send a StopWaiting with every ACK in QUIC 34

fixes #185

ackhandler/interfaces.go

@@ -13,6 +13,8 @@ type SentPacketHandler interface {
 	SentPacket(packet *ackhandlerlegacy.Packet) error
 	ReceivedAck(ackFrame *frames.AckFrame, withPacketNumber protocol.PacketNumber) error
 
+	GetStopWaitingFrame() *frames.StopWaitingFrame
+
 	ProbablyHasPacketForRetransmission() bool
 	DequeuePacketForRetransmission() (packet *ackhandlerlegacy.Packet)
 
@@ -35,6 +37,7 @@ type ReceivedPacketHandler interface {
 }
 
 // StopWaitingManager manages StopWaitings for sent packets
+// TODO: remove once we drop support for QUIC 33
 type StopWaitingManager interface {
 	RegisterPacketForRetransmission(packet *ackhandlerlegacy.Packet)
 	GetStopWaitingFrame() *frames.StopWaitingFrame

ackhandler/sent_packet_handler.go

@@ -272,6 +272,16 @@ func (h *sentPacketHandler) GetLargestAcked() protocol.PacketNumber {
 	return h.LargestAcked
 }
 
+func (h *sentPacketHandler) GetStopWaitingFrame() *frames.StopWaitingFrame {
+	if h.LargestAcked == 0 {
+		return nil
+	}
+
+	return &frames.StopWaitingFrame{
+		LeastUnacked: h.LargestAcked + 1,
+	}
+}
+
 func (h *sentPacketHandler) CongestionAllowsSending() bool {
 	return h.BytesInFlight() <= h.congestion.GetCongestionWindow()
 }

ackhandler/sent_packet_handler_test.go

@@ -350,6 +350,17 @@ var _ = Describe("SentPacketHandler", func() {
 			})
 		})
 
+		Context("StopWaitings", func() {
+			It("does not get a StopWaiting if no ACKs haven't been received yet", func() {
+				Expect(handler.GetStopWaitingFrame()).To(BeNil())
+			})
+
+			It("gets a StopWaitingFrame", func() {
+				handler.LargestAcked = 1336
+				Expect(handler.GetStopWaitingFrame()).To(Equal(&frames.StopWaitingFrame{LeastUnacked: 1337}))
+			})
+		})
+
 		Context("calculating RTT", func() {
 			It("calculates the RTT", func() {
 				now := time.Now()