Set DataChannel SCTPTransport before OnDataChannel

ORTC API would return a nil SCTPTransport for DataChannels returned via
Callback

datachannel.go

@@ -67,7 +67,7 @@ type DataChannel struct {
 // This constructor is part of the ORTC API. It is not
 // meant to be used together with the basic WebRTC API.
 func (api *API) NewDataChannel(transport *SCTPTransport, params *DataChannelParameters) (*DataChannel, error) {
-	d, err := api.newDataChannel(params, api.settingEngine.LoggerFactory.NewLogger("ortc"))
+	d, err := api.newDataChannel(params, nil, api.settingEngine.LoggerFactory.NewLogger("ortc"))
 	if err != nil {
 		return nil, err
 	}
@@ -82,13 +82,14 @@ func (api *API) NewDataChannel(transport *SCTPTransport, params *DataChannelPara
 
 // newDataChannel is an internal constructor for the data channel used to
 // create the DataChannel object before the networking is set up.
-func (api *API) newDataChannel(params *DataChannelParameters, log logging.LeveledLogger) (*DataChannel, error) {
+func (api *API) newDataChannel(params *DataChannelParameters, sctpTransport *SCTPTransport, log logging.LeveledLogger) (*DataChannel, error) {
 	// https://w3c.github.io/webrtc-pc/#peer-to-peer-data-api (Step #5)
 	if len(params.Label) > 65535 {
 		return nil, &rtcerr.TypeError{Err: ErrStringSizeLimit}
 	}
 
 	d := &DataChannel{
+		sctpTransport:     sctpTransport,
 		statsID:           fmt.Sprintf("DataChannel-%d", time.Now().UnixNano()),
 		label:             params.Label,
 		protocol:          params.Protocol,

ortc_datachannel_test.go

@@ -12,6 +12,36 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestDataChannel_ORTC_SCTPTransport(t *testing.T) {
+	lim := test.TimeOut(time.Second * 20)
+	defer lim.Stop()
+
+	report := test.CheckRoutines(t)
+	defer report()
+
+	stackA, stackB, err := newORTCPair()
+	assert.NoError(t, err)
+
+	getSelectedCandidatePairErrChan := make(chan error)
+	stackB.sctp.OnDataChannel(func(d *DataChannel) {
+		_, getSelectedCandidatePairErr := d.Transport().Transport().ICETransport().GetSelectedCandidatePair()
+		getSelectedCandidatePairErrChan <- getSelectedCandidatePairErr
+	})
+
+	assert.NoError(t, signalORTCPair(stackA, stackB))
+
+	var id uint16 = 1
+	_, err = stackA.api.NewDataChannel(stackA.sctp, &DataChannelParameters{
+		Label: "Foo",
+		ID:    &id,
+	})
+	assert.NoError(t, err)
+
+	assert.NoError(t, <-getSelectedCandidatePairErrChan)
+	assert.NoError(t, stackA.close())
+	assert.NoError(t, stackB.close())
+}
+
 func TestDataChannel_ORTCE2E(t *testing.T) {
 	lim := test.TimeOut(time.Second * 20)
 	defer lim.Stop()

peerconnection.go

@@ -1991,7 +1991,7 @@ func (pc *PeerConnection) CreateDataChannel(label string, options *DataChannelIn
 		}
 	}
 
-	d, err := pc.api.newDataChannel(params, pc.log)
+	d, err := pc.api.newDataChannel(params, nil, pc.log)
 	if err != nil {
 		return nil, err
 	}

sctptransport.go

@@ -224,7 +224,7 @@ ACCEPT:
 			Ordered:           ordered,
 			MaxPacketLifeTime: maxPacketLifeTime,
 			MaxRetransmits:    maxRetransmits,
-		}, r.api.settingEngine.LoggerFactory.NewLogger("ortc"))
+		}, r, r.api.settingEngine.LoggerFactory.NewLogger("ortc"))
 		if err != nil {
 			r.log.Errorf("Failed to accept data channel: %v", err)
 			r.onError(err)