Issue 361 - patterns.ini cleared when writing to file got interrupted

lib/filesystem/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
@@ skipping 89 matching lines @@
           {
             if (writer.error)
               callback(writer.error);
             else
               nextOperation();
           }.bind(this);
 
           op();
         }.bind(this);
 
-        executeWriteOperation(writer.truncate.bind(writer, 0), function()
+        var blob;
+
+        try
         {
-          var blob;
-          try
-          {
-            blob = new Blob([data.join(this.lineBreak) + this.lineBreak], {type: "text/plain"});
-          }
-          catch (e)
-          {
-            if (!(e instanceof TypeError))
-              throw e;
+          blob = new Blob([data.join(this.lineBreak) + this.lineBreak], {type: "text/plain"});
+        }
+        catch (e)
+        {
+          if (!(e instanceof TypeError))
+            throw e;
 
-            // Blob wasn't a constructor before Chrome 20
-            var builder = new (window.BlobBuilder || window.WebKitBlobBuilder);
-            builder.append(data.join(this.lineBreak) + this.lineBreak);
-            blob = builder.getBlob("text/plain");
-          }
-          executeWriteOperation(writer.write.bind(writer, blob), callback.bind(null, null));
-        }.bind(this));
+          // Blob wasn't a constructor before Chrome 20
+          var builder = new (window.BlobBuilder || window.WebKitBlobBuilder);
+          builder.append(data.join(this.lineBreak) + this.lineBreak);
+          blob = builder.getBlob("text/plain");
+        }
+        executeWriteOperation(writer.write.bind(writer, blob), function()
+        {
+          executeWriteOperation(writer.truncate.bind(writer, writer.position), callback.bind(null, null));
+        });
       }.bind(this), callback);
     }.bind(this), callback);
   },
 
   copyFile: function(fromFile, toFile, callback)
   {
     // Simply combine read and write operations
     var data = [];
     this.readFromFile(fromFile, {
       process: function(line)
@@ skipping 58 matching lines @@
             exists: true,
             isDirectory: fileEntry.isDirectory,
             isFile: fileEntry.isFile,
             lastModified: metadata.modificationTime.getTime()
           });
         }, callback);
       }, callback);
     }.bind(this));
   }
 };