chore: add new bbr implementation

transport/tuic/congestion_v2/pacer.go

@@ -0,0 +1,71 @@
+package congestion
+
+import (
+	"math"
+	"time"
+
+	"github.com/metacubex/quic-go/congestion"
+)
+
+const (
+	maxBurstPackets = 10
+)
+
+// Pacer implements a token bucket pacing algorithm.
+type Pacer struct {
+	budgetAtLastSent congestion.ByteCount
+	maxDatagramSize  congestion.ByteCount
+	lastSentTime     time.Time
+	getBandwidth     func() congestion.ByteCount // in bytes/s
+}
+
+func NewPacer(getBandwidth func() congestion.ByteCount) *Pacer {
+	p := &Pacer{
+		budgetAtLastSent: maxBurstPackets * congestion.InitialPacketSizeIPv4,
+		maxDatagramSize:  congestion.InitialPacketSizeIPv4,
+		getBandwidth:     getBandwidth,
+	}
+	return p
+}
+
+func (p *Pacer) SentPacket(sendTime time.Time, size congestion.ByteCount) {
+	budget := p.Budget(sendTime)
+	if size > budget {
+		p.budgetAtLastSent = 0
+	} else {
+		p.budgetAtLastSent = budget - size
+	}
+	p.lastSentTime = sendTime
+}
+
+func (p *Pacer) Budget(now time.Time) congestion.ByteCount {
+	if p.lastSentTime.IsZero() {
+		return p.maxBurstSize()
+	}
+	budget := p.budgetAtLastSent + (p.getBandwidth()*congestion.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9
+	return Min(p.maxBurstSize(), budget)
+}
+
+func (p *Pacer) maxBurstSize() congestion.ByteCount {
+	return Max(
+		congestion.ByteCount((congestion.MinPacingDelay+time.Millisecond).Nanoseconds())*p.getBandwidth()/1e9,
+		maxBurstPackets*p.maxDatagramSize,
+	)
+}
+
+// TimeUntilSend returns when the next packet should be sent.
+// It returns the zero value of time.Time if a packet can be sent immediately.
+func (p *Pacer) TimeUntilSend() time.Time {
+	if p.budgetAtLastSent >= p.maxDatagramSize {
+		return time.Time{}
+	}
+	return p.lastSentTime.Add(Max(
+		congestion.MinPacingDelay,
+		time.Duration(math.Ceil(float64(p.maxDatagramSize-p.budgetAtLastSent)*1e9/
+			float64(p.getBandwidth())))*time.Nanosecond,
+	))
+}
+
+func (p *Pacer) SetMaxDatagramSize(s congestion.ByteCount) {
+	p.maxDatagramSize = s
+}