一、黏包与半包
1. 黏包现象演示
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();}}}
打印结果
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] REGISTERED08:24:55 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x94132411, L:/127.0.0.1:8080 - R:/127.0.0.1:58177] ACTIVE08:24:55 [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
2. 半包现象演示
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
补充
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
3. 现象分析
1. 黏包
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
2. 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
3. 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
4. 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
5. 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
6. 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
方案一：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();
}
}
}
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
方案二：固定长度
服务器端加入下面处理器，让所有数据包长度固定（假设长度为 8 字节）
ch.pipeline().addLast(new FixedLengthFrameDecoder(8));
客户端测试代码，注意, 采用这种方法后，客户端什么时候 flush 都可以
public class HelloWorldClient {
static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);
public static void main(String[] args) {
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.channel(NioSocketChannel.class);
bootstrap.group(worker);
bootstrap.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.debug("connetted...");
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.debug("sending...");
// 发送内容随机的数据包
Random r = new Random();
char c = 'a';
ByteBuf buffer = ctx.alloc().buffer();
for (int i = 0; i < 10; i++) {
byte[] bytes = new byte[8];
for (int j = 0; j < r.nextInt(8); j++) {
bytes[j] = (byte) c;
}
c++;
buffer.writeBytes(bytes);
}
ctx.writeAndFlush(buffer);
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect("localhost", 8080).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
log.error("client error", e);
} finally {
worker.shutdownGracefully();
}
}
}
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: /localhost:8080
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/localhost:53155 - R:/localhost:8080] 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:/localhost:53155 - R:/localhost:8080] 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:/localhost:53155 - R:/localhost:8080] 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
方案三：固定分隔符
服务端加入，默认以 \n 或 \r\n 作为分隔符，如果超出指定长度仍未出现分隔符，则抛出异常
ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
客户端在每条消息之后，加入 \n 分隔符
@Slf4j
public class nianBaoBanBaoClient {
public static void main(String[] args) {
send();
System.out.println("finish");
}
public static StringBuilder makeString(char c, int len) {
StringBuilder sb = new StringBuilder(len + 2);
for (int i = 0; i < len; i++) {
sb.append(c);
}
sb.append("\n");
return sb;
}
private static void send() {
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 {
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
// 会在连接 channel 建立成功后，会触发 active 事件
@Override
public void channelActive(ChannelHandlerContext ctx) {
ByteBuf buf = ctx.alloc().buffer();
char c = '0';
Random r = new Random();
for (int i = 0; i < 10; i++) {
StringBuilder sb = makeString(c, r.nextInt(256) + 1);
c++;
buf.writeBytes(sb.toString().getBytes());
}
