Netty应用

粘包和半包

服务器代码

public class StudyServer {
    static final Logger log = LoggerFactory.getLogger(StudyServer.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) {
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            // 连接建立时会执行该方法
                            log.debug("connected {}", ctx.channel());
                            super.channelActive(ctx);
                        }

                        @Override
                        public void channelInactive(ChannelHandlerContext ctx) throws Exception {
                            // 连接断开时会执行该方法
                            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());
            // 关闭channel
            channelFuture.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            log.error("server error", e);
        } finally {
            boss.shutdownGracefully();
            worker.shutdownGracefully();
            log.debug("stopped");
        }
    }

    public static void main(String[] args) {
        new StudyServer().start();
    }
}

客户端代码

public class StudyClient {
    static final Logger log = LoggerFactory.getLogger(StudyClient.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("connected...");
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.debug("sending...");
                            // 每次发送16个字节的数据，共发送10次
                            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();
        }
    }
}

输出

7999 [nioEventLoopGroup-3-1] DEBUG io.netty.handler.logging.LoggingHandler  - [id: 0x5b43ecb0, L:/127.0.0.1:8080 - R:/127.0.0.1:53797] 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 |................|
+--------+-------------------------------------------------+----------------+

可见虽然客户端是分别以16字节为单位，通过channel向服务器发送了10次数据，可是服务器端却只接收了一次，接收数据的大小为160B，即客户端发送的数据总大小，这就是粘包现象

半包现象

调整服务器端channel容量

serverBootstrap.option(ChannelOption.SO_RCVBUF, 10);

注意

serverBootstrap.option(ChannelOption.SO_RCVBUF, 10) 影响的是底层接收缓冲区（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

输出

5901 [nioEventLoopGroup-3-1] DEBUG io.netty.handler.logging.LoggingHandler  - [id: 0xc73284f3, L:/127.0.0.1:8080 - R:/127.0.0.1:49679] 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                                     |....            |
+--------+-------------------------------------------------+----------------+

5901 [nioEventLoopGroup-3-1] DEBUG io.netty.handler.logging.LoggingHandler  - [id: 0xc73284f3, L:/127.0.0.1:8080 - R:/127.0.0.1:49679] READ: 40B
         +-------------------------------------------------+
         |  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                         |........        |
+--------+-------------------------------------------------+----------------+

5901 [nioEventLoopGroup-3-1] DEBUG io.netty.handler.logging.LoggingHandler  - [id: 0xc73284f3, L:/127.0.0.1:8080 - R:/127.0.0.1:49679] READ: 40B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 0c 0d 0e 0f 00 01 02 03 04 05 06 07 08 09 0a 0b |................|
|00000010| 0c 0d 0e 0f 00 01 02 03 04 05 06 07 08 09 0a 0b |................|
|00000020| 0c 0d 0e 0f 00 01 02 03                         |........        |
+--------+-------------------------------------------------+----------------+

5901 [nioEventLoopGroup-3-1] DEBUG io.netty.handler.logging.LoggingHandler  - [id: 0xc73284f3, L:/127.0.0.1:8080 - R:/127.0.0.1:49679] READ: 40B
         +-------------------------------------------------+
         |  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                         |........        |
+--------+-------------------------------------------------+----------------+

5901 [nioEventLoopGroup-3-1] DEBUG io.netty.handler.logging.LoggingHandler  - [id: 0xc73284f3, L:/127.0.0.1:8080 - R:/127.0.0.1:49679] READ: 4B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 0c 0d 0e 0f                                     |....            |
+--------+-------------------------------------------------+----------------+

可见客户端每次发送的数据，因channel容量不足，无法将发送的数据一次性接收，便产生了半包现象

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

解决方案

短连接

客户端每次向服务器发送数据以后，就与服务器断开连接，此时的消息边界为连接建立到连接断开。这时便无需使用滑动窗口等技术来缓冲数据，则不会发生粘包现象。但如果一次性数据发送过多，接收方无法一次性容纳所有数据，还是会发生半包现象，所以短链接无法解决半包现象

客户端代码

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();
        }
    }
}

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("localhost", 8080).sync();
            channelFuture.channel().closeFuture().sync();

        } catch (InterruptedException e) {
            log.error("client error", e);
        } finally {
            worker.shutdownGracefully();
        }
    }
}

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:/192.168.0.103:8080] bound...
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:8080 - R:/192.168.0.103:53155] REGISTERED
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:8080 - R:/192.168.0.103:53155] ACTIVE
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0xd739f137, L:/192.168.0.103:8080 - R:/192.168.0.103:53155]
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:8080 - 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

