use go 1.12

Signed-off-by: hongming <talonwan@yunify.com>

vendor/github.com/lucas-clemente/quic-go/internal/congestion/bandwidth.go

@@ -0,0 +1,22 @@
+package congestion
+
+import (
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+)
+
+// Bandwidth of a connection
+type Bandwidth uint64
+
+const (
+	// BitsPerSecond is 1 bit per second
+	BitsPerSecond Bandwidth = 1
+	// BytesPerSecond is 1 byte per second
+	BytesPerSecond = 8 * BitsPerSecond
+)
+
+// BandwidthFromDelta calculates the bandwidth from a number of bytes and a time delta
+func BandwidthFromDelta(bytes protocol.ByteCount, delta time.Duration) Bandwidth {
+	return Bandwidth(bytes) * Bandwidth(time.Second) / Bandwidth(delta) * BytesPerSecond
+}

vendor/github.com/lucas-clemente/quic-go/internal/congestion/clock.go

@@ -0,0 +1,18 @@
+package congestion
+
+import "time"
+
+// A Clock returns the current time
+type Clock interface {
+	Now() time.Time
+}
+
+// DefaultClock implements the Clock interface using the Go stdlib clock.
+type DefaultClock struct{}
+
+var _ Clock = DefaultClock{}
+
+// Now gets the current time
+func (DefaultClock) Now() time.Time {
+	return time.Now()
+}

