Check on copy. (#2525)

Should not happen, but just being defensive.

pkg/sfu/downtrack.go

@@ -89,9 +89,9 @@ var (
 	ErrOutOfOrderSequenceNumberCacheMiss = errors.New("out-of-order sequence number not found in cache")
 	ErrPaddingOnlyPacket                 = errors.New("padding only packet that need not be forwarded")
 	ErrDuplicatePacket                   = errors.New("duplicate packet")
-	ErrSequenceNumberOffsetNotFound      = errors.New("sequence number offset not found")
 	ErrPaddingNotOnFrameBoundary         = errors.New("padding cannot send on non-frame boundary")
 	ErrDownTrackAlreadyBound             = errors.New("already bound")
+	ErrPayloadOverflow                   = errors.New("payload overflow")
 )
 
 var (
@@ -694,8 +694,13 @@ func (d *DownTrack) WriteRTP(extPkt *buffer.ExtPacket, layer int32) error {
 		PacketFactory.Put(poolEntity)
 		return err
 	}
-	copy(payload[outgoingHeaderSize:], extPkt.Packet.Payload[incomingHeaderSize:])
-	payload = payload[:outgoingHeaderSize+len(extPkt.Packet.Payload)-incomingHeaderSize]
+	n := copy(payload[outgoingHeaderSize:], extPkt.Packet.Payload[incomingHeaderSize:])
+	if n != len(extPkt.Packet.Payload[incomingHeaderSize:]) {
+		d.params.Logger.Errorw("payload overflow", nil, "want", len(extPkt.Packet.Payload[incomingHeaderSize:]), "have", n)
+		PacketFactory.Put(poolEntity)
+		return ErrPayloadOverflow
+	}
+	payload = payload[:outgoingHeaderSize+n]
 
 	hdr, err := d.getTranslatedRTPHeader(extPkt, &tp)
 	if err != nil {