Issue 4580 - Stop using ext.onMessage in background page

lib/messaging.js

Index: lib/messaging.js
===================================================================
--- a/lib/messaging.js
+++ b/lib/messaging.js
@@ -17,56 +17,48 @@
 
 /** @module messaging */
 
 "use strict";
 
 const {EventEmitter} = require("events");
 
 /**
- * Communication port wrapping ext.onMessage to receive messages.
+ * Communication port wrapping runtime.onMessage to receive messages.
  *
  * @constructor
  */
 function Port()
 {
   this._eventEmitter = new EventEmitter();
   this._onMessage = this._onMessage.bind(this);
-  ext.onMessage.addListener(this._onMessage);
+  browser.runtime.onMessage.addListener(this._onMessage);
 }
 
 Port.prototype = {
-  _onMessage(message, sender, sendResponse)
+  _onMessage(message, sender)
   {
-    let async = false;
-    let callbacks = this._eventEmitter.listeners(message.type);
-
-    for (let callback of callbacks)
+    // Add "page" and "frame" if the message was sent by a content script.

[Manish Jethani, 2018/03/22 19:56:55]

This used to be in ext/background.js

+    // If sent by popup or the background page itself, there is no "tab".
+    if ("tab" in sender)
     {
-      let response = callback(message, sender);
-
-      if (response && typeof response.then == "function")
-      {
-        response.then(
-          sendResponse,
-          reason =>
-          {
-            console.error(reason);
-            sendResponse(undefined);
-          }
-        );
-        async = true;
-      }
-      else if (typeof response != "undefined")
-      {
-        sendResponse(response);
-      }
+      sender = {
+        page: new ext.Page(sender.tab),
+        frame: new ext.Frame(sender.tab.id, sender.frameId, sender.url)
+      };
     }
 
-    return async;
+    // The message sender receives only the first response.

[Manish Jethani, 2018/03/22 19:56:55]

Note: using Promise.race here to resolve with first resolved value, which is
equivalent to what was happening earlier, but we could also just use Promise.all
and return all resolved values (but this will require more changes elsewhere and
also the response might take longer).

+    // https://developer.chrome.com/apps/messaging
+    // https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/runtime/onMessage
+    return Promise.race(
+      this._eventEmitter.listeners(message.type)
+      .map(callback => callback(message, sender))
+      .filter(response => typeof response != "undefined")
+    );
   },
 
   /**
    * Function to be called when a particular message is received.
    *
    * @callback Port~messageCallback
    * @param {object} message
    * @param {object} sender
@@ -98,17 +90,17 @@
     this._eventEmitter.off(name, callback);
   },
 
   /**
    * Disables the port and makes it stop listening to incoming messages.
    */
   disconnect()
   {
-    ext.onMessage.removeListener(this._onMessage);
+    brower.runtime.onMessage.removeListener(this._onMessage);
   }
 };
 
 /**
  * The default port to receive messages.
  *
  * @type {Port}
  */