From b50d3ba805cdad20e9352398a3d2054219ebcddd Mon Sep 17 00:00:00 2001
From: Alexander Neumann <alexander@bumpern.de>
Date: Tue, 7 Mar 2017 11:12:34 +0100
Subject: [PATCH 1/2] Refuse to create empty snapshots

Closes #862
---
 src/restic/archiver/archiver.go | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/restic/archiver/archiver.go b/src/restic/archiver/archiver.go
index 6a5b84a31..e90cfd8f8 100644
--- a/src/restic/archiver/archiver.go
+++ b/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 {

From bb144436c7280bef06af65abbc11187e8375111f Mon Sep 17 00:00:00 2001
From: Alexander Neumann <alexander@bumpern.de>
Date: Tue, 7 Mar 2017 11:17:15 +0100
Subject: [PATCH 2/2] Add test for empty snapshot

---
 src/restic/archiver/archiver_test.go | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/restic/archiver/archiver_test.go b/src/restic/archiver/archiver_test.go
index 3cb8ba183..72e3b3a96 100644
--- a/src/restic/archiver/archiver_test.go
+++ b/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)
+	}
+}