cmd/cli: check local DNS using Windows API

cmd/cli/cli.go

@@ -709,7 +709,7 @@ NOTE: Uninstalling will set DNS to values provided by DHCP.`,
 					return nil
 				})
 				// Windows forwarders file.
-				if windowsHasLocalDnsServerRunning() {
+				if hasLocalDnsServerRunning() {
 					files = append(files, absHomeDir(windowsForwardersFilename))
 				}
 				// Binary itself.
@@ -2107,7 +2107,7 @@ func tryUpdateListenerConfig(cfg *ctrld.Config, infoLogger *zerolog.Logger, fata
 	cdMode := cdUID != ""
 	nextdnsMode := nextdns != ""
 	// For Windows server with local Dns server running, we can only try on random local IP.
-	hasLocalDnsServer := windowsHasLocalDnsServerRunning()
+	hasLocalDnsServer := hasLocalDnsServerRunning()
 	for n, listener := range cfg.Listener {
 		lcc[n] = &listenerConfigCheck{}
 		if listener.IP == "" {
@@ -2614,21 +2614,6 @@ func exchangeContextWithTimeout(c *dns.Client, timeout time.Duration, msg *dns.M
 	return c.ExchangeContext(ctx, msg, addr)
 }
 
-// powershell runs the given powershell command.
-func powershell(cmd string) ([]byte, error) {
-	out, err := exec.Command("powershell", "-Command", cmd).CombinedOutput()
-	return bytes.TrimSpace(out), err
-}
-
-// windowsHasLocalDnsServerRunning reports whether we are on Windows and having Dns server running.
-func windowsHasLocalDnsServerRunning() bool {
-	if runtime.GOOS == "windows" {
-		_, err := powershell("Get-Process -Name DNS")
-		return err == nil
-	}
-	return false
-}
-
 // absHomeDir returns the absolute path to given filename using home directory as root dir.
 func absHomeDir(filename string) string {
 	if homedir != "" {

cmd/cli/os_windows.go

@@ -1,11 +1,13 @@
 package cli
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"net"
 	"net/netip"
 	"os"
+	"os/exec"
 	"slices"
 	"strings"
 	"sync"
@@ -39,7 +41,7 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 	setDNSOnce.Do(func() {
 		// If there's a Dns server running, that means we are on AD with Dns feature enabled.
 		// Configuring the Dns server to forward queries to ctrld instead.
-		if windowsHasLocalDnsServerRunning() {
+		if hasLocalDnsServerRunning() {
 			file := absHomeDir(windowsForwardersFilename)
 			oldForwardersContent, _ := os.ReadFile(file)
 			hasLocalIPv6Listener := needLocalIPv6Listener()
@@ -101,7 +103,7 @@ func resetDnsIgnoreUnusableInterface(iface *net.Interface) error {
 func resetDNS(iface *net.Interface) error {
 	resetDNSOnce.Do(func() {
 		// See corresponding comment in setDNS.
-		if windowsHasLocalDnsServerRunning() {
+		if hasLocalDnsServerRunning() {
 			file := absHomeDir(windowsForwardersFilename)
 			content, err := os.ReadFile(file)
 			if err != nil {
@@ -241,3 +243,9 @@ func removeDnsServerForwarders(nameservers []string) error {
 	}
 	return nil
 }
+
+// powershell runs the given powershell command.
+func powershell(cmd string) ([]byte, error) {
+	out, err := exec.Command("powershell", "-Command", cmd).CombinedOutput()
+	return bytes.TrimSpace(out), err
+}

cmd/cli/service_others.go

@@ -13,3 +13,6 @@ func hasElevatedPrivilege() (bool, error) {
 func openLogFile(path string, flags int) (*os.File, error) {
 	return os.OpenFile(path, flags, os.FileMode(0o600))
 }
+
+// hasLocalDnsServerRunning reports whether we are on Windows and having Dns server running.
+func hasLocalDnsServerRunning() bool { return false }

cmd/cli/service_windows.go

@@ -2,7 +2,9 @@ package cli
 
 import (
 	"os"
+	"strings"
 	"syscall"
+	"unsafe"
 
 	"golang.org/x/sys/windows"
 )
@@ -79,3 +81,23 @@ func openLogFile(path string, mode int) (*os.File, error) {
 
 	return os.NewFile(uintptr(handle), path), nil
 }
+
+const processEntrySize = uint32(unsafe.Sizeof(windows.ProcessEntry32{}))
+
+// hasLocalDnsServerRunning reports whether we are on Windows and having Dns server running.
+func hasLocalDnsServerRunning() bool {
+	h, e := windows.CreateToolhelp32Snapshot(windows.TH32CS_SNAPPROCESS, 0)
+	if e != nil {
+		return false
+	}
+	p := windows.ProcessEntry32{Size: processEntrySize}
+	for {
+		e := windows.Process32Next(h, &p)
+		if e != nil {
+			return false
+		}
+		if strings.ToLower(windows.UTF16ToString(p.ExeFile[:])) == "dns.exe" {
+			return true
+		}
+	}
+}

cmd/cli/service_windows_test.go

@@ -0,0 +1,25 @@
+package cli
+
+import (
+	"testing"
+	"time"
+)
+
+func Test_hasLocalDnsServerRunning(t *testing.T) {
+	start := time.Now()
+	hasDns := hasLocalDnsServerRunning()
+	t.Logf("Using Windows API takes: %d", time.Since(start).Milliseconds())
+
+	start = time.Now()
+	hasDnsPowershell := hasLocalDnsServerRunningPowershell()
+	t.Logf("Using Powershell takes: %d", time.Since(start).Milliseconds())
+
+	if hasDns != hasDnsPowershell {
+		t.Fatalf("result mismatch, want: %v, got: %v", hasDnsPowershell, hasDns)
+	}
+}
+
+func hasLocalDnsServerRunningPowershell() bool {
+	_, err := powershell("Get-Process -Name DNS")
+	return err == nil
+}