由浅入深Netty粘包与半包解决方案

傷城~ 2024-03-22 19:44 74阅读 0赞

#### 目录 ####

*  1 粘包现象
 *  2 半包现象
 *  3 现象分析
 *  4 解决方案
 *   *  4.1 方法1：短链接
     *  4.2：方法2：固定长度
     *  4.3 方法3：固定分隔符
     *  4.4 方法4：预设长度

--------------------

## 1 粘包现象 ##

![在这里插入图片描述][977f5adca88048b1be0e4a76a7092980.png]

服务端代码

public class HelloWorldServer {
        
        static final Logger log = LoggerFactory.getLogger(HelloWorldServer.class);
        void start() {
        
            NioEventLoopGroup boss = new NioEventLoopGroup(1);
            NioEventLoopGroup worker = new NioEventLoopGroup();
            try {
        
                ServerBootstrap serverBootstrap = new ServerBootstrap();
                serverBootstrap.channel(NioServerSocketChannel.class);
                serverBootstrap.group(boss, worker);
                serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
        
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
        
                        ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
        
                            @Override
                            public void channelActive(ChannelHandlerContext ctx) throws Exception {
        
                                log.debug("connected {}", ctx.channel());
                                super.channelActive(ctx);
                            }
    
                            @Override
                            public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        
                                log.debug("disconnect {}", ctx.channel());
                                super.channelInactive(ctx);
                            }
                        });
                    }
                });
                ChannelFuture channelFuture = serverBootstrap.bind(8080);
                log.debug("{} binding...", channelFuture.channel());
                channelFuture.sync();
                log.debug("{} bound...", channelFuture.channel());
                channelFuture.channel().closeFuture().sync();
            } catch (InterruptedException e) {
        
                log.error("server error", e);
            } finally {
        
                boss.shutdownGracefully();
                worker.shutdownGracefully();
                log.debug("stoped");
            }
        }
    
        public static void main(String[] args) {
        
            new HelloWorldServer().start();
        }
    }

客户端代码希望发送 10 个消息，每个消息是 16 字节

public class HelloWorldClient {
        
        static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
        public static void main(String[] args) {
        
            NioEventLoopGroup worker = new NioEventLoopGroup();
            try {
        
                Bootstrap bootstrap = new Bootstrap();
                bootstrap.channel(NioSocketChannel.class);
                bootstrap.group(worker);
                bootstrap.handler(new ChannelInitializer<SocketChannel>() {
        
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
        
                        log.debug("connetted...");
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
        
                            @Override
                            public void channelActive(ChannelHandlerContext ctx) throws Exception {
        
                                log.debug("sending...");
                                Random r = new Random();
                                char c = 'a';
                                for (int i = 0; i < 10; i++) {
        
                                    ByteBuf buffer = ctx.alloc().buffer();
                                    buffer.writeBytes(new byte[]{
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15});
                                    ctx.writeAndFlush(buffer);
                                }
                            }
                        });
                    }
                });
                ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8080).sync();
                channelFuture.channel().closeFuture().sync();
    
            } catch (InterruptedException e) {
        
                log.error("client error", e);
            } finally {
        
                worker.shutdownGracefully();
            }
        }
    }

服务器端的某次输出，可以看到一次就接收了 160 个字节，而非分 10 次接收

08:24:46 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0x81e0fda5] binding...
    08:24:46 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0x81e0fda5, L:/0:0:0:0:0:0:0:0:8080] bound...
    08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] REGISTERED
    08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] ACTIVE
    08:24:55 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177]
    08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] READ: 160B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000010| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000020| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000030| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000040| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000050| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000060| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000070| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000080| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000090| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    +--------+-------------------------------------------------+----------------+
    08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] READ COMPLETE

## 2 半包现象 ##

客户端代码希望发送 1 个消息，这个消息是 160 字节，代码改为

ByteBuf buffer = ctx.alloc().buffer();
    for (int i = 0; i < 10; i++) {
        
        buffer.writeBytes(new byte[]{
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15});
    }
    ctx.writeAndFlush(buffer);

为现象明显，服务端修改一下接收缓冲区，其它代码不变

serverBootstrap.option(ChannelOption.SO_RCVBUF, 10);

