return err
	}

	wk, err := workers.New(workerSize)
	if err != nil {
		// invalid worker size.
		return err
	}

	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	results := make(chan ObjectInfo, workerSize)
	if err := api.Walk(ctx, r.Bucket, r.Prefix, results, WalkOptions{
		Marker:       lastObject,