Netty进阶-黏包半包
黏包半包
-
- 1. 粘包与半包
-
- 1.1 粘包现象
- 1.3 现象分析
- 1.4 解决方案
-
- 方法1，短链接
- 方法2，固定长度
- 方法3，固定分隔符
- 方法4，预设长度LengthFieldBasedFrameDecoder
1. 粘包与半包
1.1 粘包现象
服务端代码
@Slf4j
public class HelloWorldServer {
public static void main(String[] args) {
NioEventLoopGroup boss = new NioEventLoopGroup(1);
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.channel(NioServerSocketChannel.class);
serverBootstrap.group(boss, worker);
serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
}
});
ChannelFuture channelFuture = serverBootstrap.bind(8080).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
log.error("server error", e);
} finally {
boss.shutdownGracefully();
worker.shutdownGracefully();
}
}
}
客户端代码
@Slf4j
public class HelloWorldClient {
public static void main(String[] args) {
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.channel(NioSocketChannel.class);
bootstrap.group(worker);
bootstrap.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.debug("connetted...");
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.debug("sending...");
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();
}
}
}
客户端是发10次，每次发16字节，而看到的结果是一次接收了160字节的数据，黏包现象
14:21:25 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x9ed7ee45, L:/127.0.0.1:8080 - R:/127.0.0.1:51527] REGISTERED
14:21:25 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x9ed7ee45, L:/127.0.0.1:8080 - R:/127.0.0.1:51527] ACTIVE
14:21:25 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x9ed7ee45, L:/127.0.0.1:8080 - R:/127.0.0.1:51527] 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 |................|
+--------+-------------------------------------------------+----------------+
14:21:25 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x9ed7ee45, L:/127.0.0.1:8080 - R:/127.0.0.1:51527] READ COMPLETE
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，出现半包现象
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] REGISTERED
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] ACTIVE
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] READ: 36B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000010| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000020| 00 01 02 03 |.... |
+--------+-------------------------------------------------+----------------+
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] READ COMPLETE
14:26:40 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8bb7f3ee, L:/127.0.0.1:8080 - R:/127.0.0.1:52017] READ: 50B
+-------------------------------------------------+
| 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 |.. |
+--------+-------------------------------------------------+----------------+
注意
serverBootstrap.option(ChannelOption.SO_RCVBUF, 10) 影响的底层接收缓冲区（即滑动窗口）大小，仅决定了 netty 读取的最小单位，netty 实际每次读取的一般是它的整数倍
1.3 现象分析
粘包
- 现象，发送 abc def，接收 abcdef
- 原因
- 应用层：接收方 ByteBuf 设置太大（Netty 默认 1024）
- 滑动窗口：假设发送方 256 bytes 表示一个完整报文，但由于接收方处理不及时且窗口大小足够大，这 256 bytes 字节就会缓冲在接收方的滑动窗口中，当滑动窗口中缓冲了多个报文就会粘包
- Nagle 算法：会造成粘包
半包
- 现象，发送 abcdef，接收 abc def
- 原因
- 应用层：接收方 ByteBuf 小于实际发送数据量
- 滑动窗口：假设接收方的窗口只剩了 128 bytes，发送方的报文大小是 256 bytes，这时放不下了，只能先发送前 128 bytes，等待 ack 后才能发送剩余部分，这就造成了半包
- MSS 限制：当发送的数据超过 MSS 限制后，会将数据切分发送，就会造成半包
本质是因为 TCP 是流式协议，消息无边界
滑动窗口
TCP 以一个段（segment）为单位，每发送一个段就需要进行一次确认应答（ack）处理，但如果这么做，缺点是包的往返时间越长性能就越差
为了解决此问题，引入了窗口概念，窗口大小即决定了无需等待应答而可以继续发送的数据最大值
窗口实际就起到一个缓冲区的作用，同时也能起到流量控制的作用
- 图中深色的部分即要发送的数据，高亮的部分即窗口
- 窗口内的数据才允许被发送，当应答未到达前，窗口必须停止滑动
- 如果 1001~2000 这个段的数据 ack 回来了，窗口就可以向前滑动
- 接收方也会维护一个窗口，只有落在窗口内的数据才能允许接收
MSS 限制
链路层对一次能够发送的最大数据有限制，这个限制称之为 MTU（maximum transmission unit），不同的链路设备的 MTU 值也有所不同，例如
以太网的 MTU 是 1500
FDDI（光纤分布式数据接口）的 MTU 是 4352
本地回环地址的 MTU 是 65535 - 本地测试不走网卡
MSS 是最大段长度（maximum segment size），它是 MTU 刨去 tcp 头和 ip 头后剩余能够作为数据传输的字节数
ipv4 tcp 头占用 20 bytes，ip 头占用 20 bytes，因此以太网 MSS 的值为 1500 - 40 = 1460
TCP 在传递大量数据时，会按照 MSS 大小将数据进行分割发送
MSS 的值在三次握手时通知对方自己 MSS 的值，然后在两者之间选择一个小值作为 MSS
Nagle 算法
- 即使发送一个字节，也需要加入 tcp 头和 ip 头，也就是总字节数会使用 41 bytes，非常不经济。因此为了提高网络利用率，tcp 希望尽可能发送足够大的数据，这就是 Nagle 算法产生的缘由
- 该算法是指发送端即使还有应该发送的数据，但如果这部分数据很少的话，则进行延迟发送
- 如果 SO_SNDBUF 的数据达到 MSS，则需要发送
- 如果 SO_SNDBUF 中含有 FIN（表示需要连接关闭）这时将剩余数据发送，再关闭
- 如果 TCP_NODELAY = true，则需要发送
- 已发送的数据都收到 ack 时，则需要发送
- 上述条件不满足，但发生超时（一般为 200ms）则需要发送
- 除上述情况，延迟发送
1.4 解决方案
- 短链接，发一个包建立一次连接，这样连接建立到连接断开之间就是消息的边界，缺点效率太低
- 每一条消息采用固定长度，缺点浪费空间
- 每一条消息采用分隔符，例如 \n，缺点需要转义
- 每一条消息分为 head 和 body，head 中包含 body 的长度
方法1，短链接
以解决粘包为例
修改客户端代码，每次发16字节后，断开连接
@Slf4j
public class HelloWorldClient {
public static void main(String[] args) {
for (int i = 0; i < 10; i++) {
NioEventLoopGroup worker = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.channel(NioSocketChannel.class);
bootstrap.group(worker);
bootstrap.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.debug("connetted...");
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.debug("sending...");
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);
ctx.channel().close();
}
});
}
});
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();
}
}
}
}
结果
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] REGISTERED
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] ACTIVE
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] READ: 16B
+-------------------------------------------------+
| 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 |................|
+--------+-------------------------------------------------+----------------+
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] READ COMPLETE
