Netty 快速入门系列 - Chapter 7 数据包协议【第十九讲】解决方案-粘包分包原理

1. 消息如何在管道中流转

当前的一个handler如何往下面的一个handler传递一个对象

一个管道中会有多个handler，其中handler往下传递对象的方法是sendUpstream(event)

源码讲解：

NioWorker read 方法用于 读取Nio byte数据

  final ChannelBuffer buffer = bufferFactory.getBuffer(readBytes);
  buffer.setBytes(0, bb);
  buffer.writerIndex(readBytes);

  // Fire the event. 第一个upstream 介绍到数据是 ChannelBuffer 
  Channels.fireMessageReceived(channel, buffer);

public class NioWorker extends AbstractNioWorker 

 protected boolean read(SelectionKey k) {
        final SocketChannel ch = (SocketChannel) k.channel();
        final NioSocketChannel channel = (NioSocketChannel) k.attachment();

        final ReceiveBufferSizePredictor predictor =
            channel.getConfig().getReceiveBufferSizePredictor();
        final int predictedRecvBufSize = predictor.nextReceiveBufferSize();
        final ChannelBufferFactory bufferFactory = channel.getConfig().getBufferFactory();


        int ret = 0;
        int readBytes = 0;
        boolean failure = true;

        ByteBuffer bb = recvBufferPool.get(predictedRecvBufSize).order(bufferFactory.getDefaultOrder());
        try {
            while ((ret = ch.read(bb)) > 0) {
                readBytes += ret;
                if (!bb.hasRemaining()) {
                    break;
                }
            }
            failure = false;
        } catch (ClosedChannelException e) {
            // Can happen, and does not need a user attention.
        } catch (Throwable t) {
            fireExceptionCaught(channel, t);
        }


        if (readBytes > 0) {
            bb.flip();

            final ChannelBuffer buffer = bufferFactory.getBuffer(readBytes);
            buffer.setBytes(0, bb);
            buffer.writerIndex(readBytes);


            // Update the predictor.
            predictor.previousReceiveBufferSize(readBytes);


            // Fire the event.
            Channels.fireMessageReceived(channel, buffer);
        }


        if (ret < 0 || failure) {
            k.cancel(); // Some JDK implementations run into an infinite loop without this.
            close(channel, succeededFuture(channel));
            return false;
        }


        return true;
    }
 

Channels：Channel 是 Netty封装的Channel对象， 包含 nio channe 、sink 和  pipeline 等

Pipeline 是 DefaultChannelPipeline ， UpstreamMessageEvent 是 MessageEvent

public static void fireMessageReceived(Channel channel, Object message, SocketAddress remoteAddress) {
    channel.getPipeline().sendUpstream(new UpstreamMessageEvent(channel, message, remoteAddress));

 }

DefaultChannelPipeline： Upstream 从 head 开始 到 tailer 

getActualUpstreamContext(this.head); 获取Pipeline中第一个upstream handler

public void sendUpstream(ChannelEvent e) {
        DefaultChannelHandlerContext head = getActualUpstreamContext(this.head);
        if (head == null) {
            if (logger.isWarnEnabled()) {
                logger.warn(
                        "The pipeline contains no upstream handlers; discarding: " + e);
            }


            return;
        }


        sendUpstream(head, e);
    }


    void sendUpstream(DefaultChannelHandlerContext ctx, ChannelEvent e) {
        try {
            ((ChannelUpstreamHandler) ctx.getHandler()).handleUpstream(ctx, e);
        } catch (Throwable t) {
            notifyHandlerException(e, t);
        }
    }
 

ChannelHandlerContext：DefaultChannelHandlerContext  保存next 和 prev 处理节点，是一个双向链表

ChannelHandler--》ChannelUpstreamHandler

((ChannelUpstreamHandler) ctx.getHandler()).handleUpstream(ctx, e); 

--handleUpstream 继续查找下一个netxt 处理upstream ，主要 handleUpstream 传入当前Context，可以find next handler

private final class DefaultChannelHandlerContext implements ChannelHandlerContext {


  volatile DefaultChannelHandlerContext next;
        volatile DefaultChannelHandlerContext prev;
        private final String name;
        private final ChannelHandler handler;
        private final boolean canHandleUpstream;
        private final boolean canHandleDownstream;
        private volatile Object attachment;


        DefaultChannelHandlerContext(
                DefaultChannelHandlerContext prev, DefaultChannelHandlerContext next,
                String name, ChannelHandler handler) {


            if (name == null) {
                throw new NullPointerException("name");
            }
            if (handler == null) {
                throw new NullPointerException("handler");
            }
            canHandleUpstream = handler instanceof ChannelUpstreamHandler;
            canHandleDownstream = handler instanceof ChannelDownstreamHandler;


            if (!canHandleUpstream && !canHandleDownstream) {
                throw new IllegalArgumentException(
                        "handler must be either " +
                        ChannelUpstreamHandler.class.getName() + " or " +
                        ChannelDownstreamHandler.class.getName() + '.');
            }


            this.prev = prev;
            this.next = next;
            this.name = name;
            this.handler = handler;
        }


        public void sendDownstream(ChannelEvent e) {
            DefaultChannelHandlerContext prev = getActualDownstreamContext(this.prev);
            if (prev == null) {
                try {
                    getSink().eventSunk(DefaultChannelPipeline.this, e);
                } catch (Throwable t) {
                    notifyHandlerException(e, t);
                }
            } else {
                DefaultChannelPipeline.this.sendDownstream(prev, e);
            }
        }


        public void sendUpstream(ChannelEvent e) {
            DefaultChannelHandlerContext next = getActualUpstreamContext(this.next);
            if (next != null) {
                DefaultChannelPipeline.this.sendUpstream(next, e);
            }
        }

ChannelUpstreamHandler 中 SimpleChannelHandler 通过 ctx.sendUpstream(e);  find next 节点处理handler

public class SimpleChannelHandler implements ChannelUpstreamHandler, ChannelDownstreamHandler {

 public void handleUpstream(
            ChannelHandlerContext ctx, ChannelEvent e) throws Exception {


        if (e instanceof MessageEvent) {
            messageReceived(ctx, (MessageEvent) e);
   ..........
     .........
  }


    public void messageReceived(
            ChannelHandlerContext ctx, MessageEvent e) throws Exception {
        ctx.sendUpstream(e);
    }
 

所有源码下载 ：https://download.youkuaiyun.com/download/netcobol/10308871