Cache early ICE candidates.

client.go

@@ -654,7 +654,7 @@ func getDownConn(c *client, id string) *downConnection {
 	return conn
 }
 
-func getConn(c *client, id string) connection {
+func getConn(c *client, id string) iceConnection {
 	up := getUpConn(c, id)
 	if up != nil {
 		return up
@@ -1053,6 +1053,11 @@ func gotOffer(c *client, id string, offer webrtc.SessionDescription, labels map[
 
 	up.labels = labels
 
+	err = up.flushICECandidates()
+	if err != nil {
+		log.Printf("ICE: %v", err)
+	}
+
 	return c.write(clientMessage{
 		Type:   "answer",
 		Id:     id,
@@ -1061,17 +1066,22 @@ func gotOffer(c *client, id string, offer webrtc.SessionDescription, labels map[
 }
 
 func gotAnswer(c *client, id string, answer webrtc.SessionDescription) error {
-	conn := getDownConn(c, id)
+	down := getDownConn(c, id)
-	if conn == nil {
+	if down == nil {
 		return protocolError("unknown id in answer")
 	}
-	err := conn.pc.SetRemoteDescription(answer)
+	err := down.pc.SetRemoteDescription(answer)
 	if err != nil {
 		return err
 	}
 
-	for _, t := range conn.tracks {
+	err = down.flushICECandidates()
-		activateDownTrack(conn, t)
+	if err != nil {
+		log.Printf("ICE: %v", err)
+	}
+
+	for _, t := range down.tracks {
+		activateDownTrack(down, t)
 	}
 	return nil
 }
@@ -1081,7 +1091,7 @@ func gotICE(c *client, candidate *webrtc.ICECandidateInit, id string) error {
 	if conn == nil {
 		return errors.New("unknown id in ICE")
 	}
-	return conn.getPC().AddICECandidate(*candidate)
+	return conn.addICECandidate(candidate)
 }
 
 func (c *client) setRequested(requested map[string]uint32) error {

conn.go

@@ -6,6 +6,7 @@
 package main
 
 import (
+	"errors"
 	"sync"
 	"sync/atomic"
 
@@ -16,8 +17,9 @@ import (
 	"github.com/pion/webrtc/v2"
 )
 
-type connection interface {
+type iceConnection interface {
-	getPC() *webrtc.PeerConnection
+	addICECandidate(candidate *webrtc.ICECandidateInit) error
+	flushICECandidates() error
 }
 
 type upTrack struct {
@@ -30,6 +32,7 @@ type upTrack struct {
 	lastPLI              uint64
 	lastSenderReport     uint32
 	lastSenderReportTime uint32
+	iceCandidates        []*webrtc.ICECandidateInit
 
 	localCh    chan struct{} // signals that local has changed
 	writerDone chan struct{} // closed when the loop dies
@@ -103,6 +106,35 @@ func (up *upConnection) getPC() *webrtc.PeerConnection {
 	return up.pc
 }
 
+func (up *upConnection) addICECandidate(candidate *webrtc.ICECandidateInit) error {
+	if up.pc.RemoteDescription() != nil {
+		return up.pc.AddICECandidate(*candidate)
+	}
+	up.iceCandidates = append(up.iceCandidates, candidate)
+	return nil
+}
+
+func flushICECandidates(pc *webrtc.PeerConnection, candidates []*webrtc.ICECandidateInit) error {
+	if pc.RemoteDescription() == nil {
+		return errors.New("flushICECandidates called in bad state")
+	}
+
+	var err error
+	for _, candidate := range candidates {
+		err2 := pc.AddICECandidate(*candidate)
+		if err == nil {
+			err = err2
+		}
+	}
+	return err
+}
+
+func (up *upConnection) flushICECandidates() error {
+	err := flushICECandidates(up.pc, up.iceCandidates)
+	up.iceCandidates = nil
+	return err
+}
+
 func getUpMid(pc *webrtc.PeerConnection, track *webrtc.Track) string {
 	for _, t := range pc.GetTransceivers() {
 		if t.Receiver() != nil && t.Receiver().Track() == track {
@@ -201,3 +233,17 @@ type downConnection struct {
 func (down *downConnection) getPC() *webrtc.PeerConnection {
 	return down.pc
 }
+
+func (down *downConnection) addICECandidate(candidate *webrtc.ICECandidateInit) error {
+	if down.pc.RemoteDescription() != nil {
+		return down.pc.AddICECandidate(*candidate)
+	}
+	down.iceCandidates = append(down.iceCandidates, candidate)
+	return nil
+}
+
+func (down *downConnection) flushICECandidates() error {
+	err := flushICECandidates(down.pc, down.iceCandidates)
+	down.iceCandidates = nil
+	return err
+}