Issue 3823 - Split up message responder code

lib/messaging.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 /** @module messaging */
 
 "use strict";
 
 /**
  * Communication port wrapping ext.onMessage to receive messages.
  *
  * @constructor
  */
 function Port()
 {
   this._callbacks = Object.create(null);
-  ext.onMessage.addListener(this._onMessage.bind(this));

[kzar, 2016/03/18 15:22:10]

I guess this could be a memory leak, if the port is deleted the onMessage
listener remains?

[Sebastian Noack, 2016/03/18 15:26:22]

Who cares? This class is used as a singleton.

[kzar, 2016/03/18 15:52:40]

Acknowledged.

+  this._onMessage = this._onMessage.bind(this);
+  ext.onMessage.addListener(this._onMessage);
 };
 
 Port.prototype = {
   _onMessage: function(message, sender, sendResponse)
   {
     let async = false;
-    let callbacks = this._callbacks[message.type] || [];
+    let callbacks = this._callbacks[message.type];
 
-    for (let callback of callbacks)
+    if (callbacks)
     {
-      let response = callback(message, sender);
+      for (let callback of callbacks)
+      {
+        let response = callback(message, sender);
 
-      if (response instanceof Promise)
-      {
-        response.then(
-          sendResponse,
-          reason => {
-            console.error(reason);
-            sendResponse(undefined);
-          }
-        );
-        async = true;
-      }
-      else if (typeof response != "undefined")
-      {
-        sendResponse(response);
+        if (response && typeof response.then == "function")
+        {
+          response.then(
+            sendResponse,
+            reason => {
+              console.error(reason);
+              sendResponse(undefined);
+            }
+          );
+          async = true;
+        }
+        else if (typeof response != "undefined")
+        {
+          sendResponse(response);
+        }
       }
     }
 
     return async;
   },
 
   /**
    * Function to be called when a particular message is received.
    *
    * @callback Port~messageCallback
@@ skipping 27 matching lines @@
    */
   off: function(name, callback)
   {
     let callbacks = this._callbacks[name];
     if (callbacks)
     {
       let idx = callbacks.indexOf(callback);
       if (idx != -1)
         callbacks.splice(idx, 1);
     }
+  },
+
+  /**
+   * Disables the port and makes it stop listening to incoming messages.
+   */
+  disconnect: function()
+  {
+    ext.onMessage.removeListener(this._onMessage);
   }
 };
 
 /**
  * The default port to receive messages.
  *
  * @type {Port}
  */
 exports.port = new Port();
+
+/**
+ * Creates a new port that is disconnected when the given window is unloaded.
+ *
+ * @param {Window} window
+ * @return {Port}
+ */
+exports.getPort = function(window)
+{
+  let port = new Port();
+  window.addEventListener("unload", () =>
+  {
+    port.disconnect();
+  });
+  return port;
+};
+