Merge GetRTP and Nack into GetPacket.

The two function were always called together.  This factors out
the NACKing logic into the track.

conn/conn.go

@@ -25,9 +25,9 @@ type UpTrack interface {
 	Kind() webrtc.RTPCodecType
 	Label() string
 	Codec() webrtc.RTPCodecCapability
-	// get a recent packet.  Returns 0 if the packet is not in cache.
-	GetRTP(seqno uint16, result []byte) uint16
-	Nack(seqnos []uint16) error
+	// GetPacket fetches a recent packet.  Returns 0 if the packet is
+	// not in cache, and, in that case, optionally schedules a NACK.
+	GetPacket(seqno uint16, result []byte, nack bool) uint16
 	RequestKeyframe() error
 }
 

diskwriter/diskwriter.go

@@ -494,23 +494,18 @@ func (t *diskTrack) Write(buf []byte) (int, error) {
 		if ((p.SequenceNumber - lastSeqno) & 0x8000) == 0 {
 			count := p.SequenceNumber - lastSeqno
 			if count > 0 && count < 128 {
-				var nacks []uint16
 				for i := lastSeqno + 1; i != p.SequenceNumber; i++ {
 					// different buf each time
 					buf := make([]byte, 1504)
-					n := t.remote.GetRTP(i, buf)
-					if n > 0 {
-						p := new(rtp.Packet)
-						err := p.Unmarshal(buf)
-						if err == nil {
-							t.writeRTP(p)
-						}
-					} else {
-						nacks = append(nacks, i)
+					n := t.remote.GetPacket(i, buf, true)
+					if n == 0 {
+						continue
+					}
+					p := new(rtp.Packet)
+					err := p.Unmarshal(buf)
+					if err == nil {
+						t.writeRTP(p)
 					}
-				}
-				if len(nacks) > 0 {
-					t.remote.Nack(nacks)
 				}
 			}
 		}

rtpconn/rtpconn.go

@@ -430,10 +430,6 @@ func (up *rtpUpTrack) getLocal() []conn.DownTrack {
 	return local
 }
 
-func (up *rtpUpTrack) GetRTP(seqno uint16, result []byte) uint16 {
-	return up.cache.Get(seqno, result)
-}
-
 func (up *rtpUpTrack) Label() string {
 	return up.track.RID()
 }
@@ -712,7 +708,6 @@ func sendNACKs(pc *webrtc.PeerConnection, ssrc webrtc.SSRC, nacks []rtcp.NackPai
 }
 
 func gotNACK(track *rtpDownTrack, p *rtcp.TransportLayerNack) {
-	var unhandled []uint16
 	buf := make([]byte, packetcache.BufSize)
 	for _, nack := range p.Nacks {
 		nack.Range(func(s uint16) bool {
@@ -720,9 +715,8 @@ func gotNACK(track *rtpDownTrack, p *rtcp.TransportLayerNack) {
 			if !ok {
 				return true
 			}
-			l := track.remote.GetRTP(seqno, buf)
+			l := track.remote.GetPacket(seqno, buf, true)
 			if l == 0 {
-				unhandled = append(unhandled, seqno)
 				return true
 			}
 			_, err := track.Write(buf[:l])
@@ -733,33 +727,30 @@ func gotNACK(track *rtpDownTrack, p *rtcp.TransportLayerNack) {
 			return true
 		})
 	}
-	if len(unhandled) == 0 {
-		return
-	}
-
-	track.remote.Nack(unhandled)
 }
 
-func (track *rtpUpTrack) Nack(nacks []uint16) error {
+func (track *rtpUpTrack) GetPacket(seqno uint16, result []byte, nack bool) uint16 {
+	n := track.cache.Get(seqno, result)
+	if n > 0 || !nack {
+		return n
+	}
+
 	track.mu.Lock()
 	defer track.mu.Unlock()
 
 	doit := len(track.bufferedNACKs) == 0
 
-outer:
-	for _, nack := range nacks {
-		for _, seqno := range track.bufferedNACKs {
-			if seqno == nack {
-				continue outer
-			}
+	for _, s := range track.bufferedNACKs {
+		if s == seqno {
+			return 0
 		}
-		track.bufferedNACKs = append(track.bufferedNACKs, nack)
 	}
+	track.bufferedNACKs = append(track.bufferedNACKs, seqno)
 
 	if doit {
 		go nackWriter(track)
 	}
-	return nil
+	return 0
 }
 
 func rtcpUpListener(conn *rtpUpConnection, track *rtpUpTrack, r *webrtc.RTPReceiver) {