feat: add permission-aware file copy and move

chfs-ng/internal/storage/storage.go

@@ -26,6 +26,7 @@ type Storage interface {
 	Create(path string) (*os.File, error)
 	Remove(path string) error
 	Rename(oldPath, newPath string) error
+	Copy(oldPath, newPath string) error
 	MkdirAll(path string) error
 	List(path string) ([]os.FileInfo, error)
 }
@@ -275,6 +276,23 @@ func copyPath(src, dst string) error {
 	return os.Chtimes(dst, info.ModTime(), info.ModTime())
 }
 
+func (s Local) Copy(a, b string) error {
+	pa, e := s.real(a)
+	if e != nil {
+		return e
+	}
+	pb, e := s.real(b)
+	if e != nil {
+		return e
+	}
+	if _, e := os.Lstat(pb); e == nil {
+		return os.ErrExist
+	} else if !os.IsNotExist(e) {
+		return e
+	}
+	return copyPath(pa, pb)
+}
+
 func (s Local) Rename(a, b string) error {
 	pa, e := s.real(a)
 	if e != nil {