ctx.writeAndFlush(buf);
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8080).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
log.error("client error", e);
} finally {
worker.shutdownGracefully();
}
}
}
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
方案四：预设长度
io.netty.handler.codec.LengthFieldBasedFrameDecoder 官方案例
参数解析
- lengthFieldoffset：长度字段偏移量
- lengthFieldLength：长度字段长度
- lengthAdjustment：长度字段为基准，还有几个字节是内容
- initialBytesTostrip：从头剥离几个字节
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
二、协议与解析
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. Redis协议举例
@Slf4j
public class RedisAgreementClient {
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) {
ch.pipeline().addLast(new LoggingHandler());
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
// 会在连接 channel 建立成功后，会触发 active 事件
@Override
public void channelActive(ChannelHandlerContext ctx) {
set(ctx);
get(ctx);
}
private void get(ChannelHandlerContext ctx) {
ByteBuf buf = ctx.alloc().buffer();
buf.writeBytes("*2".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("$3".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("get".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("$3".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("aaa".getBytes());
buf.writeBytes(LINE);
ctx.writeAndFlush(buf);
}
private void set(ChannelHandlerContext ctx) {
ByteBuf buf = ctx.alloc().buffer();
buf.writeBytes("*3".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("$3".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("set".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("$3".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("aaa".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("$3".getBytes());
buf.writeBytes(LINE);
buf.writeBytes("bbb".getBytes());
buf.writeBytes(LINE);
ctx.writeAndFlush(buf);
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
ByteBuf buf = (ByteBuf) msg;
System.out.println(buf.toString(Charset.defaultCharset()));
}
});
}
});
ChannelFuture channelFuture = bootstrap.connect("localhost", 6379).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
log.error("client error", e);
} finally {
worker.shutdownGracefully();
}
}
}
开启客户端后查看Redis中的key
3. Http协议举例
import io.netty.bootstrap.Bootstrap;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.http.*;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;
import java.nio.charset.StandardCharsets;
@Slf4j
public class HttpServer {
public static void main(String[] args) {
new ServerBootstrap()
.group(new NioEventLoopGroup())
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<NioSocketChannel>() {
@Override
protected void initChannel(NioSocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new LoggingHandler(LogLevel.DEBUG));
pipeline.addLast(new HttpServerCodec());
//SimpleChannelInboundHandler<HttpRequest>：仅处理请求行、请求头中的内容
pipeline.addLast(new SimpleChannelInboundHandler<HttpRequest>() {
/*@Override
protected void channelRead0(ChannelHandlerContext ctx, HttpContent msg) throws Exception {
System.out.println(msg.content());
}*/
@Override
protected void channelRead0(ChannelHandlerContext ctx, HttpRequest msg) throws Exception {
log.debug(msg.getClass().toString());
log.debug(msg.uri());
