handle Retry packets in the session

internal/ackhandler/interfaces.go

@@ -14,6 +14,7 @@ type SentPacketHandler interface {
 	SentPacketsAsRetransmission(packets []*Packet, retransmissionOf protocol.PacketNumber)
 	ReceivedAck(ackFrame *wire.AckFrame, withPacketNumber protocol.PacketNumber, encLevel protocol.EncryptionLevel, recvTime time.Time) error
 	SetHandshakeComplete()
+	ResetForRetry() error
 
 	// The SendMode determines if and what kind of packets can be sent.
 	SendMode() SendMode

internal/ackhandler/sent_packet_handler.go

@@ -578,3 +578,22 @@ func (h *sentPacketHandler) computePTOTimeout() time.Duration {
 	duration := utils.MaxDuration(h.rttStats.SmoothedOrInitialRTT()+4*h.rttStats.MeanDeviation(), granularity)
 	return duration << h.ptoCount
 }
+
+func (h *sentPacketHandler) ResetForRetry() error {
+	h.cryptoCount = 0
+	h.bytesInFlight = 0
+	var packets []*Packet
+	h.packetHistory.Iterate(func(p *Packet) (bool, error) {
+		if p.canBeRetransmitted {
+			packets = append(packets, p)
+		}
+		return true, nil
+	})
+	for _, p := range packets {
+		h.logger.Debugf("Queueing packet %#x for retransmission.", p.PacketNumber)
+		h.retransmissionQueue = append(h.retransmissionQueue, p)
+	}
+	h.packetHistory = newSentPacketHistory()
+	h.updateLossDetectionAlarm()
+	return nil
+}

internal/ackhandler/sent_packet_handler_test.go

@@ -873,4 +873,28 @@ var _ = Describe("SentPacketHandler", func() {
 			Expect(handler.PopPacketNumber()).To(BeNumerically(">", 42))
 		})
 	})
+
+	Context("resetting for retry", func() {
+		It("queues outstanding packets for retransmission and cancels alarms", func() {
+			packet := &Packet{
+				PacketNumber:    42,
+				EncryptionLevel: protocol.EncryptionInitial,
+				Frames:          []wire.Frame{&wire.CryptoFrame{Data: []byte("foobar")}},
+				Length:          100,
+			}
+			handler.SentPacket(packet)
+			Expect(handler.GetAlarmTimeout()).ToNot(BeZero())
+			Expect(handler.bytesInFlight).ToNot(BeZero())
+			Expect(handler.DequeuePacketForRetransmission()).To(BeNil())
+			Expect(handler.SendMode()).To(Equal(SendAny))
+			// now receive a Retry
+			Expect(handler.ResetForRetry()).To(Succeed())
+			Expect(handler.bytesInFlight).To(BeZero())
+			Expect(handler.GetAlarmTimeout()).To(BeZero())
+			Expect(handler.SendMode()).To(Equal(SendRetransmission))
+			p := handler.DequeuePacketForRetransmission()
+			Expect(p.PacketNumber).To(Equal(packet.PacketNumber))
+			Expect(p.Frames).To(Equal(packet.Frames))
+		})
+	})
 })