From 46f8930fef3d8f78ba013da7bb3d54cf6d4ecd0c Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Sat, 17 Mar 2018 11:13:55 +0000
Subject: [PATCH] calculate loss alarm based on send time of last
 retransmittable packet

---
 internal/ackhandler/sent_packet_handler.go    | 23 +++++++++++--------
 .../ackhandler/sent_packet_handler_test.go    |  4 +++-
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/internal/ackhandler/sent_packet_handler.go b/internal/ackhandler/sent_packet_handler.go
index 47c3ddee7..8ba51fb3f 100644
--- a/internal/ackhandler/sent_packet_handler.go
+++ b/internal/ackhandler/sent_packet_handler.go
@@ -30,9 +30,11 @@ const (
 )
 
 type sentPacketHandler struct {
-	lastSentPacketNumber protocol.PacketNumber
-	nextPacketSendTime   time.Time
-	skippedPackets       []protocol.PacketNumber
+	lastSentPacketNumber              protocol.PacketNumber
+	lastSentRetransmittablePacketTime time.Time
+
+	nextPacketSendTime time.Time
+	skippedPackets     []protocol.PacketNumber
 
 	largestAcked                 protocol.PacketNumber
 	largestReceivedPacketWithAck protocol.PacketNumber
@@ -115,8 +117,8 @@ func (h *sentPacketHandler) SentPacket(packet *Packet) {
 	packet.sendTime = time.Now()
 	if isRetransmittable := h.sentPacketImpl(packet); isRetransmittable {
 		h.packetHistory.SentPacket(packet)
+		h.updateLossDetectionAlarm()
 	}
-	h.updateLossDetectionAlarm(packet.sendTime)
 }
 
 func (h *sentPacketHandler) SentPacketsAsRetransmission(packets []*Packet, retransmissionOf protocol.PacketNumber) {
@@ -129,7 +131,7 @@ func (h *sentPacketHandler) SentPacketsAsRetransmission(packets []*Packet, retra
 		}
 	}
 	h.packetHistory.SentPacketsAsRetransmission(p, retransmissionOf)
-	h.updateLossDetectionAlarm(now)
+	h.updateLossDetectionAlarm()
 }
 
 func (h *sentPacketHandler) sentPacketImpl(packet *Packet) bool /* isRetransmittable */ {
@@ -154,6 +156,7 @@ func (h *sentPacketHandler) sentPacketImpl(packet *Packet) bool /* isRetransmitt
 
 	if isRetransmittable {
 		packet.largestAcked = largestAcked
+		h.lastSentRetransmittablePacketTime = packet.sendTime
 		h.bytesInFlight += packet.Length
 	}
 	h.congestion.OnPacketSent(packet.sendTime, h.bytesInFlight, packet.PacketNumber, packet.Length, isRetransmittable)
@@ -209,7 +212,7 @@ func (h *sentPacketHandler) ReceivedAck(ackFrame *wire.AckFrame, withPacketNumbe
 	if err := h.detectLostPackets(rcvTime); err != nil {
 		return err
 	}
-	h.updateLossDetectionAlarm(rcvTime)
+	h.updateLossDetectionAlarm()
 
 	h.garbageCollectSkippedPackets()
 	h.stopWaitingManager.ReceivedAck(ackFrame)
@@ -264,7 +267,7 @@ func (h *sentPacketHandler) maybeUpdateRTT(largestAcked protocol.PacketNumber, a
 	return false
 }
 
-func (h *sentPacketHandler) updateLossDetectionAlarm(now time.Time) {
+func (h *sentPacketHandler) updateLossDetectionAlarm() {
 	// Cancel the alarm if no packets are outstanding
 	if h.packetHistory.Len() == 0 {
 		h.alarm = time.Time{}
@@ -273,13 +276,13 @@ func (h *sentPacketHandler) updateLossDetectionAlarm(now time.Time) {
 
 	// TODO(#497): TLP
 	if !h.handshakeComplete {
-		h.alarm = now.Add(h.computeHandshakeTimeout())
+		h.alarm = h.lastSentRetransmittablePacketTime.Add(h.computeHandshakeTimeout())
 	} else if !h.lossTime.IsZero() {
 		// Early retransmit timer or time loss detection.
 		h.alarm = h.lossTime
 	} else {
 		// RTO
-		h.alarm = now.Add(h.computeRTOTimeout())
+		h.alarm = h.lastSentRetransmittablePacketTime.Add(h.computeRTOTimeout())
 	}
 }
 
@@ -336,7 +339,7 @@ func (h *sentPacketHandler) OnAlarm() error {
 	if err != nil {
 		return err
 	}
-	h.updateLossDetectionAlarm(now)
+	h.updateLossDetectionAlarm()
 	return nil
 }
 
diff --git a/internal/ackhandler/sent_packet_handler_test.go b/internal/ackhandler/sent_packet_handler_test.go
index cfa4484f3..729322e2a 100644
--- a/internal/ackhandler/sent_packet_handler_test.go
+++ b/internal/ackhandler/sent_packet_handler_test.go
@@ -114,12 +114,14 @@ var _ = Describe("SentPacketHandler", func() {
 
 		It("stores the sent time", func() {
 			handler.SentPacket(retransmittablePacket(1))
-			Expect(getPacket(1).sendTime.Unix()).To(BeNumerically("~", time.Now().Unix(), 1))
+			Expect(getPacket(1).sendTime).To(BeTemporally("~", time.Now(), 100*time.Millisecond))
+			Expect(handler.lastSentRetransmittablePacketTime).To(BeTemporally("~", time.Now(), 100*time.Millisecond))
 		})
 
 		It("does not store non-retransmittable packets", func() {
 			handler.SentPacket(nonRetransmittablePacket(1))
 			Expect(handler.packetHistory.Len()).To(BeZero())
+			Expect(handler.lastSentRetransmittablePacketTime).To(BeZero())
 		})
 
 		Context("skipped packet numbers", func() {