Do not forget CreatedBy in mutate.Canonical (#978)

* Add check for missing CreatedBy in canonical image

* Remember CreatedBy in mutate.Canonical

* Format comparison

* fix

pkg/v1/mutate/mutate.go

@@ -371,8 +371,13 @@ func Time(img v1.Image, t time.Time) (v1.Image, error) {
 	// Strip away timestamps from the config file
 	cfg.Created = v1.Time{Time: t}
 
-	for _, h := range cfg.History {
+	for i, h := range cfg.History {
 		h.Created = v1.Time{Time: t}
+		h.CreatedBy = ocf.History[i].CreatedBy
+		h.Comment = ocf.History[i].Comment
+		h.EmptyLayer = ocf.History[i].EmptyLayer
+		// Explicitly ignore Author field; which hinders reproducibility
+		cfg.History[i] = h
 	}
 
 	return ConfigFile(newImage, cfg)

pkg/v1/mutate/mutate_test.go

@@ -503,6 +503,13 @@ func TestCanonical(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	for _, h := range cf.History {
+		want := "bazel build ..."
+		got := h.CreatedBy
+		if want != got {
+			t.Errorf("%q != %q", want, got)
+		}
+	}
 	var want, got string
 	want = cf.Architecture
 	got = sourceCf.Architecture