[3.12] GH-106684: Close asyncio.StreamWriter when asyncio.StreamWriter is not closed by application (GH-107650)

[miss-islington]

(cherry picked from commit 41178e4)

Co-authored-by: Kumar Aditya kumaraditya@python.org

• Issue: asyncio: potential leak of TLS connections #106684

[Yhg1s]

I think this should go into rc2, but without the warning. I think the warning is too potentially disruptive this late in the release cycle.

[miss-islington]

Thanks @miss-islington for the PR, and @Yhg1s for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

[bedevere-bot]

GH-107836 is a backport of this pull request to the 3.11 branch.

[rigens]

It seems that closing the connection in the StreamWriter's __del__ method is not a good idea. Consider the following use case

import asyncio

HOST = 'ifconfig.me'
PORT = 80


async def connect() -> asyncio.Transport:
    reader, writer = await asyncio.open_connection(
        host=HOST,
        port=PORT,
    )
    return writer.transport


async def fetch():
    loop = asyncio.get_running_loop()

    transport = await connect()
    # !!! transport is already closed here after this PR merged

    reader = asyncio.StreamReader(limit=2**16, loop=loop)
    protocol = asyncio.StreamReaderProtocol(reader, loop=loop)

    transport.set_protocol(protocol)
    loop.call_soon(protocol.connection_made, transport)
    loop.call_soon(transport.resume_reading)

    writer = asyncio.StreamWriter(
        transport=transport,
        protocol=protocol,
        reader=reader,
        loop=loop,
    )

    request = f'GET /ip HTTP/1.1\r\nHost: {HOST}\r\nConnection: close\r\n\r\n'.encode()
    writer.write(request)
    await writer.drain()

    response = await reader.read(-1)
    print(response)


if __name__ == '__main__':
    asyncio.run(fetch())