fuchsia/runners/cast/cast_channel_bindings.js

// Copyright 2019 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.

// Implementation of the cast.__platform__.channel API which uses MessagePort
// IPC to communicate with an actual Cast Channel implementation provided by
// the content embedder. There is at most one channel which may be opened (able
// to send & receive messages) or closed.
cast.__platform__.channel = new class {
  constructor() {
    this.master_port_ = cast.__platform__.connector.bind(
        'cast.__platform__.channel',
        function(ignored) {
          // |master_port_| is send-only, so ignore all incoming messages.
        });
  }

  // Signals to the peer that the Cast Channel is opened.
  // |openHandler|: A callback function which is invoked on channel open with
  //                a boolean indicating success.
  // |messageHandler|: Invoked when a message arrives from the peer.
  open(openHandler, messageHandler) {
    if (this.current_port_) {
      console.error('open() called on an open Cast Channel.');
      openHandler(false);
      return;
    }

    if (!messageHandler) {
      console.error('Null messageHandler passed to open().');
      openHandler(false);
      return;
    }

    // Create the MessageChannel for Cast Channel and distribute its ports.
    var channel = new MessageChannel();
    this.master_port_.sendMessage('', [channel.port1]);

    this.current_port_ = channel.port2;
    this.current_port_.onmessage = function(message) {
      messageHandler(message.data);
    };
    this.current_port_.onerror = function() {
      console.error('Cast Channel was closed unexpectedly by peer.');
      return;
    };

    openHandler(true);
  }

  // Closes the Cast Channel.
  close(closeHandler) {
    if (this.current_port_) {
      this.current_port_.close();
      this.current_port_ = null;
    }
  }

  // Sends a message to the Cast Channel's peer.
  send(message) {
    if (!this.current_port_) {
      console.error('send() called on a closed Cast Channel.');
      return;
    }

    this.current_port_.postMessage(message);
  }

  // Used to send newly opened Cast Channel ports to C++.
  master_port_ = null;

  // The current opened Cast Channel.
  current_port_ = null;
};