服务器端的某次输出，可以看到接收的消息被分为两节，第一次 20 字节，第二次 140 字节

08:43:49 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0x4d6c6a84] binding...
    08:43:49 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0x4d6c6a84, L:/0:0:0:0:0:0:0:0:8080] bound...
    08:44:23 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] REGISTERED
    08:44:23 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] ACTIVE
    08:44:23 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221]
    08:44:24 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] READ: 20B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
    |00000010| 00 01 02 03                                     |....            |
    +--------+-------------------------------------------------+----------------+
    08:44:24 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] READ COMPLETE
    08:44:24 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] READ: 140B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
    |00000010| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
    |00000020| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
    |00000030| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
    |00000040| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
    |00000050| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
    |00000060| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
    |00000070| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
    |00000080| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f             |............    |
    +--------+-------------------------------------------------+----------------+
    08:44:24 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] READ COMPLETE

> **注意**
> 
> serverBootstrap.option(ChannelOption.SO\_RCVBUF, 10) 影响的底层接收缓冲区（即滑动窗口）大小，仅决定了 netty 读取的最小单位，netty 实际每次读取的一般是它的整数倍

## 3 现象分析 ##

粘包

*  现象，发送 abc def，接收 abcdef
 *  原因
    
     *  应用层：接收方 ByteBuf 设置太大（Netty 默认 1024）
     *  滑动窗口：假设发送方 256 bytes 表示一个完整报文，但由于接收方处理不及时且窗口大小足够大，这 256 bytes 字节就会缓冲在接收方的滑动窗口中，当滑动窗口中缓冲了多个报文就会粘包
     *  Nagle 算法：会造成粘包

半包

*  现象，发送 abcdef，接收 abc def
 *  原因
    
     *  应用层：接收方 ByteBuf 小于实际发送数据量
     *  滑动窗口：假设接收方的窗口只剩了 128 bytes，发送方的报文大小是 256 bytes，这时放不下了，只能先发送前 128 bytes，等待 ack 后才能发送剩余部分，这就造成了半包
     *  MSS 限制：当发送的数据超过 MSS 限制后，会将数据切分发送，就会造成半包

本质是因为 TCP 是流式协议，消息无边界

> 滑动窗口
> 
>  *  TCP 以一个段（segment）为单位，每发送一个段就需要进行一次确认应答（ack）处理，但如果这么做，缺点是包的往返时间越长性能就越差

![在这里插入图片描述][a630af845427451aa7bb8bf5c5e8f4e8.png]

>  *  为了解决此问题，引入了窗口概念，窗口大小即决定了无需等待应答而可以继续发送的数据最大值

![在这里插入图片描述][e1e0e670a3fa4cf5817e472eaad5b287.png]

>  *  窗口实际就起到一个缓冲区的作用，同时也能起到流量控制的作用
>     
>      *  图中深色的部分即要发送的数据，高亮的部分即窗口
>      *  窗口内的数据才允许被发送，当应答未到达前，窗口必须停止滑动
>      *  如果 1001~2000 这个段的数据 ack 回来了，窗口就可以向前滑动
>      *  接收方也会维护一个窗口，只有落在窗口内的数据才能允许接收

> MSS 限制
> 
>  *  链路层对一次能够发送的最大数据有限制，这个限制称之为 MTU（maximum transmission unit），不同的链路设备的 MTU 值也有所不同，例如
>  *  以太网的 MTU 是 1500
>  *  FDDI（光纤分布式数据接口）的 MTU 是 4352
>  *  本地回环地址的 MTU 是 65535 - 本地测试不走网卡
>  *  MSS 是最大段长度（maximum segment size），它是 MTU 刨去 tcp 头和 ip 头后剩余能够作为数据传输的字节数
>  *  ipv4 tcp 头占用 20 bytes，ip 头占用 20 bytes，因此以太网 MSS 的值为 1500 - 40 = 1460
>  *  TCP 在传递大量数据时，会按照 MSS 大小将数据进行分割发送
>  *  MSS 的值在三次握手时通知对方自己 MSS 的值，然后在两者之间选择一个小值作为 MSS

![在这里插入图片描述][0efab6e4a13f4c32a00239ddef0f1305.png]

> Nagle 算法
> 
>  *  即使发送一个字节，也需要加入 tcp 头和 ip 头，也就是总字节数会使用 41 bytes，非常不经济。因此为了提高网络利用率，tcp 希望尽可能发送足够大的数据，这就是 Nagle 算法产生的缘由
>  *  该算法是指发送端即使还有应该发送的数据，但如果这部分数据很少的话，则进行延迟发送
>     
>      *  如果 SO\_SNDBUF 的数据达到 MSS，则需要发送
>      *  如果 SO\_SNDBUF 中含有 FIN（表示需要连接关闭）这时将剩余数据发送，再关闭
>      *  如果 TCP\_NODELAY = true，则需要发送
>      *  已发送的数据都收到 ack 时，则需要发送
>      *  上述条件不满足，但发生超时（一般为 200ms）则需要发送
>      *  除上述情况，延迟发送