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();
        }
    }
}

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

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

public LengthFieldBasedFrameDecoder(
    int maxFrameLength,
    int lengthFieldOffset, int lengthFieldLength,
    int lengthAdjustment, int initialBytesToStrip)

• maxFrameLength: 数据最大长度
• lengthFieldOffset:长度偏移,用于指明数据第几个字节开始是用于标识有用字节长度的，因为前面可能还有其他附加信息
• lengthFieldLength:长度占用字节,数据中用于表示有用数据长度的标识所占的字节数
• lengthAdjustment:长度调整,用于指明数据长度标识和有用数据之间的距离，因为两者之间还可能有附加信息
• initialBytesToStrip:剥离字节数,读取起点，不读取0 ~ initialBytesToStrip之间的数据
  

通过EmbeddedChannel对 handler 进行测试

@Slf4j
public class Server {
    public static void main(String[] args) {
        EmbeddedChannel channel = new EmbeddedChannel(
                new LengthFieldBasedFrameDecoder(1024, 0, 4, 0, 4),//剥离4个字节
                new LoggingHandler(LogLevel.DEBUG)
        );

        ByteBuf buffer = ByteBufAllocator.DEFAULT.buffer();
        send(buffer,"Hello,World!");
        send(buffer,"Hi!");
        channel.writeInbound(buffer);
    }
    public static void send(ByteBuf buf,String msg){
        byte[] bytes = msg.getBytes();
        int length = bytes.length;
        buf.writeInt(length);
        buf.writeBytes(bytes);
    }
}

输出

2023-04-08 21:50:22.929 [main] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 12B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 65 6c 6c 6f 2c 57 6f 72 6c 64 21             |Hello,World!    |
+--------+-------------------------------------------------+----------------+
2023-04-08 21:50:22.929 [main] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 3B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 69 21                                        |Hi!             |
+--------+-------------------------------------------------+----------------+
2023-04-08 21:50:22.929 [main] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE

测试2

@Slf4j
public class Server2 {
    public static void main(String[] args) {
        EmbeddedChannel channel = new EmbeddedChannel(
                new LengthFieldBasedFrameDecoder(1024, 0, 4, 1, 4),//长度与实际数据之间的其他数据长度为1
                new LoggingHandler(LogLevel.DEBUG)
        );

        ByteBuf buffer = ByteBufAllocator.DEFAULT.buffer();
        send(buffer,"Hello,World!");
        send(buffer,"Hi!");
        channel.writeInbound(buffer);
    }
    public static void send(ByteBuf buf,String msg){
        byte[] bytes = msg.getBytes();
        int length = bytes.length;
        buf.writeInt(length);
        buf.writeByte(1);
        buf.writeBytes(bytes);
    }
}

输出

2023-04-08 21:53:12.424 [main] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 13B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 01 48 65 6c 6c 6f 2c 57 6f 72 6c 64 21          |.Hello,World!   |
+--------+-------------------------------------------------+----------------+
2023-04-08 21:53:12.425 [main] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 4B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 01 48 69 21                                     |.Hi!            |
+--------+-------------------------------------------------+----------------+
2023-04-08 21:53:12.425 [main] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE

协议设计与解析

协议的作用

TCP/IP 中消息传输基于流的方式，没有边界

协议的目的就是划定消息的边界，制定通信双方要共同遵守的通信规则

Redis协议

如果我们要向Redis服务器发送一条set name zss的指令，需要遵守如下协议

// 该指令一共有3部分，每条指令之后都要添加回车与换行符
*3\r\n
// 第一个指令的长度是3
$3\r\n
// 第一个指令是set指令
set\r\n
// 下面的指令以此类推
$4\r\n
name\r\n
$5\r\n
zss\r\n

