五、Netty5解决TCP粘包问题

我们在前面的Demo中并没有考虑到读半包问题，这在功能测试中往往没有问题，但是一旦压力上来，或者发送大报文之后，就会存在粘包和拆包问题，如果代码没有考虑，往往就会出现解码错位或者错误，导致程序不能正常运行。下面使用netty的半包解码器来解决TCP粘包和拆包问题。

工具：IntelliJ IDEA 2016.2.2(64)

netty版本：netty-all-5.0.0.Alpha1

服务端程序：

package TCPTimeServer;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.SocketChannel;import io.netty.channel.socket.nio.NioServerSocketChannel;import io.netty.handler.codec.LineBasedFrameDecoder;import io.netty.handler.codec.string.StringDecoder;/** * Created by L_kanglin on 2017/6/4. */public class TCPTimeServer {        public void bind(int port){            // 配置服务端的NIO线程组            EventLoopGroup bossGroup = new NioEventLoopGroup();            EventLoopGroup workerGroup = new NioEventLoopGroup();            try {                ServerBootstrap b = new ServerBootstrap();                // 设置线程组及Socket参数                b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 1024)                        .childHandler(new ChildChannelHandler());                // 绑定端口，同步等待成功                ChannelFuture f = b.bind(port).sync();                System.out.println("服务已经启动,端口:" + port);                f.channel().closeFuture().sync();            } catch (Exception e) {            } finally {                // 退出释放线程池资源                bossGroup.shutdownGracefully();                workerGroup.shutdownGracefully();                System.out.println("服务销毁!");            }        }        public class ChildChannelHandler extends ChannelInitializer<SocketChannel> {            @Override            protected void initChannel(SocketChannel ch) throws Exception {                // 以下两行代码为了解决半包读问题                ch.pipeline().addLast(new LineBasedFrameDecoder(1024));                ch.pipeline().addLast(new StringDecoder());                ch.pipeline().addLast(new TimerServerHandler());            }        }    public static void main(String[] args) {        int port = 8080;        if (null != args && args.length > 0) {            try {                port = Integer.valueOf(args[0]);            } catch (Exception e) {                // 采用默认值            }        }        new TCPTimeServer().bind(port);    }}

package TCPTimeServer;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.SimpleChannelInboundHandler;import java.net.InetAddress;import java.util.Date;/** * Created by L_kanglin on 2017/6/4. */public class TimerServerHandler extends ChannelHandlerAdapter {    private int counter;    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {        String body = (String) msg;        System.out.println("The time server receive order:" + body + ";the counter is:" + (++counter));        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(System.currentTimeMillis()).toString()                : "BAD ORDER";        currentTime = currentTime + System.getProperty("line.separator");        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());        ctx.write(resp);    }    public void channelReadComplete(ChannelHandlerContext ctx) {        ctx.flush();    }    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {        ctx.close();    }}

客户端程序：

package TCPTimeClient;import io.netty.bootstrap.Bootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.SocketChannel;import io.netty.channel.socket.nio.NioSocketChannel;import io.netty.handler.codec.LineBasedFrameDecoder;import io.netty.handler.codec.string.StringDecoder;/** * Created by L_kanglin on 2017/6/4. */public class TCPTimeClient {    public void connect(int port, String host) {        // 配置客户端的NIO线程组        EventLoopGroup group = new NioEventLoopGroup();        try {            Bootstrap b = new Bootstrap();            b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true)                    .handler(new ChannelInitializer<SocketChannel>() {                        @Override                        public void initChannel(SocketChannel ch) throws Exception {                            // 以下两行代码为了解决半包读问题                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));                            ch.pipeline().addLast(new StringDecoder());                            ch.pipeline().addLast(new TimeClientHandler());                        }                    });            // 发起异步连接操作            ChannelFuture f = b.connect(host, port).sync();            // 等待链路关闭            f.channel().closeFuture().sync();        } catch (Exception e) {        } finally {            // 退出，释放NIO线程组            group.shutdownGracefully();        }    }    public static void main(String[] args) {        int port = 8080;        if (null != args && args.length > 0) {            try {                port = Integer.valueOf(args[0]);            } catch (Exception e) {            }        }        new TCPTimeClient().connect(port, "127.0.0.1");    }}

package TCPTimeClient;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import java.util.logging.Logger;/** * Created by L_kanglin on 2017/6/5. */public class TimeClientHandler extends ChannelHandlerAdapter {    private static final Logger logger = Logger.getLogger(TimeClientHandler.class.getName());    private int counter;    private byte[] req;    public TimeClientHandler() {        req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes();    }    public void channelActive(ChannelHandlerContext ctx) {        ByteBuf message = null;        for (int i = 0; i < 50; i++) {            message = Unpooled.buffer(req.length);            message.writeBytes(req);            ctx.writeAndFlush(message);        }    }    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {        String body = (String) msg;        System.out.println("Now is:" + body + "; the counter is:" + (++counter));    }    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {        logger.warning("Unexcepted exception from downstream:" + cause.getMessage());        ctx.close();    }}

