Netty - 粘包、半包

4. 粘包、半包

4.1 粘包

FullPackServer

package com.sw.netty._05;

import io.netty.bootstrap.ServerBootstrap;
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.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;

@Slf4j
public class FullPackServer {
    public static void main(String[] args) {
        new FullPackServer().start();
        // 23:08:22.078 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2615b37f, L:/127.0.0.1:8088 - R:/127.0.0.1:62128] READ: 360B
        //         +-------------------------------------------------+
        //         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
        // +--------+-------------------------------------------------+----------------+
        // |00000000| 64 35 33 64 34 38 37 33 2d 38 65 31 64 2d 34 62 |d53d4873-8e1d-4b|
        // |00000010| 31 31 2d 39 65 65 31 2d 31 33 34 36 30 35 62 38 |11-9ee1-134605b8|
        // |00000020| 37 34 32 63 34 35 38 64 30 66 63 62 2d 34 31 61 |742c458d0fcb-41a|
        // |00000030| 34 2d 34 62 61 33 2d 62 33 30 61 2d 66 38 66 65 |4-4ba3-b30a-f8fe|
        // |00000040| 65 36 31 65 64 65 34 61 31 38 33 39 37 61 34 37 |e61ede4a18397a47|
        // |00000050| 2d 61 35 36 34 2d 34 62 37 38 2d 61 62 37 39 2d |-a564-4b78-ab79-|
        // |00000060| 66 35 39 32 36 61 32 64 62 65 38 33 62 38 31 31 |f5926a2dbe83b811|
        // |00000070| 31 37 37 66 2d 66 36 63 62 2d 34 66 36 63 2d 38 |177f-f6cb-4f6c-8|
        // |00000080| 31 32 63 2d 38 61 38 64 61 62 34 32 62 66 32 38 |12c-8a8dab42bf28|
        // |00000090| 39 62 63 35 64 33 32 31 2d 35 36 64 63 2d 34 33 |9bc5d321-56dc-43|
        // |000000a0| 31 34 2d 62 30 61 39 2d 34 62 65 64 65 39 66 63 |14-b0a9-4bede9fc|
        // |000000b0| 35 33 35 66 66 38 61 32 33 65 37 63 2d 35 36 30 |535ff8a23e7c-560|
        // |000000c0| 33 2d 34 62 66 30 2d 62 34 66 33 2d 35 30 37 32 |3-4bf0-b4f3-5072|
        // |000000d0| 30 33 35 37 66 37 64 62 63 39 31 39 66 32 32 39 |0357f7dbc919f229|
        // |000000e0| 2d 30 32 63 34 2d 34 65 35 31 2d 62 63 30 36 2d |-02c4-4e51-bc06-|
        // |000000f0| 63 33 65 63 33 66 34 35 65 61 34 30 62 32 38 35 |c3ec3f45ea40b285|
        // |00000100| 38 65 30 36 2d 33 64 36 30 2d 34 35 64 32 2d 61 |8e06-3d60-45d2-a|
        // |00000110| 64 65 63 2d 35 36 35 62 35 61 35 31 30 61 37 35 |dec-565b5a510a75|
        // |00000120| 62 62 64 65 35 65 63 31 2d 63 62 62 62 2d 34 62 |bbde5ec1-cbbb-4b|
        // |00000130| 31 61 2d 61 39 36 35 2d 63 38 32 65 37 61 30 34 |1a-a965-c82e7a04|
        // |00000140| 34 32 33 32 35 39 32 65 61 33 38 34 2d 33 32 34 |4232592ea384-324|
        // |00000150| 30 2d 34 31 63 63 2d 39 66 35 65 2d 35 65 33 63 |0-41cc-9f5e-5e3c|
        // |00000160| 33 66 62 66 37 31 34 33                         |3fbf7143        |
        // +--------+-------------------------------------------------+----------------+
    }

    private void start() {
        NioEventLoopGroup main = new NioEventLoopGroup(1);
        NioEventLoopGroup worker = new NioEventLoopGroup();
        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.channel(NioServerSocketChannel.class);
            serverBootstrap.group(main, worker);
            serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.INFO));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.info("connected {}", ctx.channel());
                            super.channelActive(ctx);
                        }

