Get original dest addr for FreeBSD pf

pf_get_orig_dst.py

import os
import fcntl
import ctypes
import socket
import struct

PF_OUT = 2
DIOCNATLOOK = 0xc04c4417

class pf_addr(ctypes.Structure):
    class _pfa(ctypes.Union):
        _fields_ = [
            ('v4', ctypes.c_uint32),
            ('v6', ctypes.c_uint32 * 4),
            ('addr8', ctypes.c_uint8 * 16),
            ('addr16', ctypes.c_uint16 * 8),
            ('addr32', ctypes.c_uint32 * 4),
        ]

    _fields_ = [('pfa', _pfa)]
    _anonymous_ = ('pfa',)

class pfioc_natlook(ctypes.Structure):
    _fields_ = [
        ('saddr', pf_addr),
        ('daddr', pf_addr),
        ('rsaddr', pf_addr),
        ('rdaddr', pf_addr),
        ('sport', ctypes.c_uint16),
        ('dport', ctypes.c_uint16),
        ('rsport', ctypes.c_uint16),
        ('rdport', ctypes.c_uint16),
        ('af', ctypes.c_uint8),
        ('proto', ctypes.c_uint8),
        ('direction', ctypes.c_uint8),
    ]

def get_orig_dst(sock):
    saddr, sport = sock.getpeername()
    daddr, dport = sock.getsockname()
    nl = pfioc_natlook()
    nl.saddr.v4, = struct.unpack('<I', socket.inet_aton(saddr))
    nl.daddr.v4, = struct.unpack('<I', socket.inet_aton(daddr))
    nl.sport = socket.htons(sport)
    nl.dport = socket.htons(dport)
    nl.af = socket.AF_INET
    nl.proto = socket.IPPROTO_TCP
    nl.direction = PF_OUT
    fd = os.open('/dev/pf', os.O_RDONLY)
    fcntl.ioctl(fd, DIOCNATLOOK, nl)
    os.close(fd)
    rdaddr = socket.inet_ntoa(struct.pack('<I', nl.rdaddr.v4))
    rdport = socket.ntohs(nl.rdport)
    return rdaddr, rdport

s = socket.socket()
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(('127.0.0.1', 10080))
s.listen(1)

while True:
    c, _ = s.accept()
    print get_orig_dst(c)
    c.close()