protected function setUtf8Mode()
    {
        if ($this->utf8) {
            $response = ftp_raw($this->connection, "OPTS UTF8 ON");
            if (substr($response[0], 0, 3) !== '200') {
                throw new RuntimeException(
                    'Could not set UTF-8 mode for connection: ' . $this->getHost() . '::' . $this->getPort()
                );
            }
        }
    }