def METHOD_NAME(backend=None, rec_status=0, opts=None):
    """
    Convert a signed integer to a Recording Status String
     and cache the result.
    rec_status defaults to 0, which currently (29.0) means 'Unknown'
    """
    if not backend:
        LOG.error('rec_status_to_string(): Error: backend not set.')
        return None
    try:
        try:
            str(REC_STATUS_CACHE[rec_status])
            return REC_STATUS_CACHE[rec_status]
        except (KeyError, NameError, ValueError):
            endpoint = 'Dvr/RecStatusToString'
            rest = 'RecStatus={}'.format(rec_status)
            resp_dict = backend.send(endpoint=endpoint, rest=rest, opts=opts)
            REC_STATUS_CACHE[rec_status] = resp_dict['String']
            return REC_STATUS_CACHE[rec_status]
    except (RuntimeError, RuntimeWarning) as error:
        LOG.error('rec_status_to_string(): warning/failure: %s.', error)
        return None