Refactor route manager to use sync.Once for wgInterface access

- Added `toInterface` helper to ensure `wgInterface.ToInterface()` is called once.
- Updated route addition/removal methods to use `toInterface` for efficiency.

client/internal/dns/host_windows.go

@@ -42,6 +42,10 @@ const (
 	dnsPolicyConfigConfigOptionsKey     = "ConfigOptions"
 	dnsPolicyConfigConfigOptionsValue   = 0x8
 
+	// NRPT rules cannot handle more than 50 domains per rule.
+	// This is an undocumented Windows limitation.
+	nrptMaxDomainsPerRule = 50
+
 	interfaceConfigPath          = `SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces`
 	interfaceConfigNameServerKey = "NameServer"
 	interfaceConfigSearchListKey = "SearchList"
@@ -239,23 +243,32 @@ func (r *registryConfigurator) addDNSSetupForAll(ip netip.Addr) error {
 func (r *registryConfigurator) addDNSMatchPolicy(domains []string, ip netip.Addr) (int, error) {
 	// if the gpo key is present, we need to put our DNS settings there, otherwise our config might be ignored
 	// see https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-gpnrpt/8cc31cb9-20cb-4140-9e85-3e08703b4745
-	for i, domain := range domains {
-		localPath := fmt.Sprintf("%s-%d", dnsPolicyConfigMatchPath, i)
-		gpoPath := fmt.Sprintf("%s-%d", gpoDnsPolicyConfigMatchPath, i)
 
-		singleDomain := []string{domain}
+	// NRPT rules have an undocumented restriction: each rule can only handle up to 50 domains.
+	// We need to batch domains into chunks and create one NRPT rule per batch.
+	ruleIndex := 0
+	for i := 0; i < len(domains); i += nrptMaxDomainsPerRule {
+		end := i + nrptMaxDomainsPerRule
+		if end > len(domains) {
+			end = len(domains)
+		}
+		batchDomains := domains[i:end]
 
-		if err := r.configureDNSPolicy(localPath, singleDomain, ip); err != nil {
-			return i, fmt.Errorf("configure DNS Local policy for domain %s: %w", domain, err)
+		localPath := fmt.Sprintf("%s-%d", dnsPolicyConfigMatchPath, ruleIndex)
+		gpoPath := fmt.Sprintf("%s-%d", gpoDnsPolicyConfigMatchPath, ruleIndex)
+
+		if err := r.configureDNSPolicy(localPath, batchDomains, ip); err != nil {
+			return ruleIndex, fmt.Errorf("configure DNS Local policy for rule %d: %w", ruleIndex, err)
 		}
 
 		if r.gpo {
-			if err := r.configureDNSPolicy(gpoPath, singleDomain, ip); err != nil {
-				return i, fmt.Errorf("configure gpo DNS policy: %w", err)
+			if err := r.configureDNSPolicy(gpoPath, batchDomains, ip); err != nil {
+				return ruleIndex, fmt.Errorf("configure gpo DNS policy for rule %d: %w", ruleIndex, err)
 			}
 		}
 
-		log.Debugf("added NRPT entry for domain: %s", domain)
+		log.Debugf("added NRPT rule %d with %d domains", ruleIndex, len(batchDomains))
+		ruleIndex++
 	}
 
 	if r.gpo {
@@ -264,8 +277,8 @@ func (r *registryConfigurator) addDNSMatchPolicy(domains []string, ip netip.Addr
 		}
 	}
 
-	log.Infof("added %d separate NRPT entries. Domain list: %s", len(domains), domains)
-	return len(domains), nil
+	log.Infof("added %d NRPT rules for %d domains. Domain list: %s", ruleIndex, len(domains), domains)
+	return ruleIndex, nil
 }
 
 func (r *registryConfigurator) configureDNSPolicy(policyPath string, domains []string, ip netip.Addr) error {

