inital commit

Overlord-Client/cmd/agent/mutex/mutex.go

@@ -0,0 +1,33 @@
+package mutex
+
+import (
+	"fmt"
+	"strings"
+)
+
+const maxMutexLength = 64
+
+func sanitizeName(name string) (string, error) {
+	trimmed := strings.TrimSpace(name)
+	if trimmed == "" {
+		return "", fmt.Errorf("empty mutex name")
+	}
+
+	var builder strings.Builder
+	for _, r := range trimmed {
+		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '-' || r == '_' || r == '.' {
+			builder.WriteRune(r)
+		}
+	}
+
+	sanitized := builder.String()
+	if sanitized == "" {
+		return "", fmt.Errorf("mutex name has no valid characters")
+	}
+
+	if len(sanitized) > maxMutexLength {
+		sanitized = sanitized[:maxMutexLength]
+	}
+
+	return sanitized, nil
+}

Overlord-Client/cmd/agent/mutex/mutex_unix.go

@@ -0,0 +1,44 @@
+//go:build !windows
+
+package mutex
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/sys/unix"
+)
+
+func Acquire(name string) (func(), bool, error) {
+	if name == "" {
+		return func() {}, true, nil
+	}
+
+	sanitized, err := sanitizeName(name)
+	if err != nil {
+		return nil, false, err
+	}
+
+	lockPath := filepath.Join(os.TempDir(), fmt.Sprintf("overlord-%s.lock", sanitized))
+	file, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0o644)
+	if err != nil {
+		return nil, false, fmt.Errorf("open mutex file: %w", err)
+	}
+
+	if err := unix.Flock(int(file.Fd()), unix.LOCK_EX|unix.LOCK_NB); err != nil {
+		_ = file.Close()
+		if errors.Is(err, unix.EWOULDBLOCK) {
+			return func() {}, false, nil
+		}
+		return nil, false, fmt.Errorf("lock mutex file: %w", err)
+	}
+
+	release := func() {
+		_ = unix.Flock(int(file.Fd()), unix.LOCK_UN)
+		_ = file.Close()
+	}
+
+	return release, true, nil
+}

Overlord-Client/cmd/agent/mutex/mutex_windows.go

@@ -0,0 +1,38 @@
+//go:build windows
+
+package mutex
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/windows"
+)
+
+func Acquire(name string) (func(), bool, error) {
+	if name == "" {
+		return func() {}, true, nil
+	}
+
+	sanitized, err := sanitizeName(name)
+	if err != nil {
+		return nil, false, err
+	}
+
+	fullName := "Global\\Overlord-" + sanitized
+	handle, err := windows.CreateMutex(nil, false, windows.StringToUTF16Ptr(fullName))
+	if err != nil {
+		return nil, false, fmt.Errorf("create mutex: %w", err)
+	}
+
+	if windows.GetLastError() == windows.ERROR_ALREADY_EXISTS {
+		windows.CloseHandle(handle)
+		return func() {}, false, nil
+	}
+
+	release := func() {
+		_ = windows.ReleaseMutex(handle)
+		_ = windows.CloseHandle(handle)
+	}
+
+	return release, true, nil
+}