def file_record_to_url(file_records, urls=[]):
    """
    Translate a Json dictionary to an usable http url for downlading files.

    :param file_records: json containing a 'data_url' field
    :type file_records: dict
    :param urls: a list of strings containing previous data_urls on which new urls
     will be appended
    :type urls: list

    :return: urls: (list) a list of strings representing full data urls
    """
    for fr in file_records:
        if fr['data_url'] is not None:
            urls.append(fr['data_url'])
    return urls
