// org.apache.rocketmq.remoting.protocol.RemotingCommand#encode

public ByteBuffer encode() {

    // 1> header length size

    int length = 4;

    // 2> header data length

    byte[] headerData = this.headerEncode();

    length += headerData.length;

    // 3> body data length

    if (this.body != null) {

        length += body.length;

    }

    ByteBuffer result = ByteBuffer.allocate(4 + length);

    // length

    result.putInt(length);

    // header length

    result.put(markProtocolType(headerData.length, serializeTypeCurrentRPC));

    // header data

    result.put(headerData);

    // body data;

    if (this.body != null) {

        result.put(this.body);

    }

    result.flip();

    return result;

}

public class NettyDecoder extends LengthFieldBasedFrameDecoder {

    private static final InternalLogger log = InternalLoggerFactory.getLogger(RemotingHelper.ROCKETMQ_REMOTING);

    private static final int FRAME_MAX_LENGTH =

        Integer.parseInt(System.getProperty("com.rocketmq.remoting.frameMaxLength", "16777216"));

    public NettyDecoder() {

        super(FRAME_MAX_LENGTH, 0, 4, 0, 4);

    }

}