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Merge pull request #3152 from lucas-clemente/pmtu-early-retransmit
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declare Path MTU probe packets lost with the early retransmit timer
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@marten-seemann
marten-seemann authored Apr 30, 2021
2 parents d2739ab + dd05265 commit ddeb228
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Showing 2 changed files with 84 additions and 60 deletions.
110 changes: 53 additions & 57 deletions internal/ackhandler/sent_packet_handler.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -439,20 +439,20 @@ func (h *sentPacketHandler) getLossTimeAndSpace() (time.Time, protocol.Encryptio
}

// same logic as getLossTimeAndSpace, but for lastAckElicitingPacketTime instead of lossTime
func (h *sentPacketHandler) getPTOTimeAndSpace() (time.Time, protocol.EncryptionLevel) {
if !h.hasOutstandingPackets() {
func (h *sentPacketHandler) getPTOTimeAndSpace() (pto time.Time, encLevel protocol.EncryptionLevel, ok bool) {
// We only send application data probe packets once the handshake is confirmed,
// because before that, we don't have the keys to decrypt ACKs sent in 1-RTT packets.
if !h.handshakeConfirmed && !h.hasOutstandingCryptoPackets() {
if h.peerCompletedAddressValidation {
return
}
t := time.Now().Add(h.rttStats.PTO(false) << h.ptoCount)
if h.initialPackets != nil {
return t, protocol.EncryptionInitial
return t, protocol.EncryptionInitial, true
}
return t, protocol.EncryptionHandshake
return t, protocol.EncryptionHandshake, true
}

var (
encLevel protocol.EncryptionLevel
pto time.Time
)

if h.initialPackets != nil {
encLevel = protocol.EncryptionInitial
if t := h.initialPackets.lastAckElicitingPacketTime; !t.IsZero() {
Expand All @@ -473,7 +473,7 @@ func (h *sentPacketHandler) getPTOTimeAndSpace() (time.Time, protocol.Encryption
encLevel = protocol.Encryption1RTT
}
}
return pto, encLevel
return pto, encLevel, true
}

func (h *sentPacketHandler) hasOutstandingCryptoPackets() bool {
Expand All @@ -488,10 +488,7 @@ func (h *sentPacketHandler) hasOutstandingCryptoPackets() bool {
}

func (h *sentPacketHandler) hasOutstandingPackets() bool {
// We only send application data probe packets once the handshake completes,
// because before that, we don't have the keys to decrypt ACKs sent in 1-RTT packets.
return (h.handshakeConfirmed && h.appDataPackets.history.HasOutstandingPackets()) ||
h.hasOutstandingCryptoPackets()
return h.appDataPackets.history.HasOutstandingPackets() || h.hasOutstandingCryptoPackets()
}

func (h *sentPacketHandler) setLossDetectionTimer() {
Expand Down Expand Up @@ -531,7 +528,10 @@ func (h *sentPacketHandler) setLossDetectionTimer() {
}

// PTO alarm
ptoTime, encLevel := h.getPTOTimeAndSpace()
ptoTime, encLevel, ok := h.getPTOTimeAndSpace()
if !ok {
return
}
h.alarm = ptoTime
if h.tracer != nil && h.alarm != oldAlarm {
h.tracer.SetLossTimer(logging.TimerTypePTO, encLevel, h.alarm)
Expand Down Expand Up @@ -599,20 +599,7 @@ func (h *sentPacketHandler) detectLostPackets(now time.Time, encLevel protocol.E
}

func (h *sentPacketHandler) OnLossDetectionTimeout() error {
// When all outstanding are acknowledged, the alarm is canceled in
// setLossDetectionTimer. This doesn't reset the timer in the session though.
// When OnAlarm is called, we therefore need to make sure that there are
// actually packets outstanding.
if h.hasOutstandingPackets() || !h.peerCompletedAddressValidation {
if err := h.onVerifiedLossDetectionTimeout(); err != nil {
return err
}
}
h.setLossDetectionTimer()
return nil
}

func (h *sentPacketHandler) onVerifiedLossDetectionTimeout() error {
defer h.setLossDetectionTimer()
earliestLossTime, encLevel := h.getLossTimeAndSpace()
if !earliestLossTime.IsZero() {
if h.logger.Debug() {
Expand All @@ -626,34 +613,12 @@ func (h *sentPacketHandler) onVerifiedLossDetectionTimeout() error {
}

// PTO
h.ptoCount++
if h.bytesInFlight > 0 {
_, encLevel = h.getPTOTimeAndSpace()
if h.logger.Debug() {
h.logger.Debugf("Loss detection alarm for %s fired in PTO mode. PTO count: %d", encLevel, h.ptoCount)
}
if h.tracer != nil {
h.tracer.LossTimerExpired(logging.TimerTypePTO, encLevel)
h.tracer.UpdatedPTOCount(h.ptoCount)
}
h.numProbesToSend += 2
//nolint:exhaustive // We never arm a PTO timer for 0-RTT packets.
switch encLevel {
case protocol.EncryptionInitial:
h.ptoMode = SendPTOInitial
case protocol.EncryptionHandshake:
h.ptoMode = SendPTOHandshake
case protocol.Encryption1RTT:
// skip a packet number in order to elicit an immediate ACK
_ = h.PopPacketNumber(protocol.Encryption1RTT)
h.ptoMode = SendPTOAppData
default:
return fmt.Errorf("PTO timer in unexpected encryption level: %s", encLevel)
}
} else {
if h.perspective == protocol.PerspectiveServer {
return errors.New("sentPacketHandler BUG: PTO fired, but bytes_in_flight is 0")
}
// When all outstanding are acknowledged, the alarm is canceled in
// setLossDetectionTimer. This doesn't reset the timer in the session though.
// When OnAlarm is called, we therefore need to make sure that there are
// actually packets outstanding.
if h.bytesInFlight == 0 && !h.peerCompletedAddressValidation {
h.ptoCount++
h.numProbesToSend++
if h.initialPackets != nil {
h.ptoMode = SendPTOInitial
Expand All @@ -662,6 +627,37 @@ func (h *sentPacketHandler) onVerifiedLossDetectionTimeout() error {
} else {
return errors.New("sentPacketHandler BUG: PTO fired, but bytes_in_flight is 0 and Initial and Handshake already dropped")
}
return nil
}

