Issue 3251 - Simplify messaging from child scripts to parent

lib/utils.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 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
@@ skipping 511 matching lines @@
       if (label != origLabel)
         element.setAttribute(attr, label);
       if (accesskey != "")
         element.setAttribute("accesskey", accesskey);
 
       // Labels forward changes of the accessKey property to their control, only
       // set it for actual controls.
       if (element.localName != "label")
         element.accessKey = accesskey;
     }
+  },
+
+  /**
+   * Adds a message handler that will respond to both synchronous and
+   * asynchonous messages.
+   * @param {string} messageName  name of the message to listen to
+   * @param {Function} handler  handler to be called with the message data. The
+   *                            return value will be sent back to the child.
+   */
+  addChildMessageListener: function(messageName, handler)
+  {
+    let messageManager = Cc["@mozilla.org/parentprocessmessagemanager;1"]
+                           .getService(Ci.nsIMessageListenerManager);
+    let wrapper = (message) => {
+      let {callbackID, data} = message.data;
+      let response = undefined;
+      try
+      {
+        response = handler(data);
+      }
+      catch (e)
+      {
+        Cu.reportError(e);
+      }
+
+      if (callbackID)
+      {
+        let target = message.target.QueryInterface(Ci.nsIMessageSender);
+        target.sendAsyncMessage("AdblockPlus:Response", {
+          callbackID,
+          response
+        });
+      }
+      else
+        return JSON.stringify(response);
+    };
+    messageManager.addMessageListener(messageName, wrapper);
+    onShutdown.add(() => messageManager.removeMessageListener(messageName, wrapper));
   }
 };
 
 /**
  * A cache with a fixed capacity, newer entries replace entries that have been
  * stored first.
  * @constructor
  */
 function Cache(/**Integer*/ size)
 {
@@ skipping 240 matching lines @@
     Cu.reportError(e);
     // Expected, ctypes isn't supported in Gecko 1.9.2
     return null;
   }
 });
 
 if ("@mozilla.org/messenger/headerparser;1" in Cc)
   XPCOMUtils.defineLazyServiceGetter(Utils, "headerParser", "@mozilla.org/messenger/headerparser;1", "nsIMsgHeaderParser");
 else
   Utils.headerParser = null;