Enable syslog when running as Windows service

This writes logs to the Windows event log.

server/log.go

@@ -37,11 +37,18 @@ func (s *Server) ConfigureLogger() {
 		opts = s.getOpts()
 	)
 
+	syslog := opts.Syslog
+	if isWindowsService() && opts.LogFile == "" {
+		// Enable syslog if no log file is specified and we're running as a
+		// Windows service so that logs are written to the Windows event log.
+		syslog = true
+	}
+
 	if opts.LogFile != "" {
 		log = logger.NewFileLogger(opts.LogFile, opts.Logtime, opts.Debug, opts.Trace, true)
 	} else if opts.RemoteSyslog != "" {
 		log = logger.NewRemoteSysLogger(opts.RemoteSyslog, opts.Debug, opts.Trace)
-	} else if opts.Syslog {
+	} else if syslog {
 		log = logger.NewSysLogger(opts.Debug, opts.Trace)
 	} else {
 		colors := true

server/service.go

@@ -9,3 +9,8 @@ func Run(server *Server) error {
 	server.Start()
 	return nil
 }
+
+// isWindowsService indicates if NATS is running as a Windows service.
+func isWindowsService() bool {
+	return false
+}

server/service_windows.go

@@ -86,3 +86,9 @@ func Run(server *Server) error {
 	}
 	return run(serviceName, &winServiceWrapper{server})
 }
+
+// isWindowsService indicates if NATS is running as a Windows service.
+func isWindowsService() bool {
+	isInteractive, _ := svc.IsAnInteractiveSession()
+	return !isInteractive
+}