Java-第十七部分-NIO和Netty-Handler链调用机制和TCP粘包拆包

Language 2022-02-25 12:27:50 views: null

NIO和Netty全文

Handler链调用机制

  • ChannelHandler处理入站和出站数据的逻辑容器
  1. ChannelInboundHandler处理入站数据，读取，从头到尾
  2. ChannelOutboundHandler处理出站数据，发送，从尾到头

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  • 入站数据被解码inbound，出站数据被编码outbound，根据添加的顺序独立运行，通过inbound/outbound来判断是否执行该handler
  • ProtobufEncoder编码器

image.png

  • ProtobufDecoder解码器

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  • ctx调用writeAndFlush交给当前handler的下一个outHandler；ctx.channel.writeAndFlush 从pipeline中最后一个outHandler开始调用

解码器

  • ByteToMessageDecoder继承关系，对入站数据进行缓冲，直到数据准备好被处理，读取全部信息

image.png

  • 由于不知道远程节点是否会一次性发送一个完整的信息，tcp可能会出现沾包拆包的问题
  • 解码int的例子

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自定义编解码器

  • 双向传递long类型数据

image.png

LongToByteEncoder

public class LongToByteEncoder extends MessageToByteEncoder<Long> {
    @Override
    protected void encode(ChannelHandlerContext ctx, Long msg, ByteBuf out) throws Exception {
        System.out.println("LongToByteEncoder - encode");
        System.out.println("msg: " + msg);
        out.writeLong(msg);
    }
}
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ByteToLongDecoder

public class ByteToLongDecoder extends ByteToMessageDecoder {
    /**
     * decode会根据接受的数据，被调用多次，知道没有新的元素被添加到list，或者buf没有更多可读的字节
     * 如果out不为空，就会将list的内容传递给下一个inboundhandler，那么该处理器的方法也会被调用多次
     * @param ctx 上下文
     * @param in 入站buf
     * @param out list集合，将解码后的数据传递给下一个handler
     * @throws Exception
     */
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        //long 8个字节，至少有8个字节才能读取
        System.out.println("ByteToLongDecoder - decode");
        //满8个字节读取一次
        if (in.readableBytes() >= 8) {
            out.add(in.readLong());
        }
    }
}
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ClientInitializer

public class ClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        //出站handler，进行编码
        ch.pipeline().addLast(new LongToByteEncoder());
        //解码器，inbound
        ch.pipeline().addLast(new ByteToLongDecoder());
        //业务handler
        ch.pipeline().addLast(new ClientHandler());
    }
}
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ServerInitializer

public class ServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        //入站handler
        pipeline.addLast(new ByteToLongDecoder());
        //出站handler
        pipeline.addLast(new LongToByteEncoder());
        pipeline.addLast(new ServerHandler());
    }
}
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public class ClientHandler extends SimpleChannelInboundHandler<Long> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Long msg) throws Exception {
        System.out.println("server: " + ctx.channel().remoteAddress() + " long: "+ msg);
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("ClientHandler - channelActive");
        ctx.writeAndFlush(12345L);
        //该处理器的前一个处理器为 `LongToByteEncoder`，只能处理long类型的数据
        //ctx.writeAndFlush(Unpooled.copiedBuffer("abcdabcdabcdabce", StandardCharsets.UTF_8));
    }
}
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  • 当写String时，服务器收到的结果，为分开两次读
ByteToLongDecoder - decode
[12345]
client: /127.0.0.1:64208 long: 12345
ByteToLongDecoder - decode
[7017280452178371428] abcdabcd
client: /127.0.0.1:64208 long: 7017280452178371428
ByteToLongDecoder - decode
[7017280452178371429] abcdabce
client: /127.0.0.1:64208 long: 7017280452178371429
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ServerHandler

public class ServerHandler extends SimpleChannelInboundHandler<Long> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Long msg) throws Exception {
        System.out.println("client: " + ctx.channel().remoteAddress() + " long: " + msg);
        //发送long
        ctx.writeAndFlush(98773L);
    }

