1 files changed, 31 insertions, 0 deletions
diff --git a/fikenauth/lock_unix.go b/fikenauth/lock_unix.go
new file mode 100644
index 0000000..e29472d
--- /dev/null
+++ b/fikenauth/lock_unix.go
@@ -0,0 +1,31 @@
+//go:build unix
+
+package fikenauth
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"syscall"
+)
+
+// lock takes an exclusive lock beside the token file, held until unlock is
+// called. It is advisory: it only orders programs that also take it, which is
+// every program using this package.
+func (s *Store) lock() (unlock func(), err error) {
+	if err := os.MkdirAll(filepath.Dir(s.path), 0o700); err != nil {
+		return nil, fmt.Errorf("create %s: %w", filepath.Dir(s.path), err)
+	}
+	f, err := os.OpenFile(s.path+".lock", os.O_CREATE|os.O_RDWR, 0o600)
+	if err != nil {
+		return nil, fmt.Errorf("lock %s: %w", s.path, err)
+	}
+	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX); err != nil {
+		f.Close()
+		return nil, fmt.Errorf("lock %s: %w", s.path, err)
+	}
+	return func() {
+		syscall.Flock(int(f.Fd()), syscall.LOCK_UN) //nolint:errcheck // closing releases it anyway
+		f.Close()
+	}, nil
+}