[webtransport] Suppress benign error from StreamWriter.close()

The error is logged when the client initially checks for connectivity,
which is unnecessarily confusing to users.

Needed for Chromium's python3.8 -> python3.11 upgrade.

tools/webtransport/h3/webtransport_h3_server.py

@@ -1,6 +1,7 @@
 # mypy: allow-subclassing-any, no-warn-return-any
 
 import asyncio
+import contextlib
 import logging
 import os
 import ssl
@@ -9,17 +10,21 @@
 import traceback
 from enum import IntEnum
 from urllib.parse import urlparse
-from typing import Any, Dict, List, Optional, Tuple
+from typing import Any, Dict, List, Optional, Tuple, cast
 
 # TODO(bashi): Remove import check suppressions once aioquic dependency is resolved.
 from aioquic.buffer import Buffer # type: ignore
 from aioquic.asyncio import QuicConnectionProtocol, serve # type: ignore
 from aioquic.asyncio.client import connect # type: ignore
+from aioquic.asyncio.protocol import QuicStreamAdapter # type: ignore
 from aioquic.h3.connection import H3_ALPN, FrameType, H3Connection, ProtocolError, SettingsError # type: ignore
 from aioquic.h3.events import H3Event, HeadersReceived, WebTransportStreamDataReceived, DatagramReceived, DataReceived # type: ignore
 from aioquic.quic.configuration import QuicConfiguration # type: ignore
 from aioquic.quic.connection import logger as quic_connection_logger # type: ignore
-from aioquic.quic.connection import stream_is_unidirectional
+from aioquic.quic.connection import (
+ stream_is_client_initiated,
+ stream_is_unidirectional,
+)
 from aioquic.quic.events import QuicEvent, ProtocolNegotiated, ConnectionTerminated, StreamReset # type: ignore
 from aioquic.tls import SessionTicket # type: ignore
 
@@ -602,12 +607,32 @@ async def _connect_server_with_timeout(host: str, port: int, timeout: float) ->
  return True
 
 
+def _close_unusable_writer(reader: asyncio.StreamReader, writer: asyncio.StreamWriter) -> None:
+ # Starting in python3.11, `StreamWriter.__del__` implicitly `close()`s
+ # itself [0], if it has not done so already. Because aioquic sometimes
+ # models a unidirectional stream with a bidirectional transport [1], the
+ # `writer` here for a server -> client stream may log a benign but
+ # scary-looking exception when it's GC'ed and unsuccessfully writes EOF.
+ #
+ # For the purpose of checking connectivity, work around this for now by
+ # preemptively closing such streams and suppressing the resulting
+ # exceptions.
+ #
+ # [0]: https://github.com/python/cpython/blob/3.11/Lib/asyncio/streams.py#L413
+ # [1]: https://github.com/aiortc/aioquic/blob/1.2.0/src/aioquic/asyncio/protocol.py#L241
+ stream_id = cast(QuicStreamAdapter, writer.transport).stream_id
+ if stream_is_unidirectional(stream_id) and not stream_is_client_initiated(stream_id):
+ with contextlib.suppress(ValueError):
+ writer.close()
+
+
 async def _connect_to_server(host: str, port: int) -> None:
  configuration = QuicConfiguration(
  alpn_protocols=H3_ALPN,
  is_client=True,
  verify_mode=ssl.CERT_NONE,
  )
 
- async with connect(host, port, configuration=configuration) as protocol:
+ async with connect(host, port, configuration=configuration,
+ stream_handler=_close_unusable_writer) as protocol:
  await protocol.ping()