initial hybrid slow start implementation

congestion/hybrid_slow_start.go

@@ -0,0 +1,25 @@
+package congestion
+
+import "time"
+
+// HybridSlowStart implements the TCP hybrid slow start algorithm
+type HybridSlowStart struct {
+	endPacketNumber      uint64
+	lastSentPacketNumber uint64
+	started              bool
+	currentMinRTT        time.Duration
+	rttSampleCount       uint32
+}
+
+// StartReceiveRound is called for the start of each receive round (burst) in the slow start phase.
+func (s *HybridSlowStart) StartReceiveRound(last_sent uint64) {
+	s.endPacketNumber = last_sent
+	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 uint64) bool {
+	return s.endPacketNumber < ack
+}