我正在参加「掘金·启航计划」,结合上一章,讲解Netty 的协议设计
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Netty 协议设计 （Settlement）
1. 粘包与半包
1.1 粘包现象
服务器代码
public class Server1 {
public static void main(String[] args) {
NioEventLoopGroup boss = new NioEventLoopGroup();
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.channel(NioServerSocketChannel.class);
bootstrap.group(boss,worker);
// 调整 netty 缓冲区的大小, (byteBuf) 最低就是 16byte
//bootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR, new AdaptiveRecvByteBufAllocator(16,16,16));
bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new LoggingHandler(LogLevel.DEBUG));
}
});
ChannelFuture channelFuture = bootstrap.bind(9999).sync();
channelFuture.channel().closeFuture().sync();
}catch (Exception e){
e.printStackTrace();
}finally {
boss.shutdownGracefully();
worker.shutdownGracefully();
}
}
客户端代码希望发送 10 个消息，每个消息是 18 字节
public class Client1 {
static final Logger log = LoggerFactory.getLogger(Client1.class);
public static void main(String[] args) throws InterruptedException {
extracted();
System.out.println("finish");
}
private static void extracted() {
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.channel(NioSocketChannel.class);
bootstrap.group(worker);
bootstrap.handler(new ChannelInitializer<NioSocketChannel>() {
@Override
protected void initChannel(NioSocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
// channelActive 会在连接建立后触发
pipeline.addLast(new ChannelInboundHandlerAdapter(){
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
for (int i = 0; i < 10; i++) {
ByteBuf buf = ctx.alloc().buffer(16);
buf.writeBytes(new byte[]{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17});
ctx.writeAndFlush(buf);
}
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect(new InetSocketAddress(9999)).sync();
} catch (Exception e){
e.printStackTrace();
}finally {
worker.shutdownGracefully();
}
}
服务器的某次输出，可以看到一次就接收了 180 个字节，而非分 10 次接收
22:52:49 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x390ea221, L:/172.17.64.1:9999 - R:/172.17.64.1:53555] REGISTERED
22:52:49 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x390ea221, L:/172.17.64.1:9999 - R:/172.17.64.1:53555] ACTIVE
22:52:49 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x390ea221, L:/172.17.64.1:9999 - R:/172.17.64.1:53555] READ: 180B
+-------------------------------------------------+
| 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| 10 11 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d |................|
|00000020| 0e 0f 10 11 00 01 02 03 04 05 06 07 08 09 0a 0b |................|
|00000030| 0c 0d 0e 0f 10 11 00 01 02 03 04 05 06 07 08 09 |................|
|00000040| 0a 0b 0c 0d 0e 0f 10 11 00 01 02 03 04 05 06 07 |................|
|00000050| 08 09 0a 0b 0c 0d 0e 0f 10 11 00 01 02 03 04 05 |................|
|00000060| 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 00 01 02 03 |................|
|00000070| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 00 01 |................|
|00000080| 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 |................|
|00000090| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|000000a0| 10 11 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d |................|
|000000b0| 0e 0f 10 11 |.... |
+--------+-------------------------------------------------+----------------+
22:52:49 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x390ea221, L:/172.17.64.1:9999 - R:/172.17.64.1:53555] READ COMPLETE
22:52:49 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x390ea221, L:/172.17.64.1:9999 - R:/172.17.64.1:53555] READ COMPLETE
22:52:49 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x390ea221, L:/172.17.64.1:9999 ! R:/172.17.64.1:53555] INACTIVE
22:52:49 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x390ea221, L:/172.17.64.1:9999 ! R:/172.17.64.1:53555] UNREGISTERED
1.2 半包现象
客户端代码希望发送 1 个消息，这个消息是 180 字节，代码改为
ByteBuf buf = ctx.alloc().buffer(16);
for (int i = 0; i < 10; i++) {
buf.writeBytes(new byte[]{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17});
}
ctx.writeAndFlush(buf);
为现象明显，服务器修改一下接收缓冲区，其他代码不变
bootstrap.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 160 字节
23:05:48 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xf0b2af7e, L:/172.17.64.1:9999 - R:/172.17.64.1:54488] REGISTERED
