Merge pull request #865 from restic/handle-empty-snapshots

Refuse to create empty snapshots

src/restic/archiver/archiver.go

@@ -734,6 +734,21 @@ func (arch *Archiver) Snapshot(p *restic.Progress, paths, tags []string, hostnam
 		return nil, restic.ID{}, err
 	}
 
+	// receive the top-level tree
+	root := (<-resCh).(*restic.Node)
+	debug.Log("root node received: %v", root.Subtree.Str())
+	sn.Tree = root.Subtree
+
+	// load top-level tree again to see if it is empty
+	toptree, err := arch.repo.LoadTree(*root.Subtree)
+	if err != nil {
+		return nil, restic.ID{}, err
+	}
+
+	if len(toptree.Nodes) == 0 {
+		return nil, restic.ID{}, errors.Fatal("no files/dirs saved, refusing to create empty snapshot")
+	}
+
 	// save index
 	err = arch.repo.SaveIndex()
 	if err != nil {
@@ -743,11 +758,6 @@ func (arch *Archiver) Snapshot(p *restic.Progress, paths, tags []string, hostnam
 
 	debug.Log("saved indexes")
 
-	// receive the top-level tree
-	root := (<-resCh).(*restic.Node)
-	debug.Log("root node received: %v", root.Subtree.Str())
-	sn.Tree = root.Subtree
-
 	// save snapshot
 	id, err := arch.repo.SaveJSONUnpacked(restic.SnapshotFile, sn)
 	if err != nil {

src/restic/archiver/archiver_test.go

@@ -294,3 +294,23 @@ func assertNoUnreferencedPacks(t *testing.T, chkr *checker.Checker) {
 		OK(t, err)
 	}
 }
+
+func TestArchiveEmptySnapshot(t *testing.T) {
+	repo, cleanup := repository.TestRepository(t)
+	defer cleanup()
+
+	arch := archiver.New(repo)
+
+	sn, id, err := arch.Snapshot(nil, []string{"file-does-not-exist-123123213123", "file2-does-not-exist-too-123123123"}, nil, "localhost", nil)
+	if err == nil {
+		t.Errorf("expected error for empty snapshot, got nil")
+	}
+
+	if !id.IsNull() {
+		t.Errorf("expected null ID for empty snapshot, got %v", id.Str())
+	}
+
+	if sn != nil {
+		t.Errorf("expected null snapshot for empty snapshot, got %v", sn)
+	}
+}