Suppress the exception thrown when responding to message with no response callback.

chrome/browser/resources/hotword_helper/manager.js

 // Copyright (c) 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 'use strict';
 
 /**
  * @fileoverview This extension manages communications between Chrome,
  * Google.com pages and the Chrome Hotword extension.
  *
@@ skipping 40 matching lines @@
 
 /**
  * @param {Tab} tab Tab to inject.
  * @param {function(HotwordStatus)} sendResponse Callback function to respond
  *     to sender.
  * @param {HotwordStatus} hotwordStatus Status of the hotword extension.
  * @private
  */
 OptInManager.prototype.injectTab_ = function(
     tab, sendResponse, hotwordStatus) {
-  if (tab.incognito || !hotwordStatus.available) {
+  try {
+    if (tab.incognito || !hotwordStatus.available) {
+      sendResponse({'doNotShowOptinMessage': true});
+      return;
+    }
+
+    if (!hotwordStatus.enabledSet) {
+      sendResponse(hotwordStatus);
+      return;
+    }
+
+    if (hotwordStatus.enabled)
+      chrome.tabs.executeScript(tab.id, {'file': 'audio_client.js'});
     sendResponse({'doNotShowOptinMessage': true});

[Dan Beam, 2014/09/23 03:35:38]

^ which of these lines actually throw?

[Anand Mistry (off Chromium), 2014/09/23 03:55:07]

In theory, any of these calls to sendResponse() could throw (hence the large try
block), but it's the last one that I've seen in practice.

-    return;
+  } catch (err) {
+    // Suppress the exception thrown when the page doesn't specify a response
+    // callback. Unfortunately, there doesn't appear to be a way to detect
+    // one-way messages without explicitly saying in the message itself.
+    // This message is defined as a constant in
+    // extensions/renderer/messaging_bindings.cc
+    if (err.message == 'Attempting to use a disconnected port object')

[Dan Beam, 2014/09/23 03:35:38]

does sendResponse() need to be invoked here?

[Anand Mistry (off Chromium), 2014/09/23 03:55:07]

No. It's the sendResponse() that threw the exception. I've clarified the comment
to say that sendResponse throws.

+      return;
+    throw err;
   }
-
-  if (!hotwordStatus.enabledSet) {
-    sendResponse(hotwordStatus);
-    return;
-  }
-
-  if (hotwordStatus.enabled)
-    chrome.tabs.executeScript(tab.id, {'file': 'audio_client.js'});
-  sendResponse({'doNotShowOptinMessage': true});
 };
 
 
 /**
  * Handles messages from the helper content script.
  * @param {*} request Message from the sender.
  * @param {MessageSender} sender Information about the sender.
  * @param {function(HotwordStatus)} sendResponse Callback function to respond
  *     to sender.
  * @return {boolean} Whether to maintain the port open to call sendResponse.
@@ skipping 120 matching lines @@
   // TODO(rlp): Possibly remove the next line. It's proably not used, but
   // leaving for now to be safe. We should remove it once all messsage
   // relaying is removed form the content scripts.
   chrome.runtime.onMessage.addListener(this.handleMessage_.bind(this));
   chrome.runtime.onMessageExternal.addListener(
       this.handleMessage_.bind(this));
 };
 
 
 new OptInManager().initialize();