Issue 4579 - Ignore runtime.lastError caused by wrapper

polyfill.js

Index: polyfill.js
===================================================================
--- a/polyfill.js
+++ b/polyfill.js
@@ -38,16 +38,42 @@
     "tabs.sendMessage",
     "tabs.update",
     "webNavigation.getAllFrames",
     "webRequest.handlerBehaviorChanged",
     "windows.create",
     "windows.update"
   ];
 
+  // Errors that occur only when we show an interest in the response from an
+  // API call.
+  const noFulfillmentErrors = [
+    "The message port closed before a response was received."
+  ];
+
+  const fulfillmentInterestFlag = Symbol();

[Manish Jethani, 2017/10/19 01:59:46]

We use a symbol here so it becomes like a private property.

+
+  function SpecialPromise(...args)
+  {
+    return Reflect.construct(Promise, args, SpecialPromise);

[Manish Jethani, 2017/10/19 01:59:46]

Essentially an extended promise.

+  }
+
+  SpecialPromise.prototype = Object.create(
+    Object.assign({}, Promise.prototype, {
+      then(...args)
+      {
+        // Set this flag to indicate that there is interest in the fulfillment
+        // of this promise.
+        this[fulfillmentInterestFlag] = true;
+
+        return Promise.prototype.then.apply(this, args);
+      }
+    })
+  );
+
   function wrapAPI(api)
   {
     let object = browser;
     let path = api.split(".");
     let name = path.pop();
 
     for (let node of path)
     {
@@ -66,27 +92,42 @@
       // If the last argument is undefined, we drop it from the list assuming
       // it stands for the optional callback. We must do this, because we have
       // to replace it with our own callback. If we simply append our own
       // callback to the list, it won't match the signature of the function and
       // will cause an exception.
       if (typeof args[args.length - 1] == "undefined")
         args.pop();
 
-      return new Promise((resolve, reject) =>
+      let promise = new SpecialPromise((resolve, reject) =>
       {
         func.call(object, ...args, result =>
         {
           let error = browser.runtime.lastError;
           if (error)
+          {
+            // If is this an error we got only because we passed in a callback
+            // and there's no actual interest in the response, ignore the
+            // error.
+            if (noFulfillmentErrors.includes(error.message) &&
+                !promise[fulfillmentInterestFlag])
+            {
+              return;
+            }
+
             reject(error);
+          }
           else
+          {
             resolve(result);
+          }
         });
       });
+
+      return promise;
     };
   }
 
   function shouldWrapAPIs()
   {
     try
     {
       return !(browser.storage.local.get([]) instanceof Promise);