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三. Netty 进阶
三. Netty 进阶
1. 粘包与半包
1.1 粘包现象
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(); } }- 1
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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(); } } }- 1
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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- 1
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1.2 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);- 1
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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);- 1
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- 1
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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
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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
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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
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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
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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
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以太网的 MTU 是 1500
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FDDI（光纤分布式数据接口）的 MTU 是 4352
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本地回环地址的 MTU 是 65535 - 本地测试不走网卡
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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
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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
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TCP 在传递大量数据时，会按照 MSS 大小将数据进行分割发送
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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
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(); } } }- 1
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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
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));- 1
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(); } } }- 1
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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- 1
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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- 1
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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));- 1
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(); } } }- 1
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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- 1
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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- 1
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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
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));- 1
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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(); } } }- 1
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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- 1
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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- 1
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2. 协议设计与解析
2.1 为什么需要协议？
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
例如：在网络上传输
下雨天留客天留我不留- 1
是中文一句著名的无标点符号句子，在没有标点符号情况下，这句话有数种拆解方式，而意思却是完全不同，所以常被用作讲述标点符号的重要性
一种解读
下雨天留客，天留，我不留- 1
另一种解读
下雨天，留客天，留我不？留- 1
如何设计协议呢？其实就是给网络传输的信息加上“标点符号”。但通过分隔符来断句不是很好，因为分隔符本身如果用于传输，那么必须加以区分。因此，下面一种协议较为常用
定长字节表示内容长度 + 实际内容- 1
例如，假设一个中文字符长度为 3，按照上述协议的规则，发送信息方式如下，就不会被接收方弄错意思了
0f下雨天留客06天留09我不留- 1
小故事
很久很久以前，一位私塾先生到一家任教。双方签订了一纸协议：“无鸡鸭亦可无鱼肉亦可白菜豆腐不可少不得束修金”。此后，私塾先生虽然认真教课，但主人家则总是给私塾先生以白菜豆腐为菜，丝毫未见鸡鸭鱼肉的款待。私塾先生先是很不解，可是后来也就想通了：主人把鸡鸭鱼肉的钱都会换为束修金的，也罢。至此双方相安无事。
年关将至，一个学年段亦告结束。私塾先生临行时，也不见主人家为他交付束修金，遂与主家理论。然主家亦振振有词：“有协议为证——无鸡鸭亦可，无鱼肉亦可，白菜豆腐不可少，不得束修金。这白纸黑字明摆着的，你有什么要说的呢？”
私塾先生据理力争：“协议是这样的——无鸡，鸭亦可；无鱼，肉亦可；白菜豆腐不可，少不得束修金。”
双方唇枪舌战，你来我往，真个是不亦乐乎！
这里的束修金，也作“束脩”，应当是泛指教师应当得到的报酬
2.2 redis 协议举例
NioEventLoopGroup worker = new NioEventLoopGroup(); byte[] LINE = {13, 10}; 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()); 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) { set(ctx); get(ctx); } private void get(ChannelHandlerContext ctx) { ByteBuf buf = ctx.alloc().buffer(); buf.writeBytes("*2".getBytes()); buf.writeBytes(LINE); buf.writeBytes("$3".getBytes()); buf.writeBytes(LINE); buf.writeBytes("get".getBytes()); buf.writeBytes(LINE); buf.writeBytes("$3".getBytes()); buf.writeBytes(LINE); buf.writeBytes("aaa".getBytes()); buf.writeBytes(LINE); ctx.writeAndFlush(buf); } private void set(ChannelHandlerContext ctx) { ByteBuf buf = ctx.alloc().buffer(); buf.writeBytes("*3".getBytes()); buf.writeBytes(LINE); buf.writeBytes("$3".getBytes()); buf.writeBytes(LINE); buf.writeBytes("set".getBytes()); buf.writeBytes(LINE); buf.writeBytes("$3".getBytes()); buf.writeBytes(LINE); buf.writeBytes("aaa".getBytes()); buf.writeBytes(LINE); buf.writeBytes("$3".getBytes()); buf.writeBytes(LINE); buf.writeBytes("bbb".getBytes()); buf.writeBytes(LINE); ctx.writeAndFlush(buf); } @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ByteBuf buf = (ByteBuf) msg; System.out.println(buf.toString(Charset.defaultCharset())); } }); } }); ChannelFuture channelFuture = bootstrap.connect("localhost", 6379).sync(); channelFuture.channel().closeFuture().sync(); } catch (InterruptedException e) { log.error("client error", e); } finally { worker.shutdownGracefully(); }- 1
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2.3 http 协议举例
NioEventLoopGroup boss = new NioEventLoopGroup(); 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 HttpServerCodec()); ch.pipeline().addLast(new SimpleChannelInboundHandler<HttpRequest>() { @Override protected void channelRead0(ChannelHandlerContext ctx, HttpRequest msg) throws Exception { // 获取请求 log.debug(msg.uri()); // 返回响应 DefaultFullHttpResponse response = new DefaultFullHttpResponse(msg.protocolVersion(), HttpResponseStatus.OK); byte[] bytes = "Hello, world!
