Kafka GroupCoordinator机制(十三)：GroupCoordinator之HeartbeatRequest分析

每个消费者都会通过HeartbeatTask任务定时向GroupCoordinator发送heartbeatRequest，告知GroupCoordinator自己正常在线。
HeartBeatRequest首先由KafkaApi.handleHeartbeatRequest方法进行处理，它负责验证权限，定义回调函数，并将请求委托给GroupCoordinator处理。

  def handleHeartbeatRequest(request: RequestChannel.Request) {
    val heartbeatRequest = request.body.asInstanceOf[HeartbeatRequest]
    val respHeader = new ResponseHeader(request.header.correlationId)

    // the callback for sending a heartbeat response
    // 定义回调函数，把heartbeatResponse放入requestChannel等待发送
    def sendResponseCallback(errorCode: Short) {
      val response = new HeartbeatResponse(errorCode)
      trace("Sending heartbeat response %s for correlation id %d to client %s."
        .format(response, request.header.correlationId, request.header.clientId))
      requestChannel.sendResponse(new RequestChannel.Response(request, new ResponseSend(request.connectionId, respHeader, response)))
    }

    if (!authorize(request.session, Read, new Resource(Group, heartbeatRequest.groupId))) {
      val heartbeatResponse = new HeartbeatResponse(Errors.GROUP_AUTHORIZATION_FAILED.code)
      requestChannel.sendResponse(new Response(request, new ResponseSend(request.connectionId, respHeader, heartbeatResponse)))
    }
    else {
      // let the coordinator to handle heartbeat
      // 把heartbeat委托给GroupCoordinator处理
      coordinator.handleHeartbeat(
        heartbeatRequest.groupId(),
        heartbeatRequest.memberId(),
        heartbeatRequest.groupGenerationId(),
        sendResponseCallback)
    }
  }

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