docs: @Override
      public boolean isValid() {
          LOGGER.debug("check connection status of {} ", this);
          try {
              byte[] header = new byte[OtherConstants.FDFS_PROTO_PKG_LEN_SIZE + 2];
              Arrays.fill(header, (byte) 0);
  
              byte[] hex_len = BytesUtil.long2buff(0);
              System.arraycopy(hex_len, 0, header, 0, hex_len.length);
              header[OtherConstants.PROTO_HEADER_CMD_INDEX] = CmdConstants.FDFS_PROTO_CMD_ACTIVE_TEST;
              header[OtherConstants.PROTO_HEADER_STATUS_INDEX] = (byte) 0;
              socket.getOutputStream().write(header);
              if (socket.getInputStream().read(header) != header.length) {
                  return false;
              }
  
              return header[OtherConstants.PROTO_HEADER_STATUS_INDEX] == 0 ? true : false;
          } catch (IOException e) {
              LOGGER.error("valid connection error", e);
              return false;
          }
      }