Merge branch 'main' into reduce-embed-wg-pool

client/internal/engine.go

@@ -2477,6 +2477,8 @@ func convertToOfferAnswer(msg *sProto.Message) (*peer.OfferAnswer, error) {
 		}
 	}
 
+	relayIP := decodeRelayIP(msg.GetBody().GetRelayServerIP())
+
 	offerAnswer := peer.OfferAnswer{
 		IceCredentials: peer.IceCredentials{
 			UFrag: remoteCred.UFrag,
@@ -2487,7 +2489,23 @@ 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/notifier_test.go

@@ -8,6 +8,7 @@ import (
 type mocListener struct {
 	lastState int
 	wg        sync.WaitGroup
+	peersWg   sync.WaitGroup
 	peers     int
 }
 
@@ -33,6 +34,7 @@ func (l *mocListener) OnAddressChanged(host, addr string) {
 }
 func (l *mocListener) OnPeersListChanged(size int) {
 	l.peers = size
+	l.peersWg.Done()
 }
 
 func (l *mocListener) setWaiter() {
@@ -43,6 +45,14 @@ func (l *mocListener) wait() {
 	l.wg.Wait()
 }
 
+func (l *mocListener) setPeersWaiter() {
+	l.peersWg.Add(1)
+}
+
+func (l *mocListener) waitPeers() {
+	l.peersWg.Wait()
+}
+
 func Test_notifier_serverState(t *testing.T) {
 
 	type scenario struct {
@@ -72,11 +82,13 @@ func Test_notifier_serverState(t *testing.T) {
 func Test_notifier_SetListener(t *testing.T) {
 	listener := &mocListener{}
 	listener.setWaiter()
+	listener.setPeersWaiter()
 
 	n := newNotifier()
 	n.lastNotification = stateConnecting
 	n.setListener(listener)
 	listener.wait()
+	listener.waitPeers()
 	if listener.lastState != n.lastNotification {
 		t.Errorf("invalid state: %d, expected: %d", listener.lastState, n.lastNotification)
 	}
@@ -85,9 +97,14 @@ func Test_notifier_SetListener(t *testing.T) {
 func Test_notifier_RemoveListener(t *testing.T) {
 	listener := &mocListener{}
 	listener.setWaiter()
+	listener.setPeersWaiter()
 	n := newNotifier()
 	n.lastNotification = stateConnecting
 	n.setListener(listener)
+	// setListener replays cached state on a goroutine; wait for both the state
+	// and peers callbacks to finish so we don't race on listener.peers.
+	listener.wait()
+	listener.waitPeers()
 	n.removeListener()
 	n.peerListChanged(1)
 

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

@@ -320,10 +320,10 @@ func (d *Status) RemovePeer(peerPubKey string) error {
 // UpdatePeerState updates peer status
 func (d *Status) UpdatePeerState(receivedState State) error {
 	d.mux.Lock()
-	defer d.mux.Unlock()
 
 	peerState, ok := d.peers[receivedState.PubKey]
 	if !ok {
+		d.mux.Unlock()
 		return errors.New("peer doesn't exist")
 	}
 
@@ -343,23 +343,29 @@ func (d *Status) UpdatePeerState(receivedState State) error {
 
 	d.peers[receivedState.PubKey] = peerState
 
-	if hasConnStatusChanged(oldState, receivedState.ConnStatus) {
-		d.notifyPeerListChanged()
-	}
-
+	notifyList := hasConnStatusChanged(oldState, receivedState.ConnStatus)
 	// when we close the connection we will not notify the router manager
-	if receivedState.ConnStatus == StatusIdle {
-		d.notifyPeerStateChangeListeners(receivedState.PubKey)
+	notifyRouter := receivedState.ConnStatus == StatusIdle
+	routerSnapshot := d.snapshotRouterPeersLocked(receivedState.PubKey, notifyRouter)
+	numPeers := d.numOfPeers()
+
+	d.mux.Unlock()
+
+	if notifyList {
+		d.notifier.peerListChanged(numPeers)
+	}
+	if notifyRouter {
+		d.dispatchRouterPeers(receivedState.PubKey, routerSnapshot)
 	}
 	return nil
 }
 
 func (d *Status) AddPeerStateRoute(peer string, route string, resourceId route.ResID) error {
 	d.mux.Lock()
-	defer d.mux.Unlock()
 
 	peerState, ok := d.peers[peer]
 	if !ok {
+		d.mux.Unlock()
 		return errors.New("peer doesn't exist")
 	}
 
@@ -371,17 +377,20 @@ func (d *Status) AddPeerStateRoute(peer string, route string, resourceId route.R
 		d.routeIDLookup.AddRemoteRouteID(resourceId, pref)
 	}
 
