tcp粘包与拆包

TCP是基于数据流的协议，TCP为提高传输效率，默认使用Nagle算法，会有延迟，往往要收集到足够多的数据后才发送一个TCP段。TCP底层不了解业务数据的含义，它会根据TCP缓冲区的实际情况进行包的划分，所以业务上认为，一个完整的包可能被TCP拆分为多个包进行发送，也可能把多个小包封装成一个大的数据包进行发送，这就是所谓的TCP粘包和拆包问题。

netty实现自定义协议

定义了消息格式的类：

public class MyProtocol {
    
    private int length;
    private byte[] content;
    
    public int getLength() {
    
        return length;
    }
    public void setLength(int length) {
    
        this.length = length;
    }

    public byte[] getContent() {
    
        return content;
    }
    public void setContent(byte[] content) {
    
        this.content = content;
    }
    @Override
    public String toString() {
    
        return "MyProtocol{" +
                "length=" + length +
                ", content=" + new String(content,Charset.forName("utf-8")) +
                '}';
    }
}

自定义协议解码器：

public class MyProtocolDecoder extends ReplayingDecoder<Void> {
    
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
    
        int length = in.readInt();
        byte[] content = new byte[length];
        in.readBytes(content);
        MyProtocol myProtocol = new MyProtocol();
        myProtocol.setLength(length);
        myProtocol.setContent(content);
        out.add(myProtocol);
    }
}

自定义协议编码器：

public class MyProtocolEncoder extends MessageToByteEncoder<MyProtocol> {
    
    @Override
    protected void encode(ChannelHandlerContext ctx, MyProtocol msg, ByteBuf out) throws Exception {
    
        int length=msg.getLength();
        byte[] content = msg.getContent();
        out.writeInt(length);
        out.writeBytes(content);
    }
}

客户端业务handler，通道建立连接后，向服务器发送10条数据：

public class MyClientHandler extends SimpleChannelInboundHandler<MyProtocol> {
    
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, MyProtocol msg) throws Exception {
     }
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
    
        for(int i=0;i<10;i++){
    
            String message = "from the client";
            int length = message.getBytes(Charset.forName("utf-8")).length;
            byte[] content = message.getBytes(Charset.forName("utf-8"));
            MyProtocol myProtocol = new MyProtocol();
            myProtocol.setLength(length);
            myProtocol.setContent(content);
            ctx.writeAndFlush(myProtocol);
        }
    }
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
    
        cause.printStackTrace();
        ctx.close();
    }
}

服务端业务handler：

public class MyServerHandler extends SimpleChannelInboundHandler<MyProtocol> {
    
    private int count;
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, MyProtocol msg) throws Exception {
    
        System.out.println(msg);
        System.out.println(++count);
    }
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
    
        cause.printStackTrace();
        ctx.close();
    }
}

最终在服务器上接收的结果：