webrtc/sdp.go

// +build !js

package webrtc

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"

	"github.com/pion/ice/v2"
	"github.com/pion/logging"
	"github.com/pion/sdp/v3"
)

// trackDetails represents any media source that can be represented in a SDP
// This isn't keyed by SSRC because it also needs to support rid based sources
type trackDetails struct {
	mid   string
	kind  RTPCodecType
	label string
	id    string
	ssrc  uint32
	rids  []string
}

func trackDetailsForSSRC(trackDetails []trackDetails, ssrc uint32) *trackDetails {
	for i := range trackDetails {
		if trackDetails[i].ssrc == ssrc {
			return &trackDetails[i]
		}
	}
	return nil
}

func filterTrackWithSSRC(incomingTracks []trackDetails, ssrc uint32) []trackDetails {
	filtered := []trackDetails{}
	for i := range incomingTracks {
		if incomingTracks[i].ssrc != ssrc {
			filtered = append(filtered, incomingTracks[i])
		}
	}
	return filtered
}

// SDPSectionType specifies media type sections
type SDPSectionType string

// Common SDP sections
const (
	SDPSectionGlobal = SDPSectionType("global")
	SDPSectionVideo  = SDPSectionType("video")
	SDPSectionAudio  = SDPSectionType("audio")
)

// extract all trackDetails from an SDP.
func trackDetailsFromSDP(log logging.LeveledLogger, s *sdp.SessionDescription) []trackDetails { // nolint:gocognit
	incomingTracks := []trackDetails{}
	rtxRepairFlows := map[uint32]bool{}

	for _, media := range s.MediaDescriptions {
		// Plan B can have multiple tracks in a signle media section
		trackLabel := ""
		trackID := ""

		// If media section is recvonly or inactive skip
		if _, ok := media.Attribute(sdp.AttrKeyRecvOnly); ok {
			continue
		} else if _, ok := media.Attribute(sdp.AttrKeyInactive); ok {
			continue
		}

		midValue := getMidValue(media)
		if midValue == "" {
			continue
		}

		codecType := NewRTPCodecType(media.MediaName.Media)
		if codecType == 0 {
			continue
		}

		for _, attr := range media.Attributes {
			switch attr.Key {
			case sdp.AttrKeySSRCGroup:
				split := strings.Split(attr.Value, " ")
				if split[0] == sdp.SemanticTokenFlowIdentification {
					// Add rtx ssrcs to blacklist, to avoid adding them as tracks
					// Essentially lines like `a=ssrc-group:FID 2231627014 632943048` are processed by this section
					// as this declares that the second SSRC (632943048) is a rtx repair flow (RFC4588) for the first
					// (2231627014) as specified in RFC5576
					if len(split) == 3 {
						_, err := strconv.ParseUint(split[1], 10, 32)
						if err != nil {
							log.Warnf("Failed to parse SSRC: %v", err)
							continue
						}
						rtxRepairFlow, err := strconv.ParseUint(split[2], 10, 32)
						if err != nil {
							log.Warnf("Failed to parse SSRC: %v", err)
							continue
						}
						rtxRepairFlows[uint32(rtxRepairFlow)] = true
						incomingTracks = filterTrackWithSSRC(incomingTracks, uint32(rtxRepairFlow)) // Remove if rtx was added as track before
					}
				}

			// Handle `a=msid:<stream_id> <track_label>` for Unified plan. The first value is the same as MediaStream.id
			// in the browser and can be used to figure out which tracks belong to the same stream. The browser should
			// figure this out automatically when an ontrack event is emitted on RTCPeerConnection.
			case sdp.AttrKeyMsid:
				split := strings.Split(attr.Value, " ")
				if len(split) == 2 {
					trackLabel = split[0]
					trackID = split[1]
				}

			case sdp.AttrKeySSRC:
				split := strings.Split(attr.Value, " ")
				ssrc, err := strconv.ParseUint(split[0], 10, 32)
				if err != nil {
					log.Warnf("Failed to parse SSRC: %v", err)
					continue
				}

				if rtxRepairFlow := rtxRepairFlows[uint32(ssrc)]; rtxRepairFlow {
					continue // This ssrc is a RTX repair flow, ignore
				}

				if len(split) == 3 && strings.HasPrefix(split[1], "msid:") {
					trackLabel = split[1][len("msid:"):]
					trackID = split[2]
				}

				isNewTrack := true
				trackDetails := &trackDetails{}
				for i := range incomingTracks {
					if incomingTracks[i].ssrc == uint32(ssrc) {
						trackDetails = &incomingTracks[i]
						isNewTrack = false
					}
				}