代码

public class RedisClient {
    static final Logger log = LoggerFactory.getLogger(StudyServer.class);
    public static void main(String[] args) {
        NioEventLoopGroup group =  new NioEventLoopGroup();
        try {
            ChannelFuture channelFuture = new Bootstrap()
                    .group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) {
                            // 打印日志
                            ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                            ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                                @Override
                                public void channelActive(ChannelHandlerContext ctx) throws Exception {
                                    // 回车与换行符
                                    final byte[] LINE = {'\r','\n'};
                                    // 获得ByteBuf
                                    ByteBuf buffer = ctx.alloc().buffer();
                                    // 连接建立后，向Redis中发送一条指令，注意添加回车与换行
                                    // set name Nyima
                                    buffer.writeBytes("*3".getBytes());
                                    buffer.writeBytes(LINE);
                                    buffer.writeBytes("$3".getBytes());
                                    buffer.writeBytes(LINE);
                                    buffer.writeBytes("set".getBytes());
                                    buffer.writeBytes(LINE);
                                    buffer.writeBytes("$4".getBytes());
                                    buffer.writeBytes(LINE);
                                    buffer.writeBytes("name".getBytes());
                                    buffer.writeBytes(LINE);
                                    buffer.writeBytes("$5".getBytes());
                                    buffer.writeBytes(LINE);
                                    buffer.writeBytes("zss".getBytes());
                                    buffer.writeBytes(LINE);
                                    ctx.writeAndFlush(buffer);
                                }

                            });
                        }
                    })
                    .connect(new InetSocketAddress("localhost", 6379));
            channelFuture.sync();
            // 关闭channel
            channelFuture.channel().close().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            // 关闭group
            group.shutdownGracefully();
        }
    }
}

输出

1600 [nioEventLoopGroup-2-1] DEBUG io.netty.handler.logging.LoggingHandler  - [id: 0x28c994f1, L:/127.0.0.1:60792 - R:localhost/127.0.0.1:6379] WRITE: 34B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 2a 33 0d 0a 24 33 0d 0a 73 65 74 0d 0a 24 34 0d |*3..$3..set..$4.|
|00000010| 0a 6e 61 6d 65 0d 0a 24 35 0d 0a 4e 79 69 6d 61 |.name..$5..zss|
|00000020| 0d 0a                                           |..              |
+--------+-------------------------------------------------+----------------+

HTTP协议

HTTP协议在请求行请求头中都有很多的内容，自己实现较为困难，可以使用HttpServerCodec作为服务器端的解码器与编码器，来处理HTTP请求

// HttpServerCodec 中既有请求的解码器 HttpRequestDecoder 又有响应的编码器 HttpResponseEncoder
// Codec(CodeCombine) 一般代表该类既作为 编码器 又作为 解码器
public final class HttpServerCodec extends CombinedChannelDuplexHandler<HttpRequestDecoder, HttpResponseEncoder>
        implements HttpServerUpgradeHandler.SourceCodec

服务器端代码

package com.vmware.netty.http;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.http.*;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;

import java.nio.charset.Charset;

import static io.netty.handler.codec.http.HttpHeaderNames.CONTENT_LENGTH;

@Slf4j
public class HttpServer {
    public static void main(String[] args) {
        new ServerBootstrap()
                .group(new NioEventLoopGroup())
                .channel(NioServerSocketChannel.class)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        socketChannel.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
                        socketChannel.pipeline().addLast(new HttpServerCodec());
                        //可以使用SimpleChannelInboundHandler处理指定类型的请求
                        socketChannel.pipeline().addLast(new SimpleChannelInboundHandler<HttpRequest>() {
                            @Override
                            protected void channelRead0(ChannelHandlerContext channelHandlerContext, HttpRequest httpRequest) throws Exception {
                                String uri = httpRequest.uri();
                                log.info("uri:{}",uri);
                                DefaultFullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK);
                                byte[] bytes = "<h1>Hello,Netty!</h1>".getBytes(Charset.defaultCharset());
                                response.headers().setInt(CONTENT_LENGTH,bytes.length);
                                response.content().writeBytes(bytes);
                                channelHandlerContext.writeAndFlush(response);
                            }
                        });
                    }
                })
                .bind(8888);
    }
}

服务器负责处理请求并响应浏览器。所以只需要处理HTTP请求即可

ch.pipeline().addLast(new SimpleChannelInboundHandler<HttpRequest>()

获得请求后，需要返回响应给浏览器。需要创建响应对象DefaultFullHttpResponse，设置HTTP版本号及状态码，为避免浏览器获得响应后，因为获得CONTENT_LENGTH而一直空转，需要添加CONTENT_LENGTH字段，表明响应体中数据的具体长度

[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-cH228fyJ-1680981721651)(img/http.png)]

