Move hello message from It2MeService to It2MeChannel

remoting/webapp/background/it2me_helper_channel.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
  *
  * It2MeHelperChannel relays messages between Hangouts and Chrome Remote Desktop
  * (webapp) for the helper (the Hangouts participant who is giving remote
  * assistance).
  *
  * It runs in the background page and contains two chrome.runtime.Port objects,
- * respresenting connections to the webapp and hangout, respectively.
+ * representing connections to the webapp and hangout, respectively.
  *
- * Connection is always initiated from Hangouts.
+ * Connection is always initiated from Hangouts by calling
+ *   var port = chrome.runtime.connect({name:'it2me.helper.hangout'}, extId).
+ *   port.postMessage('hello')
+ * If the webapp is not installed, |port.onDisconnect| will fire.
+ * If the webapp is installed, Hangouts will receive a hello response with the
+ * list of supported features.
  *
  *   Hangout                     It2MeHelperChannel        Chrome Remote Desktop
  *      |-----runtime.connect() ------>|                                |
- *      |------connect message-------->|                                |
+ *      |--------hello message-------->|                                |
+ *      |                              |<-----helloResponse message-----|
+ *      |-------connect message------->|                                |
  *      |                              |-------appLauncher.launch()---->|
  *      |                              |<------runtime.connect()------- |
  *      |                              |<-----sessionStateChanged------ |
  *      |<----sessionStateChanged------|                                |
  *
  * Disconnection can be initiated from either side:
  * 1. In the normal flow initiated from hangout
  *    Hangout                    It2MeHelperChannel        Chrome Remote Desktop
  *       |-----disconnect message------>|                               |
  *       |<-sessionStateChanged(CLOSED)-|                               |
@@ skipping 73 matching lines @@
 
   this.onWebappMessageRef_ = this.onWebappMessage_.bind(this);
   this.onWebappDisconnectRef_ = this.onWebappDisconnect_.bind(this);
   this.onHangoutMessageRef_ = this.onHangoutMessage_.bind(this);
   this.onHangoutDisconnectRef_ = this.onHangoutDisconnect_.bind(this);
 };
 
 /** @enum {string} */
 remoting.It2MeHelperChannel.HangoutMessageTypes = {
   CONNECT: 'connect',
-  DISCONNECT: 'disconnect'
+  DISCONNECT: 'disconnect',
+  HELLO: 'hello'
 };
 
 /** @enum {string} */
 remoting.It2MeHelperChannel.WebappMessageTypes = {
   SESSION_STATE_CHANGED: 'sessionStateChanged'
 };
 
 remoting.It2MeHelperChannel.prototype.init = function() {
   this.hangoutPort_.onMessage.addListener(this.onHangoutMessageRef_);
   this.hangoutPort_.onDisconnect.addListener(this.onHangoutDisconnectRef_);
@@ skipping 12 matching lines @@
 remoting.It2MeHelperChannel.prototype.onHangoutMessage_ = function(message) {
   try {
     var MessageTypes = remoting.It2MeHelperChannel.HangoutMessageTypes;
     switch (message.method) {
       case MessageTypes.CONNECT:
         this.launchWebapp_(message);
         return true;
       case MessageTypes.DISCONNECT:
         this.closeWebapp_(message);
         return true;
+      case MessageTypes.HELLO:
+        this.hangoutPort_.postMessage({
+          method: message.method + 'Response',

[Jamie, 2014/08/15 19:11:46]

I think that helloResponse would be better declared explicitly in the
HangoutMessageTypes enum. That way, the enum documents all the messages that can
be sent, including replies.

[kelvinp, 2014/08/15 21:28:32]

Done.

+          supportedFeatures:
+              base.values(remoting.It2MeHelperChannel.HangoutMessageTypes)

[Jamie, 2014/08/15 19:11:46]

I don't think that requiring a 1-1 mapping of features to messages is the right
approach. Better to have a separate HangoutFeatures enum. For example, it's not
really necessary to advertise that we support the "hello" feature, since that's
the mechanism by which features are advertised. Similarly, "connect" and
"disconnect" are really separate messages offered by the same feature, which
might be called something like "RemoteAssistance". Or you could take the view
that they're fundamental to the operation of the extension and so don't need to
be advertised (you could call the enum HangoutOptionalFeatures to make it clear
that it's used to future-proofing against features we might add later on).

[kelvinp, 2014/08/15 21:28:32]

Done.

+        });
+        return true;
     }
   } catch(e) {
     var error = /** @type {Error} */ e;
     console.error(error);
     this.hangoutPort_.postMessage({
       method: message.method + 'Response',
       error: error.message
     });
   }
   return false;
@@ skipping 125 matching lines @@
     this.hangoutPort_.onDisconnect.removeListener(this.onHangoutDisconnectRef_);
     this.hangoutPort_.disconnect();
     this.hangoutPort_ = null;
   }
 
   if (this.onDisconnectCallback_) {
     this.onDisconnectCallback_(this);
     this.onDisconnectCallback_  = null;
   }
 };