docs: public byte[] toByte() {
          byte[] header;
          byte[] hex_len;
  
          header = new byte[HEAD_LENGTH];
          Arrays.fill(header, (byte) 0);
          hex_len = BytesUtil.long2buff(contentLength);
          System.arraycopy(hex_len, 0, header, 0, hex_len.length);
          header[OtherConstants.PROTO_HEADER_CMD_INDEX] = cmd;
          header[OtherConstants.PROTO_HEADER_STATUS_INDEX] = status;
          return header;
      }