Fixes SDP session id

SDP session id should stay unchanged for subsequent offers/answers

fmtp.go

@@ -21,7 +21,7 @@ func parseFmtp(line string) fmtp {
 	return f
 }
 
-// fmtpConsist checks that two FTMP parameters are not inconsistent.
+// fmtpConsist checks that two FMTP parameters are not inconsistent.
 func fmtpConsist(a, b fmtp) bool {
 	for k, v := range a {
 		if vb, ok := b[k]; ok && !strings.EqualFold(vb, v) {

peerconnection.go

@@ -31,6 +31,8 @@ type PeerConnection struct {
 	statsID string
 	mu      sync.RWMutex
 
+	sdpOrigin sdp.Origin
+
 	// ops is an operations queue which will ensure the enqueued actions are
 	// executed in order. It is used for asynchronously, but serially processing
 	// remote and local descriptions
@@ -672,6 +674,7 @@ func (pc *PeerConnection) CreateOffer(options *OfferOptions) (SessionDescription
 			return SessionDescription{}, err
 		}
 
+		updateSDPOrigin(&pc.sdpOrigin, d)
 		sdpBytes, err := d.Marshal()
 		if err != nil {
 			return SessionDescription{}, err
@@ -809,6 +812,7 @@ func (pc *PeerConnection) CreateAnswer(options *AnswerOptions) (SessionDescripti
 		return SessionDescription{}, err
 	}
 
+	updateSDPOrigin(&pc.sdpOrigin, d)
 	sdpBytes, err := d.Marshal()
 	if err != nil {
 		return SessionDescription{}, err

peerconnection_go_test.go

@@ -1350,3 +1350,50 @@ func TestPeerConnection_TransceiverDirection(t *testing.T) {
 		})
 	}
 }
+
+func TestPeerConnection_SessionID(t *testing.T) {
+	defer test.TimeOut(time.Second * 10).Stop()
+	defer test.CheckRoutines(t)()
+
+	pcOffer, pcAnswer, err := newPair()
+	assert.NoError(t, err)
+	var offerSessionID uint64
+	var offerSessionVersion uint64
+	var answerSessionID uint64
+	var answerSessionVersion uint64
+	for i := 0; i < 10; i++ {
+		assert.NoError(t, signalPair(pcOffer, pcAnswer))
+		offer := pcOffer.LocalDescription().parsed
+		sessionID := offer.Origin.SessionID
+		sessionVersion := offer.Origin.SessionVersion
+		if offerSessionID == 0 {
+			offerSessionID = sessionID
+			offerSessionVersion = sessionVersion
+		} else {
+			if offerSessionID != sessionID {
+				t.Errorf("offer[%v] session id mismatch: expected=%v, got=%v", i, offerSessionID, sessionID)
+			}
+			if offerSessionVersion+1 != sessionVersion {
+				t.Errorf("offer[%v] session version mismatch: expected=%v, got=%v", i, offerSessionVersion+1, sessionVersion)
+			}
+			offerSessionVersion++
+		}
+
+		answer := pcAnswer.LocalDescription().parsed
+		sessionID = answer.Origin.SessionID
+		sessionVersion = answer.Origin.SessionVersion
+		if answerSessionID == 0 {
+			answerSessionID = sessionID
+			answerSessionVersion = sessionVersion
+		} else {
+			if answerSessionID != sessionID {
+				t.Errorf("answer[%v] session id mismatch: expected=%v, got=%v", i, answerSessionID, sessionID)
+			}
+			if answerSessionVersion+1 != sessionVersion {
+				t.Errorf("answer[%v] session version mismatch: expected=%v, got=%v", i, answerSessionVersion+1, sessionVersion)
+			}
+			answerSessionVersion++
+		}
+	}
+	closePairNow(t, pcOffer, pcAnswer)
+}

sdp.go

@@ -8,6 +8,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"sync/atomic"
 
 	"github.com/pion/ice/v2"
 	"github.com/pion/logging"
@@ -271,8 +272,9 @@ func populateLocalCandidates(sessionDescription *SessionDescription, i *ICEGathe
 	}
 
 	return &SessionDescription{
-		SDP:  string(sdp),
-		Type: sessionDescription.Type,
+		SDP:    string(sdp),
+		Type:   sessionDescription.Type,
+		parsed: parsed,
 	}
 }
 
@@ -641,3 +643,22 @@ func rtpExtensionsFromMediaDescription(m *sdp.MediaDescription) (map[string]int,
 
 	return out, nil
 }
+
+// updateSDPOrigin saves sdp.Origin in PeerConnection when creating 1st local SDP;
+// for subsequent calling, it updates Origin for SessionDescription from saved one
+// and increments session version by one.
+// https://tools.ietf.org/html/draft-ietf-rtcweb-jsep-25#section-5.2.2
+// https://tools.ietf.org/html/draft-ietf-rtcweb-jsep-25#section-5.3.2
+func updateSDPOrigin(origin *sdp.Origin, d *sdp.SessionDescription) {
+	if atomic.CompareAndSwapUint64(&origin.SessionVersion, 0, d.Origin.SessionVersion) { // store
+		atomic.StoreUint64(&origin.SessionID, d.Origin.SessionID)
+	} else { // load
+		for { // awaiting for saving session id
+			d.Origin.SessionID = atomic.LoadUint64(&origin.SessionID)
+			if d.Origin.SessionID != 0 {
+				break
+			}
+		}
+		d.Origin.SessionVersion = atomic.AddUint64(&origin.SessionVersion, 1)
+	}
+}