RabbitMQ客户端源码分析(二)之Frame与FrameHandler

版本声明

1. com.rabbitmq:amqp-client:4.3.0
2. RabbitMQ版本声明: 3.6.15

Frame(帧)分析

AMQP帧(Frame)的格式

1. tcp/ip是一个流协议，amqp没有采用在流中添加帧定界符来区分帧数据（原因官方认为简单，但是很慢），而是采用在header中写入帧大小来区分不同的帧（官方认为简单而且很快）。

2. Frame(帧)就是传输协议的具体实现,即传输的具体数据包

   • 帧类型 通道编号 帧大小 内容 结束标记
     

3. 从上面可以看到读取一个Frame，大概要实现的逻辑

   • 第一步:读取header，检查Frame的类型(1,2,3,8四种类型,AMQP.java类中定义)和Channel编号
   • 第二步:根据帧的类型(type)和payload的长度(size)来读取指定大小的payload进行处理
   • 第三步:读取最后一个字节(结束帧)。
   • 从上面的三步骤来看其实就是在做自定义协议解析的工作，不只是针对AMQP，其实自己定义的协议很多时候也是这么做的。

4. AMQP协议定义了五种类型的帧:协议头帧、method frame(方法帧)、content header frame(内容头帧)、content body(消息体帧)、HEARTBEAT(心跳帧)

5. 方法帧:一个Method Frame(方法帧)携带一个命令，方法帧payload有下面的格式
   

6. Content Header的payload格式如下:
   

7. Content Body Frame:内容是我们通常AMQP服务器在客户端与客户端之间传送和应用数据,内容头帧包含一条消息的大小和属性
   

Frame源码分析

0. 详细的中文注释请访问Frame.java

1. Frame的属性

   public class Frame {
       /** Frame type code */
       public final int type;
   
       /** Frame channel number, 0-65535 通道编号，一个TCPIP连接，多个通道，每个通道都有自己的编号*/
       public final int channel;
   
       /** Frame payload bytes (for inbound frames) 有效载荷,就是除了协议头之外的内容*/
       private final byte[] payload;
   
       /** Frame payload (for outbound frames) 字节流的累加器，用于*/
       private final ByteArrayOutputStream accumulator;
   
       /**
        * 自定义协议都是 【协议头】+【协议体】,NON_BODY_SIZE指的是没有协议体内容的情况下最小的传输
        * 长度。从这里可以看出【协议头】=type(1B)+channel(2B)+payloadSize(4B)+1(1B),总共占用8B(8个字节)
        */
       private static final int NON_BODY_SIZE = 1 /* type */ + 2 /* channel */ + 4 /* payload size */ + 1 /* end character */;
           
   }
   
   

2. 读取Frame

   public static Frame readFrom(DataInputStream is) throws IOException {
       int type;
       int channel;
   
       try {
           //读取1B
           type = is.readUnsignedByte();
       } catch (SocketTimeoutException ste) {
           // System.err.println("Timed out waiting for a frame.");
           return null; // failed
       }
   
       if (type == 'A') {
           /*
            * Probably an AMQP.... header indicating a version
            * mismatch.
            */
           /*
            * Otherwise meaningless, so try to read the version,
            * and throw an exception, whether we read the version
            * okay or not.检查协议版本
            */
           protocolVersionMismatch(is);
       }
       //读取2B
       channel = is.readUnsignedShort();
       //读取4B
       int payloadSize = is.readInt();
       //构造存放内容的字节数组
       byte[] payload = new byte[payloadSize];
       /**
        *  readFully数据缓冲区的空间还有剩余时会阻塞等待读取，直到装满。
        *  此处不能使用is.read(payload),
        *  read(byte[] b)一直阻塞等待读取字节，直到字节流中的数据已经全部读完。
        *  而readFully(byte[] b)是当数据缓冲区的空间还有剩余时会阻塞等待读取，直到装满。
        */
   
       is.readFully(payload);
   
       int frameEndMarker = is.readUnsignedByte();
       //如果读取完body之后最后一个字节不是结束帧，就代表数据格式不正确，以此来判断Frame的传输的正确性
       if (frameEndMarker != AMQP.FRAME_END) {
           throw new MalformedFrameException("Bad frame end marker: " + frameEndMarker);
       }
   
       return new Frame(type, channel, payload);
   }
   

FrameHandler

1. UML图
   
2. rabbitmq-java-client(4.0.3)版本提供了两种处理模式，NIO和BIO

SocketFrameHandler

1. BIO模式,代码详细分析参考SocketFrameHandler

SocketChannelFrameHandler

1. NIO模式，SocketChannelFrameHandler
2. SocketChannelFrameHandler委托SocketChannelFrameHandlerState进行读写以及Socket选项设置
3. SocketChannelFrameHandlerState,解析

