feat: add support for running CoreDNS as a Windows service (#7962)

* feat: add support for running CoreDNS as a Windows service

Signed-off-by: John-Michael Mulesa <jmulesa@gmail.com>

* Use non-deprecated service check function.

Signed-off-by: John-Michael Mulesa <jmulesa@gmail.com>

* refactor: remove deprecated build tags and clean up imports in service files

Signed-off-by: John-Michael Mulesa <jmulesa@gmail.com>

* ci: add Windows test workflow and fix log field access in service_windows.go

Signed-off-by: John-Michael Mulesa <jmulesa@gmail.com>

* test: implement cross-platform file permission restriction for Windows compatibility in run_test.go

Signed-off-by: John-Michael Mulesa <jmulesa@gmail.com>

* refactor: remove Windows-specific icacls test logic and restrict unreadable file test to non-Windows platforms

Signed-off-by: John-Michael Mulesa <jmulesa@gmail.com>

* docs: add documentation for -windows-service flag in man page

Signed-off-by: John-Michael Mulesa <jmulesa@gmail.com>

---------

Signed-off-by: John-Michael Mulesa <jmulesa@gmail.com>

coremain/service_windows.go

@@ -0,0 +1,63 @@
+//go:build windows
+
+package coremain
+
+import (
+	"flag"
+	"log"
+
+	"github.com/coredns/caddy"
+
+	"golang.org/x/sys/windows/svc"
+)
+
+var windowsService bool
+
+func init() {
+	flag.BoolVar(&windowsService, "windows-service", false, "Run as a Windows service")
+}
+
+type corednsService struct {
+	instance *caddy.Instance
+}
+
+func (s *corednsService) Execute(args []string, r <-chan svc.ChangeRequest, changes chan<- svc.Status) (svcSpecificEC bool, exitCode uint32) {
+	changes <- svc.Status{State: svc.StartPending}
+	changes <- svc.Status{State: svc.Running, Accepts: svc.AcceptStop | svc.AcceptShutdown}
+
+	for req := range r {
+		switch req.Cmd {
+		case svc.Interrogate:
+			changes <- req.CurrentStatus
+		case svc.Stop, svc.Shutdown:
+			changes <- svc.Status{State: svc.StopPending}
+			if s.instance != nil {
+				s.instance.Stop()
+			}
+			return false, 0
+		default:
+			log.Printf("unexpected control request #%d", req.Cmd)
+		}
+	}
+
+	return false, 0
+}
+
+func runService(instance *caddy.Instance) {
+	if windowsService {
+		isService, err := svc.IsWindowsService()
+		if err != nil {
+			log.Fatalf("failed to determine if running as service: %v", err)
+		}
+		if isService {
+			err = svc.Run("CoreDNS", &corednsService{instance: instance})
+			if err != nil {
+				log.Fatalf("failed to start service: %v", err)
+			}
+			return
+		} else {
+			log.Printf("Windows service flag provided, but not running as a Windows service.")
+		}
+	}
+	instance.Wait()
+}