+	numPeers := d.numOfPeers()
+	d.mux.Unlock()
+
 	// todo: consider to make sense of this notification or not
-	d.notifyPeerListChanged()
+	d.notifier.peerListChanged(numPeers)
 	return nil
 }
 
 func (d *Status) RemovePeerStateRoute(peer string, route string) error {
 	d.mux.Lock()
-	defer d.mux.Unlock()
 
 	peerState, ok := d.peers[peer]
 	if !ok {
+		d.mux.Unlock()
 		return errors.New("peer doesn't exist")
 	}
 
@@ -393,8 +402,11 @@ func (d *Status) RemovePeerStateRoute(peer string, route string) error {
 		d.routeIDLookup.RemoveRemoteRouteID(pref)
 	}
 
+	numPeers := d.numOfPeers()
+	d.mux.Unlock()
+
 	// todo: consider to make sense of this notification or not
-	d.notifyPeerListChanged()
+	d.notifier.peerListChanged(numPeers)
 	return nil
 }
 
@@ -410,10 +422,10 @@ func (d *Status) CheckRoutes(ip netip.Addr) ([]byte, bool) {
 
 func (d *Status) UpdatePeerICEState(receivedState State) error {
 	d.mux.Lock()
-	defer d.mux.Unlock()
 
 	peerState, ok := d.peers[receivedState.PubKey]
 	if !ok {
+		d.mux.Unlock()
 		return errors.New("peer doesn't exist")
 	}
 
@@ -431,22 +443,28 @@ func (d *Status) UpdatePeerICEState(receivedState State) error {
 
 	d.peers[receivedState.PubKey] = peerState
 
-	if hasConnStatusChanged(oldState, receivedState.ConnStatus) {
-		d.notifyPeerListChanged()
-	}
+	notifyList := hasConnStatusChanged(oldState, receivedState.ConnStatus)
+	notifyRouter := hasStatusOrRelayedChange(oldState, receivedState.ConnStatus, oldIsRelayed, receivedState.Relayed)
+	routerSnapshot := d.snapshotRouterPeersLocked(receivedState.PubKey, notifyRouter)
+	numPeers := d.numOfPeers()
 
-	if hasStatusOrRelayedChange(oldState, receivedState.ConnStatus, oldIsRelayed, receivedState.Relayed) {
-		d.notifyPeerStateChangeListeners(receivedState.PubKey)
+	d.mux.Unlock()
+
+	if notifyList {
+		d.notifier.peerListChanged(numPeers)
+	}
+	if notifyRouter {
+		d.dispatchRouterPeers(receivedState.PubKey, routerSnapshot)
 	}
 	return nil
 }
 
 func (d *Status) UpdatePeerRelayedState(receivedState State) error {
 	d.mux.Lock()
-	defer d.mux.Unlock()
 
 	peerState, ok := d.peers[receivedState.PubKey]
 	if !ok {
+		d.mux.Unlock()
 		return errors.New("peer doesn't exist")
 	}
 
@@ -461,22 +479,28 @@ func (d *Status) UpdatePeerRelayedState(receivedState State) error {
 
 	d.peers[receivedState.PubKey] = peerState
 
-	if hasConnStatusChanged(oldState, receivedState.ConnStatus) {
-		d.notifyPeerListChanged()
-	}
+	notifyList := hasConnStatusChanged(oldState, receivedState.ConnStatus)
+	notifyRouter := hasStatusOrRelayedChange(oldState, receivedState.ConnStatus, oldIsRelayed, receivedState.Relayed)
+	routerSnapshot := d.snapshotRouterPeersLocked(receivedState.PubKey, notifyRouter)
+	numPeers := d.numOfPeers()
 
-	if hasStatusOrRelayedChange(oldState, receivedState.ConnStatus, oldIsRelayed, receivedState.Relayed) {
-		d.notifyPeerStateChangeListeners(receivedState.PubKey)
+	d.mux.Unlock()
+
+	if notifyList {
+		d.notifier.peerListChanged(numPeers)
+	}
+	if notifyRouter {
+		d.dispatchRouterPeers(receivedState.PubKey, routerSnapshot)
 	}
 	return nil
 }
 
 func (d *Status) UpdatePeerRelayedStateToDisconnected(receivedState State) error {
 	d.mux.Lock()
-	defer d.mux.Unlock()
 
 	peerState, ok := d.peers[receivedState.PubKey]
 	if !ok {
+		d.mux.Unlock()
 		return errors.New("peer doesn't exist")
 	}
 
