public function getJSON()
    {
        /* convert to proper types */
        $o = new \stdClass;
        $o->command = (string) $this->command;
        $o->command_id = $this->command_id;
        $o->params = (object) $this->params;
        $o->variables = (object) $this->variables;
        /* json */
        return json_encode($o);
    }