Fix DTMF deduplication to use (timestamp, event code) composite key

pkg/sip/media_port.go

@@ -415,7 +415,7 @@ func NewMediaPortWith(tid traceid.ID, log logger.Logger, mon *stats.CallMonitor,
 		audioIn:          msdk.NewSwitchWriter(inSampleRate),
 		stats:            opts.Stats,
 	}
-	p.lastDTMFTimestamp.Store(math.MaxUint32)
+	p.lastDTMFEvent.Store(math.MaxUint64)
 	if p.opts.IgnorePreanswerData {
 		p.port.startDiscarding()
 	}
@@ -463,7 +463,7 @@ type MediaPort struct {
 	audioIn           *msdk.SwitchWriter // SIP RTP -> LK PCM
 	audioInHandler    rtp.Handler        // for debug only
 	dtmfIn            atomic.Pointer[func(ev dtmf.Event)]
-	lastDTMFTimestamp atomic.Uint32 // rtp timestamp of last DTMF packet seen
+	lastDTMFEvent atomic.Uint64 // (rtp timestamp, event code) of last DTMF packet seen
 }
 
 func (p *MediaPort) DisableOut() {
@@ -1030,16 +1030,19 @@ func (p *MediaPort) dtmfHandler(h *rtp.Header, payload []byte) error {
 	if fnc == nil {
 		return nil
 	}
-	// RFC 4733 requires all packets of a given digit to share identical timestamps.
-	// The marker bit could be used instead, but it is prone to occasional loss.
-	if h.Timestamp == p.lastDTMFTimestamp.Load() {
-		return nil
-	}
 	ev, err := dtmf.Decode(payload)
 	if err != nil {
 		return nil
 	}
-	p.lastDTMFTimestamp.Store(h.Timestamp)
+	// RFC 4733 requires all packets of a given digit to share identical timestamps.
+	// Some SIP devices or carriers may reuse the timestamp of the previous digit
+	// for the next one, so we combine timestamp and event code for deduplication.
+	// The marker bit could be used instead, but it is prone to occasional loss.
+	eventID := uint64(h.Timestamp)<<8 | uint64(ev.Code)
+	if eventID == p.lastDTMFEvent.Load() {
+		return nil
+	}
+	p.lastDTMFEvent.Store(eventID)
 	fnc(ev)
 	return nil
 }

pkg/sip/media_port_test.go

@@ -872,7 +872,7 @@ func TestMediaPortDTMF(t *testing.T) {
 		for _, lossPackets := range lossCases {
 			t.Run(fmt.Sprintf("digits=%s/loss=%s", digits, lossPackets), func(t *testing.T) {
 				p := &MediaPort{}
-				p.lastDTMFTimestamp.Store(math.MaxUint32)
+				p.lastDTMFEvent.Store(math.MaxUint64)
 				got := ""
 				p.HandleDTMF(func(ev dtmf.Event) {
 					t.Logf("received DTMF event: %+v", ev)
@@ -895,6 +895,44 @@ func TestMediaPortDTMF(t *testing.T) {
 	}
 }
 
+// TestMediaPortDTMFSameTimestamp verifies that DTMF digits sharing the same
+// RTP timestamp (a non-RFC-compliant but observed behaviour from some SIP
+// devices/carriers) are still reported individually after the (timestamp,
+// event code) deduplication fix.
+func TestMediaPortDTMFSameTimestamp(t *testing.T) {
+	// Generate packets for two individual digits, then force the second
+	// digit's packets to reuse the first digit's timestamp.
+	first := generateDTMFPackets(t, "0")[0]
+	second := generateDTMFPackets(t, "1")[0]
+
+	sharedTS := first[0].Header.Timestamp
+	for i := range second {
+		second[i].Header.Timestamp = sharedTS
+	}
+
+	p := &MediaPort{}
+	p.lastDTMFEvent.Store(math.MaxUint64)
+	got := ""
+	p.HandleDTMF(func(ev dtmf.Event) {
+		t.Logf("received DTMF event: %+v", ev)
+		got = fmt.Sprintf("%s%s", got, strconv.Itoa(int(ev.Code)))
+	})
+
+	for _, pkt := range first {
+		h := pkt.Header
+		t.Logf("sending first digit packet: seq=%d, ts=%d, marker=%t", h.SequenceNumber, h.Timestamp, h.Marker)
+		require.NoError(t, p.dtmfHandler(&h, pkt.Payload))
+	}
+	for _, pkt := range second {
+		h := pkt.Header
+		t.Logf("sending second digit packet: seq=%d, ts=%d, marker=%t", h.SequenceNumber, h.Timestamp, h.Marker)
+		require.NoError(t, p.dtmfHandler(&h, pkt.Payload))
+	}
+
+	t.Logf("got: %s", got)
+	require.Equal(t, "01", got)
+}
+
 // Test util for incrementing prometheus counter metrics.
 func gatherCounter(t testing.TB, name string, labels map[string]string) float64 {
 	t.Helper()