Auth_OpenID_FileStore::_isFilenameSafe PHP Method

    function _isFilenameSafe($char)
    {
        $_Auth_OpenID_filename_allowed = Auth_OpenID_letters . Auth_OpenID_digits . ".";
        return strpos($_Auth_OpenID_filename_allowed, $char) !== false;
    }

 /**
  * @access private
  */
 function _filenameEscape($str)
 {
     $filename = "";
     $b = Auth_OpenID::toBytes($str);
     for ($i = 0; $i < count($b); $i++) {
         $c = $b[$i];
         if (Auth_OpenID_FileStore::_isFilenameSafe($c)) {
             $filename .= $c;
         } else {
             $filename .= sprintf("_%02X", ord($c));
         }
     }
     return $filename;
 }