@@ -490,22 +514,28 @@ func (d *Status) UpdatePeerRelayedStateToDisconnected(receivedState State) error
 
 	d.peers[receivedState.PubKey] = peerState
 
-	if hasConnStatusChanged(oldState, receivedState.ConnStatus) {
-		d.notifyPeerListChanged()
-	}
+	notifyList := hasConnStatusChanged(oldState, receivedState.ConnStatus)
+	notifyRouter := hasStatusOrRelayedChange(oldState, receivedState.ConnStatus, oldIsRelayed, receivedState.Relayed)
+	routerSnapshot := d.snapshotRouterPeersLocked(receivedState.PubKey, notifyRouter)
+	numPeers := d.numOfPeers()
 
-	if hasStatusOrRelayedChange(oldState, receivedState.ConnStatus, oldIsRelayed, receivedState.Relayed) {
-		d.notifyPeerStateChangeListeners(receivedState.PubKey)
+	d.mux.Unlock()
+
+	if notifyList {
+		d.notifier.peerListChanged(numPeers)
+	}
+	if notifyRouter {
+		d.dispatchRouterPeers(receivedState.PubKey, routerSnapshot)
 	}
 	return nil
 }
 
 func (d *Status) UpdatePeerICEStateToDisconnected(receivedState State) error {
 	d.mux.Lock()
-	defer d.mux.Unlock()
 
 	peerState, ok := d.peers[receivedState.PubKey]
 	if !ok {
+		d.mux.Unlock()
 		return errors.New("peer doesn't exist")
 	}
 
@@ -522,12 +552,18 @@ func (d *Status) UpdatePeerICEStateToDisconnected(receivedState State) error {
 
 	d.peers[receivedState.PubKey] = peerState
 
-	if hasConnStatusChanged(oldState, receivedState.ConnStatus) {
-		d.notifyPeerListChanged()
-	}
+	notifyList := hasConnStatusChanged(oldState, receivedState.ConnStatus)
+	notifyRouter := hasStatusOrRelayedChange(oldState, receivedState.ConnStatus, oldIsRelayed, receivedState.Relayed)
+	routerSnapshot := d.snapshotRouterPeersLocked(receivedState.PubKey, notifyRouter)
+	numPeers := d.numOfPeers()
 
-	if hasStatusOrRelayedChange(oldState, receivedState.ConnStatus, oldIsRelayed, receivedState.Relayed) {
-		d.notifyPeerStateChangeListeners(receivedState.PubKey)
+	d.mux.Unlock()
+
+	if notifyList {
+		d.notifier.peerListChanged(numPeers)
+	}
+	if notifyRouter {
+		d.dispatchRouterPeers(receivedState.PubKey, routerSnapshot)
 	}
 	return nil
 }
@@ -594,17 +630,33 @@ func (d *Status) UpdatePeerSSHHostKey(peerPubKey string, sshHostKey []byte) erro
 // FinishPeerListModifications this event invoke the notification
 func (d *Status) FinishPeerListModifications() {
 	d.mux.Lock()
-	defer d.mux.Unlock()
 
 	if !d.peerListChangedForNotification {
+		d.mux.Unlock()
 		return
 	}
 	d.peerListChangedForNotification = false
 
-	d.notifyPeerListChanged()
+	numPeers := d.numOfPeers()
 
+	// snapshot per-peer router state to deliver after the lock is released
+	type routerDispatch struct {
+		peerID   string
+		snapshot map[string]RouterState
+	}
+	dispatches := make([]routerDispatch, 0, len(d.peers))
 	for key := range d.peers {
-		d.notifyPeerStateChangeListeners(key)
+		snapshot := d.snapshotRouterPeersLocked(key, true)
+		if snapshot != nil {
+			dispatches = append(dispatches, routerDispatch{peerID: key, snapshot: snapshot})
+		}
+	}
+
+	d.mux.Unlock()
+
+	d.notifier.peerListChanged(numPeers)
+	for _, rd := range dispatches {
+		d.dispatchRouterPeers(rd.peerID, rd.snapshot)
 	}
 }
 
@@ -655,10 +707,12 @@ func (d *Status) GetLocalPeerState() LocalPeerState {
 // UpdateLocalPeerState updates local peer status
 func (d *Status) UpdateLocalPeerState(localPeerState LocalPeerState) {
 	d.mux.Lock()
-	defer d.mux.Unlock()
-
 	d.localPeer = localPeerState
-	d.notifyAddressChanged()
+	fqdn := d.localPeer.FQDN
+	ip := d.localPeer.IP
+	d.mux.Unlock()
+
+	d.notifier.localAddressChanged(fqdn, ip)
 }
 
