import re


def original_url_from_httrack_comment(html):
    """ Extracts the original url from HTTrack comment """
    url = "unknown_url"
    for m in re.finditer(
            "<!-- Mirrored from ([^>]+) by HTTrack Website Copier", html):
        url = m.groups()[0]
        if not url.startswith('http://'):
            url = "http://" + url
    return url