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limit the exponential PTO backoff to 60s #3595

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merged 4 commits into from Nov 15, 2022
Merged

limit the exponential PTO backoff to 60s #3595

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bb179ed
limiting exponential pto delay to a constant
cliffc-spirent Oct 14, 2022
f5d43b0
updating maximum pto to 60s, referring to rfc
cliffc-spirent Oct 17, 2022
de80d4a
updating exponential backoff test for truncation
cliffc-spirent Oct 20, 2022
9ec71c1
Apply suggestions from code review
marten-seemann Nov 15, 2022
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18 changes: 14 additions & 4 deletions internal/ackhandler/sent_packet_handler.go
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Expand Up @@ -23,6 +23,8 @@ const (
amplificationFactor = 3
// We use Retry packets to derive an RTT estimate. Make sure we don't set the RTT to a super low value yet.
minRTTAfterRetry = 5 * time.Millisecond
// PTO duration is exponential but truncated to the following maximum as allowed by RFC 8961 Section 4.4.
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maxPTODuration = 60 * time.Second
)

type packetNumberSpace struct {
Expand Down Expand Up @@ -457,6 +459,14 @@ func (h *sentPacketHandler) getLossTimeAndSpace() (time.Time, protocol.Encryptio
return lossTime, encLevel
}

func (h *sentPacketHandler) getScaledPTO(includeMaxAckDelay bool) time.Duration {
pto := h.rttStats.PTO(includeMaxAckDelay) << h.ptoCount
if pto > maxPTODuration {
return maxPTODuration
}
return pto
}

// same logic as getLossTimeAndSpace, but for lastAckElicitingPacketTime instead of lossTime
func (h *sentPacketHandler) getPTOTimeAndSpace() (pto time.Time, encLevel protocol.EncryptionLevel, ok bool) {
// We only send application data probe packets once the handshake is confirmed,
Expand All @@ -465,7 +475,7 @@ func (h *sentPacketHandler) getPTOTimeAndSpace() (pto time.Time, encLevel protoc
if h.peerCompletedAddressValidation {
return
}
t := time.Now().Add(h.rttStats.PTO(false) << h.ptoCount)
t := time.Now().Add(h.getScaledPTO(false))
if h.initialPackets != nil {
return t, protocol.EncryptionInitial, true
}
Expand All @@ -475,18 +485,18 @@ func (h *sentPacketHandler) getPTOTimeAndSpace() (pto time.Time, encLevel protoc
if h.initialPackets != nil {
encLevel = protocol.EncryptionInitial
if t := h.initialPackets.lastAckElicitingPacketTime; !t.IsZero() {
pto = t.Add(h.rttStats.PTO(false) << h.ptoCount)
pto = t.Add(h.getScaledPTO(false))
}
}
if h.handshakePackets != nil && !h.handshakePackets.lastAckElicitingPacketTime.IsZero() {
t := h.handshakePackets.lastAckElicitingPacketTime.Add(h.rttStats.PTO(false) << h.ptoCount)
t := h.handshakePackets.lastAckElicitingPacketTime.Add(h.getScaledPTO(false))
if pto.IsZero() || (!t.IsZero() && t.Before(pto)) {
pto = t
encLevel = protocol.EncryptionHandshake
}
}
if h.handshakeConfirmed && !h.appDataPackets.lastAckElicitingPacketTime.IsZero() {
t := h.appDataPackets.lastAckElicitingPacketTime.Add(h.rttStats.PTO(true) << h.ptoCount)
t := h.appDataPackets.lastAckElicitingPacketTime.Add(h.getScaledPTO(true))
if pto.IsZero() || (!t.IsZero() && t.Before(pto)) {
pto = t
encLevel = protocol.Encryption1RTT
Expand Down