DefaultFullHttpResponse response = new DefaultFullHttpResponse(msg.protocolVersion(), HttpResponseStatus.OK);
byte[] bytes = "<h1>Hello World</h1>".getBytes(StandardCharsets.UTF_8);
response.headers().setInt(HttpHeaderNames.CONTENT_LENGTH, bytes.length);
response.content().writeBytes(bytes);
ctx.writeAndFlush(response);
}
});
pipeline.addLast(new SimpleChannelInboundHandler<HttpContent>() {
@Override
protected void channelRead0(ChannelHandlerContext ctx, HttpContent msg) throws Exception {
System.out.println(msg.content());
}
});
}
})
.bind("localhost", 8080);
}
}
向服务端发起请求
查看控制台打印
15:06:34 [DEBUG] [nioEventLoopGroup-2-5] i.n.h.l.LoggingHandler - [id: 0xe4b33518, L:/127.0.0.1:8080 - R:/127.0.0.1:10557] READ: 1002B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 47 45 54 20 2f 69 6e 64 65 78 20 48 54 54 50 2f |GET /index HTTP/|
|00000010| 31 2e 31 0d 0a 78 2d 61 75 74 68 2d 74 6f 6b 65 |1.1..x-auth-toke|
|00000020| 6e 3a 20 65 79 4a 68 62 47 63 69 4f 69 4a 49 55 |n: eyJhbGciOiJIU|
|00000030| 7a 49 31 4e 69 4a 39 2e 65 79 4a 7a 64 57 49 69 |zI1NiJ9.eyJzdWIi|
|00000040| 4f 69 4a 48 54 55 59 69 4c 43 4a 68 64 58 52 6f |OiJHTUYiLCJhdXRo|
|00000050| 49 6a 70 62 65 79 4a 79 62 32 78 6c 53 57 51 69 |IjpbeyJyb2xlSWQi|
|00000060| 4f 6a 45 73 49 6e 4a 76 62 47 56 4f 59 57 31 6c |OjEsInJvbGVOYW1l|
|00000070| 49 6a 6f 69 35 37 4f 37 35 37 75 66 35 36 36 68 |Ijoi57O757uf566h|
|00000080| 35 35 43 47 35 5a 47 59 49 69 77 69 63 6d 39 73 |55CG5ZGYIiwicm9s|
|00000090| 5a 55 52 6c 63 32 4d 69 4f 6d 35 31 62 47 77 73 |ZURlc2MiOm51bGws|
|000000a0| 49 6e 4a 76 62 47 56 47 62 47 46 6e 49 6a 70 75 |InJvbGVGbGFnIjpu|
|000000b0| 64 57 78 73 4c 43 4a 31 63 32 56 79 63 79 49 36 |dWxsLCJ1c2VycyI6|
|000000c0| 62 6e 56 73 62 43 77 69 59 58 56 30 61 47 39 79 |bnVsbCwiYXV0aG9y|
|000000d0| 61 58 52 70 5a 58 4d 69 4f 6d 35 31 62 47 77 73 |aXRpZXMiOm51bGws|
|000000e0| 49 6d 46 31 64 47 68 76 63 6d 6c 30 65 53 49 36 |ImF1dGhvcml0eSI6|
|000000f0| 49 75 65 7a 75 2d 65 37 6e 2d 65 75 6f 65 65 51 |Iuezu-e7n-euoeeQ|
|00000100| 68 75 57 52 6d 43 4a 39 58 53 77 69 64 58 4e 79 |huWRmCJ9XSwidXNy|
|00000110| 54 6d 46 74 5a 53 49 36 49 75 53 37 73 75 65 55 |TmFtZSI6IuS7sueU|
|00000120| 71 79 49 73 49 6e 56 7a 63 6b 46 32 59 58 52 68 |qyIsInVzckF2YXRh|
|00000130| 63 69 49 36 49 69 39 68 63 47 6b 76 61 57 31 6e |ciI6Ii9hcGkvaW1n|
|00000140| 4c 32 46 32 59 58 52 68 63 69 39 6f 5a 57 46 6b |L2F2YXRhci9oZWFk|
|00000150| 5a 58 4a 4a 62 57 63 78 4c 6d 70 77 5a 79 49 73 |ZXJJbWcxLmpwZyIs|
|00000160| 49 6e 56 7a 63 6b 6c 6b 49 6a 6f 78 4c 43 4a 6a |InVzcklkIjoxLCJj|
|00000170| 63 6d 56 68 64 47 56 45 59 58 52 6c 49 6a 6f 78 |cmVhdGVEYXRlIjox|
|00000180| 4e 6a 4d 78 4d 44 41 7a 4e 6a 67 31 4f 44 67 33 |NjMxMDAzNjg1ODg3|
|00000190| 4c 43 4a 6c 65 48 42 70 63 6d 46 30 61 57 39 75 |LCJleHBpcmF0aW9u|
|000001a0| 52 47 46 30 5a 53 49 36 4d 54 59 7a 4d 54 41 77 |RGF0ZSI6MTYzMTAw|
|000001b0| 4d 7a 6b 34 4e 54 67 34 4e 79 77 69 61 57 46 30 |Mzk4NTg4NywiaWF0|
|000001c0| 49 6a 6f 78 4e 6a 4d 78 4d 44 41 7a 4e 6a 67 31 |IjoxNjMxMDAzNjg1|
|000001d0| 4c 43 4a 6c 65 48 41 69 4f 6a 45 32 4d 7a 45 77 |LCJleHAiOjE2MzEw|
|000001e0| 4f 54 41 77 4f 44 56 39 2e 5f 4a 53 2d 75 56 36 |OTAwODV9._JS-uV6|
|000001f0| 41 46 34 43 49 72 37 66 37 45 77 4b 35 63 43 31 |AF4CIr7f7EwK5cC1|
|00000200| 31 34 6d 71 63 4f 30 5f 31 6e 47 4e 68 74 69 61 |14mqcO0_1nGNhtia|
