Issue 3251 - Simplify messaging from child scripts to parent

lib/utils.js

Index: lib/utils.js
===================================================================
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -524,16 +524,54 @@ let Utils = exports.Utils =
       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
  */