                        @Override
                        public void channelInactive(ChannelHandlerContext ctx) throws Exception {
                            log.info("disconnected {}", ctx.channel());
                            super.channelInactive(ctx);
                        }
                    });
                }
            });

            ChannelFuture channelFuture = serverBootstrap.bind(8088);
            log.info("{} binding...", channelFuture.channel());
            channelFuture.sync();
            log.info("{} bound...", channelFuture.channel());
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("server error {}", e.getMessage());
        } finally {
            main.shutdownGracefully();
            worker.shutdownGracefully();
            log.info("server stoped");
        }
    }
}

FullPackClient

package com.sw.netty._05;

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 lombok.extern.slf4j.Slf4j;

import java.util.UUID;

@Slf4j
public class FullPackClient {
    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.info("connected...");
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.info("sending data...");
                            for (int i = 0; i < 10; i++) {
                                String data = UUID.randomUUID().toString();
                                ByteBuf bf = ctx.alloc().buffer();
                                bf.writeBytes(data.getBytes());
                                ctx.writeAndFlush(bf);
                            }
                        }
                    });
                }
            });
            ChannelFuture channelFuture = bootstrap.connect("localhost", 8088);
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("client error {}", e.getMessage());
        } finally {
            worker.shutdownGracefully();
        }
    }
}

如上 demo 所示，服务端期望分10次接收客户端发过来的数据，但实际情况是一次就收到了 360B 的数据（粘包现象）

4.2 半包

HalfPackServer

package com.sw.netty._05;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
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 lombok.extern.slf4j.Slf4j;

@Slf4j
public class HalfPackServer {
    public static void main(String[] args) {
        new HalfPackServer().start();
    }

    private void start() {
        NioEventLoopGroup main = new NioEventLoopGroup(1);
        NioEventLoopGroup worker = new NioEventLoopGroup();
        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.channel(NioServerSocketChannel.class);
            serverBootstrap.group(main, worker);
            // 服务端指定接收缓冲区大小为 16 字节
            serverBootstrap.option(ChannelOption.SO_RCVBUF, 16);
            serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.INFO));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.info("connected {}", ctx.channel());
                            super.channelActive(ctx);
                        }

                        @Override
                        public void channelInactive(ChannelHandlerContext ctx) throws Exception {
                            log.info("disconnected {}", ctx.channel());
                            super.channelInactive(ctx);
                        }
                    });
                }
            });

            ChannelFuture channelFuture = serverBootstrap.bind(8088);
            log.info("{} binding...", channelFuture.channel());
            channelFuture.sync();
            log.info("{} bound...", channelFuture.channel());
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("server error {}", e.getMessage());
        } finally {
            main.shutdownGracefully();
            worker.shutdownGracefully();
            log.info("server stoped");
        }
    }
}

HalfPackClient

package com.sw.netty._05;

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 lombok.extern.slf4j.Slf4j;

import java.util.UUID;

@Slf4j
public class HalfPackClient {
    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.info("connected...");
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.info("sending data...");
                            for (int i = 0; i < 10; i++) {
                                String data = UUID.randomUUID().toString();
                                ByteBuf bf = ctx.alloc().buffer();
                                bf.writeBytes(data.getBytes());
                                ctx.writeAndFlush(bf);
                            }
                        }
                    });
                }
            });
            ChannelFuture channelFuture = bootstrap.connect("localhost", 8088);
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("client error {}", e.getMessage());
        } finally {
            worker.shutdownGracefully();
        }
    }
}