|00000210| 4e 7a 57 45 0d 0a 55 73 65 72 2d 41 67 65 6e 74 |NzWE..User-Agent|
|00000220| 3a 20 50 6f 73 74 6d 61 6e 52 75 6e 74 69 6d 65 |: PostmanRuntime|
|00000230| 2f 37 2e 32 38 2e 34 0d 0a 41 63 63 65 70 74 3a |/7.28.4..Accept:|
|00000240| 20 2a 2f 2a 0d 0a 50 6f 73 74 6d 61 6e 2d 54 6f | */*..Postman-To|
|00000250| 6b 65 6e 3a 20 31 62 37 62 30 39 31 64 2d 65 31 |ken: 1b7b091d-e1|
|00000260| 31 62 2d 34 35 36 66 2d 39 33 34 61 2d 63 36 30 |1b-456f-934a-c60|
|00000270| 36 65 63 35 66 39 66 37 39 0d 0a 48 6f 73 74 3a |6ec5f9f79..Host:|
|00000280| 20 6c 6f 63 61 6c 68 6f 73 74 3a 38 30 38 30 0d | localhost:8080.|
|00000290| 0a 41 63 63 65 70 74 2d 45 6e 63 6f 64 69 6e 67 |.Accept-Encoding|
|000002a0| 3a 20 67 7a 69 70 2c 20 64 65 66 6c 61 74 65 2c |: gzip, deflate,|
|000002b0| 20 62 72 0d 0a 43 6f 6e 6e 65 63 74 69 6f 6e 3a | br..Connection:|
|000002c0| 20 6b 65 65 70 2d 61 6c 69 76 65 0d 0a 43 6f 6e | keep-alive..Con|
|000002d0| 74 65 6e 74 2d 54 79 70 65 3a 20 6d 75 6c 74 69 |tent-Type: multi|
|000002e0| 70 61 72 74 2f 66 6f 72 6d 2d 64 61 74 61 3b 20 |part/form-data; |
|000002f0| 62 6f 75 6e 64 61 72 79 3d 2d 2d 2d 2d 2d 2d 2d |boundary=-------|
|00000300| 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |----------------|
|00000310| 2d 2d 2d 32 30 33 38 34 33 35 34 37 33 33 30 39 |---2038435473309|
|00000320| 37 33 39 36 39 32 30 30 31 34 33 0d 0a 43 6f 6e |73969200143..Con|
|00000330| 74 65 6e 74 2d 4c 65 6e 67 74 68 3a 20 31 36 36 |tent-Length: 166|
|00000340| 0d 0a 0d 0a 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |....------------|
|00000350| 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |----------------|
|00000360| 32 30 33 38 34 33 35 34 37 33 33 30 39 37 33 39 |2038435473309739|
|00000370| 36 39 32 30 30 31 34 33 0d 0a 43 6f 6e 74 65 6e |69200143..Conten|
|00000380| 74 2d 44 69 73 70 6f 73 69 74 69 6f 6e 3a 20 66 |t-Disposition: f|
|00000390| 6f 72 6d 2d 64 61 74 61 3b 20 6e 61 6d 65 3d 22 |orm-data; name="|
|000003a0| 61 61 61 22 0d 0a 0d 0a 62 62 62 62 62 62 62 62 |aaa"....bbbbbbbb|
|000003b0| 0d 0a 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |..--------------|
|000003c0| 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 32 30 |--------------20|
|000003d0| 33 38 34 33 35 34 37 33 33 30 39 37 33 39 36 39 |3843547330973969|
|000003e0| 32 30 30 31 34 33 2d 2d 0d 0a |200143--.. |
+--------+-------------------------------------------------+----------------+
15:06:34 [DEBUG] [nioEventLoopGroup-2-5] c.g.n.HttpServer - class io.netty.handler.codec.http.DefaultHttpRequest
15:06:34 [DEBUG] [nioEventLoopGroup-2-5] c.g.n.HttpServer - /index
15:06:34 [DEBUG] [nioEventLoopGroup-2-5] i.n.h.l.LoggingHandler - [id: 0xe4b33518, L:/127.0.0.1:8080 - R:/127.0.0.1:10557] WRITE: 59B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b 0d |HTTP/1.1 200 OK.|
|00000010| 0a 63 6f 6e 74 65 6e 74 2d 6c 65 6e 67 74 68 3a |.content-length:|
|00000020| 20 32 30 0d 0a 0d 0a 3c 68 31 3e 48 65 6c 6c 6f | 20....<h1>Hello|
|00000030| 20 57 6f 72 6c 64 3c 2f 68 31 3e | World</h1> |
+--------+-------------------------------------------------+----------------+
15:06:34 [DEBUG] [nioEventLoopGroup-2-5] i.n.h.l.LoggingHandler - [id: 0xe4b33518, L:/127.0.0.1:8080 - R:/127.0.0.1:10557] FLUSH