".getBytes(); response.headers().setInt(CONTENT_LENGTH, bytes.length); response.content().writeBytes(bytes); // 写回响应 ctx.writeAndFlush(response); } }); /*ch.pipeline().addLast(new ChannelInboundHandlerAdapter() { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { log.debug("{}", msg.getClass()); if (msg instanceof HttpRequest) { // 请求行，请求头 } else if (msg instanceof HttpContent) { //请求体 } } });*/ } }); ChannelFuture channelFuture = serverBootstrap.bind(8080).sync(); channelFuture.channel().closeFuture().sync(); } catch (InterruptedException e) { log.error("server error", e); } finally { boss.shutdownGracefully(); worker.shutdownGracefully(); }- 1
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2.4 自定义协议要素
- 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
编解码器
根据上面的要素，设计一个登录请求消息和登录响应消息，并使用 Netty 完成收发
@Slf4j public class MessageCodec extends ByteToMessageCodec<Message> { @Override protected void encode(ChannelHandlerContext ctx, 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 ctx, 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); } }- 1
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测试
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); // decode 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);- 1
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解读
💡 什么时候可以加 @Sharable
- 当 handler 不保存状态时，就可以安全地在多线程下被共享
- 但要注意对于编解码器类，不能继承 ByteToMessageCodec 或 CombinedChannelDuplexHandler 父类，他们的构造方法对 @Sharable 有限制
- 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 /** * 必须和 LengthFieldBasedFrameDecoder 一起使用，确保接到的 ByteBuf 消息是完整的 */ public class MessageCodecSharable extends MessageToMessageCodec<ByteBuf, Message> { @Override protected void encode(ChannelHandlerContext ctx, Message msg, List<Object> outList) 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); outList.add(out); } @Override protected void decode(ChannelHandlerContext ctx, 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); } }- 1
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3. 聊天室案例
3.1 聊天室业务介绍
/** * 用户管理接口 */ public interface UserService { /** * 登录 * @param username 用户名 * @param password 密码 * @return 登录成功返回 true, 否则返回 false */ boolean login(String username, String password); }- 1
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/** * 会话管理接口 */ public interface Session { /** * 绑定会话 * @param channel 哪个 channel 要绑定会话 * @param username 会话绑定用户 */ void bind(Channel channel, String username); /** * 解绑会话 * @param channel 哪个 channel 要解绑会话 */ void unbind(Channel channel); /** * 获取属性 * @param channel 哪个 channel * @param name 属性名 * @return 属性值 */ Object getAttribute(Channel channel, String name); /** * 设置属性 * @param channel 哪个 channel * @param name 属性名 * @param value 属性值 */ void setAttribute(Channel channel, String name, Object value); /** * 根据用户名获取 channel * @param username 用户名 * @return channel */ Channel getChannel(String username); }- 1
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/** * 聊天组会话管理接口 */ public interface GroupSession { /** * 创建一个聊天组, 如果不存在才能创建成功, 否则返回 null * @param name 组名 * @param members 成员 * @return 成功时返回组对象, 失败返回 null */ Group createGroup(String name, Set<String> members); /** * 加入聊天组 * @param name 组名 * @param member 成员名 * @return 如果组不存在返回 null, 否则返回组对象 */ Group joinMember(String name, String member); /** * 移除组成员 * @param name 组名 * @param member 成员名 * @return 如果组不存在返回 null, 否则返回组对象 */ Group removeMember(String name, String member); /** * 移除聊天组 * @param name 组名 * @return 如果组不存在返回 null, 否则返回组对象 */ Group removeGroup(String name); /** * 获取组成员 * @param name 组名 * @return 成员集合, 没有成员会返回 empty set */ Set<String> getMembers(String name); /** * 获取组成员的 channel 集合, 只有在线的 channel 才会返回 * @param name 组名 * @return 成员 channel 集合 */ List<Channel> getMembersChannel(String name); }- 1
