fix: make webdav put atomic

chfs-ng/internal/api/server.go

@@ -1110,32 +1110,34 @@ func (f *webdavStorageFS) Create(ctx context.Context, name string, body io.ReadC
 		return nil, false, statErr
 	}
 	exclusive := opts != nil && opts.IfNoneMatch.IsWildcard()
-	var file *os.File
 	if exclusive {
-		file, err = createExclusive(f.store, p)
+		file, createErr := createExclusive(f.store, p)
+		if createErr != nil {
+			if os.IsExist(createErr) {
+				return nil, false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))
+			}
+			return nil, false, createErr
+		}
+		_, copyErr := io.Copy(file, body)
+		closeErr := file.Close()
+		body.Close()
+		if copyErr != nil {
+			_ = f.store.Remove(p)
+			return nil, false, copyErr
+		}
+		if closeErr != nil {
+			_ = f.store.Remove(p)
+			return nil, false, closeErr
+		}
 	} else {
-		file, err = f.store.Create(p)
-	}
-	if err != nil {
-		if exclusive && os.IsExist(err) {
-			return nil, false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))
+		// Write into a sibling temporary file and atomically replace the
+		// destination only after the complete request body has been received.
+		// A failed PUT therefore cannot truncate or corrupt the old file.
+		if err := copyFileToDestination(f.store, body, p); err != nil {
+			body.Close()
+			return nil, false, err
 		}
-		return nil, false, err
-	}
-	_, copyErr := io.Copy(file, body)
-	closeErr := file.Close()
-	body.Close()
-	if copyErr != nil {
-		if exclusive {
-			_ = f.store.Remove(p)
-		}
-		return nil, false, copyErr
-	}
-	if closeErr != nil {
-		if exclusive {
-			_ = f.store.Remove(p)
-		}
-		return nil, false, closeErr
+		body.Close()
 	}
 	fi, err := f.info(p)
 	return fi, true, err