[client] Clean up match domain reg entries between config changes (#4676)

client/internal/dns/host_windows.go

@@ -17,6 +17,7 @@ import (
 
 	nberrors "github.com/netbirdio/netbird/client/errors"
 	"github.com/netbirdio/netbird/client/internal/statemanager"
+	"github.com/netbirdio/netbird/client/internal/winregistry"
 )
 
 var (
@@ -197,6 +198,10 @@ func (r *registryConfigurator) applyDNSConfig(config HostDNSConfig, stateManager
 		matchDomains = append(matchDomains, "."+strings.TrimSuffix(dConf.Domain, "."))
 	}
 
+	if err := r.removeDNSMatchPolicies(); err != nil {
+		log.Errorf("cleanup old dns match policies: %s", err)
+	}
+
 	if len(matchDomains) != 0 {
 		count, err := r.addDNSMatchPolicy(matchDomains, config.ServerIP)
 		if err != nil {
@@ -204,9 +209,6 @@ func (r *registryConfigurator) applyDNSConfig(config HostDNSConfig, stateManager
 		}
 		r.nrptEntryCount = count
 	} else {
-		if err := r.removeDNSMatchPolicies(); err != nil {
-			return fmt.Errorf("remove dns match policies: %w", err)
-		}
 		r.nrptEntryCount = 0
 	}
 
@@ -273,9 +275,9 @@ func (r *registryConfigurator) configureDNSPolicy(policyPath string, domains []s
 		return fmt.Errorf("remove existing dns policy: %w", err)
 	}
 
-	regKey, _, err := registry.CreateKey(registry.LOCAL_MACHINE, policyPath, registry.SET_VALUE)
+	regKey, _, err := winregistry.CreateVolatileKey(registry.LOCAL_MACHINE, policyPath, registry.SET_VALUE)
 	if err != nil {
-		return fmt.Errorf("create registry key HKEY_LOCAL_MACHINE\\%s: %w", policyPath, err)
+		return fmt.Errorf("create volatile registry key HKEY_LOCAL_MACHINE\\%s: %w", policyPath, err)
 	}
 	defer closer(regKey)
 

client/internal/dns/host_windows_test.go

@@ -0,0 +1,102 @@
+package dns
+
+import (
+	"fmt"
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/windows/registry"
+)
+
+// TestNRPTEntriesCleanupOnConfigChange tests that old NRPT entries are properly cleaned up
+// when the number of match domains decreases between configuration changes.
+func TestNRPTEntriesCleanupOnConfigChange(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,
+	}
+
+	config5 := HostDNSConfig{
+		ServerIP: testIP,
+		Domains: []DomainConfig{
+			{Domain: "domain1.com", MatchOnly: true},
+			{Domain: "domain2.com", MatchOnly: true},
+			{Domain: "domain3.com", MatchOnly: true},
+			{Domain: "domain4.com", MatchOnly: true},
+			{Domain: "domain5.com", MatchOnly: true},
+		},
+	}
+
+	err = cfg.applyDNSConfig(config5, nil)
+	require.NoError(t, err)
+
+	// Verify all 5 entries exist
+	for i := 0; i < 5; i++ {
+		exists, err := registryKeyExists(fmt.Sprintf("%s-%d", dnsPolicyConfigMatchPath, i))
+		require.NoError(t, err)
+		assert.True(t, exists, "Entry %d should exist after first config", i)
+	}
+
+	config2 := HostDNSConfig{
+		ServerIP: testIP,
+		Domains: []DomainConfig{
+			{Domain: "domain1.com", MatchOnly: true},
+			{Domain: "domain2.com", MatchOnly: true},
+		},
+	}
+
+	err = cfg.applyDNSConfig(config2, nil)
+	require.NoError(t, err)
+
+	// Verify first 2 entries exist
+	for i := 0; i < 2; i++ {
+		exists, err := registryKeyExists(fmt.Sprintf("%s-%d", dnsPolicyConfigMatchPath, i))
+		require.NoError(t, err)
+		assert.True(t, exists, "Entry %d should exist after second config", i)
+	}
+
+	// Verify entries 2-4 are cleaned up
+	for i := 2; i < 5; i++ {
+		exists, err := registryKeyExists(fmt.Sprintf("%s-%d", dnsPolicyConfigMatchPath, i))
+		require.NoError(t, err)
+		assert.False(t, exists, "Entry %d should NOT exist after reducing to 2 domains", i)
+	}
+}
+
+func registryKeyExists(path string) (bool, error) {
+	k, err := registry.OpenKey(registry.LOCAL_MACHINE, path, registry.QUERY_VALUE)
+	if err != nil {
+		if err == registry.ErrNotExist {
+			return false, nil
+		}
+		return false, err
+	}
+	k.Close()
+	return true, nil
+}
+
+func cleanupRegistryKeys(*testing.T) {
+	cfg := &registryConfigurator{nrptEntryCount: 10}
+	_ = cfg.removeDNSMatchPolicies()
+}