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3.2 聊天室业务-登录
@Slf4j public class ChatServer { public static void main(String[] args) { NioEventLoopGroup boss = new NioEventLoopGroup(); NioEventLoopGroup worker = new NioEventLoopGroup(); LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG); MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable(); 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 ProcotolFrameDecoder()); ch.pipeline().addLast(LOGGING_HANDLER); ch.pipeline().addLast(MESSAGE_CODEC); ch.pipeline().addLast(new SimpleChannelInboundHandler<LoginRequestMessage>() { @Override protected void channelRead0(ChannelHandlerContext ctx, LoginRequestMessage msg) throws Exception { String username = msg.getUsername(); String password = msg.getPassword(); boolean login = UserServiceFactory.getUserService().login(username, password); LoginResponseMessage message; if(login) { message = new LoginResponseMessage(true, "登录成功"); } else { message = new LoginResponseMessage(false, "用户名或密码不正确"); } ctx.writeAndFlush(message); } }); } }); Channel channel = serverBootstrap.bind(8080).sync().channel(); channel.closeFuture().sync(); } catch (InterruptedException e) { log.error("server error", e); } finally { boss.shutdownGracefully(); worker.shutdownGracefully(); } } }- 1
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@Slf4j public class ChatClient { public static void main(String[] args) { NioEventLoopGroup group = new NioEventLoopGroup(); LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG); MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable(); CountDownLatch WAIT_FOR_LOGIN = new CountDownLatch(1); AtomicBoolean LOGIN = new AtomicBoolean(false); try { Bootstrap bootstrap = new Bootstrap(); bootstrap.channel(NioSocketChannel.class); bootstrap.group(group); bootstrap.handler(new ChannelInitializer<SocketChannel>() { @Override protected void initChannel(SocketChannel ch) throws Exception { ch.pipeline().addLast(new ProcotolFrameDecoder()); // ch.pipeline().addLast(LOGGING_HANDLER); ch.pipeline().addLast(MESSAGE_CODEC); ch.pipeline().addLast("client handler", new ChannelInboundHandlerAdapter() { // 接收响应消息 @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { log.debug("msg: {}", msg); if ((msg instanceof LoginResponseMessage)) { LoginResponseMessage response = (LoginResponseMessage) msg; if (response.isSuccess()) { // 如果登录成功 LOGIN.set(true); } // 唤醒 system in 线程 WAIT_FOR_LOGIN.countDown(); } } // 在连接建立后触发 active 事件 @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { // 负责接收用户在控制台的输入，负责向服务器发送各种消息 new Thread(() -> { Scanner scanner = new Scanner(System.in); System.out.println("请输入用户名:"); String username = scanner.nextLine(); System.out.println("请输入密码:"); String password = scanner.nextLine(); // 构造消息对象 LoginRequestMessage message = new LoginRequestMessage(username, password); // 发送消息 ctx.writeAndFlush(message); System.out.println("等待后续操作..."); try { WAIT_FOR_LOGIN.await(); } catch (InterruptedException e) { e.printStackTrace(); } // 如果登录失败 if (!LOGIN.get()) { ctx.channel().close(); return; } while (true) { System.out.println("=================================="); System.out.println("send [username] [content]"); System.out.println("gsend [group name] [content]"); System.out.println("gcreate [group name] [m1,m2,m3...]"); System.out.println("gmembers [group name]"); System.out.println("gjoin [group name]"); System.out.println("gquit [group name]"); System.out.println("quit"); System.out.println("=================================="); String command = scanner.nextLine(); String[] s = command.split(" "); switch (s[0]){ case "send": ctx.writeAndFlush(new ChatRequestMessage(username, s[1], s[2])); break; case "gsend": ctx.writeAndFlush(new GroupChatRequestMessage(username, s[1], s[2])); break; case "gcreate": Set<String> set = new HashSet<>(Arrays.asList(s[2].split(","))); set.add(username); // 加入自己 ctx.writeAndFlush(new GroupCreateRequestMessage(s[1], set)); break; case "gmembers": ctx.writeAndFlush(new GroupMembersRequestMessage(s[1])); break; case "gjoin": ctx.writeAndFlush(new GroupJoinRequestMessage(username, s[1])); break; case "gquit": ctx.writeAndFlush(new GroupQuitRequestMessage(username, s[1])); break; case "quit": ctx.channel().close(); return; } } }, "system in").start(); } }); } }); Channel channel = bootstrap.connect("localhost", 8080).sync().channel(); channel.closeFuture().sync(); } catch (Exception e) { log.error("client error", e); } finally { group.shutdownGracefully(); } } }- 1
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3.3 聊天室业务-单聊
服务器端将 handler 独立出来
登录 handler
@ChannelHandler.Sharable public class LoginRequestMessageHandler extends SimpleChannelInboundHandler<LoginRequestMessage> { @Override protected void channelRead0(ChannelHandlerContext ctx, LoginRequestMessage msg) throws Exception { String username = msg.getUsername(); String password = msg.getPassword(); boolean login = UserServiceFactory.getUserService().login(username, password); LoginResponseMessage message; if(login) { SessionFactory.getSession().bind(ctx.channel(), username); message = new LoginResponseMessage(true, "登录成功"); } else { message = new LoginResponseMessage(false, "用户名或密码不正确"); } ctx.writeAndFlush(message); } }- 1
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单聊 handler
@ChannelHandler.Sharable public class ChatRequestMessageHandler extends SimpleChannelInboundHandler<ChatRequestMessage> { @Override protected void channelRead0(ChannelHandlerContext ctx, ChatRequestMessage msg) throws Exception { String to = msg.getTo(); Channel channel = SessionFactory.getSession().getChannel(to); // 在线 if(channel != null) { channel.writeAndFlush(new ChatResponseMessage(msg.getFrom(), msg.getContent())); } // 不在线 else { ctx.writeAndFlush(new ChatResponseMessage(false, "对方用户不存在或者不在线")); } } }- 1
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3.4 聊天室业务-群聊
创建群聊
@ChannelHandler.Sharable public class GroupCreateRequestMessageHandler extends SimpleChannelInboundHandler<GroupCreateRequestMessage> { @Override protected void channelRead0(ChannelHandlerContext ctx, GroupCreateRequestMessage msg) throws Exception { String groupName = msg.getGroupName(); Set<String> members = msg.getMembers(); // 群管理器 GroupSession groupSession = GroupSessionFactory.getGroupSession(); Group group = groupSession.createGroup(groupName, members); if (group == null) { // 发生成功消息 ctx.writeAndFlush(new GroupCreateResponseMessage(true, groupName + "创建成功")); // 发送拉群消息 List<Channel> channels = groupSession.getMembersChannel(groupName); for (Channel channel : channels) { channel.writeAndFlush(new GroupCreateResponseMessage(true, "您已被拉入" + groupName)); } } else { ctx.writeAndFlush(new GroupCreateResponseMessage(false, groupName + "已经存在")); } } }- 1
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群聊
@ChannelHandler.Sharable public class GroupChatRequestMessageHandler extends SimpleChannelInboundHandler<GroupChatRequestMessage> { @Override protected void channelRead0(ChannelHandlerContext ctx, GroupChatRequestMessage msg) throws Exception { List<Channel> channels = GroupSessionFactory.getGroupSession() .getMembersChannel(msg.getGroupName()); for (Channel channel : channels) { channel.writeAndFlush(new GroupChatResponseMessage(msg.getFrom(), msg.getContent())); } } }- 1
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加入群聊
