Server closes connection if wrong type returned by handler

[Fogapod]

🐞 Describe the bug

Server closes session if handler returns anything else that Response instance.

💡 To Reproduce

from aiohttp import web


async def handler(req):
    return 1

app = web.Application()
app.add_routes([web.get("/", handler)])
web.run_app(app)

~ curl localhost:8080
curl: (52) Empty reply from server

💡 Expected behavior

Error message in console and returned status 500.

📋 Your version of the Python

$ python --version
Python 3.8.1

📋 Your version of the aiohttp/yarl/multidict distributions

Tested with aiohttp 3.6.2 and master branch fresh installations.

[webknjaz]

@Fogapod thanks for the report! It'd be cool if you could submit a failing test marked with xfail in a PR as per https://pganssle-talks.github.io/xfail-lightning.

[Fogapod]

@webknjaz alright, I'll try to make a test for this issue.

I found that returning HTTPException instance in aiohttp 3.6.2 resulted in returning corresponding status code by server, in master branch it results in closed connection.
Is returning exceptions deprecated? I didn't find it in documentation, there is no traceback in console.

[webknjaz]

I think it is, or should be. Exceptions must be raised.

[Fogapod]

RuntimeError is raised here

aiohttp/aiohttp/web_protocol.py

Lines 577 to 579 in f80029b

	raise RuntimeError("Web-handler should return "
	"a response instance, "
	"got {!r}".format(resp))

after calling

aiohttp/aiohttp/web_protocol.py

Line 480 in f80029b

resp, reset = await task

and catched here

aiohttp/aiohttp/web_protocol.py

Lines 523 to 526 in f80029b

	except RuntimeError as exc:
	if self._loop.get_debug():
	self.log_exception(
	'Unhandled runtime exception', exc_info=exc)

For some reason these are only logged in asyncio debug mode.

I'm not sure how this could be fixed. Returning status 500 for all Runtime errors?

[webknjaz]

Returning status 500 for all Runtime errors?

I think so

[webknjaz]

Is returning exceptions deprecated? I didn't find it in documentation, there is no traceback in console.

v3.6 deprecates returning exceptions but it still works (see the red warning box): https://docs.aiohttp.org/en/stable/web_quickstart.html#exceptions

master/v4.0 doesn't support this anymore and doesn't mention returning exceptions: https://docs.aiohttp.org/en/latest/web_exceptions.html

[Fogapod]

I don't understand this condition:

aiohttp/aiohttp/web_protocol.py

Lines 524 to 526 in f80029b

	if self._loop.get_debug():
	self.log_exception(
	'Unhandled runtime exception', exc_info=exc)

What kind of exceptions can happen there and why they are silenced by default?
If there are exceptions that should be silenced and cause server to close connection without response, what could a workaround be? Raising different kind of exception from handler if wrong type returned?

Edit: according to this comment #1790 (comment), runtime exceptions should not be handled, but in this case it can be, so exception type should be changed?