def _read_header_byte_data(header_structure):
    """ Reads the byte data from the data file for a PDS4 Header.

    Determines, from the structure's meta data, the relevant start and stop bytes in the data file prior to
    reading.

    Parameters
    ----------
    header_structure : HeaderStructure
        The PDS4 Header data structure for which the byte data needs to be read. Should have been
        initialized via `HeaderStructure.from_file` method, or contain the required meta data.

    Returns
    -------
    str or bytes
        The exact byte data for the header.
    """
    from .core import read_byte_data
    meta_data = header_structure.meta_data
    start_byte = meta_data['offset']
    stop_byte = start_byte + meta_data['object_length']
    return read_byte_data(header_structure.parent_filename, start_byte,
        stop_byte)
