[RFE] Default response to OPTIONS requests are incomplete

[ajknv]

Checklist

• [X] I have verified that that issue exists against the master branch of Django REST framework.
• [X] I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• [X] This is not a usage question. (Those should be directed to the discussion group instead.)
• [X] This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• [X] I have reduced the issue to the simplest possible case.
• [X] I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.) ** Sort of: I have fixed the test cases that start failing in response to adding this improved functionality.

Steps to reproduce

Without overriding the default OPTIONS handler, make such a request when methods other than POST and PATCH are permitted for the authorized (if applicable) user -- most notably GET.

Expected behavior

The response should include all relevant HTTP methods as available "actions". If a client can make a GET request to the API, then an OPTIONS request should include that as a valid action. This would be consistent with W3C specification and implementation/documentation by others, e.g.:

• Mozilla - https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/OPTIONS
• Widely used Spring framework - https://docs.spring.io/spring-framework/docs/current/reference/html/web.html#mvc-ann-requestmapping-head-options

Highly related is that "choices" can be used as filters on requests, so being able to query for them even on read-only resources is also vitally useful to creating well-designed client libraries of APIs. The current behavior of reporting that no requests are possible on objects that are in fact queryable unnecessarily forces externalization of source-of-truth data about choices onto clients and creates maintenance overhead to avoid desynchronization in the face of API updates.

https://github.com/encode/django-rest-framework/pull/7644

Actual behavior

Only POST and PATCH are reported as available actions, despite GET requests being accepted for the object.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[ajknv]

I believe the rationale for this is still valid, and the pull request for this change is already prepared.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[ajknv]

I believe the rationale for this is still valid, and the pull request for this change is already prepared.

[tomchristie]

This is a nice idea for many use cases, but in others the choice fields might contain many thousands of possible options.

I don't think we'd want this generally on for all sites.