conn.go: Include selected candidate pair to Addr

conn.go

@@ -143,6 +143,10 @@ func (*Conn) SetWriteDeadline(time.Time) error {
 func (c *Conn) LocalAddr() net.Addr {
 	addr := c.local
 	addr.ConnectionID = c.id
+	pair, _ := c.ice.GetSelectedCandidatePair()
+	if pair != nil {
+		addr.SelectedCandidate = pair.Local
+	}
 	return &addr
 }
 
@@ -154,6 +158,11 @@ func (c *Conn) RemoteAddr() net.Addr {
 	c.candidatesMu.Lock()
 	addr.Candidates = slices.Clone(c.candidates)
 	c.candidatesMu.Unlock()
+
+	pair, _ := c.ice.GetSelectedCandidatePair()
+	if pair != nil {
+		addr.SelectedCandidate = pair.Remote
+	}
 	return addr
 }
 
@@ -176,9 +185,15 @@ func (c *Conn) Close() (err error) {
 
 		c.negotiator.handleClose(c)
 
+		if c.reliable != nil {
+			err = c.reliable.Close()
+		}
+		if c.unreliable != nil {
+			err = errors.Join(err, c.unreliable.Close())
+		}
+
 		err = errors.Join(
-			c.reliable.Close(),
-			c.unreliable.Close(),
+			err,
 			c.sctp.Stop(),
 			c.dtls.Stop(),
 			c.ice.Stop(),
@@ -254,7 +269,6 @@ func (c *Conn) handleSignal(signal *Signal) error {
 			Typ:        webrtc.ICECandidateType(candidate.Type()),
 			TCPType:    candidate.TCPType().String(),
 		}
-
 		if r := candidate.RelatedAddress(); r != nil {
 			i.RelatedAddress, i.RelatedPort = r.Address, uint16(r.Port)
 		}
@@ -323,9 +337,9 @@ func parseDescription(d *sdp.SessionDescription) (*description, error) {
 	}
 	var role webrtc.DTLSRole
 	switch attr {
-	case "active":
+	case sdp.ConnectionRoleActive.String():
 		role = webrtc.DTLSRoleClient
-	case "actpass":
+	case sdp.ConnectionRoleActpass.String():
 		role = webrtc.DTLSRoleServer
 	default:
 		return nil, fmt.Errorf("invalid setup attribute: %s", attr)
@@ -360,14 +374,6 @@ func parseDescription(d *sdp.SessionDescription) (*description, error) {
 	}, nil
 }
 