2023-04-08 22:46:08.395 [nioEventLoopGroup-2-2] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0x31176e79, L:/[0:0:0:0:0:0:0:1]:8888 - R:/[0:0:0:0:0:0:0:1]:47158] READ: 602B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 47 45 54 20 2f 66 61 76 69 63 6f 6e 2e 69 63 6f |GET /favicon.ico|
|00000010| 20 48 54 54 50 2f 31 2e 31 0d 0a 48 6f 73 74 3a | HTTP/1.1..Host:|
|00000020| 20 6c 6f 63 61 6c 68 6f 73 74 3a 38 38 38 38 0d | localhost:8888.|
|00000030| 0a 43 6f 6e 6e 65 63 74 69 6f 6e 3a 20 6b 65 65 |.Connection: kee|
|00000040| 70 2d 61 6c 69 76 65 0d 0a 73 65 63 2d 63 68 2d |p-alive..sec-ch-|
|00000050| 75 61 3a 20 22 47 6f 6f 67 6c 65 20 43 68 72 6f |ua: "Google Chro|
|00000060| 6d 65 22 3b 76 3d 22 31 31 31 22 2c 20 22 4e 6f |me";v="111", "No|
|00000070| 74 28 41 3a 42 72 61 6e 64 22 3b 76 3d 22 38 22 |t(A:Brand";v="8"|
|00000080| 2c 20 22 43 68 72 6f 6d 69 75 6d 22 3b 76 3d 22 |, "Chromium";v="|
|00000090| 31 31 31 22 0d 0a 73 65 63 2d 63 68 2d 75 61 2d |111"..sec-ch-ua-|
|000000a0| 6d 6f 62 69 6c 65 3a 20 3f 30 0d 0a 55 73 65 72 |mobile: ?0..User|
|000000b0| 2d 41 67 65 6e 74 3a 20 4d 6f 7a 69 6c 6c 61 2f |-Agent: Mozilla/|
|000000c0| 35 2e 30 20 28 58 31 31 3b 20 4c 69 6e 75 78 20 |5.0 (X11; Linux |
|000000d0| 78 38 36 5f 36 34 29 20 41 70 70 6c 65 57 65 62 |x86_64) AppleWeb|
|000000e0| 4b 69 74 2f 35 33 37 2e 33 36 20 28 4b 48 54 4d |Kit/537.36 (KHTM|
|000000f0| 4c 2c 20 6c 69 6b 65 20 47 65 63 6b 6f 29 20 43 |L, like Gecko) C|
|00000100| 68 72 6f 6d 65 2f 31 31 31 2e 30 2e 30 2e 30 20 |hrome/111.0.0.0 |
|00000110| 53 61 66 61 72 69 2f 35 33 37 2e 33 36 0d 0a 73 |Safari/537.36..s|
|00000120| 65 63 2d 63 68 2d 75 61 2d 70 6c 61 74 66 6f 72 |ec-ch-ua-platfor|
|00000130| 6d 3a 20 22 4c 69 6e 75 78 22 0d 0a 41 63 63 65 |m: "Linux"..Acce|
|00000140| 70 74 3a 20 69 6d 61 67 65 2f 61 76 69 66 2c 69 |pt: image/avif,i|
|00000150| 6d 61 67 65 2f 77 65 62 70 2c 69 6d 61 67 65 2f |mage/webp,image/|
|00000160| 61 70 6e 67 2c 69 6d 61 67 65 2f 73 76 67 2b 78 |apng,image/svg+x|
|00000170| 6d 6c 2c 69 6d 61 67 65 2f 2a 2c 2a 2f 2a 3b 71 |ml,image/*,*/*;q|
|00000180| 3d 30 2e 38 0d 0a 53 65 63 2d 46 65 74 63 68 2d |=0.8..Sec-Fetch-|
|00000190| 53 69 74 65 3a 20 73 61 6d 65 2d 6f 72 69 67 69 |Site: same-origi|
|000001a0| 6e 0d 0a 53 65 63 2d 46 65 74 63 68 2d 4d 6f 64 |n..Sec-Fetch-Mod|
|000001b0| 65 3a 20 6e 6f 2d 63 6f 72 73 0d 0a 53 65 63 2d |e: no-cors..Sec-|
|000001c0| 46 65 74 63 68 2d 44 65 73 74 3a 20 69 6d 61 67 |Fetch-Dest: imag|
|000001d0| 65 0d 0a 52 65 66 65 72 65 72 3a 20 68 74 74 70 |e..Referer: http|
|000001e0| 3a 2f 2f 6c 6f 63 61 6c 68 6f 73 74 3a 38 38 38 |://localhost:888|
|000001f0| 38 2f 69 6e 64 65 78 2e 68 74 6d 6c 0d 0a 41 63 |8/index.html..Ac|
|00000200| 63 65 70 74 2d 45 6e 63 6f 64 69 6e 67 3a 20 67 |cept-Encoding: g|
|00000210| 7a 69 70 2c 20 64 65 66 6c 61 74 65 2c 20 62 72 |zip, deflate, br|
|00000220| 0d 0a 41 63 63 65 70 74 2d 4c 61 6e 67 75 61 67 |..Accept-Languag|
|00000230| 65 3a 20 65 6e 2d 55 53 2c 65 6e 3b 71 3d 30 2e |e: en-US,en;q=0.|
|00000240| 39 2c 7a 68 2d 43 4e 3b 71 3d 30 2e 38 2c 7a 68 |9,zh-CN;q=0.8,zh|
|00000250| 3b 71 3d 30 2e 37 0d 0a 0d 0a                   |;q=0.7....      |
+--------+-------------------------------------------------+----------------+
2023-04-08 22:46:08.395 [nioEventLoopGroup-2-2] INFO  com.vmware.netty.http.HttpServer - uri:/favicon.ico
2023-04-08 22:46:08.396 [nioEventLoopGroup-2-2] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0x31176e79, L:/[0:0:0:0:0:0:0:1]:8888 - R:/[0:0:0:0:0:0:0:1]:47158] WRITE: 60B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b 0d |HTTP/1.1 200 OK.|
|00000010| 0a 63 6f 6e 74 65 6e 74 2d 6c 65 6e 67 74 68 3a |.content-length:|
|00000020| 20 32 31 0d 0a 0d 0a 3c 68 31 3e 48 65 6c 6c 6f | 21....<h1>Hello|
|00000030| 2c 4e 65 74 74 79 21 3c 2f 68 31 3e             |,Netty!</h1>    |
+--------+-------------------------------------------------+----------------+
2023-04-08 22:46:08.396 [nioEventLoopGroup-2-2] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0x31176e79, L:/[0:0:0:0:0:0:0:1]:8888 - R:/[0:0:0:0:0:0:0:1]:47158] FLUSH

