move calculation of RTO delay to the sent packet handler

internal/ackhandler/sent_packet_handler.go

@@ -545,9 +545,12 @@ func (h *sentPacketHandler) computeHandshakeTimeout() time.Duration {
 }
 
 func (h *sentPacketHandler) computeRTOTimeout() time.Duration {
-	rto := h.congestion.RetransmissionDelay()
+	var rto time.Duration
-	if rto == 0 {
+	rtt := h.rttStats.SmoothedRTT()
+	if rtt == 0 {
 		rto = defaultRTOTimeout
+	} else {
+		rto = rtt + 4*h.rttStats.MeanDeviation()
 	}
 	rto = utils.MaxDuration(rto, minRTOTimeout)
 	// Exponential backoff

internal/ackhandler/sent_packet_handler_test.go

@@ -512,7 +512,6 @@ var _ = Describe("SentPacketHandler", func() {
 
 		BeforeEach(func() {
 			cong = mocks.NewMockSendAlgorithm(mockCtrl)
-			cong.EXPECT().RetransmissionDelay().AnyTimes()
 			handler.congestion = cong
 		})
 
@@ -693,8 +692,10 @@ var _ = Describe("SentPacketHandler", func() {
 
 		It("uses RTO from rttStats", func() {
 			rtt := time.Second
-			expected := rtt + rtt/2*4
 			handler.rttStats.UpdateRTT(rtt, 0, time.Now())
+			Expect(handler.rttStats.SmoothedRTT()).To(Equal(rtt))
+			Expect(handler.rttStats.MeanDeviation()).To(Equal(rtt / 2))
+			expected := rtt + rtt/2*4
 			Expect(handler.computeRTOTimeout()).To(Equal(expected))
 		})
 

internal/congestion/cubic_sender.go

@@ -292,11 +292,3 @@ func (c *cubicSender) OnConnectionMigration() {
 func (c *cubicSender) SetSlowStartLargeReduction(enabled bool) {
 	c.slowStartLargeReduction = enabled
 }
-
-// RetransmissionDelay gives the time to retransmission
-func (c *cubicSender) RetransmissionDelay() time.Duration {
-	if c.rttStats.SmoothedRTT() == 0 {
-		return 0
-	}
-	return c.rttStats.SmoothedRTT() + c.rttStats.MeanDeviation()*4
-}

internal/congestion/cubic_sender_test.go

@@ -397,33 +397,6 @@ var _ = Describe("Cubic Sender", func() {
 		Expect(sender.GetCongestionWindow()).To(Equal(defaultWindowTCP))
 	})
 
-	It("retransmission delay", func() {
-		const rtt = 10 * time.Millisecond
-		const deviation = 3 * time.Millisecond
-		Expect(sender.RetransmissionDelay()).To(BeZero())
-
-		rttStats.UpdateRTT(rtt, 0, clock.Now())
-
-		// Initial value is to set the median deviation to half of the initial
-		// rtt, the median in then multiplied by a factor of 4 and finally the
-		// smoothed rtt is added which is the initial rtt.
-		expectedDelay := rtt + rtt/2*4
-		Expect(sender.RetransmissionDelay()).To(Equal(expectedDelay))
-
-		for i := 0; i < 100; i++ {
-			// run to make sure that we converge.
-			rttStats.UpdateRTT(rtt+deviation, 0, clock.Now())
-			rttStats.UpdateRTT(rtt-deviation, 0, clock.Now())
-		}
-		expectedDelay = rtt + deviation*4
-
-		Expect(rttStats.SmoothedRTT()).To(BeNumerically("~", rtt, time.Millisecond))
-		Expect(sender.RetransmissionDelay()).To(BeNumerically("~", expectedDelay, time.Millisecond))
-		Expect(sender.BandwidthEstimate() / BytesPerSecond).To(Equal(Bandwidth(
-			sender.GetCongestionWindow() * protocol.ByteCount(time.Second) / protocol.ByteCount(rttStats.SmoothedRTT()),
-		)))
-	})
-
 	It("slow start max send window", func() {
 		const maxCongestionWindowTCP = 50
 		const numberOfAcks = 100

internal/congestion/interface.go

@@ -17,7 +17,6 @@ type SendAlgorithm interface {
 	SetNumEmulatedConnections(n int)
 	OnRetransmissionTimeout(packetsRetransmitted bool)
 	OnConnectionMigration()
-	RetransmissionDelay() time.Duration
 
 	// Experiments
 	SetSlowStartLargeReduction(enabled bool)

internal/mocks/congestion.go

@@ -109,18 +109,6 @@ func (mr *MockSendAlgorithmMockRecorder) OnRetransmissionTimeout(arg0 interface{
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "OnRetransmissionTimeout", reflect.TypeOf((*MockSendAlgorithm)(nil).OnRetransmissionTimeout), arg0)
 }
 
-// RetransmissionDelay mocks base method
-func (m *MockSendAlgorithm) RetransmissionDelay() time.Duration {
-	ret := m.ctrl.Call(m, "RetransmissionDelay")
-	ret0, _ := ret[0].(time.Duration)
-	return ret0
-}
-
-// RetransmissionDelay indicates an expected call of RetransmissionDelay
-func (mr *MockSendAlgorithmMockRecorder) RetransmissionDelay() *gomock.Call {
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "RetransmissionDelay", reflect.TypeOf((*MockSendAlgorithm)(nil).RetransmissionDelay))
-}
-
 // SetNumEmulatedConnections mocks base method
 func (m *MockSendAlgorithm) SetNumEmulatedConnections(arg0 int) {
 	m.ctrl.Call(m, "SetNumEmulatedConnections", arg0)