From 66abcdfc5cb67d3fbd66b0519eaba11c9eb1a151 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Sat, 29 Jun 2019 14:49:33 +0700
Subject: [PATCH] move calculation of the PTO to the rttStats

The PTO value is needed at various places in the protocol. Calculating
it on the rttStats struct will allow us to pass around this struct.
---
 internal/ackhandler/sent_packet_handler.go      |  6 +-----
 internal/ackhandler/sent_packet_handler_test.go | 14 --------------
 internal/congestion/rtt_stats.go                |  5 +++++
 internal/congestion/rtt_stats_test.go           | 17 +++++++++++++++++
 4 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/internal/ackhandler/sent_packet_handler.go b/internal/ackhandler/sent_packet_handler.go
index 9f302228..2ffa77a0 100644
--- a/internal/ackhandler/sent_packet_handler.go
+++ b/internal/ackhandler/sent_packet_handler.go
@@ -342,7 +342,7 @@ func (h *sentPacketHandler) updateLossDetectionAlarm() {
 		// Early retransmit timer or time loss detection.
 		h.alarm = h.lossTime
 	} else { // PTO alarm
-		h.alarm = h.lastSentAckElicitingPacketTime.Add(h.computePTOTimeout() << h.ptoCount)
+		h.alarm = h.lastSentAckElicitingPacketTime.Add(h.rttStats.PTO() << h.ptoCount)
 	}
 }
 
@@ -657,10 +657,6 @@ func (h *sentPacketHandler) computeCryptoTimeout() time.Duration {
 	return duration << h.cryptoCount
 }
 
-func (h *sentPacketHandler) computePTOTimeout() time.Duration {
-	return h.rttStats.SmoothedOrInitialRTT() + utils.MaxDuration(4*h.rttStats.MeanDeviation(), protocol.TimerGranularity) + h.rttStats.MaxAckDelay()
-}
-
 func (h *sentPacketHandler) ResetForRetry() error {
 	h.cryptoCount = 0
 	h.bytesInFlight = 0
diff --git a/internal/ackhandler/sent_packet_handler_test.go b/internal/ackhandler/sent_packet_handler_test.go
index 3942a3fe..db6ffc3d 100644
--- a/internal/ackhandler/sent_packet_handler_test.go
+++ b/internal/ackhandler/sent_packet_handler_test.go
@@ -611,20 +611,6 @@ var _ = Describe("SentPacketHandler", func() {
 	})
 
 	Context("probe packets", func() {
-		It("uses the RTT from RTT stats", func() {
-			rtt := 2 * time.Second
-			updateRTT(rtt)
-			Expect(handler.rttStats.SmoothedOrInitialRTT()).To(Equal(2 * time.Second))
-			Expect(handler.rttStats.MeanDeviation()).To(Equal(time.Second))
-			Expect(handler.computePTOTimeout()).To(Equal(time.Duration(2+4) * time.Second))
-		})
-
-		It("uses the granularity for short RTTs", func() {
-			rtt := time.Microsecond
-			updateRTT(rtt)
-			Expect(handler.computePTOTimeout()).To(Equal(rtt + protocol.TimerGranularity))
-		})
-
 		It("implements exponential backoff", func() {
 			sendTime := time.Now().Add(-time.Hour)
 			handler.SentPacket(ackElicitingPacket(&Packet{PacketNumber: 1, SendTime: sendTime}))
diff --git a/internal/congestion/rtt_stats.go b/internal/congestion/rtt_stats.go
index 7c9b79ed..a44d7991 100644
--- a/internal/congestion/rtt_stats.go
+++ b/internal/congestion/rtt_stats.go
@@ -3,6 +3,7 @@ package congestion
 import (
 	"time"
 
+	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/utils"
 )
 
@@ -56,6 +57,10 @@ func (r *RTTStats) MeanDeviation() time.Duration { return r.meanDeviation }
 
 func (r *RTTStats) MaxAckDelay() time.Duration { return r.maxAckDelay }
 
+func (r *RTTStats) PTO() time.Duration {
+	return r.SmoothedOrInitialRTT() + utils.MaxDuration(4*r.MeanDeviation(), protocol.TimerGranularity) + r.MaxAckDelay()
+}
+
 // UpdateRTT updates the RTT based on a new sample.
 func (r *RTTStats) UpdateRTT(sendDelta, ackDelay time.Duration, now time.Time) {
 	if sendDelta == utils.InfDuration || sendDelta <= 0 {
diff --git a/internal/congestion/rtt_stats_test.go b/internal/congestion/rtt_stats_test.go
index 2d3114aa..d7ddc8bd 100644
--- a/internal/congestion/rtt_stats_test.go
+++ b/internal/congestion/rtt_stats_test.go
@@ -3,6 +3,7 @@ package congestion
 import (
 	"time"
 
+	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/utils"
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
@@ -64,6 +65,22 @@ var _ = Describe("RTT stats", func() {
 		Expect(rttStats.MaxAckDelay()).To(Equal(42 * time.Minute))
 	})
 
+	It("computes the PTO", func() {
+		maxAckDelay := 42 * time.Minute
+		rttStats.SetMaxAckDelay(maxAckDelay)
+		rtt := time.Second
+		rttStats.UpdateRTT(rtt, 0, time.Time{})
+		Expect(rttStats.SmoothedRTT()).To(Equal(rtt))
+		Expect(rttStats.MeanDeviation()).To(Equal(rtt / 2))
+		Expect(rttStats.PTO()).To(Equal(rtt + 4*(rtt/2) + maxAckDelay))
+	})
+
+	It("uses the granularity for computing the PTO for short RTTs", func() {
+		rtt := time.Microsecond
+		rttStats.UpdateRTT(rtt, 0, time.Time{})
+		Expect(rttStats.PTO()).To(Equal(rtt + protocol.TimerGranularity))
+	})
+
 	It("ExpireSmoothedMetrics", func() {
 		initialRtt := (10 * time.Millisecond)
 		rttStats.UpdateRTT(initialRtt, 0, time.Time{})