 // AddLocalPeerStateRoute adds a route to the local peer state
@@ -721,30 +775,36 @@ func (d *Status) CleanLocalPeerStateRoutes() {
 // CleanLocalPeerState cleans local peer status
 func (d *Status) CleanLocalPeerState() {
 	d.mux.Lock()
-	defer d.mux.Unlock()
-
 	d.localPeer = LocalPeerState{}
-	d.notifyAddressChanged()
+	fqdn := d.localPeer.FQDN
+	ip := d.localPeer.IP
+	d.mux.Unlock()
+
+	d.notifier.localAddressChanged(fqdn, ip)
 }
 
 // MarkManagementDisconnected sets ManagementState to disconnected
 func (d *Status) MarkManagementDisconnected(err error) {
 	d.mux.Lock()
-	defer d.mux.Unlock()
-	defer d.onConnectionChanged()
-
 	d.managementState = false
 	d.managementError = err
+	mgm := d.managementState
+	sig := d.signalState
+	d.mux.Unlock()
+
+	d.notifier.updateServerStates(mgm, sig)
 }
 
 // MarkManagementConnected sets ManagementState to connected
 func (d *Status) MarkManagementConnected() {
 	d.mux.Lock()
-	defer d.mux.Unlock()
-	defer d.onConnectionChanged()
-
 	d.managementState = true
 	d.managementError = nil
+	mgm := d.managementState
+	sig := d.signalState
+	d.mux.Unlock()
+
+	d.notifier.updateServerStates(mgm, sig)
 }
 
 // UpdateSignalAddress update the address of the signal server
@@ -778,21 +838,25 @@ func (d *Status) UpdateLazyConnection(enabled bool) {
 // MarkSignalDisconnected sets SignalState to disconnected
 func (d *Status) MarkSignalDisconnected(err error) {
 	d.mux.Lock()
-	defer d.mux.Unlock()
-	defer d.onConnectionChanged()
-
 	d.signalState = false
 	d.signalError = err
+	mgm := d.managementState
+	sig := d.signalState
+	d.mux.Unlock()
+
+	d.notifier.updateServerStates(mgm, sig)
 }
 
 // MarkSignalConnected sets SignalState to connected
 func (d *Status) MarkSignalConnected() {
 	d.mux.Lock()
-	defer d.mux.Unlock()
-	defer d.onConnectionChanged()
-
 	d.signalState = true
 	d.signalError = nil
+	mgm := d.managementState
+	sig := d.signalState
+	d.mux.Unlock()
+
+	d.notifier.updateServerStates(mgm, sig)
 }
 
 func (d *Status) UpdateRelayStates(relayResults []relay.ProbeResult) {
@@ -919,7 +983,7 @@ 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() {
@@ -1012,18 +1076,17 @@ func (d *Status) RemoveConnectionListener() {
 	d.notifier.removeListener()
 }
 
-func (d *Status) onConnectionChanged() {
-	d.notifier.updateServerStates(d.managementState, d.signalState)
-}
-
-// notifyPeerStateChangeListeners notifies route manager about the change in peer state
-func (d *Status) notifyPeerStateChangeListeners(peerID string) {
-	subs, ok := d.changeNotify[peerID]
-	if !ok {
-		return
+// snapshotRouterPeersLocked builds the RouterState map for a peer's subscribers.
+// Caller MUST hold d.mux. Returns nil when there are no subscribers for peerID
+// or when notify is false. The snapshot is consumed later by dispatchRouterPeers
+// outside the lock so the channel send cannot stall any d.mux holder.
+func (d *Status) snapshotRouterPeersLocked(peerID string, notify bool) map[string]RouterState {
+	if !notify {
+		return nil
+	}
+	if _, ok := d.changeNotify[peerID]; !ok {
+		return nil
 	}
-
-	// collect the relevant data for router peers
 	routerPeers := make(map[string]RouterState, len(d.changeNotify))
 	for pid := range d.changeNotify {
 		s, ok := d.peers[pid]
@@ -1031,13 +1094,35 @@ func (d *Status) notifyPeerStateChangeListeners(peerID string) {
 			log.Warnf("router peer not found in peers list: %s", pid)
 			continue
 		}
-
 		routerPeers[pid] = RouterState{
 			Status:  s.ConnStatus,
 			Relayed: s.Relayed,
 			Latency: s.Latency,
 		}
 	}
+	return routerPeers
+}
+
+// dispatchRouterPeers delivers a previously snapshotted router-state map to
+// the peer's subscribers. Caller MUST NOT hold d.mux. The method takes a
+// fresh, short read of d.changeNotify under the lock to grab subscriber
+// channels, then sends outside the lock so a slow consumer cannot block other
+// d.mux holders. The send itself stays blocking (only short-circuited by the
+// subscriber's context) so peer state transitions are not silently dropped.
+func (d *Status) dispatchRouterPeers(peerID string, routerPeers map[string]RouterState) {
+	if routerPeers == nil {
+		return
+	}
+
+	d.mux.Lock()
+	subsMap, ok := d.changeNotify[peerID]
+	subs := make([]*StatusChangeSubscription, 0, len(subsMap))
+	if ok {
+		for _, sub := range subsMap {
+			subs = append(subs, sub)
+		}
+	}
+	d.mux.Unlock()
 
