cmd/tailscaled: run as a service on Windows

Updates #1232

cmd/tailscaled/tailscaled.go

@@ -132,6 +132,16 @@ func run() error {
 		pol.Shutdown(ctx)
 	}()
 
+	if isWindowsService() {
+		// Run the IPN server from the Windows service manager.
+		log.Printf("Running service...")
+		if err := runWindowsService(pol); err != nil {
+			log.Printf("runservice: %v", err)
+		}
+		log.Printf("Service ended.")
+		return nil
+	}
+
 	var logf logger.Logf = log.Printf
 	if v, _ := strconv.ParseBool(os.Getenv("TS_DEBUG_MEMORY")); v {
 		logf = logger.RusagePrefixLog(logf)

cmd/tailscaled/tailscaled_notwindows.go

@@ -0,0 +1,13 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !windows
+
+package main // import "tailscale.com/cmd/tailscaled"
+
+import "tailscale.com/logpolicy"
+
+func isWindowsService() bool { return false }
+
+func runWindowsService(pol *logpolicy.Policy) error { panic("unreachable") }

cmd/tailscaled/tailscaled_windows.go

@@ -0,0 +1,64 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main // import "tailscale.com/cmd/tailscaled"
+
+import (
+	"context"
+	"log"
+
+	"golang.org/x/sys/windows"
+	"golang.org/x/sys/windows/svc"
+	"tailscale.com/ipn/ipnserver"
+	"tailscale.com/logpolicy"
+)
+
+const serviceName = "Tailscale IPN"
+
+func isWindowsService() bool {
+	v, err := svc.IsWindowsService()
+	if err != nil {
+		log.Fatalf("svc.IsWindowsService failed: %v", err)
+	}
+	return v
+}
+
+func runWindowsService(pol *logpolicy.Policy) error {
+	return svc.Run(serviceName, &ipnService{Policy: pol})
+}
+
+type ipnService struct {
+	Policy *logpolicy.Policy
+}
+
+// Called by Windows to execute the windows service.
+func (service *ipnService) Execute(args []string, r <-chan svc.ChangeRequest, changes chan<- svc.Status) (bool, uint32) {
+	changes <- svc.Status{State: svc.StartPending}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	doneCh := make(chan struct{})
+	go func() {
+		defer close(doneCh)
+		args := []string{"/subproc", service.Policy.PublicID.String()}
+		ipnserver.BabysitProc(ctx, args, log.Printf)
+	}()
+
+	changes <- svc.Status{State: svc.Running, Accepts: svc.AcceptStop}
+
+	for ctx.Err() == nil {
+		select {
+		case <-doneCh:
+		case cmd := <-r:
+			switch cmd.Cmd {
+			case svc.Stop:
+				cancel()
+			case svc.Interrogate:
+				changes <- cmd.CurrentStatus
+			}
+		}
+	}
+
+	changes <- svc.Status{State: svc.StopPending}
+	return false, windows.NO_ERROR
+}