PooledSlicedByteBuf(ridx: 0, widx: 166, cap: 166/166, unwrapped: PooledUnsafeDirectByteBuf(ridx: 1002, widx: 1002, cap: 8192))
15:06:34 [DEBUG] [nioEventLoopGroup-2-5] i.n.h.l.LoggingHandler - [id: 0xe4b33518, L:/127.0.0.1:8080 - R:/127.0.0.1:10557] READ COMPLETE
4. 自定义协议
1. 规则
- 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（同时处理多个请求，能够确保响应的数据发送到指定的请求通信上）
- 正文长度
- 消息正文
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 ```java import com.gmf.message.Message; import io.netty.buffer.ByteBuf; import io.netty.channel.ChannelHandlerContext; import io.netty.handler.codec.ByteToMessageCodec; import lombok.extern.slf4j.Slf4j;
2. 编解码器
import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.nio.charset.StandardCharsets; import java.util.List;
@Slf4j
public class MessageCodec extends ByteToMessageCodec
@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
```java
public static void main(String[] args) throws Exception {
EmbeddedChannel channel = new EmbeddedChannel(
new LoggingHandler(),
new LengthFieldBasedFrameDecoder(1024, 12, 4, 0, 0),
new MessageCodec());
//encode
LoginRequestMessage message = new LoginRequestMessage("zhangsan", "123");
//channel.writeOutbound(message);
//decode
ByteBuf buffer = ByteBufAllocator.DEFAULT.buffer();
new MessageCodec().encode(null, message, buffer);
ByteBuf s1 = buffer.slice(0, 100);
ByteBuf s2 = buffer.slice(100, buffer.readableBytes() - 100);
s1.retain(); // 引用计数 2
channel.writeInbound(s1); // release 1
channel.writeInbound(s2);
}
解读
3. 线程间共享的Handler
在创建的多个EventLoop之间它们的Handler是否能共享使用呢
在Handler类上的注解 @Sharable 表明可被共享使用
4. 💡 什么时候可以加 @Sharable
- 当 handler 不保存状态时，就可以安全地在多线程下被共享
- 但要注意对于编解码器类，不能继承 ByteToMessageCodec 或 CombinedChannelDuplexHandler 父类，他们的构造方法对 @Sharable 有限制
如果能确保编解码器不会保存状态，可以继承 MessageToMessageCodec 父类
@Slf4j @ChannelHandler.Sharable /** * 必须和 LengthFieldBasedFrameDecoder 一起使用，确保接到的 ByteBuf 消息是完整的 */ public class MessageCodecSharable extends MessageToMessageCodec<ByteBuf, Message> { @Override protected void encode(ChannelHandlerContext ctx, Message msg, List<Object> outList) throws Exception { ByteBuf out = ctx.alloc().buffer(); // 1. 4 字节的魔数 out.writeBytes(new byte[]{1, 2, 3, 4}); // 2. 1 字节的版本, out.writeByte(1); // 3. 1 字节的序列化方式 jdk 0 , json 1 out.writeByte(0); // 4. 1 字节的指令类型 out.writeByte(msg.getMessageType()); // 5. 4 个字节 out.writeInt(msg.getSequenceId()); // 无意义，对齐填充 out.writeByte(0xff); // 6. 获取内容的字节数组 ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(bos); oos.writeObject(msg); byte[] bytes = bos.toByteArray(); // 7. 长度 out.writeInt(bytes.length); // 8. 写入内容 out.writeBytes(bytes); outList.add(out); } @Override protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception { int magicNum = in.readInt(); byte version = in.readByte(); byte serializerType = in.readByte(); byte messageType = in.readByte(); int sequenceId = in.readInt(); in.readByte(); int length = in.readInt(); byte[] bytes = new byte[length]; in.readBytes(bytes, 0, length); ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bytes)); Message message = (Message) ois.readObject(); log.debug("{}, {}, {}, {}, {}, {}", magicNum, version, serializerType, messageType, sequenceId, length); log.debug("{}", message); out.add(message); } }