 	for _, sub := range subs {
 		select {
@@ -1047,14 +1132,6 @@ func (d *Status) notifyPeerStateChangeListeners(peerID string) {
 	}
 }
 
-func (d *Status) notifyPeerListChanged() {
-	d.notifier.peerListChanged(d.numOfPeers())
-}
-
-func (d *Status) notifyAddressChanged() {
-	d.notifier.localAddressChanged(d.localPeer.FQDN, d.localPeer.IP)
-}
-
 func (d *Status) numOfPeers() int {
 	return len(d.peers) + len(d.offlinePeers)
 }

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()
 }
 

client/internal/portforward/pcp/nat.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"net/netip"
+	"runtime"
 	"sync"
 	"time"
 
@@ -177,7 +178,12 @@ func getDefaultGateway() (gateway net.IP, localIP net.IP, err error) {
 		return nil, nil, err
 	}
 
-	_, gateway, localIP, err = router.Route(net.IPv4zero)
+	dst := net.IPv4zero
+	if runtime.GOOS == "linux" {
+		// go-netroute v0.4.0 rejects unspecified destinations client-side on Linux.
+		dst = net.IPv4(0, 0, 0, 1)
+	}
+	_, gateway, localIP, err = router.Route(dst)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -196,7 +202,12 @@ func getDefaultGateway6() (gateway net.IP, localIP net.IP, err error) {
 		return nil, nil, err
 	}
 
-	_, gateway, localIP, err = router.Route(net.IPv6zero)
+	dst := net.IPv6zero
+	if runtime.GOOS == "linux" {
+		// ::2
+		dst = net.IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2}
+	}
+	_, gateway, localIP, err = router.Route(dst)
 	if err != nil {
 		return nil, nil, err
 	}

client/internal/routemanager/systemops/systemops_generic.go

@@ -342,6 +342,22 @@ func GetNextHop(ip netip.Addr) (Nexthop, error) {
 	if err != nil {
 		return Nexthop{}, fmt.Errorf("new netroute: %w", err)
 	}
+
+	// go-netroute v0.4.0 rejects unspecified destinations on Linux with a hard
+	// client-side check. Substitute the lowest non-loopback address so the
+	// lookup falls through to the default route (::1 / 127.0.0.1 would match
+	// loopback, ::/0.0.0.0 are unspec). BSD/Windows pass the query straight to
+	// the kernel and need no substitution.
+	if runtime.GOOS == "linux" && ip.IsUnspecified() {
+		if ip.Is6() {
+			// ::2
+			ip = netip.AddrFrom16([16]byte{15: 2})
+		} else {
+			// 0.0.0.1
+			ip = netip.AddrFrom4([4]byte{0, 0, 0, 1})
+		}
+	}
+
 	intf, gateway, preferredSrc, err := r.Route(ip.AsSlice())
 	if err != nil {
 		log.Debugf("Failed to get route for %s: %v", ip, err)

client/internal/routemanager/systemops/systemops_generic_test.go

@@ -354,9 +354,13 @@ func TestAddRouteToNonVPNIntf(t *testing.T) {
 			require.NoError(t, err, "Should be able to get IPv4 default route")
 			t.Logf("Initial IPv4 next hop: %s", initialNextHopV4)
 
+			if testCase.prefix.Addr().Is6() && !testCase.expectError {
+				ensureIPv6DefaultRoute(t)
+			}
+
 			initialNextHopV6, err := GetNextHop(netip.IPv6Unspecified())
 			if testCase.prefix.Addr().Is6() &&
-				(errors.Is(err, vars.ErrRouteNotFound) || initialNextHopV6.Intf != nil && strings.HasPrefix(initialNextHopV6.Intf.Name, "utun")) {
+				initialNextHopV6.Intf != nil && strings.HasPrefix(initialNextHopV6.Intf.Name, "utun") {
 				t.Skip("Skipping test as no ipv6 default route is available")
 			}
 			if err != nil && !errors.Is(err, vars.ErrRouteNotFound) {

