chore: merge some quic-go fix

go.mod

@@ -19,8 +19,8 @@ require (
 	github.com/lunixbochs/struc v0.0.0-20200707160740-784aaebc1d40
 	github.com/mdlayher/netlink v1.7.2
 	github.com/metacubex/gopacket v1.1.20-0.20230608035415-7e2f98a3e759
-	github.com/metacubex/quic-go v0.39.1-0.20230930051114-b486c7799a55
-	github.com/metacubex/sing-quic v0.0.0-20230930052455-ae588c275b9c
+	github.com/metacubex/quic-go v0.39.1-0.20231001052253-5776efe31623
+	github.com/metacubex/sing-quic v0.0.0-20230926004739-7c7c534c2255
 	github.com/metacubex/sing-shadowsocks v0.2.5
 	github.com/metacubex/sing-shadowsocks2 v0.1.4
 	github.com/metacubex/sing-tun v0.1.13-0.20230926010214-4e9d1add2aee
@@ -32,7 +32,7 @@ require (
 	github.com/oschwald/maxminddb-golang v1.12.0
 	github.com/puzpuzpuz/xsync/v2 v2.5.0
 	github.com/sagernet/netlink v0.0.0-20220905062125-8043b4a9aa97
-	github.com/sagernet/sing v0.2.11
+	github.com/sagernet/sing v0.2.12
 	github.com/sagernet/sing-mux v0.1.3
 	github.com/sagernet/sing-shadowtls v0.1.4
 	github.com/sagernet/tfo-go v0.0.0-20230816093905-5a5c285d44a6
@@ -105,4 +105,4 @@ require (
 	golang.org/x/tools v0.13.0 // indirect
 )
 
-replace github.com/sagernet/sing => github.com/metacubex/sing v0.0.0-20230926010351-b23b466642d1
+replace github.com/sagernet/sing => github.com/metacubex/sing v0.0.0-20231001053806-1230641572b9

go.sum

@@ -93,12 +93,12 @@ github.com/metacubex/gopacket v1.1.20-0.20230608035415-7e2f98a3e759 h1:cjd4biTvO
 github.com/metacubex/gopacket v1.1.20-0.20230608035415-7e2f98a3e759/go.mod h1:UHOv2xu+RIgLwpXca7TLrXleEd4oR3sPatW6IF8wU88=
 github.com/metacubex/gvisor v0.0.0-20230611153922-78842f086475 h1:qSEOvPPaMrWggFyFhFYGyMR8i1HKyhXjdi1QYUAa2ww=
 github.com/metacubex/gvisor v0.0.0-20230611153922-78842f086475/go.mod h1:wehEpqiogdeyncfhckJP5gD2LtBgJW0wnDC24mJ+8Jg=
-github.com/metacubex/quic-go v0.39.1-0.20230930051114-b486c7799a55 h1:cAqp0BFOTr/1TpFicH1dA1q/6fp7E/JkqHBORfohqr4=
-github.com/metacubex/quic-go v0.39.1-0.20230930051114-b486c7799a55/go.mod h1:4pe6cY+nAMFU/Uxn1rfnxNIowsaJGDQ3uyy4VuiPkP4=
-github.com/metacubex/sing v0.0.0-20230926010351-b23b466642d1 h1:MkYAvDyhb7cwuqL4ZLKU3Oi6tYjFnz1sz5LS82JmtDo=
-github.com/metacubex/sing v0.0.0-20230926010351-b23b466642d1/go.mod h1:GQ673iPfUnkbK/dIPkfd1Xh1MjOGo36gkl/mkiHY7Jg=
-github.com/metacubex/sing-quic v0.0.0-20230930052455-ae588c275b9c h1:j7PKIUUhOAxJaLf/NmUKuIs9R06xNoYizwYgqf5HSrA=
-github.com/metacubex/sing-quic v0.0.0-20230930052455-ae588c275b9c/go.mod h1:TPAXFCHCtzW9Dm+wq1l1R/p0v/S/xmuRU0qfPR7WlOA=
+github.com/metacubex/quic-go v0.39.1-0.20231001052253-5776efe31623 h1:lxXUXdS2GB4Ktn3ocnzQ53v1lqd6LYYfYIKICugTaJM=
+github.com/metacubex/quic-go v0.39.1-0.20231001052253-5776efe31623/go.mod h1:4pe6cY+nAMFU/Uxn1rfnxNIowsaJGDQ3uyy4VuiPkP4=
+github.com/metacubex/sing v0.0.0-20231001053806-1230641572b9 h1:F0+IuW0tZ96QHEmrebXAdYnz7ab7Gz4l5yYC4g6Cg8k=
+github.com/metacubex/sing v0.0.0-20231001053806-1230641572b9/go.mod h1:GQ673iPfUnkbK/dIPkfd1Xh1MjOGo36gkl/mkiHY7Jg=
+github.com/metacubex/sing-quic v0.0.0-20230926004739-7c7c534c2255 h1:NfdM4hDFIhq9QxDStJ9Rz1h73sRUO/2L4pRZ6lGWRz8=
+github.com/metacubex/sing-quic v0.0.0-20230926004739-7c7c534c2255/go.mod h1:asoMecRyaA6pLSLVR+qFdp/vD24m8KZ1O/QDxWa7RsM=
 github.com/metacubex/sing-shadowsocks v0.2.5 h1:O2RRSHlKGEpAVG/OHJQxyHqDy8uvvdCW/oW2TDBOIhc=
 github.com/metacubex/sing-shadowsocks v0.2.5/go.mod h1:Xz2uW9BEYGEoA8B4XEpoxt7ERHClFCwsMAvWaruoyMo=
 github.com/metacubex/sing-shadowsocks2 v0.1.4 h1:OOCf8lgsVcpTOJUeaFAMzyKVebaQOBnKirDdUdBoKIE=

