test: drain multicast queues before TOCTOU race assertion

bdraco · bdraco · commit f9167cf6738f · 2026-05-17T09:58:12.000-07:00
`test_service_info_async_request` patches `_is_complete` to False
to keep the loop running. With `quick_timing` registrations
complete within ~30ms, leaving multicast responses pending in
`out_queue` / `out_delay_queue` that snapshot the records as
they were *before* `async_update_service` swapped the registry
to `new_info`. When those stale answers flush after
`_clear_cache`, they re-cache `xxxyyy._test1-srvc-type._tcp.local.
-&gt; ash-1.local. -&gt; 10.0.1.2` and set the AsyncServiceInfo's
server to `ash-1.local.`. The patched `_is_complete=False` loop
then keeps asking for A records for `ash-1.local.`, which nothing
in the registry answers, so the assertion fails:

    AssertionError: assert [b'\\n\\x00\\x01\\x02'] == [b'\\n\\x00\\x01\\x03']

Sleep 1.5s before clearing the cache so both queues drain (max
~620ms for `out_queue` and ~1320ms for `out_delay_queue`) and
only the up-to-date registry state is left for the loop to
observe.
diff --git a/tests/test_asyncio.py b/tests/test_asyncio.py
@@ -695,6 +695,16 @@ async def test_service_info_async_request(quick_timing: None) -> None:
     assert aiosinfos[1] is not None
     assert aiosinfos[1].addresses == [socket.inet_aton("10.0.1.5")]
 
+    # Drain the multicast outgoing queues before clearing the cache.
+    # Responses to the earlier `async_get_service_info` queries can
+    # sit in `out_queue` (up to ~620ms) or `out_delay_queue`
+    # (up to ~1320ms) carrying snapshots of the records taken
+    # *before* `async_update_service` swapped the registry to
+    # `new_info`. If those stale answers flush after `_clear_cache`,
+    # they poison `aiosinfo.server` with `ash-1.local.` and the
+    # `_is_complete=False` loop never recovers because subsequent
+    # queries ask for an A record nobody answers.
+    await asyncio.sleep(1.5)
     aiosinfo = AsyncServiceInfo(type_, registration_name)
     _clear_cache(aiozc.zeroconf)
     # Generating the race condition is almost impossible