				trackDetails.mid = midValue
				trackDetails.kind = codecType
				trackDetails.label = trackLabel
				trackDetails.id = trackID
				trackDetails.ssrc = uint32(ssrc)

				if isNewTrack {
					incomingTracks = append(incomingTracks, *trackDetails)
				}
			}
		}

		if rids := getRids(media); len(rids) != 0 && trackID != "" && trackLabel != "" {
			newTrack := trackDetails{
				mid:   midValue,
				kind:  codecType,
				label: trackLabel,
				id:    trackID,
				rids:  []string{},
			}
			for rid := range rids {
				newTrack.rids = append(newTrack.rids, rid)
			}

			incomingTracks = append(incomingTracks, newTrack)
		}
	}
	return incomingTracks
}

func getRids(media *sdp.MediaDescription) map[string]string {
	rids := map[string]string{}
	for _, attr := range media.Attributes {
		if attr.Key == "rid" {
			split := strings.Split(attr.Value, " ")
			rids[split[0]] = attr.Value
		}
	}
	return rids
}

func addCandidatesToMediaDescriptions(candidates []ICECandidate, m *sdp.MediaDescription, iceGatheringState ICEGatheringState) error {
	appendCandidateIfNew := func(c ice.Candidate, attributes []sdp.Attribute) {
		marshaled := c.Marshal()
		for _, a := range attributes {
			if marshaled == a.Value {
				return
			}
		}

		m.WithValueAttribute("candidate", marshaled)
	}

	for _, c := range candidates {
		candidate, err := c.toICE()
		if err != nil {
			return err
		}

		candidate.SetComponent(1)
		appendCandidateIfNew(candidate, m.Attributes)

		candidate.SetComponent(2)
		appendCandidateIfNew(candidate, m.Attributes)
	}

	if iceGatheringState != ICEGatheringStateComplete {
		return nil
	}
	for _, a := range m.Attributes {
		if a.Key == "end-of-candidates" {
			return nil
		}
	}

	m.WithPropertyAttribute("end-of-candidates")
	return nil
}

func addDataMediaSection(d *sdp.SessionDescription, shouldAddCandidates bool, dtlsFingerprints []DTLSFingerprint, midValue string, iceParams ICEParameters, candidates []ICECandidate, dtlsRole sdp.ConnectionRole, iceGatheringState ICEGatheringState) error {
	media := (&sdp.MediaDescription{
		MediaName: sdp.MediaName{
			Media:   mediaSectionApplication,
			Port:    sdp.RangedPort{Value: 9},
			Protos:  []string{"DTLS", "SCTP"},
			Formats: []string{"5000"},
		},
		ConnectionInformation: &sdp.ConnectionInformation{
			NetworkType: "IN",
			AddressType: "IP4",
			Address: &sdp.Address{
				Address: "0.0.0.0",
			},
		},
	}).
		WithValueAttribute(sdp.AttrKeyConnectionSetup, dtlsRole.String()).
		WithValueAttribute(sdp.AttrKeyMID, midValue).
		WithPropertyAttribute(RTPTransceiverDirectionSendrecv.String()).
		WithPropertyAttribute("sctpmap:5000 webrtc-datachannel 1024").
		WithICECredentials(iceParams.UsernameFragment, iceParams.Password)

	for _, f := range dtlsFingerprints {
		media = media.WithFingerprint(f.Algorithm, strings.ToUpper(f.Value))
	}

	if shouldAddCandidates {
		if err := addCandidatesToMediaDescriptions(candidates, media, iceGatheringState); err != nil {
			return err
		}
	}

	d.WithMedia(media)
	return nil
}

func populateLocalCandidates(sessionDescription *SessionDescription, i *ICEGatherer, iceGatheringState ICEGatheringState) *SessionDescription {
	if sessionDescription == nil || i == nil {
		return sessionDescription
	}

	candidates, err := i.GetLocalCandidates()
	if err != nil {
		return sessionDescription
	}

	parsed := sessionDescription.parsed
	for _, m := range parsed.MediaDescriptions {
		if err = addCandidatesToMediaDescriptions(candidates, m, iceGatheringState); err != nil {
			return sessionDescription
		}
	}

	sdp, err := parsed.Marshal()
	if err != nil {
		return sessionDescription
	}

	return &SessionDescription{
		SDP:  string(sdp),
		Type: sessionDescription.Type,
	}
}

