private function _writeToFile($filename, $contents)
    {
        // Check local tmp directory
        if (!is_dir($this->config['tmp']) || !is_writeable($this->config['tmp'])) {
            $this->fail('tmp directory not found or is not writable');
        }

        // Build temp file
        $tmp_file = $this->config['tmp'] . "/ftp_data_file.tmp";
        file_put_contents($tmp_file, $contents);

        // Update variables
        $this->filepath = $filename;
        $this->file = $contents;

        // Upload the file to server
        if ($this->isSFTP()) {
            $flag = defined('NET_SFTP_LOCAL_FILE') ? NET_SFTP_LOCAL_FILE : \phpseclib\Net\SFTP::SOURCE_LOCAL_FILE;

            $uploaded = @$this->ftp->put($filename, $tmp_file, $flag);
        } else {
            $uploaded = ftp_put($this->ftp, $filename, $tmp_file, FTP_BINARY);
        }
        if (!$uploaded) {
            $this->fail('failed to upload file to server');
        }
    }