grpc 检测客户端连接是否存在

var kasp = keepalive.ServerParameters{
            Time:    5 * time.Second, // Ping the client if it is idle for 5 seconds to ensure the connection is still active
            Timeout: 1 * time.Second, // Wait 1 second for the ping ack before assuming the connection is dead
        }

lis, err := net.Listen("tcp", fmt.Sprintf(":%d", port))
if err != nil {
    log.Fatalf("failed to listen: %v", err)
}
s := grpc.NewServer(grpc.KeepaliveParams(kasp))

pb.RegisterHelloServer(s, &svc{})
if err := s.Serve(lis); err != nil {
    log.Fatalf("failed to serve: %v", err)
}

func (s *svc) HelloStream(stream pb.Hello_HelloStreamServer) error {
    now := time.Now().Unix()
    log.Println("enter stream", now)

    req, err := stream.Recv()
    if err != nil {
        return err
    }
    name := req.Greetings

loop:
    for {
        out := new(pb.HelloRsp)
        out.Resp = fmt.Sprintf("hello,%v", name)
        sendctx, sendcancel := context.WithCancel(context.Background())
        go func() {
            err := stream.Send(out) // 在协程中send，使得context.Done响应能被处理
            if err != nil {
                log.Println(err)
            }
            sendcancel()
        }()

        select {
        case <-sendctx.Done():
        case <-stream.Context().Done()://当keepalive连接超时，这里的逻辑被执行，服务端退出
            log.Println("client closed")
            break loop
        }
        time.Sleep(time.Second)
    }
    log.Println("exit stream")
    return nil
}