[client] Pull fresh TUN settings on Android rebuild instead of pushing state

The Android TUN rebuild consumed state pushed through notifications and
a Java-side snapshot, and both sources were unreliable. The DNS
search-domain notifier fired OnNetworkChanged with an empty string,
which the rebuild handler treated as the new route list, so any search
domain change rebuilt the TUN with zero routes and cut all tunnel
traffic. The rebuild also reused the search domains cached at the last
establish, so search domain updates never reached the TUN at runtime.

Make the notification a pure trigger and let the Java side pull a fresh
snapshot instead. Expose GetTunSettings on the Android SDK client: it
returns the current TUN route ranges, derived on demand by the route
manager from the client routes, the exit-node selection and the fake IP
blocks, together with the DNS search domains. The route notifier keeps
only its last-announced baseline to suppress triggers for unchanged
syncs; the TUN route state is owned by the route manager. SearchDomains
now locks the DNS server mutex since the pull arrives from a Java
thread.

Requires the matching android-client change that switches recreateTUN
to the pull API.

client/android/client.go

@@ -57,6 +57,12 @@ type DnsReadyListener interface {
 	dns.ReadyListener
 }
 
+// TunSettings is a snapshot of the settings the TUN device is rebuilt with
+type TunSettings struct {
+	Routes        string
+	SearchDomains string
+}
+
 func init() {
 	formatter.SetLogcatFormatter(log.StandardLogger())
 }
@@ -240,6 +246,24 @@ func (c *Client) RenewTun(fd int) error {
 	return e.RenewTun(fd)
 }
 
+func (c *Client) GetTunSettings() (*TunSettings, error) {
+	cc := c.getConnectClient()
+	if cc == nil {
+		return nil, fmt.Errorf("engine not running")
+	}
+
+	e := cc.Engine()
+	if e == nil {
+		return nil, fmt.Errorf("engine not initialized")
+	}
+
+	routes, searchDomains := e.TunSettings()
+	return &TunSettings{
+		Routes:        strings.Join(routes, ";"),
+		SearchDomains: strings.Join(searchDomains, ";"),
+	}, nil
+}
+
 // DebugBundle generates a debug bundle, uploads it, and returns the upload key.
 // It works both with and without a running engine.
 func (c *Client) DebugBundle(platformFiles PlatformFiles, anonymize bool) (string, error) {

client/internal/connect.go

@@ -113,11 +113,14 @@ func (c *ConnectClient) RunOnAndroid(
 	stateFilePath string,
 	cacheDir string,
 ) error {
+	notifier := tunnelnotifier.New(networkChangeListener, nil)
+	defer notifier.Close()
+
 	// in case of non Android os these variables will be nil
 	mobileDependency := MobileDependency{
 		TunAdapter:            tunAdapter,
 		IFaceDiscover:         iFaceDiscover,
-		NetworkChangeListener: networkChangeListener,
+		NetworkChangeListener: notifier,
 		HostDNSAddresses:      dnsAddresses,
 		DnsReadyListener:      dnsReadyListener,
 		StateFilePath:         stateFilePath,

client/internal/dns/notifier.go

@@ -51,7 +51,5 @@ func (n *notifier) notify() {
 		return
 	}
 
-	go func(l listener.NetworkChangeListener) {
-		l.OnNetworkChanged("")
-	}(n.listener)
+	n.listener.OnNetworkChanged("")
 }

client/internal/dns/server.go

@@ -252,7 +252,7 @@ func NewDefaultServerPermanentUpstream(
 	ds.hostsDNSHolder.set(hostsDnsList)
 	ds.permanent = true
 	ds.currentConfig = dnsConfigToHostDNSConfig(config, ds.service.RuntimeIP(), ds.service.RuntimePort())
-	ds.searchDomainNotifier = newNotifier(ds.SearchDomains())
+	ds.searchDomainNotifier = newNotifier(ds.searchDomains())
 	ds.searchDomainNotifier.setListener(listener)
 	setServerDns(ds)
 	return ds
@@ -602,6 +602,12 @@ func (s *DefaultServer) UpdateDNSServer(serial uint64, update nbdns.Config) erro
 }
 
 func (s *DefaultServer) SearchDomains() []string {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+	return s.searchDomains()
+}
+
+func (s *DefaultServer) searchDomains() []string {
 	var searchDomains []string
 
