Add some closureised JS bindings for DevTools for use by headless embedder

headless/lib/browser/devtools_api/devtools_connection.js

+// 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.
+
+/**
+ * @fileoverview Contains a class which marshals DevTools protocol messages over
+ * a provided low level message transport. This transport might be a headless
+ * TabSocket, or a WebSocket or a mock for testing.
+ */
+
+'use strict';
+
+goog.provide('chromium.DevTools.Connection');
+
+/**
+ * @class Handles sending and receiving DevTools JSON protocol messages over the
+ *   provided low level message transport.
+ * @param {!Object} transport The API providing transport for devtools commands.
+ * @constructor
+ */
+chromium.DevTools.Connection = function(transport) {
+  /**
+   * The DevTools connection.
+   *
+   * @private {!Object}
+   */
+  this.transport_ = transport;
+
+  /**
+   * @private {number}
+   */
+  this.commandId_ = 1;
+
+  /**
+   * An object containing pending DevTools protocol commands keyed by id.
+   *
+   * @type {!Object<!function(!Object)>}
+   * @private
+   */
+  this.pendingCommands_ = {};
+
+  /**
+   * An object containing DevTools protocol events we are listening for keyed by
+   * name.
+   *
+   * @type {!Object<!Array<!function(!Object)>>}
+   * @private
+   */
+  this.eventListeners_ = {};
+
+  this.transport_.onmessage = this.onMessage_.bind(this);
+};
+
+
+/**
+ * Listens for DevTools protocol events of the specified name and issues the
+ * callback upon reception.
+ *
+ * @param {string} eventName Name of the DevTools protocol event to listen for.
+ * @param {!function(!Object)} listener The callback issued
+ *   when we receive a DevTools protocol event corresponding to the given name.
+ */
+chromium.DevTools.Connection.prototype.addEventListener = function(eventName,
+                                                               listener) {

[Sami, 2017/05/26 15:55:54]

nit: this line wrapping looks a little off (same below)

[alex clarke (OOO till 29th), 2017/05/26 19:51:11]

Done.

+  if (!this.eventListeners_.hasOwnProperty(eventName)) {
+    this.eventListeners_[eventName] = [];
+  }
+  this.eventListeners_[eventName].push(listener);
+};
+
+/**
+ * Removes an event listener previously added by <code>addEventListener</code>.
+ *
+ * @param {string} eventName Name of the DevTools protocol event to remove.
+ * @param {!function(!Object)} listener The callback to remove.
+ */
+chromium.DevTools.Connection.prototype.removeEventListener = function(eventName,
+                                                                  listener) {
+  if (!this.eventListeners_.hasOwnProperty(eventName))
+    return;
+  let index = this.eventListeners_[eventName].indexOf(listener);
+  if (index === -1)
+    return;
+  this.eventListeners_[eventName].splice(index, 1);
+};
+
+
+/**
+ * Issues a DevTools protocol command and returns a promise for the results.
+ *
+ * @param {string} method The name of the DevTools protocol command method.
+ * @param {!Object=} opt_params An object containing the command parameters if
+ *    any.
+ * @return {Promise<!Object>} A promise for the results object.
+ */
+chromium.DevTools.Connection.prototype.sendDevToolsMessage = function(method,
+                                                                  opt_params) {
+  if (opt_params === undefined) {
+    opt_params = {};
+  }
+  let id = this.commandId_;
+  // We increment by two because these bindings are intended to be used in
+  // conjunction with HeadlessDevToolsClient::RawProtocolListener and using odd
+  // numbers for js generated IDs lets the implementation of OnProtocolMessage
+  // easily distinguish between C++ and JS generated commands and route the
+  // response accordingly.
+  this.commandId_ += 2;
+  this.transport_.send(
+      JSON.stringify({'method': method, 'id': id, 'params': opt_params}));
+  return new Promise((resolve, reject) => {
+    this.pendingCommands_[id] = resolve;
+  });
+};
+
+
+/**
+ * @param {string} json_message An object containing a DevTools protocol
+ *    message.
+ * @private
+ */
+chromium.DevTools.Connection.prototype.onMessage_ = function(json_message) {
+  const message = JSON.parse(json_message);
+  if (message.hasOwnProperty('id')) {
+    if (!this.pendingCommands_.hasOwnProperty(message.id))
+      throw new Error('Unrecognized id:' + json_message);
+    this.pendingCommands_[message.id](message.result);
+    delete this.pendingCommands_[message.id];
+  } else {
+    if (!message.hasOwnProperty('method') ||
+        !message.hasOwnProperty('params')) {
+      throw new Error('Bad message:' + json_message);
+    }
+    const method = message['method'];
+    const params = message['params'];
+    if (this.eventListeners_.hasOwnProperty(method)) {
+      const listeners = this.eventListeners_[method];
+      for (let i = 0; i < listeners.length; i++) {
+        listeners[i](params);
+      }
+    }
+  }
+};