## 4 解决方案 ##

1.  短链接，发一个包建立一次连接，这样连接建立到连接断开之间就是消息的边界，缺点效率太低
2.  每一条消息采用固定长度，缺点浪费空间
3.  每一条消息采用分隔符，例如 \\n，缺点需要转义
4.  每一条消息分为 head 和 body，head 中包含 body 的长度

### 4.1 方法1：短链接 ###

以解决粘包为例

public class HelloWorldClient {
        
        static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
    
        public static void main(String[] args) {
        
            // 分 10 次发送
            for (int i = 0; i < 10; i++) {
        
                send();
            }
        }
    
        private static void send() {
        
            NioEventLoopGroup worker = new NioEventLoopGroup();
            try {
        
                Bootstrap bootstrap = new Bootstrap();
                bootstrap.channel(NioSocketChannel.class);
                bootstrap.group(worker);
                bootstrap.handler(new ChannelInitializer<SocketChannel>() {
        
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
        
                        log.debug("conneted...");
                        ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
        
                            @Override
                            public void channelActive(ChannelHandlerContext ctx) throws Exception {
        
                                log.debug("sending...");
                                ByteBuf buffer = ctx.alloc().buffer();
                                buffer.writeBytes(new byte[]{
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15});
                                ctx.writeAndFlush(buffer);
                                // 发完即关
                                ctx.close();
                            }
                        });
                    }
                });
                ChannelFuture channelFuture = bootstrap.connect("localhost", 8080).sync();
                channelFuture.channel().closeFuture().sync();
    
            } catch (InterruptedException e) {
        
                log.error("client error", e);
            } finally {
        
                worker.shutdownGracefully();
            }
        }
    }

输出，略

> 半包用这种办法还是不好解决，因为接收方的缓冲区大小是有限的

### 4.2：方法2：固定长度 ###

让所有数据包长度固定（假设长度为 8 字节），服务器端加入

ch.pipeline().addLast(new FixedLengthFrameDecoder(8));

客户端测试代码，注意, 采用这种方法后，客户端什么时候 flush 都可以

public class HelloWorldClient {
        
        static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
    
        public static void main(String[] args) {
        
            NioEventLoopGroup worker = new NioEventLoopGroup();
            try {
        
                Bootstrap bootstrap = new Bootstrap();
                bootstrap.channel(NioSocketChannel.class);
                bootstrap.group(worker);
                bootstrap.handler(new ChannelInitializer<SocketChannel>() {
        
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
        
                        log.debug("connetted...");
                        ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
        
                            @Override
                            public void channelActive(ChannelHandlerContext ctx) throws Exception {
        
                                log.debug("sending...");
                                // 发送内容随机的数据包
                                Random r = new Random();
                                char c = 'a';
                                ByteBuf buffer = ctx.alloc().buffer();
                                for (int i = 0; i < 10; i++) {
        
                                    byte[] bytes = new byte[8];
                                    for (int j = 0; j < r.nextInt(8); j++) {
        
                                        bytes[j] = (byte) c;
                                    }
                                    c++;
                                    buffer.writeBytes(bytes);
                                }
                                ctx.writeAndFlush(buffer);
                            }
                        });
                    }
                });
                ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();
                channelFuture.channel().closeFuture().sync();
    
            } catch (InterruptedException e) {
        
                log.error("client error", e);
            } finally {
        
                worker.shutdownGracefully();
            }
        }
    }

客户端输出

12:07:00 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
    12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2] REGISTERED
    12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2] CONNECT: /192.168.0.103:9090
    12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] ACTIVE
    12:07:00 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
    12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] WRITE: 80B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 61 61 61 61 00 00 00 00 62 00 00 00 00 00 00 00 |aaaa....b.......|
    |00000010| 63 63 00 00 00 00 00 00 64 00 00 00 00 00 00 00 |cc......d.......|
    |00000020| 00 00 00 00 00 00 00 00 66 66 66 66 00 00 00 00 |........ffff....|
    |00000030| 67 67 67 00 00 00 00 00 68 00 00 00 00 00 00 00 |ggg.....h.......|
    |00000040| 69 69 69 69 69 00 00 00 6a 6a 6a 6a 00 00 00 00 |iiiii...jjjj....|
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] FLUSH

