/**
  * @see ExternalStoreMedium::store()
  */
 public function store($backend, $data)
 {
     $be = FileBackendGroup::singleton()->get($backend);
     if ($be instanceof FileBackend) {
         // Get three random base 36 characters to act as shard directories
         $rand = wfBaseConvert(mt_rand(0, 46655), 10, 36, 3);
         // Make sure ID is roughly lexicographically increasing for performance
         $id = str_pad(UIDGenerator::newTimestampedUID128(32), 26, '0', STR_PAD_LEFT);
         // Segregate items by wiki ID for the sake of bookkeeping
         $wiki = isset($this->params['wiki']) ? $this->params['wiki'] : wfWikiID();
         $url = $be->getContainerStoragePath('data') . '/' . rawurlencode($wiki) . "/{$rand[0]}/{$rand[1]}/{$rand[2]}/{$id}";
         $be->prepare(array('dir' => dirname($url), 'noAccess' => 1, 'noListing' => 1));
         if ($be->create(array('dst' => $url, 'content' => $data))->isOK()) {
             return $url;
         }
     }
     return false;
 }