add method to ask SendPacketHandler if any retransmissions queued

ackhandler/interfaces.go

@@ -12,6 +12,7 @@ type SentPacketHandler interface {
 	SentPacket(packet *Packet) error
 	ReceivedAck(ackFrame *frames.AckFrame) (time.Duration, []*Packet, []*Packet, error)
 
+	HasPacketForRetransmission() bool
 	DequeuePacketForRetransmission() (packet *Packet)
 
 	BytesInFlight() protocol.ByteCount

ackhandler/sent_packet_handler.go

@@ -206,10 +206,18 @@ func (h *sentPacketHandler) ReceivedAck(ackFrame *frames.AckFrame) (time.Duratio
 	return timeDelta, ackedPackets, lostPackets, nil
 }
 
+func (h *sentPacketHandler) HasPacketForRetransmission() bool {
+	if len(h.retransmissionQueue) > 0 {
+		return true
+	}
+	return false
+}
+
 func (h *sentPacketHandler) DequeuePacketForRetransmission() (packet *Packet) {
-	if len(h.retransmissionQueue) == 0 {
+	if !h.HasPacketForRetransmission() {
 		return nil
 	}
+
 	queueLen := len(h.retransmissionQueue)
 	// packets are usually NACKed in descending order. So use the slice as a stack
 	packet = h.retransmissionQueue[queueLen-1]

ackhandler/sent_packet_handler_test.go

@@ -365,9 +365,16 @@ var _ = Describe("SentPacketHandler", func() {
 			Expect(handler.BytesInFlight()).To(Equal(protocol.ByteCount(6)))
 		})
 
+		It("does not dequeue a packet if no packet has been nacked", func() {
+			handler.nackPacket(2)
+			Expect(handler.HasPacketForRetransmission()).To(BeFalse())
+			Expect(handler.DequeuePacketForRetransmission()).To(BeNil())
+		})
+
 		It("queues a packet for retransmission", func() {
 			handler.nackPacket(2)
 			handler.nackPacket(2)
+			Expect(handler.HasPacketForRetransmission()).To(BeTrue())
 			Expect(len(handler.retransmissionQueue)).To(Equal(1))
 			Expect(handler.retransmissionQueue[0].PacketNumber).To(Equal(protocol.PacketNumber(2)))
 		})

packet_packer_test.go

@@ -27,6 +27,10 @@ func (h *mockSentPacketHandler) DequeuePacketForRetransmission() (packet *ackhan
 	return nil
 }
 
+func (h *mockSentPacketHandler) HasPacketForRetransmission() bool {
+	return false
+}
+
 func (h *mockSentPacketHandler) BytesInFlight() protocol.ByteCount {
 	return 0
 }