protected function multipartGetTags($part_num, $s3_results, &$parts_etags)
    {
        foreach ($s3_results as $result) {
            if (isset($result['value']) && $result['value']) {
                $etag = $result['value']->getHeader('ETag')[0];
                $part_etag = sprintf('%s:%s', $part_num, $etag);
                array_push($parts_etags, $part_etag);
            }
        }
    }