Own implementation of getaddrinfo by calling libc directly from Python + ctypes, supporting IPv4 and IPv6 (experimental)

getaddrinfo_via_libc.py

from ctypes import (
    byref,
    c_char_p, c_uint32, c_uint16, c_ubyte,
    CDLL,
    POINTER,
    pointer,
    Structure, Union,
    sizeof,
)
import platform
from socket import (
    inet_ntop,
    AF_INET,
    AF_INET6,
)


libc = CDLL(None)


class c_sockaddr_in4(Structure):
    _fields_ = [
        ('sin_family', c_uint16),
        ('sin_port', c_uint16),
        ('sin_addr', c_ubyte * 4),
    ]


class c_sockaddr_in6(Structure):
    _fields_ = [
        ('sin_family', c_uint16),
        ('sin_port', c_uint16),
        ('sin_flowinfo', c_uint32),
        ('sin_addr', c_ubyte * 16),
        ('sin_scope_id', c_uint32),
    ]


class c_sockaddr_in(Union):
    _fields_ = [
        ('ai_addr4', c_sockaddr_in4),
        ('ai_addr6', c_sockaddr_in6),
    ]


class c_addrinfo(Structure):
    pass


c_addrinfo._fields_ = [
    ('ai_flags', c_uint32),
    ('ai_family', c_uint32),
    ('ai_socktype', c_uint32),
    ('ai_protocol', c_uint32),
    ('ai_addrlen', c_uint32),
] + ([
    ('ai_canonname', c_char_p),
    ('ai_addr', POINTER(c_sockaddr_in)),
] if platform.system() == 'Darwin' else [
    ('ai_addr', POINTER(c_sockaddr_in)),
    ('ai_canonname', c_char_p),
]) + [
    ('ai_next', POINTER(c_addrinfo)),
]

c_addrinfo_p = POINTER(c_addrinfo)

address_field_names = {
    AF_INET: 'ai_addr4',
    AF_INET6: 'ai_addr6',
}

def getaddrinfo(host, port, family=0, type=0, proto=0, flags=0):
    result = c_addrinfo_p()
    hints = c_addrinfo()

    hints.flags = flags
    hints.ai_family = family
    hints.ai_socktype = type
    hints.proto = proto

    result = c_addrinfo_p()
    error = libc.getaddrinfo(
        c_char_p(host),
        c_char_p(port) if port is not None else None,
        byref(hints),
        byref(result),
    )
    if error:
        raise Exception(error)

    result_addrinfo = result.contents
    family = result_addrinfo.ai_family
    address_field_name = address_field_names[family]
    address_field = getattr(result_addrinfo.ai_addr.contents, address_field_name)
    address_raw = address_field.sin_addr

    address = inet_ntop(family, address_raw)
    libc.freeaddrinfo(result)

    return (family, address)


print(getaddrinfo(b'www.google.com', None, family=AF_INET6))