vendor/github.com/lucas-clemente/quic-go/internal/congestion/cubic.go

@@ -0,0 +1,210 @@
+package congestion
+
+import (
+	"math"
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+	"github.com/lucas-clemente/quic-go/internal/utils"
+)
+
+// This cubic implementation is based on the one found in Chromiums's QUIC
+// implementation, in the files net/quic/congestion_control/cubic.{hh,cc}.
+
+// Constants based on TCP defaults.
+// The following constants are in 2^10 fractions of a second instead of ms to
+// allow a 10 shift right to divide.
+
+// 1024*1024^3 (first 1024 is from 0.100^3)
+// where 0.100 is 100 ms which is the scaling round trip time.
+const cubeScale = 40
+const cubeCongestionWindowScale = 410
+const cubeFactor protocol.ByteCount = 1 << cubeScale / cubeCongestionWindowScale / protocol.DefaultTCPMSS
+
+const defaultNumConnections = 2
+
+// Default Cubic backoff factor
+const beta float32 = 0.7
+
+// Additional backoff factor when loss occurs in the concave part of the Cubic
+// curve. This additional backoff factor is expected to give up bandwidth to
+// new concurrent flows and speed up convergence.
+const betaLastMax float32 = 0.85
+
+// Cubic implements the cubic algorithm from TCP
+type Cubic struct {
+	clock Clock
+
+	// Number of connections to simulate.
+	numConnections int
+
+	// Time when this cycle started, after last loss event.
+	epoch time.Time
+
+	// Max congestion window used just before last loss event.
+	// Note: to improve fairness to other streams an additional back off is
+	// applied to this value if the new value is below our latest value.
+	lastMaxCongestionWindow protocol.ByteCount
+
+	// Number of acked bytes since the cycle started (epoch).
+	ackedBytesCount protocol.ByteCount
+
+	// TCP Reno equivalent congestion window in packets.
+	estimatedTCPcongestionWindow protocol.ByteCount
+
+	// Origin point of cubic function.
+	originPointCongestionWindow protocol.ByteCount
+
+	// Time to origin point of cubic function in 2^10 fractions of a second.
+	timeToOriginPoint uint32
+
+	// Last congestion window in packets computed by cubic function.
+	lastTargetCongestionWindow protocol.ByteCount
+}
+
+// NewCubic returns a new Cubic instance
+func NewCubic(clock Clock) *Cubic {
+	c := &Cubic{
+		clock:          clock,
+		numConnections: defaultNumConnections,
+	}
+	c.Reset()
+	return c
+}
+
+// Reset is called after a timeout to reset the cubic state
+func (c *Cubic) Reset() {
+	c.epoch = time.Time{}
+	c.lastMaxCongestionWindow = 0
+	c.ackedBytesCount = 0
+	c.estimatedTCPcongestionWindow = 0
+	c.originPointCongestionWindow = 0
+	c.timeToOriginPoint = 0
+	c.lastTargetCongestionWindow = 0
+}
+
+func (c *Cubic) alpha() float32 {
+	// TCPFriendly alpha is described in Section 3.3 of the CUBIC paper. Note that
+	// beta here is a cwnd multiplier, and is equal to 1-beta from the paper.
+	// We derive the equivalent alpha for an N-connection emulation as:
+	b := c.beta()
+	return 3 * float32(c.numConnections) * float32(c.numConnections) * (1 - b) / (1 + b)
+}
+
+func (c *Cubic) beta() float32 {
+	// kNConnectionBeta is the backoff factor after loss for our N-connection
+	// emulation, which emulates the effective backoff of an ensemble of N
+	// TCP-Reno connections on a single loss event. The effective multiplier is
+	// computed as:
+	return (float32(c.numConnections) - 1 + beta) / float32(c.numConnections)
+}
+
+func (c *Cubic) betaLastMax() float32 {
+	// betaLastMax is the additional backoff factor after loss for our
+	// N-connection emulation, which emulates the additional backoff of
+	// an ensemble of N TCP-Reno connections on a single loss event. The
+	// effective multiplier is computed as:
+	return (float32(c.numConnections) - 1 + betaLastMax) / float32(c.numConnections)
+}
+
+// OnApplicationLimited is called on ack arrival when sender is unable to use
+// the available congestion window. Resets Cubic state during quiescence.
+func (c *Cubic) OnApplicationLimited() {
+	// When sender is not using the available congestion window, the window does
+	// not grow. But to be RTT-independent, Cubic assumes that the sender has been
+	// using the entire window during the time since the beginning of the current
+	// "epoch" (the end of the last loss recovery period). Since
+	// application-limited periods break this assumption, we reset the epoch when
