From a6de3e42b3f1b2059b00ec72757d311e24c23f92 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Sun, 2 Nov 2025 12:53:30 -0500
Subject: [PATCH] ackhandler: fix qlogging of RTT values (#5418)

---
 internal/ackhandler/sent_packet_handler.go | 22 ++++++++++++++++++++++
 internal/utils/rtt_stats.go                |  4 ++++
 internal/utils/rtt_stats_test.go           |  6 ++++++
 3 files changed, 32 insertions(+)

diff --git a/internal/ackhandler/sent_packet_handler.go b/internal/ackhandler/sent_packet_handler.go
index 274accd27..2c41f7f7f 100644
--- a/internal/ackhandler/sent_packet_handler.go
+++ b/internal/ackhandler/sent_packet_handler.go
@@ -333,6 +333,28 @@ func (h *sentPacketHandler) SentPacket(
 func (h *sentPacketHandler) qlogMetricsUpdated() {
 	var metricsUpdatedEvent qlog.MetricsUpdated
 	var updated bool
+	if h.rttStats.HasMeasurement() {
+		if h.lastMetrics.MinRTT == nil || *h.lastMetrics.MinRTT != h.rttStats.MinRTT() {
+			metricsUpdatedEvent.MinRTT = pointer(h.rttStats.MinRTT())
+			h.lastMetrics.MinRTT = pointer(h.rttStats.MinRTT())
+			updated = true
+		}
+		if h.lastMetrics.SmoothedRTT == nil || *h.lastMetrics.SmoothedRTT != h.rttStats.SmoothedRTT() {
+			metricsUpdatedEvent.SmoothedRTT = pointer(h.rttStats.SmoothedRTT())
+			h.lastMetrics.SmoothedRTT = pointer(h.rttStats.SmoothedRTT())
+			updated = true
+		}
+		if h.lastMetrics.LatestRTT == nil || *h.lastMetrics.LatestRTT != h.rttStats.LatestRTT() {
+			metricsUpdatedEvent.LatestRTT = pointer(h.rttStats.LatestRTT())
+			h.lastMetrics.LatestRTT = pointer(h.rttStats.LatestRTT())
+			updated = true
+		}
+		if h.lastMetrics.RTTVariance == nil || *h.lastMetrics.RTTVariance != h.rttStats.MeanDeviation() {
+			metricsUpdatedEvent.RTTVariance = pointer(h.rttStats.MeanDeviation())
+			h.lastMetrics.RTTVariance = pointer(h.rttStats.MeanDeviation())
+			updated = true
+		}
+	}
 	if h.lastMetrics.CongestionWindow == nil || *h.lastMetrics.CongestionWindow != int(h.congestion.GetCongestionWindow()) {
 		metricsUpdatedEvent.CongestionWindow = pointer(int(h.congestion.GetCongestionWindow()))
 		h.lastMetrics.CongestionWindow = pointer(int(h.congestion.GetCongestionWindow()))
diff --git a/internal/utils/rtt_stats.go b/internal/utils/rtt_stats.go
index fab1de8c2..275313073 100644
--- a/internal/utils/rtt_stats.go
+++ b/internal/utils/rtt_stats.go
@@ -115,6 +115,10 @@ func (r *RTTStats) UpdateRTT(sendDelta, ackDelay time.Duration) {
 	}
 }
 
+func (r *RTTStats) HasMeasurement() bool {
+	return r.hasMeasurement
+}
+
 // SetMaxAckDelay sets the max_ack_delay
 func (r *RTTStats) SetMaxAckDelay(mad time.Duration) {
 	r.maxAckDelay.Store(int64(mad))
diff --git a/internal/utils/rtt_stats_test.go b/internal/utils/rtt_stats_test.go
index 75c94886c..b7504de13 100644
--- a/internal/utils/rtt_stats_test.go
+++ b/internal/utils/rtt_stats_test.go
@@ -10,14 +10,17 @@ import (
 
 func TestRTTStatsDefaults(t *testing.T) {
 	rttStats := NewRTTStats()
+	require.False(t, rttStats.HasMeasurement())
 	require.Equal(t, DefaultInitialRTT, rttStats.MinRTT())
 	require.Equal(t, DefaultInitialRTT, rttStats.SmoothedRTT())
 }
 
 func TestRTTStatsSmoothedRTT(t *testing.T) {
 	rttStats := NewRTTStats()
+	require.False(t, rttStats.HasMeasurement())
 	// verify that ack_delay is ignored in the first measurement
 	rttStats.UpdateRTT(300*time.Millisecond, 100*time.Millisecond)
+	require.True(t, rttStats.HasMeasurement())
 	require.Equal(t, 300*time.Millisecond, rttStats.LatestRTT())
 	require.Equal(t, 300*time.Millisecond, rttStats.SmoothedRTT())
 	// verify that smoothed RTT includes max ack delay if it's reasonable
@@ -122,11 +125,13 @@ func TestRTTStatsResetForPathMigration(t *testing.T) {
 	rttStats.SetMaxAckDelay(42 * time.Millisecond)
 	rttStats.UpdateRTT(time.Second, 0)
 	rttStats.UpdateRTT(10*time.Second, 0)
+	require.True(t, rttStats.HasMeasurement())
 	require.Equal(t, time.Second, rttStats.MinRTT())
 	require.Equal(t, 10*time.Second, rttStats.LatestRTT())
 	require.NotZero(t, rttStats.SmoothedRTT())
 
 	rttStats.ResetForPathMigration()
+	require.False(t, rttStats.HasMeasurement())
 	require.Equal(t, DefaultInitialRTT, rttStats.MinRTT())
 	require.Equal(t, DefaultInitialRTT, rttStats.LatestRTT())
 	require.Equal(t, DefaultInitialRTT, rttStats.SmoothedRTT())
@@ -135,6 +140,7 @@ func TestRTTStatsResetForPathMigration(t *testing.T) {
 	require.Equal(t, 42*time.Millisecond, rttStats.MaxAckDelay())
 
 	rttStats.UpdateRTT(10*time.Millisecond, 0)
+	require.True(t, rttStats.HasMeasurement())
 	require.Equal(t, 10*time.Millisecond, rttStats.SmoothedRTT())
 	require.Equal(t, 10*time.Millisecond, rttStats.LatestRTT())
 }