Issue 530 - patterns.ini isn`t being written on Firefox 20 (Permission denied)

lib/io.js

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2014 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/>.
  */
 
 /**
  * @fileOverview Module containing file I/O helpers.
  */
 
 let {Services} = Cu.import("resource://gre/modules/Services.jsm", null);
 let {FileUtils} = Cu.import("resource://gre/modules/FileUtils.jsm", null);
 let {OS} = Cu.import("resource://gre/modules/osfile.jsm", null);
 let {Task} = Cu.import("resource://gre/modules/Task.jsm", null);
 
 let {TimeLine} = require("timeline");
+let {Prefs} = require("prefs");
 let {Utils} = require("utils");
 
+let firstRead = true;
 const BUFFER_SIZE = 0x8000;  // 32kB
 
 let IO = exports.IO =
 {
   /**
    * Retrieves the platform-dependent line break string.
    */
   get lineBreak()
   {
     let lineBreak = (Services.appinfo.OS == "WINNT" ? "\r\n" : "\n");
@@ skipping 132 matching lines @@
         if (timeLineID)
         {
           TimeLine.asyncDone(timeLineID);
         }
       };
 
       let decoder = new TextDecoder();
       let array = new Uint8Array(BUFFER_SIZE);
       Task.spawn(function()
       {
+        if (firstRead && Services.vc.compare(Utils.platformVersion, "23.0a1") <= 0)
+        {
+          // See https://issues.adblockplus.org/ticket/530 - the first file
+          // opened cannot be closed due to Gecko bug 858723. Make sure that
+          // our patterns.ini file doesn't stay locked by opening a dummy file
+          // first.
+          try
+          {
+            let dummyPath = IO.resolveFilePath(Prefs.data_directory + "/dummy").path;
+            let dummy = yield OS.File.open(dummyPath, {write: true, truncate: true});
+            yield dummy.close();
+          }
+          catch (e)
+          {
+            // Dummy might be locked already, we don't care
+          }
+        }
+        firstRead = false;
+
         let f = yield OS.File.open(file.path, {read: true});
         let numBytes;
         do
         {
           numBytes = yield f.readTo(array);
           if (numBytes)
           {
             let data = decoder.decode(numBytes == BUFFER_SIZE ?
                                       array :
                                       array.subarray(0, numBytes), {stream: true});
@@ skipping 143 matching lines @@
         else
           callback(e);
       });
     }
     catch(e)
     {
       callback(e);
     }
   }
 }