Async write headers

[asvetlov]

Make writer.write_headers() a coroutine

[kxepal]

LGFM, but could you remind me, please, why all this need? What's the goal?

[webknjaz]

I guess it's related to #2743 (comment), right?

[asvetlov]

No, it is for #2698

[asvetlov]

After switching all writes to coroutines we can drop write buffers.

[codecov-io]

Codecov Report

Merging #2762 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2762      +/-   ##
==========================================
+ Coverage   97.97%   97.98%   +0.01%     
==========================================
  Files          39       39              
  Lines        7340     7339       -1     
  Branches     1285     1284       -1     
==========================================
  Hits         7191     7191              
  Misses         47       47              
+ Partials      102      101       -1

Impacted Files	Coverage Δ
aiohttp/web_response.py	98.18% <100%> (ø)	⬆️
aiohttp/client_reqrep.py	97.39% <100%> (ø)	⬆️
aiohttp/test_utils.py	98.85% <100%> (+0.37%)	⬆️
aiohttp/http_writer.py	100% <100%> (ø)	⬆️

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[kxepal]

Cool! Thanks.

[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