23:05:48 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xf0b2af7e, L:/172.17.64.1:9999 - R:/172.17.64.1:54488] ACTIVE
23:05:48 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xf0b2af7e, L:/172.17.64.1:9999 - R:/172.17.64.1:54488] 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| 10 11 00 01 |.... |
+--------+-------------------------------------------------+----------------+
23:05:48 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xf0b2af7e, L:/172.17.64.1:9999 - R:/172.17.64.1:54488] READ COMPLETE
23:05:48 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xf0b2af7e, L:/172.17.64.1:9999 - R:/172.17.64.1:54488] READ: 160B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 |................|
|00000010| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000020| 10 11 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d |................|
|00000030| 0e 0f 10 11 00 01 02 03 04 05 06 07 08 09 0a 0b |................|
|00000040| 0c 0d 0e 0f 10 11 00 01 02 03 04 05 06 07 08 09 |................|
|00000050| 0a 0b 0c 0d 0e 0f 10 11 00 01 02 03 04 05 06 07 |................|
|00000060| 08 09 0a 0b 0c 0d 0e 0f 10 11 00 01 02 03 04 05 |................|
|00000070| 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 00 01 02 03 |................|
|00000080| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 00 01 |................|
|00000090| 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 |................|
+--------+-------------------------------------------------+----------------+
23:05:48 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xf0b2af7e, L:/172.17.64.1:9999 - R:/172.17.64.1:54488] READ COMPLETE
注意
bootstrap.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>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.debug("conneted...");
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.debug("sending...");
ByteBuf buffer = ctx.alloc().buffer();
buffer.writeBytes(new byte[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15});
ctx.writeAndFlush(buffer);
// 发完即关
ctx.close();
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect("localhost", 8080).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
log.error("client error", e);
} finally {
worker.shutdownGracefully();
}
}
}
输出，略
半包用这种办法还是不好解决，因为接收方的缓冲区大小是有限的
方法2，固定长度
让所有数据包长度固定（假设长度为 8 字节），服务器端加入
ch.pipeline().addLast(new FixedLengthFrameDecoder(8));
客户端测试代码，注意, 采用这种方法后，客户端什么时候 flush 都可以
public class HelloWorldClient {
static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
public static void main(String[] args) {
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.channel(NioSocketChannel.class);
bootstrap.group(worker);
bootstrap.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.debug("connetted...");
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.debug("sending...");
// 发送内容随机的数据包
Random r = new Random();
char c = 'a';
ByteBuf buffer = ctx.alloc().buffer();
for (int i = 0; i < 10; i++) {
byte[] bytes = new byte[8];
for (int j = 0; j < r.nextInt(8); j++) {
bytes[j] = (byte) c;
}
c++;
buffer.writeBytes(bytes);
}
ctx.writeAndFlush(buffer);
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
log.error("client error", e);
} finally {
worker.shutdownGracefully();
}
}
}
客户端输出
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2] REGISTERED
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2] CONNECT: /192.168.0.103:9090
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] ACTIVE
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] WRITE: 80B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 61 61 61 00 00 00 00 62 00 00 00 00 00 00 00 |aaaa....b.......|
|00000010| 63 63 00 00 00 00 00 00 64 00 00 00 00 00 00 00 |cc......d.......|
|00000020| 00 00 00 00 00 00 00 00 66 66 66 66 00 00 00 00 |........ffff....|
|00000030| 67 67 67 00 00 00 00 00 68 00 00 00 00 00 00 00 |ggg.....h.......|
|00000040| 69 69 69 69 69 00 00 00 6a 6a 6a 6a 00 00 00 00 |iiiii...jjjj....|
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] FLUSH
服务端输出
12:06:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xe3d9713f] binding...
12:06:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xe3d9713f, L:/192.168.0.103:9090] bound...
