django.test.client:conditional_content_removal() is not compliant with RFC7230

[Ed Morley]

​RFC7230 section 3.3.2 says:

A server MAY send a Content-Length header field in a 304 (Not Modified) response to a conditional GET request (Section 4.1 of [RFC7232]); a server MUST NOT send Content-Length in such a response unless its field-value equals the decimal number of octets that would have been sent in the payload body of a 200 (OK) response to the same request.

A server MUST NOT send a Content-Length header field in any response with a status code of 1xx (Informational) or 204 (No Content). A server MUST NOT send a Content-Length header field in any 2xx (Successful) response to a CONNECT request (Section 4.3.6 of [RFC7231]).

However conditional_content_removal() sets Content-Type: 0 in these cases:
​https://github.com/django/django/blob/941b8691351d4739cd9391b0a1326abd0b1c29c0/django/test/client.py#L91-L108

...which is not compliant with the specification.

The fix is to not set Content-Type at all in conditional_content_removal().

Note: After #26052 conditional_content_removal() is only used by the django.test.client, though that caused the regression #28054, for which the fix will be making runserver use it too.

[Tim Graham]

​PR

[Tim Graham <timograham@…>]

In 3db84b55:

Fixed #28081 -- Stopped setting Content-Length=0 in conditional_content_removal() per RFC 7230.