Issue 6599 - Detect data corruption of storage.local

lib/prefs.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present 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 286 matching lines @@
   // saved frequently as a side-effect.
   const MIN_UPDATE_INTERVAL = 60 * 1000;
   let lastUpdate = -MIN_UPDATE_INTERVAL;
   let promise = null;
   customSave.set("blocked_total", pref =>
   {
     if (!promise)
     {
       promise = new Promise((resolve, reject) =>
       {
-        let callback = () =>
-        {
-          lastUpdate = performance.now();
-          promise = null;

[Sebastian Noack, 2018/04/27 16:58:58]

Since callback() were potentially called synchronously below, this will
potentially reset promise to null before it gets returned. I figured the
simplest solution is to just always call setTimeout().

[Thomas Greiner, 2018/04/27 17:03:32]

Acknowledged.

-          savePref(pref).then(resolve, reject);
-        };
-
-        let timeElapsed = performance.now() - lastUpdate;
-        if (timeElapsed < MIN_UPDATE_INTERVAL)
-          setTimeout(callback, MIN_UPDATE_INTERVAL - timeElapsed);
-        else
-          callback();
+        setTimeout(
+          () =>
+          {
+            lastUpdate = performance.now();
+            promise = null;
+            savePref(pref).then(resolve, reject);
+          },
+          lastUpdate + MIN_UPDATE_INTERVAL - performance.now()
+        );
       });
     }
     return promise;
   });
 }
 
 function addPreference(pref)
 {
   Object.defineProperty(Prefs, pref, {
     get() { return (pref in overrides ? overrides : defaults)[pref]; },
@@ skipping 56 matching lines @@
           eventEmitter.emit(pref);
         }
       }
     });
   }
 
   Prefs.untilLoaded = Promise.all([localLoaded, managedLoaded]).then(onLoaded);
 }
 
 init();