affected/package: stream send need a timeout option to avoid slow client attack

[ArmstrongCN]

Is your feature request related to a problem?

Slow client read under a high speed server send connection, may hang the server go routine and resource util client destroy. we observe more than 6k seconds hang in a case.

What is the solution you'd like?

add a timeout for every server send calling, so the go routine has the chance to abort or drop some buffer.

What alternatives have you considered?

may be server read has the same problem?

[WineChord]

The design of trpc's stream is somewhat like grpc; the stream does not have a timeout on each send/recv but on the whole stream.

You can add a timeout control by yourself such as

func (s *testStreamImpl) ServerStream(req *pb.HelloReq, stream pb.TestStream_ServerStreamServer) error {
	log.Infof("ServerStream receive Msg: %s", req.GetMsg())
	for i := 0; i < 5; i++ {
		// Continuously call Send to send the response.
		t := time.NewTimer(time.Second)
		done := make(chan struct{})
		go func() {
			defer func() {
				close(done)
			}()
			if err := stream.SendMsg(&pb.HelloRsp{Msg: fmt.Sprintf(" pong: %v", i)}); err != nil {
				// ...
			}
		}()
		select {
		case <-t.C:
			return errors.New("server stream send timeout")
		case <-done:
			continue
		}
	}
	return nil
}