transport/hysteria/congestion/brutal.go

@@ -100,10 +100,6 @@ func (b *BrutalSender) OnCongestionEvent(number congestion.PacketNumber, lostByt
 	b.updateAckRate(currentTimestamp)
 }
 
-func (b *BrutalSender) OnCongestionEventEx(priorInFlight congestion.ByteCount, eventTime time.Time, ackedPackets []congestion.AckedPacketInfo, lostPackets []congestion.LostPacketInfo) {
-	// Stub
-}
-
 func (b *BrutalSender) SetMaxDatagramSize(size congestion.ByteCount) {
 	b.maxDatagramSize = size
 	b.pacer.SetMaxDatagramSize(size)

transport/tuic/common/congestion.go

@@ -18,6 +18,22 @@ func SetCongestionController(quicConn quic.Connection, cc string, cwnd int) {
 		cwnd = 32
 	}
 	switch cc {
+	case "cubic":
+		quicConn.SetCongestionControl(
+			congestion.NewCubicSender(
+				congestion.DefaultClock{},
+				congestion.GetInitialPacketSize(quicConn.RemoteAddr()),
+				false,
+			),
+		)
+	case "new_reno":
+		quicConn.SetCongestionControl(
+			congestion.NewCubicSender(
+				congestion.DefaultClock{},
+				congestion.GetInitialPacketSize(quicConn.RemoteAddr()),
+				true,
+			),
+		)
 	case "bbr_meta_v1":
 		quicConn.SetCongestionControl(
 			congestion.NewBBRSender(

transport/tuic/congestion/cubic.go

@@ -0,0 +1,213 @@
+package congestion
+
+import (
+	"math"
+	"time"
+
+	"github.com/metacubex/quic-go/congestion"
+)
+
+// 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
+	cubeCongestionWindowScale                      = 410
+	cubeFactor                congestion.ByteCount = 1 << cubeScale / cubeCongestionWindowScale / maxDatagramSize
+	// TODO: when re-enabling cubic, make sure to use the actual packet size here
+	maxDatagramSize = congestion.ByteCount(InitialPacketSizeIPv4)
+)
+
+const defaultNumConnections = 1
+
+// 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 congestion.ByteCount
+
+	// Number of acked bytes since the cycle started (epoch).
+	ackedBytesCount congestion.ByteCount
+
+	// TCP Reno equivalent congestion window in packets.
+	estimatedTCPcongestionWindow congestion.ByteCount
+
+	// Origin point of cubic function.
+	originPointCongestionWindow congestion.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 congestion.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 congestion.ByteCount) congestion.ByteCount {
+	if currentCongestionWindow+maxDatagramSize < 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 = congestion.ByteCount(c.betaLastMax() * float32(currentCongestionWindow))
+	} else {
+		c.lastMaxCongestionWindow = currentCongestionWindow
+	}
+	c.epoch = time.Time{} // Reset time.
+	return congestion.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 congestion.ByteCount,
+	currentCongestionWindow congestion.ByteCount,
+	delayMin time.Duration,
+	eventTime time.Time,
+) congestion.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 := congestion.ByteCount(cubeCongestionWindowScale*offset*offset*offset) * maxDatagramSize >> cubeScale
+	var targetCongestionWindow congestion.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 = Min(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 += congestion.ByteCount(float32(c.ackedBytesCount) * c.alpha() * float32(maxDatagramSize) / 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
+}