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] REGISTERED
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] ACTIVE
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155]
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 61 61 61 00 00 00 00 |aaaa.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 00 00 00 00 00 00 00 |b....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 63 63 00 00 00 00 00 00 |cc...... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 64 00 00 00 00 00 00 00 |d....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 00 00 00 00 00 |........ |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 66 66 66 66 00 00 00 00 |ffff.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 67 67 67 00 00 00 00 00 |ggg..... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 00 00 00 00 00 00 00 |h....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 69 69 69 69 00 00 00 |iiiii... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6a 6a 6a 6a 00 00 00 00 |jjjj.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ COMPLETE
缺点是，数据包的大小不好把握
- 长度定的太大，浪费
- 长度定的太小，对某些数据包又显得不够
方法3，固定分隔符
服务端加入，默认以 \n 或 \r\n 作为分隔符，如果超出指定长度仍未出现分隔符，则抛出异常
ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
客户端在每条消息之后，加入 \n 分隔符
public class HelloWorldClient {
static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
public static void main(String[] args) {
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.channel(NioSocketChannel.class);
bootstrap.group(worker);
bootstrap.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.debug("connetted...");
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.debug("sending...");
Random r = new Random();
char c = 'a';
ByteBuf buffer = ctx.alloc().buffer();
for (int i = 0; i < 10; i++) {
for (int j = 1; j <= r.nextInt(16)+1; j++) {
buffer.writeByte((byte) c);
}
buffer.writeByte(10);
c++;
}
ctx.writeAndFlush(buffer);
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
log.error("client error", e);
} finally {
worker.shutdownGracefully();
}
}
}
客户端输出
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755] REGISTERED
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755] CONNECT: /192.168.0.103:9090
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] ACTIVE
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] WRITE: 60B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 0a 62 62 62 0a 63 63 63 0a 64 64 0a 65 65 65 |a.bbb.ccc.dd.eee|
|00000010| 65 65 65 65 65 65 65 0a 66 66 0a 67 67 67 67 67 |eeeeeee.ff.ggggg|
|00000020| 67 67 0a 68 68 68 68 0a 69 69 69 69 69 69 69 0a |gg.hhhh.iiiiiii.|
|00000030| 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 0a |jjjjjjjjjjj. |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] FLUSH
服务端输出
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] c.i.n.HelloWorldServer - connected [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641]
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 1B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 |a |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 3B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 62 62 |bbb |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 3B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 63 63 63 |ccc |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 2B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 64 64 |dd |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 10B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 65 65 65 65 65 65 65 65 65 65 |eeeeeeeeee |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 2B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 66 66 |ff |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 7B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 67 67 67 67 67 67 67 |ggggggg |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 4B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 68 68 68 |hhhh |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 7B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 69 69 69 69 69 69 |iiiiiii |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 11B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a |jjjjjjjjjjj |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ COMPLETE
缺点，处理字符数据比较合适，但如果内容本身包含了分隔符（字节数据常常会有此情况），那么就会解析错误
方法4，预设长度
在发送消息前，先约定用定长字节表示接下来数据的长度
// 最大长度，长度偏移，长度占用字节，长度调整，剥离字节数
ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 1, 0, 1));
客户端代码
public class HelloWorldClient {
static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
public static void main(String[] args) {
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.channel(NioSocketChannel.class);
bootstrap.group(worker);
bootstrap.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.debug("connetted...");
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.debug("sending...");
Random r = new Random();
char c = 'a';
ByteBuf buffer = ctx.alloc().buffer();
for (int i = 0; i < 10; i++) {
byte length = (byte) (r.nextInt(16) + 1);
// 先写入长度
buffer.writeByte(length);
// 再
for (int j = 1; j <= length; j++) {
buffer.writeByte((byte) c);
}
c++;
}
ctx.writeAndFlush(buffer);
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
log.error("client error", e);
} finally {
worker.shutdownGracefully();
}
}
}
客户端输出
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8] REGISTERED
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8] CONNECT: /192.168.0.103:9090
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] ACTIVE
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] WRITE: 97B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 09 61 61 61 61 61 61 61 61 61 09 62 62 62 62 62 |.aaaaaaaaa.bbbbb|
|00000010| 62 62 62 62 06 63 63 63 63 63 63 08 64 64 64 64 |bbbb.cccccc.dddd|
|00000020| 64 64 64 64 0f 65 65 65 65 65 65 65 65 65 65 65 |dddd.eeeeeeeeeee|
|00000030| 65 65 65 65 0d 66 66 66 66 66 66 66 66 66 66 66 |eeee.fffffffffff|
|00000040| 66 66 02 67 67 02 68 68 0e 69 69 69 69 69 69 69 |ff.gg.hh.iiiiiii|
|00000050| 69 69 69 69 69 69 69 09 6a 6a 6a 6a 6a 6a 6a 6a |iiiiiii.jjjjjjjj|
|00000060| 6a |j |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xf0f347b8, L:/192.168.0.103:49979 - R:/192.168.0.103:9090] FLUSH
服务端输出
14:36:50 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xdff439d3] binding...
