public function keepAlive($id)
    {
        $params = [
            'ID' => $id,
        ];

        $body = $this->request(self::URI_KEEPALIVE, $params);

        if (!isset($body['result'])) {
            return $body;
        }
        // response "result" field, etcd bug?
        return [
            'ID' => $body['result']['ID'],
            'TTL' => $body['result']['TTL'],
        ];
    }