move the initial RTT estimate to the congestion package

internal/congestion/rtt_stats.go

@@ -11,6 +11,8 @@ const (
 	oneMinusAlpha float32 = (1 - rttAlpha)
 	rttBeta       float32 = 0.25
 	oneMinusBeta  float32 = (1 - rttBeta)
+	// The default RTT used before an RTT sample is taken.
+	defaultInitialRTT = 100 * time.Millisecond
 )
 
 // RTTStats provides round-trip statistics
@@ -38,6 +40,15 @@ func (r *RTTStats) LatestRTT() time.Duration { return r.latestRTT }
 // May return Zero if no valid updates have occurred.
 func (r *RTTStats) SmoothedRTT() time.Duration { return r.smoothedRTT }
 
+// SmoothedOrInitialRTT returns the EWMA smoothed RTT for the connection.
+// If no valid updates have occurred, it returns the initial RTT.
+func (r *RTTStats) SmoothedOrInitialRTT() time.Duration {
+	if r.smoothedRTT != 0 {
+		return r.smoothedRTT
+	}
+	return defaultInitialRTT
+}
+
 // MeanDeviation gets the mean deviation
 func (r *RTTStats) MeanDeviation() time.Duration { return r.meanDeviation }
 

internal/congestion/rtt_stats_test.go

@@ -37,6 +37,12 @@ var _ = Describe("RTT stats", func() {
 		Expect(rttStats.SmoothedRTT()).To(Equal((287500 * time.Microsecond)))
 	})
 
+	It("SmoothedOrInitialRTT", func() {
+		Expect(rttStats.SmoothedOrInitialRTT()).To(Equal(defaultInitialRTT))
+		rttStats.UpdateRTT((300 * time.Millisecond), (100 * time.Millisecond), time.Time{})
+		Expect(rttStats.SmoothedOrInitialRTT()).To(Equal((300 * time.Millisecond)))
+	})
+
 	It("MinRTT", func() {
 		rttStats.UpdateRTT((200 * time.Millisecond), 0, time.Time{})
 		Expect(rttStats.MinRTT()).To(Equal((200 * time.Millisecond)))