only delete a Packet from history in SentPacketHandler once it has been ACKed

ackhandler/packet.go

@@ -13,4 +13,5 @@ type Packet struct {
 	Entropy      EntropyAccumulator
 
 	MissingReports uint8
+	Retransmitted  bool // has this Packet ever been retransmitted
 }

ackhandler/sent_packet_handler.go

@@ -50,6 +50,12 @@ func (h *sentPacketHandler) nackPacket(packetNumber protocol.PacketNumber) error
 		return ErrMapAccess
 	}
 
+	// if the packet has already been retransmit, do nothing
+	// we're probably only receiving another NACK for this packet because the retransmission has not yet arrived at the client
+	if packet.Retransmitted {
+		return nil
+	}
+
 	packet.MissingReports++
 
 	if packet.MissingReports > retransmissionThreshold {
@@ -58,20 +64,9 @@ func (h *sentPacketHandler) nackPacket(packetNumber protocol.PacketNumber) error
 	return nil
 }
 
-func (h *sentPacketHandler) recalculateHighestInOrderAckedPacketNumberFromPacketHistory() {
-	for i := h.highestInOrderAckedPacketNumber; i <= h.lastSentPacketNumber; i++ {
-		_, ok := h.packetHistory[i]
-		if ok {
-			break
-		}
-		h.highestInOrderAckedPacketNumber = i
-	}
-}
-
 func (h *sentPacketHandler) queuePacketForRetransmission(packet *Packet) {
 	h.retransmissionQueue = append(h.retransmissionQueue, packet)
-	h.ackPacket(packet.PacketNumber)
-	h.recalculateHighestInOrderAckedPacketNumberFromPacketHistory()
+	packet.Retransmitted = true
 }
 
 func (h *sentPacketHandler) SentPacket(packet *Packet) error {

ackhandler/sent_packet_handler_test.go

@@ -340,15 +340,16 @@ var _ = Describe("SentPacketHandler", func() {
 			Expect(handler.DequeuePacketForRetransmission()).To(BeNil())
 		})
 
-		It("recalculates the highestInOrderAckedPacketNumber after queueing a retransmission", func() {
+		It("does not change the highestInOrderAckedPacketNumber after queueing a retransmission", func() {
 			ack := frames.AckFrame{
 				LargestObserved: 4,
 				NackRanges:      []frames.NackRange{frames.NackRange{FirstPacketNumber: 3, LastPacketNumber: 3}},
 			}
 			err := handler.ReceivedAck(&ack)
 			Expect(err).ToNot(HaveOccurred())
+			Expect(handler.highestInOrderAckedPacketNumber).To(Equal(protocol.PacketNumber(2)))
 			handler.nackPacket(3) // this is the second NACK for this packet
-			Expect(handler.highestInOrderAckedPacketNumber).To(Equal(protocol.PacketNumber(4)))
+			Expect(handler.highestInOrderAckedPacketNumber).To(Equal(protocol.PacketNumber(2)))
 		})
 	})
 })