14:36:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xdff439d3, L:/192.168.0.103:9090] bound...
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] REGISTERED
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] ACTIVE
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979]
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 61 61 61 61 61 61 61 61 |aaaaaaaaa |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 62 62 62 62 62 62 62 62 |bbbbbbbbb |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 6B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 63 63 63 63 63 63 |cccccc |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 8B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 64 64 64 64 64 64 64 64 |dddddddd |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 15B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 |eeeeeeeeeeeeeee |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 13B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 66 66 66 66 66 66 66 66 66 66 66 66 66 |fffffffffffff |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 2B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 67 67 |gg |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 2B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 68 |hh |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 14B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 69 69 69 69 69 69 69 69 69 69 69 69 69 |iiiiiiiiiiiiii |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ: 9B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6a 6a 6a 6a 6a 6a 6a 6a 6a |jjjjjjjjj |
+--------+-------------------------------------------------+----------------+
14:37:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x744f2b47, L:/192.168.0.103:9090 - R:/192.168.0.103:49979] READ COMPLETE
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
是中文一句著名的无标点符号的句子，在没有标点符号的情况下，这句话有数种拆解方式，而意思却是完全不同的，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？其实协议本质上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，发送信息的方式如下，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
2.2 redis 协议举例
package com.aodi.test.decode;
import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.logging.LoggingHandler;
import java.nio.charset.Charset;
/**
* @author: aodi.smile
* @create: 2022-07-15 21:14
**/
public class TestRedis {
/*
set name zhangsan
*3 数组的长度 set:1 name:1 zhangsan:1
$3 set 的长度 3
set
$4 key 的长度 name 长度 4
name
$8 value 的长度 zhangsan 长度 8
zhangsan
*/
public static void main(String[] args) {
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) throws Exception {
ch.pipeline().addLast(new LoggingHandler());
ch.pipeline().addLast(new ChannelInboundHandlerAdapter(){
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
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("$4".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("name".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("$8".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("zhangsan".getBytes());
buf.writeBytes(LINE);
ctx.writeAndFlush(buf);
//super.channelActive(ctx);
}
});
ch.pipeline().addLast(new ChannelInboundHandlerAdapter(){
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
ByteBuf buf = (ByteBuf) msg;
System.out.println(buf.toString(Charset.defaultCharset()));
//super.channelRead(ctx, msg);
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect("192.168.123.182", 6379).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
worker.shutdownGracefully();
}
}
}
2.3 http协议举例
package com.aodi.test.decode;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.http.DefaultFullHttpResponse;
import io.netty.handler.codec.http.HttpRequest;
import io.netty.handler.codec.http.HttpResponseStatus;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;
import static io.netty.handler.codec.http.HttpHeaderNames.CONTENT_LENGTH;
/**
* @author: aodi.smile
* @create: 2022-07-15 22:19
**/
@Slf4j
public class TestHttp {
public static void main(String[] args) {
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));
// Http 编解码器
