Content-Length header is ignored in web.Response constructor

[major12]

Long story short

Header Content-Length is ignored in web.Response constructor.
It is set to 0 when body parameter is not passed to constructor.

Expected behaviour

Either to get warning like "your header was ignored" or to have it not ignored.

Actual behaviour

Header value is silently updated.

Steps to reproduce

>>> headers = {'Content-Length':555}
>>> r = web.Response(headers=headers)
>>> r.headers
<CIMultiDict('Content-Type': 'application/octet-stream', 'Content-Length': '0')>

Your environment

aiohttp (1.1.3)
Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:18:55) [MSC v.1900 64 bit (AMD64)] on win32
Win10

[asvetlov]

What is use case for providing Content-Length without BODY?

[major12]

Respond to HEAD request.
The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response.

[asvetlov]

Good point, thank for report.

[lock]

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