'Searches for user directories.
:param fuzzable_request: A fuzzable_request instance that contains
(among other things) the URL to test.'

@runonce(exc_class=RunOnce)
def crawl(self, fuzzable_request):

    base_url = fuzzable_request.get_url().base_url()
    non_existent = self._create_non_existent_signature(base_url)
    test_generator = self._create_tests(base_url, non_existent)
    self.worker_pool.map_multi_args(self._check_user_dir, test_generator)