        public SocketChannelFrameHandlerState(SocketChannel channel, NioLoopContext nioLoopsState, NioParams nioParams, SSLEngine sslEngine) {
               this.channel = channel;
               //读Selector
               this.readSelectorState = nioLoopsState.readSelectorState;
               //写Selector
               this.writeSelectorState = nioLoopsState.writeSelectorState;
               //写操作存入阻塞队列，数组形式保存数据
               this.writeQueue = new ArrayBlockingQueue<WriteRequest>(nioParams.getWriteQueueCapacity(), true);
               this.writeEnqueuingTimeoutInMs = nioParams.getWriteEnqueuingTimeoutInMs();
               this.sslEngine = sslEngine;
               if(this.sslEngine == null) {
                   this.ssl = false;
                   this.plainOut = nioLoopsState.writeBuffer;
                   this.cipherOut = null;
                   this.plainIn = nioLoopsState.readBuffer;
                   this.cipherIn = null;
       
                   this.outputStream = new DataOutputStream(
                       new ByteBufferOutputStream(channel, plainOut)
                   );
                   this.inputStream = new DataInputStream(
                       new ByteBufferInputStream(channel, plainIn)
                   );
       
               } else {
                   this.ssl = true;
                   this.plainOut = ByteBuffer.allocate(sslEngine.getSession().getApplicationBufferSize());
                   this.cipherOut = ByteBuffer.allocate(sslEngine.getSession().getPacketBufferSize());
                   this.plainIn = ByteBuffer.allocate(sslEngine.getSession().getApplicationBufferSize());
                   this.cipherIn = ByteBuffer.allocate(sslEngine.getSession().getPacketBufferSize());
       
                   this.outputStream = new DataOutputStream(
                       new SslEngineByteBufferOutputStream(sslEngine, plainOut, cipherOut, channel)
                   );
                   this.inputStream = new DataInputStream(
                       new SslEngineByteBufferInputStream(sslEngine, plainIn, cipherIn, channel)
                   );
               }
       
           }
   
   

FramehandlerFactory

1. uml图
   

2. 接口方法

   public interface FrameHandlerFactory {
   
       FrameHandler create(Address addr) throws IOException;
   
   }
   

AbstractFrameHandlerFactory

1. AbstractFrameHandlerFactory源码

      public abstract class AbstractFrameHandlerFactory implements FrameHandlerFactory {
   
       //连接超时时间
       protected final int connectionTimeout;
       //socket选项，此SocketConfigurator接口目前只有一个实现类DefaultSocketConfigurator
       protected final SocketConfigurator configurator;
       //是否ssl
       protected final boolean ssl;
   
       protected AbstractFrameHandlerFactory(int connectionTimeout, SocketConfigurator configurator, boolean ssl) {
           this.connectionTimeout = connectionTimeout;
           this.configurator = configurator;
           this.ssl = ssl;
       }
   }    
   

2. DefaultSocketConfigurator源码

       public class DefaultSocketConfigurator implements SocketConfigurator {
       @Override
       public void configure(Socket socket) throws IOException {
           // disable Nagle's algorithm, for more consistently low latency
           /**
            * 禁用Nagle算法，默认这里只是设置了一个socket选项，我们完全可以自己定义自己想要设置的socket选项
            * 传输给ConnectionFactory。比如我们可以设置SO_LINGER选项来进行延迟关闭连接.事实上在SocketFrameHandler类
            * 中close方法就设置了setSoLinger();
            */
   
   
           socket.setTcpNoDelay(true);
       }
   }
   
   

SocketFrameHandlerFactory

1. SocketFrameHandlerFactory用于创建SocketFrameHandler,SocketFrameHandlerFactory源码

       public class SocketFrameHandlerFactory extends AbstractFrameHandlerFactory {
   
       private final SocketFactory factory;
       //用于关闭socket的线程池
       private final ExecutorService shutdownExecutor;
   
       public SocketFrameHandlerFactory(int connectionTimeout, SocketFactory factory, SocketConfigurator configurator, boolean ssl) {
           this(connectionTimeout, factory, configurator, ssl, null);
       }
   
       public SocketFrameHandlerFactory(int connectionTimeout, SocketFactory factory, SocketConfigurator configurator, boolean ssl, ExecutorService shutdownExecutor) {
           super(connectionTimeout, configurator, ssl);
           this.factory = factory;
           this.shutdownExecutor = shutdownExecutor;
       }
   