+	// in such a period. This reset effectively freezes congestion window growth
+	// through application-limited periods and allows Cubic growth to continue
+	// when the entire window is being used.
+	c.epoch = time.Time{}
+}
+
+// CongestionWindowAfterPacketLoss computes a new congestion window to use after
+// a loss event. Returns the new congestion window in packets. The new
+// congestion window is a multiplicative decrease of our current window.
+func (c *Cubic) CongestionWindowAfterPacketLoss(currentCongestionWindow protocol.ByteCount) protocol.ByteCount {
+	if currentCongestionWindow+protocol.DefaultTCPMSS < c.lastMaxCongestionWindow {
+		// We never reached the old max, so assume we are competing with another
+		// flow. Use our extra back off factor to allow the other flow to go up.
+		c.lastMaxCongestionWindow = protocol.ByteCount(c.betaLastMax() * float32(currentCongestionWindow))
+	} else {
+		c.lastMaxCongestionWindow = currentCongestionWindow
+	}
+	c.epoch = time.Time{} // Reset time.
+	return protocol.ByteCount(float32(currentCongestionWindow) * c.beta())
+}
+
+// CongestionWindowAfterAck computes a new congestion window to use after a received ACK.
+// Returns the new congestion window in packets. The new congestion window
+// follows a cubic function that depends on the time passed since last
+// packet loss.
+func (c *Cubic) CongestionWindowAfterAck(
+	ackedBytes protocol.ByteCount,
+	currentCongestionWindow protocol.ByteCount,
+	delayMin time.Duration,
+	eventTime time.Time,
+) protocol.ByteCount {
+	c.ackedBytesCount += ackedBytes
+
+	if c.epoch.IsZero() {
+		// First ACK after a loss event.
+		c.epoch = eventTime            // Start of epoch.
+		c.ackedBytesCount = ackedBytes // Reset count.
+		// Reset estimated_tcp_congestion_window_ to be in sync with cubic.
+		c.estimatedTCPcongestionWindow = currentCongestionWindow
+		if c.lastMaxCongestionWindow <= currentCongestionWindow {
+			c.timeToOriginPoint = 0
+			c.originPointCongestionWindow = currentCongestionWindow
+		} else {
+			c.timeToOriginPoint = uint32(math.Cbrt(float64(cubeFactor * (c.lastMaxCongestionWindow - currentCongestionWindow))))
+			c.originPointCongestionWindow = c.lastMaxCongestionWindow
+		}
+	}
+
+	// Change the time unit from microseconds to 2^10 fractions per second. Take
+	// the round trip time in account. This is done to allow us to use shift as a
+	// divide operator.
+	elapsedTime := int64(eventTime.Add(delayMin).Sub(c.epoch)/time.Microsecond) << 10 / (1000 * 1000)
+
+	// Right-shifts of negative, signed numbers have implementation-dependent
+	// behavior, so force the offset to be positive, as is done in the kernel.
+	offset := int64(c.timeToOriginPoint) - elapsedTime
+	if offset < 0 {
+		offset = -offset
+	}
+
+	deltaCongestionWindow := protocol.ByteCount(cubeCongestionWindowScale*offset*offset*offset) * protocol.DefaultTCPMSS >> cubeScale
+	var targetCongestionWindow protocol.ByteCount
+	if elapsedTime > int64(c.timeToOriginPoint) {
+		targetCongestionWindow = c.originPointCongestionWindow + deltaCongestionWindow
+	} else {
+		targetCongestionWindow = c.originPointCongestionWindow - deltaCongestionWindow
+	}
+	// Limit the CWND increase to half the acked bytes.
+	targetCongestionWindow = utils.MinByteCount(targetCongestionWindow, currentCongestionWindow+c.ackedBytesCount/2)
+
+	// Increase the window by approximately Alpha * 1 MSS of bytes every
+	// time we ack an estimated tcp window of bytes.  For small
+	// congestion windows (less than 25), the formula below will
+	// increase slightly slower than linearly per estimated tcp window
+	// of bytes.
+	c.estimatedTCPcongestionWindow += protocol.ByteCount(float32(c.ackedBytesCount) * c.alpha() * float32(protocol.DefaultTCPMSS) / float32(c.estimatedTCPcongestionWindow))
+	c.ackedBytesCount = 0
+
+	// We have a new cubic congestion window.
+	c.lastTargetCongestionWindow = targetCongestionWindow
+
+	// Compute target congestion_window based on cubic target and estimated TCP
+	// congestion_window, use highest (fastest).
+	if targetCongestionWindow < c.estimatedTCPcongestionWindow {
+		targetCongestionWindow = c.estimatedTCPcongestionWindow
+	}
+	return targetCongestionWindow
+}
+
+// SetNumConnections sets the number of emulated connections
+func (c *Cubic) SetNumConnections(n int) {
+	c.numConnections = n
+}

