upstream-dns-lookups.py

import sys
import socket
import subprocess

LOOKUPS = [
    "unity.rc.umass.edu.",
    "ood.unity.rc.umass.edu.",
    "docs.unity.rc.umass.edu.",
]

def dig_query(name, nameserver="8.8.8.8"):
    try:
        result = subprocess.check_output(["dig", "+short", f"@{nameserver}", name])
        return [x.strip() for x in result.decode().split('\n') if x]
    except subprocess.CalledProcessError:
        return []

# https://stackoverflow.com/a/81899
def is_ipv4_addr(x: str) -> bool:
    try:
        socket.inet_pton(socket.AF_INET, x)
        return True
    except socket.error:
        return False

# https://stackoverflow.com/a/81899
def is_ipv6_addr(x: str) -> bool:
    try:
        socket.inet_pton(socket.AF_INET6, x)
        return True
    except socket.error:
        return False

def is_ip_addr(x: str) -> bool:
    return is_ipv4_addr(x) or is_ipv6_addr(x)

def mapping2zone_file(name: str, result: str) -> str:
    if is_ipv4_addr(result):
        return f"{name} IN A {result}"
    if is_ipv6_addr(result):
        return f"{name} IN AAAA {result}"
    return f"{name} IN CNAME {result}"

for lookup in LOOKUPS:
    results = dig_query(lookup)
    if len(results) == 0:
        print(f"NXDOMAIN {lookup}", file=sys.stderr)
        continue
    # if any one of the results is not an IP address, then delete all non IP address results
    if not all([is_ip_addr(x) for x in results]):
        results = [x for x in results if not is_ip_addr(x)]
    for result in results:
        print(mapping2zone_file(lookup, result))