fix: Windows 11/Windows Server 2025 service compatibility (#1841)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

cmd/windows_exporter/0_service.go

@@ -0,0 +1,147 @@
+// Copyright 2025 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"golang.org/x/sys/windows"
+	"golang.org/x/sys/windows/svc"
+	"golang.org/x/sys/windows/svc/eventlog"
+)
+
+const serviceName = "windows_exporter"
+
+//nolint:gochecknoglobals
+var (
+	// exitCodeCh is a channel to send an exit code from the main function to the service manager.
+	// Additionally, if there is an error in the IsService var declaration,
+	// the exit code is sent to the service manager as well.
+	exitCodeCh = make(chan int, 1)
+
+	// stopCh is a channel to send a signal to the service manager that the service is stopping.
+	stopCh = make(chan struct{})
+)
+
+// IsService variable declaration allows initiating time-sensitive components like registering the Windows service
+// as early as possible in the startup process.
+// init functions are called in the order they are declared, so this package should be imported first.
+//
+// Ref: https://github.com/prometheus-community/windows_exporter/issues/551#issuecomment-1220774835
+//
+// Declare imports on this package should be avoided where possible.
+// var declaration run before init function, so it guarantees that windows_exporter respond to service manager early
+// and avoid timeout.
+// The order of the var declaration and init functions depends on the filename as well. The filename should be 0_service.go
+// Ref: https://medium.com/@markbates/go-init-order-dafa89fcef22
+//
+//nolint:gochecknoglobals
+var IsService = func() bool {
+	defer func() {
+		go func() {
+			err := svc.Run(serviceName, &windowsExporterService{})
+			if err == nil {
+				return
+			}
+
+			_ = logToEventToLog(windows.EVENTLOG_ERROR_TYPE, fmt.Sprintf("failed to start service: %v", err))
+		}()
+	}()
+
+	var err error
+
+	isService, err := svc.IsWindowsService()
+	if err != nil {
+		_ = logToEventToLog(windows.EVENTLOG_ERROR_TYPE, fmt.Sprintf("failed to detect service: %v", err))
+
+		exitCodeCh <- 1
+	}
+
+	if !isService {
+		return false
+	}
+
+	if err := logToEventToLog(windows.EVENTLOG_INFORMATION_TYPE, "attempting to start exporter service"); err != nil {
+		//nolint:gosec
+		_ = os.WriteFile("C:\\Program Files\\windows_exporter\\start-service.error.log", []byte(fmt.Sprintf("failed sent log to event log: %v", err)), 0o644)
+
+		exitCodeCh <- 2
+	}
+
+	return true
+}()
+
+type windowsExporterService struct{}
+
+// Execute is the entry point for the Windows service manager.
+func (s *windowsExporterService) Execute(_ []string, r <-chan svc.ChangeRequest, changes chan<- svc.Status) (bool, uint32) {
+	changes <- svc.Status{State: svc.StartPending}
+	changes <- svc.Status{State: svc.Running, Accepts: svc.AcceptStop | svc.AcceptShutdown}
+
+	for {
+		select {
+		case exitCodeCh := <-exitCodeCh:
+			// Stop the service if an exit code from the main function is received.
+			changes <- svc.Status{State: svc.StopPending}
+
+			return true, uint32(exitCodeCh)
+		case c := <-r:
+			// Handle the service control request.
+			switch c.Cmd {
+			case svc.Interrogate:
+				changes <- c.CurrentStatus
+			case svc.Stop, svc.Shutdown:
+				// Stop the service if a stop or shutdown request is received.
+				_ = logToEventToLog(windows.EVENTLOG_INFORMATION_TYPE, "service stop received")
+
+				changes <- svc.Status{State: svc.StopPending}
+
+				// Send a signal to the main function to stop the service.
+				stopCh <- struct{}{}
+
+				// Wait for the main function to stop the service.
+				return false, uint32(<-exitCodeCh)
+			default:
+				_ = logToEventToLog(windows.EVENTLOG_ERROR_TYPE, fmt.Sprintf("unexpected control request #%d", c))
+			}
+		}
+	}
+}
+
+// logToEventToLog logs a message to the Windows event log.
+func logToEventToLog(eType uint16, msg string) error {
+	eventLog, err := eventlog.Open("windows_exporter")
+	if err != nil {
+		return fmt.Errorf("failed to open event log: %w", err)
+	}
+	defer func(eventLog *eventlog.Log) {
+		_ = eventLog.Close()
+	}(eventLog)
+
+	p, err := windows.UTF16PtrFromString(msg)
+	if err != nil {
+		return fmt.Errorf("error convert string to UTF-16: %w", err)
+	}
+
+	zero := uint16(0)
+	ss := []*uint16{p, &zero, &zero, &zero, &zero, &zero, &zero, &zero, &zero}
+
+	err = windows.ReportEvent(eventLog.Handle, eType, 0, 3299, 0, 9, 0, &ss[0], nil)
+	if err != nil {
+		return fmt.Errorf("error report event: %w", err)
+	}
+
+	return nil
+}