::current());
+
+  // Generate and keep track of a "client id" which is sent to the browser
+  // to ask permission to talk to MIDI hardware.
+  // This id is handed back when we receive the answer in OnAccessApproved().
+  if (clients_.find(client) == clients_.end()) {
+    int client_id = next_available_id_++;
+    clients_[client] = client_id;
+
+    io_message_loop_->PostTask(FROM_HERE,
+        base::Bind(&MIDIMessageFilter::RequestAccessOnIOThread, this,
+                   client_id, access));
+  }
+}
+
+void MIDIMessageFilter::RequestAccessOnIOThread(int client_id, int access) {
+  Send(new MIDIHostMsg_RequestAccess(client_id, access));
+}
+
+void MIDIMessageFilter::RemoveClient(WebKit::WebMIDIAccessorClient* client) {
+  ClientsMap::iterator i = clients_.find(client);
+  if (i != clients_.end())
+    clients_.erase(i);
+}
+
+// Received from browser.
+
+void MIDIMessageFilter::OnAccessApproved(
+    int client_id,
+    int access,
+    bool success,
+    MIDIPortInfoList inputs,
+    MIDIPortInfoList outputs) {
+  if (client_message_loop_) {
+    // Handle on the main JS thread.
+    client_message_loop_->PostTask(FROM_HERE,
+        base::Bind(&MIDIMessageFilter::HandleAccessApproved, this,
+                   client_id, access, success, inputs, outputs));
+  }
+}
+
+void MIDIMessageFilter::HandleAccessApproved(
+    int client_id,
+    int access,
+    bool success,
+    MIDIPortInfoList inputs,
+    MIDIPortInfoList outputs) {
+  WebKit::WebMIDIAccessorClient* client = GetClientFromId(client_id);
+  if (!client)
+    return;
+
+  if (success) {
+    // Add the client's input and output ports.
+    for (size_t i = 0; i < inputs.size(); ++i) {
+      client->didAddInputPort(
+          UTF8ToUTF16(inputs[i].id),
+          UTF8ToUTF16(inputs[i].manufacturer),
+          UTF8ToUTF16(inputs[i].name),
+          UTF8ToUTF16(inputs[i].version));
+    }
+
+    for (size_t i = 0; i < outputs.size(); ++i) {
+      client->didAddOutputPort(
+          UTF8ToUTF16(outputs[i].id),
+          UTF8ToUTF16(outputs[i].manufacturer),
+          UTF8ToUTF16(outputs[i].name),
+          UTF8ToUTF16(outputs[i].version));
+    }
+  }
+
+  if (success)
+    client->didAllowAccess();
+  else
+    client->didBlockAccess();
+}
+
+WebKit::WebMIDIAccessorClient*
+MIDIMessageFilter::GetClientFromId(int client_id) {
+  // Iterating like this seems inefficient, but in practice there generally
+  // will be very few clients (usually one).  Additionally, this lookup
+  // usually happens one time during page load. So the performance hit is
+  // negligible.
+  for (ClientsMap::iterator i = clients_.begin(); i != clients_.end(); ++i) {
+    if ((*i).second == client_id)
+      return (*i).first;
+  }
+  return NULL;
+}
+
+void MIDIMessageFilter::OnDataReceived(int port,
+                                       const std::vector<uint8>& data,
+                                       double timestamp) {
+  TRACE_EVENT0("midi", "MIDIMessageFilter::OnDataReceived");
+
+  if (client_message_loop_) {
+    client_message_loop_->PostTask(FROM_HERE,
+        base::Bind(&MIDIMessageFilter::HandleDataReceived, this,
+                   port, data, timestamp));
+  }
+}
+
+void MIDIMessageFilter::HandleDataReceived(int port,
+                                           const std::vector<uint8>& data,
+                                           double timestamp) {
+  TRACE_EVENT0("midi", "MIDIMessageFilter::HandleDataReceived");
+
+  for (ClientsMap::iterator i = clients_.begin(); i != clients_.end(); ++i)
+    (*i).first->didReceiveMIDIData(port, data.data(), data.size(), timestamp);
+}
+
+void MIDIMessageFilter::SendMIDIData(int port,
+                                     const uint8* data,
+                                     size_t length,
+                                     double timestamp) {
+  // TODO(crogers): we need more work to check the amount of data sent,
+  // throttle if necessary, and filter out the SYSEX messages if not
+  // approved. For now, we will not implement the sending of MIDI data.
+  NOTIMPLEMENTED();
+  // std::vector<uint8> v(data, data + length);
+  // io_message_loop_->PostTask(FROM_HERE,
+  //     base::Bind(&MIDIMessageFilter::SendMIDIDataOnIOThread, this,
+  //                port, v, timestamp));
+}
+
+void MIDIMessageFilter::SendMIDIDataOnIOThread(int port,
+                                               const std::vector<uint8>& data,
+                                               double timestamp) {
+  // Send to the browser.
+  Send(new MIDIHostMsg_SendData(port, data, timestamp));
+}
+
+}  // namespace content