Server Log

23:17:26.613 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ: 80B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 35 38 37 65 66 34 33 33 2d 30 34 35 34 2d 34 62 |587ef433-0454-4b|
|00000010| 66 61 2d 61 63 62 61 2d 34 32 63 32 66 61 32 30 |fa-acba-42c2fa20|
|00000020| 62 31 36 32 62 32 31 39 61 32 35 31 2d 33 35 63 |b162b219a251-35c|
|00000030| 65 2d 34 61 37 63 2d 62 66 65 34 2d 30 39 63 39 |e-4a7c-bfe4-09c9|
|00000040| 31 35 33 63 34 36 62 38 66 31 30 32 36 34 35 33 |153c46b8f1026453|
+--------+-------------------------------------------------+----------------+
23:17:26.613 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded inbound message PooledUnsafeDirectByteBuf(ridx: 0, widx: 80, cap: 1024) that reached at the tail of the pipeline. Please check your pipeline configuration.
23:17:26.613 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded message pipeline : [LoggingHandler#0, HalfPackServer$1$1#0, DefaultChannelPipeline$TailContext#0]. Channel : [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753].
23:17:26.613 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ COMPLETE
23:17:26.613 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ: 64B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 2d 35 63 63 31 2d 34 39 65 34 2d 61 61 32 38 2d |-5cc1-49e4-aa28-|
|00000010| 65 33 36 61 65 64 38 37 64 66 35 36 65 35 35 62 |e36aed87df56e55b|
|00000020| 37 61 31 62 2d 64 35 33 38 2d 34 37 66 62 2d 62 |7a1b-d538-47fb-b|
|00000030| 36 61 64 2d 33 65 66 34 66 34 34 64 62 62 36 66 |6ad-3ef4f44dbb6f|
+--------+-------------------------------------------------+----------------+
23:17:26.613 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded inbound message PooledUnsafeDirectByteBuf(ridx: 0, widx: 64, cap: 1024) that reached at the tail of the pipeline. Please check your pipeline configuration.
23:17:26.613 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded message pipeline : [LoggingHandler#0, HalfPackServer$1$1#0, DefaultChannelPipeline$TailContext#0]. Channel : [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753].
23:17:26.613 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ COMPLETE
23:17:26.614 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ: 80B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 65 30 39 64 66 35 64 62 2d 66 31 37 31 2d 34 39 |e09df5db-f171-49|
|00000010| 66 36 2d 61 64 64 35 2d 64 33 64 33 39 31 33 66 |f6-add5-d3d3913f|
|00000020| 37 39 35 30 65 37 62 39 35 35 34 62 2d 64 39 63 |7950e7b9554b-d9c|
|00000030| 63 2d 34 33 63 63 2d 62 36 38 38 2d 31 35 65 66 |c-43cc-b688-15ef|
|00000040| 62 62 61 66 34 37 63 39 61 64 32 65 35 38 35 35 |bbaf47c9ad2e5855|
+--------+-------------------------------------------------+----------------+
23:17:26.614 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded inbound message PooledUnsafeDirectByteBuf(ridx: 0, widx: 80, cap: 512) that reached at the tail of the pipeline. Please check your pipeline configuration.
23:17:26.614 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded message pipeline : [LoggingHandler#0, HalfPackServer$1$1#0, DefaultChannelPipeline$TailContext#0]. Channel : [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753].
23:17:26.614 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ COMPLETE
23:17:26.614 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ: 64B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 2d 35 39 33 34 2d 34 62 38 36 2d 62 39 33 62 2d |-5934-4b86-b93b-|
|00000010| 36 66 31 34 62 35 33 66 35 39 36 30 30 32 32 31 |6f14b53f59600221|
|00000020| 64 64 64 61 2d 39 39 65 31 2d 34 38 62 32 2d 39 |ddda-99e1-48b2-9|
|00000030| 66 62 65 2d 39 39 37 30 35 66 66 66 64 65 37 64 |fbe-99705fffde7d|
+--------+-------------------------------------------------+----------------+
23:17:26.614 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded inbound message PooledUnsafeDirectByteBuf(ridx: 0, widx: 64, cap: 512) that reached at the tail of the pipeline. Please check your pipeline configuration.
23:17:26.614 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded message pipeline : [LoggingHandler#0, HalfPackServer$1$1#0, DefaultChannelPipeline$TailContext#0]. Channel : [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753].
23:17:26.614 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ COMPLETE
23:17:26.614 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ: 72B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 37 32 62 61 38 64 31 62 2d 62 34 33 34 2d 34 63 |72ba8d1b-b434-4c|
|00000010| 38 35 2d 62 63 39 64 2d 63 35 61 38 61 37 31 32 |85-bc9d-c5a8a712|
|00000020| 66 38 38 34 34 39 61 37 34 33 32 66 2d 31 37 34 |f88449a7432f-174|
|00000030| 64 2d 34 30 34 63 2d 61 33 65 33 2d 62 64 63 34 |d-404c-a3e3-bdc4|
|00000040| 32 30 31 31 33 30 32 35                         |20113025        |
+--------+-------------------------------------------------+----------------+
23:17:26.614 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded inbound message PooledUnsafeDirectByteBuf(ridx: 0, widx: 72, cap: 496) that reached at the tail of the pipeline. Please check your pipeline configuration.
23:17:26.614 [nioEventLoopGroup-3-1] DEBUG io.netty.channel.DefaultChannelPipeline - Discarded message pipeline : [LoggingHandler#0, HalfPackServer$1$1#0, DefaultChannelPipeline$TailContext#0]. Channel : [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753].
23:17:26.614 [nioEventLoopGroup-3-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0x2b332ddd, L:/127.0.0.1:8088 - R:/127.0.0.1:62753] READ COMPLETE