ch.pipeline().addLast(new HttpServerCodec());
ch.pipeline().addLast(new SimpleChannelInboundHandler<HttpRequest>() {
@Override
protected void channelRead0(ChannelHandlerContext ctx, HttpRequest msg) {
// 获取请求
log.debug("{}",msg.uri());
// 返回响应
DefaultFullHttpResponse response = new DefaultFullHttpResponse(msg.protocolVersion(), HttpResponseStatus.OK);
byte[] bytes = "<h1>SUCCESS</h1>".getBytes();
response.headers().setInt(CONTENT_LENGTH, bytes.length);
response.content().writeBytes(bytes);
// 写回响应
ctx.writeAndFlush(response);
}
});
}
});
ChannelFuture channelFuture = serverBootstrap.bind(9999).sync();
channelFuture.channel().closeFuture().sync();
} catch (Exception e) {
e.printStackTrace();
} finally {
boss.shutdownGracefully();
worker.shutdownGracefully();
}
}
}
自定义协议要素
- 魔数，用来在第一时间判断是否是无效数据包，相当于数据的密码
- 版本号，可以支持协议的升级
- 序列化算法，消息正文到底采用那种序列化反序列化的方式，可以由此扩展，例如：json、protobuf、hessian、jdk
- 指令类似，是登录，注册，单聊，群聊，跟业务相关的操作
- 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
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
package com.aodi.protocol;
import com.aodi.message.Message;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageCodec;
import lombok.extern.slf4j.Slf4j;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.List;
@Slf4j
public class MessageCodec extends ByteToMessageCodec<Message> {
@Override
public 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);
}
}
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
什么时候可以加 @Sharable
- 当 Handler 不保存状态时，就可以安全的在多线程下被共享
- 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
package com.aodi.protocol;
import com.aodi.client.config.Config;
import com.aodi.message.Message;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToMessageCodec;
import lombok.extern.slf4j.Slf4j;
import java.util.List;
@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(Config.getSerializerAlgorithm().ordinal());
// 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
byte[] bytes = Config.getSerializerAlgorithm().serialize(msg);
// 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);
Object deserialize = Serializer.Algorithm.values()[serializerType].deserialize(Message.getMessageClass(messageType), bytes);
log.debug("{}, {}, {}, {}, {}, {}", magicNum, version, serializerType, messageType, sequenceId, length);
log.debug("deserialize.{}", deserialize);
out.add(deserialize);
}
}
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);
}
/**
* 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);
}
/**
* 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);
}
3.2 聊天室业务-登录
package com.aodi.server;
import com.aodi.protocol.MessageCodecSharable;
import com.aodi.protocol.ProcotolFrameDecoder;
import com.aodi.server.handler.*;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.timeout.IdleState;
import io.netty.handler.timeout.IdleStateEvent;
import io.netty.handler.timeout.IdleStateHandler;
import lombok.extern.slf4j.Slf4j;
@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();
LoginRequestMessageHandler LOGIN_HANDLER = new LoginRequestMessageHandler();
ChatRequestMessageHandler CHAT_HANDLER = new ChatRequestMessageHandler();
GroupCreateHandler GROUP_CRATE_HANDLER = new GroupCreateHandler();
GroupChatHandler GROUP_CHAT_HANDLER = new GroupChatHandler();
GroupJoinHandler GROUP_JOIN_HANDLER = new GroupJoinHandler();
GroupRemoveHandler GROUP_REMOVE_HANDLER = new GroupRemoveHandler();
QuitHandler QUIT_HANDLER = new QuitHandler();
GroupMembersHandler GROUP_MEMBERS_HANDLER = new GroupMembersHandler();
PingHandler PING_HANDLER = new PingHandler();
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(MESSAGE_CODEC);
ch.pipeline().addLast(LOGIN_HANDLER);
ch.pipeline().addLast(CHAT_HANDLER);
ch.pipeline().addLast(GROUP_CRATE_HANDLER);
ch.pipeline().addLast(GROUP_CHAT_HANDLER);
ch.pipeline().addLast(GROUP_JOIN_HANDLER);
ch.pipeline().addLast(GROUP_REMOVE_HANDLER);
ch.pipeline().addLast(QUIT_HANDLER);
ch.pipeline().addLast(GROUP_MEMBERS_HANDLER);
ch.pipeline().addLast(PING_HANDLER);
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