vendor/github.com/lucas-clemente/quic-go/internal/congestion/cubic_sender.go

@@ -0,0 +1,318 @@
+package congestion
+
+import (
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+	"github.com/lucas-clemente/quic-go/internal/utils"
+)
+
+const (
+	maxBurstBytes                                     = 3 * protocol.DefaultTCPMSS
+	renoBeta                       float32            = 0.7 // Reno backoff factor.
+	defaultMinimumCongestionWindow protocol.ByteCount = 2 * protocol.DefaultTCPMSS
+)
+
+type cubicSender struct {
+	hybridSlowStart HybridSlowStart
+	prr             PrrSender
+	rttStats        *RTTStats
+	stats           connectionStats
+	cubic           *Cubic
+
+	reno bool
+
+	// Track the largest packet that has been sent.
+	largestSentPacketNumber protocol.PacketNumber
+
+	// Track the largest packet that has been acked.
+	largestAckedPacketNumber protocol.PacketNumber
+
+	// Track the largest packet number outstanding when a CWND cutback occurs.
+	largestSentAtLastCutback protocol.PacketNumber
+
+	// Whether the last loss event caused us to exit slowstart.
+	// Used for stats collection of slowstartPacketsLost
+	lastCutbackExitedSlowstart bool
+
+	// When true, exit slow start with large cutback of congestion window.
+	slowStartLargeReduction bool
+
+	// Congestion window in packets.
+	congestionWindow protocol.ByteCount
+
+	// Minimum congestion window in packets.
+	minCongestionWindow protocol.ByteCount
+
+	// Maximum congestion window.
+	maxCongestionWindow protocol.ByteCount
+
+	// Slow start congestion window in bytes, aka ssthresh.
+	slowstartThreshold protocol.ByteCount
+
+	// Number of connections to simulate.
+	numConnections int
+
+	// ACK counter for the Reno implementation.
+	numAckedPackets uint64
+
+	initialCongestionWindow    protocol.ByteCount
+	initialMaxCongestionWindow protocol.ByteCount
+
+	minSlowStartExitWindow protocol.ByteCount
+}
+
+var _ SendAlgorithm = &cubicSender{}
+var _ SendAlgorithmWithDebugInfo = &cubicSender{}
+
+// NewCubicSender makes a new cubic sender
+func NewCubicSender(clock Clock, rttStats *RTTStats, reno bool, initialCongestionWindow, initialMaxCongestionWindow protocol.ByteCount) SendAlgorithmWithDebugInfo {
+	return &cubicSender{
+		rttStats:                   rttStats,
+		initialCongestionWindow:    initialCongestionWindow,
+		initialMaxCongestionWindow: initialMaxCongestionWindow,
+		congestionWindow:           initialCongestionWindow,
+		minCongestionWindow:        defaultMinimumCongestionWindow,
+		slowstartThreshold:         initialMaxCongestionWindow,
+		maxCongestionWindow:        initialMaxCongestionWindow,
+		numConnections:             defaultNumConnections,
+		cubic:                      NewCubic(clock),
+		reno:                       reno,
+	}
+}
+
+// TimeUntilSend returns when the next packet should be sent.
+func (c *cubicSender) TimeUntilSend(bytesInFlight protocol.ByteCount) time.Duration {
+	if c.InRecovery() {
+		// PRR is used when in recovery.
+		if c.prr.CanSend(c.GetCongestionWindow(), bytesInFlight, c.GetSlowStartThreshold()) {
+			return 0
+		}
+	}
+	delay := c.rttStats.SmoothedRTT() / time.Duration(2*c.GetCongestionWindow())
+	if !c.InSlowStart() { // adjust delay, such that it's 1.25*cwd/rtt
+		delay = delay * 8 / 5
+	}
+	return delay
+}
+
+func (c *cubicSender) OnPacketSent(
+	sentTime time.Time,
+	bytesInFlight protocol.ByteCount,
+	packetNumber protocol.PacketNumber,
+	bytes protocol.ByteCount,
+	isRetransmittable bool,
+) {
+	if !isRetransmittable {
+		return
+	}
+	if c.InRecovery() {
+		// PRR is used when in recovery.
+		c.prr.OnPacketSent(bytes)
+	}
+	c.largestSentPacketNumber = packetNumber
+	c.hybridSlowStart.OnPacketSent(packetNumber)
+}
+
+func (c *cubicSender) InRecovery() bool {
+	return c.largestAckedPacketNumber <= c.largestSentAtLastCutback && c.largestAckedPacketNumber != 0
+}
+
+func (c *cubicSender) InSlowStart() bool {
+	return c.GetCongestionWindow() < c.GetSlowStartThreshold()
+}
+
+func (c *cubicSender) GetCongestionWindow() protocol.ByteCount {
+	return c.congestionWindow
+}
+
+func (c *cubicSender) GetSlowStartThreshold() protocol.ByteCount {
+	return c.slowstartThreshold
+}
+
+func (c *cubicSender) ExitSlowstart() {
+	c.slowstartThreshold = c.congestionWindow
+}
+
+func (c *cubicSender) SlowstartThreshold() protocol.ByteCount {
+	return c.slowstartThreshold
+}
+
+func (c *cubicSender) MaybeExitSlowStart() {
+	if c.InSlowStart() && c.hybridSlowStart.ShouldExitSlowStart(c.rttStats.LatestRTT(), c.rttStats.MinRTT(), c.GetCongestionWindow()/protocol.DefaultTCPMSS) {
+		c.ExitSlowstart()
+	}
+}
+
+func (c *cubicSender) OnPacketAcked(
+	ackedPacketNumber protocol.PacketNumber,
+	ackedBytes protocol.ByteCount,
+	priorInFlight protocol.ByteCount,
+	eventTime time.Time,
+) {
+	c.largestAckedPacketNumber = utils.MaxPacketNumber(ackedPacketNumber, c.largestAckedPacketNumber)
+	if c.InRecovery() {
+		// PRR is used when in recovery.
+		c.prr.OnPacketAcked(ackedBytes)
+		return
+	}
+	c.maybeIncreaseCwnd(ackedPacketNumber, ackedBytes, priorInFlight, eventTime)
+	if c.InSlowStart() {
+		c.hybridSlowStart.OnPacketAcked(ackedPacketNumber)
+	}
+}
+
+func (c *cubicSender) OnPacketLost(
+	packetNumber protocol.PacketNumber,
+	lostBytes protocol.ByteCount,
+	priorInFlight protocol.ByteCount,
+) {
+	// TCP NewReno (RFC6582) says that once a loss occurs, any losses in packets
