【Netty-进阶】学习笔记
2024-05-30 23:18:25
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>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("connected {}", ctx.channel());super.channelActive(ctx);}@Overridepublic void channelInactive(ChannelHandlerContext ctx) throws Exception {log.debug("disconnect {}", ctx.channel());super.channelInactive(ctx);}});}});ChannelFuture channelFuture = serverBootstrap.bind(8080);log.debug("{} binding...", channelFuture.channel());channelFuture.sync();log.debug("{} bound...", channelFuture.channel());channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("server error", e);} finally {boss.shutdownGracefully();worker.shutdownGracefully();log.debug("stoped");}}public static void main(String[] args) {new HelloWorldServer().start();}
}
客户端代码希望发送 10 个消息，每个消息是 16 字节
public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);public static void main(String[] args) {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connetted...");ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");Random r = new Random();char c = 'a';for (int i = 0; i < 10; i++) {ByteBuf buffer = ctx.alloc().buffer();buffer.writeBytes(new byte[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15});ctx.writeAndFlush(buffer);}}});}});ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}
服务器端的某次输出，可以看到一次就接收了 160 个字节，而非分 10 次接收
08:24:46 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0x81e0fda5] binding...
08:24:46 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0x81e0fda5, L:/0:0:0:0:0:0:0:0:8080] bound...
08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] REGISTERED
08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] ACTIVE
08:24:55 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177]
08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] READ: 160B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000010| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000020| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000030| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000040| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000050| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000060| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000070| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000080| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000090| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
+--------+-------------------------------------------------+----------------+
08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] READ COMPLETE
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);
为现象明显，服务端修改一下接收缓冲区，其它代码不变
serverBootstrap.option(ChannelOption.SO_RCVBUF, 10);
服务器端的某次输出，可以看到接收的消息被分为两节，第一次 20 字节，第二次 140 字节
08:43:49 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0x4d6c6a84] binding...
08:43:49 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0x4d6c6a84, L:/0:0:0:0:0:0:0:0:8080] bound...
08:44:23 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] REGISTERED
08:44:23 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] ACTIVE
08:44:23 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221]
08:44:24 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] READ: 20B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000010| 00 01 02 03 |.... |
+--------+-------------------------------------------------+----------------+
08:44:24 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] READ COMPLETE
08:44:24 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] READ: 140B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000010| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000020| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000030| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000040| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000050| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000060| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000070| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000080| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |............ |
