fix: align WebDAV overwrite and missing-resource errors

chfs-ng/internal/api/server.go

@@ -825,6 +825,12 @@ func (f *webdavStorageFS) RemoveAll(ctx context.Context, name string, opts *webd
 	if p == "" {
 		return fmt.Errorf("cannot remove storage root")
 	}
+	if _, err := f.store.Stat(p); err != nil {
+		if os.IsNotExist(err) {
+			return webdav.NewHTTPError(http.StatusNotFound, err)
+		}
+		return err
+	}
 	if f.removeMode == 1 {
 		if t, ok := f.store.(storage.Trashable); ok {
 			return t.Trash(p)
@@ -847,12 +853,24 @@ func (f *webdavStorageFS) Mkdir(ctx context.Context, name string) error {
 	if p == "" {
 		return fmt.Errorf("cannot create storage root")
 	}
+	if _, err := f.store.Stat(p); err == nil {
+		return webdav.NewHTTPError(http.StatusMethodNotAllowed, fmt.Errorf("resource already exists"))
+	} else if !os.IsNotExist(err) {
+		return err
+	}
 	return f.store.MkdirAll(p)
 }
 
 func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *webdav.CopyOptions) (bool, error) {
 	src := davStoragePath(name)
 	dst := davStoragePath(dest)
+	if opts != nil && opts.NoOverwrite {
+		if _, err := f.store.Stat(dst); err == nil {
+			return false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))
+		} else if !os.IsNotExist(err) {
+			return false, err
+		}
+	}
 	if m, ok := f.store.(storage.Multi); ok {
 		srcRoot, _, srcOK := m.FindRoot(src)
 		dstRoot, _, dstOK := m.FindRoot(dst)