import socket
import threading
import time
import urllib.request
from unittest.mock import patch

URL = "https://docs.python.org/3/objects.inv"

_real_getaddrinfo = socket.getaddrinfo


def _mock_getaddrinfo(host, port, *args, **kwargs):
   real = _real_getaddrinfo(host, port, socket.AF_INET, socket.SOCK_STREAM)
   ipv4 = real[0][4][0]
   return [
       (socket.AF_INET6, socket.SOCK_STREAM, 6, "", ("2001:db8::1", port, 0, 0)),
       (socket.AF_INET,  socket.SOCK_STREAM, 6, "", (ipv4, port)),
   ]


def fetch(timeout: float | None = None) -> None:
   label = f"timeout={timeout}s" if timeout else "no timeout"
   t0 = time.monotonic()
   with patch("socket.getaddrinfo", side_effect=_mock_getaddrinfo):
       try:
           with urllib.request.urlopen(URL, timeout=timeout) as resp:  # noqa: S310
               resp.read(64)
           print(f"  [{label}] OK in {time.monotonic() - t0:.1f}s (fell back to IPv4)")
       except Exception as e:
           print(f"  [{label}] {type(e).__name__} after {time.monotonic() - t0:.1f}s")


print("Bug: no timeout — hangs indefinitely on blackholed AAAA")
t = threading.Thread(target=fetch, daemon=True)
t.start()
t.join(timeout=10)
if t.is_alive():
   print("  [no timeout] confirmed still hanging after 10s")

print("\nFix: timeout=5 — IPv6 times out, falls back to A record")
fetch(timeout=5)