+--------+-------------------------------------------------+----------------+
08:44:24 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x1719abf7, L:/127.0.0.1:8080 - R:/127.0.0.1:59221] READ COMPLETE
注意
serverBootstrap.option(ChannelOption.SO_RCVBUF, 10) 影响的底层接收缓冲区（即滑动窗口）大小，仅决定了 netty 读取的最小单位，netty 实际每次读取的一般是它的整数倍
1.3 现象分析
粘包
- 现象，发送 abc def，接收 abcdef
- 原因
- 应用层：接收方 ByteBuf 设置太大（Netty 默认 1024）
- 滑动窗口：假设发送方 256 bytes 表示一个完整报文，但由于接收方处理不及时且窗口大小足够大，这 256 bytes 字节就会缓冲在接收方的滑动窗口中，当滑动窗口中缓冲了多个报文就会粘包
- Nagle 算法：会造成粘包
半包
- 现象，发送 abcdef，接收 abc def
- 原因
- 应用层：接收方 ByteBuf 小于实际发送数据量
- 滑动窗口：假设接收方的窗口只剩了 128 bytes，发送方的报文大小是 256 bytes，这时放不下了，只能先发送前 128 bytes，等待 ack 后才能发送剩余部分，这就造成了半包
- MSS 限制：当发送的数据超过 MSS 限制后，会将数据切分发送，就会造成半包
本质是因为 TCP 是流式协议，消息无边界
滑动窗口
- TCP 以一个段（segment）为单位，每发送一个段就需要进行一次确认应答（ack）处理，但如果这么做，缺点是包的往返时间越长性能就越差
为了解决此问题，引入了窗口概念，窗口大小即决定了无需等待应答而可以继续发送的数据最大值
窗口实际就起到一个缓冲区的作用，同时也能起到流量控制的作用
- 图中深色的部分即要发送的数据，高亮的部分即窗口
- 窗口内的数据才允许被发送，当应答未到达前，窗口必须停止滑动
- 如果 1001~2000 这个段的数据 ack 回来了，窗口就可以向前滑动
- 接收方也会维护一个窗口，只有落在窗口内的数据才能允许接收
MSS 限制
链路层对一次能够发送的最大数据有限制，这个限制称之为 MTU（maximum transmission unit），不同的链路设备的 MTU 值也有所不同，例如
以太网的 MTU 是 1500
FDDI（光纤分布式数据接口）的 MTU 是 4352
本地回环地址的 MTU 是 65535 - 本地测试不走网卡
MSS 是最大段长度（maximum segment size），它是 MTU 刨去 tcp 头和 ip 头后剩余能够作为数据传输的字节数
ipv4 tcp 头占用 20 bytes，ip 头占用 20 bytes，因此以太网 MSS 的值为 1500 - 40 = 1460
TCP 在传递大量数据时，会按照 MSS 大小将数据进行分割发送
MSS 的值在三次握手时通知对方自己 MSS 的值，然后在两者之间选择一个小值作为 MSS
Nagle 算法
- 即使发送一个字节，也需要加入 tcp 头和 ip 头，也就是总字节数会使用 41 bytes，非常不经济。因此为了提高网络利用率，tcp 希望尽可能发送足够大的数据，这就是 Nagle 算法产生的缘由
- 该算法是指发送端即使还有应该发送的数据，但如果这部分数据很少的话，则进行延迟发送
- 如果 SO_SNDBUF 的数据达到 MSS，则需要发送
- 如果 SO_SNDBUF 中含有 FIN（表示需要连接关闭）这时将剩余数据发送，再关闭
- 如果 TCP_NODELAY = true，则需要发送
- 已发送的数据都收到 ack 时，则需要发送
- 上述条件不满足，但发生超时（一般为 200ms）则需要发送
- 除上述情况，延迟发送
1.4 解决方案
- 短链接，发一个包建立一次连接，这样连接建立到连接断开之间就是消息的边界，缺点效率太低
- 每一条消息采用固定长度，缺点浪费空间
- 每一条消息采用分隔符，例如 \n，缺点需要转义
- 每一条消息分为 head 和 body，head 中包含 body 的长度
方法1，短链接
以解决粘包为例
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>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("conneted...");ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");ByteBuf buffer = ctx.alloc().buffer();buffer.writeBytes(new byte[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15});ctx.writeAndFlush(buffer);// 发完即关ctx.close();}});}});ChannelFuture channelFuture = bootstrap.connect("localhost", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}
输出，略
半包用这种办法还是不好解决，因为接收方的缓冲区大小是有限的
方法2，固定长度
让所有数据包长度固定（假设长度为 8 字节），服务器端加入
ch.pipeline().addLast(new FixedLengthFrameDecoder(8));
客户端测试代码，注意, 采用这种方法后，客户端什么时候 flush 都可以
public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);public static void main(String[] args) {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connetted...");ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");// 发送内容随机的数据包Random r = new Random();char c = 'a';ByteBuf buffer = ctx.alloc().buffer();for (int i = 0; i < 10; i++) {byte[] bytes = new byte[8];for (int j = 0; j < r.nextInt(8); j++) {bytes[j] = (byte) c;}c++;buffer.writeBytes(bytes);}ctx.writeAndFlush(buffer);}});}});ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}
客户端输出
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2] REGISTERED
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2] CONNECT: /192.168.0.103:9090
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] ACTIVE
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] WRITE: 80B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 61 61 61 00 00 00 00 62 00 00 00 00 00 00 00 |aaaa....b.......|
|00000010| 63 63 00 00 00 00 00 00 64 00 00 00 00 00 00 00 |cc......d.......|
|00000020| 00 00 00 00 00 00 00 00 66 66 66 66 00 00 00 00 |........ffff....|
|00000030| 67 67 67 00 00 00 00 00 68 00 00 00 00 00 00 00 |ggg.....h.......|
|00000040| 69 69 69 69 69 00 00 00 6a 6a 6a 6a 00 00 00 00 |iiiii...jjjj....|
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] FLUSH
服务端输出
12:06:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xe3d9713f] binding...
12:06:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xe3d9713f, L:/192.168.0.103:9090] bound...
