def _agg_data(data_strs):
    """
    Auxiliary function that aggregates data of a job to a single byte string
    """
    ranges = []
    pos = 0
    for datum in data_strs:
        datum_len = len(datum)
        ranges.append((pos, pos+datum_len-1))
        pos += datum_len
    return b"".join(data_strs), ranges