HTML MessagePort as mojo::MessagePipeHandle

content/common/message_port.cc

+// Copyright 2017 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/common/message_port.h"
+
+#include "base/logging.h"
+
+namespace content {
+
+MessagePort::~MessagePort() {
+}
+
+MessagePort::MessagePort() : state_(new State()) {
+}
+
+MessagePort::MessagePort(const MessagePort& other) : state_(other.state_) {
+}
+
+MessagePort& MessagePort::operator=(const MessagePort& other) {
+  state_ = other.state_;
+  return *this;
+}
+
+MessagePort::MessagePort(mojo::ScopedMessagePipeHandle handle)
+    : state_(new State(std::move(handle))) {
+}
+
+const mojo::ScopedMessagePipeHandle& MessagePort::GetHandle() const {
+  return state_->handle_;
+}
+
+mojo::ScopedMessagePipeHandle MessagePort::ReleaseHandle() const {
+  state_->CancelWatch();
+  return std::move(state_->handle_);
+}
+
+// static
+std::vector<mojo::ScopedMessagePipeHandle> MessagePort::ReleaseHandles(
+    const std::vector<MessagePort>& ports) {
+  std::vector<mojo::ScopedMessagePipeHandle> handles(ports.size());
+  for (size_t i = 0; i < ports.size(); ++i)
+    handles[i] = ports[i].ReleaseHandle();
+  return handles;
+}
+
+void MessagePort::PostMessage(const base::string16& encoded_message,
+                              std::vector<MessagePort> ports) {
+  DCHECK(state_->handle_.is_valid());
+
+  uint32_t num_bytes = encoded_message.size() * sizeof(base::char16);
+
+  // NOTE: It is OK to ignore the return value of MojoWriteMessage here. HTML
+  // MessagePorts have no way of reporting when the peer is gone.

[sgurun-gerrit only, 2017/02/08 21:47:50]

I wonder, if we it make sense to add this capability in future for WebView, so
that apps get to know when their peer is gone?
Just loudly thinking.

[darin (slow to review), 2017/02/09 00:13:17]

Yeah, I think it could be quite valuable. Mojo has the ability to tell you when
the peer is gone. Sadly, that is not part of the HTML5 MessagePort API because
folks didn't want web developers to be able to observe GC behavior.

+
+  if (ports.empty()) {
+    MojoWriteMessage(state_->handle_.get().value(),
+                     encoded_message.data(),
+                     num_bytes,
+                     nullptr,
+                     0,
+                     MOJO_WRITE_MESSAGE_FLAG_NONE);
+  } else {
+    uint32_t num_handles = static_cast<uint32_t>(ports.size());
+    std::unique_ptr<MojoHandle[]> handles(new MojoHandle[num_handles]);
+    for (uint32_t i = 0; i < num_handles; ++i)
+      handles[i] = ports[i].ReleaseHandle().release().value();
+    MojoWriteMessage(state_->handle_.get().value(),
+                     encoded_message.data(),
+                     num_bytes,
+                     handles.get(),
+                     num_handles,
+                     MOJO_WRITE_MESSAGE_FLAG_NONE);
+  }
+}
+
+bool MessagePort::GetMessage(base::string16* encoded_message,
+                             std::vector<MessagePort>* ports) {
+  DCHECK(state_->handle_.is_valid());
+
+  uint32_t num_bytes = 0;
+  uint32_t num_handles = 0;
+
+  MojoResult rv = MojoReadMessage(state_->handle_.get().value(),
+                                  nullptr,
+                                  &num_bytes,
+                                  nullptr,
+                                  &num_handles,
+                                  MOJO_READ_MESSAGE_FLAG_NONE);
+  if (rv == MOJO_RESULT_OK) {
+    encoded_message->clear();
+    ports->clear();
+    return true;
+  }
+  if (rv != MOJO_RESULT_RESOURCE_EXHAUSTED)
+    return false;
+
+  CHECK(num_bytes % 2 == 0);
+
+  base::string16 buffer;
+  buffer.resize(num_bytes / sizeof(base::char16));
+
+  std::unique_ptr<MojoHandle[]> handles;
+  if (num_handles)
+    handles.reset(new MojoHandle[num_handles]);
+
+  rv = MojoReadMessage(state_->handle_.get().value(),
+                       num_bytes ? &buffer[0] : nullptr,
+                       &num_bytes,
+                       handles.get(),
+                       &num_handles,
+                       MOJO_READ_MESSAGE_FLAG_NONE);
+  if (rv != MOJO_RESULT_OK)
+    return false;
+
+  buffer.swap(*encoded_message);
+
+  if (num_handles) {
+    ports->resize(static_cast<size_t>(num_handles));
+    for (uint32_t i = 0; i < num_handles; ++i) {
+      ports->at(i) = MessagePort(
+          mojo::ScopedMessagePipeHandle(mojo::MessagePipeHandle(handles[i])));
+    }
+  }
+  return true;
+}
+
+void MessagePort::SetCallback(const base::Closure& callback) {
+  state_->CancelWatch();
+  state_->callback_ = callback;
+  state_->AddWatch();
+}
+
+void MessagePort::ClearCallback() {
+  state_->CancelWatch();
+  state_->callback_.Reset();
+}
+
+MessagePort::State::State() {
+}
+
+MessagePort::State::State(mojo::ScopedMessagePipeHandle handle)
+    : handle_(std::move(handle)) {
+}
+
+void MessagePort::State::AddWatch() {
+  if (!callback_)
+    return;
+
+  // NOTE: An HTML MessagePort does not receive an event to tell it when the
+  // peer has gone away, so we only watch for readability here.
+  MojoResult rv = MojoWatch(handle_.get().value(),
+                            MOJO_HANDLE_SIGNAL_READABLE,
+                            &MessagePort::State::OnHandleReady,
+                            reinterpret_cast<uintptr_t>(this));
+  if (rv != MOJO_RESULT_OK)
+    DVLOG(1) << this << " MojoWatch failed: " << rv;
+}
+
+void MessagePort::State::CancelWatch() {
+  if (!callback_)
+    return;
+
+  // NOTE: This synchronizes with the thread where OnHandleReady runs so we are
+  // sure to not be racing with it.
+  MojoCancelWatch(handle_.get().value(), reinterpret_cast<uintptr_t>(this));
+}
+
+// static
+void MessagePort::State::OnHandleReady(
+    uintptr_t context,
+    MojoResult result,
+    MojoHandleSignalsState signals_state,
+    MojoWatchNotificationFlags flags) {
+  if (result == MOJO_RESULT_OK) {
+    reinterpret_cast<MessagePort::State*>(context)->callback_.Run();
+  } else {
+    // And now his watch is ended.
+  }
+}
+
+MessagePort::State::~State() {
+  CancelWatch();
+}
+
+}  // namespace content