fix: sendMessage promise should resolve to undefined when no listeners reply

src/browser-polyfill.js

@@ -7,6 +7,7 @@
 "use strict";
 
 if (typeof browser === "undefined") {
+  const CHROME_SEND_MESSAGE_CALLBACK_NO_RESPONSE_MESSAGE = "The message port closed before a response was received.";
   const SEND_RESPONSE_DEPRECATION_WARNING = `
       Returning a Promise is the preferred way to send a reply from an
       onMessage/onMessageExternal listener, as the sendResponse will be
@@ -446,7 +447,14 @@ if (typeof browser === "undefined") {
 
     const wrappedSendMessageCallback = ({reject, resolve}, reply) => {
       if (chrome.runtime.lastError) {
-        reject(chrome.runtime.lastError);
+        // Detect when none of the listers replied to the sendMessage call and resolve
+        // the promise to undefined as in Firefox.
+        // See https://github.com/mozilla/webextension-polyfill/issues/130
+        if (chrome.runtime.lastError.message === CHROME_SEND_MESSAGE_CALLBACK_NO_RESPONSE_MESSAGE) {
+          resolve();
+        } else {
+          reject(chrome.runtime.lastError);
+        }
       } else if (reply && reply.__mozWebExtensionPolyfillReject__) {
         // Convert back the JSON representation of the error into
         // an Error instance.

test/fixtures/runtime-messaging-extension/background.js

@@ -45,6 +45,9 @@ browser.runtime.onMessage.addListener((msg, sender, sendResponse) => {
     case "test - sendMessage with listener callback throws":
       throw new Error("listener throws");
 
+    case "test - sendMessage and no listener answers":
+      return undefined;
+
     default:
       return Promise.resolve(
         `Unxpected message received by the background page: ${JSON.stringify(msg)}\n`);
@@ -52,6 +55,10 @@ browser.runtime.onMessage.addListener((msg, sender, sendResponse) => {
 });
 
 browser.runtime.onMessage.addListener((msg, sender, sendResponse) => {
+  if (msg === "test - sendMessage and no listener answers") {
+    return undefined;
+  }
+
   setTimeout(() => {
     sendResponse("second listener reply");
   }, 100);

test/fixtures/runtime-messaging-extension/content.js

@@ -75,3 +75,8 @@ test("sendMessage with listener callback throws", async (t) => {
     t.equal(err.message, "listener throws", "Got an error with the expected message");
   }
 });
+
+test("sendMessage and no listener answers", async (t) => {
+  const reply = await browser.runtime.sendMessage("test - sendMessage and no listener answers");
+  t.equal(reply, undefined, "Got undefined reply as expected");
+});

test/test-runtime-onMessage.js

@@ -238,5 +238,30 @@ describe("browser-polyfill", () => {
         });
       });
     });
+
+    it("resolves to undefined when no listeners reply", () => {
+      const fakeChrome = {
+        runtime: {
+          // This error message is defined as CHROME_SEND_MESSAGE_CALLBACK_NO_RESPONSE_MESSAGE
+          // in the polyfill sources and it is used to recognize when Chrome has detected that
+          // none of the listeners replied.
+          lastError: {
+            message: "The message port closed before a response was received.",
+          },
+          sendMessage: sinon.stub(),
+        },
+      };
+
+      fakeChrome.runtime.sendMessage.onFirstCall().callsArgWith(1, [undefined]);
+
+      return setupTestDOMWindow(fakeChrome).then(window => {
+        const promise = window.browser.runtime.sendMessage("some_message");
+        ok(fakeChrome.runtime.sendMessage.calledOnce, "sendMessage has been called once");
+
+        return promise.then(reply => {
+          deepEqual(reply, undefined, "sendMessage promise should be resolved to undefined");
+        });
+      });
+    });
   });
 });