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 - R:/127.0.0.1:54604] READ COMPLETE
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 ! R:/127.0.0.1:54604] INACTIVE
14:51:26 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0x3d5ee483, L:/127.0.0.1:8080 ! R:/127.0.0.1:54604] UNREGISTERED
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] REGISTERED
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] ACTIVE
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] READ: 16B
+-------------------------------------------------+
| 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 |................|
+--------+-------------------------------------------------+----------------+
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] READ COMPLETE
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 - R:/127.0.0.1:54637] READ COMPLETE
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 ! R:/127.0.0.1:54637] INACTIVE
14:51:26 [DEBUG] [nioEventLoopGroup-3-3] i.n.h.l.LoggingHandler - [id: 0xc8b44aa0, L:/127.0.0.1:8080 ! R:/127.0.0.1:54637] UNREGISTERED
......
但是无法解决半包问题
修改服务端代码，让netty的缓冲区最大为16字节
serverBootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR,new AdaptiveRecvByteBufAllocator(16,16,16));
修改客户端代码，每次传18个字节
buffer.writeBytes(new byte[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17});
结果
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] REGISTERED
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] ACTIVE
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] REGISTERED
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] ACTIVE
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] READ: 16B
+-------------------------------------------------+
| 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 |................|
+--------+-------------------------------------------------+----------------+
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] READ: 16B
+-------------------------------------------------+
| 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 |................|
+--------+-------------------------------------------------+----------------+
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] READ COMPLETE
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] READ COMPLETE
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] READ: 2B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 10 11 |.. |
+--------+-------------------------------------------------+----------------+
14:55:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8c0a3ec6, L:/127.0.0.1:8080 - R:/127.0.0.1:55275] READ COMPLETE
14:55:17 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xd59829e2, L:/127.0.0.1:8080 - R:/127.0.0.1:55308] READ: 2B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 10 11 |.. |
+--------+-------------------------------------------------+----------------+
方法2，固定长度
让所有数据包长度固定（假设长度为 10 字节），服务器端加入
//每10个字节拆分一次
ch.pipeline().addLast(new FixedLengthFrameDecoder(10));
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
客户端代码
@Slf4j
public class Client2 {
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) {
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
@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++) {
byte[] bytes = fill10Bytes(c, r.nextInt(10) + 1);
c++;
buf.writeBytes(bytes);
}
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();
}
System.out.println("finish");
}
public static byte[] fill10Bytes(char c, int len) {
byte[] bytes = new byte[10];
Arrays.fill(bytes, (byte) '_');
for (int i = 0; i < len; i++) {
bytes[i] = (byte) c;
}
System.out.println(new String(bytes));
return bytes;
}
}
客户端输出，一次将100字节全发过去了
15:13:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xa592b591, L:/127.0.0.1:56680 - R:/127.0.0.1:8080] WRITE: 100B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 5f 5f 5f 5f 5f 5f 5f 5f 31 5f 5f 5f 5f 5f |00________1_____|
|00000010| 5f 5f 5f 5f 32 5f 5f 5f 5f 5f 5f 5f 5f 5f 33 33 |____2_________33|
|00000020| 33 33 5f 5f 5f 5f 5f 5f 34 34 34 34 34 5f 5f 5f |33______44444___|
|00000030| 5f 5f 35 35 35 35 35 35 35 35 5f 5f 36 5f 5f 5f |__55555555__6___|
|00000040| 5f 5f 5f 5f 5f 5f 37 37 37 37 37 37 37 5f 5f 5f |______7777777___|
|00000050| 38 38 38 38 38 5f 5f 5f 5f 5f 39 39 39 39 39 39 |88888_____999999|
|00000060| 39 39 39 39 |9999 |
+--------+-------------------------------------------------+----------------+
15:13:10 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xa592b591, L:/127.0.0.1:56680 - R:/127.0.0.1:8080] FLUSH
服务端输出
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] REGISTERED
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] ACTIVE
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] READ: 10B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 5f 5f 5f 5f 5f 5f 5f 5f |00________ |
+--------+-------------------------------------------------+----------------+
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] READ COMPLETE
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] READ: 10B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 31 5f 5f 5f 5f 5f 5f 5f 5f 5f |1_________ |
+--------+-------------------------------------------------+----------------+
15:13:10 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x08cd3f55, L:/127.0.0.1:8080 - R:/127.0.0.1:56680] READ: 10B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 32 5f 5f 5f 5f 5f 5f 5f 5f 5f |2_________ |
+--------+-------------------------------------------------+----------------+
......
