'Searches for links on the html.
:param fuzzable_req: A fuzzable_req instance that contains
(among other things) the URL to test.'

def crawl(self, fuzzable_req):

    self._handle_first_run()
    data_container = fuzzable_req.get_raw_data()
    if isinstance(data_container, Form):
        if (fuzzable_req.get_url() in self._already_filled_form):
            return
        self._already_filled_form.add(fuzzable_req.get_url())
        data_container.smart_fill()
    resp = self._uri_opener.send_mutant(fuzzable_req)
    if (resp.get_code() == http_constants.UNAUTHORIZED):
        return
    if resp.is_image():
        return
    if is_404(resp):
        return
    self._extract_html_forms(resp, fuzzable_req)
    self._extract_links_and_verify(resp, fuzzable_req)
