[docs] Add clarification regarding order of middleware execution

[amitsaha]

Long story short

Clarify/Explain the order of execution when multiple middleware factories are registered.

Expected behaviour

Consider the following application:

from aiohttp import web
def test(request):
    print('Handler function called')
    return web.Response(text="Hello")

async def middleware1(app, handler):
    async def middleware_handler(request):
        print('Middleware 1 called')
        response = await handler(request)
        print('Middleware 1 finished')

        return response
    return middleware_handler

async def middleware2(app, handler):
    async def middleware_handler(request):
        print('Middleware 2 called')
        response = await handler(request)
        print('Middleware 2 finished')

        return response
    return middleware_handler


app = web.Application(middlewares=[middleware1, middleware2])
app.router.add_get('/', test)
web.run_app(app)

The above code would produce the following output:

Middleware 1 called
Middleware 2 called
Handler function called
Middleware 2 finished
Middleware 1 finished

I think an explanation like this may improve the current documentation which is brief.

Actual behaviour

IMHO, the current explanation linked above is brief and perhaps is not clear to someone new to aiohttp.

Steps to reproduce

NA

Your environment

NA

[amitsaha]

Would be happy to work on a PR.

[asvetlov]

Please do.
I love documentation updates for covering not obvious dark corners.

[amitsaha]

Thanks, sorry I never submitted the PR :-(

[asvetlov]

NP

[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