'Returns filename for given timestamp.
:param timestamp: the object timestamp, an instance of
:class:`~swift.common.utils.Timestamp`
:param ext: an optional string representing a file extension to be
appended to the returned file name
:param ctype_timestamp: an optional content-type timestamp, an instance
of :class:`~swift.common.utils.Timestamp`
:returns: a file name'

def make_on_disk_filename(self, timestamp, ext=None, ctype_timestamp=None, *a, **kw):

    rv = timestamp.internal
    if ((ext == '.meta') and ctype_timestamp):
        rv = encode_timestamps(timestamp, ctype_timestamp, explicit=True)
    if ext:
        rv = ('%s%s' % (rv, ext))
    return rv
