Quickly check if an IPv4 is contained in a list of subnets.

subnetlist.py

import struct
import socket

class SubnetList:
    """Quickly check if an IPv4 is contained in a list of subnets.
    - by @nil0x42
    - inspired by @nigel222's solution: https://stackoverflow.com/a/44264136
    >>> cloudflare_ips = SubnetList("/wordlists/cloudflare-ips.txt")
    >>> "103.31.4.12" in cloudflare_ips
    True
    >>> "127.0.0.1" in cloudflare_ips
    False
    """
    def __init__(self, subnets_path=None):
        self.subnets = [set() for x in range(32+1)]
        if subnets_path:
            for line in open(subnets_path):
                line = line.strip()
                if not line or line.startswith("#"):
                    continue
                self.add(line)

    def __contains__(self, ip):
        ip = self._ip2int(ip)
        for N in range(32, 7, -1): # check N from 32 to 8
            mask = 0xffffffff >> 32-N << 32-N
            if ip & mask in self.subnets[N]:
                return True
        return False

    def add(self, subnet):
        if "/" in subnet:
            network, N = subnet.split('/')
            N = int(N)
            assert 8 <= N <= 32, "invalid subnet mask in %r" % subnet
        else:
            network, N = subnet, 32
        network = self._ip2int(network)
        self.subnets[N].add(network >> 32-N << 32-N)

    def _ip2int(self, ip):
        return struct.unpack("!I", socket.inet_aton(ip))[0]