从服务端打印的日志可以看出，接收到的消息被分为了不同字节大小，且分为多次接收，serverBootstrap.option(ChannelOption.SO_RCVBUF, 16) 方法仅设置接收缓冲区的大小（滑动窗口），实际 netty 读取时是这个参数的整数倍（由日志中的 64B、80B 可见）

4.3 粘包、半包产生原因

（1）粘包

• 现象：发送方依次发送 123，456，接收方接收到的数据为 123456

• 原因：

  • 应用层：接收方 ByteBuf 初始容量大小不同（Netty 默认 1024）
  • 滑动窗口：发送方的一个完整报文为 256 字节，由于接收方处理不及时或滑动窗口足够大，这时发送方的发送的数据就会累积在接收方的滑动窗口中，窗口中的多个报文就会发生粘包
  • Nagle 算法也会产生粘包

（2）半包

• 现象：发送方发送 123456，接收方收到的数据为 1，23，456

• 原因：

  • 应用层：接收方 ByteBuf 初始容量大小小于发送方此次发送的数据量
  • 滑动窗口：接收方此时的滑动窗口仅剩 256 字节，但发送方发过来的数据是 512 字节，这时接收方收到数据后到达此次滑动窗口的处理阈值，窗口开始处理之前的数据和此次 512 字节中的 256 字节，剩余的 256 字节只能等 ack 后才能继续接收处理，就产生了半包
  • MSS 限制：发送的数据超过 MSS 限制后，就会产生半包（如：超过 MTU 大小）

（3）补充

• 滑动窗口：

  TCP 以段（segment）为单位，每发送一个段就需要一次 ack，当包的往返时间越长时，性能越差

  

  为了解决这个问题，引入了窗口的概念，窗口的大小表示无需等待应答可以继续发送的数据最大值

  

  • 窗口具有缓冲区和流控的作用
  • 窗口内的数据才允许被发送，应答未到达前，必须停止滑动
  • 接收方同样也会维护一个滑动窗口，与发送方的职责一致

• MSS 限制

  • 链路层对一次能够发送的最大数据有限制（MTU maximum transmission unit）
  • 以太网 1500、FDDI 光纤 4352、本地回环不走网卡（MTU为65535）

  • MSS 最大段长度（maximum segment size），即刨除 tcp 头和 ip 头后剩余能够作为传输数据的字节数

    • IPv4 tcp头 20 字节，ip 头 20 字节，MTU 为 1500 - 20 - 20 = 1460
    • 服务端、客户端在 tcp 三次握手时，交换（互相通知）各自的 MTU，然后取双方值最小的那个

• Nagle 算法

  当发送一个字节的数据时，也需要加入 tcp 头和 ip 头（即总字节数为 41），为了提高网络利用率，产生了 Nagle 算法（发送端还有数据未发送，但数据量很少，则延迟发送）：

  • 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完执行关闭
  • 如果 TCP_NODELAY = true，则发送
  • 已发送的数据都收到 ack 时，则需要发送
  • 上述条件不满足，但达到超时阈值（一般为 200ms）则需要发送
  • 除上述情况外，执行延迟发送

4.4 解决方案

（1）短链接

发一个包建立一次连接，以连接建立到连接断开作为消息边界，效率较低

package com.sw.netty._05;