+	// already sent should be treated as a single loss event, since it's expected.
+	if packetNumber <= c.largestSentAtLastCutback {
+		if c.lastCutbackExitedSlowstart {
+			c.stats.slowstartPacketsLost++
+			c.stats.slowstartBytesLost += lostBytes
+			if c.slowStartLargeReduction {
+				// Reduce congestion window by lost_bytes for every loss.
+				c.congestionWindow = utils.MaxByteCount(c.congestionWindow-lostBytes, c.minSlowStartExitWindow)
+				c.slowstartThreshold = c.congestionWindow
+			}
+		}
+		return
+	}
+	c.lastCutbackExitedSlowstart = c.InSlowStart()
+	if c.InSlowStart() {
+		c.stats.slowstartPacketsLost++
+	}
+
+	c.prr.OnPacketLost(priorInFlight)
+
+	// TODO(chromium): Separate out all of slow start into a separate class.
+	if c.slowStartLargeReduction && c.InSlowStart() {
+		if c.congestionWindow >= 2*c.initialCongestionWindow {
+			c.minSlowStartExitWindow = c.congestionWindow / 2
+		}
+		c.congestionWindow -= protocol.DefaultTCPMSS
+	} else if c.reno {
+		c.congestionWindow = protocol.ByteCount(float32(c.congestionWindow) * c.RenoBeta())
+	} else {
+		c.congestionWindow = c.cubic.CongestionWindowAfterPacketLoss(c.congestionWindow)
+	}
+	if c.congestionWindow < c.minCongestionWindow {
+		c.congestionWindow = c.minCongestionWindow
+	}
+	c.slowstartThreshold = c.congestionWindow
+	c.largestSentAtLastCutback = c.largestSentPacketNumber
+	// reset packet count from congestion avoidance mode. We start
+	// counting again when we're out of recovery.
+	c.numAckedPackets = 0
+}
+
+func (c *cubicSender) RenoBeta() float32 {
+	// kNConnectionBeta is the backoff factor after loss for our N-connection
+	// emulation, which emulates the effective backoff of an ensemble of N
+	// TCP-Reno connections on a single loss event. The effective multiplier is
+	// computed as:
+	return (float32(c.numConnections) - 1. + renoBeta) / float32(c.numConnections)
+}
+
+// Called when we receive an ack. Normal TCP tracks how many packets one ack
+// represents, but quic has a separate ack for each packet.
+func (c *cubicSender) maybeIncreaseCwnd(
+	ackedPacketNumber protocol.PacketNumber,
+	ackedBytes protocol.ByteCount,
+	priorInFlight protocol.ByteCount,
+	eventTime time.Time,
+) {
+	// Do not increase the congestion window unless the sender is close to using
+	// the current window.
+	if !c.isCwndLimited(priorInFlight) {
+		c.cubic.OnApplicationLimited()
+		return
+	}
+	if c.congestionWindow >= c.maxCongestionWindow {
+		return
+	}
+	if c.InSlowStart() {
+		// TCP slow start, exponential growth, increase by one for each ACK.
+		c.congestionWindow += protocol.DefaultTCPMSS
+		return
+	}
+	// Congestion avoidance
+	if c.reno {
+		// Classic Reno congestion avoidance.
+		c.numAckedPackets++
+		// Divide by num_connections to smoothly increase the CWND at a faster
+		// rate than conventional Reno.
+		if c.numAckedPackets*uint64(c.numConnections) >= uint64(c.congestionWindow)/uint64(protocol.DefaultTCPMSS) {
+			c.congestionWindow += protocol.DefaultTCPMSS
+			c.numAckedPackets = 0
+		}
+	} else {
+		c.congestionWindow = utils.MinByteCount(c.maxCongestionWindow, c.cubic.CongestionWindowAfterAck(ackedBytes, c.congestionWindow, c.rttStats.MinRTT(), eventTime))
+	}
+}
+
+func (c *cubicSender) isCwndLimited(bytesInFlight protocol.ByteCount) bool {
+	congestionWindow := c.GetCongestionWindow()
+	if bytesInFlight >= congestionWindow {
+		return true
+	}
+	availableBytes := congestionWindow - bytesInFlight
+	slowStartLimited := c.InSlowStart() && bytesInFlight > congestionWindow/2
+	return slowStartLimited || availableBytes <= maxBurstBytes
+}
+
+// BandwidthEstimate returns the current bandwidth estimate
+func (c *cubicSender) BandwidthEstimate() Bandwidth {
+	srtt := c.rttStats.SmoothedRTT()
+	if srtt == 0 {
+		// If we haven't measured an rtt, the bandwidth estimate is unknown.
+		return 0
+	}
+	return BandwidthFromDelta(c.GetCongestionWindow(), srtt)
+}
+
+// HybridSlowStart returns the hybrid slow start instance for testing
+func (c *cubicSender) HybridSlowStart() *HybridSlowStart {
+	return &c.hybridSlowStart
+}
+
+// SetNumEmulatedConnections sets the number of emulated connections
+func (c *cubicSender) SetNumEmulatedConnections(n int) {
+	c.numConnections = utils.Max(n, 1)
+	c.cubic.SetNumConnections(c.numConnections)
+}
+
+// OnRetransmissionTimeout is called on an retransmission timeout
+func (c *cubicSender) OnRetransmissionTimeout(packetsRetransmitted bool) {
+	c.largestSentAtLastCutback = 0
+	if !packetsRetransmitted {
+		return
+	}
+	c.hybridSlowStart.Restart()
+	c.cubic.Reset()
+	c.slowstartThreshold = c.congestionWindow / 2
+	c.congestionWindow = c.minCongestionWindow
+}
+
+// OnConnectionMigration is called when the connection is migrated (?)
+func (c *cubicSender) OnConnectionMigration() {
+	c.hybridSlowStart.Restart()
+	c.prr = PrrSender{}
+	c.largestSentPacketNumber = 0
+	c.largestAckedPacketNumber = 0
+	c.largestSentAtLastCutback = 0
+	c.lastCutbackExitedSlowstart = false
+	c.cubic.Reset()
+	c.numAckedPackets = 0
+	c.congestionWindow = c.initialCongestionWindow
+	c.slowstartThreshold = c.initialMaxCongestionWindow
+	c.maxCongestionWindow = c.initialMaxCongestionWindow
+}
+
+// SetSlowStartLargeReduction allows enabling the SSLR experiment
+func (c *cubicSender) SetSlowStartLargeReduction(enabled bool) {
+	c.slowStartLargeReduction = enabled
+}

