Handle nil stats getter in collect stats

It is possible to call GetStats() after the peer connection is closed.
The statsGetter gets cleared when peer connection is closed. That is
causing a panic when RtpReceiver.collectStats runs.

Author: boks1971

rtpreceiver.go

@@ -404,6 +404,10 @@ func (r *RTPReceiver) Stop() error { //nolint:cyclop
 }
 
 func (r *RTPReceiver) collectStats(collector *statsReportCollector, statsGetter stats.Getter) {
+	if statsGetter == nil {
+		return
+	}
+
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
@@ -438,32 +442,7 @@ func (r *RTPReceiver) collectStats(collector *statsReportCollector, statsGetter
 			TransportID: "iceTransport",
 			CodecID:     codecID,
 		}
-
-		stats := statsGetter.Get(uint32(remoteTrack.SSRC()))
-		if stats != nil { //nolint:nestif // nested to keep mapping local
-			// Wrap-around casting by design, with warnings if overflow/underflow is detected.
-			pr := stats.InboundRTPStreamStats.PacketsReceived
-			if pr > math.MaxUint32 {
-				r.log.Warnf("Inbound PacketsReceived exceeds uint32 and will wrap: %d", pr)
-			}
-			inboundStats.PacketsReceived = uint32(pr) //nolint:gosec
-
-			pl := stats.InboundRTPStreamStats.PacketsLost
-			if pl > math.MaxInt32 || pl < math.MinInt32 {
-				r.log.Warnf("Inbound PacketsLost exceeds int32 range and will wrap: %d", pl)
-			}
-			inboundStats.PacketsLost = int32(pl) //nolint:gosec
-
-			inboundStats.Jitter = stats.InboundRTPStreamStats.Jitter
-			inboundStats.BytesReceived = stats.InboundRTPStreamStats.BytesReceived
-			inboundStats.HeaderBytesReceived = stats.InboundRTPStreamStats.HeaderBytesReceived
-			timestamp := stats.InboundRTPStreamStats.LastPacketReceivedTimestamp
-			inboundStats.LastPacketReceivedTimestamp = StatsTimestamp(
-				timestamp.UnixNano() / int64(time.Millisecond))
-			inboundStats.FIRCount = stats.InboundRTPStreamStats.FIRCount
-			inboundStats.PLICount = stats.InboundRTPStreamStats.PLICount
-			inboundStats.NACKCount = stats.InboundRTPStreamStats.NACKCount
-		}
+		r.populateInboundStats(&inboundStats, statsGetter, remoteTrack)
 
 		collector.Collect(inboundID, inboundStats)
 
@@ -473,6 +452,40 @@ func (r *RTPReceiver) collectStats(collector *statsReportCollector, statsGetter
 	}
 }
 
+func (r *RTPReceiver) populateInboundStats(
+	inboundStats *InboundRTPStreamStats,
+	statsGetter stats.Getter,
+	remoteTrack *TrackRemote,
+) {
+	stats := statsGetter.Get(uint32(remoteTrack.SSRC()))
+	if stats == nil {
+		return
+	}
+
+	// Wrap-around casting by design, with warnings if overflow/underflow is detected.
+	pr := stats.InboundRTPStreamStats.PacketsReceived
+	if pr > math.MaxUint32 {
+		r.log.Warnf("Inbound PacketsReceived exceeds uint32 and will wrap: %d", pr)
+	}
+	inboundStats.PacketsReceived = uint32(pr) //nolint:gosec
+
+	pl := stats.InboundRTPStreamStats.PacketsLost
+	if pl > math.MaxInt32 || pl < math.MinInt32 {
+		r.log.Warnf("Inbound PacketsLost exceeds int32 range and will wrap: %d", pl)
+	}
+	inboundStats.PacketsLost = int32(pl) //nolint:gosec
+
+	inboundStats.Jitter = stats.InboundRTPStreamStats.Jitter
+	inboundStats.BytesReceived = stats.InboundRTPStreamStats.BytesReceived
+	inboundStats.HeaderBytesReceived = stats.InboundRTPStreamStats.HeaderBytesReceived
+	timestamp := stats.InboundRTPStreamStats.LastPacketReceivedTimestamp
+	inboundStats.LastPacketReceivedTimestamp = StatsTimestamp(
+		timestamp.UnixNano() / int64(time.Millisecond))
+	inboundStats.FIRCount = stats.InboundRTPStreamStats.FIRCount
+	inboundStats.PLICount = stats.InboundRTPStreamStats.PLICount
+	inboundStats.NACKCount = stats.InboundRTPStreamStats.NACKCount
+}
+
 func (r *RTPReceiver) collectAudioPlayoutStats(
 	collector *statsReportCollector,
 	nowTime time.Time,

rtpreceiver_test.go

@@ -100,19 +100,24 @@ func TestRTPReceiver_CollectStats_Mapping(t *testing.T) {
 	}}
 
 	// Minimal RTPReceiver with one track
-	r := &RTPReceiver{
+	receiver := &RTPReceiver{
 		kind: RTPCodecTypeVideo,
 		log:  logging.NewDefaultLoggerFactory().NewLogger("RTPReceiverTest"),
 	}
-	tr := newTrackRemote(RTPCodecTypeVideo, ssrc, 0, "", r)
-	r.tracks = []trackStreams{{track: tr}}
+	tr := newTrackRemote(RTPCodecTypeVideo, ssrc, 0, "", receiver)
+	receiver.tracks = []trackStreams{{track: tr}}
 
 	collector := newStatsReportCollector()
-	r.collectStats(collector, fg)
+	receiver.collectStats(collector, nil)
 	report := collector.Ready()
 
 	// Fetch the generated inbound-rtp stat by ID
 	statID := "inbound-rtp-1234"
+	_, ok := report[statID]
+	require.False(t, ok, "unexpected inbound stat")
+
+	receiver.collectStats(collector, fg)
+	report = collector.Ready()
 	got, ok := report[statID]
 	require.True(t, ok, "missing inbound stat")