client/internal/dns/host_windows_test.go

@@ -97,6 +97,107 @@ func registryKeyExists(path string) (bool, error) {
 }
 
 func cleanupRegistryKeys(*testing.T) {
-	cfg := &registryConfigurator{nrptEntryCount: 10}
+	// Clean up more entries to account for batching tests with many domains
+	cfg := &registryConfigurator{nrptEntryCount: 20}
 	_ = cfg.removeDNSMatchPolicies()
 }
+
+// TestNRPTDomainBatching verifies that domains are correctly batched into NRPT rules
+// with a maximum of 50 domains per rule (Windows limitation).
+func TestNRPTDomainBatching(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping registry integration test in short mode")
+	}
+
+	defer cleanupRegistryKeys(t)
+	cleanupRegistryKeys(t)
+
+	testIP := netip.MustParseAddr("100.64.0.1")
+
+	// Create a test interface registry key so updateSearchDomains doesn't fail
+	testGUID := "{12345678-1234-1234-1234-123456789ABC}"
+	interfacePath := `SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\` + testGUID
+	testKey, _, err := registry.CreateKey(registry.LOCAL_MACHINE, interfacePath, registry.SET_VALUE)
+	require.NoError(t, err, "Should create test interface registry key")
+	testKey.Close()
+	defer func() {
+		_ = registry.DeleteKey(registry.LOCAL_MACHINE, interfacePath)
+	}()
+
+	cfg := &registryConfigurator{
+		guid: testGUID,
+		gpo:  false,
+	}
+
+	testCases := []struct {
+		name              string
+		domainCount       int
+		expectedRuleCount int
+	}{
+		{
+			name:              "Less than 50 domains (single rule)",
+			domainCount:       30,
+			expectedRuleCount: 1,
+		},
+		{
+			name:              "Exactly 50 domains (single rule)",
+			domainCount:       50,
+			expectedRuleCount: 1,
+		},
+		{
+			name:              "51 domains (two rules)",
+			domainCount:       51,
+			expectedRuleCount: 2,
+		},
+		{
+			name:              "100 domains (two rules)",
+			domainCount:       100,
+			expectedRuleCount: 2,
+		},
+		{
+			name:              "125 domains (three rules: 50+50+25)",
+			domainCount:       125,
+			expectedRuleCount: 3,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// Clean up before each subtest
+			cleanupRegistryKeys(t)
+
+			// Generate domains
+			domains := make([]DomainConfig, tc.domainCount)
+			for i := 0; i < tc.domainCount; i++ {
+				domains[i] = DomainConfig{
+					Domain:    fmt.Sprintf("domain%d.com", i+1),
+					MatchOnly: true,
+				}
+			}
+
+			config := HostDNSConfig{
+				ServerIP: testIP,
+				Domains:  domains,
+			}
+
+			err := cfg.applyDNSConfig(config, nil)
+			require.NoError(t, err)
+
+			// Verify that exactly expectedRuleCount rules were created
+			assert.Equal(t, tc.expectedRuleCount, cfg.nrptEntryCount,
+				"Should create %d NRPT rules for %d domains", tc.expectedRuleCount, tc.domainCount)
+
+			// Verify all expected rules exist
+			for i := 0; i < tc.expectedRuleCount; i++ {
+				exists, err := registryKeyExists(fmt.Sprintf("%s-%d", dnsPolicyConfigMatchPath, i))
+				require.NoError(t, err)
+				assert.True(t, exists, "NRPT rule %d should exist", i)
+			}
+
+			// Verify no extra rules were created
+			exists, err := registryKeyExists(fmt.Sprintf("%s-%d", dnsPolicyConfigMatchPath, tc.expectedRuleCount))
+			require.NoError(t, err)
+			assert.False(t, exists, "No NRPT rule should exist at index %d", tc.expectedRuleCount)
+		})
+	}
+}

client/internal/dns/mock_server.go

@@ -84,3 +84,13 @@ func (m *MockServer) UpdateServerConfig(domains dnsconfig.ServerDomains) error {
 func (m *MockServer) PopulateManagementDomain(mgmtURL *url.URL) error {
 	return nil
 }
+
+// BeginBatch mock implementation of BeginBatch from Server interface
+func (m *MockServer) BeginBatch() {
+	// Mock implementation - no-op
+}
+
+// EndBatch mock implementation of EndBatch from Server interface
+func (m *MockServer) EndBatch() {
+	// Mock implementation - no-op
+}

client/internal/dns/server.go

@@ -41,6 +41,8 @@ type IosDnsManager interface {
 type Server interface {
 	RegisterHandler(domains domain.List, handler dns.Handler, priority int)
 	DeregisterHandler(domains domain.List, priority int)
+	BeginBatch()
+	EndBatch()
 	Initialize() error
 	Stop()
 	DnsIP() netip.Addr
@@ -83,6 +85,7 @@ type DefaultServer struct {
 	currentConfigHash  uint64
 	handlerChain       *HandlerChain
 	extraDomains       map[domain.Domain]int
+	batchMode          bool
 
 	mgmtCacheResolver *mgmt.Resolver
 
@@ -230,7 +233,9 @@ func (s *DefaultServer) RegisterHandler(domains domain.List, handler dns.Handler
 		// convert to zone with simple ref counter
 		s.extraDomains[toZone(domain)]++
 	}
-	s.applyHostConfig()
+	if !s.batchMode {
+		s.applyHostConfig()
+	}
 }
 