三、聊天室案例
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);
}
2. 聊天室业务-登录
客户端
@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();
//计数使线程等待，0则线程向下运行
CountDownLatch WAIT_FOR_LOGIN = new CountDownLatch(1);
//标记是否登陆成功
AtomicBoolean LOGIN = new AtomicBoolean(false);
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.channel(NioSocketChannel.class);
bootstrap.group(group);
bootstrap.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new ProcotolFrameDecoder());
//ch.pipeline().addLast(LOGGING_HANDLER);
ch.pipeline().addLast(MESSAGE_CODEC);
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
//开辟一个新线程处理登陆
new Thread(() -> {
Scanner scanner = new Scanner(System.in);
System.out.print("请输入用户名：");
String username = scanner.next();
System.out.print("请输入密码：");
String password = scanner.next();
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[] line = scanner.nextLine().split(" ");
switch (line[0]){
case "send":
ctx.writeAndFlush(new ChatRequestMessage(username, line[1], line[2]));
break;
case "gsend":
ctx.writeAndFlush(new GroupChatRequestMessage(username, line[1], line[2]));
break;
case "gcreate":
Set<String> set = new HashSet<>(Arrays.asList(line[2].split(",")));
set.add(username); // 加入自己
ctx.writeAndFlush(new GroupCreateRequestMessage(line[1], set));
break;
case "gmembers":
ctx.writeAndFlush(new GroupMembersRequestMessage(line[1]));
break;
case "gjoin":
ctx.writeAndFlush(new GroupJoinRequestMessage(username, line[1]));
break;
case "gquit":
ctx.writeAndFlush(new GroupQuitRequestMessage(username, line[1]));
break;
case "quit":
ctx.channel().close();
return;
}
}
}, "login").start();
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
log.debug("msg: {}", msg);
if ((msg instanceof LoginResponseMessage)) {
LoginResponseMessage response = (LoginResponseMessage) msg;
LOGIN.set(response.isSuccess());
// 唤醒 login 线程
WAIT_FOR_LOGIN.countDown();
}
}
});
}
});
Channel channel = bootstrap.connect("localhost", 8080).sync().channel();
channel.closeFuture().sync();
} catch (Exception e) {
log.error("client error", e);
} finally {
group.shutdownGracefully();
}
}
}
服务端
@Slf4j
public class ChatServer {
public static void main(String[] args) {
NioEventLoopGroup boss = new NioEventLoopGroup();
NioEventLoopGroup worker = new NioEventLoopGroup();
LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG);
MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable();
try {
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.channel(NioServerSocketChannel.class);
serverBootstrap.group(boss, worker);
serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new ProcotolFrameDecoder());
ch.pipeline().addLast(LOGGING_HANDLER);
ch.pipeline().addLast(MESSAGE_CODEC);
ch.pipeline().addLast(new SimpleChannelInboundHandler<LoginRequestMessage>() {
@Override
protected void channelRead0(ChannelHandlerContext ctx, LoginRequestMessage msg) throws Exception {
String username = msg.getUsername();
String password = msg.getPassword();
boolean login = UserServiceFactory.getUserService().login(username, password);
LoginResponseMessage message;
if(login) {
//将用户channel与用户名绑定
SessionFactory.getSession().bind(ctx.channel(), msg.getUsername());
message = new LoginResponseMessage(true, "登录成功");
} else {