服务端运行程序如下：

服务已经启动,端口:8080The time server receive order:QUERY TIME ORDER;the counter is:1The time server receive order:QUERY TIME ORDER;the counter is:2The time server receive order:QUERY TIME ORDER;the counter is:3The time server receive order:QUERY TIME ORDER;the counter is:4The time server receive order:QUERY TIME ORDER;the counter is:5The time server receive order:QUERY TIME ORDER;the counter is:6The time server receive order:QUERY TIME ORDER;the counter is:7The time server receive order:QUERY TIME ORDER;the counter is:8The time server receive order:QUERY TIME ORDER;the counter is:9The time server receive order:QUERY TIME ORDER;the counter is:10The time server receive order:QUERY TIME ORDER;the counter is:11The time server receive order:QUERY TIME ORDER;the counter is:12The time server receive order:QUERY TIME ORDER;the counter is:13The time server receive order:QUERY TIME ORDER;the counter is:14The time server receive order:QUERY TIME ORDER;the counter is:15The time server receive order:QUERY TIME ORDER;the counter is:16The time server receive order:QUERY TIME ORDER;the counter is:17The time server receive order:QUERY TIME ORDER;the counter is:18The time server receive order:QUERY TIME ORDER;the counter is:19The time server receive order:QUERY TIME ORDER;the counter is:20The time server receive order:QUERY TIME ORDER;the counter is:21The time server receive order:QUERY TIME ORDER;the counter is:22The time server receive order:QUERY TIME ORDER;the counter is:23The time server receive order:QUERY TIME ORDER;the counter is:24The time server receive order:QUERY TIME ORDER;the counter is:25The time server receive order:QUERY TIME ORDER;the counter is:26The time server receive order:QUERY TIME ORDER;the counter is:27The time server receive order:QUERY TIME ORDER;the counter is:28The time server receive order:QUERY TIME ORDER;the counter is:29The time server receive order:QUERY TIME ORDER;the counter is:30The time server receive order:QUERY TIME ORDER;the counter is:31The time server receive order:QUERY TIME ORDER;the counter is:32The time server receive order:QUERY TIME ORDER;the counter is:33The time server receive order:QUERY TIME ORDER;the counter is:34The time server receive order:QUERY TIME ORDER;the counter is:35The time server receive order:QUERY TIME ORDER;the counter is:36The time server receive order:QUERY TIME ORDER;the counter is:37The time server receive order:QUERY TIME ORDER;the counter is:38The time server receive order:QUERY TIME ORDER;the counter is:39The time server receive order:QUERY TIME ORDER;the counter is:40The time server receive order:QUERY TIME ORDER;the counter is:41The time server receive order:QUERY TIME ORDER;the counter is:42The time server receive order:QUERY TIME ORDER;the counter is:43The time server receive order:QUERY TIME ORDER;the counter is:44The time server receive order:QUERY TIME ORDER;the counter is:45The time server receive order:QUERY TIME ORDER;the counter is:46The time server receive order:QUERY TIME ORDER;the counter is:47The time server receive order:QUERY TIME ORDER;the counter is:48The time server receive order:QUERY TIME ORDER;the counter is:49The time server receive order:QUERY TIME ORDER;the counter is:50

客户端运行程序如下：

Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:1Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:2Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:3Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:4Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:5Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:6Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:7Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:8Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:9Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:10Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:11Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:12Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:13Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:14Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:15Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:16Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:17Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:18Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:19Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:20Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:21Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:22Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:23Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:24Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:25Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:26Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:27Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:28Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:29Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:30Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:31Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:32Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:33Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:34Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:35Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:36Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:37Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:38Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:39Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:40Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:41Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:42Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:43Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:44Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:45Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:46Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:47Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:48Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:49Now is:Mon Jun 05 10:29:49 CST 2017; the counter is:50

模拟TCP粘包和半包场景，采用简单的压力测试，通信链路建立成功之后，客户端连续发送100条消息给服务端，然后查看服务端和客户端的运行结果。

LineBasedFrameDecoder和StringDecoder的原理分析：
LineBasedFrameDecoder的工作原理是它依次遍历ByteBuf中的可读字节，判断看是否有“\n”或者“\r\n”，如果有，就以此位置为结束位置，从可读索引到结束位置区间的字节就组成了一行。它是以换行符为结束标志的解码器，支持携带结束符或者不携带结束符两种解码方式，同时支持配置单行的最大长度。如果连续读取到最大长度后仍然没有发现换行符，就会抛出异常，同时忽略掉之前读到的异常码流。

StringDecoder就是将接收到的对象转换成字符串，然后继续调用后面的handler。LineBasedFrameDecoder+StringDecoder组合就是按行切换的文本解码器，它被设计用来支持TCP的粘包和拆包。