Sync directory to disk after upload

After a file was uploaded, also sync its containing directory to disk to
make sure that also the directory entry is persisted after a system
crash.

repo/repo.go

@@ -627,9 +627,28 @@ func (h *Handler) saveBlob(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if err := syncDir(filepath.Dir(path)); err != nil {
+		// Don't call os.Remove(path) as this is prone to race conditions with parallel upload retries
+		h.internalServerError(w, err)
+		return
+	}
+
 	h.sendMetric(objectType, BlobWrite, uint64(written))
 }
 
+func syncDir(dirname string) error {
+	dir, err := os.Open(dirname)
+	if err != nil {
+		return err
+	}
+	err = dir.Sync()
+	if err != nil {
+		_ = dir.Close()
+		return err
+	}
+	return dir.Close()
+}
+
 // deleteBlob deletes a blob from the repository.
 func (h *Handler) deleteBlob(w http.ResponseWriter, r *http.Request) {
 	if h.opt.Debug {