message = new LoginResponseMessage(false, "用户名或密码不正确");
}
ctx.writeAndFlush(message);
}
});
}
});
Channel channel = serverBootstrap.bind(8080).sync().channel();
channel.closeFuture().sync();
} catch (InterruptedException e) {
log.error("server error", e);
} finally {
boss.shutdownGracefully();
worker.shutdownGracefully();
}
}
}
3. 聊天室业务-单聊
将服务端handler的代码独立出来进行重构
LoginRequestMessageHandler.java
@Slf4j
@ChannelHandler.Sharable
public class LoginRequestMessageHandler extends SimpleChannelInboundHandler<LoginRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, LoginRequestMessage msg) throws Exception {
UserService userService = UserServiceFactory.getUserService();
boolean login = userService.login(msg.getUsername(), msg.getPassword());
LoginResponseMessage response;
if (login) {
//将用户channel与用户名绑定
SessionFactory.getSession().bind(ctx.channel(), msg.getUsername());
response = new LoginResponseMessage(true, "登陆成功");
} else {
response = new LoginResponseMessage(false, "用户名或密码错误");
}
ctx.writeAndFlush(response);
}
}
ChatRequestMessageHandler.java
@ChannelHandler.Sharable
public class ChatRequestMessageHandler extends SimpleChannelInboundHandler<ChatRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, ChatRequestMessage msg) throws Exception {
Channel channel = SessionFactory.getSession().getChannel(msg.getTo());
if (channel != null) {
//对方在线
channel.writeAndFlush(new ChatResponseMessage(msg.getFrom(), msg.getContent()));
}else {
//对方不在线
ctx.writeAndFlush(new ChatResponseMessage(false, "对方用户不存在或者不在线"));
}
}
}
服务端
将处理单聊的Handler加入到pipeline中
ch.pipeline().addLast(CHAT_REQUEST_HANDLER);
4. 聊天室业务-群聊
1. 创建群聊
同样是创建处理 “群聊创建” 的Handler，并添加至服务端pipeline中
GroupCreateRequestMessageHandler.java
@ChannelHandler.Sharable
public class GroupCreateRequestMessageHandler extends SimpleChannelInboundHandler<GroupCreateRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupCreateRequestMessage msg) throws Exception {
GroupSession groupSession = GroupSessionFactory.getGroupSession();
Group group = groupSession.createGroup(msg.getGroupName(), msg.getMembers());
if (group == null){
ctx.writeAndFlush(new GroupCreateResponseMessage(true, "群聊创建成功"));
List<Channel> channels = groupSession.getMembersChannel(msg.getGroupName());
channels.forEach(channel -> {
channel.writeAndFlush(new GroupCreateResponseMessage(true, "您被拉进群聊：" + msg.getGroupName()));
});
}else {
ctx.writeAndFlush(new GroupCreateResponseMessage(false, "该群聊已存在"));
}
}
}
2. 推送消息
GroupChatRequestMessageHandler.java
@ChannelHandler.Sharable
public class GroupChatRequestMessageHandler extends SimpleChannelInboundHandler<GroupChatRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupChatRequestMessage msg) throws Exception {
List<Channel> channels = GroupSessionFactory.getGroupSession().getMembersChannel(msg.getGroupName());
channels.forEach(channel -> {
//排除对自己发送
if (channel != ctx.channel()){
channel.writeAndFlush(new GroupChatResponseMessage(msg.getFrom(), msg.getContent()));
}
});
}
}
3. 加入群聊
GroupJoinRequestMessageHandler.java
@ChannelHandler.Sharable
public class GroupJoinRequestMessageHandler extends SimpleChannelInboundHandler<GroupJoinRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupJoinRequestMessage msg) throws Exception {
