storage/remote/read.go
func ExternalLabelsHandler(next storage.Queryable, externalLabels labels.Labels) storage.Queryable {
	return storage.QueryableFunc(func(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
		q, err := next.Querier(ctx, mint, maxt)
		if err != nil {
			return nil, err
		}
		return &externalLabelsQuerier{Querier: q, externalLabels: externalLabels}, nil
	})
}
func ExternalLabelsHandler(next storage.Queryable, externalLabels labels.Labels) storage.Queryable {
	return storage.QueryableFunc(func(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
		q, err := next.Querier(ctx, mint, maxt)
		if err != nil {
			return nil, err
		}
		return &externalLabelsQuerier{Querier: q, externalLabels: externalLabels}, nil
	})
}
// ExternalLabelsHandler returns a storage.Queryable which creates a
// externalLabelsQuerier.