Hangouts remote desktop part III - It2MeService

remoting/webapp/background/it2me_service.js

+// Copyright 2014 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
+ * It2MeService listens to incoming connections requests from Hangouts
+ * and the webapp and creates a It2MeHelperChannel between them.
+ * It supports multiple concurrent helper sessions.

[Jamie, 2014/08/13 01:44:53]

Add ", but only a single helpee."

+ */
+
+'use strict';
+
+/** @suppress {duplicate} */
+var remoting = remoting || {};
+
+/**
+ * @param {remoting.AppLauncher} appLauncher
+ * @constructor
+ */
+remoting.It2MeService = function(appLauncher) {
+  /**
+   * @type {remoting.AppLauncher}
+   * @private
+   */
+  this.appLauncher_ = appLauncher;
+
+  /**
+   * @type {Array.<remoting.It2MeHelperChannel>}
+   * @private
+   */
+  this.helpers_ = [];
+
+  /** @private */

[Jamie, 2014/08/13 01:44:53]

Type?

[kelvinp, 2014/08/13 23:44:10]

Will be filled on the next CL

+  this.helpee_ = null;
+
+  this.onWebappConnectRef_ = this.onWebappConnect_.bind(this);
+  this.onMessageExternalRef_ = this.onMessageExternal_.bind(this);
+  this.onConnectExternalRef_ = this.onConnectExternal_.bind(this);
+};
+
+/** @enum {string} */
+remoting.It2MeService.ConnectionTypes = {

[kelvinp, 2014/08/13 00:08:48]

These names are not global.  They only needs to be unique within our extension.

[Jamie, 2014/08/13 01:44:53]

Acknowledged.

+  HELPER_HANGOUT: 'it2me.helper.hangout',
+  HELPEE_HANGOUT: 'it2me.helpee.hangout',
+  HELPER_WEBAPP: 'it2me.helper.webapp'
+};
+
+/**
+ * Starts listening to external connection from Hangouts and the webapp.
+ */
+remoting.It2MeService.prototype.init = function() {
+  chrome.runtime.onConnect.addListener(this.onWebappConnectRef_);
+  chrome.runtime.onMessageExternal.addListener(this.onMessageExternalRef_);
+  chrome.runtime.onConnectExternal.addListener(this.onConnectExternalRef_);
+};
+
+remoting.It2MeService.prototype.dispose = function() {
+  chrome.runtime.onConnect.removeListener(this.onWebappConnectRef_);
+  chrome.runtime.onMessageExternal.removeListener(
+      this.onMessageExternalRef_);
+  chrome.runtime.onConnectExternal.removeListener(
+      this.onConnectExternalRef_);
+};
+
+/**
+ * This function is called when a runtime message is received from an external
+ * web page (hangout) or extension.
+ *
+ * @param {{method:string, data:Object.<string,*>}} message
+ * @param {chrome.runtime.MessageSender} sender
+ * @param {Function} sendResponse

[Jamie, 2014/08/13 01:44:53]

s/Function/function/

Ideally, it should have a prototype as well, but looking at the code, it would
be difficult to express in JSDoc.

[kelvinp, 2014/08/13 23:44:10]

Acknowledged.

+ */
+remoting.It2MeService.prototype.onMessageExternal_ =
+    function(message, sender, sendResponse) {
+  try {
+    var method = message.method;
+    var isHandled = false;

[Jamie, 2014/08/13 01:44:53]

You're not using this.

[kelvinp, 2014/08/13 23:44:10]

Done.

+
+    if (method == 'hello') {
+      // The hello message is used by hangouts to detect whether the app is
+      // installed and what features are supported.
+      sendResponse({
+        method: 'helloResponse',
+        supportedFeatures: ['it2me']
+      });
+      return true;
+    }
+    throw new Error('Unknown method: ' + method);
+  } catch (e) {
+    var error = /** @type {Error} */ e;

[Jamie, 2014/08/13 01:44:53]

I think you should log this error.

+    sendResponse({
+      method: message.method + 'Response',

[Jamie, 2014/08/13 01:44:53]

Does the API guarantee that message is an object? If not, then your catch block
is going to throw if it isn't.

[kelvinp, 2014/08/13 23:44:10]

Yes, the messaging API requires the message object to not be null. 