Group group = GroupSessionFactory.getGroupSession().joinMember(msg.getGroupName(), msg.getUsername());
if (group == null){
ctx.writeAndFlush(new GroupQuitResponseMessage(false, "该群聊不存在"));
}else {
ctx.writeAndFlush(new GroupQuitResponseMessage(true, "加入成功"));
}
}
}
4. 退出群聊
GroupQuitRequestMessageHandler.java
@ChannelHandler.Sharable
public class GroupQuitRequestMessageHandler extends SimpleChannelInboundHandler<GroupQuitRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupQuitRequestMessage msg) throws Exception {
Group group = GroupSessionFactory.getGroupSession().removeMember(msg.getGroupName(), msg.getUsername());
if (group == null){
ctx.writeAndFlush(new GroupQuitResponseMessage(false, "该群聊不存在"));
}else {
ctx.writeAndFlush(new GroupQuitResponseMessage(true, "退出成功"));
}
}
}
5. 查看群成员
GroupMembersRequestMessageHandler.java
@ChannelHandler.Sharable
public class GroupMembersRequestMessageHandler extends SimpleChannelInboundHandler<GroupMembersRequestMessage> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, GroupMembersRequestMessage msg) throws Exception {
Set<String> members = GroupSessionFactory.getGroupSession().getMembers(msg.getGroupName());
ctx.writeAndFlush(new GroupMembersResponseMessage(members));
}
}
5. 聊天室业务-退出
QuitHandler.java
@Slf4j
@ChannelHandler.Sharable
public class QuitHandler extends ChannelInboundHandlerAdapter {
/**
* 连接正常断开时调用该方法
* @param ctx
* @return void
*/
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
//取消登陆状态绑定
SessionFactory.getSession().unbind(ctx.channel());
//super.channelInactive(ctx);
log.debug("连接正常断开{}", ctx.channel());
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
SessionFactory.getSession().unbind(ctx.channel());
log.debug("连接异常断开{}", cause.getMessage());
}
}
6. 聊天室案例-空闲检测
1. 连接假死
原因
- 网络设备出现故障，例如网卡，机房等，底层的 TCP 连接已经断开了，但应用程序没有感知到，仍然占用着资源。
- 公网网络不稳定，出现丢包。如果连续出现丢包，这时现象就是客户端数据发不出去，服务端也一直收不到数据，就这么一直耗着
-
问题
假死的连接占用的资源不能自动释放
-
服务器端解决
怎么判断客户端连接是否假死呢？如果能收到客户端数据，说明没有假死。因此策略就可以定为，每隔一段时间就检查这段时间内是否接收到客户端数据，没有就可以判定为连接假死
IdleStateHandler.java 构造方法
- observeOutput：在评估写空闲时是否应该考虑字节的消耗。默认为false
- readerIdleTime：其状态为IdleState。当在指定的时间内没有执行读操作时，将触发READER_IDLE。指定0禁用
- writerIdleTime：其状态为IdleState。当在指定的时间内没有执行写操作时，会触发WRITER_IDLE。指定0禁用
- allIdleTime：其状态为IdleState。在一定时间内不读不写会触发ALL_IDLE。指定0禁用
- unit：时间单位
// 用来判断是不是 读空闲时间过长，或 写空闲时间过长
// 5s 内如果没有收到 channel 的数据，会触发一个 IdleState#READER_IDLE 事件
ch.pipeline().addLast(new IdleStateHandler(5, 0, 0));
// ChannelDuplexHandler 可以同时作为入站和出站处理器
ch.pipeline().addLast(new ChannelDuplexHandler(){
/**
* 触发特殊事件
*/
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
IdleStateEvent event = (IdleStateEvent) evt;
//如果触发的是读空闲事件
if (event.state() == IdleState.READER_IDLE){
log.debug("客户端超过5秒未发送数据");
ctx.channel().close();
}
}
});
2. 客户端定时心跳
客户端可以定时向服务器端发送数据，只要这个时间间隔小于服务器定义的空闲检测的时间间隔，那么就能防止前面提到的误判，客户端可以定义如下心跳处理器
// 用来判断是不是 读空闲时间过长，或 写空闲时间过长
// 3s 内如果没有向服务器写数据，会触发一个 IdleState#WRITER_IDLE 事件
ch.pipeline().addLast(new IdleStateHandler(0, 3, 0));
ch.pipeline().addLast(new ChannelDuplexHandler(){
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
//触发一个空闲事件
IdleStateEvent event = (IdleStateEvent) evt;
if (event.state() == IdleState.WRITER_IDLE) {
//log.debug("3s 没有写数据了，发送一个心跳包");
ctx.writeAndFlush(new PingMessage());
}
}
});
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