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.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;

@Slf4j
public class ShortConnClientTest {
    public static void main(String[] args) {
        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.info("connected...");
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.INFO));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.info("send data...");
                            ByteBuf bf = ctx.alloc().buffer();
                            bf.writeBytes(new byte[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12});
                            ctx.writeAndFlush(bf);
                            ctx.close();
                        }
                    });
                }
            });
            ChannelFuture channelFuture = bootstrap.connect("localhost", 8088);
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("ShortConnClient error: {}", e.getMessage());
        } finally {
            worker.shutdownGracefully();
        }
    }
}

短连接不能解决半包问题，因为不同接收方的缓冲区大小不同且有限

（2）固定长度

每条消息采用固定的长度，内存空间使用效率不高

服务端 decoder 自定义长度

ch.pipeline().addLast(new FixedLengthFrameDecoder(8));

客户端

package com.sw.netty._05;

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.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;

import java.util.Random;
import java.util.UUID;

@Slf4j
public class FixedLengthClientTest {
    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.info("connected...");
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.INFO));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.info("send data...");
                            Random random = new Random();
                            ByteBuf bf = ctx.alloc().buffer();
                            for (int i = 0; i < 10; i++) {
                                String data = UUID.randomUUID().toString().replace("-", "").substring(random.nextInt(i + 1));
                                bf.writeBytes(data.getBytes());
                            }
                            ctx.writeAndFlush(bf);
                        }
                    });
                }
            });
            ChannelFuture channelFuture = bootstrap.connect("localhost", 8088);
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("FixedLengthClient error: {}", e.getMessage());
        } finally {
            worker.shutdownGracefully();
        }
    }
}

服务端每次处理 8 个字节的消息，如果长度太长，会造成浪费，太短会产生半包问题

（3）固定分隔符

如以 \n 作为消息的分隔符，每次对消息的处理都需要先进行转义

服务端加入分隔符 decoder（如果超出指定长度仍未找到目标分隔符，则报错）

ch.pipeline().addLast(new LineBasedFrameDecoder(1024));

客户端

package com.sw.netty._05;

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.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;

import java.util.Random;
import java.util.UUID;

@Slf4j
public class LineBasedClientTest {
    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.info("connected...");
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.INFO));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.info("send data...");
                            Random random = new Random();
                            ByteBuf bf = ctx.alloc().buffer();
                            for (int i = 0; i < 10; i++) {
                                String data = UUID.randomUUID().toString().replace("-", "").substring(random.nextInt(i + 1));
                                bf.writeBytes(data.getBytes());
                            }
                            ctx.writeAndFlush(bf);
                        }
                    });
                }
            });
            ChannelFuture channelFuture = bootstrap.connect("localhost", 8088);
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("LineBasedClient error: {}", e.getMessage());
        } finally {
            worker.shutdownGracefully();
        }
    }
}

适合处理纯字符数据，如果消息中包含分隔符，则解析会存在问题

（4）预设长度

每条消息分 head 和 body，head 中包含 body 的长度

服务端、客户端发送消息前用定长字节约定数据的长度

// 最大长度，长度偏移量，长度占用字节，剥离字节
ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 1, 0, 1));

客户端

package com.sw.netty._05;

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.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;

import java.util.Random;
import java.util.UUID;

@Slf4j
public class LengthFieldBasedClientTest {
    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.info("connected...");
                    ch.pipeline().addLast(new LoggingHandler(LogLevel.INFO));
                    ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            log.info("send data...");
                            Random random = new Random();
                            ByteBuf bf = ctx.alloc().buffer();
                            for (int i = 0; i < 10; i++) {
                                String data = UUID.randomUUID().toString().replace("-", "").substring(random.nextInt(i + 1));
                                // 先写入长度
                                bf.writeByte(random.nextInt(i + 1) + 1);
                                bf.writeBytes(data.getBytes());
                            }
                            ctx.writeAndFlush(bf);
                        }
                    });
                }
            });
            ChannelFuture channelFuture = bootstrap.connect("localhost", 8088);
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            log.error("LengthFieldBasedClient error: {}", e.getMessage());
        } finally {
            worker.shutdownGracefully();
        }
    }
}