recvmsg_example.py

# Based on http://carnivore.it/2012/10/12/python3.3_sendmsg_and_recvmsg
# Example of using the new recvmsg() method of the sockets module

import ipaddress
import socket
import ctypes

# First, we have to tell the socket we want to receive this additional data. 
# As the socket module lacks some constants, we need to define them too. 
IP_PKTINFO = 8
IPV6_PKTINFO = 50
IPV6_RECVPKTINFO = 49
SOL_IPV6 = 41

uint32_t = ctypes.c_uint32
in_addr_t = uint32_t

class in_addr(ctypes.Structure):
    _fields_ = [('s_addr', in_addr_t)]

class in_pktinfo(ctypes.Structure):
    _fields_ = [
        ('ipi_ifindex', ctypes.c_int),
        ('ipi_spec_dst', in_addr),
        ('ipi_addr', in_addr),
    ]

print("Setting up a broadcast beacon on %s:%s" %('255.255.255.255', 1200))
udp_sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
udp_sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)       
udp_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
if socket.SO_REUSEPORT in dir(socket):
    udp_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
udp_sock.setsockopt(socket.SOL_IP, IP_PKTINFO, 1)
udp_sock.bind(('255.255.255.255', 1200))

while True:
    data, ancdata, msg_flags, _from = udp_sock.recvmsg(5120, socket.CMSG_LEN(5120 * 5))
    for anc in ancdata:
        if anc[0] == socket.SOL_IP and anc[1] == IP_PKTINFO:
            inf = in_pktinfo.from_buffer_copy(anc[2])
            addr = ipaddress.IPv4Address(memoryview(inf.ipi_addr).tobytes())
            daddr = ipaddress.IPv4Address(memoryview(inf.ipi_spec_dst).tobytes())
            idx = inf.ipi_ifindex
            print(data, addr, daddr, idx)