transport/tuic/congestion/cubic_sender.go

@@ -0,0 +1,297 @@
+package congestion
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/metacubex/quic-go/congestion"
+)
+
+const (
+	maxBurstPackets            = 3
+	renoBeta                   = 0.7 // Reno backoff factor.
+	minCongestionWindowPackets = 2
+	initialCongestionWindow    = 32
+)
+
+const InvalidPacketNumber congestion.PacketNumber = -1
+const MaxCongestionWindowPackets = 20000
+const MaxByteCount = congestion.ByteCount(1<<62 - 1)
+
+type cubicSender struct {
+	hybridSlowStart HybridSlowStart
+	rttStats        congestion.RTTStatsProvider
+	cubic           *Cubic
+	pacer           *pacer
+	clock           Clock
+
+	reno bool
+
+	// Track the largest packet that has been sent.
+	largestSentPacketNumber congestion.PacketNumber
+
+	// Track the largest packet that has been acked.
+	largestAckedPacketNumber congestion.PacketNumber
+
+	// Track the largest packet number outstanding when a CWND cutback occurs.
+	largestSentAtLastCutback congestion.PacketNumber
+
+	// Whether the last loss event caused us to exit slowstart.
+	// Used for stats collection of slowstartPacketsLost
+	lastCutbackExitedSlowstart bool
+
+	// Congestion window in bytes.
+	congestionWindow congestion.ByteCount
+
+	// Slow start congestion window in bytes, aka ssthresh.
+	slowStartThreshold congestion.ByteCount
+
+	// ACK counter for the Reno implementation.
+	numAckedPackets uint64
+
+	initialCongestionWindow    congestion.ByteCount
+	initialMaxCongestionWindow congestion.ByteCount
+
+	maxDatagramSize congestion.ByteCount
+}
+
+var (
+	_ congestion.CongestionControl = &cubicSender{}
+)
+
+// NewCubicSender makes a new cubic sender
+func NewCubicSender(
+	clock Clock,
+	initialMaxDatagramSize congestion.ByteCount,
+	reno bool,
+) *cubicSender {
+	return newCubicSender(
+		clock,
+		reno,
+		initialMaxDatagramSize,
+		initialCongestionWindow*initialMaxDatagramSize,
+		MaxCongestionWindowPackets*initialMaxDatagramSize,
+	)
+}
+
+func newCubicSender(
+	clock Clock,
+	reno bool,
+	initialMaxDatagramSize,
+	initialCongestionWindow,
+	initialMaxCongestionWindow congestion.ByteCount,
+) *cubicSender {
+	c := &cubicSender{
+		largestSentPacketNumber:    InvalidPacketNumber,
+		largestAckedPacketNumber:   InvalidPacketNumber,
+		largestSentAtLastCutback:   InvalidPacketNumber,
+		initialCongestionWindow:    initialCongestionWindow,
+		initialMaxCongestionWindow: initialMaxCongestionWindow,
+		congestionWindow:           initialCongestionWindow,
+		slowStartThreshold:         MaxByteCount,
+		cubic:                      NewCubic(clock),
+		clock:                      clock,
+		reno:                       reno,
+		maxDatagramSize:            initialMaxDatagramSize,
+	}
+	c.pacer = newPacer(c.BandwidthEstimate)
+	return c
+}
+
+func (c *cubicSender) SetRTTStatsProvider(provider congestion.RTTStatsProvider) {
+	c.rttStats = provider
+}
+
+// TimeUntilSend returns when the next packet should be sent.
+func (c *cubicSender) TimeUntilSend(_ congestion.ByteCount) time.Time {
+	return c.pacer.TimeUntilSend()
+}
+
+func (c *cubicSender) HasPacingBudget(now time.Time) bool {
+	return c.pacer.Budget(now) >= c.maxDatagramSize
+}
+
+func (c *cubicSender) maxCongestionWindow() congestion.ByteCount {
+	return c.maxDatagramSize * MaxCongestionWindowPackets
+}
+
+func (c *cubicSender) minCongestionWindow() congestion.ByteCount {
+	return c.maxDatagramSize * minCongestionWindowPackets
+}
+
+func (c *cubicSender) OnPacketSent(
+	sentTime time.Time,
+	_ congestion.ByteCount,
+	packetNumber congestion.PacketNumber,
+	bytes congestion.ByteCount,
+	isRetransmittable bool,
+) {
+	c.pacer.SentPacket(sentTime, bytes)
+	if !isRetransmittable {
+		return
+	}
+	c.largestSentPacketNumber = packetNumber
+	c.hybridSlowStart.OnPacketSent(packetNumber)
+}
+
+func (c *cubicSender) CanSend(bytesInFlight congestion.ByteCount) bool {
+	return bytesInFlight < c.GetCongestionWindow()
+}
+
+func (c *cubicSender) InRecovery() bool {
+	return c.largestAckedPacketNumber != InvalidPacketNumber && c.largestAckedPacketNumber <= c.largestSentAtLastCutback
+}
+
+func (c *cubicSender) InSlowStart() bool {