client/internal/routemanager/systemops/v6route_bsd_test.go

@@ -0,0 +1,30 @@
+//go:build darwin || dragonfly || freebsd || netbsd || openbsd
+
+package systemops
+
+import (
+	"bytes"
+	"os/exec"
+	"testing"
+)
+
+// ensureIPv6DefaultRoute installs an IPv6 default route via the loopback
+// interface so route lookups for global IPv6 prefixes resolve in environments
+// without v6 connectivity. If a default already exists it is left alone.
+func ensureIPv6DefaultRoute(t *testing.T) {
+	t.Helper()
+
+	out, err := exec.Command("route", "-6", "add", "default", "-iface", "lo0").CombinedOutput()
+	if err != nil {
+		// Existing default; nothing to install or clean up.
+		if bytes.Contains(out, []byte("route already in table")) {
+			return
+		}
+		t.Skipf("install IPv6 fallback default route: %v: %s", err, out)
+	}
+	t.Cleanup(func() {
+		if out, err := exec.Command("route", "-6", "delete", "default").CombinedOutput(); err != nil {
+			t.Logf("delete IPv6 fallback default route: %v: %s", err, out)
+		}
+	})
+}

client/internal/routemanager/systemops/v6route_linux_test.go

@@ -0,0 +1,41 @@
+//go:build linux && !android
+
+package systemops
+
+import (
+	"errors"
+	"net"
+	"syscall"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/vishvananda/netlink"
+)
+
+// ensureIPv6DefaultRoute installs a low-preference IPv6 default route via the
+// loopback interface so route lookups for global IPv6 prefixes resolve in
+// environments without v6 connectivity. Any pre-existing default route wins
+// because of its lower metric.
+func ensureIPv6DefaultRoute(t *testing.T) {
+	t.Helper()
+
+	lo, err := netlink.LinkByName("lo")
+	require.NoError(t, err, "find loopback interface")
+
+	route := &netlink.Route{
+		Dst:       &net.IPNet{IP: net.IPv6zero, Mask: net.CIDRMask(0, 128)},
+		LinkIndex: lo.Attrs().Index,
+		Priority:  1 << 20,
+	}
+	if err := netlink.RouteAdd(route); err != nil {
+		if errors.Is(err, syscall.EEXIST) {
+			return
+		}
+		t.Skipf("install IPv6 fallback default route: %v", err)
+	}
+	t.Cleanup(func() {
+		if err := netlink.RouteDel(route); err != nil && !errors.Is(err, syscall.ESRCH) {
+			t.Logf("delete IPv6 fallback default route: %v", err)
+		}
+	})
+}

client/internal/routemanager/systemops/v6route_windows_test.go

@@ -0,0 +1,34 @@
+//go:build windows
+
+package systemops
+
+import (
+	"bytes"
+	"os/exec"
+	"testing"
+)
+
+const loopbackIfaceWindows = "Loopback Pseudo-Interface 1"
+
+// ensureIPv6DefaultRoute installs an IPv6 default route via the loopback
+// interface so route lookups for global IPv6 prefixes resolve in environments
+// without v6 connectivity. If a default already exists it is left alone.
+func ensureIPv6DefaultRoute(t *testing.T) {
+	t.Helper()
+
+	script := `New-NetRoute -DestinationPrefix "::/0" -InterfaceAlias "` + loopbackIfaceWindows + `" -RouteMetric 9999 -PolicyStore ActiveStore -ErrorAction Stop`
+	out, err := exec.Command("powershell", "-Command", script).CombinedOutput()
+	if err != nil {
+		// Existing default; nothing to install or clean up.
+		if bytes.Contains(out, []byte("already exists")) {
+			return
+		}
+		t.Skipf("install IPv6 fallback default route: %v: %s", err, out)
+	}
+	t.Cleanup(func() {
+		script := `Remove-NetRoute -DestinationPrefix "::/0" -InterfaceAlias "` + loopbackIfaceWindows + `" -Confirm:$false -ErrorAction Stop`
+		if out, err := exec.Command("powershell", "-Command", script).CombinedOutput(); err != nil {
+			t.Logf("delete IPv6 fallback default route: %v: %s", err, out)
+		}
+	})
+}

client/internal/wg_iface_monitor.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"net"
 	"runtime"
-	"time"
 
 	log "github.com/sirupsen/logrus"
 
@@ -28,6 +27,10 @@ func NewWGIfaceMonitor() *WGIfaceMonitor {
 
 // Start begins monitoring the WireGuard interface.
 // It relies on the provided context cancellation to stop.
+//
+// On Linux the watcher is event-driven (RTNLGRP_LINK netlink subscription)
+// to avoid the allocation churn of repeatedly dumping the kernel link
+// table; on other platforms it falls back to a low-frequency poll.
 func (m *WGIfaceMonitor) Start(ctx context.Context, ifaceName string) (shouldRestart bool, err error) {
 	defer close(m.done)
 