super.channelActive(ctx);
}
});
Channel channel = serverBootstrap.bind(8080).sync().channel();
channel.closeFuture().sync();
} catch (InterruptedException e) {
log.error("server error", e);
} finally {
boss.shutdownGracefully();
worker.shutdownGracefully();
}
}
}
package com.aodi.client;
import com.aodi.message.*;
import com.aodi.protocol.MessageCodecSharable;
import com.aodi.protocol.ProcotolFrameDecoder;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.timeout.IdleState;
import io.netty.handler.timeout.IdleStateEvent;
import io.netty.handler.timeout.IdleStateHandler;
import lombok.extern.slf4j.Slf4j;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicBoolean;
@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(MESSAGE_CODEC);
ch.pipeline().addLast(new ChannelInboundHandlerAdapter(){
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
log.debug("msg:{}",msg);
if (msg instanceof LoginResponseMessage) {
LoginResponseMessage message = (LoginResponseMessage) msg;
if (message.isSuccess()) {
// 登录成功
LOGIN.set(true);
}
// 唤醒系统线程
WAIT_FOR_LOGIN.countDown();
}
if (msg instanceof ChatResponseMessage) {
ChatResponseMessage message = (ChatResponseMessage) msg;
log.debug("{}:{}",message.getFrom(),message.getContent());
}
if (msg instanceof GroupChatResponseMessage) {
GroupChatResponseMessage message = (GroupChatResponseMessage) msg;
log.debug("{}->{}:{}",message.getGroupName(),message.getFrom(),message.getContent());
}
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.debug("连接已建立");
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();
LoginRequestMessage message = new LoginRequestMessage(userName, passWord);
ctx.writeAndFlush(message);
try {
WAIT_FOR_LOGIN.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
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 menu = scanner.nextLine();
String[] option = menu.split(" ");
switch (option[0]) {
case "send":
ctx.writeAndFlush(new ChatRequestMessage(userName,option[1],option[2]));
break;
case "gsend":
ctx.writeAndFlush(new GroupChatRequestMessage(userName,option[1],option[2]));
break;
case "gcreate":
Set<String> set = new HashSet<>(Arrays.asList(option[2].split(",")));
set.add(userName);
ctx.writeAndFlush(new GroupCreateRequestMessage(option[1],set));
break;
case "gmembers":
ctx.writeAndFlush(new GroupMembersRequestMessage(option[1]));
break;
case "gjoin":
ctx.writeAndFlush(new GroupJoinRequestMessage(userName,option[1]));
break;
case "gquit":
ctx.writeAndFlush(new GroupQuitRequestMessage(userName,option[1]));
break;
case "quit":
ctx.channel().close();
return;
}
}
},"input,stream").start();
}
});
}
});
Channel channel = bootstrap.connect("localhost", 8080).sync().channel();
channel.closeFuture().sync();
} catch (Exception e) {
log.error("client error", e);
} finally {
group.shutdownGracefully();
}
}
}
3.3 聊天室业务-单聊
服务器端将 handler 独立出来
登录 handler
/**
* login handler
* @author: aodi.smile
* @create: 2022-07-19 20:37
**/
@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);
if (login) {
// 用户 与 通道绑定
SessionFactory.getSession().bind(ctx.channel(),username);
LoginResponseMessage message = new LoginResponseMessage(true, "登录成功！");
ctx.writeAndFlush(message);
} else {
LoginResponseMessage message = new LoginResponseMessage(false, "用户名或密码错误");
ctx.writeAndFlush(message);
}
}
}
单聊 handler
/**
* @author: aodi.smile
* @create: 2022-07-19 20:41
**/
@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);
// 离线
if (channel == null) {
ctx.writeAndFlush(new ChatResponseMessage(false,"对方不存在,或已离线"));
return;
} else {
// 在线
channel.writeAndFlush(new ChatResponseMessage(msg.getFrom(),msg.getContent()));
}
}
}
3.3 + 1 聊天室业务-群聊
创建群聊
/**
* @author: aodi.smile
* @create: 2022-07-19 21:25
**/
@ChannelHandler.Sharable
public class GroupCreateHandler extends SimpleChannelInboundHandler<GroupCreateRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupCreateRequestMessage msg) throws Exception {
String groupName = msg.getGroupName();
Set<String> members = msg.getMembers();
Group group = GroupSessionFactory.getGroupSession().createGroup(groupName, members);
