import ctypes
import socket

from libnl.error import errmsg
from libnl.handlers import NL_CB_CUSTOM, NL_CB_VALID, NL_OK
from libnl.linux_private.if_link import IFLA_IFNAME, IFLA_RTA
from libnl.linux_private.netlink import NETLINK_ROUTE, NLMSG_LENGTH, NLM_F_DUMP, NLM_F_REQUEST
from libnl.linux_private.rtnetlink import RTA_DATA, RTA_NEXT, RTA_OK, RTM_GETLINK, ifinfomsg, rtgenmsg
from libnl.misc import get_string
from libnl.msg import nlmsg_data, nlmsg_hdr
from libnl.nl import nl_connect, nl_recvmsgs_default, nl_send_simple
from libnl.socket_ import nl_socket_alloc, nl_socket_modify_cb


def callback(msg, _):
    nlh = nlmsg_hdr(msg)
    iface = ifinfomsg(nlmsg_data(nlh))
    hdr = IFLA_RTA(iface)
    remaining = ctypes.c_int(nlh.nlmsg_len - NLMSG_LENGTH(iface.SIZEOF))
    while RTA_OK(hdr, remaining):
        if hdr.rta_type == IFLA_IFNAME:
            print('Found interface {0}: {1}'.format(iface.ifi_index, get_string(RTA_DATA(hdr)).decode('ascii')))
        hdr = RTA_NEXT(hdr, remaining)
    return NL_OK


sk = nl_socket_alloc()  # Creates an nl_sock instance.
ret = nl_connect(sk, NETLINK_ROUTE)  # Create file descriptor and bind socket.
if ret < 0:
    raise RuntimeError('nl_connect() returned {0} ({1})'.format(ret, errmsg[abs(ret)]))
rt_hdr = rtgenmsg(rtgen_family=socket.AF_PACKET)
ret = nl_send_simple(sk, RTM_GETLINK, NLM_F_REQUEST | NLM_F_DUMP, rt_hdr, rt_hdr.SIZEOF)
if ret < 0:
    raise RuntimeError('nl_send_simple() returned {0} ({1})'.format(ret, errmsg[abs(ret)]))
nl_socket_modify_cb(sk, NL_CB_VALID, NL_CB_CUSTOM, callback, None)  # Add callback to the nl_sock instance.
ret = nl_recvmsgs_default(sk)  # Get kernel's answer, and call attached callbacks.
if ret < 0:
    raise RuntimeError('nl_recvmsgs_default() returned {0} ({1})'.format(ret, errmsg[abs(ret)]))