ClientResponse.raise_for_status() raises an AssertionError for empty reason

[rhwlo]

Long story short

ClientResponse.raise_for_status() raises an AssertionError for a >= 400 status code if its reason is an empty string.

Expected behaviour

I expect ClientResponse.raise_for_status() to raise a ClientResponseError if it’s invoked on a ClientResponse with a status >= 400, and to either:

• raise a ClientError (or some subclass of ClientError) if it’s called on a ClientResponse with a reason = None, regardless of the HTTP status code, if this can only happen when raise_for_status() has been called before start() has been called; or
• convert a ClientResponse.reason of None into "" if None is a valid value for ClientResponse.reason

Actual behaviour

• ClientResponse.raise_for_status() raises an AssertionError if it’s invoked on a ClientResponse when a status >= 400 and bool(reason) is False, which includes reason == ""
• ClientResponse.raise_for_status() raises a ClientResponseError if it’s invoked on a ClientResponse with a status >= 400 if the reason is not falsey
• ClientResponse.raise_for_status() raises no error if it’s invoked on a ClientResponse with a status < 400 and a reason = None

Steps to reproduce

A colleague and I uncovered this using aioresponses, which currently doesn’t set a reason on the ClientResponse at all – see pnuckowski/aioresponses#114.

You can reproduce this with the example client and server in this gist: https://gist.github.com/rhwlo/5ff3cb6bae8deb6abb4a1e527ad9583e

Your environment

I’m using the latest aiohttp from the repository, but this problem shows up only in v3.5.0 and newer.

[aio-libs-bot]

GitMate.io thinks the contributor most likely able to help you is @asvetlov.

Possibly related issues are #1177 (Static handler raises AssertionError), #156 (ClientResponse.content.read() raises ConnectionResetError), #1670 (ClientResponse ergonomics), #3248 (history tuple on ClientResponseError empty with raise_for_status() or ClientSession(raise_for_status=True)), and #1633 (Testing with pytest-aiohttp test_client raises an AssertionError.).