Issue 3687 - Add experimental support for Safari content blockers

safari/contentBlocking.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 20 matching lines @@
   function onLegacyAPISupported(msg, sender)
   {
     port.off("safari.legacyAPISupported", onLegacyAPISupported);
     resolve(msg.legacyAPISupported);
   }
   port.on("safari.legacyAPISupported", onLegacyAPISupported);
 });
 let contentBlockingActive = false;
 let afterContentBlockingFinished = null;
 let contentBlockListDirty = true;
-let lastSetContentBlockerResult;
+let lastSetContentBlockerError;
 
 function clearBlockCounters()
 {
   ext.pages.query({}, pages =>
   {
     for (let page of pages)
       page.browserAction.setBadge();
   });
 }
 
 function setContentBlocker(callback)
 {
-  // setContentBlocker returns null if given the same blocklist as last time,
-  // even when there was an error. (It's also wasteful to re-generate the
-  // blocklist when nothing has changed!)
+  // When given the same rules as last time setContentBlocker will always give
+  // null (success) to the callback, even when there was actually an error. We
+  // cache the last result therefore so that we can provide a consistent result
+  // and also to avoid wastefully regenerating an identical blocklist.
   if (!contentBlockListDirty)
   {
-    callback(lastSetContentBlockerResult);
+    callback(lastSetContentBlockerError);
     return;
   }
 
   let contentBlockerList = new ContentBlockerList();
   for (let subscription of FilterStorage.subscriptions)
     if (!subscription.disabled)
       for (let filter of subscription.filters)
         contentBlockerList.addFilter(filter);
 
   contentBlockListDirty = false;
   safari.extension.setContentBlocker(
-    // setContentBlocker seems to not work in Safari 9 when a callback is passed
-    // unless the rules are converted to JSON first. (An error is thrown:
-    // "Extension compilation failed: Failed to parse the JSON String.")
+    // There is a strange bug in setContentBlocker for Safari 9 where if both
+    // the callback parameter is provided and the rules aren't converted to a
+    // JSON string it fails. Worse still it actually performs the callback twice
+    // too, firstly with an empty string and then with an Error:
+    //   "Extension compilation failed: Failed to parse the JSON String."
+    // To mitigate this we convert the rules to JSON here and also ignore
+    // callback values of "". (Usually the callback is performed with either
+    // null for success or an Error on failure.)
+    // Bug #26322821 filed on bugreport.apple.com
     JSON.stringify(contentBlockerList.generateRules()),
-    function (result)
+    function(error)
     {
-      // Safari 9 performs the callback twice under some conditions, first with
-      // an empty string and then with an Error!
-      if (result == "")
+      if (error == "")
         return;
 
-      lastSetContentBlockerResult = result;
-      callback(result);
+      lastSetContentBlockerError = error;
+      callback(error);
     }
   );
 }
 
 function updateContentBlocker(isStartup, legacyAPISupported)
 {
   afterContentBlockingFinished = new Promise(resolve =>
   {
-    setContentBlocker(result =>
+    setContentBlocker(error =>
     {
-      if (result instanceof Error)
+      if (error instanceof Error)
       {
         let suppressErrorMessage = false;
 
         // If the content blocking API fails the first time it's used the
         // legacy blocking API (if available) won't have been disabled.
         if (!contentBlockingActive && legacyAPISupported)
         {
           Prefs.safariContentBlocker = false;
           // If content blocking failed on startup and we're switching back to
           // the legacy API anyway we don't need to show an error message.
           if (isStartup)
             suppressErrorMessage = true;
         }
 
         if (!suppressErrorMessage)
-          alert(result.message);
+          alert(error.message);
       }
       else if (!contentBlockingActive)
       {
         contentBlockingActive = true;
         clearBlockCounters();
       }
 
       resolve(contentBlockingActive);
       afterContentBlockingFinished = null;
     });
@@ skipping 27 matching lines @@
     });
   });
 }
 
 port.on("safari.contentBlockingActive", (msg, sender) =>
 {
   if (!contentBlockingActive && afterContentBlockingFinished)
     return afterContentBlockingFinished;
   return contentBlockingActive;
 });