Netty-TCP粘包和拆包及解决方案
TCP粘包和拆包基本介绍
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、拆包问题
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D1和D2，没有粘包和拆包
- 服务端一次接收到了两个数据包，D1和D2粘合在一起，称为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D2包的剩余内容，这称为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，也称为TCP拆包
TCP粘包和拆包现象实例
在编写Netty程序时，如果没有做处理，就会发生粘包和拆包的问题
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| public class MyServer {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyServerHandler());
}
});
ChannelFuture channelFuture = b.bind(7000).sync();
channelFuture.channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
class MyServerHandler extends SimpleChannelInboundHandler<ByteBuf> {
private int count = 0;
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
byte[] buffer = new byte[msg.readableBytes()];
msg.readBytes(buffer);
String message = new String(buffer, CharsetUtil.UTF_8);
System.out.println("服务器接收数据：" + message);
System.out.println("服务器接收消息量=" + (++this.count));
ctx.writeAndFlush(Unpooled.copiedBuffer(UUID.randomUUID().toString() + " ", CharsetUtil.UTF_8));
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
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| public class MyClient {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup eventLoopGroup = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap();
b.group(eventLoopGroup)
.channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyClientHandler());
}
});
ChannelFuture channelFuture = b.connect("127.0.0.1", 7000).sync();
channelFuture.channel().closeFuture().sync();
} finally {
eventLoopGroup.shutdownGracefully();
}
}
}
class MyClientHandler extends SimpleChannelInboundHandler<ByteBuf>{
private int count = 0;
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
byte[] buffer = new byte[msg.readableBytes()];
msg.readBytes(buffer);
String message = new String(buffer, CharsetUtil.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："+(++count));
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
for (int i = 0; i < 10; i++) {
ByteBuf buf = Unpooled.copiedBuffer("hello server "+i, CharsetUtil.UTF_8);
ctx.writeAndFlush(buf);
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
|
TCP粘包和拆包解决方案
- 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TCP粘包、拆包
具体实例
- 要求客户端发送5个Message对象，客户端每次发送一个Message对象
- 服务器端每次接收一个Message，分5次进行解码，每读取到一个Message，会回复一个Message对象给客户端
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|
public class MessageProtocol {
private int len;
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;
}
}
|
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| public class MyServer {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyMessageDecoder());
pipeline.addLast(new MyMessageEncoder());
pipeline.addLast(new MyServerHandler());
}
});
ChannelFuture channelFuture = b.bind(7000).sync();
channelFuture.channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
class MyMessageDecoder extends ReplayingDecoder<Void>{
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
System.out.println("MyMessageDecoder decode被调用");
int length = in.readInt();
byte[] content = new byte[length];
in.readBytes(content);
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(length);
messageProtocol.setContent(content);
out.add(messageProtocol);
}
}
class MyServerHandler extends SimpleChannelInboundHandler<MessageProtocol> {
private int count = 0;
@Override
protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception {
int length = msg.getLen();
byte[] content = msg.getContent();
System.out.println("服务器接收信息:");
System.out.println("长度="+length);
System.out.println("内容="+new String(content, CharsetUtil.UTF_8));
System.out.println("服务器接收到消息包数量:"+(++this.count));
System.out.println("------------------");
String responseContent = UUID.randomUUID().toString();
int responseLength = responseContent.getBytes(CharsetUtil.UTF_8).length;
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(responseLength);
messageProtocol.setContent(responseContent.getBytes(CharsetUtil.UTF_8));
ctx.writeAndFlush(messageProtocol);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
|
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| public class MyClient {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup eventLoopGroup = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap();
b.group(eventLoopGroup)
.channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyMessageEncoder());
pipeline.addLast(new MyMessageDecoder());
pipeline.addLast(new MyClientHandler());
}
});
ChannelFuture channelFuture = b.connect("127.0.0.1", 7000).sync();
channelFuture.channel().closeFuture().sync();
} finally {
eventLoopGroup.shutdownGracefully();
}
}
}
class MyClientHandler extends SimpleChannelInboundHandler<MessageProtocol>{
private int count = 0;
@Override
protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception {
int len = msg.getLen();
byte[] content = msg.getContent();
System.out.println("客户端接收到的消息:");
System.out.println("长度="+len);
System.out.println("内容="+new String(content,CharsetUtil.UTF_8));
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 < 5; i++) {
String msg = "今天星期六";
byte[] content = msg.getBytes(CharsetUtil.UTF_8);
int length = msg.getBytes(CharsetUtil.UTF_8).length;
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(length);
messageProtocol.setContent(content);
ctx.writeAndFlush(messageProtocol);
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
class MyMessageEncoder extends MessageToByteEncoder<MessageProtocol>{
@Override
protected void encode(ChannelHandlerContext ctx, MessageProtocol msg, ByteBuf out) throws Exception {
System.out.println("MyMessageEncoder encode被调用");
out.writeInt(msg.getLen());
out.writeBytes(msg.getContent());
}
}
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