Netty 之 TCP粘包拆包基本解决方案

上个小节我们浅析了在Netty的使用的时候TCP的粘包和拆包的现象，Netty对此问题提供了相对比较丰富的解决方案

Netty提供了几个常用的解码器，帮助我们解决这些问题，其实上述的粘包和拆包的问题，归根结底的解决方案就是发送端给远程端一个标记，告诉远程端，每个信息的结束标志是什么，这样，远程端获取到数据后，根据跟发送端约束的标志，将接收的信息分切或者合并成我们需要的信息，这样我们就可以获取到正确的信息了

例如，我们刚才的例子中，我们可以在发送的信息中，加一个结束标志，例如两个远程端规定以行来切分数据，那么发送端，就需要在每个信息体的末尾加上行结束的标志，部分代码如下：

修改BaseClientHandler的req的构造：

 public BaseClientHandler() {
 //        req = ("BazingaLyncc is learner").getBytes();
         req = ("In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. His book w"
                 + "ill give We’ve reached an exciting point—in the next chapter we’ll discuss bootstrapping, the process "
                 + "of configuring and connecting all of Netty’s components to bring your learned about threading models in ge"
                 + "neral and Netty’s threading model in particular, whose performance and consistency advantages we discuss"
                 + "ed in detail In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. Hi"
                 + "s book will give We’ve reached an exciting point—in the next chapter we’ll discuss bootstrapping, the"
                 + " process of configuring and connecting all of Netty’s components to bring your learned about threading "
                 + "models in general and Netty’s threading model in particular, whose performance and consistency advantag"
                 + "es we discussed in detailIn this chapter you general, we recommend Java Concurrency in Practice by Bri"
                 + "an Goetz. His book will give We’ve reached an exciting point—in the next chapter;the counter is: 1 2222"
                 + "sdsa ddasd asdsadas dsadasdas" + System.getProperty("line.separator")).getBytes();
     }

我们在我们巨长的req中末尾加了System.getProperty("line.separator")，这样相当于给req打了一个标记

打完标记，其实我们这个示例中的server中还不知道是以行为结尾的，所以我们需要修改server的handler链，在inbound链中加一个额外的处理链，判断一下，获取的信息按照行来切分，我们很庆幸，这样枯燥的代码Netty已经帮我们完美地完成了，Netty提供了一个LineBasedFrameDecoder这个类，顾名思义，这个类名字中有decoder，说明是一个解码器，我们再看看它的详细声明：

 /**
  * A decoder that splits the received {@link ByteBuf}s on line endings.
  *
  * Both {@code "\n"} and {@code "\r\n"} are handled.
  * For a more general delimiter-based decoder, see {@link DelimiterBasedFrameDecoder}.
  */
 public class LineBasedFrameDecoder extends ByteToMessageDecoder {

     /** Maximum length of a frame we're willing to decode.  */
     private final int maxLength;
     /** Whether or not to throw an exception as soon as we exceed maxLength. */
     private final boolean failFast;
     private final boolean stripDelimiter;

     /** True if we're discarding input because we're already over maxLength.  */
     private boolean discarding;
     private int discardedBytes;

它是继承ByteToMessageDecoder的，是将byte类型转化成Message的，所以我们应该将这个解码器放在inbound处理器链的第一个，所以我们修改一下Server端的启动代码：

 package com.lyncc.netty.stickpackage.myself;

 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;

 import java.net.InetSocketAddress;

 public class BaseServer {

     private int port;

     public BaseServer(int port) {
         this.port = port;
     }

     public void start(){
         EventLoopGroup bossGroup = new NioEventLoopGroup(1);
         EventLoopGroup workerGroup = new NioEventLoopGroup();
         try {
             ServerBootstrap sbs = new ServerBootstrap().group(bossGroup,workerGroup).channel(NioServerSocketChannel.class).localAddress(new InetSocketAddress(port))
                     .childHandler(new ChannelInitializer() {

                         protected void initChannel(SocketChannel ch) throws Exception {
                             ch.pipeline().addLast(new LineBasedFrameDecoder(2048));
                             ch.pipeline().addLast(new StringDecoder());
                             ch.pipeline().addLast(new BaseServerHandler());
                         };

                     }).option(ChannelOption.SO_BACKLOG, 128)
                     .childOption(ChannelOption.SO_KEEPALIVE, true);
              // 绑定端口，开始接收进来的连接
              ChannelFuture future = sbs.bind(port).sync();

              System.out.println("Server start listen at " + port );
              future.channel().closeFuture().sync();
         } catch (Exception e) {
             bossGroup.shutdownGracefully();
             workerGroup.shutdownGracefully();
         }
     }

     public static void main(String[] args) throws Exception {
         int port;
         if (args.length > 0) {
             port = Integer.parseInt(args[0]);
         } else {
             port = 8080;
         }
         new BaseServer(port).start();
     }
 }

这样，我们只是在initChannel方法中增加了一个LineBasedFrameDecoder这个类，其中2048是规定一行数据最大的字节数

我们再次运行，我们再看看效果：

可以看到客户端发送的两次msg，被服务器端成功地两次接收了，我们要的效果达到了

我们将LineBasedFrameDecoder中的2048参数，缩小一半，变成1024，我们再看看效果：

出现了异常，这个异常时TooLongFrameException,这个异常在Netty in Action中介绍过，帧的大小太大，在我们这个场景中，就是我们发送的一行信息大小是1076，大于了我们规定的1024所以报错了

我们再解决另一个粘包的问题，我们可以看到上节中介绍的那个粘包案例中，我们发送了100次的信息“BazingaLyncc is learner”，这个案例很特殊，这个信息是一个特长的数据，字节长度是23，所以我们可以使用Netty为我们提供的FixedLengthFrameDecoder这个解码器，看到这个名字就明白了大半，定长数据帧的解码器，所以我们修改一下代码：

BaseClientHandler：

 package com.lyncc.netty.stickpackage.myself;

 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelInboundHandlerAdapter;

 public class BaseClientHandler extends ChannelInboundHandlerAdapter{

     private byte[] req;

     public BaseClientHandler() {
         req = ("BazingaLyncc is learner").getBytes();
 //        req = ("In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. His book w"
 //                + "ill give We’ve reached an exciting point—in the next chapter we’ll discuss bootstrapping, the process "
 //                + "of configuring and connecting all of Netty’s components to bring your learned about threading models in ge"
 //                + "neral and Netty’s threading model in particular, whose performance and consistency advantages we discuss"
 //                + "ed in detail In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. Hi"
 //                + "s book will give We’ve reached an exciting point—in the next chapter we’ll discuss bootstrapping, the"
 //                + " process of configuring and connecting all of Netty’s components to bring your learned about threading "
 //                + "models in general and Netty’s threading model in particular, whose performance and consistency advantag"
 //                + "es we discussed in detailIn this chapter you general, we recommend Java Concurrency in Practice by Bri"
 //                + "an Goetz. His book will give We’ve reached an exciting point—in the next chapter;the counter is: 1 2222"
 //                + "sdsa ddasd asdsadas dsadasdas" + System.getProperty("line.separator")).getBytes();
     }


     @Override
     public void channelActive(ChannelHandlerContext ctx) throws Exception {
         ByteBuf message = null;
         for (int i = 0; i < 100; i++) {
             message = Unpooled.buffer(req.length);
             message.writeBytes(req);
             ctx.writeAndFlush(message);
         }
 //        message = Unpooled.buffer(req.length);
 //        message.writeBytes(req);
 //        ctx.writeAndFlush(message);
 //        message = Unpooled.buffer(req.length);
 //        message.writeBytes(req);
 //        ctx.writeAndFlush(message);
     }

     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
         ctx.close();
     }

 }

BaseServer：

 package com.lyncc.netty.stickpackage.myself;

 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.FixedLengthFrameDecoder;
 import io.netty.handler.codec.string.StringDecoder;

 import java.net.InetSocketAddress;

 public class BaseServer {

     private int port;

     public BaseServer(int port) {
         this.port = port;
     }

     public void start(){
         EventLoopGroup bossGroup = new NioEventLoopGroup(1);
         EventLoopGroup workerGroup = new NioEventLoopGroup();
         try {
             ServerBootstrap sbs = new ServerBootstrap().group(bossGroup,workerGroup).channel(NioServerSocketChannel.class).localAddress(new InetSocketAddress(port))
                     .childHandler(new ChannelInitializer() {

                         protected void initChannel(SocketChannel ch) throws Exception {
                             ch.pipeline().addLast(new FixedLengthFrameDecoder(23));
                             ch.pipeline().addLast(new StringDecoder());
                             ch.pipeline().addLast(new BaseServerHandler());
                         };

                     }).option(ChannelOption.SO_BACKLOG, 128)
                     .childOption(ChannelOption.SO_KEEPALIVE, true);
              // 绑定端口，开始接收进来的连接
              ChannelFuture future = sbs.bind(port).sync();

              System.out.println("Server start listen at " + port );
              future.channel().closeFuture().sync();
         } catch (Exception e) {
             bossGroup.shutdownGracefully();
             workerGroup.shutdownGracefully();
         }
     }

     public static void main(String[] args) throws Exception {
         int port;
         if (args.length > 0) {
             port = Integer.parseInt(args[0]);
         } else {
             port = 8080;
         }
         new BaseServer(port).start();
     }
 }

我们就是在channelhandler链中，加入了FixedLengthFrameDecoder，且参数是23，告诉Netty，获取的帧数据有23个字节就切分一次

运行结果：

可以看见，我们获取到了我们想要的效果

当然Netty还提供了一些其他的解码器，有他们自己的使用场景，例如有按照某个固定字符切分的DelimiterBasedFrameDecoder的解码器

我们再次修改代码：

BaseClientHandler.java

 package com.lyncc.netty.stickpackage.myself;

 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelInboundHandlerAdapter;

 public class BaseClientHandler extends ChannelInboundHandlerAdapter{

     private byte[] req;

     public BaseClientHandler() {
 //        req = ("BazingaLyncc is learner").getBytes();
         req = ("In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. $$__ His book w"
                 + "ill give We’ve reached an exciting point—in the next chapter we’ll $$__ discuss bootstrapping, the process "
                 + "of configuring and connecting all of Netty’s components to bring $$__ your learned about threading models in ge"
                 + "neral and Netty’s threading model in particular, whose performance $$__ and consistency advantages we discuss"
                 + "ed in detail In this chapter you general, we recommend Java  $$__Concurrency in Practice by Brian Goetz. Hi"
                 + "s book will give We’ve reached an exciting point—in the next $$__ chapter we’ll discuss bootstrapping, the"
                 + " process of configuring and connecting all of Netty’s components $$__ to bring your learned about threading "
                 + "models in general and Netty’s threading model in particular, $$__ whose performance and consistency advantag"
                 + "es we discussed in detailIn this chapter you general, $$__ we recommend Java Concurrency in Practice by Bri"
                 + "an Goetz. His book will give We’ve reached an exciting $$__ point—in the next chapter;the counter is: 1 2222"
                 + "sdsa ddasd asdsadas dsadasdas" + System.getProperty("line.separator")).getBytes();
     }


     @Override
     public void channelActive(ChannelHandlerContext ctx) throws Exception {
         ByteBuf message = null;
 //        for (int i = 0; i < 100; i++) {
 //            message = Unpooled.buffer(req.length);
 //            message.writeBytes(req);
 //            ctx.writeAndFlush(message);
 //        }
         message = Unpooled.buffer(req.length);
         message.writeBytes(req);
         ctx.writeAndFlush(message);
         message = Unpooled.buffer(req.length);
         message.writeBytes(req);
         ctx.writeAndFlush(message);
     }

     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
         ctx.close();
     }

 }

我们在req的字符串中增加了“$$__”这样的切割符，然后再Server中照例增加一个DelimiterBasedFrameDecoder，来切割字符串：

 ServerBootstrap sbs = new ServerBootstrap().group(bossGroup,workerGroup).channel(NioServerSocketChannel.class).localAddress(new InetSocketAddress(port))
                     .childHandler(new ChannelInitializer<SocketChannel>() {

                         protected void initChannel(SocketChannel ch) throws Exception {
                             ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,Unpooled.copiedBuffer("$$__".getBytes())));
                             ch.pipeline().addLast(new StringDecoder());
                             ch.pipeline().addLast(new BaseServerHandler());
                         };

                     }).option(ChannelOption.SO_BACKLOG, 128)
                     .childOption(ChannelOption.SO_KEEPALIVE, true);

我们在initChannel中第一个inbound中增加了DelimiterBasedFrameDecoder，且规定切割符就是“$$__”，这样就能正常切割了，我们看看运行效果：

可以看到被分了20次读取，我们可以这样理解，客户端发送了2次req字节，每个req中有10个“$$__”，这样就是第11次切割的时候其实发送了粘包，第一个req中末尾部分和第二次的头部粘在了一起，作为第11部分的内容

而最后一部分的内容因为没有"$$__"切割，所以没有打印在控制台上~

其实这类的Handler还是相对比较简单的，真实的生产环境这些decoder只是作为比较基本的切分类，但是这些decoder还是很好用的~

希望讲的对您有所帮助~END~