-// description contains parameters for calling the Start method of ICE, DTLS and SCTP transport.
-//
-// A description may be parsed by a negotiator (Listener or Dialer) using parseDescription
-// with a [sdp.SessionDescription] decoded from a Signal of SignalTypeOffer or SignalTypeAnswer.
-//
-// A description may be filled in by a negotiator (Listener or Dialer) to encode
-// a local description of a Conn.
-
 // description contains parameters necessary for starting ICE, DTLS, and SCTP transport within a Conn.
 //
 // It may be created by parsing a [sdp.SessionDescription] signaled from a remote connection or filed
@@ -386,7 +392,7 @@ type description struct {
 // parameters of each transport within a Conn.
 func (desc description) encode() ([]byte, error) {
 	d := &sdp.SessionDescription{
-		Version: 0x2,
+		Version: 0x0,
 		Origin: sdp.Origin{
 			Username:       "-",
 			SessionID:      rand.Uint64(),
@@ -400,53 +406,50 @@ func (desc description) encode() ([]byte, error) {
 			{},
 		},
 		Attributes: []sdp.Attribute{
-			{Key: "group", Value: "BUNDLE 0"},
-			{Key: "extmap-allow-mixed", Value: ""},
-			{Key: "msid-semantic", Value: " WMS"},
+			{Key: sdp.AttrKeyGroup, Value: "BUNDLE 0"},
+			sdp.NewPropertyAttribute(sdp.AttrKeyExtMapAllowMixed),
+			{Key: sdp.AttrKeyMsidSemantic, Value: " WMS"},
 		},
-		MediaDescriptions: []*sdp.MediaDescription{
-			{
-				MediaName: sdp.MediaName{
-					Media:   "application",
-					Port:    sdp.RangedPort{Value: 9},
-					Protos:  []string{"UDP", "DTLS", "SCTP"},
-					Formats: []string{"webrtc-datachannel"},
-				},
-				ConnectionInformation: &sdp.ConnectionInformation{
-					NetworkType: "IN",
-					AddressType: "IP4",
-					Address:     &sdp.Address{Address: "0.0.0.0"},
-				},
-				Attributes: []sdp.Attribute{
-					{Key: "ice-ufrag", Value: desc.ice.UsernameFragment},
-					{Key: "ice-pwd", Value: desc.ice.Password},
-					{Key: "ice-options", Value: "trickle"},
-					{Key: "fingerprint", Value: fmt.Sprintf("%s %s",
-						desc.dtls.Fingerprints[0].Algorithm,
-						desc.dtls.Fingerprints[0].Value,
-					)},
-					desc.setupAttribute(),
-					{Key: "mid", Value: "0"},
-					{Key: "sctp-port", Value: "5000"},
-					{Key: "max-message-size", Value: strconv.FormatUint(uint64(desc.sctp.MaxMessageSize), 10)},
-				},
+	}
+
+	media := &sdp.MediaDescription{
+		MediaName: sdp.MediaName{
+			Media:   "application",
+			Port:    sdp.RangedPort{Value: 9},
+			Protos:  []string{"UDP", "DTLS", "SCTP"},
+			Formats: []string{"webrtc-datachannel"},
+		},
+		ConnectionInformation: &sdp.ConnectionInformation{
+			NetworkType: "IN",
+			AddressType: "IP4",
+			Address: &sdp.Address{
+				Address: "0.0.0.0",
 			},
 		},
 	}
-	return d.Marshal()
+	media.WithICECredentials(desc.ice.UsernameFragment, desc.ice.Password)
+	media.WithValueAttribute("ice-options", "trickle")
+	for _, fingerprint := range desc.dtls.Fingerprints {
+		media.WithFingerprint(fingerprint.Algorithm, fingerprint.Value)
+	}
+	media.WithValueAttribute(sdp.AttrKeyConnectionSetup, desc.connectionRole(desc.dtls.Role).String())
+	media.WithValueAttribute(sdp.AttrKeyMID, "0")
+	media.WithValueAttribute("sctp-port", "5000")
+	media.WithValueAttribute("max-message-size", strconv.FormatUint(uint64(desc.sctp.MaxMessageSize), 10))
+
+	return d.WithMedia(media).Marshal()
 }
 
-// setupAttribute returns a [sdp.Attribute] with the key 'setup' indicating the local
-// DTLS role as either 'active' or 'actpass'. It is called by encode to include the role
-// in the media description of the local [sdp.SessionDescription].
-func (desc description) setupAttribute() sdp.Attribute {
-	attr := sdp.Attribute{Key: "setup"}
-	if desc.dtls.Role == webrtc.DTLSRoleServer {
-		attr.Value = "actpass"
-	} else {
-		attr.Value = "active"
+// connectionRole returns a [sdp.ConnectionRole] indicating the local DTLS role. It is called
+// by encode to include the role into the media description of local [sdp.SessionDescription]
+// as a [sdp.Attribute] of 'setup'.
+func (desc description) connectionRole(role webrtc.DTLSRole) sdp.ConnectionRole {
+	switch role {
+	case webrtc.DTLSRoleServer:
+		return sdp.ConnectionRoleActpass
+	default:
+		return sdp.ConnectionRoleActive
 	}
-	return attr
 }
 
 // newConn creates a Conn from the ICE, DTLS and SCTP transport associated with the IDs.

dial.go

@@ -25,10 +25,6 @@ type Dialer struct {
 	// has been negotiated by Dialer.
 	Log *slog.Logger
 
-	// API specifies custom configuration for WebRTC transports, and data channels. If left as nil, a new [webrtc.API]
-	// will be set from [webrtc.NewAPI]. The webrtc.SettingEngine of the API should not allow detaching data channels
-	// (by calling [webrtc.SettingEngine.DetachDataChannels]) as it requires additional steps on the Conn.
-
 	// API specifies custom configuration for WebRTC transports and data channels. If nil, a new [webrtc.API] will be
 	// set from [webrtc.NewAPI]. The [webrtc.SettingEngine] of the API should not allow detaching data channels, as it requires
 	// additional steps on the Conn (which cannot be determined by the Conn).
@@ -248,17 +244,21 @@ func (d Dialer) startTransports(ctx context.Context, conn *Conn, desc *descripti
 	if err := withContext(ctx, func() error {
 		var err error
 		conn.reliable, err = d.API.NewDataChannel(conn.sctp, &webrtc.DataChannelParameters{
-			Label: "ReliableDataChannel",
+			Label:   "ReliableDataChannel",
+			Ordered: true,
 		})
 		return err
 	}); err != nil {
 		return fmt.Errorf("create ReliableDataChannel: %w", err)
 	}
 	if err := withContext(ctx, func() error {
-		var err error
+		var (
+			err            error
+			maxRetransmits uint16 = 0
+		)
 		conn.unreliable, err = d.API.NewDataChannel(conn.sctp, &webrtc.DataChannelParameters{
-			Label:   "UnreliableDataChannel",
-			Ordered: false,
+			Label:          "UnreliableDataChannel",
+			MaxRetransmits: &maxRetransmits,
 		})
 		return err
 	}); err != nil {

