[client] Add GetSelectedClientRoutes to route manager and update DNS route check (#5802)

- DNS resolution broke after deselecting an exit node because the route checker used all client routes (including deselected ones) to decide how to forward upstream DNS
  queries
  - Added GetSelectedClientRoutes() to the route manager that filters out deselected exit nodes, and switched the DNS route checker to use it
  - Confirmed fix via device testing: after deselecting exit node, DNS queries now correctly use a regular network socket instead of binding to the utun interface

client/internal/engine.go

@@ -500,7 +500,7 @@ func (e *Engine) Start(netbirdConfig *mgmProto.NetbirdConfig, mgmtURL *url.URL)
 	e.routeManager.SetRouteChangeListener(e.mobileDep.NetworkChangeListener)
 
 	e.dnsServer.SetRouteChecker(func(ip netip.Addr) bool {
-		for _, routes := range e.routeManager.GetClientRoutes() {
+		for _, routes := range e.routeManager.GetSelectedClientRoutes() {
 			for _, r := range routes {
 				if r.Network.Contains(ip) {
 					return true

client/internal/routemanager/manager.go

@@ -52,6 +52,7 @@ type Manager interface {
 	TriggerSelection(route.HAMap)
 	GetRouteSelector() *routeselector.RouteSelector
 	GetClientRoutes() route.HAMap
+	GetSelectedClientRoutes() route.HAMap
 	GetClientRoutesWithNetID() map[route.NetID][]*route.Route
 	SetRouteChangeListener(listener listener.NetworkChangeListener)
 	InitialRouteRange() []string
@@ -465,6 +466,16 @@ func (m *DefaultManager) GetClientRoutes() route.HAMap {
 	return maps.Clone(m.clientRoutes)
 }
 
+// GetSelectedClientRoutes returns only the currently selected/active client routes,
+// filtering out deselected exit nodes. Use this instead of GetClientRoutes when checking
+// if traffic should be routed through the tunnel.
+func (m *DefaultManager) GetSelectedClientRoutes() route.HAMap {
+	m.mux.Lock()
+	defer m.mux.Unlock()
+
+	return m.routeSelector.FilterSelectedExitNodes(maps.Clone(m.clientRoutes))
+}
+
 // GetClientRoutesWithNetID returns the current routes from the route map, but the keys consist of the network ID only
 func (m *DefaultManager) GetClientRoutesWithNetID() map[route.NetID][]*route.Route {
 	m.mux.Lock()

client/internal/routemanager/mock.go

@@ -18,6 +18,7 @@ type MockManager struct {
 	TriggerSelectionFunc         func(haMap route.HAMap)
 	GetRouteSelectorFunc         func() *routeselector.RouteSelector
 	GetClientRoutesFunc          func() route.HAMap
+	GetSelectedClientRoutesFunc  func() route.HAMap
 	GetClientRoutesWithNetIDFunc func() map[route.NetID][]*route.Route
 	StopFunc                     func(manager *statemanager.Manager)
 }
@@ -61,7 +62,7 @@ func (m *MockManager) GetRouteSelector() *routeselector.RouteSelector {
 	return nil
 }
 
-// GetClientRoutes mock implementation of GetClientRoutes from Manager interface
+// GetClientRoutes mock implementation of GetClientRoutes from the Manager interface
 func (m *MockManager) GetClientRoutes() route.HAMap {
 	if m.GetClientRoutesFunc != nil {
 		return m.GetClientRoutesFunc()
@@ -69,6 +70,14 @@ func (m *MockManager) GetClientRoutes() route.HAMap {
 	return nil
 }
 
+// GetSelectedClientRoutes mock implementation of GetSelectedClientRoutes from the Manager interface
+func (m *MockManager) GetSelectedClientRoutes() route.HAMap {
+	if m.GetSelectedClientRoutesFunc != nil {
+		return m.GetSelectedClientRoutesFunc()
+	}
+	return nil
+}
+
 // GetClientRoutesWithNetID mock implementation of GetClientRoutesWithNetID from Manager interface
 func (m *MockManager) GetClientRoutesWithNetID() map[route.NetID][]*route.Route {
 	if m.GetClientRoutesWithNetIDFunc != nil {