_, encLevel, ok := h.getPTOTimeAndSpace()
if !ok {
return nil
}
if ps := h.getPacketNumberSpace(encLevel); !ps.history.HasOutstandingPackets() && !h.peerCompletedAddressValidation {
return nil
}
h.ptoCount++
if h.logger.Debug() {
h.logger.Debugf("Loss detection alarm for %s fired in PTO mode. PTO count: %d", encLevel, h.ptoCount)
}
if h.tracer != nil {
h.tracer.LossTimerExpired(logging.TimerTypePTO, encLevel)
h.tracer.UpdatedPTOCount(h.ptoCount)
}
h.numProbesToSend += 2
//nolint:exhaustive // We never arm a PTO timer for 0-RTT packets.
switch encLevel {
case protocol.EncryptionInitial:
h.ptoMode = SendPTOInitial
case protocol.EncryptionHandshake:
h.ptoMode = SendPTOHandshake
case protocol.Encryption1RTT:
// skip a packet number in order to elicit an immediate ACK
_ = h.PopPacketNumber(protocol.Encryption1RTT)
h.ptoMode = SendPTOAppData
default:
return fmt.Errorf("PTO timer in unexpected encryption level: %s", encLevel)
}
return nil
}
Expand Down
34 changes: 31 additions & 3 deletions internal/ackhandler/sent_packet_handler_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -832,7 +832,7 @@ var _ = Describe("SentPacketHandler", func() {
handler.ReceivedPacket(protocol.EncryptionHandshake)
handler.SentPacket(ackElicitingPacket(&Packet{PacketNumber: 1}))
updateRTT(time.Hour)
Expect(handler.OnLossDetectionTimeout()).To(Succeed()) // TLP
Expect(handler.OnLossDetectionTimeout()).To(Succeed())
Expect(handler.GetLossDetectionTimeout()).To(BeZero())
Expect(handler.SendMode()).To(Equal(SendAny))
handler.SetHandshakeConfirmed()
Expand All @@ -845,7 +845,7 @@ var _ = Describe("SentPacketHandler", func() {
handler.ReceivedPacket(protocol.EncryptionHandshake)
handler.SetHandshakeConfirmed()
handler.SentPacket(ackElicitingPacket(&Packet{PacketNumber: 1, SendTime: time.Now().Add(-time.Hour)}))
handler.rttStats.UpdateRTT(time.Second, 0, time.Now())
updateRTT(time.Second)
Expect(handler.OnLossDetectionTimeout()).To(Succeed())
Expect(handler.SendMode()).To(Equal(SendPTOAppData))
ack := &wire.AckFrame{AckRanges: []wire.AckRange{{Smallest: 1, Largest: 1}}}
Expand All @@ -857,10 +857,18 @@ var _ = Describe("SentPacketHandler", func() {
It("handles ACKs for the original packet", func() {
handler.ReceivedPacket(protocol.EncryptionHandshake)
handler.SentPacket(ackElicitingPacket(&Packet{PacketNumber: 5, SendTime: time.Now().Add(-time.Hour)}))
handler.rttStats.UpdateRTT(time.Second, 0, time.Now())
updateRTT(time.Second)
Expect(handler.OnLossDetectionTimeout()).To(Succeed())
Expect(handler.OnLossDetectionTimeout()).To(Succeed())
})

It("doesn't set the PTO timer for Path MTU probe packets", func() {
handler.ReceivedPacket(protocol.EncryptionHandshake)
handler.SetHandshakeConfirmed()
updateRTT(time.Second)
handler.SentPacket(ackElicitingPacket(&Packet{PacketNumber: 5, SendTime: time.Now(), IsPathMTUProbePacket: true}))
Expect(handler.GetLossDetectionTimeout()).To(BeZero())
})
})

Context("amplification limit, for the server", func() {
Expand Down Expand Up @@ -1093,6 +1101,26 @@ var _ = Describe("SentPacketHandler", func() {
expectInPacketHistory([]protocol.PacketNumber{3}, protocol.EncryptionInitial)
Expect(handler.SendMode()).To(Equal(SendAny))
})

It("sets the early retransmit alarm for Path MTU probe packets", func() {
var mtuPacketDeclaredLost bool
now := time.Now()
handler.SentPacket(ackElicitingPacket(&Packet{
PacketNumber: 1,
SendTime: now.Add(-3 * time.Second),
IsPathMTUProbePacket: true,
Frames: []Frame{{Frame: &wire.PingFrame{}, OnLost: func(wire.Frame) { mtuPacketDeclaredLost = true }}},
}))
handler.SentPacket(ackElicitingPacket(&Packet{PacketNumber: 2, SendTime: now.Add(-3 * time.Second)}))
ack := &wire.AckFrame{AckRanges: []wire.AckRange{{Smallest: 2, Largest: 2}}}
_, err := handler.ReceivedAck(ack, protocol.Encryption1RTT, now.Add(-time.Second))
Expect(err).ToNot(HaveOccurred())
Expect(mtuPacketDeclaredLost).To(BeFalse())
Expect(handler.GetLossDetectionTimeout()).ToNot(BeZero())
Expect(handler.OnLossDetectionTimeout()).To(Succeed())
Expect(mtuPacketDeclaredLost).To(BeTrue())
Expect(handler.GetLossDetectionTimeout()).To(BeZero())
})
})

Context("crypto packets", func() {
Expand Down

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