limit number of packets stored in SentPacketHandler

fixes #140

ackhandler/interfaces.go

@@ -19,6 +19,7 @@ type SentPacketHandler interface {
 	GetLargestObserved() protocol.PacketNumber
 
 	CongestionAllowsSending() bool
+	CheckForError() error
 
 	TimeToFirstRTO() time.Duration
 }

ackhandler/sent_packet_handler.go

@@ -17,8 +17,10 @@ var (
 	// ErrEntropy occurs when an ACK with incorrect entropy is received
 	ErrEntropy = qerr.Error(qerr.InvalidAckData, "wrong entropy")
 	// ErrMapAccess occurs when a NACK contains invalid NACK ranges
-	ErrMapAccess          = qerr.Error(qerr.InvalidAckData, "Packet does not exist in PacketHistory")
-	errAckForUnsentPacket = qerr.Error(qerr.InvalidAckData, "Received ACK for an unsent package")
+	ErrMapAccess = qerr.Error(qerr.InvalidAckData, "Packet does not exist in PacketHistory")
+	// ErrTooManyTrackedSentPackets occurs when the sentPacketHandler has to keep track of too many packets
+	ErrTooManyTrackedSentPackets = errors.New("To many outstanding not-acked and not retransmitted packets.")
+	errAckForUnsentPacket        = qerr.Error(qerr.InvalidAckData, "Received ACK for an unsent package")
 )
 
 var (
@@ -103,6 +105,8 @@ func (h *sentPacketHandler) queuePacketForRetransmission(packet *Packet) {
 	h.bytesInFlight -= packet.Length
 	h.retransmissionQueue = append(h.retransmissionQueue, packet)
 	packet.Retransmitted = true
+
+	// TODO: delete from packetHistory once we drop support for version smaller than QUIC 33
 }
 
 func (h *sentPacketHandler) SentPacket(packet *Packet) error {
@@ -278,6 +282,14 @@ func (h *sentPacketHandler) CongestionAllowsSending() bool {
 	return h.BytesInFlight() <= h.congestion.GetCongestionWindow()
 }
 
+func (h *sentPacketHandler) CheckForError() error {
+	length := len(h.retransmissionQueue) + len(h.packetHistory)
+	if uint32(length) > protocol.MaxTrackedSentPackets {
+		return ErrTooManyTrackedSentPackets
+	}
+	return nil
+}
+
 func (h *sentPacketHandler) getRTO() time.Duration {
 	rto := h.congestion.RetransmissionDelay()
 	if rto == 0 {

ackhandler/sent_packet_handler_test.go

@@ -162,6 +162,20 @@ var _ = Describe("SentPacketHandler", func() {
 		})
 	})
 
+	Context("DOS mitigation", func() {
+		It("checks the size of the packet history, for unacked packets", func() {
+			for i := uint32(1); i < protocol.MaxTrackedSentPackets+10; i++ {
+				packet := Packet{PacketNumber: protocol.PacketNumber(i), Frames: []frames.Frame{&streamFrame}, Length: 1}
+				err := handler.SentPacket(&packet)
+				Expect(err).ToNot(HaveOccurred())
+			}
+			err := handler.CheckForError()
+			Expect(err).To(MatchError(ErrTooManyTrackedSentPackets))
+		})
+
+		// TODO: add a test that the length of the retransmission queue is considered, even if packets have already been ACKed. Relevant once we drop support for QUIC 33 and earlier
+	})
+
 	Context("ACK entropy calculations", func() {
 		var packets []*Packet
 		var entropy EntropyAccumulator