vendor/github.com/lucas-clemente/quic-go/internal/congestion/hybrid_slow_start.go

@@ -0,0 +1,111 @@
+package congestion
+
+import (
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+	"github.com/lucas-clemente/quic-go/internal/utils"
+)
+
+// Note(pwestin): the magic clamping numbers come from the original code in
+// tcp_cubic.c.
+const hybridStartLowWindow = protocol.ByteCount(16)
+
+// Number of delay samples for detecting the increase of delay.
+const hybridStartMinSamples = uint32(8)
+
+// Exit slow start if the min rtt has increased by more than 1/8th.
+const hybridStartDelayFactorExp = 3 // 2^3 = 8
+// The original paper specifies 2 and 8ms, but those have changed over time.
+const hybridStartDelayMinThresholdUs = int64(4000)
+const hybridStartDelayMaxThresholdUs = int64(16000)
+
+// HybridSlowStart implements the TCP hybrid slow start algorithm
+type HybridSlowStart struct {
+	endPacketNumber      protocol.PacketNumber
+	lastSentPacketNumber protocol.PacketNumber
+	started              bool
+	currentMinRTT        time.Duration
+	rttSampleCount       uint32
+	hystartFound         bool
+}
+
+// StartReceiveRound is called for the start of each receive round (burst) in the slow start phase.
+func (s *HybridSlowStart) StartReceiveRound(lastSent protocol.PacketNumber) {
+	s.endPacketNumber = lastSent
+	s.currentMinRTT = 0
+	s.rttSampleCount = 0
+	s.started = true
+}
+
+// IsEndOfRound returns true if this ack is the last packet number of our current slow start round.
+func (s *HybridSlowStart) IsEndOfRound(ack protocol.PacketNumber) bool {
+	return s.endPacketNumber < ack
+}
+
+// ShouldExitSlowStart should be called on every new ack frame, since a new
+// RTT measurement can be made then.
+// rtt: the RTT for this ack packet.
+// minRTT: is the lowest delay (RTT) we have seen during the session.
+// congestionWindow: the congestion window in packets.
+func (s *HybridSlowStart) ShouldExitSlowStart(latestRTT time.Duration, minRTT time.Duration, congestionWindow protocol.ByteCount) bool {
+	if !s.started {
+		// Time to start the hybrid slow start.
+		s.StartReceiveRound(s.lastSentPacketNumber)
+	}
+	if s.hystartFound {
+		return true
+	}
+	// Second detection parameter - delay increase detection.
+	// Compare the minimum delay (s.currentMinRTT) of the current
+	// burst of packets relative to the minimum delay during the session.
+	// Note: we only look at the first few(8) packets in each burst, since we
+	// only want to compare the lowest RTT of the burst relative to previous
+	// bursts.
+	s.rttSampleCount++
+	if s.rttSampleCount <= hybridStartMinSamples {
+		if s.currentMinRTT == 0 || s.currentMinRTT > latestRTT {
+			s.currentMinRTT = latestRTT
+		}
+	}
+	// We only need to check this once per round.
+	if s.rttSampleCount == hybridStartMinSamples {
+		// Divide minRTT by 8 to get a rtt increase threshold for exiting.
+		minRTTincreaseThresholdUs := int64(minRTT / time.Microsecond >> hybridStartDelayFactorExp)
+		// Ensure the rtt threshold is never less than 2ms or more than 16ms.
+		minRTTincreaseThresholdUs = utils.MinInt64(minRTTincreaseThresholdUs, hybridStartDelayMaxThresholdUs)
+		minRTTincreaseThreshold := time.Duration(utils.MaxInt64(minRTTincreaseThresholdUs, hybridStartDelayMinThresholdUs)) * time.Microsecond
+
+		if s.currentMinRTT > (minRTT + minRTTincreaseThreshold) {
+			s.hystartFound = true
+		}
+	}
+	// Exit from slow start if the cwnd is greater than 16 and
+	// increasing delay is found.
+	return congestionWindow >= hybridStartLowWindow && s.hystartFound
+}
+
+// OnPacketSent is called when a packet was sent
+func (s *HybridSlowStart) OnPacketSent(packetNumber protocol.PacketNumber) {
+	s.lastSentPacketNumber = packetNumber
+}
+
+// OnPacketAcked gets invoked after ShouldExitSlowStart, so it's best to end
+// the round when the final packet of the burst is received and start it on
+// the next incoming ack.
+func (s *HybridSlowStart) OnPacketAcked(ackedPacketNumber protocol.PacketNumber) {
+	if s.IsEndOfRound(ackedPacketNumber) {
+		s.started = false
+	}
+}
+
+// Started returns true if started
+func (s *HybridSlowStart) Started() bool {
+	return s.started
+}
+
+// Restart the slow start phase
+func (s *HybridSlowStart) Restart() {
+	s.started = false
+	s.hystartFound = false
+}

