Given a URL, turn it into (host, port) for a blockstack server.
    Return (None, None) on invalid URL

def url_to_host_port(url, port=None):
    """
    Given a URL, turn it into (host, port) for a blockstack server.
    Return (None, None) on invalid URL
    """
    if not url.startswith('http://') and not url.startswith('https://'):
        url = 'http://' + url

    if not port:
        port = RPC_SERVER_PORT

    urlinfo = urllib2.urlparse.urlparse(url)
    hostport = urlinfo.netloc

    parts = hostport.split('@')
    if len(parts) > 2:
        return None, None

    if len(parts) == 2:
        hostport = parts[1]

    parts = hostport.split(':')
    if len(parts) > 2:
        return None, None

    if len(parts) == 2:
        try:
            port = int(parts[1])
            assert 0 < port and port < 65535, 'Invalid port'
        except TypeError:
            return None, None

    return parts[0], port