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/utils/rtt_stats.go

@@ -0,0 +1,127 @@
+package utils
+
+import (
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+)
+
+const (
+	rttAlpha      = 0.125
+	oneMinusAlpha = 1 - rttAlpha
+	rttBeta       = 0.25
+	oneMinusBeta  = 1 - rttBeta
+	// The default RTT used before an RTT sample is taken.
+	defaultInitialRTT = 100 * time.Millisecond
+)
+
+// RTTStats provides round-trip statistics
+type RTTStats struct {
+	hasMeasurement bool
+
+	minRTT        time.Duration
+	latestRTT     time.Duration
+	smoothedRTT   time.Duration
+	meanDeviation time.Duration
+
+	maxAckDelay 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 smoothed RTT for the connection.
+// May return Zero if no valid updates have occurred.
+func (r *RTTStats) SmoothedRTT() time.Duration { return r.smoothedRTT }
+
+// MeanDeviation gets the mean deviation
+func (r *RTTStats) MeanDeviation() time.Duration { return r.meanDeviation }
+
+// MaxAckDelay gets the max_ack_delay advertised by the peer
+func (r *RTTStats) MaxAckDelay() time.Duration { return r.maxAckDelay }
+
+// PTO gets the probe timeout duration.
+func (r *RTTStats) PTO(includeMaxAckDelay bool) time.Duration {
+	if r.SmoothedRTT() == 0 {
+		return 2 * defaultInitialRTT
+	}
+	pto := r.SmoothedRTT() + MaxDuration(4*r.MeanDeviation(), protocol.TimerGranularity)
+	if includeMaxAckDelay {
+		pto += r.MaxAckDelay()
+	}
+	return pto
+}
+
+// UpdateRTT updates the RTT based on a new sample.
+func (r *RTTStats) UpdateRTT(sendDelta, ackDelay time.Duration, now time.Time) {
+	if sendDelta == 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.hasMeasurement {
+		r.hasMeasurement = true
+		r.smoothedRTT = sample
+		r.meanDeviation = sample / 2
+	} else {
+		r.meanDeviation = time.Duration(oneMinusBeta*float32(r.meanDeviation/time.Microsecond)+rttBeta*float32(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
+	}
+}
+
+// SetMaxAckDelay sets the max_ack_delay
+func (r *RTTStats) SetMaxAckDelay(mad time.Duration) {
+	r.maxAckDelay = mad
+}
+
+// SetInitialRTT sets the initial RTT.
+// It is used during the 0-RTT handshake when restoring the RTT stats from the session state.
+func (r *RTTStats) SetInitialRTT(t time.Duration) {
+	if r.hasMeasurement {
+		panic("initial RTT set after first measurement")
+	}
+	r.smoothedRTT = t
+	r.latestRTT = t
+}
+
+// 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 = MaxDuration(r.meanDeviation, AbsDuration(r.smoothedRTT-r.latestRTT))
+	r.smoothedRTT = MaxDuration(r.smoothedRTT, r.latestRTT)
+}