@ChannelHandler.Sharable public class GroupJoinRequestMessageHandler extends SimpleChannelInboundHandler<GroupJoinRequestMessage> { @Override protected void channelRead0(ChannelHandlerContext ctx, GroupJoinRequestMessage msg) throws Exception { Group group = GroupSessionFactory.getGroupSession().joinMember(msg.getGroupName(), msg.getUsername()); if (group != null) { ctx.writeAndFlush(new GroupJoinResponseMessage(true, msg.getGroupName() + "群加入成功")); } else { ctx.writeAndFlush(new GroupJoinResponseMessage(true, msg.getGroupName() + "群不存在")); } } }- 1
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退出群聊
@ChannelHandler.Sharable public class GroupQuitRequestMessageHandler extends SimpleChannelInboundHandler<GroupQuitRequestMessage> { @Override protected void channelRead0(ChannelHandlerContext ctx, GroupQuitRequestMessage msg) throws Exception { Group group = GroupSessionFactory.getGroupSession().removeMember(msg.getGroupName(), msg.getUsername()); if (group != null) { ctx.writeAndFlush(new GroupJoinResponseMessage(true, "已退出群" + msg.getGroupName())); } else { ctx.writeAndFlush(new GroupJoinResponseMessage(true, msg.getGroupName() + "群不存在")); } } }- 1
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查看成员
@ChannelHandler.Sharable public class GroupMembersRequestMessageHandler extends SimpleChannelInboundHandler<GroupMembersRequestMessage> { @Override protected void channelRead0(ChannelHandlerContext ctx, GroupMembersRequestMessage msg) throws Exception { Set<String> members = GroupSessionFactory.getGroupSession() .getMembers(msg.getGroupName()); ctx.writeAndFlush(new GroupMembersResponseMessage(members)); } }- 1
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3.5 聊天室业务-退出
@Slf4j @ChannelHandler.Sharable public class QuitHandler extends ChannelInboundHandlerAdapter { // 当连接断开时触发 inactive 事件 @Override public void channelInactive(ChannelHandlerContext ctx) throws Exception { SessionFactory.getSession().unbind(ctx.channel()); log.debug("{} 已经断开", ctx.channel()); } // 当出现异常时触发 @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { SessionFactory.getSession().unbind(ctx.channel()); log.debug("{} 已经异常断开 异常是{}", ctx.channel(), cause.getMessage()); } }- 1
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3.6 聊天室业务-空闲检测
连接假死
原因
- 网络设备出现故障，例如网卡，机房等，底层的 TCP 连接已经断开了，但应用程序没有感知到，仍然占用着资源。
- 公网网络不稳定，出现丢包。如果连续出现丢包，这时现象就是客户端数据发不出去，服务端也一直收不到数据，就这么一直耗着
- 应用程序线程阻塞，无法进行数据读写
问题
- 假死的连接占用的资源不能自动释放
- 向假死的连接发送数据，得到的反馈是发送超时
服务器端解决
- 怎么判断客户端连接是否假死呢？如果能收到客户端数据，说明没有假死。因此策略就可以定为，每隔一段时间就检查这段时间内是否接收到客户端数据，没有就可以判定为连接假死
// 用来判断是不是 读空闲时间过长，或 写空闲时间过长 // 5s 内如果没有收到 channel 的数据，会触发一个 IdleState#READER_IDLE 事件 ch.pipeline().addLast(new IdleStateHandler(5, 0, 0)); // ChannelDuplexHandler 可以同时作为入站和出站处理器 ch.pipeline().addLast(new ChannelDuplexHandler() { // 用来触发特殊事件 @Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception{ IdleStateEvent event = (IdleStateEvent) evt; // 触发了读空闲事件 if (event.state() == IdleState.READER_IDLE) { log.debug("已经 5s 没有读到数据了"); ctx.channel().close(); } } });- 1
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客户端定时心跳
- 客户端可以定时向服务器端发送数据，只要这个时间间隔小于服务器定义的空闲检测的时间间隔，那么就能防止前面提到的误判，客户端可以定义如下心跳处理器
// 用来判断是不是 读空闲时间过长，或 写空闲时间过长 // 3s 内如果没有向服务器写数据，会触发一个 IdleState#WRITER_IDLE 事件 ch.pipeline().addLast(new IdleStateHandler(0, 3, 0)); // ChannelDuplexHandler 可以同时作为入站和出站处理器 ch.pipeline().addLast(new ChannelDuplexHandler() { // 用来触发特殊事件 @Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception{ IdleStateEvent event = (IdleStateEvent) evt; // 触发了写空闲事件 if (event.state() == IdleState.WRITER_IDLE) { // log.debug("3s 没有写数据了，发送一个心跳包"); ctx.writeAndFlush(new PingMessage()); } } });- 1
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- 原文地址：https://blog.csdn.net/u010022158/article/details/125888933
