[client, relay] Advertise relay server IP via signal for foreign-relay fallback dial (#6004)

client/internal/engine.go

@@ -2454,6 +2454,8 @@ func convertToOfferAnswer(msg *sProto.Message) (*peer.OfferAnswer, error) {
 		}
 	}
 
+	relayIP := decodeRelayIP(msg.GetBody().GetRelayServerIP())
+
 	offerAnswer := peer.OfferAnswer{
 		IceCredentials: peer.IceCredentials{
 			UFrag: remoteCred.UFrag,
@@ -2464,7 +2466,23 @@ func convertToOfferAnswer(msg *sProto.Message) (*peer.OfferAnswer, error) {
 		RosenpassPubKey: rosenpassPubKey,
 		RosenpassAddr:   rosenpassAddr,
 		RelaySrvAddress: msg.GetBody().GetRelayServerAddress(),
+		RelaySrvIP:      relayIP,
 		SessionID:       sessionID,
 	}
 	return &offerAnswer, nil
 }
+
+// decodeRelayIP decodes the proto relayServerIP bytes (4 or 16) into a
+// netip.Addr. Returns the zero value for empty input and logs a warning
+// for malformed payloads.
+func decodeRelayIP(b []byte) netip.Addr {
+	if len(b) == 0 {
+		return netip.Addr{}
+	}
+	ip, ok := netip.AddrFromSlice(b)
+	if !ok {
+		log.Warnf("invalid relayServerIP in signal message (%d bytes), ignoring", len(b))
+		return netip.Addr{}
+	}
+	return ip.Unmap()
+}

client/internal/peer/handshaker.go

@@ -3,6 +3,7 @@ package peer
 import (
 	"context"
 	"errors"
+	"net/netip"
 	"sync"
 	"sync/atomic"
 
@@ -40,6 +41,10 @@ type OfferAnswer struct {
 
 	// relay server address
 	RelaySrvAddress string
+	// RelaySrvIP is the IP the remote peer is connected to on its
+	// relay server. Used as a dial target if DNS for RelaySrvAddress
+	// fails. Zero value if the peer did not advertise an IP.
+	RelaySrvIP netip.Addr
 	// SessionID is the unique identifier of the session, used to discard old messages
 	SessionID *ICESessionID
 }
@@ -217,8 +222,9 @@ func (h *Handshaker) buildOfferAnswer() OfferAnswer {
 		answer.SessionID = &sid
 	}
 
-	if addr, err := h.relay.RelayInstanceAddress(); err == nil {
+	if addr, ip, err := h.relay.RelayInstanceAddress(); err == nil {
 		answer.RelaySrvAddress = addr
+		answer.RelaySrvIP = ip
 	}
 
 	return answer

client/internal/peer/signaler.go

@@ -54,19 +54,19 @@ func (s *Signaler) signalOfferAnswer(offerAnswer OfferAnswer, remoteKey string,
 			log.Warnf("failed to get session ID bytes: %v", err)
 		}
 	}
-	msg, err := signal.MarshalCredential(
-		s.wgPrivateKey,
-		offerAnswer.WgListenPort,
-		remoteKey,
-		&signal.Credential{
+	msg, err := signal.MarshalCredential(s.wgPrivateKey, remoteKey, signal.CredentialPayload{
+		Type:         bodyType,
+		WgListenPort: offerAnswer.WgListenPort,
+		Credential: &signal.Credential{
 			UFrag: offerAnswer.IceCredentials.UFrag,
 			Pwd:   offerAnswer.IceCredentials.Pwd,
 		},
-		bodyType,
-		offerAnswer.RosenpassPubKey,
-		offerAnswer.RosenpassAddr,
-		offerAnswer.RelaySrvAddress,
-		sessionIDBytes)
+		RosenpassPubKey: offerAnswer.RosenpassPubKey,
+		RosenpassAddr:   offerAnswer.RosenpassAddr,
+		RelaySrvAddress: offerAnswer.RelaySrvAddress,
+		RelaySrvIP:      offerAnswer.RelaySrvIP,
+		SessionID:       sessionIDBytes,
+	})
 	if err != nil {
 		return err
 	}

client/internal/peer/status.go

@@ -919,7 +919,7 @@ func (d *Status) GetRelayStates() []relay.ProbeResult {
 
 	// if the server connection is not established then we will use the general address
 	// in case of connection we will use the instance specific address
-	instanceAddr, err := d.relayMgr.RelayInstanceAddress()
+	instanceAddr, _, err := d.relayMgr.RelayInstanceAddress()
 	if err != nil {
 		// TODO add their status
 		for _, r := range d.relayMgr.ServerURLs() {

client/internal/peer/worker_relay.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"net"
+	"net/netip"
 	"sync"
 	"sync/atomic"
 
@@ -53,15 +54,19 @@ func (w *WorkerRelay) OnNewOffer(remoteOfferAnswer *OfferAnswer) {
 	w.relaySupportedOnRemotePeer.Store(true)
 
 	// the relayManager will return with error in case if the connection has lost with relay server
-	currentRelayAddress, err := w.relayManager.RelayInstanceAddress()
+	currentRelayAddress, _, err := w.relayManager.RelayInstanceAddress()
 	if err != nil {
 		w.log.Errorf("failed to handle new offer: %s", err)
 		return
 	}
 
 	srv := w.preferredRelayServer(currentRelayAddress, remoteOfferAnswer.RelaySrvAddress)
+	var serverIP netip.Addr
+	if srv == remoteOfferAnswer.RelaySrvAddress {
+		serverIP = remoteOfferAnswer.RelaySrvIP
+	}
 
-	relayedConn, err := w.relayManager.OpenConn(w.peerCtx, srv, w.config.Key)
+	relayedConn, err := w.relayManager.OpenConn(w.peerCtx, srv, w.config.Key, serverIP)
 	if err != nil {
 		if errors.Is(err, relayClient.ErrConnAlreadyExists) {
 			w.log.Debugf("handled offer by reusing existing relay connection")
@@ -90,7 +95,7 @@ func (w *WorkerRelay) OnNewOffer(remoteOfferAnswer *OfferAnswer) {
 	})
 }
 
-func (w *WorkerRelay) RelayInstanceAddress() (string, error) {
+func (w *WorkerRelay) RelayInstanceAddress() (string, netip.Addr, error) {
 	return w.relayManager.RelayInstanceAddress()
 }