vendor/github.com/lucas-clemente/quic-go/internal/congestion/interface.go

@@ -0,0 +1,36 @@
+package congestion
+
+import (
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+)
+
+// A SendAlgorithm performs congestion control and calculates the congestion window
+type SendAlgorithm interface {
+	TimeUntilSend(bytesInFlight protocol.ByteCount) time.Duration
+	OnPacketSent(sentTime time.Time, bytesInFlight protocol.ByteCount, packetNumber protocol.PacketNumber, bytes protocol.ByteCount, isRetransmittable bool)
+	GetCongestionWindow() protocol.ByteCount
+	MaybeExitSlowStart()
+	OnPacketAcked(number protocol.PacketNumber, ackedBytes protocol.ByteCount, priorInFlight protocol.ByteCount, eventTime time.Time)
+	OnPacketLost(number protocol.PacketNumber, lostBytes protocol.ByteCount, priorInFlight protocol.ByteCount)
+	SetNumEmulatedConnections(n int)
+	OnRetransmissionTimeout(packetsRetransmitted bool)
+	OnConnectionMigration()
+
+	// Experiments
+	SetSlowStartLargeReduction(enabled bool)
+}
+
+// SendAlgorithmWithDebugInfo adds some debug functions to SendAlgorithm
+type SendAlgorithmWithDebugInfo interface {
+	SendAlgorithm
+	BandwidthEstimate() Bandwidth
+
+	// Stuff only used in testing
+
+	HybridSlowStart() *HybridSlowStart
+	SlowstartThreshold() protocol.ByteCount
+	RenoBeta() float32
+	InRecovery() bool
+}

vendor/github.com/lucas-clemente/quic-go/internal/congestion/prr_sender.go

@@ -0,0 +1,54 @@
+package congestion
+
+import (
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+)
+
+// PrrSender implements the Proportional Rate Reduction (PRR) per RFC 6937
+type PrrSender struct {
+	bytesSentSinceLoss      protocol.ByteCount
+	bytesDeliveredSinceLoss protocol.ByteCount
+	ackCountSinceLoss       protocol.ByteCount
+	bytesInFlightBeforeLoss protocol.ByteCount
+}
+
+// OnPacketSent should be called after a packet was sent
+func (p *PrrSender) OnPacketSent(sentBytes protocol.ByteCount) {
+	p.bytesSentSinceLoss += sentBytes
+}
+
+// OnPacketLost should be called on the first loss that triggers a recovery
+// period and all other methods in this class should only be called when in
+// recovery.
+func (p *PrrSender) OnPacketLost(priorInFlight protocol.ByteCount) {
+	p.bytesSentSinceLoss = 0
+	p.bytesInFlightBeforeLoss = priorInFlight
+	p.bytesDeliveredSinceLoss = 0
+	p.ackCountSinceLoss = 0
+}
+
+// OnPacketAcked should be called after a packet was acked
+func (p *PrrSender) OnPacketAcked(ackedBytes protocol.ByteCount) {
+	p.bytesDeliveredSinceLoss += ackedBytes
+	p.ackCountSinceLoss++
+}
+
+// CanSend returns if packets can be sent
+func (p *PrrSender) CanSend(congestionWindow, bytesInFlight, slowstartThreshold protocol.ByteCount) bool {
+	// Return QuicTime::Zero In order to ensure limited transmit always works.
+	if p.bytesSentSinceLoss == 0 || bytesInFlight < protocol.DefaultTCPMSS {
+		return true
+	}
+	if congestionWindow > bytesInFlight {
+		// During PRR-SSRB, limit outgoing packets to 1 extra MSS per ack, instead
+		// of sending the entire available window. This prevents burst retransmits
+		// when more packets are lost than the CWND reduction.
+		//   limit = MAX(prr_delivered - prr_out, DeliveredData) + MSS
+		return p.bytesDeliveredSinceLoss+p.ackCountSinceLoss*protocol.DefaultTCPMSS > p.bytesSentSinceLoss
+	}
+	// Implement Proportional Rate Reduction (RFC6937).
+	// Checks a simplified version of the PRR formula that doesn't use division:
+	// AvailableSendWindow =
+	//   CEIL(prr_delivered * ssthresh / BytesInFlightAtLoss) - prr_sent
+	return p.bytesDeliveredSinceLoss*slowstartThreshold > p.bytesSentSinceLoss*p.bytesInFlightBeforeLoss
+}