func addTransceiverSDP(d *sdp.SessionDescription, isPlanB, shouldAddCandidates bool, dtlsFingerprints []DTLSFingerprint, mediaEngine *MediaEngine, midValue string, iceParams ICEParameters, candidates []ICECandidate, dtlsRole sdp.ConnectionRole, iceGatheringState ICEGatheringState, extMaps map[SDPSectionType][]sdp.ExtMap, mediaSection mediaSection) (bool, error) {
	transceivers := mediaSection.transceivers
	if len(transceivers) < 1 {
		return false, errSDPZeroTransceivers
	}
	// Use the first transceiver to generate the section attributes
	t := transceivers[0]
	media := sdp.NewJSEPMediaDescription(t.kind.String(), []string{}).
		WithValueAttribute(sdp.AttrKeyConnectionSetup, dtlsRole.String()).
		WithValueAttribute(sdp.AttrKeyMID, midValue).
		WithICECredentials(iceParams.UsernameFragment, iceParams.Password).
		WithPropertyAttribute(sdp.AttrKeyRTCPMux).
		WithPropertyAttribute(sdp.AttrKeyRTCPRsize)

	codecs := mediaEngine.GetCodecsByKind(t.kind)
	for _, codec := range codecs {
		media.WithCodec(codec.PayloadType, codec.Name, codec.ClockRate, codec.Channels, codec.SDPFmtpLine)

		for _, feedback := range codec.RTPCodecCapability.RTCPFeedback {
			media.WithValueAttribute("rtcp-fb", fmt.Sprintf("%d %s %s", codec.PayloadType, feedback.Type, feedback.Parameter))
		}
	}
	if len(codecs) == 0 {
		// Explicitly reject track if we don't have the codec
		d.WithMedia(&sdp.MediaDescription{
			MediaName: sdp.MediaName{
				Media:   t.kind.String(),
				Port:    sdp.RangedPort{Value: 0},
				Protos:  []string{"UDP", "TLS", "RTP", "SAVPF"},
				Formats: []string{"0"},
			},
		})
		return false, nil
	}

	// Add extmaps
	if maps, ok := extMaps[SDPSectionType(t.kind.String())]; ok {
		for _, m := range maps {
			media.WithExtMap(m)
		}
	}

	if len(mediaSection.ridMap) > 0 {
		recvRids := make([]string, 0, len(mediaSection.ridMap))

		for rid := range mediaSection.ridMap {
			media.WithValueAttribute("rid", rid+" recv")
			recvRids = append(recvRids, rid)
		}
		// Simulcast
		media.WithValueAttribute("simulcast", "recv "+strings.Join(recvRids, ";"))
	}

	for _, mt := range transceivers {
		if mt.Sender() != nil && mt.Sender().Track() != nil {
			track := mt.Sender().Track()
			media = media.WithMediaSource(track.SSRC(), track.Label() /* cname */, track.Label() /* streamLabel */, track.ID())
			if !isPlanB {
				media = media.WithPropertyAttribute("msid:" + track.Label() + " " + track.ID())
				break
			}
		}
	}

	media = media.WithPropertyAttribute(t.Direction().String())

	for _, fingerprint := range dtlsFingerprints {
		media = media.WithFingerprint(fingerprint.Algorithm, strings.ToUpper(fingerprint.Value))
	}

	if shouldAddCandidates {
		if err := addCandidatesToMediaDescriptions(candidates, media, iceGatheringState); err != nil {
			return false, err
		}
	}

	d.WithMedia(media)

	return true, nil
}

type mediaSection struct {
	id           string
	transceivers []*RTPTransceiver
	data         bool
	ridMap       map[string]string
}

// populateSDP serializes a PeerConnections state into an SDP
func populateSDP(d *sdp.SessionDescription, isPlanB bool, dtlsFingerprints []DTLSFingerprint, mediaDescriptionFingerprint bool, isICELite bool, mediaEngine *MediaEngine, connectionRole sdp.ConnectionRole, candidates []ICECandidate, iceParams ICEParameters, mediaSections []mediaSection, iceGatheringState ICEGatheringState, extMaps map[SDPSectionType][]sdp.ExtMap) (*sdp.SessionDescription, error) {
	var err error
	mediaDtlsFingerprints := []DTLSFingerprint{}

	if mediaDescriptionFingerprint {
		mediaDtlsFingerprints = dtlsFingerprints
	}

	bundleValue := "BUNDLE"
	bundleCount := 0
	appendBundle := func(midValue string) {
		bundleValue += " " + midValue
		bundleCount++
	}

	for i, m := range mediaSections {
		if m.data && len(m.transceivers) != 0 {
			return nil, errSDPMediaSectionMediaDataChanInvalid
		} else if !isPlanB && len(m.transceivers) > 1 {
			return nil, errSDPMediaSectionMultipleTrackInvalid
		}

