Fix data race of RTX packet

AUTHORS.txt

@@ -8,6 +8,7 @@ Aaron Boushley <[email protected]>
 Aaron France <[email protected]>
 Adam Kiss <[email protected]>
 Aditya Kumar <[email protected]>
+Adrian Cable <[email protected]>
 Adrian Cable <[email protected]>
 adwpc <[email protected]>
 aggresss <[email protected]>
@@ -200,6 +201,7 @@ Steffen Vogel <[email protected]>
 stephanrotolante <[email protected]>
 streamer45 <[email protected]>
 Suhas Gaddam <[email protected]>
+sukun <[email protected]>
 Suzuki Takeo <[email protected]>
 sylba2050 <[email protected]>
 Tarrence van As <[email protected]>

rtpreceiver.go

@@ -43,6 +43,15 @@ type trackStreams struct {
 type rtxPacketWithAttributes struct {
 	pkt        []byte
 	attributes interceptor.Attributes
+	pool       *sync.Pool
+}
+
+func (p *rtxPacketWithAttributes) release() {
+	if p.pkt != nil {
+		b := p.pkt[:cap(p.pkt)]
+		p.pool.Put(b) // nolint:staticcheck
+		p.pkt = nil
+	}
 }
 
 // RTPReceiver allows an application to inspect the receipt of a TrackRemote
@@ -59,6 +68,8 @@ type RTPReceiver struct {
 
 	// A reference to the associated api object
 	api *API
+
+	rtxPool sync.Pool
 }
 
 // NewRTPReceiver constructs a new RTPReceiver
@@ -74,6 +85,9 @@ func (api *API) NewRTPReceiver(kind RTPCodecType, transport *DTLSTransport) (*RT
 		closed:    make(chan interface{}),
 		received:  make(chan interface{}),
 		tracks:    []trackStreams{},
+		rtxPool: sync.Pool{New: func() interface{} {
+			return make([]byte, api.settingEngine.getReceiveMTU())
+		}},
 	}
 
 	return r, nil
@@ -420,10 +434,11 @@ func (r *RTPReceiver) receiveForRtx(ssrc SSRC, rsid string, streamInfo *intercep
 	track.repairStreamChannel = make(chan rtxPacketWithAttributes)
 
 	go func() {
-		b := make([]byte, r.api.settingEngine.getReceiveMTU())
 		for {
+			b := r.rtxPool.Get().([]byte) // nolint:forcetypeassert
 			i, attributes, err := track.repairInterceptor.Read(b, nil)
 			if err != nil {
+				r.rtxPool.Put(b) // nolint:staticcheck
 				return
 			}
 
@@ -444,6 +459,7 @@ func (r *RTPReceiver) receiveForRtx(ssrc SSRC, rsid string, streamInfo *intercep
 
 			if i-int(headerLength)-paddingLength < 2 {
 				// BWE probe packet, ignore
+				r.rtxPool.Put(b) // nolint:staticcheck
 				continue
 			}
 
@@ -459,8 +475,9 @@ func (r *RTPReceiver) receiveForRtx(ssrc SSRC, rsid string, streamInfo *intercep
 
 			select {
 			case <-r.closed:
+				r.rtxPool.Put(b) // nolint:staticcheck
 				return
-			case track.repairStreamChannel <- rtxPacketWithAttributes{pkt: b[:i-2], attributes: attributes}:
+			case track.repairStreamChannel <- rtxPacketWithAttributes{pkt: b[:i-2], attributes: attributes, pool: &r.rtxPool}:
 			}
 		}
 	}()

track_remote.go

@@ -131,6 +131,7 @@ func (t *TrackRemote) Read(b []byte) (n int, attributes interceptor.Attributes,
 	if rtxPacketReceived := r.readRTX(t); rtxPacketReceived != nil {
 		n = copy(b, rtxPacketReceived.pkt)
 		attributes = rtxPacketReceived.attributes
+		rtxPacketReceived.release()
 		err = nil
 	} else {
 		// If there's no separate RTX track (or there's a separate RTX track but no RTX packet waiting), wait for and return