 func (s *DefaultServer) registerHandler(domains []string, handler dns.Handler, priority int) {
@@ -259,6 +264,28 @@ func (s *DefaultServer) DeregisterHandler(domains domain.List, priority int) {
 			delete(s.extraDomains, zone)
 		}
 	}
+	if !s.batchMode {
+		s.applyHostConfig()
+	}
+}
+
+// BeginBatch starts batch mode for DNS handler registration/deregistration.
+// In batch mode, applyHostConfig() is not called after each handler operation,
+// allowing multiple handlers to be registered/deregistered efficiently.
+// Must be followed by EndBatch() to apply the accumulated changes.
+func (s *DefaultServer) BeginBatch() {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+	log.Infof("DNS batch mode enabled")
+	s.batchMode = true
+}
+
+// EndBatch ends batch mode and applies all accumulated DNS configuration changes.
+func (s *DefaultServer) EndBatch() {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+	log.Infof("DNS batch mode disabled, applying accumulated changes")
+	s.batchMode = false
 	s.applyHostConfig()
 }
 
@@ -508,7 +535,9 @@ func (s *DefaultServer) applyConfiguration(update nbdns.Config) error {
 		s.currentConfig.RouteAll = false
 	}
 
-	s.applyHostConfig()
+	if !s.batchMode {
+		s.applyHostConfig()
+	}
 
 	s.shutdownWg.Add(1)
 	go func() {
@@ -872,7 +901,9 @@ func (s *DefaultServer) upstreamCallbacks(
 			}
 		}
 
-		s.applyHostConfig()
+		if !s.batchMode {
+			s.applyHostConfig()
+		}
 
 		go func() {
 			if err := s.stateManager.PersistState(s.ctx); err != nil {
@@ -907,7 +938,9 @@ func (s *DefaultServer) upstreamCallbacks(
 			s.registerHandler([]string{nbdns.RootZone}, handler, priority)
 		}
 
-		s.applyHostConfig()
+		if !s.batchMode {
+			s.applyHostConfig()
+		}
 
 		s.updateNSState(nsGroup, nil, true)
 	}

client/internal/dns/server_export_test.go

@@ -18,7 +18,12 @@ func TestGetServerDns(t *testing.T) {
 		t.Errorf("invalid dns server instance: %s", err)
 	}
 
-	if srvB != srv {
+	mockSrvB, ok := srvB.(*MockServer)
+	if !ok {
+		t.Errorf("returned server is not a MockServer")
+	}
+
+	if mockSrvB != srv {
 		t.Errorf("mismatch dns instances")
 	}
 }

client/internal/engine.go

@@ -828,6 +828,10 @@ func (e *Engine) handleAutoUpdateVersion(autoUpdateSettings *mgmProto.AutoUpdate
 }
 
 func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
+	started := time.Now()
+	defer func() {
+		log.Infof("sync finished in %s", time.Since(started))
+	}()
 	e.syncMsgMux.Lock()
 	defer e.syncMsgMux.Unlock()
 

client/internal/routemanager/manager.go

@@ -173,12 +173,21 @@ func (m *DefaultManager) setupAndroidRoutes(config ManagerConfig) {
 }
 
 func (m *DefaultManager) setupRefCounters(useNoop bool) {
+	var once sync.Once
+	var wgIface *net.Interface
+	toInterface := func() *net.Interface {
+		once.Do(func() {
+			wgIface = m.wgInterface.ToInterface()
+		})
+		return wgIface
+	}
+
 	m.routeRefCounter = refcounter.New(
 		func(prefix netip.Prefix, _ struct{}) (struct{}, error) {
-			return struct{}{}, m.sysOps.AddVPNRoute(prefix, m.wgInterface.ToInterface())
+			return struct{}{}, m.sysOps.AddVPNRoute(prefix, toInterface())
 		},
 		func(prefix netip.Prefix, _ struct{}) error {
-			return m.sysOps.RemoveVPNRoute(prefix, m.wgInterface.ToInterface())
+			return m.sysOps.RemoveVPNRoute(prefix, toInterface())
 		},
 	)
 
@@ -337,6 +346,13 @@ func (m *DefaultManager) updateSystemRoutes(newRoutes route.HAMap) error {
 	}
 
 	var merr *multierror.Error
+
+	// Begin batch mode to avoid calling applyHostConfig() after each DNS handler operation
+	if m.dnsServer != nil {
+		m.dnsServer.BeginBatch()
+		defer m.dnsServer.EndBatch()
+	}
+
 	for id, handler := range toRemove {
 		if err := handler.RemoveRoute(); err != nil {
 			merr = multierror.Append(merr, fmt.Errorf("remove route %s: %w", handler.String(), err))