Db::escape_string PHP Method

    public function escape_string($str)
    {
        // $res = @mysql_escape_string($str);
        // $res === false && $res = $str;
        // return $res;
        return $str;
    }

 /** Return ID of currently logged in user or NULL if no user is logged in. */
 public static function get_user_id()
 {
     static $cached_result = false;
     if ($cached_result !== false) {
         return $cached_result;
     }
     $cookie_name = Settings::get('OC_COOKIE_NAME');
     if (!isset($_COOKIE[$cookie_name])) {
         return null;
     }
     $OC_data = unserialize(base64_decode($_COOKIE[$cookie_name]));
     if (!isset($OC_data['sessionid'])) {
         return null;
     }
     $OC_sessionid = $OC_data['sessionid'];
     if (!$OC_sessionid) {
         return null;
     }
     return Db::select_value("\n            select sys_sessions.user_id\n            from sys_sessions, user\n            where sys_sessions.uuid = '" . Db::escape_string($OC_sessionid) . "'\n            and user.user_id = sys_sessions.user_id\n            and user.is_active_flag = 1\n        ");
 }