@@ -56,31 +59,7 @@ func (m *WGIfaceMonitor) Start(ctx context.Context, ifaceName string) (shouldRes
 
 	log.Infof("Interface monitor: watching %s (index: %d)", ifaceName, expectedIndex)
 
-	ticker := time.NewTicker(2 * time.Second)
-	defer ticker.Stop()
-
-	for {
-		select {
-		case <-ctx.Done():
-			log.Infof("Interface monitor: stopped for %s", ifaceName)
-			return false, fmt.Errorf("wg interface monitor stopped: %v", ctx.Err())
-		case <-ticker.C:
-			currentIndex, err := getInterfaceIndex(ifaceName)
-			if err != nil {
-				// Interface was deleted
-				log.Infof("Interface monitor: %s deleted", ifaceName)
-				return true, fmt.Errorf("interface %s deleted: %w", ifaceName, err)
-			}
-
-			// Check if interface index changed (interface was recreated)
-			if currentIndex != expectedIndex {
-				log.Infof("Interface monitor: %s recreated (index changed from %d to %d), restarting engine",
-					ifaceName, expectedIndex, currentIndex)
-				return true, nil
-			}
-		}
-	}
-
+	return watchInterface(ctx, ifaceName, expectedIndex)
 }
 
 // getInterfaceIndex returns the index of a network interface by name.

client/internal/wg_iface_monitor_linux.go

@@ -0,0 +1,134 @@
+//go:build linux
+
+package internal
+
+import (
+	"context"
+	"fmt"
+	"syscall"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/vishvananda/netlink"
+)
+
+// watchInterface uses an RTNLGRP_LINK netlink subscription to detect
+// deletion or recreation of the WireGuard interface.
+//
+// The previous implementation polled net.InterfaceByName every 2 s, which
+// on Linux issues syscall.NetlinkRIB(RTM_GETLINK, ...) and dumps the
+// entire kernel link table on every call. On hosts with many veth
+// interfaces (containers, bridges) the resulting allocation churn was on
+// the order of ~1 GB/day from this single ticker, which on small ARM
+// hosts manifested as a slow RSS climb (see netbirdio/netbird#3678).
+//
+// The event-driven version below allocates only when the kernel actually
+// publishes a link event for the tracked interface — typically zero
+// allocations between events.
+func watchInterface(ctx context.Context, ifaceName string, expectedIndex int) (bool, error) {
+	done := make(chan struct{})
+	defer close(done)
+
+	// Buffer the channel to absorb event bursts (e.g. when many veth
+	// pairs are created/destroyed at once by container runtimes).
+	linkChan := make(chan netlink.LinkUpdate, 32)
+	if err := netlink.LinkSubscribe(linkChan, done); err != nil {
+		// Return shouldRestart=true so the engine recovers monitoring
+		// via triggerClientRestart instead of silently losing it for
+		// the rest of the process lifetime.
+		return true, fmt.Errorf("subscribe to link updates: %w", err)
+	}
+
+	// Race window: the interface could have been deleted (or recreated)
+	// between the initial getInterfaceIndex() in Start and LinkSubscribe
+	// completing its handshake with the kernel. Re-check explicitly so we
+	// do not block forever waiting for an event that already fired.
+	if currentIndex, err := getInterfaceIndex(ifaceName); err != nil {
+		log.Infof("Interface monitor: %s deleted before subscription completed", ifaceName)
+		return true, fmt.Errorf("interface %s deleted: %w", ifaceName, err)
+	} else if currentIndex != expectedIndex {
+		log.Infof("Interface monitor: %s recreated (index changed from %d to %d) before subscription completed",
+			ifaceName, expectedIndex, currentIndex)
+		return true, nil
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			log.Infof("Interface monitor: stopped for %s", ifaceName)
+			return false, fmt.Errorf("wg interface monitor stopped: %w", ctx.Err())
+
+		case update, ok := <-linkChan:
+			if !ok {
+				// The vishvananda/netlink subscription goroutine closes
+				// the channel on receive errors. Signal the engine to
+				// restart so monitoring is re-established instead of
+				// silently ending.
+				log.Warnf("Interface monitor: link subscription channel closed unexpectedly for %s", ifaceName)
+				return true, fmt.Errorf("link subscription channel closed unexpectedly")
+			}
+			if restart, err := inspectLinkEvent(update, ifaceName, expectedIndex); restart {
+				return true, err
+			}
+		}
+	}
+}
+
+// inspectLinkEvent classifies a single netlink link update against the
+// tracked WireGuard interface. It returns (true, err) when the engine
+// should restart monitoring; (false, nil) means the event is unrelated
+// and the caller should keep waiting.
+//
+// The error component, when non-nil, describes the kernel-side reason
+// (deletion or rename); the recreation case returns (true, nil) since
+// no error condition is reported.
+func inspectLinkEvent(update netlink.LinkUpdate, ifaceName string, expectedIndex int) (bool, error) {
+	eventIndex := int(update.Index)
+	eventName := ""
+	if attrs := update.Attrs(); attrs != nil {
+		eventName = attrs.Name
+	}
+
+	switch update.Header.Type {
+	case syscall.RTM_DELLINK:
+		return inspectDelLink(eventIndex, ifaceName, expectedIndex)
+	case syscall.RTM_NEWLINK:
+		return inspectNewLink(eventIndex, eventName, ifaceName, expectedIndex)
+	}
+	return false, nil
+}
+
+// inspectDelLink reports a restart when an RTM_DELLINK arrives for the
+// tracked interface index.
+func inspectDelLink(eventIndex int, ifaceName string, expectedIndex int) (bool, error) {
+	if eventIndex != expectedIndex {
+		return false, nil
+	}
+	log.Infof("Interface monitor: %s deleted", ifaceName)
+	return true, fmt.Errorf("interface %s deleted", ifaceName)
+}
+
+// inspectNewLink reports a restart when an RTM_NEWLINK either:
+//
+//  1. Introduces a link with our name at a different index (recreation
+//     after a delete), or
+//
+//  2. Reports a link still at our index but with a different name
+//     (in-place rename). The previous polling implementation caught
+//     this implicitly because net.InterfaceByName(ifaceName) would
+//     start failing; the event-driven version has to test it.
+//
+// Same name + same index is just a flag/state change on the existing
+// interface and is ignored.
+func inspectNewLink(eventIndex int, eventName, ifaceName string, expectedIndex int) (bool, error) {
+	if eventName == ifaceName && eventIndex != expectedIndex {
+		log.Infof("Interface monitor: %s recreated (index changed from %d to %d), restarting engine",
+			ifaceName, expectedIndex, eventIndex)
+		return true, nil
+	}
+	if eventIndex == expectedIndex && eventName != "" && eventName != ifaceName {
+		log.Infof("Interface monitor: %s renamed to %s (index %d), restarting engine",
+			ifaceName, eventName, expectedIndex)
+		return true, fmt.Errorf("interface %s renamed to %s", ifaceName, eventName)
+	}
+	return false, nil
+}