 	for _, dConf := range s.currentConfig.Domains {
@@ -686,7 +692,7 @@ func (s *DefaultServer) applyConfiguration(update nbdns.Config) error {
 	}()
 
 	if s.searchDomainNotifier != nil {
-		s.searchDomainNotifier.onNewSearchDomains(s.SearchDomains())
+		s.searchDomainNotifier.onNewSearchDomains(s.searchDomains())
 	}
 
 	s.updateNSGroupStates(update.NameServerGroups)

client/internal/engine_tunsettings.go

@@ -0,0 +1,20 @@
+package internal
+
+func (e *Engine) TunSettings() ([]string, []string) {
+	e.syncMsgMux.Lock()
+	routeManager := e.routeManager
+	dnsServer := e.dnsServer
+	e.syncMsgMux.Unlock()
+
+	var routes []string
+	if routeManager != nil {
+		routes = routeManager.CurrentRouteRange()
+	}
+
+	var searchDomains []string
+	if dnsServer != nil {
+		searchDomains = dnsServer.SearchDomains()
+	}
+
+	return routes, searchDomains
+}

client/internal/routemanager/dnsinterceptor/handler.go

@@ -479,7 +479,7 @@ func (d *DnsInterceptor) removeDNATMappings(realPrefixes []netip.Prefix, logger
 
 // internalDnatFw checks if the firewall supports internal DNAT
 func (d *DnsInterceptor) internalDnatFw() (internalDNATer, bool) {
-	if d.firewall == nil || runtime.GOOS != "android" {
+	if d.firewall == nil || d.fakeIPManager == nil || runtime.GOOS != "android" {
 		return nil, false
 	}
 	fw, ok := d.firewall.(internalDNATer)

client/internal/routemanager/manager.go

@@ -9,6 +9,7 @@ import (
 	"net/url"
 	"runtime"
 	"slices"
+	"sort"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -63,6 +64,7 @@ type Manager interface {
 	GetClientRoutesWithNetID() map[route.NetID][]*route.Route
 	SetRouteChangeListener(listener listener.NetworkChangeListener)
 	InitialRouteRange() []string
+	CurrentRouteRange() []string
 	SetFirewall(firewall.Manager) error
 	SetDNSForwarderPort(port uint16)
 	ReconcilePeerAllowedIPs(peerKey string) error
@@ -165,31 +167,36 @@ func (m *DefaultManager) setupAndroidRoutes(config ManagerConfig) {
 	routesForComparison := slices.Clone(cr)
 
 	if config.DNSFeatureFlag {
-		m.fakeIPManager = fakeip.NewManager()
-
-		v4ID := uuid.NewString()
-		fakeIPRoute := &route.Route{
-			ID:          route.ID(v4ID),
-			Network:     m.fakeIPManager.GetFakeIPBlock(),
-			NetID:       route.NetID(v4ID),
-			Peer:        m.pubKey,
-			NetworkType: route.IPv4Network,
-		}
-		v6ID := uuid.NewString()
-		fakeIPv6Route := &route.Route{
-			ID:          route.ID(v6ID),
-			Network:     m.fakeIPManager.GetFakeIPv6Block(),
-			NetID:       route.NetID(v6ID),
-			Peer:        m.pubKey,
-			NetworkType: route.IPv6Network,
-		}
-		cr = append(cr, fakeIPRoute, fakeIPv6Route)
-		m.notifier.SetFakeIPRoutes([]*route.Route{fakeIPRoute, fakeIPv6Route})
+		cr = append(cr, m.enableFakeIPRoutes()...)
 	}
 
 	m.notifier.SetInitialClientRoutes(cr, routesForComparison)
 }
 
+func (m *DefaultManager) enableFakeIPRoutes() []*route.Route {
+	m.fakeIPManager = fakeip.NewManager()
+
+	v4ID := uuid.NewString()
+	fakeIPRoute := &route.Route{
+		ID:          route.ID(v4ID),
+		Network:     m.fakeIPManager.GetFakeIPBlock(),
+		NetID:       route.NetID(v4ID),
+		Peer:        m.pubKey,
+		NetworkType: route.IPv4Network,
+	}
+	v6ID := uuid.NewString()
+	fakeIPv6Route := &route.Route{
+		ID:          route.ID(v6ID),
+		Network:     m.fakeIPManager.GetFakeIPv6Block(),
+		NetID:       route.NetID(v6ID),
+		Peer:        m.pubKey,
+		NetworkType: route.IPv6Network,
+	}
+	fakeRoutes := []*route.Route{fakeIPRoute, fakeIPv6Route}
+	m.notifier.NotifyRouteChange()
+	return fakeRoutes
+}
+
 func (m *DefaultManager) setupRefCounters(useNoop bool) {
 	var once sync.Once
 	var wgIface *net.Interface
@@ -464,6 +471,9 @@ func (m *DefaultManager) UpdateRoutes(
 
