Allow disabling sendfile w/ env 'AIOHTTP_NOSENDFILE=1'

[jashandeep-sohi]

StaticRoute can now be forced to not use sendfile system call if environment variable AIOHTTP_NOSENDFILE=1.

See issue #628

[asvetlov]

Perfect!

[imbusy]

Wouldn't it be better to do this in line 257 of web_urldispatcher.py, where the implementation of sendfile is chosen?

[asvetlov]

Maybe you are right. I dont care too much honestly

[jashandeep-sohi]

I wouldn't be able to mock.patch.dict(os.environ, ...) in the tests then.

Perhaps, the other section should be moved into the constructor as well, so we can mock test that as well and get rid of no coverage pragma.

It's fine for now, but it's something to consider in the static route refactoring (issue #468)

[rutsky]

I'm concerned that definition of this environment variable switch is differs from other environment variable switches used in asyncio/aiohttp.

AIOHTTP_NO_EXTENSIONS is checked in the following way:

if bool(os.environ.get('AIOHTTP_NO_EXTENSIONS')):

At least inside aiohttp library environment variables switches should work in the same way.

[jashandeep-sohi]

It was fixed after the merge: 9dc529b

[rutsky]

Ok, thanks!

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