Allowing patch_vary_headers() caching utility to handle '*' value.

[Alexander-TX]

Function "patch_vary_headers", simply appends new headers to list. If view code sets Vary header to asterisk, the resulting header (after applying SessionMiddleware and LocaleMiddleware) looks like this:

Vary: *, Accept-Language, Cookie

This is unnecessary and possible violates HTTP spec:

The "Vary" header field in a response describes what parts of a
   request message, aside from the method, Host header field, and
   request target, might influence the origin server's process for
   selecting and representing this response.  The value consists of
   either a single asterisk ("*") or a list of header field names
   (case-insensitive).

     Vary = "*" / 1#field-name

(from ​https://tools.ietf.org/html/rfc7231#page-70)

I am using Django to implement REST API, so I'd like it to speak robust HTTP, that works with all present and future caching libraries, — even if widely used browsers and Nginx can correctly interpret current form of the header.

[Carlton Gibson]

Hi Alexander. Thanks for the report.

Happy to accept this as an enhancement. (It's clear from the existing test cases that '*' was never considered.)

I was going to uncheck "Easy Pickings" but perhaps it is simple enough...

[Adnan Umer]

​PR

[Carlton Gibson]

PR Looks good.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 6805c0f9:

Fixed #30701 -- Updated patch_vary_headers() to handle an asterisk according to RFC 7231.