RabbitMQ 客户端源码系列 - Pulish Message

/** Public API - {@inheritDoc} */
@Override
public void basicPublish(String exchange, String routingKey,
                         boolean mandatory,
                         BasicProperties props, byte[] body)
  throws IOException
{
  basicPublish(exchange, routingKey, mandatory, false, props, body);
}
/** Public API - {@inheritDoc} */
@Override
public void basicPublish(String exchange, String routingKey,
                         boolean mandatory, boolean immediate,
                         BasicProperties props, byte[] body)
  throws IOException
{
  // Pulisher 配置了 `Confirm.Select` nextPublishSeqNo 设置从 1 开始
  // 将未确认的消息 放入 unconfirmedSet，并 自增加一
  if (nextPublishSeqNo > 0) {
    unconfirmedSet.add(getNextPublishSeqNo());
    nextPublishSeqNo++;
  }
  BasicProperties useProps = props;
  if (props == null) {
    useProps = MessageProperties.MINIMAL_BASIC;
  }
  // 构造 AMQCommand 并传输
  transmit(new AMQCommand(new Basic.Publish.Builder()
                          .exchange(exchange)
                          .routingKey(routingKey)
                          .mandatory(mandatory)
                          .immediate(immediate)
                          .build(),
                          useProps, body));
  // 用于指标统计和监控，默认是 NoOpMetricsCollector，需要配置才会可以使用 提供的 MicrometerMetricsCollector 和 StandardMetricsCollector（引入对应的包和配置 开箱即可食用～）
  metricsCollector.basicPublish(this);
}

public class Frame {
    /** Frame type code */
   // FRAME_HEARTBEAT :心跳， FRAME_METHOD: 方法， FRAME_HEADER : 头部信息， FRAME_BODY 内容主题
    public final int type;
    /** Frame channel number, 0-65535 */
   // channel 序列号
    public final int channel;
    /** Frame payload bytes (for inbound frames) */
   // 消息内容字节
    private final byte[] payload;
    /** Frame payload (for outbound frames) */
    // 写出数据
    private final ByteArrayOutputStream accumulator;
    private static final int NON_BODY_SIZE = 1 /* type */ + 2 /* channel */ + 4 /* payload size */ + 1 /* end character */;
  ...  
}

/**
* Construct a command with a specified method, header and body.
* @param method the wrapped method
* @param contentHeader the wrapped content header
* @param body the message body data
*/
public AMQCommand(com.rabbitmq.client.Method method, AMQContentHeader contentHeader, byte[] body) {
 this.assembler = new CommandAssembler((Method) method, contentHeader, body);
}
// AMQP 0-9-1 特定的Command，构造 方法、头部和正文
public CommandAssembler(Method method, AMQContentHeader contentHeader, byte[] body) {
  this.method = method;
  this.contentHeader = contentHeader;
  this.bodyN = new ArrayList<byte[]>(2);
  this.bodyLength = 0;
  this.remainingBodyBytes = 0;
  appendBodyFragment(body);
  if (method == null) {
    this.state = CAState.EXPECTING_METHOD;
  } else if (contentHeader == null) {
    this.state = method.hasContent() ? CAState.EXPECTING_CONTENT_HEADER : CAState.COMPLETE;
  } else {
    this.remainingBodyBytes = contentHeader.getBodySize() - this.bodyLength;
    updateContentBodyState();
  }
}

public void transmit(AMQCommand c) throws IOException {
  synchronized (_channelMutex) {
    // 确认 channel 是否打开（逻辑比较简单：判断 shutdownCause 为空即是打开）
    ensureIsOpen();
    quiescingTransmit(c);
  }
}
public void quiescingTransmit(AMQCommand c) throws IOException {
  // 防止并发同时使用 同一个channel
  synchronized (_channelMutex) {
    // 判断 该消息是否 携带content，如果有 需要判断该 channel是否是阻塞（如果channel state为 `FLOW` 即为 阻塞 _blockContent = true）
    if (c.getMethod().hasContent()) {
      while (_blockContent) {
        try {
          _channelMutex.wait();
        } catch (InterruptedException ignored) {}
        // 防止 从阻塞中被唤醒时，channel 已经关闭（挺好的一个 多线程操作的案例）
        ensureIsOpen();
      }
    }
    c.transmit(this);
  }
}

/**
 * Public API - sends a frame directly to the broker.
 */
public void writeFrame(Frame f) throws IOException {
  _frameHandler.writeFrame(f);
  // lastActivityTime
  _heartbeatSender.signalActivity();
}
@Override
public void writeFrame(Frame frame) throws IOException {
  synchronized (_outputStream) {
    frame.writeTo(_outputStream);
  }
}
/**
 * Public API - writes this Frame to the given DataOutputStream
 */
public void writeTo(DataOutputStream os) throws IOException {
  // 1. 写type 类型
  os.writeByte(type);
  // 2. 写channel 序列号
  os.writeShort(channel);
  if (accumulator != null) {
    // 3. 写出数据大小
    os.writeInt(accumulator.size());
    // 4. 输出数据
    accumulator.writeTo(os);
  } else {
    // 3. 写消息内容字节大小
    os.writeInt(payload.length);
    // 4. 写消息内容
    os.write(payload);
  }
  // 5. 帧结束标志位
  os.write(AMQP.FRAME_END);
}