 	var merr *multierror.Error
 	if !m.disableClientRoutes {
+		if runtime.GOOS == "android" && useNewDNSRoute && m.fakeIPManager == nil {
+			m.enableFakeIPRoutes()
+		}
 
 		// Update route selector based on management server's isSelected status
 		m.updateRouteSelectorFromManagement(clientRoutes)
@@ -505,6 +515,34 @@ func (m *DefaultManager) InitialRouteRange() []string {
 	return m.notifier.GetInitialRouteRanges()
 }
 
+// CurrentRouteRange returns the current TUN route list. It is used by mobile systems
+func (m *DefaultManager) CurrentRouteRange() []string {
+	m.mux.Lock()
+	defer m.mux.Unlock()
+
+	if m.disableClientRoutes {
+		return nil
+	}
+
+	filtered := m.routeSelector.FilterSelectedExitNodes(m.clientRoutes)
+	var nets []string
+	for _, routes := range filtered {
+		for _, r := range routes {
+			if r.IsDynamic() {
+				continue
+			}
+			nets = append(nets, r.NetString())
+		}
+	}
+
+	if m.fakeIPManager != nil {
+		nets = append(nets, m.fakeIPManager.GetFakeIPBlock().String(), m.fakeIPManager.GetFakeIPv6Block().String())
+	}
+
+	sort.Strings(nets)
+	return nets
+}
+
 // GetRouteSelector returns the route selector
 func (m *DefaultManager) GetRouteSelector() *routeselector.RouteSelector {
 	return m.routeSelector

client/internal/routemanager/mock.go

@@ -35,6 +35,11 @@ func (m *MockManager) InitialRouteRange() []string {
 	return nil
 }
 
+// CurrentRouteRange mock implementation of CurrentRouteRange from Manager interface
+func (m *MockManager) CurrentRouteRange() []string {
+	return nil
+}
+
 // UpdateRoutes mock implementation of UpdateRoutes from Manager interface
 func (m *MockManager) UpdateRoutes(updateSerial uint64, newRoutes map[route.ID]*route.Route, clientRoutes route.HAMap, useNewDNSRoute bool) error {
 	if m.UpdateRoutesFunc != nil {

client/internal/routemanager/notifier/notifier_android.go

@@ -6,7 +6,6 @@ import (
 	"net/netip"
 	"slices"
 	"sort"
-	"strings"
 	"sync"
 
 	"github.com/netbirdio/netbird/client/internal/listener"
@@ -14,12 +13,16 @@ import (
 )
 
 type Notifier struct {
-	initialRoutes []*route.Route
-	currentRoutes []*route.Route
-	fakeIPRoutes  []*route.Route
+	mu sync.Mutex
 
-	listener    listener.NetworkChangeListener
-	listenerMux sync.Mutex
+	initialRoutes []*route.Route
+	// currentRoutes is the last announced route set. It exists only to
+	// suppress noise: without it every network map sync would trigger the
+	// Java side, even when the routes did not change. The actual TUN route
+	// state is owned by the route manager and pulled from there.
+	currentRoutes []*route.Route
+
+	listener listener.NetworkChangeListener
 }
 
 func NewNotifier() *Notifier {
@@ -27,20 +30,23 @@ func NewNotifier() *Notifier {
 }
 
 func (n *Notifier) SetListener(listener listener.NetworkChangeListener) {
-	n.listenerMux.Lock()
-	defer n.listenerMux.Unlock()
+	n.mu.Lock()
+	defer n.mu.Unlock()
 	n.listener = listener
 }
 
 // SetInitialClientRoutes stores the initial route sets for TUN configuration.
 func (n *Notifier) SetInitialClientRoutes(initialRoutes []*route.Route, routesForComparison []*route.Route) {
+	n.mu.Lock()
+	defer n.mu.Unlock()
 	n.initialRoutes = filterStatic(initialRoutes)
 	n.currentRoutes = filterStatic(routesForComparison)
 }
 