自定义协议

协议组成要素

• 魔数，用来在第一时间判定是否是无效数据包
• 版本号，可以支持协议的升级
• 序列化算法，消息正文到底采用哪种序列化反序列化方式，可以由此扩展，例如：json、protobuf、hessian、jdk
• 指令类型，是登录、注册、单聊、群聊… 跟业务相关
• 请求序号，为了双工通信，提供异步能力
• 正文长度
• 消息正文

编码器与解码器

@Slf4j
public class MessageCodec extends ByteToMessageCodec<Message> {
    @Override
    protected void encode(ChannelHandlerContext channelHandlerContext, Message msg, ByteBuf out) throws Exception {
        // 1. 4 字节的魔数
        out.writeBytes(new byte[]{1, 2, 3, 4});
        // 2. 1 字节的版本,
        out.writeByte(1);
        // 3. 1 字节的序列化方式 jdk 0 , json 1
        out.writeByte(0);
        // 4. 1 字节的指令类型
        out.writeByte(msg.getMessageType());
        // 5. 4 个字节
        out.writeInt(msg.getSequenceId());
        // 无意义，对齐填充
        out.writeByte(0xff);
        // 6. 获取内容的字节数组
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(msg);
        byte[] bytes = bos.toByteArray();
        // 7. 长度
        out.writeInt(bytes.length);
        // 8. 写入内容
        out.writeBytes(bytes);
    }

    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf in, List<Object> out) throws Exception {
        int magicNum = in.readInt();
        byte version = in.readByte();
        byte serializerType = in.readByte();
        byte messageType = in.readByte();
        int sequenceId = in.readInt();
        in.readByte();
        int length = in.readInt();
        byte[] bytes = new byte[length];
        in.readBytes(bytes, 0, length);
        ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bytes));
        Message message = (Message) ois.readObject();
        log.debug("{}, {}, {}, {}, {}, {}", magicNum, version, serializerType, messageType, sequenceId, length);
        log.debug("{}", message);
        out.add(message);
    }
}

• 编码器与解码器方法源于父类ByteToMessageCodec，通过该类可以自定义编码器与解码器，泛型类型为被编码与被解码的类

• 编码器负责将附加信息与正文信息写入到ByteBuf中，其中附加信息总字节数最好为2n，不足需要补齐。正文内容如果为对象，需要通过序列化将其放入到ByteBuf中
• 解码器负责将ByteBuf中的信息取出，并放入List中，该List用于将信息传递给下一个handler