+	return c.GetCongestionWindow() < c.slowStartThreshold
+}
+
+func (c *cubicSender) GetCongestionWindow() congestion.ByteCount {
+	return c.congestionWindow
+}
+
+func (c *cubicSender) MaybeExitSlowStart() {
+	if c.InSlowStart() &&
+		c.hybridSlowStart.ShouldExitSlowStart(c.rttStats.LatestRTT(), c.rttStats.MinRTT(), c.GetCongestionWindow()/c.maxDatagramSize) {
+		// exit slow start
+		c.slowStartThreshold = c.congestionWindow
+	}
+}
+
+func (c *cubicSender) OnPacketAcked(
+	ackedPacketNumber congestion.PacketNumber,
+	ackedBytes congestion.ByteCount,
+	priorInFlight congestion.ByteCount,
+	eventTime time.Time,
+) {
+	c.largestAckedPacketNumber = Max(ackedPacketNumber, c.largestAckedPacketNumber)
+	if c.InRecovery() {
+		return
+	}
+	c.maybeIncreaseCwnd(ackedPacketNumber, ackedBytes, priorInFlight, eventTime)
+	if c.InSlowStart() {
+		c.hybridSlowStart.OnPacketAcked(ackedPacketNumber)
+	}
+}
+
+func (c *cubicSender) OnCongestionEvent(packetNumber congestion.PacketNumber, lostBytes, priorInFlight congestion.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 {
+		return
+	}
+	c.lastCutbackExitedSlowstart = c.InSlowStart()
+
+	if c.reno {
+		c.congestionWindow = congestion.ByteCount(float64(c.congestionWindow) * renoBeta)
+	} else {
+		c.congestionWindow = c.cubic.CongestionWindowAfterPacketLoss(c.congestionWindow)
+	}
+	if minCwnd := c.minCongestionWindow(); c.congestionWindow < minCwnd {
+		c.congestionWindow = minCwnd
+	}
+	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 (b *cubicSender) OnCongestionEventEx(priorInFlight congestion.ByteCount, eventTime time.Time, ackedPackets []congestion.AckedPacketInfo, lostPackets []congestion.LostPacketInfo) {
+	// Stub
+}
+
+// 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(
+	_ congestion.PacketNumber,
+	ackedBytes congestion.ByteCount,
+	priorInFlight congestion.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 += c.maxDatagramSize
+		return
+	}
+	// Congestion avoidance
+	if c.reno {
+		// Classic Reno congestion avoidance.
+		c.numAckedPackets++
+		if c.numAckedPackets >= uint64(c.congestionWindow/c.maxDatagramSize) {
+			c.congestionWindow += c.maxDatagramSize
+			c.numAckedPackets = 0
+		}
+	} else {
+		c.congestionWindow = Min(c.maxCongestionWindow(), c.cubic.CongestionWindowAfterAck(ackedBytes, c.congestionWindow, c.rttStats.MinRTT(), eventTime))
+	}
+}
+
+func (c *cubicSender) isCwndLimited(bytesInFlight congestion.ByteCount) bool {
+	congestionWindow := c.GetCongestionWindow()
+	if bytesInFlight >= congestionWindow {
+		return true
+	}
+	availableBytes := congestionWindow - bytesInFlight
+	slowStartLimited := c.InSlowStart() && bytesInFlight > congestionWindow/2
+	return slowStartLimited || availableBytes <= maxBurstPackets*c.maxDatagramSize
+}
+
+// BandwidthEstimate returns the current bandwidth estimate
+func (c *cubicSender) BandwidthEstimate() Bandwidth {
+	if c.rttStats == nil {
+		return infBandwidth
+	}
+	srtt := c.rttStats.SmoothedRTT()
+	if srtt == 0 {
+		// If we haven't measured an rtt, the bandwidth estimate is unknown.
+		return infBandwidth
+	}
+	return BandwidthFromDelta(c.GetCongestionWindow(), srtt)
+}
+
+// OnRetransmissionTimeout is called on an retransmission timeout
+func (c *cubicSender) OnRetransmissionTimeout(packetsRetransmitted bool) {
+	c.largestSentAtLastCutback = InvalidPacketNumber
+	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.largestSentPacketNumber = InvalidPacketNumber
+	c.largestAckedPacketNumber = InvalidPacketNumber
+	c.largestSentAtLastCutback = InvalidPacketNumber
+	c.lastCutbackExitedSlowstart = false
+	c.cubic.Reset()
+	c.numAckedPackets = 0
+	c.congestionWindow = c.initialCongestionWindow
+	c.slowStartThreshold = c.initialMaxCongestionWindow
+}
+
+func (c *cubicSender) SetMaxDatagramSize(s congestion.ByteCount) {
+	if s < c.maxDatagramSize {
+		panic(fmt.Sprintf("congestion BUG: decreased max datagram size from %d to %d", c.maxDatagramSize, s))
+	}
+	cwndIsMinCwnd := c.congestionWindow == c.minCongestionWindow()
+	c.maxDatagramSize = s
+	if cwndIsMinCwnd {
+		c.congestionWindow = c.minCongestionWindow()
+	}
+	c.pacer.SetMaxDatagramSize(s)
+}

