feat(backups): warn on the BackupJob when the Redis snapshot is empty

A valid RDB snapshot always carries a header, so a 0-byte object means
the backup is broken. sizeBytes is omitempty, though, so such a Backup
read exactly like one whose size was never measured. The controller
still records the artifact, and now raises a Warning EmptySnapshot
Event on the BackupJob once the Backup is created.

A test now also pins that a retry over an existing Backup returns it
without calling Create.

Assisted-by: LLM
Signed-off-by: Andrey Kolkov <androndo@gmail.com>

internal/backupcontroller/redis_artifact_size_test.go

@@ -17,6 +17,7 @@ import (
 	"k8s.io/client-go/tools/record"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 	clientfake "sigs.k8s.io/controller-runtime/pkg/client/fake"
+	"sigs.k8s.io/controller-runtime/pkg/client/interceptor"
 
 	backupsv1alpha1 "github.com/cozystack/cozystack/api/backups/v1alpha1"
 )
@@ -367,16 +368,39 @@ func TestCreateRedisBackupArtifact_Artifact(t *testing.T) {
 		}
 	})
 
-	t.Run("an existing Backup is returned without probing", func(t *testing.T) {
+	t.Run("an existing Backup is returned without probing or creating", func(t *testing.T) {
 		existing := &backupsv1alpha1.Backup{ObjectMeta: metav1.ObjectMeta{Namespace: "tenant", Name: "bj-1"}}
 		l := &fakeS3Lister{statSize: 777}
 		r := redisReconciler(t, l, j, existing, projectedCredsSecret(nil))
+		creates := 0
+		r.Client = interceptor.NewClient(r.Client.(client.WithWatch), interceptor.Funcs{
+			Create: func(ctx context.Context, cl client.WithWatch, obj client.Object, opts ...client.CreateOption) error {
+				creates++
+				return cl.Create(ctx, obj, opts...)
+			},
+		})
 		if _, err := r.createRedisBackupArtifact(context.Background(), j, &ResolvedBackupConfig{}, redisTestKey, nil); err != nil {
 			t.Fatalf("createRedisBackupArtifact: %v", err)
 		}
 		if l.calls != 0 {
 			t.Errorf("S3 probed %d times for a Backup that already exists", l.calls)
 		}
+		if creates != 0 {
+			t.Errorf("Create called %d times for a Backup that already exists", creates)
+		}
+	})
+
+	t.Run("an empty snapshot is recorded and warned about", func(t *testing.T) {
+		r := redisReconciler(t, &fakeS3Lister{statSize: 0}, j, projectedCredsSecret(nil))
+		rec := record.NewFakeRecorder(4)
+		r.Recorder = rec
+		got, err := r.createRedisBackupArtifact(context.Background(), j, &ResolvedBackupConfig{}, redisTestKey, nil)
+		if err != nil || got == nil || got.Status.Artifact == nil || got.Status.Artifact.URI != "s3://cozy-backups/"+redisTestKey {
+			t.Fatalf("createRedisBackupArtifact = %#v, %v; want the artifact recorded", got, err)
+		}
+		if ev := nextEvent(rec); !strings.HasPrefix(ev, "Warning EmptySnapshot ") {
+			t.Errorf("event = %q, want Warning EmptySnapshot", ev)
+		}
 	})
 }
 

internal/backupcontroller/redisstrategy_controller.go

@@ -526,8 +526,15 @@ func (r *BackupJobReconciler) createRedisBackupArtifact(
 	}
 	// Only once the Backup exists: a terminal Create error fails the
 	// BackupJob, and a collision returns a Backup another pass measured.
-	if unmeasured != "" && r.Recorder != nil {
-		r.Recorder.Eventf(j, corev1.EventTypeNormal, "ArtifactNotMeasured", "The backup succeeded, but its location and size were not recorded: %s", unmeasured)
+	if r.Recorder != nil {
+		switch {
+		case unmeasured != "":
+			r.Recorder.Eventf(j, corev1.EventTypeNormal, "ArtifactNotMeasured", "The backup succeeded, but its location and size were not recorded: %s", unmeasured)
+		case backup.Status.Artifact != nil && backup.Status.Artifact.SizeBytes == 0:
+			// sizeBytes is omitempty, so a 0 reads as "not measured" on the
+			// Backup; a valid RDB snapshot always carries a header.
+			r.Recorder.Event(j, corev1.EventTypeWarning, "EmptySnapshot", "The backup's RDB snapshot is empty (0 bytes); a valid snapshot is never empty, so this backup is likely broken.")
+		}
 	}
 	return backup, nil
 }