internalize ackhandler and congestion

internal/congestion/prr_sender.go

@@ -0,0 +1,63 @@
+package congestion
+
+import (
+	"time"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
+	"github.com/lucas-clemente/quic-go/internal/utils"
+)
+
+// 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(bytesInFlight protocol.ByteCount) {
+	p.bytesSentSinceLoss = 0
+	p.bytesInFlightBeforeLoss = bytesInFlight
+	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++
+}
+
+// TimeUntilSend calculates the time until a packet can be sent
+func (p *PrrSender) TimeUntilSend(congestionWindow, bytesInFlight, slowstartThreshold protocol.ByteCount) time.Duration {
+	// Return QuicTime::Zero In order to ensure limited transmit always works.
+	if p.bytesSentSinceLoss == 0 || bytesInFlight < protocol.DefaultTCPMSS {
+		return 0
+	}
+	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
+		if p.bytesDeliveredSinceLoss+p.ackCountSinceLoss*protocol.DefaultTCPMSS <= p.bytesSentSinceLoss {
+			return utils.InfDuration
+		}
+		return 0
+	}
+	// 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
+	if p.bytesDeliveredSinceLoss*slowstartThreshold > p.bytesSentSinceLoss*p.bytesInFlightBeforeLoss {
+		return 0
+	}
+	return utils.InfDuration
+}