Add some simple data track stats (#4431)

pkg/rtc/datatrack.go

@@ -48,6 +48,8 @@ type DataTrack struct {
 
 	downTrackSpreader *sfuutils.DownTrackSpreader[types.DataTrackSender]
 
+	stats *dataTrackStats
+
 	closed core.Fuse
 }
 
@@ -60,6 +62,7 @@ func NewDataTrack(params DataTrackParams, dti *livekit.DataTrackInfo) *DataTrack
 			Threshold: 20,
 			Logger:    params.Logger,
 		}),
+		stats: newDataTrackStats(dataTrackStatsParams{Logger: params.Logger}),
 	}
 	d.params.Logger.Infow("created data track", "name", d.Name())
 	return d
@@ -68,6 +71,8 @@ func NewDataTrack(params DataTrackParams, dti *livekit.DataTrackInfo) *DataTrack
 func (d *DataTrack) Close() {
 	d.params.Logger.Infow("closing data track", "name", d.Name())
 	d.closed.Break()
+
+	d.stats.Close()
 }
 
 func (d *DataTrack) PublisherID() livekit.ParticipantID {
@@ -156,6 +161,8 @@ func (d *DataTrack) DeleteDataDownTrack(subscriberID livekit.ParticipantID) {
 }
 
 func (d *DataTrack) HandlePacket(data []byte, packet *datatrack.Packet, arrivalTime int64) {
+	d.stats.Update(packet, arrivalTime)
+
 	d.downTrackSpreader.Broadcast(func(dts types.DataTrackSender) {
 		dts.WritePacket(data, packet, arrivalTime)
 	})

pkg/rtc/datatrack/packet.go

@@ -85,7 +85,7 @@ type Header struct {
 	┆*  0                   1                   2                   3
 	┆*  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 	┆* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-	┆* |V    |F|L|X| reserved          | handle                        |
+	┆* |V    |S|F|X| reserved          | handle                        |
 	┆* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 	┆* | sequence number               | frame number                  |
 	┆* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

pkg/rtc/datatrack_stats.go

@@ -0,0 +1,103 @@
+// Copyright 2023 LiveKit, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package rtc
+
+import (
+	"sync"
+	"time"
+
+	"github.com/livekit/livekit-server/pkg/rtc/datatrack"
+	"github.com/livekit/protocol/logger"
+	"github.com/livekit/protocol/utils/mono"
+)
+
+type dataTrackStatsParams struct {
+	Logger logger.Logger
+}
+
+type dataTrackStats struct {
+	params dataTrackStatsParams
+
+	lock                  sync.Mutex
+	startTime             int64
+	endTime               int64
+	highestSequenceNumber uint16
+	numPackets            int
+	numPacketsLost        int
+	numPacketsOutOfOrder  int
+	numFrames             int // count of `F` tagged packets, i. e. packets with final packet of frame marker
+}
+
+func newDataTrackStats(params dataTrackStatsParams) *dataTrackStats {
+	return &dataTrackStats{
+		params: params,
+	}
+}
+
+func (d *dataTrackStats) Update(packet *datatrack.Packet, arrivalTime int64) {
+	d.lock.Lock()
+	defer d.lock.Unlock()
+
+	if d.endTime != 0 {
+		return
+	}
+
+	if d.startTime == 0 {
+		d.startTime = arrivalTime
+		d.highestSequenceNumber = packet.SequenceNumber
+		d.numPackets = 1
+	} else {
+		diff := packet.SequenceNumber - d.highestSequenceNumber
+		switch {
+		case diff == 0: // duplicate
+			return
+
+		case diff > (1 << 15): // out of order
+			d.numPacketsOutOfOrder++
+			if d.numPacketsLost > 0 {
+				d.numPacketsLost--
+			}
+
+		default: // in order
+			d.numPackets++
+			d.numPacketsLost += int(diff) - 1
+			d.highestSequenceNumber = packet.SequenceNumber
+		}
+	}
+
+	if packet.IsFinalOfFrame {
+		d.numFrames++
+	}
+}
+
+func (d *dataTrackStats) Close() {
+	d.lock.Lock()
+	defer d.lock.Unlock()
+
+	d.endTime = mono.UnixNano()
+
+	duration := time.Duration(d.endTime - d.startTime).Seconds()
+	fps := float64(d.numFrames) / duration
+
+	d.params.Logger.Infow(
+		"data track stats",
+		"duration", duration,
+		"numPackets", d.numPackets,
+		"numPacketsLost", d.numPacketsLost,
+		"numPacketsOutOfOrder", d.numPacketsOutOfOrder,
+		"numFrames", d.numFrames,
+		"fps", fps,
+	)
+}