Timeout during AnyIOStream.start_tls causes stuck connections in the pool when using AsyncHTTPProxy

[ariallas]

Example

Hi!
Please excuse my hacky way to demonstrate the issue:

Setup:

• python 3.11.5
• httpcore[asyncio]==1.0.5
• proxy.py

import asyncio
import logging
import random

import httpcore
import httpcore._backends.anyio

# Wrapper for start_tls to artificially cause a timeout
def random_timeout_wrapper(f):
    async def _wrapper(*args, **kwargs):
        if random.randrange(2) == 1:
            if len(args) == 4:
                args = args[:3]
            kwargs["timeout"] = 0.001
            print(f"\nAbout to time out\n")
        return await f(*args, **kwargs)

    return _wrapper

httpcore._backends.anyio.AnyIOStream.start_tls = random_timeout_wrapper(
    httpcore._backends.anyio.AnyIOStream.start_tls
)

async def async_main():
    logging.basicConfig(level=0)

    async with httpcore.AsyncHTTPProxy(
        proxy_url="http://127.0.0.1:8080/", max_connections=256
    ) as proxy:
        while True:
            try:
                response = await proxy.request("GET", "https://www.example.com/")
                print(response)
                print(proxy.connections)
            except Exception as e:
                pass
            await asyncio.sleep(2)

if __name__ == "__main__":
    asyncio.run(async_main())

To replicate:

• Start proxy.py: proxy --hostname 127.0.0.1 --port 8080
• Start the script
• Shutdown and restart the proxy a couple of times

You should see that every time a timeout happens during start_tls, after just having reconnected to the proxy, there is a new stuck connection in the pool that looks like this: <AsyncTunnelHTTPConnection ['http://127.0.0.1:8080', HTTP/1.1, ACTIVE, Request Count: 1]>

Context

We have a bunch of Telegram bots on python-telegram-bot running behind a proxy. Once every couple of weeks they all simultaneously stop responding - judging by the logs this seems to be the root issue.