listener.go

@@ -77,7 +77,6 @@ type Listener struct {
 
 	stop   func()
 	closed chan struct{}
-	once   sync.Once
 }
 
 // Accept waits for and returns the next [Conn] to the Listener. An error may be
@@ -113,6 +112,12 @@ type Addr struct {
 	// signaled from a remote connection. ICE candidates are used to determine the UDP/TCP addresses
 	// for establishing ICE transport and can be used to determine the network address of the connection.
 	Candidates []webrtc.ICECandidate
+
+	// SelectedCandidate is the candidate selected to connect with the ICE transport within a Conn.
+	// An ICE candidate may be used to determine the UDP/TCP address of the connection. It may be nil
+	// if the Conn has been closed, or if the Conn has encountered an error when obtaining the selected
+	// ICE candidate pair.
+	SelectedCandidate *webrtc.ICECandidate
 }
 
 // String formats the Addr as a string.
@@ -125,6 +130,12 @@ func (addr *Addr) String() string {
 		b.WriteString(strconv.FormatUint(addr.ConnectionID, 10))
 		b.WriteByte(')')
 	}
+	if addr.SelectedCandidate != nil {
+		b.WriteByte(' ')
+		b.WriteByte('(')
+		b.WriteString(addr.SelectedCandidate.String())
+		b.WriteByte(')')
+	}
 	return b.String()
 }
 
@@ -332,7 +343,7 @@ func (l *Listener) handleConn(conn *Conn, d *description) {
 	var err error
 	defer func() {
 		if err != nil {
-			l.connections.Delete(conn.remoteAddr().String()) // Stop notifying for the Conn.
+			_ = conn.Close() // Stop notifying for the Conn.
 
 			if errors.Is(err, context.DeadlineExceeded) {
 				if err := l.signaling.Signal(&Signal{
@@ -368,6 +379,9 @@ func (l *Listener) handleConn(conn *Conn, d *description) {
 	select {
 	case <-ctx.Done():
 		err = ctx.Err()
+	case <-l.closed:
+	case <-conn.closed:
+		return
 	case <-conn.candidateReceived:
 		conn.log.Debug("received first candidate")
 		if err = l.startTransports(ctx, conn, d); err != nil {
@@ -398,21 +412,18 @@ func (l *Listener) startTransports(ctx context.Context, conn *Conn, d *descripti
 	}
 
 	conn.log.Debug("starting SCTP transport")
-	var (
-		once   = new(sync.Once)
-		opened = make(chan struct{}, 1)
-	)
+	opened := make(chan struct{}, 1)
 	conn.sctp.OnDataChannelOpened(func(channel *webrtc.DataChannel) {
 		switch channel.Label() {
 		case "ReliableDataChannel":
 			conn.reliable = channel
 		case "UnreliableDataChannel":
 			conn.unreliable = channel
+		default:
+			return
 		}
 		if conn.reliable != nil && conn.unreliable != nil {
-			once.Do(func() {
-				close(opened)
-			})
+			close(opened)
 		}
 	})
 	if err := withContext(ctx, func() error {
@@ -449,12 +460,15 @@ func withContext(ctx context.Context, f func() error) error {
 
 // Close closes the Listener, ensuring that any blocking methods will return [net.ErrClosed] as an error.
 func (l *Listener) Close() error {
-	l.once.Do(func() {
+	select {
+	case <-l.closed:
+		return nil
+	default:
 		close(l.closed)
 		close(l.incoming)
 		l.stop()
-	})
-	return nil
+		return nil
+	}
 }
 
 // A signalError may be returned by the methods of Listener to handle incoming Signals signaled from the