vendor/github.com/lucas-clemente/quic-go/internal/congestion/rtt_stats.go

@@ -0,0 +1,101 @@
+package congestion
+
+import (
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/utils"
+)
+
+const (
+	rttAlpha      float32 = 0.125
+	oneMinusAlpha float32 = (1 - rttAlpha)
+	rttBeta       float32 = 0.25
+	oneMinusBeta  float32 = (1 - rttBeta)
+	// The default RTT used before an RTT sample is taken.
+	defaultInitialRTT = 100 * time.Millisecond
+)
+
+// RTTStats provides round-trip statistics
+type RTTStats struct {
+	minRTT        time.Duration
+	latestRTT     time.Duration
+	smoothedRTT   time.Duration
+	meanDeviation time.Duration
+}
+
+// NewRTTStats makes a properly initialized RTTStats object
+func NewRTTStats() *RTTStats {
+	return &RTTStats{}
+}
+
+// MinRTT Returns the minRTT for the entire connection.
+// May return Zero if no valid updates have occurred.
+func (r *RTTStats) MinRTT() time.Duration { return r.minRTT }
+
+// LatestRTT returns the most recent rtt measurement.
+// May return Zero if no valid updates have occurred.
+func (r *RTTStats) LatestRTT() time.Duration { return r.latestRTT }
+
+// SmoothedRTT returns the EWMA smoothed RTT for the connection.
+// May return Zero if no valid updates have occurred.
+func (r *RTTStats) SmoothedRTT() time.Duration { return r.smoothedRTT }
+
+// SmoothedOrInitialRTT returns the EWMA smoothed RTT for the connection.
+// If no valid updates have occurred, it returns the initial RTT.
+func (r *RTTStats) SmoothedOrInitialRTT() time.Duration {
+	if r.smoothedRTT != 0 {
+		return r.smoothedRTT
+	}
+	return defaultInitialRTT
+}
+
+// MeanDeviation gets the mean deviation
+func (r *RTTStats) MeanDeviation() time.Duration { return r.meanDeviation }
+
+// 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 {
+		return
+	}
+
+	// Update r.minRTT first. r.minRTT does not use an rttSample corrected for
+	// ackDelay but the raw observed sendDelta, since poor clock granularity at
+	// the client may cause a high ackDelay to result in underestimation of the
+	// r.minRTT.
+	if r.minRTT == 0 || r.minRTT > sendDelta {
+		r.minRTT = sendDelta
+	}
+
+	// Correct for ackDelay if information received from the peer results in a
+	// an RTT sample at least as large as minRTT. Otherwise, only use the
+	// sendDelta.
+	sample := sendDelta
+	if sample-r.minRTT >= ackDelay {
+		sample -= ackDelay
+	}
+	r.latestRTT = sample
+	// First time call.
+	if r.smoothedRTT == 0 {
+		r.smoothedRTT = sample
+		r.meanDeviation = sample / 2
+	} else {
+		r.meanDeviation = time.Duration(oneMinusBeta*float32(r.meanDeviation/time.Microsecond)+rttBeta*float32(utils.AbsDuration(r.smoothedRTT-sample)/time.Microsecond)) * time.Microsecond
+		r.smoothedRTT = time.Duration((float32(r.smoothedRTT/time.Microsecond)*oneMinusAlpha)+(float32(sample/time.Microsecond)*rttAlpha)) * time.Microsecond
+	}
+}
+
+// OnConnectionMigration is called when connection migrates and rtt measurement needs to be reset.
+func (r *RTTStats) OnConnectionMigration() {
+	r.latestRTT = 0
+	r.minRTT = 0
+	r.smoothedRTT = 0
+	r.meanDeviation = 0
+}
+
+// ExpireSmoothedMetrics causes the smoothed_rtt to be increased to the latest_rtt if the latest_rtt
+// is larger. The mean deviation is increased to the most recent deviation if
+// it's larger.
+func (r *RTTStats) ExpireSmoothedMetrics() {
+	r.meanDeviation = utils.MaxDuration(r.meanDeviation, utils.AbsDuration(r.smoothedRTT-r.latestRTT))
+	r.smoothedRTT = utils.MaxDuration(r.smoothedRTT, r.latestRTT)
+}

vendor/github.com/lucas-clemente/quic-go/internal/congestion/stats.go

@@ -0,0 +1,8 @@
+package congestion
+
+import "github.com/lucas-clemente/quic-go/internal/protocol"
+
+type connectionStats struct {
+	slowstartPacketsLost protocol.PacketNumber
+	slowstartBytesLost   protocol.ByteCount
+}