Raise a error if web-handler returned non-response in debug mode.

[benitogf]

Long story short

Opening this as mentioned here: #3223 (comment)

Unhandled exception
Traceback (most recent call last):
  File "/tmp/tmpg2n5yr0j/pypi__aiohttp_3_4_4/aiohttp/web_protocol.py", line 410, in start
    await resp.prepare(request)
AttributeError: 'NoneType' object has no attribute 'prepare'

Expected behaviour

It should't trow

Actual behaviour

There's an unhandled exception thrown

Steps to reproduce

This happens in a websocket route handler when a client disconnects

Your environment

aiohttp 3.4.4
OS centos
no proxy

[aio-libs-bot]

GitMate.io thinks possibly related issues are #255 (Handling WebSocket disconnects), #1661 (Client exceptions refactoring), #3223 (Should not throw exception for EofStream Exception in WebSocket.), #2368 (Can't detect disconnection on wifi websocket client ), and #3291 (Websocket client hanging/blocking?).

[yogeshsajanikar]

I have same issue with streaming response.

[asvetlov]

Guys, looks like you both don't return a response object from failed web-handler.

[benitogf]

Thanks @asvetlov I was missing the return statement at the end of the handler https://aiohttp.readthedocs.io/en/stable/web_quickstart.html#websockets

[asvetlov]

That's exactly what I was suspected.
Runtime check for the return value is quite expensive but we can do it in debug mode (loop.get_debug()).

The patch is trivial, a champion is needed.

[benitogf]

@asvetlov please review above patch, I saw no use of loop.get_debug() in web_protocol so used what was around

[asvetlov]

The idea is dropping custom debug checks everywhere in the server and rely on loop.get_debug() only.
The change is scheduled to aiohttp 4.0, so self.debug check is correct now.

[asvetlov]

Fixed by #3321

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a [new issue] for related bugs.
If you feel like there's important points made in this discussion, please include those exceprts into that [new issue].
[new issue]: https://github.com/aio-libs/aiohttp/issues/new