if (group == null) {
ctx.writeAndFlush(new GroupCreateResponseMessage(true,groupName + ":创建成功"));
List<Channel> channels = GroupSessionFactory.getGroupSession().getMembersChannel(groupName);
channels.forEach(channel -> channel.writeAndFlush(new GroupCreateResponseMessage(true,"您已被拉入" + groupName + "群聊")));
} else {
ctx.writeAndFlush(new GroupCreateResponseMessage(false,groupName + "群聊已存在"));
}
}
}
群聊天
/**
* @author: aodi.smile
* @create: 2022-07-19 21:32
**/
@ChannelHandler.Sharable
public class GroupChatHandler extends SimpleChannelInboundHandler<GroupChatRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupChatRequestMessage msg) throws Exception {
String groupName = msg.getGroupName();
List<Channel> channels = GroupSessionFactory.getGroupSession().getMembersChannel(groupName);
channels.forEach(channel -> channel.writeAndFlush(new GroupChatResponseMessage(msg.getFrom(),msg.getContent(),groupName)));
}
}
加入群聊
@ChannelHandler.Sharable
public class GroupJoinHandler extends SimpleChannelInboundHandler<GroupJoinRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupJoinRequestMessage msg) throws Exception {
String groupName = msg.getGroupName();
Group group = GroupSessionFactory.getGroupSession().joinMember(groupName, msg.getUsername());
// ctx.writeAndFlush(new GroupJoinResponseMessage(true,msg.getUsername() + "加入群聊"));
if (group != null) {
List<Channel> channels = GroupSessionFactory.getGroupSession().getMembersChannel(groupName);
channels.forEach(channel -> channel.writeAndFlush(new GroupJoinResponseMessage(true,msg.getUsername() + "加入群聊")));
}
}
}
退出群聊
@ChannelHandler.Sharable
public class GroupRemoveHandler extends SimpleChannelInboundHandler<GroupQuitRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupQuitRequestMessage msg) throws Exception {
String groupName = msg.getGroupName();
GroupSession groupSession = GroupSessionFactory.getGroupSession();
Group group = groupSession.removeMember(groupName, msg.getUsername());
if (group != null) {
List<Channel> channels = groupSession.getMembersChannel(groupName);
channels.forEach(channel -> channel.writeAndFlush(new GroupQuitResponseMessage(true,msg.getUsername() + "退出群聊" + groupName)));
}
}
}
查看成员
@Slf4j
@ChannelHandler.Sharable
public class GroupMembersHandler extends SimpleChannelInboundHandler<GroupMembersRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupMembersRequestMessage msg) throws Exception {
String groupName = msg.getGroupName();
Set<String> members = GroupSessionFactory.getGroupSession().getMembers(groupName);
ctx.writeAndFlush(new GroupMembersResponseMessage(members));
}
}
3.5 聊天室业务-退出
@Slf4j
@ChannelHandler.Sharable
public class QuitHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
SessionFactory.getSession().unbind(ctx.channel());
log.debug("{} 已断开连接",ctx.channel());
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
SessionFactory.getSession().unbind(ctx.channel());
log.debug("{} 已异常断开连接 {}",ctx.channel(),cause.getMessage());
}
}
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，但是应用程序没有感知，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送不出去，服务端也一直收不到数据，就那么一直耗着
- 应用程序线程阻塞，无法进行数据读写
问题
- 假死的链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，如果能收到客户端数据，说明没有假死。因此策略就可以定义为，每隔一段时间就检查这段时间内有没有接受到客户端数据，这个策略就叫 【心跳】
// readerIdleTimeSeconds: 超过指定时间未读取到数据
// writerIdleTimeSeconds: 超过指定时间未写入数据
// allIdleTimeSeconds: 超过读和写的总时间
ch.pipeline().addLast(new IdleStateHandler(22,0,0));
ch.pipeline().addLast(new ChannelDuplexHandler(){
@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.READER_IDLE) {
log.debug("20s 没有接受到客户端数据");
}
}
});
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时间间隔，那么就能有效防止前面提到的误判，客户端可以定义如下心跳处理器
// 20 秒, 向服务器发送一个心跳包
// readerIdleTimeSeconds: 超过指定时间未读取到数据
// writerIdleTimeSeconds: 超过指定时间未写入数据
// allIdleTimeSeconds: 超过读和写的总时间
ch.pipeline().addLast(new IdleStateHandler(0,20,0));
ch.pipeline().addLast(new ChannelDuplexHandler(){
@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.WRITER_IDLE) {
ctx.writeAndFlush(new PingMessage());
}
}
});
