TUN-4597: Add a QUIC server skeleton

- Added a QUIC server to accept streams
- Unit test for this server also tests ALPN
- Temporary echo capability for HTTP ConnectionType

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

@@ -0,0 +1,316 @@
+package congestion
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+	"github.com/lucas-clemente/quic-go/internal/utils"
+	"github.com/lucas-clemente/quic-go/logging"
+)
+
+const (
+	// maxDatagramSize is the default maximum packet size used in the Linux TCP implementation.
+	// Used in QUIC for congestion window computations in bytes.
+	initialMaxDatagramSize     = protocol.ByteCount(protocol.InitialPacketSizeIPv4)
+	maxBurstPackets            = 3
+	renoBeta                   = 0.7 // Reno backoff factor.
+	minCongestionWindowPackets = 2
+	initialCongestionWindow    = 32
+)
+
+type cubicSender struct {
+	hybridSlowStart HybridSlowStart
+	rttStats        *utils.RTTStats
+	cubic           *Cubic
+	pacer           *pacer
+	clock           Clock
+
+	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
+
+	// Congestion window in packets.
+	congestionWindow protocol.ByteCount
+
+	// Slow start congestion window in bytes, aka ssthresh.
+	slowStartThreshold protocol.ByteCount
+
+	// ACK counter for the Reno implementation.
+	numAckedPackets uint64
+
+	initialCongestionWindow    protocol.ByteCount
+	initialMaxCongestionWindow protocol.ByteCount
+
+	maxDatagramSize protocol.ByteCount
+
+	lastState logging.CongestionState
+	tracer    logging.ConnectionTracer
+}
+
+var (
+	_ SendAlgorithm               = &cubicSender{}
+	_ SendAlgorithmWithDebugInfos = &cubicSender{}
+)
+
+// NewCubicSender makes a new cubic sender
+func NewCubicSender(
+	clock Clock,
+	rttStats *utils.RTTStats,
+	initialMaxDatagramSize protocol.ByteCount,
+	reno bool,
+	tracer logging.ConnectionTracer,
+) *cubicSender {
+	return newCubicSender(
+		clock,
+		rttStats,
+		reno,
+		initialMaxDatagramSize,
+		initialCongestionWindow*initialMaxDatagramSize,
+		protocol.MaxCongestionWindowPackets*initialMaxDatagramSize,
+		tracer,
+	)
+}
+
+func newCubicSender(
+	clock Clock,
+	rttStats *utils.RTTStats,
+	reno bool,
+	initialMaxDatagramSize,
+	initialCongestionWindow,
+	initialMaxCongestionWindow protocol.ByteCount,
+	tracer logging.ConnectionTracer,
+) *cubicSender {
+	c := &cubicSender{
+		rttStats:                   rttStats,
+		largestSentPacketNumber:    protocol.InvalidPacketNumber,
+		largestAckedPacketNumber:   protocol.InvalidPacketNumber,
+		largestSentAtLastCutback:   protocol.InvalidPacketNumber,
+		initialCongestionWindow:    initialCongestionWindow,
+		initialMaxCongestionWindow: initialMaxCongestionWindow,
+		congestionWindow:           initialCongestionWindow,
+		slowStartThreshold:         protocol.MaxByteCount,
+		cubic:                      NewCubic(clock),
+		clock:                      clock,
+		reno:                       reno,
+		tracer:                     tracer,
+		maxDatagramSize:            initialMaxDatagramSize,
+	}
+	c.pacer = newPacer(c.BandwidthEstimate)
+	if c.tracer != nil {
+		c.lastState = logging.CongestionStateSlowStart
+		c.tracer.UpdatedCongestionState(logging.CongestionStateSlowStart)
+	}
+	return c
+}
+
+// TimeUntilSend returns when the next packet should be sent.
+func (c *cubicSender) TimeUntilSend(_ protocol.ByteCount) time.Time {
+	return c.pacer.TimeUntilSend()
+}
+
+func (c *cubicSender) HasPacingBudget() bool {