+      error: error.message

[Jamie, 2014/08/13 01:44:53]

Are you guaranteed that error will be an object with a message field? What if
sendResponse throws?

[kelvinp, 2014/08/13 23:44:10]

Errors thrown by sendResponse will still have a message field. 

+    });
+  }

[Jamie, 2014/08/13 01:44:53]

return false

[kelvinp, 2014/08/13 23:44:10]

Done.

+};
+
+/**
+ * This function is called when Hangouts connects via chrome.runtime.connect.
+ * Only web pages that are white-listed in the manifest are allowed to connect.
+ *
+ * @param {chrome.runtime.Port} port
+ */
+remoting.It2MeService.prototype.onConnectExternal_ = function(port) {
+  var ConnectionTypes = remoting.It2MeService.ConnectionTypes;
+  try {
+    switch (port.name) {

[kelvinp, 2014/08/13 00:08:48]

Only are web-pages that are white-listed in the manifest can connect to us using
connectExternal.  It is hard to spoof.

[Jamie, 2014/08/13 01:44:53]

Acknowledged.

+      case ConnectionTypes.HELPER_HANGOUT:
+        this.handleExternalHelperConnection_(port);
+        return true;
+      default:
+        throw new Error('Unsupported port - ' + port.name);
+    }
+  } catch (e) {
+    port.disconnect();

[Jamie, 2014/08/13 01:44:53]

Log the error?

[kelvinp, 2014/08/13 23:44:10]

Done.

+  }

[Jamie, 2014/08/13 01:44:53]

return false

[kelvinp, 2014/08/13 23:44:10]

Done.

+};
+
+/**
+ * @param {chrome.runtime.Port} port
+ */
+remoting.It2MeService.prototype.onWebappConnect_ = function(port) {
+  try {
+    console.log('Incoming helper connection from webapp.');
+
+    // The senderId (tabId or windowId) of the webapp is embedded in the port
+    // name with the format port_name@senderId.
+    var parts = port.name.split('@');
+    var portName = parts[0];
+    var senderId = parts[1];
+    var ConnectionTypes = remoting.It2MeService.ConnectionTypes;
+    if (portName === ConnectionTypes.HELPER_WEBAPP && senderId !== undefined) {
+      for (var i = 0; i < this.helpers_.length; i++) {
+        var helper = this.helpers_[i];
+        if (helper.instanceId() === senderId) {
+          helper.onWebappConnect(port, senderId);
+          return;
+        }
+      }
+    }
+    throw new Error('No matching hangout connection found for ' + port.name);
+  } catch (e) {
+    var error = /** @type {Error} */ e;
+    console.error(error);
+    port.disconnect();
+  }
+};
+
+/**
+ * @param {remoting.It2MeHelperChannel} helper
+ */
+remoting.It2MeService.prototype.onHelperChannelDisconnected = function(helper) {
+  for (var i = 0; i < this.helpers_.length; i++) {
+    if (helper === this.helpers_[i]) {
+      this.helpers_.splice(i, 1);
+    }
+  }
+};
+
+/**
+ * @param {chrome.runtime.Port} port
+ */
+remoting.It2MeService.prototype.handleExternalHelperConnection_ =
+    function(port) {
+  if (this.helpee_) {
+    console.error(
+        'Cannot start a helper session while a helpee session is in process.');

[kelvinp, 2014/08/13 00:08:48]

Not sure what do you mean by making this error prominent.  In theory the hangout
code should safe guard against this scenario.

[Jamie, 2014/08/13 01:44:53]

I think I meant it should be surfaced in the UI somewhere. If you're confident
it can't happen, optionally consider using an assert instead.

[kelvinp, 2014/08/13 23:44:10]

Since this is called by external code, I think it is wrong to do assert as the
caller can call it with invalid input.  I will follow up with Dan and see if I
need to post a message to Hangouts if that happens.

+    port.disconnect();
+  }
+
+  console.log('Incoming helper connection from Hangouts');
+  var helper = new remoting.It2MeHelperChannel(
+      this.appLauncher_, port, this.onHelperChannelDisconnected.bind(this));
+  helper.init();
+  this.helpers_.push(helper);
+};