serve restic: fix temporary errors confusing restic into leaving locks behind

deleteObject() replied 404 for any error from newObject(), while
serveObject() in the same file replies 404 only for
fs.ErrorObjectNotFound and 500 otherwise.

restic treats a 404 on DELETE as final and never retries, so a
transient lookup failure while removing a lock left the lock behind
and broke the next exclusive operation (eg forget --prune failing with
"repository is already locked").

This change mirrors serveObject() handling of 404/500 errors in
deleteObject().

Fixes #10100

Co-authored-by: bunnysayzz <bunnysayzz@users.noreply.github.com>

cmd/serve/restic/restic.go

@@ -509,7 +509,11 @@ func (s *server) deleteObject(w http.ResponseWriter, r *http.Request) {
 	o, err := s.newObject(r.Context(), remote)
 	if err != nil {
 		fs.Debugf(remote, "Delete request error: %v", err)
-		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
+		if errors.Is(err, fs.ErrorObjectNotFound) {
+			http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
+		} else {
+			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		}
 		return
 	}
 

cmd/serve/restic/restic_test.go

@@ -229,6 +229,28 @@ func TestServeErrors(t *testing.T) {
 	checkRequest(t, router.ServeHTTP, req, []wantFunc{wantCode(http.StatusNotFound)})
 }
 
+func TestDeleteErrors(t *testing.T) {
+	ctx := context.Background()
+	// setup rclone with a local backend in a temporary directory
+	tempdir := t.TempDir()
+	opt := newOpt()
+
+	// make a new file system in the temp dir
+	f := &newObjectErrorFs{Fs: cmd.NewFsSrc([]string{tempdir})}
+	s, err := newServer(ctx, f, &opt)
+	require.NoError(t, err)
+	router := s.server.Router()
+
+	// a lookup failure that is not "not found" must be a 500 so
+	// restic retries the delete instead of treating it as final
+	f.err = errors.New("oops")
+	req := newRequest(t, "DELETE", "/test/locks/0123456789abcdef", nil)
+	checkRequest(t, router.ServeHTTP, req, []wantFunc{wantCode(http.StatusInternalServerError)})
+
+	f.err = fs.ErrorObjectNotFound
+	checkRequest(t, router.ServeHTTP, req, []wantFunc{wantCode(http.StatusNotFound)})
+}
+
 func TestRc(t *testing.T) {
 	servetest.TestRc(t, rc.Params{
 		"type": "restic",