limit number of packets stored in SentPacketHandler

fixes #140

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