It's impossible to throw web_exceptions.* from router's resolve()

[ikalnytskyi]

Long story short

Sometimes it's very useful to have a custom router instead of built-in one. For instance, as it was mentioned in #1373, in order to implement API versioning we may want to check that API version is passed by client. If not, we need to reject the request with some error response (e.g. 412 Precondition Failed).

Unfortunately, since 1.1 it's no longer possible as any attempt to do so fails with 500 Internal Server Error on this line (match_info is None in this case):

https://github.com/KeepSafe/aiohttp/blob/v1.1.5/aiohttp/web_reqrep.py#L736

Expected behaviour

web_exceptions.* can be thrown from router's resolve() method and are transformed to appropriate HTTP response code.

Actual behaviour

Any attempt to throw web_exceptions.* lead to the 500 Internal Server Error.

Steps to reproduce

Here's an exploit (run with pytest):

import asyncio

import aiohttp.abc
import aiohttp.web


class MyRouter(aiohttp.abc.AbstractRouter):
    async def resolve(self, request):
        raise aiohttp.web.HTTPPreconditionFailed()


def test_412_is_returned():
    loop = asyncio.new_event_loop()
    app = aiohttp.web.Application(router=MyRouter(), loop=loop)
    handler = app.make_handler()

    async def test():
        async def get(url):
            server = await loop.create_server(handler, '127.0.0.1', 0)
            address, port = server.sockets[0].getsockname()

            with aiohttp.ClientSession(loop=loop) as session:
                response = await session.get(
                    'http://%s:%s%s' % (address, port, url)
                )

            await handler.finish_connections()
            server.close()

            return response

        assert (await get('/')).status == 412

    loop.run_until_complete(test())

    loop.stop()
    loop.run_forever()
    loop.close()

Your environment

• aiohttp 1.1.5
• python3.5
• macos sierra

[asvetlov]

I'll take a look

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