add method to get ACK from ReceivedPacketHandler without dequeueing it

ackhandler/interfaces.go

@@ -24,7 +24,7 @@ type ReceivedPacketHandler interface {
 	ReceivedPacket(packetNumber protocol.PacketNumber, entropyBit bool) error
 	ReceivedStopWaiting(*frames.StopWaitingFrame) error
 
-	DequeueAckFrame() (*frames.AckFrame, error)
+	GetAckFrame(dequeue bool) (*frames.AckFrame, error)
 }
 
 // StopWaitingManager manages StopWaitings for sent packets

ackhandler/received_packet_handler.go

@@ -23,6 +23,7 @@ type receivedPacketHandler struct {
 	highestInOrderObservedEntropy EntropyAccumulator
 	largestObserved               protocol.PacketNumber
 	packetHistory                 map[protocol.PacketNumber]packetHistoryEntry
+	currentAckFrame               *frames.AckFrame
 	stateChanged                  bool // has an ACK for this state already been sent? Will be set to false every time a new packet arrives, and to false every time an ACK is sent
 }
 
@@ -43,6 +44,7 @@ func (h *receivedPacketHandler) ReceivedPacket(packetNumber protocol.PacketNumbe
 	}
 
 	h.stateChanged = true
+	h.currentAckFrame = nil
 
 	if packetNumber > h.largestObserved {
 		h.largestObserved = packetNumber
@@ -100,25 +102,31 @@ func (h *receivedPacketHandler) getNackRanges() ([]frames.NackRange, EntropyAccu
 	return ranges, entropy
 }
 
-func (h *receivedPacketHandler) DequeueAckFrame() (*frames.AckFrame, error) {
+func (h *receivedPacketHandler) GetAckFrame(dequeue bool) (*frames.AckFrame, error) {
 	if !h.stateChanged {
 		return nil, nil
 	}
 
-	h.stateChanged = false
+	if dequeue {
+		h.stateChanged = false
+	}
+
+	if h.currentAckFrame != nil {
+		return h.currentAckFrame, nil
+	}
 
 	p, ok := h.packetHistory[h.largestObserved]
 	if !ok {
-		return nil, errors.New("bla")
+		return nil, ErrMapAccess
 	}
 	packetReceivedTime := p.TimeReceived
 
 	nackRanges, entropy := h.getNackRanges()
-	ack := frames.AckFrame{
+	h.currentAckFrame = &frames.AckFrame{
 		LargestObserved:    h.largestObserved,
 		Entropy:            byte(entropy),
 		NackRanges:         nackRanges,
 		PacketReceivedTime: packetReceivedTime,
 	}
-	return &ack, nil
+	return h.currentAckFrame, nil
 }

ackhandler/received_packet_handler_test.go

@@ -249,7 +249,7 @@ var _ = Describe("receivedPacketHandler", func() {
 			Expect(err).ToNot(HaveOccurred())
 			err = handler.ReceivedPacket(protocol.PacketNumber(2), true)
 			Expect(err).ToNot(HaveOccurred())
-			ack, err := handler.DequeueAckFrame()
+			ack, err := handler.GetAckFrame(true)
 			Expect(err).ToNot(HaveOccurred())
 			Expect(ack.LargestObserved).To(Equal(protocol.PacketNumber(2)))
 			Expect(ack.Entropy).To(Equal(byte(entropy)))
@@ -263,7 +263,7 @@ var _ = Describe("receivedPacketHandler", func() {
 			Expect(err).ToNot(HaveOccurred())
 			err = handler.ReceivedPacket(protocol.PacketNumber(4), true)
 			Expect(err).ToNot(HaveOccurred())
-			ack, err := handler.DequeueAckFrame()
+			ack, err := handler.GetAckFrame(true)
 			Expect(err).ToNot(HaveOccurred())
 			Expect(ack.LargestObserved).To(Equal(protocol.PacketNumber(4)))
 			Expect(ack.Entropy).To(Equal(byte(entropy)))
@@ -275,19 +275,66 @@ var _ = Describe("receivedPacketHandler", func() {
 			Expect(err).ToNot(HaveOccurred())
 			err = handler.ReceivedPacket(protocol.PacketNumber(2), false)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(handler.DequeueAckFrame()).ToNot(BeNil())
-			Expect(handler.DequeueAckFrame()).To(BeNil())
+			ack, err := handler.GetAckFrame(true)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(ack).ToNot(BeNil())
+			ack, err = handler.GetAckFrame(true)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(ack).To(BeNil())
 		})
 
-		It("generates an ACK when an out-of-order packet arrives", func() {
+		It("does not dequeue an ACK frame if told so", func() {
+			err := handler.ReceivedPacket(protocol.PacketNumber(2), false)
+			Expect(err).ToNot(HaveOccurred())
+			ack, err := handler.GetAckFrame(false)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(ack).ToNot(BeNil())
+			ack, err = handler.GetAckFrame(false)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(ack).ToNot(BeNil())
+			ack, err = handler.GetAckFrame(false)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(ack).ToNot(BeNil())
+		})
+
+		It("returns a cached ACK frame if the ACK was not dequeued", func() {
+			err := handler.ReceivedPacket(protocol.PacketNumber(2), false)
+			Expect(err).ToNot(HaveOccurred())
+			ack, err := handler.GetAckFrame(false)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(ack).ToNot(BeNil())
+			ack2, err := handler.GetAckFrame(false)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(ack2).ToNot(BeNil())
+			Expect(&ack).To(Equal(&ack2))
+		})
+
+		It("generates a new ACK (and deletes the cached one) when a new packet arrives", func() {
+			err := handler.ReceivedPacket(protocol.PacketNumber(1), false)
+			Expect(err).ToNot(HaveOccurred())
+			ack, _ := handler.GetAckFrame(true)
+			Expect(ack).ToNot(BeNil())
+			Expect(ack.LargestObserved).To(Equal(protocol.PacketNumber(1)))
+			err = handler.ReceivedPacket(protocol.PacketNumber(3), false)
+			Expect(err).ToNot(HaveOccurred())
+			ack, _ = handler.GetAckFrame(true)
+			Expect(ack).ToNot(BeNil())
+			Expect(ack.LargestObserved).To(Equal(protocol.PacketNumber(3)))
+		})
+
+		It("generates a new ACK when an out-of-order packet arrives", func() {
 			err := handler.ReceivedPacket(protocol.PacketNumber(1), false)
 			Expect(err).ToNot(HaveOccurred())
 			err = handler.ReceivedPacket(protocol.PacketNumber(3), false)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(handler.DequeueAckFrame()).ToNot(BeNil())
+			ack, _ := handler.GetAckFrame(true)
+			Expect(ack).ToNot(BeNil())
+			Expect(len(ack.NackRanges)).To(Equal(1))
 			err = handler.ReceivedPacket(protocol.PacketNumber(2), false)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(handler.DequeueAckFrame()).ToNot(BeNil())
+			ack, _ = handler.GetAckFrame(true)
+			Expect(ack).ToNot(BeNil())
+			Expect(len(ack.NackRanges)).To(Equal(0))
 		})
 	})
 })

session.go

@@ -403,7 +403,7 @@ func (s *Session) sendPacket() error {
 
 	stopWaitingFrame := s.stopWaitingManager.GetStopWaitingFrame()
 
-	ack, err := s.receivedPacketHandler.DequeueAckFrame()
+	ack, err := s.receivedPacketHandler.GetAckFrame(true)
 	if err != nil {
 		return err
 	}