integration: test watch restore on slow follower

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

integration/v3_watch_test.go

@@ -352,6 +352,84 @@ func TestV3WatchFutureRevision(t *testing.T) {
 	}
 }
 
+// TestV3WatchRestoreSnapshotUnsync tests whether slow follower can restore
+// from leader snapshot, and still notify on watchers from an old revision
+// that were created in synced watcher group in the first place.
+func TestV3WatchRestoreSnapshotUnsync(t *testing.T) {
+	clus := NewClusterV3(t, &ClusterConfig{
+		Size:                   3,
+		SnapshotCount:          10,
+		SnapshotCatchUpEntries: 5,
+	})
+	defer clus.Terminate(t)
+
+	// spawn a watcher before shutdown, and put it in synced watcher
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+	wStream, errW := toGRPC(clus.Client(0)).Watch.Watch(ctx)
+	if errW != nil {
+		t.Fatal(errW)
+	}
+	if err := wStream.Send(&pb.WatchRequest{RequestUnion: &pb.WatchRequest_CreateRequest{
+		CreateRequest: &pb.WatchCreateRequest{Key: []byte("foo"), StartRevision: 5}}}); err != nil {
+		t.Fatalf("wStream.Send error: %v", err)
+	}
+	wresp, errR := wStream.Recv()
+	if errR != nil {
+		t.Errorf("wStream.Recv error: %v", errR)
+	}
+	if !wresp.Created {
+		t.Errorf("wresp.Created got = %v, want = true", wresp.Created)
+	}
+
+	clus.Members[0].InjectPartition(t, clus.Members[1:]...)
+	clus.waitLeader(t, clus.Members[1:])
+	time.Sleep(2 * time.Second)
+
+	kvc := toGRPC(clus.Client(1)).KV
+
+	// to trigger snapshot from the leader to the stopped follower
+	for i := 0; i < 15; i++ {
+		_, err := kvc.Put(context.TODO(), &pb.PutRequest{Key: []byte("foo"), Value: []byte("bar")})
+		if err != nil {
+			t.Errorf("#%d: couldn't put key (%v)", i, err)
+		}
+	}
+
+	// trigger snapshot send from leader to this slow follower
+	// which then calls watchable store Restore
+	clus.Members[0].RecoverPartition(t, clus.Members[1:]...)
+	clus.WaitLeader(t)
+	time.Sleep(2 * time.Second)
+
+	// slow follower now applies leader snapshot
+	// should be able to notify on old-revision watchers in unsynced
+	// make sure restore watch operation correctly moves watchers
+	// between synced and unsynced watchers
+	errc := make(chan error)
+	go func() {
+		cresp, cerr := wStream.Recv()
+		if cerr != nil {
+			errc <- cerr
+			return
+		}
+		// from start revision 5 to latest revision 16
+		if len(cresp.Events) != 12 {
+			errc <- fmt.Errorf("expected 12 events, got %+v", cresp.Events)
+			return
+		}
+		errc <- nil
+	}()
+	select {
+	case <-time.After(10 * time.Second):
+		t.Fatal("took too long to receive events from restored watcher")
+	case err := <-errc:
+		if err != nil {
+			t.Fatalf("wStream.Recv error: %v", err)
+		}
+	}
+}
+
 // TestV3WatchWrongRange tests wrong range does not create watchers.
 func TestV3WatchWrongRange(t *testing.T) {
 	defer testutil.AfterTest(t)