-// SetFakeIPRoutes stores the fake IP routes to be included in every TUN rebuild.
-func (n *Notifier) SetFakeIPRoutes(routes []*route.Route) {
-	n.fakeIPRoutes = routes
+func (n *Notifier) NotifyRouteChange() {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	n.notifyLocked()
 }
 
 func (n *Notifier) OnNewRoutes(idMap route.HAMap) {
@@ -54,33 +60,37 @@ func (n *Notifier) OnNewRoutes(idMap route.HAMap) {
 		}
 	}
 
-	if !n.hasRouteDiff(n.currentRoutes, newRoutes) {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	if !hasRouteDiff(n.currentRoutes, newRoutes) {
 		return
 	}
 
 	n.currentRoutes = newRoutes
-	n.notify()
+	n.notifyLocked()
 }
 
 func (n *Notifier) OnNewPrefixes([]netip.Prefix) {
 	// Not used on Android
 }
 
-func (n *Notifier) notify() {
-	n.listenerMux.Lock()
-	defer n.listenerMux.Unlock()
+func (n *Notifier) notifyLocked() {
 	if n.listener == nil {
 		return
 	}
+	n.listener.OnNetworkChanged("")
+}
 
-	allRoutes := slices.Clone(n.currentRoutes)
-	allRoutes = append(allRoutes, n.fakeIPRoutes...)
+func (n *Notifier) GetInitialRouteRanges() []string {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	initialStrings := routesToStrings(n.initialRoutes)
+	sort.Strings(initialStrings)
+	return initialStrings
+}
 
-	routeStrings := n.routesToStrings(allRoutes)
-	sort.Strings(routeStrings)
-	go func(l listener.NetworkChangeListener) {
-		l.OnNetworkChanged(strings.Join(routeStrings, ","))
-	}(n.listener)
+func (n *Notifier) Close() {
+	// unused
 }
 
 func filterStatic(routes []*route.Route) []*route.Route {
@@ -93,7 +103,7 @@ func filterStatic(routes []*route.Route) []*route.Route {
 	return out
 }
 
-func (n *Notifier) routesToStrings(routes []*route.Route) []string {
+func routesToStrings(routes []*route.Route) []string {
 	nets := make([]string, 0, len(routes))
 	for _, r := range routes {
 		nets = append(nets, r.NetString())
@@ -101,25 +111,10 @@ func (n *Notifier) routesToStrings(routes []*route.Route) []string {
 	return nets
 }
 
-func (n *Notifier) hasRouteDiff(a []*route.Route, b []*route.Route) bool {
-	slices.SortFunc(a, func(x, y *route.Route) int {
-		return strings.Compare(x.NetString(), y.NetString())
-	})
-	slices.SortFunc(b, func(x, y *route.Route) int {
-		return strings.Compare(x.NetString(), y.NetString())
-	})
-
-	return !slices.EqualFunc(a, b, func(x, y *route.Route) bool {
-		return x.NetString() == y.NetString()
-	})
-}
-
-func (n *Notifier) GetInitialRouteRanges() []string {
-	initialStrings := n.routesToStrings(n.initialRoutes)
-	sort.Strings(initialStrings)
-	return initialStrings
-}
-
-func (n *Notifier) Close() {
-	// unused
+func hasRouteDiff(a []*route.Route, b []*route.Route) bool {
+	as := routesToStrings(a)
+	bs := routesToStrings(b)
+	sort.Strings(as)
+	sort.Strings(bs)
+	return !slices.Equal(as, bs)
 }

client/internal/routemanager/notifier/notifier_ios.go

@@ -33,7 +33,7 @@ func (n *Notifier) SetInitialClientRoutes([]*route.Route, []*route.Route) {
 	// iOS doesn't care about initial routes
 }
 
-func (n *Notifier) SetFakeIPRoutes([]*route.Route) {
+func (n *Notifier) NotifyRouteChange() {
 	// Not used on iOS
 }
 

client/internal/routemanager/notifier/notifier_other.go

@@ -23,7 +23,7 @@ func (n *Notifier) SetInitialClientRoutes([]*route.Route, []*route.Route) {
 	// Not used on non-mobile platforms
 }
 
-func (n *Notifier) SetFakeIPRoutes([]*route.Route) {
+func (n *Notifier) NotifyRouteChange() {
 	// Not used on non-mobile platforms
 }