fix: make webdav file copy atomic

chfs-ng/internal/api/server.go

@@ -1256,21 +1256,43 @@ func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *web
 	if err != nil {
 		return false, err
 	}
-	out, err := f.store.Create(dst)
-	if err != nil {
-		in.Close()
+	defer in.Close()
+	if err := copyFileToDestination(f.store, in, dst, dstExists); err != nil {
 		return false, err
 	}
-	_, copyErr := io.Copy(out, in)
-	in.Close()
+	return !dstExists, nil
+}
+
+func copyFileToDestination(st storage.Storage, src io.Reader, dst string, dstExists bool) error {
+	tmp := fmt.Sprintf("%s.chfs-copy-%d", dst, time.Now().UnixNano())
+	for i := 0; i < 16; i++ {
+		if _, err := st.Stat(tmp); os.IsNotExist(err) {
+			break
+		} else if err != nil {
+			return err
+		}
+		tmp = fmt.Sprintf("%s.chfs-copy-%d-%d", dst, time.Now().UnixNano(), i)
+	}
+	out, err := createExclusive(st, tmp)
+	if err != nil {
+		return err
+	}
+	_, copyErr := io.Copy(out, src)
 	closeErr := out.Close()
 	if copyErr != nil {
-		return false, copyErr
+		_ = st.Remove(tmp)
+		return copyErr
 	}
 	if closeErr != nil {
-		return false, closeErr
+		_ = st.Remove(tmp)
+		return closeErr
 	}
-	return !dstExists, nil
+	if err := st.Rename(tmp, dst); err != nil {
+		_ = st.Remove(tmp)
+		return err
+	}
+	_ = dstExists
+	return nil
 }
 
 func (f *webdavStorageFS) Move(ctx context.Context, name, dest string, opts *webdav.MoveOptions) (bool, error) {