From 76634b143ae22da23f827df96b9a482176e8b10d Mon Sep 17 00:00:00 2001
From: Eric Daniels <eric@erdaniels.com>
Date: Tue, 15 Oct 2024 12:04:40 -0400
Subject: [PATCH] Add SetFireOnTrackBeforeFirstRTP

---
 peerconnection.go     |  4 ++++
 settingengine.go      | 10 ++++++++
 settingengine_test.go | 54 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+)

diff --git a/peerconnection.go b/peerconnection.go
index 35823660d2c..4b2a16e39ca 100644
--- a/peerconnection.go
+++ b/peerconnection.go
@@ -1245,6 +1245,10 @@ func (pc *PeerConnection) startReceiver(incoming trackDetails, receiver *RTPRece
 			return
 		}
 
+		if pc.api.settingEngine.fireOnTrackBeforeFirstRTP {
+			pc.onTrack(t, receiver)
+			return
+		}
 		go func(track *TrackRemote) {
 			b := make([]byte, pc.api.settingEngine.getReceiveMTU())
 			n, _, err := track.peek(b)
diff --git a/settingengine.go b/settingengine.go
index f3c70707c9a..2e37b4e74e0 100644
--- a/settingengine.go
+++ b/settingengine.go
@@ -101,6 +101,7 @@ type SettingEngine struct {
 	srtpProtectionProfiles                    []dtls.SRTPProtectionProfile
 	receiveMTU                                uint
 	iceMaxBindingRequests                     *uint16
+	fireOnTrackBeforeFirstRTP                 bool
 }
 
 // getReceiveMTU returns the configured MTU. If SettingEngine's MTU is configured to 0 it returns the default
@@ -491,3 +492,12 @@ func (e *SettingEngine) SetSCTPRTOMax(rtoMax time.Duration) {
 func (e *SettingEngine) SetICEBindingRequestHandler(bindingRequestHandler func(m *stun.Message, local, remote ice.Candidate, pair *ice.CandidatePair) bool) {
 	e.iceBindingRequestHandler = bindingRequestHandler
 }
+
+// SetFireOnTrackBeforeFirstRTP sets if firing the OnTrack event should happen
+// before any RTP packets are received. Setting this to true will
+// have the Track's Codec and PayloadTypes be initially set to their
+// zero values in the OnTrack handler.
+// Note: This does not yet affect simulcast tracks.
+func (e *SettingEngine) SetFireOnTrackBeforeFirstRTP(fireOnTrackBeforeFirstRTP bool) {
+	e.fireOnTrackBeforeFirstRTP = fireOnTrackBeforeFirstRTP
+}
diff --git a/settingengine_test.go b/settingengine_test.go
index 4a5714e1f69..6912694f497 100644
--- a/settingengine_test.go
+++ b/settingengine_test.go
@@ -340,3 +340,57 @@ func TestSetHooks(t *testing.T) {
 		t.Errorf("Failed to set DTLS Certificate Request Hook")
 	}
 }
+
+func TestSetFireOnTrackBeforeFirstRTP(t *testing.T) {
+	lim := test.TimeOut(time.Second * 30)
+	defer lim.Stop()
+
+	report := test.CheckRoutines(t)
+	defer report()
+
+	s := SettingEngine{}
+	s.SetFireOnTrackBeforeFirstRTP(true)
+
+	mediaEngineOne := &MediaEngine{}
+	assert.NoError(t, mediaEngineOne.RegisterCodec(RTPCodecParameters{
+		RTPCodecCapability: RTPCodecCapability{MimeType: "video/VP8", ClockRate: 90000, Channels: 0, SDPFmtpLine: "", RTCPFeedback: nil},
+		PayloadType:        100,
+	}, RTPCodecTypeVideo))
+
+	mediaEngineTwo := &MediaEngine{}
+	assert.NoError(t, mediaEngineTwo.RegisterCodec(RTPCodecParameters{
+		RTPCodecCapability: RTPCodecCapability{MimeType: "video/VP8", ClockRate: 90000, Channels: 0, SDPFmtpLine: "", RTCPFeedback: nil},
+		PayloadType:        200,
+	}, RTPCodecTypeVideo))
+
+	offerer, err := NewAPI(WithMediaEngine(mediaEngineOne), WithSettingEngine(s)).NewPeerConnection(Configuration{})
+	assert.NoError(t, err)
+
+	answerer, err := NewAPI(WithMediaEngine(mediaEngineTwo)).NewPeerConnection(Configuration{})
+	assert.NoError(t, err)
+
+	track, err := NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion")
+	assert.NoError(t, err)
+
+	_, err = offerer.AddTransceiverFromKind(RTPCodecTypeVideo)
+	assert.NoError(t, err)
+
+	_, err = answerer.AddTrack(track)
+	assert.NoError(t, err)
+
+	onTrackFired, onTrackFiredFunc := context.WithCancel(context.Background())
+	offerer.OnTrack(func(track *TrackRemote, _ *RTPReceiver) {
+		_, _, err = track.Read(make([]byte, 1500))
+		assert.NoError(t, err)
+		assert.Equal(t, track.PayloadType(), PayloadType(100))
+		assert.Equal(t, track.Codec().RTPCodecCapability.MimeType, "video/VP8")
+
+		onTrackFiredFunc()
+	})
+
+	assert.NoError(t, signalPair(offerer, answerer))
+
+	sendVideoUntilDone(onTrackFired.Done(), t, []*TrackLocalStaticSample{track})
+
+	closePairNow(t, offerer, answerer)
+}