内网穿透

启动

1. java -jar nat-server.jar [port, defalut 8888]
2. java -jar nat-client.jar

规则（示例）

1. 外网地址：http://www.littleredhat1997.com/
2. 内网地址：127.0.0.1
3. http://www.littleredhat1997.com:10000/ <=> 127.0.0.1:8080

机器	标识	端口（默认）
外网代理	Remote	10000
服务端	Server	8888
客户端	Client	-
内网代理	Local	8080

自定义协议

消息体 = 消息体总长度 + TYPE + length(CHANNEL_ID) + CHANNEL_ID + length(DATA) + DATA

private MessageType type;
private String channelId;
private byte[] data;

UNKNOWN(0),
REGISTER(1),
REGISTER_SUCCESS(2),
REGISTER_FAILURE(3),
CONNECTED(4),
DISCONNECTED(5),
DATA(6),
KEEPALIVE(7);

拆包粘包 LengthFieldBasedFrameDecoder

Parameters:

1. maxFrameLength - the maximum length of the frame. If the length of the frame is greater than this value, TooLongFrameException will be thrown.
2. lengthFieldOffset - the offset of the length field
3. lengthFieldLength - the length of the length field
4. lengthAdjustment - the compensation value to add to the value of the length field
5. initialBytesToStrip - the number of first bytes to strip out from the decoded frame

示例：

new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4)

public class MessageEncoder extends MessageToByteEncoder<Message> {
    @Override
    protected void encode(ChannelHandlerContext ctx, Message msg, ByteBuf out) throws Exception {
        // TODO
    }
}

public class MessageDecoder extends ByteToMessageDecoder {
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf msg, List<Object> out) throws Exception {
        // TODO
    }
}

心跳检测 IdleStateHandler

Parameters:

1. readerIdleTimeSeconds - an IdleStateEvent whose state is IdleState.READER_IDLE will be triggered when no read was performed for the specified period of time. Specify 0 to disable.
2. writerIdleTimeSeconds - an IdleStateEvent whose state is IdleState.WRITER_IDLE will be triggered when no write was performed for the specified period of time. Specify 0 to disable.
3. allIdleTimeSeconds - an IdleStateEvent whose state is IdleState.ALL_IDLE will be triggered when neither read nor write was performed for the specified period of time. Specify 0 to disable.

示例：

new IdleStateHandler(60, 30, 0)

@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
    if (evt instanceof IdleStateEvent) {
        IdleStateEvent e = (IdleStateEvent) evt;
        if (e.state() == IdleState.READER_IDLE) {
            // TODO
        } else if (e.state() == IdleState.WRITER_IDLE) {
            // TODO
        } else if (e.state() == IdleState.ALL_IDLE) {
            // TODO
        }
    }
}