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] REGISTERED
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] ACTIVE
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155]
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 61 61 61 00 00 00 00 |aaaa.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 00 00 00 00 00 00 00 |b....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 63 63 00 00 00 00 00 00 |cc...... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 64 00 00 00 00 00 00 00 |d....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 00 00 00 00 00 |........ |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 66 66 66 66 00 00 00 00 |ffff.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 67 67 67 00 00 00 00 00 |ggg..... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 00 00 00 00 00 00 00 |h....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 69 69 69 69 00 00 00 |iiiii... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6a 6a 6a 6a 00 00 00 00 |jjjj.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ COMPLETE
缺点是，数据包的大小不好把握
- 长度定的太大，浪费
- 长度定的太小，对某些数据包又显得不够
方法3，固定分隔符
服务端加入，默认以 \n 或 \r\n 作为分隔符，如果超出指定长度仍未出现分隔符，则抛出异常
ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
客户端在每条消息之后，加入 \n 分隔符
public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);public static void main(String[] args) {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connetted...");ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");Random r = new Random();char c = 'a';ByteBuf buffer = ctx.alloc().buffer();for (int i = 0; i < 10; i++) {for (int j = 1; j <= r.nextInt(16)+1; j++) {buffer.writeByte((byte) c);}buffer.writeByte(10);c++;}ctx.writeAndFlush(buffer);}});}});ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}
客户端输出
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755] REGISTERED
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755] CONNECT: /192.168.0.103:9090
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] ACTIVE
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] WRITE: 60B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 0a 62 62 62 0a 63 63 63 0a 64 64 0a 65 65 65 |a.bbb.ccc.dd.eee|
|00000010| 65 65 65 65 65 65 65 0a 66 66 0a 67 67 67 67 67 |eeeeeee.ff.ggggg|
|00000020| 67 67 0a 68 68 68 68 0a 69 69 69 69 69 69 69 0a |gg.hhhh.iiiiiii.|
|00000030| 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 0a |jjjjjjjjjjj. |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] FLUSH
服务端输出
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] c.i.n.HelloWorldServer - connected [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641]
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 1B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 |a |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 3B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 62 62 |bbb |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 3B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 63 63 63 |ccc |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 2B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 64 64 |dd |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 10B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 65 65 65 65 65 65 65 65 65 65 |eeeeeeeeee |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 2B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 66 66 |ff |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 7B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 67 67 67 67 67 67 67 |ggggggg |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 4B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 68 68 68 |hhhh |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 7B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 69 69 69 69 69 69 |iiiiiii |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 11B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a |jjjjjjjjjjj |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ COMPLETE
缺点，处理字符数据比较合适，但如果内容本身包含了分隔符（字节数据常常会有此情况），那么就会解析错误
方法4，预设长度
在发送消息前，先约定用定长字节表示接下来数据的长度
// 最大长度，长度偏移，长度占用字节，长度调整，剥离字节数
ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 1, 0, 1));
客户端代码
public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);public static void main(String[] args) {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connetted...");ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");Random r = new Random();char c = 'a';ByteBuf buffer = ctx.alloc().buffer();for (int i = 0; i < 10; i++) {byte length = (byte) (r.nextInt(16) + 1);// 先写入长度buffer.writeByte(length);// 再for (int j = 1; j <= length; j++) {buffer.writeByte((byte) c);}c++;}ctx.writeAndFlush(buffer);}});}});ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}
客户端输出
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8] REGISTERED
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8] CONNECT: /192.168.0.103:9090
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] ACTIVE
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] WRITE: 97B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 09 61 61 61 61 61 61 61 61 61 09 62 62 62 62 62 |.aaaaaaaaa.bbbbb|
|00000010| 62 62 62 62 06 63 63 63 63 63 63 08 64 64 64 64 |bbbb.cccccc.dddd|
|00000020| 64 64 64 64 0f 65 65 65 65 65 65 65 65 65 65 65 |dddd.eeeeeeeeeee|
|00000030| 65 65 65 65 0d 66 66 66 66 66 66 66 66 66 66 66 |eeee.fffffffffff|
|00000040| 66 66 02 67 67 02 68 68 0e 69 69 69 69 69 69 69 |ff.gg.hh.iiiiiii|
|00000050| 69 69 69 69 69 69 69 09 6a 6a 6a 6a 6a 6a 6a 6a |iiiiiii.jjjjjjjj|
|00000060| 6a |j |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] FLUSH
服务端输出
14:36:50 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xdff439d3] binding...
14:36:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xdff439d3, L:/192.168.0.103:9090] bound...
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] REGISTERED
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] ACTIVE
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979]
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 61 61 61 61 61 61 61 61 |aaaaaaaaa |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 62 62 62 62 62 62 62 62 |bbbbbbbbb |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 6B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 63 63 63 63 63 63 |cccccc |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 64 64 64 64 64 64 64 64 |dddddddd |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 15B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 |eeeeeeeeeeeeeee |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 13B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 66 66 66 66 66 66 66 66 66 66 66 66 66 |fffffffffffff |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 2B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 67 67 |gg |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 2B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 68 |hh |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 14B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 69 69 69 69 69 69 69 69 69 69 69 69 69 |iiiiiiiiiiiiii |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6a 6a 6a 6a 6a 6a 6a 6a 6a |jjjjjjjjj |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ COMPLETE2. 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
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
另一种解读
下雨天，留客天，留我不？留
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
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
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>() {@Overrideprotected 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@Overridepublic 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);}@Overridepublic 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();
}
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>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new HttpServerCodec());ch.pipeline().addLast(new SimpleChannelInboundHandler<HttpRequest>() {@Overrideprotected 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 = "<h1>Hello, world!</h1>".getBytes();response.headers().setInt(CONTENT_LENGTH, bytes.length);response.content().writeBytes(bytes);// 写回响应ctx.writeAndFlush(response);}});/*ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic 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();
}
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> {@Overrideprotected 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 1out.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);}@Overrideprotected 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);}
}
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);
解读
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