测试

public class MessageCodecTest {
    public static void main(String[] args) throws Exception {
        EmbeddedChannel channel = new EmbeddedChannel(
                new LoggingHandler(),
                new LengthFieldBasedFrameDecoder(
                        1024, 12, 4, 0, 0),
                new MessageCodec()
        );
        //encode
        LoginRequestMessage message = new LoginRequestMessage("zhangSan", "123", "张三");
        //channel.writeOutbound(message);
        //decodejava
        ByteBuf buf = ByteBufAllocator.DEFAULT.buffer();
        new MessageCodec().encode(null, message, buf);

        ByteBuf s1 = buf.slice(0, 100);
        ByteBuf s2 = buf.slice(100, buf.readableBytes() - 100);
        s1.retain(); // 引用计数 2
        channel.writeInbound(s1); // release 1
        channel.writeInbound(s2);

    }
}

结果

什么时候可以加Shareable?

为了提高handler的复用率，可以将handler创建为handler对象，然后在不同的channel中使用该handler对象进行处理操作

LoggingHandler loggingHandler = new LoggingHandler(LogLevel.DEBUG);
// 不同的channel中使用同一个handler对象，提高复用率
channel1.pipeline().addLast(loggingHandler);
channel2.pipeline().addLast(loggingHandler);

是并不是所有的handler都能通过这种方法来提高复用率的，例如LengthFieldBasedFrameDecoder。如果多个channel中使用同一个LengthFieldBasedFrameDecoder对象，则可能发生如下问题

• channel1中收到了一个半包，LengthFieldBasedFrameDecoder发现不是一条完整的数据，则没有继续向下传播
• 此时channel2中也收到了一个半包，因为两个channel使用了同一个LengthFieldBasedFrameDecoder，存入其中的数据刚好拼凑成了一个完整的数据包。LengthFieldBasedFrameDecoder让该数据包继续向下传播，最终引发错误

为了提高handler的复用率，同时又避免出现一些并发问题，Netty中原生的handler中用@Sharable注解来标明，该handler能否在多个channel中共享。

只有带有该注解，才能通过对象的方式被共享，否则无法被共享

自定义编解码器能否使用@Sharable注解?

如果我们的MessageCodec本身接收的是LengthFieldBasedFrameDecoder处理之后的数据，那么数据肯定是完整的，按分析来说是可以添加@Sharable注解的

但是实际情况我们并不能添加该注解，会抛出异常信息ChannelHandler cn.nyimac.study.day8.protocol.MessageCodec is not allowed to be shared

• 因为MessageCodec继承自ByteToMessageCodec，ByteToMessageCodec类的注解如下
  

这就意味着ByteToMessageCodec不能被多个channel所共享的

• 原因：因为该类的目标是：将ByteBuf转化为Message，意味着传进该handler的数据还未被处理过。所以传过来的ByteBuf可能并不是完整的数据，如果共享则会出现问题

解决方案

如果能确保编解码器不会保存状态，可以继承 MessageToMessageCodec 父类

@Slf4j
@ChannelHandler.Sharable
public class MessageCodecShareable extends MessageToMessageCodec<ByteBuf, Message> {
    @Override
    protected void encode(ChannelHandlerContext ctx, Message msg, List<Object> list) throws Exception {
        ByteBuf out = ctx.alloc().buffer();
        // 1. 4 字节的魔数
        out.writeBytes(new byte[]{1, 2, 3, 4});
        // 2. 1 字节的版本,
        out.writeByte(1);
        // 3. 1 字节的序列化方式 jdk 0 , json 1
        out.writeByte(0);
        // 4. 1 字节的指令类型
        out.writeByte(msg.getMessageType());
        // 5. 4 个字节
        out.writeInt(msg.getSequenceId());
        // 无意义，对齐填充
        out.writeByte(0xff);
        // 6. 获取内容的字节数组
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(msg);
        byte[] bytes = bos.toByteArray();
        // 7. 长度
        out.writeInt(bytes.length);
        // 8. 写入内容
        out.writeBytes(bytes);
        list.add(out);
    }

    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf in, List<Object> out) throws Exception {
        int magicNum = in.readInt();
        byte version = in.readByte();
        byte serializerType = in.readByte();
        byte messageType = in.readByte();
        int sequenceId = in.readInt();
        in.readByte();
        int length = in.readInt();
        byte[] bytes = new byte[length];
        in.readBytes(bytes, 0, length);
        ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bytes));
        Message message = (Message) ois.readObject();
        log.debug("{}, {}, {}, {}, {}, {}", magicNum, version, serializerType, messageType, sequenceId, length);
        log.debug("{}", message);
        out.add(message);
    }
}