errno attribute in the aiohttp.ClientConnectorError exception is lost after 3.10.0 when multiple connection attempts fail

[x0day]

Describe the bug

After aiohttp version 3.10.0, the errno attribute in the aiohttp.ClientConnectorError exception has changed.

To Reproduce

the case is worked before 3.10.0.

pip install pytest pytest-httpserver

import aiohttp
import pytest
import errno
from pytest_httpserver import HTTPServer

pytestmark = pytest.mark.asyncio


async def test_session_will_raise_connection_refused_error(
    httpserver: HTTPServer
):
    httpserver.expect_request("/foobar").respond_with_data("OK")
    httpserver.stop()

    session = aiohttp.ClientSession()
    try:
        await session.get(httpserver.url_for("/foobar"))
    except aiohttp.ClientConnectorError as exc:
        # check port closed error.
        assert exc.errno == errno.ECONNREFUSED
    finally:
        await session.close()

Expected behavior

testcase is passed

Logs/tracebacks

None != 61

Expected :61
Actual   :None
<Click to see difference>

../../../Library/Caches/pypoetry/virtualenvs/workspace/lib/python3.11/site-packages/aiohttp/connector.py:1036: in _wrap_create_connection
    sock = await aiohappyeyeballs.start_connection(
../../../Library/Caches/pypoetry/virtualenvs/workspace/lib/python3.11/site-packages/aiohappyeyeballs/impl.py:112: in start_connection
    raise OSError(
E   OSError: Multiple exceptions: [Errno 61] Connect call failed ('::1', 50139, 0, 0), [Errno 61] Connect call failed ('127.0.0.1', 50139)

The above exception was the direct cause of the following exception:
test4.py:17: in test_session_will_raise_connection_refused_error
    await session.get(httpserver.url_for("/foobar"))
../../../Library/Caches/pypoetry/virtualenvs/workspace/lib/python3.11/site-packages/aiohttp/client.py:648: in _request
    conn = await self._connector.connect(
../../../Library/Caches/pypoetry/virtualenvs/workspace/lib/python3.11/site-packages/aiohttp/connector.py:546: in connect
    proto = await self._create_connection(req, traces, timeout)
../../../Library/Caches/pypoetry/virtualenvs/workspace/lib/python3.11/site-packages/aiohttp/connector.py:954: in _create_connection
    _, proto = await self._create_direct_connection(req, traces, timeout)
../../../Library/Caches/pypoetry/virtualenvs/workspace/lib/python3.11/site-packages/aiohttp/connector.py:1313: in _create_direct_connection
    raise last_exc
../../../Library/Caches/pypoetry/virtualenvs/workspace/lib/python3.11/site-packages/aiohttp/connector.py:1282: in _create_direct_connection
    transp, proto = await self._wrap_create_connection(
../../../Library/Caches/pypoetry/virtualenvs/workspace/lib/python3.11/site-packages/aiohttp/connector.py:1051: in _wrap_create_connection
    raise client_error(req.connection_key, exc) from exc
E   aiohttp.client_exceptions.ClientConnectorError: Cannot connect to host localhost:50139 ssl:default [None]

During handling of the above exception, another exception occurred:
test4.py:20: in test_session_will_raise_connection_refused_error
    assert exc.errno == errno.ECONNREFUSED
E   assert None == 61
E    +  where None = ClientConnectorError(ConnectionKey(host='localhost', port=50139, is_ssl=False, ssl=True, proxy=None, proxy_auth=None, proxy_headers_hash=None), OSError("Multiple exceptions: [Errno 61] Connect call failed ('::1', 50139, 0, 0), [Errno 61] Connect call failed ('127.0.0.1', 50139)")).errno
E    +  and   61 = errno.ECONNREFUSED

Python Version

$ python --version
Python 3.11.8

aiohttp Version

$ python -m pip show aiohttp
Name: aiohttp
Version: 3.10.0
Summary: Async http client/server framework (asyncio)
Home-page: https://github.com/aio-libs/aiohttp
Author: 
Author-email: 
License: Apache 2
Requires: aiohappyeyeballs, aiosignal, attrs, frozenlist, multidict, yarl
Required-by: aiohttp-socks, aioresponses

multidict Version

$ python -m pip show multidict

yarl Version

$ python -m pip show yarl
Name: multidict
Version: 6.0.5
Summary: multidict implementation
Home-page: https://github.com/aio-libs/multidict
Author: Andrew Svetlov
Author-email: andrew.svetlov@gmail.com
License: Apache 2

OS

macos

Related component

Client

Additional context

No response

Code of Conduct

• I agree to follow the aio-libs Code of Conduct

[bdraco]

This is expected as that is how cpython combines exceptions

https://github.com/python/cpython/blob/9e551f9b351440ebae79e07a02d0e4a1b61d139e/Lib/asyncio/base_events.py#L1163

[bdraco]

I agree that behavior is less than ideal, but I don't have a good suggestion on how to improve it in cpython. Would you please open an issue at https://github.com/python/cpython/issues/new/choose Perhaps someone will have an idea on how to improve that.

[bdraco]

Ideally cpython would raise an ExceptionGroup but I think thats a breaking change.

[bdraco]

It looks like 3.12+ allows getting all the exceptions

python/cpython#93974

[bdraco]

We could backport that change to aiohappyeyeballs but there is another issue since ExceptionGroup is 3.11+ only.