Fix wrap around on out of order packet

Sequence number cycle calculation was over estimating the cycles if packets came out of order. A sequence like 65535, 0, 65534 would increment the cycle counter twice.
pion · Oct 16, 2023 · 2d3d6ab · 2d3d6ab
1 parent f918c62
commit 2d3d6ab
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Showing 2 changed files with 8 additions and 4 deletions.
diff --git a/pkg/report/receiver_interceptor_test.go b/pkg/report/receiver_interceptor_test.go
@@ -178,6 +178,10 @@ func TestReceiverInterceptor(t *testing.T) {
 			SequenceNumber: 0x00,
 		}})
 
+		stream.ReceiveRTP(&rtp.Packet{Header: rtp.Header{
+			SequenceNumber: 0xfffe,
+		}})
+
 		pkts := <-stream.WrittenRTCP()
 		assert.Equal(t, len(pkts), 1)
 		rr, ok := pkts[0].(*rtcp.ReceiverReport)

diff --git a/pkg/report/receiver_stream.go b/pkg/report/receiver_stream.go
@@ -64,10 +64,10 @@ func (stream *receiverStream) processRTP(now time.Time, pktHeader *rtp.Header) {
 	} else { // following frames
 		stream.setReceived(pktHeader.SequenceNumber)
 
-		diff := int32(pktHeader.SequenceNumber) - int32(stream.lastSeqnum)
-		if diff > 0 || diff < -0x0FFF {
-			// overflow
-			if diff < -0x0FFF {
+		diff := pktHeader.SequenceNumber - stream.lastSeqnum
+		if diff > 0 && diff < (1<<15) {
+			// wrap around
+			if pktHeader.SequenceNumber < stream.lastSeqnum {
 				stream.seqnumCycles++
 			}