How to use the sshuttle.helpers.Fatal function in sshuttle

def nft_get_handle(expression, chain):
    cmd = 'nft'
    argv = [cmd, 'list', expression, '-a']
    env = {
        'PATH': os.environ['PATH'],
        'LC_ALL': "C",
    }
    try:
        output = ssubprocess.check_output(argv, env=env)
        for line in output.decode('utf-8').split('\n'):
            if ('jump %s' % chain) in line:
                return re.sub('.*# ', '', line)
    except ssubprocess.CalledProcessError as e:
        raise Fatal('%r returned %d' % (argv, e.returncode))

def pfctl(args, stdin=None):
    argv = ['pfctl'] + shlex.split(args)
    debug1('>> %s\n' % ' '.join(argv))

    env = {
        'PATH': os.environ['PATH'],
        'LC_ALL': "C",
    }
    p = ssubprocess.Popen(argv, stdin=ssubprocess.PIPE,
                          stdout=ssubprocess.PIPE,
                          stderr=ssubprocess.PIPE,
                          env=env)
    o = p.communicate(stdin)
    if p.returncode:
        raise Fatal('%r returned %d' % (argv, p.returncode))

    return o

mux = Mux(serversock, serversock)
    handlers.append(mux)

    expected = b'SSHUTTLE0001'

    try:
        v = 'x'
        while v and v != b'\0':
            v = serversock.recv(1)
        v = 'x'
        while v and v != b'\0':
            v = serversock.recv(1)
        initstring = serversock.recv(len(expected))
    except socket.error as e:
        if e.args[0] == errno.ECONNRESET:
            raise Fatal("failed to establish ssh session (2)")
        else:
            raise

    rv = serverproc.poll()
    if rv:
        raise Fatal('server died with error code %d' % rv)

    if initstring != expected:
        raise Fatal('expected server init string %r; got %r'
                    % (expected, initstring))
    log('Connected.\n')
    sys.stdout.flush()
    if daemon:
        daemonize()
        log('daemonizing (%s).\n' % _pidname)

# These should never fail.
    # If these do fail, something is broken above.
    if subnets_v6:
        assert required.ipv6
        if redirectport_v6 == 0:
            raise Fatal("IPv6 subnets defined but not listening")

    if nslist_v6:
        assert required.dns
        assert required.ipv6
        if dnsport_v6 == 0:
            raise Fatal("IPv6 ns servers defined but not listening")

    if subnets_v4:
        if redirectport_v4 == 0:
            raise Fatal("IPv4 subnets defined but not listening")

    if nslist_v4:
        if dnsport_v4 == 0:
            raise Fatal("IPv4 ns servers defined but not listening")

    # setup method specific stuff on listeners
    fw.method.setup_tcp_listener(tcp_listener)
    if udp_listener:
        fw.method.setup_udp_listener(udp_listener)
    if dns_listener:
        fw.method.setup_udp_listener(dns_listener)

    # start the firewall
    fw.setup(subnets_include, subnets_exclude, nslist,
             redirectport_v6, redirectport_v4, dnsport_v6, dnsport_v4,
             required.udp, user)

avail = fw.method.get_supported_features()
    required = Features()

    if listenip_v6 == "auto":
        if avail.ipv6:
            listenip_v6 = ('::1', 0)
        else:
            listenip_v6 = None

    if user is not None:
        if getpwnam is None:
            raise Fatal("Routing by user not available on this system.")
        try:
            user = getpwnam(user).pw_uid
        except KeyError:
            raise Fatal("User %s does not exist." % user)

    if fw.method.name != 'nat':
        required.ipv6 = len(subnets_v6) > 0 or listenip_v6 is not None
        required.ipv4 = len(subnets_v4) > 0 or listenip_v4 is not None
    else:
        required.ipv6 = None
        required.ipv4 = None

    required.udp = avail.udp
    required.dns = len(nslist) > 0
    required.user = False if user is None else True

    # if IPv6 not supported, ignore IPv6 DNS servers
    if not required.ipv6:
        nslist_v6 = []
        nslist = nslist_v4

family = int(data)
        mux.channels[channel] = lambda cmd, data: udp_req(channel, cmd, data)
        if channel in udphandlers:
            raise Fatal('UDP connection channel %d already open' % channel)
        else:
            h = UdpProxy(mux, channel, family)
            handlers.append(h)
            udphandlers[channel] = h
    mux.got_udp_open = udp_open

    while mux.ok:
        if hw.pid:
            assert(hw.pid > 0)
            (rpid, rv) = os.waitpid(hw.pid, os.WNOHANG)
            if rpid:
                raise Fatal(
                    'hostwatch exited unexpectedly: code 0x%04x\n' % rv)

        ssnet.runonce(handlers, mux)
        if latency_control:
            mux.check_fullness()

        if dnshandlers:
            now = time.time()
            remove = []
            for channel, h in dnshandlers.items():
                if h.timeout < now or not h.ok:
                    debug3('expiring dnsreqs channel=%d\n' % channel)
                    remove.append(channel)
                    h.ok = False
            for channel in remove:
                del dnshandlers[channel]

def ipt(family, table, *args):
    if family == socket.AF_INET6:
        argv = ['ip6tables', '-t', table] + list(args)
    elif family == socket.AF_INET:
        argv = ['iptables', '-t', table] + list(args)
    else:
        raise Exception('Unsupported family "%s"' % family_to_string(family))
    debug1('>> %s\n' % ' '.join(argv))
    env = {
        'PATH': os.environ['PATH'],
        'LC_ALL': "C",
    }
    rv = ssubprocess.call(argv, env=env)
    if rv:
        raise Fatal('%r returned %d' % (argv, rv))

def setup_daemon():
    if os.getuid() != 0:
        raise Fatal('you must be root (or enable su/sudo) to set the firewall')

    # don't disappear if our controlling terminal or stdout/stderr
    # disappears; we still have to clean up.
    signal.signal(signal.SIGHUP, signal.SIG_IGN)
    signal.signal(signal.SIGPIPE, signal.SIG_IGN)
    signal.signal(signal.SIGTERM, signal.SIG_IGN)
    signal.signal(signal.SIGINT, signal.SIG_IGN)

    # ctrl-c shouldn't be passed along to me.  When the main sshuttle dies,
    # I'll die automatically.
    os.setsid()

    # because of limitations of the 'su' command, the *real* stdin/stdout
    # are both attached to stdout initially.  Clone stdout into stdin so we
    # can read from it.
    os.dup2(1, 0)

def nft(family, table, action, *args):
    if family == socket.AF_INET:
        argv = ['nft', action, 'ip', table] + list(args)
    elif family == socket.AF_INET6:
        argv = ['nft', action, 'ip6', table] + list(args)
    else:
        raise Exception('Unsupported family "%s"' % family_to_string(family))
    debug1('>> %s\n' % ' '.join(argv))
    env = {
        'PATH': os.environ['PATH'],
        'LC_ALL': "C",
    }
    rv = ssubprocess.call(argv, env=env)
    if rv:
        raise Fatal('%r returned %d' % (argv, rv))

opt.auto_nets,
                                      includes,
                                      excludes,
                                      opt.daemon,
                                      opt.to_ns,
                                      opt.pidfile,
                                      opt.user,
                                      opt.sudo_pythonpath)

            if return_code == 0:
                log('Normal exit code, exiting...')
            else:
                log('Abnormal exit code %d detected, failing...' % return_code)
            return return_code

    except Fatal as e:
        log('fatal: %s\n' % e)
        return 99
    except KeyboardInterrupt:
        log('\n')
        log('Keyboard interrupt: exiting.\n')
        return 1