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

  • MessageToByteEncoder中write方法，判断该类型是否能处理，如果不能处理，直接写出去ctx.write(msg, promise);，符合责任链模式

image.png image.png

  • 调用本地方法isInstance

image.png

  • 编码器和解码器，接受消息类型与待处理消息类型不一致，就不会执行该handler
  • 解码器进行解码，需要判断buf中的数据是否符合数据类型，否则接收到的结果与期望不一致

ReplayingDecoder

  • 继承MessageToByteDecoder，不需要判断readablelBytes() 是否有可读的区域，数据是否足够读取，内部进行管理
  • 参数类型用Void
public class ReplayByteToLongDecoder extends ReplayingDecoder<Void> {
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        System.out.println("ReplayByteToLongDecoder - decode");
        //数据量不足，会直接跳过，不传给下一个handler
        out.add(in.readLong());
    }
}
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  • 并不是所有ByteBuf的操作都支持，调用不支持的，会报异常
  • 在某些情况下，慢于MessageToByteDecoder，网络缓慢并且消息格式负责，消息会被拆成多个碎片

其他编解码器

  • LineBasedFrameDecoder 用行尾控制字符\n或者\r\n，作为分隔符来解析数据
  • DelimiteBasedFrameDecoder 自定义的特殊字符作为消息的分隔符
  • HttpObjectDecoder 解析http数据
  • LengthFieldBasedFrameDecoder 指定长度来标识整包消息，可以自动地处理黏包和半包消息

image.png image.png

TCP粘包和拆包

  • TCP面向连接，面向流，收发两端都要有一一成对的socket，发送段为了将多个发给接收端的包，更有效的发给对方，使用了优化算法 Nagle，将多次间隔较小且数据量小的数据，合并成一个数据块，进行封包

提高了效率，但是接收端难分辨出完整的数据包，面向流的通信无消息保护边界

  • 客户端分别发送了两个数据包D1和D2给服务端，服务端一次读取到的字节数是不确定的，有四种情况
  1. 服务端两次读取到了两个独立的数据包
  2. 服务端一次接收到了两个数据包，D1和D2粘合在一起，粘包
  3. 服务端分两次读取到了数据包，第一次读取到了完整的D1包和部分的D2包，第二次读取到了D2包的剩余内容，拆包
  4. 服务端分两次读取到了数据包，第一次读取到D1包的部分内容，第二次读取到部分的D1包和完整的D2包

image.png

解决粘包和拆包

  • 自定义协议+编解码器，解决服务端每次读取数据长度

协议包类

//协议包
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;
    }
    public MessageProtocol(int len, byte[] content) {
        this.len = len;
        this.content = content;
    }
}
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解码器

public class MessageDecoder extends ReplayingDecoder<Void> {
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        System.out.println("MessageDecoder - decode");
        int len = in.readInt(); //先读长度
        byte[] content = new byte[len];
        in.readBytes(content); //在读内容
        MessageProtocol mp = new MessageProtocol(len, content);
        out.add(mp);
    }
}
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编码器

public class MessageEncoder extends MessageToByteEncoder<MessageProtocol> {
    @Override
    protected void encode(ChannelHandlerContext ctx, MessageProtocol msg, ByteBuf out) throws Exception {
        System.out.println("MessageEncoder - encode");
        out.writeInt(msg.getLen());
        out.writeBytes(msg.getContent());
    }
}
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ClientHandler

public class ClientHandler extends SimpleChannelInboundHandler<MessageProtocol> {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        //发送数据
        for (int i = 0; i < 10; i++) {
            String message = "hello server - " + i;
            byte[] content = message.getBytes(StandardCharsets.UTF_8);
            int len = content.length;
            MessageProtocol mp = new MessageProtocol(len, content);
            ctx.writeAndFlush(mp);
        }
    }
    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("client len: " + len + " content: " + new String(content, StandardCharsets.UTF_8));
        System.out.println("client receive count: " + count++);
    }
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ServerHandler

public class ServerHandler 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("server: len - " + len + " - " + new String(content, StandardCharsets.UTF_8));
        System.out.println("receive count: " + count++);
        //会写
        String response = UUID.randomUUID().toString();
        int resLen = response.getBytes(StandardCharsets.UTF_8).length;
        MessageProtocol resMp = new MessageProtocol(resLen, response.getBytes(StandardCharsets.UTF_8));
        ctx.writeAndFlush(resMp);
    }
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