+	return c.pacer.Budget(c.clock.Now()) >= c.maxDatagramSize
+}
+
+func (c *cubicSender) maxCongestionWindow() protocol.ByteCount {
+	return c.maxDatagramSize * protocol.MaxCongestionWindowPackets
+}
+
+func (c *cubicSender) minCongestionWindow() protocol.ByteCount {
+	return c.maxDatagramSize * minCongestionWindowPackets
+}
+
+func (c *cubicSender) OnPacketSent(
+	sentTime time.Time,
+	_ protocol.ByteCount,
+	packetNumber protocol.PacketNumber,
+	bytes protocol.ByteCount,
+	isRetransmittable bool,
+) {
+	c.pacer.SentPacket(sentTime, bytes)
+	if !isRetransmittable {
+		return
+	}
+	c.largestSentPacketNumber = packetNumber
+	c.hybridSlowStart.OnPacketSent(packetNumber)
+}
+
+func (c *cubicSender) CanSend(bytesInFlight protocol.ByteCount) bool {
+	return bytesInFlight < c.GetCongestionWindow()
+}
+
+func (c *cubicSender) InRecovery() bool {
+	return c.largestAckedPacketNumber != protocol.InvalidPacketNumber && c.largestAckedPacketNumber <= c.largestSentAtLastCutback
+}
+
+func (c *cubicSender) InSlowStart() bool {
+	return c.GetCongestionWindow() < c.slowStartThreshold
+}
+
+func (c *cubicSender) GetCongestionWindow() protocol.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
+		c.maybeTraceStateChange(logging.CongestionStateCongestionAvoidance)
+	}
+}
+
+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() {
+		return
+	}
+	c.maybeIncreaseCwnd(ackedPacketNumber, ackedBytes, priorInFlight, eventTime)
+	if c.InSlowStart() {
+		c.hybridSlowStart.OnPacketAcked(ackedPacketNumber)
+	}
+}
+
+func (c *cubicSender) OnPacketLost(packetNumber protocol.PacketNumber, lostBytes, 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 {
+		return
+	}
+	c.lastCutbackExitedSlowstart = c.InSlowStart()
+	c.maybeTraceStateChange(logging.CongestionStateRecovery)
+
+	if c.reno {
+		c.congestionWindow = protocol.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
+}
+
+// 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(
+	_ 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()
+		c.maybeTraceStateChange(logging.CongestionStateApplicationLimited)
+		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
+		c.maybeTraceStateChange(logging.CongestionStateSlowStart)
+		return
+	}
+	// Congestion avoidance
+	c.maybeTraceStateChange(logging.CongestionStateCongestionAvoidance)
+	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 = 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 <= maxBurstPackets*c.maxDatagramSize
+}
+
+// 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 infBandwidth
+	}
+	return BandwidthFromDelta(c.GetCongestionWindow(), srtt)
+}
+
+// OnRetransmissionTimeout is called on an retransmission timeout
+func (c *cubicSender) OnRetransmissionTimeout(packetsRetransmitted bool) {
+	c.largestSentAtLastCutback = protocol.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 = protocol.InvalidPacketNumber
+	c.largestAckedPacketNumber = protocol.InvalidPacketNumber
+	c.largestSentAtLastCutback = protocol.InvalidPacketNumber
+	c.lastCutbackExitedSlowstart = false
+	c.cubic.Reset()
+	c.numAckedPackets = 0
+	c.congestionWindow = c.initialCongestionWindow
+	c.slowStartThreshold = c.initialMaxCongestionWindow
+}
+
+func (c *cubicSender) maybeTraceStateChange(new logging.CongestionState) {
+	if c.tracer == nil || new == c.lastState {
+		return
+	}
+	c.tracer.UpdatedCongestionState(new)
+	c.lastState = new
+}
+
+func (c *cubicSender) SetMaxDatagramSize(s protocol.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)
+}