Issue 2084 - Detect our content script instead checking for anonymous frames

include.preload.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 63 matching lines @@
 
 function checkSitekey()
 {
   var attr = document.documentElement.getAttribute("data-adblockkey");
   if (attr)
     ext.backgroundPage.sendMessage({type: "add-sitekey", token: attr});
 }
 
 function isFrameWithoutContentScript(element)
 {
-  var contentWindow;
+  var contentDocument;
   try
   {
-    contentWindow = element.contentWindow;

[Wladimir Palant, 2015/03/04 19:31:36]

Accessing element.contentWindow is actually allowed for third-party frames,
otherwise you wouldn't be able to call postMessage() on it for example.

You could use element.contentDocument.defaultView instead, this will also take
care of the check below (this will throw if element.contentDocument is
undefined). I would consider running into an exception here ugly however, so the
other option is keeping the contentDocument variable and merely using
contentDocument.defaultView below. Up to you.

[Sebastian Noack, 2015/03/04 20:36:13]

You are right. Also I realized that we can actually access third-party frames.
Even contentWindow.isFrameWithoutContentScript won't raise an exception, but
contentDocument does. Moreover, I realized that <object> elements only have
contentDocument, but no contentDocument anyway.

+    contentDocument = element.contentDocument;
   }
   catch (e)
   {
     // This is a third-party frame. Hence we can't access it.
     // But that's fine, our content script should already run there.
     return false;
   }
 
   // The element isn't a <frame>, <iframe> or <object> with "data" attribute.
-  if (!contentWindow)
+  if (!contentDocument)
     return false;
 
   // Return true, if the element is a first-party frame which doesn't
   // have this function, hence our content script isn't running there.
   // Those are dynamically created frames as well as frames
   // with "about:blank", "about:srcdoc" and "javascript:" URL.
-  return !("isFrameWithoutContentScript" in contentWindow);

[Wladimir Palant, 2015/03/04 19:31:36]

I wonder whether there can be any timing issues here, what if the content script
didn't load yet? I guess you tested that this works correctly?

[Sebastian Noack, 2015/03/04 20:36:13]

Yes, I tested it on a few websites of course, but timing issues aren't usually
reliably reproducible. However, we run this content script at "document_start",
but this check is performed on "load" event, so we should be safe.

For reference:
In the case of "document_start", the files are injected after any files from
css, but before any other DOM is constructed or any other script is run. 

+  return !("isFrameWithoutContentScript" in contentDocument.defaultView);
 }
 
 function reinjectRulesWhenRemoved(document, style)
 {
   var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
   if (!MutationObserver)
     return;
 
   var observer = new MutationObserver(function(mutations)
   {
@@ skipping 158 matching lines @@
   }, true);
 
   ext.backgroundPage.sendMessage({type: "get-selectors"}, setElemhideCSSRules);
 }
 
 if (document instanceof HTMLDocument)
 {
   checkSitekey();
   init(document);
 }