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_proxy.h"
+#include "base/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 {
+
+int MIDIMessageFilter::next_available_id_ = 0;
+
+MIDIMessageFilter::MIDIMessageFilter(
+    const scoped_refptr<base::MessageLoopProxy>& io_message_loop)
+    : channel_(NULL),
+      io_message_loop_(io_message_loop) {
+}
+
+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) {
+  AutoLock auto_lock(clients_lock_);
+
+  // Get the main thread message loop.
+  if (!client_message_loop_)
+    client_message_loop_ = base::MessageLoopProxy::current();
+  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;
+    Send(new MIDIHostMsg_RequestAccess(client_id, access));

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

Which thread is this running on? The doc in the header suggests that
client_message_loop_ is the main thread, but Send expects this to be called on
the IO thread.

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

Yes, good point. Fixed.

+  }
+};
+
+void MIDIMessageFilter::RemoveClient(WebKit::WebMIDIAccessorClient* client) {
+  AutoLock auto_lock(clients_lock_);
+  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) {
+  AutoLock auto_lock(clients_lock_);
+
+  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->addInputPort(
+          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->addOutputPort(
+          UTF8ToUTF16(outputs[i].id),
+          UTF8ToUTF16(outputs[i].manufacturer),
+          UTF8ToUTF16(outputs[i].name),
+          UTF8ToUTF16(outputs[i].version));
+    }
+  }
+
+  client->accessApproved(success);
+}
+
+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");
+
+  AutoLock auto_lock(clients_lock_);
+  for (ClientsMap::iterator i = clients_.begin(); i != clients_.end(); ++i)
+    (*i).first->receiveMIDIData(port, data.data(), data.size(), timestamp);
+}
+
+void MIDIMessageFilter::SendMIDIData(int port_index,
+                                     const uint8* data,
+                                     size_t length,
+                                     double timestamp) {
+  // Send to the browser.
+  std::vector<uint8> v(data, data + length);

[palmer, 2013/06/19 21:39:15]

Same copying-due-to-interface issue here. Perhaps it's necessary; just checking.

[Chris Rogers, 2013/06/20 17:41:33]

Yeah, I think at some point we have to take the hit to convert into a vector<>,
since this data originates from Blink, and we can't use std::vector<> in the
public Blink API boundary...

+  Send(new MIDIHostMsg_SendData(port_index, v, timestamp));

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

Is this called on the client thread or IO thread?

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

In this CL I have the code initially written to PostTask to
SendMIDIDataOnIOThread(), but I'm blocking allowing this code to actually
execute until a follow-up CL. 

+}
+
+}  // namespace content