transport/tuic/congestion/hybrid_slow_start.go

@@ -0,0 +1,112 @@
+package congestion
+
+import (
+	"time"
+
+	"github.com/metacubex/quic-go/congestion"
+)
+
+// Note(pwestin): the magic clamping numbers come from the original code in
+// tcp_cubic.c.
+const hybridStartLowWindow = congestion.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)
+	hybridStartDelayMaxThresholdUs = int64(16000)
+)
+
+// HybridSlowStart implements the TCP hybrid slow start algorithm
+type HybridSlowStart struct {
+	endPacketNumber      congestion.PacketNumber
+	lastSentPacketNumber congestion.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 congestion.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 congestion.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 congestion.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 = Min(minRTTincreaseThresholdUs, hybridStartDelayMaxThresholdUs)
+		minRTTincreaseThreshold := time.Duration(Max(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 congestion.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 congestion.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
+}

transport/tuic/congestion/minmax.go

@@ -0,0 +1,56 @@
+package congestion
+
+import (
+	"math"
+	"time"
+)
+
+// InfDuration is a duration of infinite length
+const InfDuration = time.Duration(math.MaxInt64)
+
+// MinNonZeroDuration return the minimum duration that's not zero.
+func MinNonZeroDuration(a, b time.Duration) time.Duration {
+	if a == 0 {
+		return b
+	}
+	if b == 0 {
+		return a
+	}
+	return Min(a, b)
+}
+
+// AbsDuration returns the absolute value of a time duration
+func AbsDuration(d time.Duration) time.Duration {
+	if d >= 0 {
+		return d
+	}
+	return -d
+}
+
+// MinTime returns the earlier time
+func MinTime(a, b time.Time) time.Time {
+	if a.After(b) {
+		return b
+	}
+	return a
+}
+
+// MinNonZeroTime returns the earlist time that is not time.Time{}
+// If both a and b are time.Time{}, it returns time.Time{}
+func MinNonZeroTime(a, b time.Time) time.Time {
+	if a.IsZero() {
+		return b
+	}
+	if b.IsZero() {
+		return a
+	}
+	return MinTime(a, b)
+}
+
+// MaxTime returns the later time
+func MaxTime(a, b time.Time) time.Time {
+	if a.After(b) {
+		return a
+	}
+	return b
+}