       public FrameHandler create(Address addr) throws IOException {
           String hostName = addr.getHost();
           int portNumber = ConnectionFactory.portOrDefault(addr.getPort(), ssl);
           Socket socket = null;
           try {
               //通过socketFactory创建Socket
               socket = factory.createSocket();
               //设置socket选项
               configurator.configure(socket);
               //开启连接
               socket.connect(new InetSocketAddress(hostName, portNumber),
                       connectionTimeout);
               return create(socket);
           } catch (IOException ioe) {
               quietTrySocketClose(socket);
               throw ioe;
           }
       }
   
       public FrameHandler create(Socket sock) throws IOException
       {
           return new SocketFrameHandler(sock, this.shutdownExecutor);
       }
   
       private static void quietTrySocketClose(Socket socket) {
           if (socket != null)
               try { socket.close(); } catch (Exception _e) {/*ignore exceptions*/}
       }
   }
   
   

SocketChannelFrameHandlerFactory

1. SocketChannelFrameHandlerFactory用于创建SocketChannelFrameHandler 并且分负责分配连接到指定的事件循环中,SocketChannelFrameHandlerFactory源码解析

       public class SocketChannelFrameHandlerFactory extends AbstractFrameHandlerFactory {
       
           final NioParams nioParams;
       
           private final SSLContext sslContext;
       
           private final Lock stateLock = new ReentrantLock();
       
       
           private final AtomicLong globalConnectionCount = new AtomicLong();
       
           //nio 事件循环上下文
           private final List<NioLoopContext> nioLoopContexts;
       
           public SocketChannelFrameHandlerFactory(int connectionTimeout, NioParams nioParams, boolean ssl, SSLContext sslContext)
               throws IOException {
               super(connectionTimeout, null, ssl);
               this.nioParams = new NioParams(nioParams);
               this.sslContext = sslContext;
               this.nioLoopContexts = new ArrayList<NioLoopContext>(this.nioParams.getNbIoThreads());
               for (int i = 0; i < this.nioParams.getNbIoThreads(); i++) {
                   this.nioLoopContexts.add(new NioLoopContext(this, this.nioParams));
               }
           }
       
           @Override
           public FrameHandler create(Address addr) throws IOException {
               int portNumber = ConnectionFactory.portOrDefault(addr.getPort(), ssl);
       
               SSLEngine sslEngine = null;
               SocketChannel channel = null;
       
               try {
                   if (ssl) {
                       sslEngine = sslContext.createSSLEngine(addr.getHost(), portNumber);
                       sslEngine.setUseClientMode(true);
                   }
       
                   SocketAddress address = new InetSocketAddress(addr.getHost(), portNumber);
                   channel = SocketChannel.open();
                   //设置为阻塞模式
                   channel.configureBlocking(true);
                   if(nioParams.getSocketChannelConfigurator() != null) {
                       nioParams.getSocketChannelConfigurator().configure(channel);
                   }
       
                   channel.connect(address);
       
                   if (ssl) {
                       sslEngine.beginHandshake();
                       boolean handshake = SslEngineHelper.doHandshake(channel, sslEngine);
                       if (!handshake) {
                           throw new SSLException("TLS handshake failed");
                       }
                   }
                   //设置通道为非阻塞模式
                   channel.configureBlocking(false);
       
                   // lock
                   stateLock.lock();
                   NioLoopContext nioLoopContext = null;
                   try {
                       //分配连接到指定的事件循环中
                       long modulo = globalConnectionCount.getAndIncrement() % nioParams.getNbIoThreads();
                       nioLoopContext = nioLoopContexts.get((int) modulo);
                       //启动事件循环
                       nioLoopContext.initStateIfNecessary();
                       SocketChannelFrameHandlerState state = new SocketChannelFrameHandlerState(
                           channel,
                           nioLoopContext,
                           nioParams,
                           sslEngine
                       );
                       //注册读事件
                       state.startReading();
                       SocketChannelFrameHandler frameHandler = new SocketChannelFrameHandler(state);
                       return frameHandler;
                   } finally {
                       stateLock.unlock();
                   }
       
       
               } catch(IOException e) {
                   try {
                       if(sslEngine != null && channel != null) {
                           SslEngineHelper.close(channel, sslEngine);
                       }
                       channel.close();
                   } catch(IOException closingException) {
                       // ignore
                   }
                   throw e;
               }
       
           }
       
           void lock() {
               stateLock.lock();
           }
       
           void unlock() {
               stateLock.unlock();
           }
       }