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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 /** @module contentBlocking */
 
 "use strict";
 
 let {Prefs} = require("prefs");
 let {ContentBlockerList} = require("abp2blocklist");
 let {FilterStorage} = require("filterStorage");
 let {FilterNotifier} = require("filterNotifier");
 let {port} = require("messaging");
 
 let contentBlockingSupported = "setContentBlocker" in safari.extension;
-let legacyApiSupported = "onbeforeload" in Element.prototype;

[kzar, 2016/04/19 14:03:49]

I remember you said we shouldn't assume both onbeforeload and canLoad will be
removed at the same time, but I can't see how else to do this. (We don't know
about canLoad here and we need to make a decision.)

[Sebastian Noack, 2016/05/12 11:12:23]

You could detect the legacy API in the content script, send the result with the
"loading" message, make legacyApiSupported a promise and resolve it when the
first loading message arrives.

[kzar, 2016/05/17 15:15:39]

Done.

-let contentBlockingActive = contentBlockingSupported && !legacyApiSupported;
-let afterContentBlockingFinished;

[Sebastian Noack, 2016/05/12 11:12:23]

If I understand the logic correctly, this variable might be accessed before
assigned. So initialize it with null here?

[kzar, 2016/05/17 15:15:39]

Done.

+let legacyAPISupported = new Promise(resolve =>
+{
+  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 work unreliably in Safari 9 unless the the
-    // given rules are converted to JSON first. (An error is sometimes 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()),

[Sebastian Noack, 2016/05/12 11:12:23]

That needs to be tracked down properly. If there is no way around then there is
no way around. But I'd rather avoid converting this huge array to a string just
to have Safari internally parse it again, if possible.

[kzar, 2016/05/17 15:15:39]

OK, I'll try again to figure out what's going on.

-    function (result)
+    function(error)
     {
-      contentBlockListDirty = false;
-      lastSetContentBlockerResult = result;
-      callback(result);
+      if (error == "")
+        return;
+
+      lastSetContentBlockerError = error;
+      callback(error);
     }
   );
 }
 
-function updateContentBlocker(onStartup)

[Sebastian Noack, 2016/05/12 11:12:23]

Nit: onStartup -> isStartup, since this value indicated whether this is the
startup not what to do on startup.

[kzar, 2016/05/17 15:15:39]

Done.

+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)
+        if (!contentBlockingActive && legacyAPISupported)
         {
-          Prefs["safariContentBlocker"] = false;
-          Prefs.on("safariContentBlocker", onSafariContentBlocker);
+          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 (onStartup)
+          if (isStartup)
             suppressErrorMessage = true;
         }
 
         if (!suppressErrorMessage)
-          alert(result.message);
+          alert(error.message);
       }
       else if (!contentBlockingActive)
       {
         contentBlockingActive = true;
         clearBlockCounters();
       }
 
       resolve(contentBlockingActive);
-      afterContentBlockingFinished = undefined;
+      afterContentBlockingFinished = null;
     });
   });
 }
 
-function onSafariContentBlocker()
-{
-  Prefs.off("safariContentBlocker", onSafariContentBlocker);
-  updateContentBlocker();
-}
-
 if (contentBlockingSupported)
 {
-  Promise.all([Prefs.untilLoaded, FilterNotifier.once("load")]).then(() =>
+  Promise.all([Prefs.untilLoaded,
+               FilterNotifier.once("load"),
+               legacyAPISupported]).then(resolvedValues =>
   {
-    // If this version of Safari only supports the new API then let's make sure
-    // the safariContentBlocker preference is set to true for consistency.
-    if (contentBlockingActive)
-      Prefs["safariContentBlocker"] = true;
+    let legacyAPISupported = resolvedValues[2];
+    if (!legacyAPISupported)
+      Prefs.safariContentBlocker = true;
 
-    if (Prefs["safariContentBlocker"])

[Sebastian Noack, 2016/05/12 11:12:23]

Nit: Prefs.safariContentBlocker

[kzar, 2016/05/17 15:15:38]

Done.

-      updateContentBlocker(true);
-    else
-      Prefs.on("safariContentBlocker", onSafariContentBlocker);

[Sebastian Noack, 2016/05/12 11:12:23]

I wonder whether the logic wouldn't be simpler if you simply always register
Prefs.on("safariContentBlocker", ) if content blocking is supported and never
unregister it, rather than registering and unregistering it in different places.

[kzar, 2016/05/17 15:15:40]

Done.

+    if (Prefs.safariContentBlocker)
+      updateContentBlocker(true, legacyAPISupported);
 
-    for (let action of ["load", "subscription.added", "subscription.removed",

[Sebastian Noack, 2016/05/12 11:12:23]

As usual, jsHydra will duplicate that array in the generated code. Anyway, it
seems that you only need to listen for "filter.behaviorChanged" here.

[kzar, 2016/05/17 15:15:38]

Done.

-                        "subscription.updated", "subscription.disabled",
-                        "filter.added", "filter.removed", "filter.disabled"])
-      FilterNotifier.on(action, () =>
-      {
-        contentBlockListDirty = true;
-        if (contentBlockingActive)
-          updateContentBlocker();
-      });
+    Prefs.on("safariContentBlocker", () =>
+    {
+      if (!contentBlockingActive && Prefs.safariContentBlocker)
+        updateContentBlocker(false, legacyAPISupported);
+    });
+
+    FilterNotifier.on("filter.behaviorChanged", () =>
+    {
+      contentBlockListDirty = true;
+      if (contentBlockingActive)
+        updateContentBlocker(false, legacyAPISupported);
+    });
   });
 }
 
-port.on("safari.contentBlockingActive", function(msg, sender)
+port.on("safari.contentBlockingActive", (msg, sender) =>
 {
   if (!contentBlockingActive && afterContentBlockingFinished)
     return afterContentBlockingFinished;
   return contentBlockingActive;
 });
-