client/internal/wg_iface_monitor_other.go

@@ -0,0 +1,56 @@
+//go:build !linux
+
+package internal
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// watchInterface polls net.InterfaceByName at a fixed interval to detect
+// deletion or recreation of the WireGuard interface.
+//
+// This is the fallback used on non-Linux desktop and server platforms
+// (darwin, windows, freebsd). It is also compiled on android and ios so
+// the package builds on every supported GOOS, but it is never reached
+// at runtime there because Start() in wg_iface_monitor.go exits early
+// on mobile platforms.
+//
+// The Linux build (see wg_iface_monitor_linux.go) uses an event-driven
+// RTNLGRP_LINK netlink subscription instead, because on Linux
+// net.InterfaceByName issues syscall.NetlinkRIB(RTM_GETLINK, ...) which
+// dumps the entire kernel link table on every call and produces
+// significant allocation churn (netbirdio/netbird#3678).
+//
+// Windows is also reported in #3678 as affected by RSS climb. A future
+// follow-up could implement an event-driven watcher there using
+// NotifyIpInterfaceChange from iphlpapi.
+func watchInterface(ctx context.Context, ifaceName string, expectedIndex int) (bool, error) {
+	ticker := time.NewTicker(2 * time.Second)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			log.Infof("Interface monitor: stopped for %s", ifaceName)
+			return false, fmt.Errorf("wg interface monitor stopped: %w", ctx.Err())
+		case <-ticker.C:
+			currentIndex, err := getInterfaceIndex(ifaceName)
+			if err != nil {
+				// Interface was deleted
+				log.Infof("Interface monitor: %s deleted", ifaceName)
+				return true, fmt.Errorf("interface %s deleted: %w", ifaceName, err)
+			}
+
+			// Check if interface index changed (interface was recreated)
+			if currentIndex != expectedIndex {
+				log.Infof("Interface monitor: %s recreated (index changed from %d to %d), restarting engine",
+					ifaceName, expectedIndex, currentIndex)
+				return true, nil
+			}
+		}
+	}
+}