		shouldAddID := true
		shouldAddCanidates := i == 0
		if m.data {
			if err = addDataMediaSection(d, shouldAddCanidates, mediaDtlsFingerprints, m.id, iceParams, candidates, connectionRole, iceGatheringState); err != nil {
				return nil, err
			}
		} else {
			shouldAddID, err = addTransceiverSDP(d, isPlanB, shouldAddCanidates, mediaDtlsFingerprints, mediaEngine, m.id, iceParams, candidates, connectionRole, iceGatheringState, extMaps, m)
			if err != nil {
				return nil, err
			}
		}

		if shouldAddID {
			appendBundle(m.id)
		}
	}

	if !mediaDescriptionFingerprint {
		for _, fingerprint := range dtlsFingerprints {
			d.WithFingerprint(fingerprint.Algorithm, strings.ToUpper(fingerprint.Value))
		}
	}

	if isICELite {
		// RFC 5245 S15.3
		d = d.WithValueAttribute(sdp.AttrKeyICELite, sdp.AttrKeyICELite)
	}

	// Add global exts
	if maps, ok := extMaps[SDPSectionGlobal]; ok {
		for _, m := range maps {
			d.WithPropertyAttribute(m.Marshal())
		}
	}

	return d.WithValueAttribute(sdp.AttrKeyGroup, bundleValue), nil
}

func getMidValue(media *sdp.MediaDescription) string {
	for _, attr := range media.Attributes {
		if attr.Key == "mid" {
			return attr.Value
		}
	}
	return ""
}

func descriptionIsPlanB(desc *SessionDescription) bool {
	if desc == nil || desc.parsed == nil {
		return false
	}

	detectionRegex := regexp.MustCompile(`(?i)^(audio|video|data)$`)
	for _, media := range desc.parsed.MediaDescriptions {
		if len(detectionRegex.FindStringSubmatch(getMidValue(media))) == 2 {
			return true
		}
	}
	return false
}

func getPeerDirection(media *sdp.MediaDescription) RTPTransceiverDirection {
	for _, a := range media.Attributes {
		if direction := NewRTPTransceiverDirection(a.Key); direction != RTPTransceiverDirection(Unknown) {
			return direction
		}
	}
	return RTPTransceiverDirection(Unknown)
}

func extractFingerprint(desc *sdp.SessionDescription) (string, string, error) {
	fingerprints := []string{}

	if fingerprint, haveFingerprint := desc.Attribute("fingerprint"); haveFingerprint {
		fingerprints = append(fingerprints, fingerprint)
	}

	for _, m := range desc.MediaDescriptions {
		if fingerprint, haveFingerprint := m.Attribute("fingerprint"); haveFingerprint {
			fingerprints = append(fingerprints, fingerprint)
		}
	}

	if len(fingerprints) < 1 {
		return "", "", ErrSessionDescriptionNoFingerprint
	}

	for _, m := range fingerprints {
		if m != fingerprints[0] {
			return "", "", ErrSessionDescriptionConflictingFingerprints
		}
	}

	parts := strings.Split(fingerprints[0], " ")
	if len(parts) != 2 {
		return "", "", ErrSessionDescriptionInvalidFingerprint
	}
	return parts[1], parts[0], nil
}

func extractICEDetails(desc *sdp.SessionDescription) (string, string, []ICECandidate, error) {
	candidates := []ICECandidate{}
	remotePwds := []string{}
	remoteUfrags := []string{}

	if ufrag, haveUfrag := desc.Attribute("ice-ufrag"); haveUfrag {
		remoteUfrags = append(remoteUfrags, ufrag)
	}
	if pwd, havePwd := desc.Attribute("ice-pwd"); havePwd {
		remotePwds = append(remotePwds, pwd)
	}

	for _, m := range desc.MediaDescriptions {
		if ufrag, haveUfrag := m.Attribute("ice-ufrag"); haveUfrag {
			remoteUfrags = append(remoteUfrags, ufrag)
		}
		if pwd, havePwd := m.Attribute("ice-pwd"); havePwd {
			remotePwds = append(remotePwds, pwd)
		}

		for _, a := range m.Attributes {
			if a.IsICECandidate() {
				c, err := ice.UnmarshalCandidate(a.Value)
				if err != nil {
					return "", "", nil, err
				}

				candidate, err := newICECandidateFromICE(c)
				if err != nil {
					return "", "", nil, err
				}

				candidates = append(candidates, candidate)
			}
		}
	}

	if len(remoteUfrags) == 0 {
		return "", "", nil, ErrSessionDescriptionMissingIceUfrag
	} else if len(remotePwds) == 0 {
		return "", "", nil, ErrSessionDescriptionMissingIcePwd
	}

