Fix TotalLost type

AUTHORS.txt

@@ -19,5 +19,6 @@ Mathis Engelbart <mathis.engelbart@gmail.com>
 Max Hawkins <maxhawkins@gmail.com>
 Sean DuBois <seaduboi@amazon.com>
 Sean DuBois <sean@siobud.com>
+seb-dev <sebapetit@protonmail.com>
 Simone Gotti <simone.gotti@gmail.com>
 Woodrow Douglass <wdouglass@carnegierobotics.com>

receiver_report_test.go

@@ -49,6 +49,40 @@ func TestReceiverReportUnmarshal(t *testing.T) {
 				ProfileExtensions: []byte{},
 			},
 		},
+		{
+			Name: "valid with negative totalLost",
+			Data: []byte{
+				// v=2, p=0, count=1, RR, len=7
+				0x81, 0xc9, 0x0, 0x7,
+				// ssrc=0x902f9e2e
+				0x90, 0x2f, 0x9e, 0x2e,
+				// ssrc=0xbc5e9a40
+				0xbc, 0x5e, 0x9a, 0x40,
+				// fracLost=0, totalLost=-1
+				0x0, 0xff, 0xff, 0xff,
+				// lastSeq=0x46e1
+				0x0, 0x0, 0x46, 0xe1,
+				// jitter=273
+				0x0, 0x0, 0x1, 0x11,
+				// lsr=0x9f36432
+				0x9, 0xf3, 0x64, 0x32,
+				// delay=150137
+				0x0, 0x2, 0x4a, 0x79,
+			},
+			Want: ReceiverReport{
+				SSRC: 0x902f9e2e,
+				Reports: []ReceptionReport{{
+					SSRC:               0xbc5e9a40,
+					FractionLost:       0,
+					TotalLost:          -1,
+					LastSequenceNumber: 0x46e1,
+					Jitter:             273,
+					LastSenderReport:   0x9f36432,
+					Delay:              150137,
+				}},
+				ProfileExtensions: []byte{},
+			},
+		},
 		{
 			Name: "valid with extension data",
 			Data: []byte{

reception_report.go

@@ -14,7 +14,10 @@ type ReceptionReport struct {
 	FractionLost uint8
 	// The total number of RTP data packets from source SSRC that have
 	// been lost since the beginning of reception.
-	TotalLost uint32
+	// https://www.ietf.org/rfc/rfc3550.txt Section 6.4 and appendix A.3
+	// The total number of packets lost is a signed number and can be
+	// negative
+	TotalLost int32
 	// The low 16 bits contain the highest sequence number received in an
 	// RTP data packet from source SSRC, and the most significant 16
 	// bits extend that sequence number with the corresponding count of
@@ -71,13 +74,17 @@ func (r ReceptionReport) Marshal() ([]byte, error) {
 	rawPacket[fractionLostOffset] = r.FractionLost
 
 	// pack TotalLost into 24 bits
-	if r.TotalLost >= (1 << 25) {
+	// we first convert signed integer to unsigned before using bit operators
+	uTotalLost := uint32(r.TotalLost)
+	if uTotalLost&0xff800000 != 0xff800000 && uTotalLost&0xff800000 != 0 {
 		return nil, errInvalidTotalLost
 	}
+	// Convert int32 to int24
+	uTotalLost = uTotalLost&0x80000000>>8 | uTotalLost&0x007fffff
 	tlBytes := rawPacket[totalLostOffset:]
-	tlBytes[0] = byte(r.TotalLost >> 16)
-	tlBytes[1] = byte(r.TotalLost >> 8)
-	tlBytes[2] = byte(r.TotalLost)
+	tlBytes[0] = byte(uTotalLost >> 16)
+	tlBytes[1] = byte(uTotalLost >> 8)
+	tlBytes[2] = byte(uTotalLost)
 
 	binary.BigEndian.PutUint32(rawPacket[lastSeqOffset:], r.LastSequenceNumber)
 	binary.BigEndian.PutUint32(rawPacket[jitterOffset:], r.Jitter)
@@ -115,7 +122,13 @@ func (r *ReceptionReport) Unmarshal(rawPacket []byte) error {
 	r.FractionLost = rawPacket[fractionLostOffset]
 
 	tlBytes := rawPacket[totalLostOffset:]
-	r.TotalLost = uint32(tlBytes[2]) | uint32(tlBytes[1])<<8 | uint32(tlBytes[0])<<16
+	uTotalLost := uint32(tlBytes[2]) | uint32(tlBytes[1])<<8 | uint32(tlBytes[0])<<16
+	// test sign
+	ua := uTotalLost & 0x007fffff
+	if uTotalLost&0x00800000 == 0x00800000 {
+		ua |= 0xff800000
+	}
+	r.TotalLost = int32(ua)
 
 	r.LastSequenceNumber = binary.BigEndian.Uint32(rawPacket[lastSeqOffset:])
 	r.Jitter = binary.BigEndian.Uint32(rawPacket[jitterOffset:])