Method CreateOffer

peerconnection.go:686–814

CreateOffer starts the PeerConnection and generates the localDescription https://w3c.github.io/webrtc-pc/#dom-rtcpeerconnection-createoffer nolint:gocognit,cyclop

(options *OfferOptions)

//
//nolint:gocognit,cyclop
func (pc *PeerConnection) CreateOffer(options *OfferOptions) (SessionDescription, error) {
	useIdentity := pc.idpLoginURL != nil
	switch {
	case useIdentity:
		return SessionDescription{}, errIdentityProviderNotImplemented
	case pc.isClosed.Load():
		return SessionDescription{}, &rtcerr.InvalidStateError{Err: ErrConnectionClosed}
	}

	if options != nil && options.ICERestart {
		if err := pc.iceTransport.restart(); err != nil {
			return SessionDescription{}, err
		}
	}

	var (
		descr *sdp.SessionDescription
		offer SessionDescription
		err   error
	)

	// This may be necessary to recompute if, for example, createOffer was called when only an
	// audio RTCRtpTransceiver was added to connection, but while performing the in-parallel
	// steps to create an offer, a video RTCRtpTransceiver was added, requiring additional
	// inspection of video system resources.
	count := 0
	pc.mu.Lock()
	defer pc.mu.Unlock()
	for {
		// We cache current transceivers to ensure they aren't
		// mutated during offer generation. We later check if they have
		// been mutated and recompute the offer if necessary.
		currentTransceivers := pc.rtpTransceivers

		// in-parallel steps to create an offer
		// https://w3c.github.io/webrtc-pc/#dfn-in-parallel-steps-to-create-an-offer
		isPlanB := pc.configuration.SDPSemantics == SDPSemanticsPlanB
		if pc.currentRemoteDescription != nil && isPlanB {
			isPlanB = descriptionPossiblyPlanB(pc.currentRemoteDescription)
		}

		// include unmatched local transceivers
		if !isPlanB { //nolint:nestif
			// update the greater mid if the remote description provides a greater one
			if pc.currentRemoteDescription != nil {
				var numericMid int
				for _, media := range pc.currentRemoteDescription.parsed.MediaDescriptions {
					mid := getMidValue(media)
					if mid == "" {
						continue
					}
					numericMid, err = strconv.Atoi(mid)
					if err != nil {
						continue
					}
					if numericMid > pc.greaterMid {
						pc.greaterMid = numericMid
					}