How to use the xandikos.webdav.traverse_resource function in xandikos

if limit is not None:
            try:
                [nresults_el] = list(limit)
            except ValueError:
                raise webdav.BadRequestError(
                    'Invalid number of subelements in limit')
            try:
                nresults = int(nresults_el.text)
            except ValueError:
                raise webdav.BadRequestError(
                    'nresults not a number')
        else:
            nresults = None

        i = 0
        async for (href, resource) in webdav.traverse_resource(
                base_resource, base_href, depth):
            if not apply_filter(filter_el, resource):
                continue
            if nresults is not None and i >= nresults:
                break
            propstat = davcommon.get_properties_with_data(
                self.data_property, href, resource, properties, environ,
                requested)
            yield webdav.Status(
                href, '200 OK', propstat=[s async for s in propstat])
            i += 1

raise webdav.BadRequestError(
                    'Unknown tag %s in report %s' % (el.tag, self.name))
        if tztext is not None:
            tz = get_pytz_from_text(tztext)
        else:
            tz = get_calendar_timezone(base_resource)

        def filter_fn(cls):
            return parse_filter(filter_el, cls(tz))

        def members(collection):
            return itertools.chain(
                collection.calendar_query(filter_fn),
                collection.subcollections())

        async for (href, resource) in webdav.traverse_resource(
                base_resource, base_href, depth,
                members=members):
            # Ideally traverse_resource would only return the right things.
            if getattr(resource, 'content_type', None) == 'text/calendar':
                propstat = davcommon.get_properties_with_data(
                    self.data_property, href, resource, properties, environ,
                    requested)
                yield webdav.Status(
                    href, '200 OK', propstat=[s async for s in propstat])

tz = get_calendar_timezone(base_resource)

        def tzify(dt):
            return as_tz_aware_ts(dt, tz).astimezone(pytz.utc)
        (start, end) = _parse_time_range(requested)
        assert start.tzinfo
        assert end.tzinfo
        ret = ICalendar()
        ret['VERSION'] = '2.0'
        ret['PRODID'] = PRODID
        fb = FreeBusy()
        fb['DTSTAMP'] = vDDDTypes(tzify(datetime.datetime.now()))
        fb['DTSTART'] = vDDDTypes(start)
        fb['DTEND'] = vDDDTypes(end)
        fb['FREEBUSY'] = [item async for item in iter_freebusy(
            webdav.traverse_resource(base_resource, base_href, depth),
            start, end, tzify)]
        ret.add_component(fb)
        return webdav.Response(status='200 OK', body=[ret.to_ical()])