服务端输出

12:06:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xe3d9713f] binding...
    12:06:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xe3d9713f, L:/192.168.0.103:9090] bound...
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] REGISTERED
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] ACTIVE
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155]
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 61 61 61 61 00 00 00 00                         |aaaa....        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 62 00 00 00 00 00 00 00                         |b.......        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 63 63 00 00 00 00 00 00                         |cc......        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 64 00 00 00 00 00 00 00                         |d.......        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 00 00 00 00 00 00 00 00                         |........        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 66 66 66 66 00 00 00 00                         |ffff....        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 67 67 67 00 00 00 00 00                         |ggg.....        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 68 00 00 00 00 00 00 00                         |h.......        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 69 69 69 69 69 00 00 00                         |iiiii...        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 6a 6a 6a 6a 00 00 00 00                         |jjjj....        |
    +--------+-------------------------------------------------+----------------+
    12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ COMPLETE

缺点是，数据包的大小不好把握

*  长度定的太大，浪费
 *  长度定的太小，对某些数据包又显得不够

### 4.3 方法3：固定分隔符 ###

服务端加入，默认以 \\n 或 \\r\\n 作为分隔符，如果超出指定长度仍未出现分隔符，则抛出异常

ch.pipeline().addLast(new LineBasedFrameDecoder(1024));

客户端在每条消息之后，加入 \\n 分隔符

public class HelloWorldClient {
        
        static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
    
        public static void main(String[] args) {
        
            NioEventLoopGroup worker = new NioEventLoopGroup();
            try {
        
                Bootstrap bootstrap = new Bootstrap();
                bootstrap.channel(NioSocketChannel.class);
                bootstrap.group(worker);
                bootstrap.handler(new ChannelInitializer<SocketChannel>() {
        
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
        
                        log.debug("connetted...");
                        ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
        
                            @Override
                            public void channelActive(ChannelHandlerContext ctx) throws Exception {
        
                                log.debug("sending...");
                                Random r = new Random();
                                char c = 'a';
                                ByteBuf buffer = ctx.alloc().buffer();
                                for (int i = 0; i < 10; i++) {
        
                                    for (int j = 1; j <= r.nextInt(16)+1; j++) {
        
                                        buffer.writeByte((byte) c);
                                    }
                                    buffer.writeByte(10);
                                    c++;
                                }
                                ctx.writeAndFlush(buffer);
                            }
                        });
                    }
                });
                ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();
                channelFuture.channel().closeFuture().sync();
    
            } catch (InterruptedException e) {
        
                log.error("client error", e);
            } finally {
        
                worker.shutdownGracefully();
            }
        }
    }

客户端输出

14:08:18 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
    14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755] REGISTERED
    14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755] CONNECT: /192.168.0.103:9090
    14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] ACTIVE
    14:08:18 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
    14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] WRITE: 60B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 61 0a 62 62 62 0a 63 63 63 0a 64 64 0a 65 65 65 |a.bbb.ccc.dd.eee|
    |00000010| 65 65 65 65 65 65 65 0a 66 66 0a 67 67 67 67 67 |eeeeeee.ff.ggggg|
    |00000020| 67 67 0a 68 68 68 68 0a 69 69 69 69 69 69 69 0a |gg.hhhh.iiiiiii.|
    |00000030| 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 0a             |jjjjjjjjjjj.    |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] FLUSH

服务端输出

14:08:18 [DEBUG] [nioEventLoopGroup-3-5] c.i.n.HelloWorldServer - connected [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641]
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 1B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 61                                              |a               |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 3B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 62 62 62                                        |bbb             |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 3B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 63 63 63                                        |ccc             |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 2B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 64 64                                           |dd              |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 10B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 65 65 65 65 65 65 65 65 65 65                   |eeeeeeeeee      |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 2B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 66 66                                           |ff              |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 7B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 67 67 67 67 67 67 67                            |ggggggg         |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 4B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 68 68 68 68                                     |hhhh            |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 7B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 69 69 69 69 69 69 69                            |iiiiiii         |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 11B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a                |jjjjjjjjjjj     |
    +--------+-------------------------------------------------+----------------+
    14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ COMPLETE

缺点，处理字符数据比较合适，但如果内容本身包含了分隔符（字节数据常常会有此情况），那么就会解析错误

### 4.4 方法4：预设长度 ###

在发送消息前，先约定用定长字节表示接下来数据的长度

// 最大长度，长度偏移，长度占用字节，长度调整，剥离字节数
    ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 1, 0, 1));

客户端代码

public class HelloWorldClient {
        
        static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
    
        public static void main(String[] args) {
        
            NioEventLoopGroup worker = new NioEventLoopGroup();
            try {
        
                Bootstrap bootstrap = new Bootstrap();
                bootstrap.channel(NioSocketChannel.class);
                bootstrap.group(worker);
                bootstrap.handler(new ChannelInitializer<SocketChannel>() {
        
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
        
                        log.debug("connetted...");
                        ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
        
                            @Override
                            public void channelActive(ChannelHandlerContext ctx) throws Exception {
        
                                log.debug("sending...");
                                Random r = new Random();
                                char c = 'a';
                                ByteBuf buffer = ctx.alloc().buffer();
                                for (int i = 0; i < 10; i++) {
        
                                    byte length = (byte) (r.nextInt(16) + 1);
                                    // 先写入长度
                                    buffer.writeByte(length);
                                    // 再
                                    for (int j = 1; j <= length; j++) {
        
                                        buffer.writeByte((byte) c);
                                    }
                                    c++;
                                }
                                ctx.writeAndFlush(buffer);
                            }
                        });
                    }
                });
                ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();
                channelFuture.channel().closeFuture().sync();
    
            } catch (InterruptedException e) {
        
                log.error("client error", e);
            } finally {
        
                worker.shutdownGracefully();
            }
        }
    }

客户端输出

14:37:10 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
    14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8] REGISTERED
    14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8] CONNECT: /192.168.0.103:9090
    14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] ACTIVE
    14:37:10 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
    14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] WRITE: 97B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 09 61 61 61 61 61 61 61 61 61 09 62 62 62 62 62 |.aaaaaaaaa.bbbbb|
    |00000010| 62 62 62 62 06 63 63 63 63 63 63 08 64 64 64 64 |bbbb.cccccc.dddd|
    |00000020| 64 64 64 64 0f 65 65 65 65 65 65 65 65 65 65 65 |dddd.eeeeeeeeeee|
    |00000030| 65 65 65 65 0d 66 66 66 66 66 66 66 66 66 66 66 |eeee.fffffffffff|
    |00000040| 66 66 02 67 67 02 68 68 0e 69 69 69 69 69 69 69 |ff.gg.hh.iiiiiii|
    |00000050| 69 69 69 69 69 69 69 09 6a 6a 6a 6a 6a 6a 6a 6a |iiiiiii.jjjjjjjj|
    |00000060| 6a                                              |j               |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] FLUSH

服务端输出

14:36:50 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xdff439d3] binding...
    14:36:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xdff439d3, L:/192.168.0.103:9090] bound...
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] REGISTERED
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] ACTIVE
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979]
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 61 61 61 61 61 61 61 61 61                      |aaaaaaaaa       |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 62 62 62 62 62 62 62 62 62                      |bbbbbbbbb       |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 6B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 63 63 63 63 63 63                               |cccccc          |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 8B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 64 64 64 64 64 64 64 64                         |dddddddd        |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 15B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65    |eeeeeeeeeeeeeee |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 13B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 66 66 66 66 66 66 66 66 66 66 66 66 66          |fffffffffffff   |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 2B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 67 67                                           |gg              |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 2B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 68 68                                           |hh              |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 14B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 69 69 69 69 69 69 69 69 69 69 69 69 69 69       |iiiiiiiiiiiiii  |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B
             +-------------------------------------------------+
             |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    +--------+-------------------------------------------------+----------------+
    |00000000| 6a 6a 6a 6a 6a 6a 6a 6a 6a                      |jjjjjjjjj       |
    +--------+-------------------------------------------------+----------------+
    14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ COMPLETE

[977f5adca88048b1be0e4a76a7092980.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/18/5a36129ec46640619ab9538fa73dc4a6.png
[a630af845427451aa7bb8bf5c5e8f4e8.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/18/1979aa0edab542ccb8c1f764887d76a7.png
[e1e0e670a3fa4cf5817e472eaad5b287.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/18/7ebed98177434cbdb682f51c2c865c50.png
[0efab6e4a13f4c32a00239ddef0f1305.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/18/d5dc6a11a3c04566b6ba42e701d5f8f8.png