	for _, m := range remoteUfrags {
		if m != remoteUfrags[0] {
			return "", "", nil, ErrSessionDescriptionConflictingIceUfrag
		}
	}

	for _, m := range remotePwds {
		if m != remotePwds[0] {
			return "", "", nil, ErrSessionDescriptionConflictingIcePwd
		}
	}

	return remoteUfrags[0], remotePwds[0], candidates, nil
}

func haveApplicationMediaSection(desc *sdp.SessionDescription) bool {
	for _, m := range desc.MediaDescriptions {
		if m.MediaName.Media == mediaSectionApplication {
			return true
		}
	}

	return false
}

func matchedAnswerExt(descriptions *sdp.SessionDescription, localMaps map[SDPSectionType][]sdp.ExtMap) (map[SDPSectionType][]sdp.ExtMap, error) {
	remoteExtMaps, err := remoteExts(descriptions)
	if err != nil {
		return nil, err
	}
	return answerExtMaps(remoteExtMaps, localMaps), nil
}

func answerExtMaps(remoteExtMaps map[SDPSectionType]map[int]sdp.ExtMap, localMaps map[SDPSectionType][]sdp.ExtMap) map[SDPSectionType][]sdp.ExtMap {
	ret := map[SDPSectionType][]sdp.ExtMap{}
	for mediaType, remoteExtMap := range remoteExtMaps {
		if _, ok := ret[mediaType]; !ok {
			ret[mediaType] = []sdp.ExtMap{}
		}
		for _, extItem := range remoteExtMap {
			// add remote ext that match locally available ones
			for _, extMap := range localMaps[mediaType] {
				if extMap.URI.String() == extItem.URI.String() {
					ret[mediaType] = append(ret[mediaType], extItem)
				}
			}
		}
	}
	return ret
}

func remoteExts(session *sdp.SessionDescription) (map[SDPSectionType]map[int]sdp.ExtMap, error) {
	remoteExtMaps := map[SDPSectionType]map[int]sdp.ExtMap{}

	maybeAddExt := func(attr sdp.Attribute, mediaType SDPSectionType) error {
		if attr.Key != "extmap" {
			return nil
		}
		em := &sdp.ExtMap{}
		if err := em.Unmarshal("extmap:" + attr.Value); err != nil {
			return fmt.Errorf("%w: %v", errSDPParseExtMap, err)
		}
		if remoteExtMap, ok := remoteExtMaps[mediaType][em.Value]; ok {
			if remoteExtMap.Value != em.Value {
				return errSDPRemoteDescriptionChangedExtMap
			}
		} else {
			remoteExtMaps[mediaType][em.Value] = *em
		}
		return nil
	}

	// populate the extmaps from the current remote description
	for _, media := range session.MediaDescriptions {
		mediaType := SDPSectionType(media.MediaName.Media)
		// populate known remote extmap and handle conflicts.
		if _, ok := remoteExtMaps[mediaType]; !ok {
			remoteExtMaps[mediaType] = map[int]sdp.ExtMap{}
		}
		for _, attr := range media.Attributes {
			if err := maybeAddExt(attr, mediaType); err != nil {
				return nil, err
			}
		}
	}

	// Add global exts
	for _, attr := range session.Attributes {
		if err := maybeAddExt(attr, SDPSectionGlobal); err != nil {
			return nil, err
		}
	}
	return remoteExtMaps, nil
}

// GetExtMapByURI return a copy of the extmap matching the provided
// URI. Note that the extmap value will change if not yet negotiated
func getExtMapByURI(exts map[SDPSectionType][]sdp.ExtMap, uri string) *sdp.ExtMap {
	for _, extList := range exts {
		for _, extMap := range extList {
			if extMap.URI.String() == uri {
				return &sdp.ExtMap{
					Value:     extMap.Value,
					Direction: extMap.Direction,
					URI:       extMap.URI,
					ExtAttr:   extMap.ExtAttr,
				}
			}
		}
	}
	return nil
}

func getByMid(searchMid string, desc *SessionDescription) *sdp.MediaDescription {
	for _, m := range desc.parsed.MediaDescriptions {
		if mid, ok := m.Attribute(sdp.AttrKeyMID); ok && mid == searchMid {
			return m
		}
	}
	return nil
}

// haveDataChannel return MediaDescription with MediaName equal application
func haveDataChannel(desc *SessionDescription) *sdp.MediaDescription {
	for _, d := range desc.parsed.MediaDescriptions {
		if d.MediaName.Media == mediaSectionApplication {
			return d
		}
	}
	return nil
}