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
@Slf4j
public class Client3 {
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) {
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(5) + 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();
}
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;
}
}
客户端输出
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad] REGISTERED
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad] CONNECT: /127.0.0.1:8080
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad, L:/127.0.0.1:57416 - R:/127.0.0.1:8080] ACTIVE
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad, L:/127.0.0.1:57416 - R:/127.0.0.1:8080] WRITE: 44B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 0a 31 31 31 31 0a 32 32 32 0a 33 33 33 0a |00.1111.222.333.|
|00000010| 34 34 34 34 34 0a 35 35 35 0a 36 36 36 0a 37 37 |44444.555.666.77|
|00000020| 37 37 37 0a 38 0a 39 39 39 39 39 0a |777.8.99999. |
+--------+-------------------------------------------------+----------------+
15:23:05 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xed85f2ad, L:/127.0.0.1:57416 - R:/127.0.0.1:8080] FLUSH
服务端输出
15:23:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xc9272026, L:/127.0.0.1:8080 ! R:/127.0.0.1:57367] INACTIVE
15:23:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xc9272026, L:/127.0.0.1:8080 ! R:/127.0.0.1:57367] UNREGISTERED
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] REGISTERED
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] ACTIVE
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] READ: 2B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 |00 |
+--------+-------------------------------------------------+----------------+
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] READ: 4B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 31 31 31 31 |1111 |
+--------+-------------------------------------------------+----------------+
15:23:05 [DEBUG] [nioEventLoopGroup-3-2] i.n.h.l.LoggingHandler - [id: 0xeda2a1a5, L:/127.0.0.1:8080 - R:/127.0.0.1:57416] READ: 3B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 32 32 32 |222 |
+--------+-------------------------------------------------+----------------+
另一种方法，修改服务端代码
ByteBuf buf= ByteBufAllocator.DEFAULT.buffer();
buf.writeByte('$');
ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,buf));
修改客户端代码
public static StringBuilder makeString(char c, int len) {
StringBuilder sb = new StringBuilder(len + 2);
for (int i = 0; i < len; i++) {
sb.append(c);
}
sb.append("$");
return sb;
}
结果一样
方法4，预设长度LengthFieldBasedFrameDecoder
官方案例：
- lengthFieldoffset：长度字段偏移量
- lengthrieldlength：长度字段长度
- lengthAdjustment：长度字段为基准，还有几个字节是内容
- initialBytosTostrip：从头剥离几个字节
代码
public class TestLengthFieldDecoder {
public static void main(String[] args) {
EmbeddedChannel channel = new EmbeddedChannel(
new LengthFieldBasedFrameDecoder(1024, 0,
4, 0, 0),
new LoggingHandler(LogLevel.DEBUG)
);
// 4 个字节的内容长度， 实际内容
ByteBuf buffer = ByteBufAllocator.DEFAULT.buffer();
send(buffer, "Hello, world");
send(buffer, "Hi!");
log(buffer);
channel.writeInbound(buffer);
}
private static void send(ByteBuf buffer, String content) {
byte[] bytes = content.getBytes(); // 实际内容
int length = bytes.length; // 实际内容长度
buffer.writeInt(length);
buffer.writeBytes(bytes);
}
}
结果
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] REGISTERED
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] ACTIVE
read index:0 write index:23 capacity:256
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 0c 48 65 6c 6c 6f 2c 20 77 6f 72 6c 64 |....Hello, world|
|00000010| 00 00 00 03 48 69 21 |....Hi! |
+--------+-------------------------------------------------+----------------+
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 16B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 0c 48 65 6c 6c 6f 2c 20 77 6f 72 6c 64 |....Hello, world|
+--------+-------------------------------------------------+----------------+
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 7B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 03 48 69 21 |....Hi! |
+--------+-------------------------------------------------+----------------+
16:16:18 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE