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Netty进阶-黏包半包

article 2024/11/19 5:37:20

黏包半包

- 1. 粘包与半包
- - 1.1 粘包现象
  - 1.3 现象分析
  - 1.4 解决方案
  - - 方法1，短链接
    - 方法2，固定长度
    - 方法3，固定分隔符
    - 方法4，预设长度LengthFieldBasedFrameDecoder

1. 粘包与半包

1.1 粘包现象

服务端代码

@Slf4j
public class HelloWorldServer {

    public static void main(String[] args) {
        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));
                }
            });
            ChannelFuture channelFuture = serverBootstrap.bind(8080).sync();
            channelFuture.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            log.error("server error", e);
        } finally {
            boss.shutdownGracefully();
            worker.shutdownGracefully();
        }
    }
}

客户端代码

@Slf4j
public class HelloWorldClient {
    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...");
                            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();
        }
    }
}

客户端是发10次，每次发16字节，而看到的结果是一次接收了160字节的数据，黏包现象

14:21:25 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x9ed7ee45, L:/127.0.0.1:8080 - R:/127.0.0.1:51527] REGISTERED
14:21:25 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x9ed7ee45, L:/127.0.0.1:8080 - R:/127.0.0.1:51527] ACTIVE
14:21:25 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x9ed7ee45, L:/127.0.0.1:8080 - R:/127.0.0.1:51527] 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 |................|
+--------+-------------------------------------------------+----------------+
14:21:25 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x9ed7ee45, L:/127.0.0.1:8080 - R:/127.0.0.1:51527] READ COMPLETE

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，出现半包现象

14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] REGISTERED
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] ACTIVE
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] READ: 36B
         +-------------------------------------------------+
         |  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                                     |....            |
+--------+-------------------------------------------------+----------------+
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] READ COMPLETE
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] READ: 50B
         +-------------------------------------------------+
         |  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                                           |..              |
+--------+-------------------------------------------------+----------------+

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

1.3 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

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

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

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

1.4 解决方案

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
每一条消息采用固定长度，缺点浪费空间
每一条消息采用分隔符，例如 \n，缺点需要转义
每一条消息分为 head 和 body，head 中包含 body 的长度

方法1，短链接

以解决粘包为例

修改客户端代码，每次发16字节后，断开连接

@Slf4j
public class HelloWorldClient {
    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            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...");
                                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);
                                ctx.channel().close();
                            }
                        });
                    }
                });
                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();
            }
        }
    }
}

结果

14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] REGISTERED
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] ACTIVE
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] READ: 16B
         +-------------------------------------------------+
         |  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 |................|
+--------+-------------------------------------------------+----------------+
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] READ COMPLETE
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] READ COMPLETE
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 ! R:/127.0.0.1:54604] INACTIVE
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 ! R:/127.0.0.1:54604] UNREGISTERED
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] REGISTERED
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] ACTIVE
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] READ: 16B
         +-------------------------------------------------+
         |  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 |................|
+--------+-------------------------------------------------+----------------+
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] READ COMPLETE
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] READ COMPLETE
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 ! R:/127.0.0.1:54637] INACTIVE
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 ! R:/127.0.0.1:54637] UNREGISTERED
......

但是无法解决半包问题

修改服务端代码，让netty的缓冲区最大为16字节

serverBootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR,new AdaptiveRecvByteBufAllocator(16,16,16));

修改客户端代码，每次传18个字节

buffer.writeBytes(new byte[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17});

结果

14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] REGISTERED
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] ACTIVE
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] REGISTERED
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] ACTIVE
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] READ: 16B
         +-------------------------------------------------+
         |  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 |................|
+--------+-------------------------------------------------+----------------+
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] READ: 16B
         +-------------------------------------------------+
         |  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 |................|
+--------+-------------------------------------------------+----------------+
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] READ COMPLETE
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] READ COMPLETE
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] READ: 2B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 10 11                                           |..              |
+--------+-------------------------------------------------+----------------+
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] READ COMPLETE
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] READ: 2B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 10 11                                           |..              |
+--------+-------------------------------------------------+----------------+

方法2，固定长度

让所有数据包长度固定（假设长度为 10 字节），服务器端加入

//每10个字节拆分一次
ch.pipeline().addLast(new FixedLengthFrameDecoder(10));

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
客户端代码

@Slf4j
public class Client2 {

    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) {
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) {
                            ByteBuf buf = ctx.alloc().buffer();
                            char c = '0';
                            Random r = new Random();
                            for (int i = 0; i < 10; i++) {
                                byte[] bytes = fill10Bytes(c, r.nextInt(10) + 1);
                                c++;
                                buf.writeBytes(bytes);
                            }
                            ctx.writeAndFlush(buf);
                        }
                    });
                }
            });
            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();
        }
        System.out.println("finish");
    }

    public static byte[] fill10Bytes(char c, int len) {
        byte[] bytes = new byte[10];
        Arrays.fill(bytes, (byte) '_');
        for (int i = 0; i < len; i++) {
            bytes[i] = (byte) c;
        }
        System.out.println(new String(bytes));
        return bytes;
    }
}

客户端输出，一次将100字节全发过去了

15:13:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xa592b591, L:/127.0.0.1:56680 - R:/127.0.0.1:8080] WRITE: 100B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 5f 5f 5f 5f 5f 5f 5f 5f 31 5f 5f 5f 5f 5f |00________1_____|
|00000010| 5f 5f 5f 5f 32 5f 5f 5f 5f 5f 5f 5f 5f 5f 33 33 |____2_________33|
|00000020| 33 33 5f 5f 5f 5f 5f 5f 34 34 34 34 34 5f 5f 5f |33______44444___|
|00000030| 5f 5f 35 35 35 35 35 35 35 35 5f 5f 36 5f 5f 5f |__55555555__6___|
|00000040| 5f 5f 5f 5f 5f 5f 37 37 37 37 37 37 37 5f 5f 5f |______7777777___|
|00000050| 38 38 38 38 38 5f 5f 5f 5f 5f 39 39 39 39 39 39 |88888_____999999|
|00000060| 39 39 39 39                                     |9999            |
+--------+-------------------------------------------------+----------------+
15:13:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xa592b591, L:/127.0.0.1:56680 - R:/127.0.0.1:8080] FLUSH

服务端输出

15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] REGISTERED
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] ACTIVE
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] READ: 10B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 5f 5f 5f 5f 5f 5f 5f 5f                   |00________      |
+--------+-------------------------------------------------+----------------+
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] READ COMPLETE
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] READ: 10B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 31 5f 5f 5f 5f 5f 5f 5f 5f 5f                   |1_________      |
+--------+-------------------------------------------------+----------------+
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] READ: 10B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 32 5f 5f 5f 5f 5f 5f 5f 5f 5f                   |2_________      |
+--------+-------------------------------------------------+----------------+
......

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

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

@Slf4j
public class Client3 {

    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) {
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        // 会在连接 channel 建立成功后，会触发 active 事件
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) {
                            ByteBuf buf = ctx.alloc().buffer();
                            char c = '0';
                            Random r = new Random();
                            for (int i = 0; i < 10; i++) {
                                StringBuilder sb = makeString(c, r.nextInt(5) + 1);
                                c++;
                                buf.writeBytes(sb.toString().getBytes());
                            }
                            ctx.writeAndFlush(buf);
                        }
                    });
                }
            });
            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();
        }
        System.out.println("finish");
    }

    public static StringBuilder makeString(char c, int len) {
        StringBuilder sb = new StringBuilder(len + 2);
        for (int i = 0; i < len; i++) {
            sb.append(c);
        }
        sb.append("\n");
        return sb;
    }

}

客户端输出

15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad] REGISTERED
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad] CONNECT: /127.0.0.1:8080
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad, L:/127.0.0.1:57416 - R:/127.0.0.1:8080] ACTIVE
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad, L:/127.0.0.1:57416 - R:/127.0.0.1:8080] WRITE: 44B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 0a 31 31 31 31 0a 32 32 32 0a 33 33 33 0a |00.1111.222.333.|
|00000010| 34 34 34 34 34 0a 35 35 35 0a 36 36 36 0a 37 37 |44444.555.666.77|
|00000020| 37 37 37 0a 38 0a 39 39 39 39 39 0a             |777.8.99999.    |
+--------+-------------------------------------------------+----------------+
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad, L:/127.0.0.1:57416 - R:/127.0.0.1:8080] FLUSH

服务端输出

15:23:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xc9272026, L:/127.0.0.1:8080 ! R:/127.0.0.1:57367] INACTIVE
15:23:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xc9272026, L:/127.0.0.1:8080 ! R:/127.0.0.1:57367] UNREGISTERED
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] REGISTERED
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] ACTIVE
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] READ: 2B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30                                           |00              |
+--------+-------------------------------------------------+----------------+
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] READ: 4B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 31 31 31 31                                     |1111            |
+--------+-------------------------------------------------+----------------+
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] READ: 3B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 32 32 32                                        |222             |
+--------+-------------------------------------------------+----------------+

另一种方法，修改服务端代码

ByteBuf buf= ByteBufAllocator.DEFAULT.buffer();
buf.writeByte('$');
ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,buf));

修改客户端代码

public static StringBuilder makeString(char c, int len) {
    StringBuilder sb = new StringBuilder(len + 2);
    for (int i = 0; i < len; i++) {
        sb.append(c);
    }
    sb.append("$");
    return sb;
}

结果一样

方法4，预设长度LengthFieldBasedFrameDecoder

官方案例：

在这里插入图片描述

lengthFieldoffset：长度字段偏移量
lengthrieldlength：长度字段长度
lengthAdjustment：长度字段为基准，还有几个字节是内容
initialBytosTostrip：从头剥离几个字节

代码

public class TestLengthFieldDecoder {

    public static void main(String[] args) {
        EmbeddedChannel channel = new EmbeddedChannel(
                new LengthFieldBasedFrameDecoder(1024, 0,
                        4, 0, 0),
                new LoggingHandler(LogLevel.DEBUG)
        );

        //  4 个字节的内容长度， 实际内容
        ByteBuf buffer = ByteBufAllocator.DEFAULT.buffer();
        send(buffer, "Hello, world");
        send(buffer, "Hi!");
        log(buffer);
        channel.writeInbound(buffer);
    }

    private static void send(ByteBuf buffer, String content) {
        byte[] bytes = content.getBytes(); // 实际内容
        int length = bytes.length; // 实际内容长度
        buffer.writeInt(length);
        buffer.writeBytes(bytes);
    }
}

结果

16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] REGISTERED
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] ACTIVE
read index:0 write index:23 capacity:256
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 0c 48 65 6c 6c 6f 2c 20 77 6f 72 6c 64 |....Hello, world|
|00000010| 00 00 00 03 48 69 21                            |....Hi!         |
+--------+-------------------------------------------------+----------------+
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 16B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 0c 48 65 6c 6c 6f 2c 20 77 6f 72 6c 64 |....Hello, world|
+--------+-------------------------------------------------+----------------+
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 7B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 03 48 69 21                            |....Hi!         |
+--------+-------------------------------------------------+----------------+
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE