文章目录
- 1 TCP 粘包和拆包介绍
- 2 Netty 粘包演示
- 3 Netty中解决TCP粘包和拆包
1 TCP 粘包和拆包介绍
TCP
是面向连接的,面向流的,提供高可靠性服务。收发两端(客户端和服务器端)都要有一一成对的socket
,因此,发送端为了将多个发给接收端的包,更有效的发给对方,使用了优化方法(Nagle
算法),将多次间隔较小且数据量小的数据,合并成一个大的数据块,然后进行封包。这样做虽然提高了效率,但是接收端就难于分辨出完整的数据包了,因为面向流的通信是无消息保护边界的- 由于
TCP
无消息保护边界,需要在接收端处理消息边界问题,也就是我们所说的粘包、拆包 TCP
粘包、拆包图解
假设客户端分别发送了两个数据包 D1
和 D2
给服务端,由于服务端一次读取到字节数是不确定的,故可能存在以下四种情况:
- 服务端分两次读取到了两个独立的数据包,分别是
D1
和D2
,没有粘包和拆包 - 服务端一次接受到了两个数据包,
D1
和D2
粘合在一起,称之为TCP
粘包 - 服务端分两次读取到了数据包,第一次读取到了完整的
D1
包和D2
包的部分内容,第二次读取到了D2
包的剩余内容,这称之为TCP
拆包 - 服务端分两次读取到了数据包,第一次读取到了
D1
包的部分内容D1_1
,第二次读取到了D1
包的剩余部分内容D1_2
和完整的D2
包,这称之为TCP
拆包。
2 Netty 粘包演示
- 服务端代码
package com.warybee.tcp;
import com.warybee.simple.NettyServerHandler;
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;
/**
*/
public class MyServer {
public static void main(String[] args) {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap=new ServerBootstrap();
bootstrap.group(bossGroup,workerGroup)
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG,128)
.childOption(ChannelOption.SO_KEEPALIVE,true)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new MyServerHandler());
}
});
ChannelFuture channelFuture = bootstrap.bind(9999).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
- 服务端handler
package com.warybee.tcp;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
import java.util.UUID;
/**
*/
public class MyServerHandler extends SimpleChannelInboundHandler<ByteBuf> {
private int count;
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
byte[] buffer = new byte[msg.readableBytes()];
msg.readBytes(buffer);
//将buffer转成字符串
String message = new String(buffer, Charset.forName("utf-8"));
System.out.println("服务器接收到数据 " + message);
System.out.println("服务器接收到消息量=" + (++this.count));
//服务器回送数据给客户端, 回送一个随机id ,
ByteBuf responseByteBuf = Unpooled.copiedBuffer(UUID.randomUUID().toString() + "\n",
Charset.forName("utf-8"));
ctx.writeAndFlush(responseByteBuf);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
服务端的 handler 主要逻辑是接收客户端发送过来的数据,看看是否是一条一条接收。然后每次接收到数据之后给客户端回复一个确认消息。
- 客户端
package com.warybee.tcp;
import com.warybee.simple.NettyClientHandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
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.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
/**
* @description
*/
public class MyClient {
public static void main(String[] args) {
EventLoopGroup eventExecutors = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(eventExecutors)
.channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new StringDecoder());
pipeline.addLast(new StringEncoder());
pipeline.addLast(new MyClientHandler());
}
});
ChannelFuture cf = bootstrap.connect("127.0.0.1", 9999).sync();
cf.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
eventExecutors.shutdownGracefully();
}
}
}
- 客户端Handler
package com.warybee.tcp;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
/**
* @author joy
* @create 2021-10-27 14:50
* @description
*/
public class MyClientHandler extends SimpleChannelInboundHandler<ByteBuf> {
private int count;
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
byte[] buffer = new byte[msg.readableBytes()];
msg.readBytes(buffer);
String message = new String(buffer, Charset.forName("utf-8"));
System.out.println("客户端接收到消息=" + message);
System.out.println("客户端接收消息数量=" + (++this.count));
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
for (int i = 0; i < 20; ++i) {
ByteBuf buffer = Unpooled.copiedBuffer("你好服务端:" + i+"rn", Charset.forName("utf-8"));
ctx.writeAndFlush(buffer);
}
}
}
客户端 handler 主要逻辑是:循环20次给服务端发送测试消息。接收服务端的确认消息
启动项目之后服务端收到的消息结果:
这里能看到多条消息被粘到一起发送了。
3 Netty中解决TCP粘包和拆包
使用自定义协议+编解码器来解决。关键就是要解决服务器端每次读取数据长度的问题,这个问题解决,就不会出现服务器多读或少读数据的问题,从而避免的 TCP
粘包、拆包。
- 自定义消息协议
package com.warybee.tcp;
/**
* @description 自定义协议包
*/
public class MessageProtocol {
//消息长度
private int len;
/**
* 消息
*/
private byte[] content;
public int getLen() {
return len;
}
public void setLen(int len) {
this.len = len;
}
public byte[] getContent() {
return content;
}
public void setContent(byte[] content) {
this.content = content;
}
}
- 自定义编码器
package com.warybee.tcp;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;
/**
* @description 自定义协议包编码
*/
public class MyMessageEncoder extends MessageToByteEncoder<MessageProtocol> {
@Override
protected void encode(ChannelHandlerContext ctx, MessageProtocol msg, ByteBuf out) throws Exception {
out.writeInt(msg.getLen());
out.writeBytes(msg.getContent());
}
}
- 自定义解码器
package com.warybee.tcp;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ReplayingDecoder;
import java.util.List;
/**
* @description
*/
public class MyMessageDecoder extends ReplayingDecoder<Void> {
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
//需要将得到二进制字节码转化为MessageProtocol 数据包(对象)
int length = in.readInt();
byte[] content = new byte[length];
in.readBytes(content);
//封装成 MessageProtocol 对象,放入 out, 传递下一个handler业务处理
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(length);
messageProtocol.setContent(content);
out.add(messageProtocol);
}
}
- 服务端代码
package com.warybee.tcp;
import com.warybee.simple.NettyServerHandler;
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;
/**
* @author joy
*/
public class MyServer {
public static void main(String[] args) {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap=new ServerBootstrap();
bootstrap.group(bossGroup,workerGroup)
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG,128)
.childOption(ChannelOption.SO_KEEPALIVE,true)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
//添加自定义编码器
pipeline.addLast("encoder",new MyMessageEncoder());
//添加自定义解码器
pipeline.addLast("decoder",new MyMessageDecoder());
pipeline.addLast(new MyServerHandler());
}
});
ChannelFuture channelFuture = bootstrap.bind(9999).sync();
channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
- 服务端handler
package com.warybee.tcp;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
import java.util.UUID;
/**
* @description
*/
public class MyServerHandler extends SimpleChannelInboundHandler<MessageProtocol> {
private int count;
@Override
protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception {
//接收到数据,并处理
int len = msg.getLen();
byte[] content = msg.getContent();
System.out.println();
System.out.println();
System.out.println();
System.out.println("服务器接收到信息如下");
System.out.println("长度=" + len);
System.out.println("内容=" + new String(content, Charset.forName("utf-8")));
System.out.println("服务器接收到消息包数量=" + (++this.count));
//回复消息
String responseContent = UUID.randomUUID().toString();
int responseLen = responseContent.getBytes("utf-8").length;
byte[] responseContent2 = responseContent.getBytes("utf-8");
//构建一个协议包
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(responseLen);
messageProtocol.setContent(responseContent2);
ctx.writeAndFlush(messageProtocol);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
服务端的 handler 主要逻辑是接收客户端发送过来的数据,看看是否是一条一条接收。然后每次接收到数据之后给客户端回复一个确认消息。**
- 客户端handler
package com.warybee.tcp;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
/**
* @author joy
* @create 2021-10-27 14:50
* @description
*/
public class MyClientHandler extends SimpleChannelInboundHandler<MessageProtocol> {
private int count;
@Override
protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception {
int len = msg.getLen();
byte[] content = msg.getContent();
System.out.println("客户端接收到消息如下");
System.out.println("长度=" + len);
System.out.println("内容=" + new String(content, Charset.forName("utf-8")));
System.out.println("客户端接收消息数量=" + (++this.count));
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
//使用客户端发送5条数据 "今天天气冷,吃火锅" 编号
for (int i = 0; i < 5; i++) {
String mes = "今天天气冷,吃火锅";
byte[] content = mes.getBytes(Charset.forName("utf-8"));
int length = mes.getBytes(Charset.forName("utf-8")).length;
//创建协议包对象
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(length);
messageProtocol.setContent(content);
ctx.writeAndFlush(messageProtocol);
}
}
}