Fix the default value of CHUNKED_UPLOAD_DIR

[dkliban]

This patch changes the default value of CHUNKED_UPLOAD_DIR to upload.
This value is a relative path inside the MEDIA_ROOT. Doc strings have
also been updated to match the actual behavior of functions used to
form the path used by the UploadChunk's file field. The documentation
was also updated to make it more clear that CHUNKED_UPLOAD_DIR is
supposed to be a relative path inside MEDIA_ROOT.

fixes: #8099
https://pulp.plan.io/issues/8099

[daviddavis]

LGTM. Needs a changelog entry.

[pulpbot]

Attached issue: https://pulp.plan.io/issues/8099

[ekohl]

This is an alternative to #1074.

[ekohl]

👍 for the actual code change. I do think the docs could steer users away from changing it.

[ekohl]

If I was my project I'd suggest the imperative mood for the commit message (see https://chris.beams.io/posts/git-commit/#imperative for the reasoning), but I'll leave that up to the actual maintainers. Resulting change looks good to me.

[mdellweg]

I don't exactly see, how this variant survives without crying for a new migration, but as the tests are green i suppose it is correct.
I second @ekohl on the commit message style.

[daviddavis]

I don't exactly see, how this variant survives without crying for a new migration, but as the tests are green i suppose it is correct.

It's because the field uses the upload_to callback rather than referring to the setting directly.

[ekohl]

What I would write as the commit message:

Make CHUNKED_UPLOAD_DIR a relative path

In 1b6c736 uploads were changed to use the default storage (uses settings.MEDIA_ROOT). Anything that's written outside of storage location raises a SuspiciousOperation. That already made the implicit requirement that CHUNKED_UPLOAD_DIR was relative.

Users could hit this if they modified MEDIA_ROOT in their settings but kept CHUNKED_UPLOAD_DIR default.

If a relative path is used, Django prepends the location and it is guaranteed to be a safe location. This changes the default value to be relative and updates the documentation to reflect this.

[daviddavis]

Actually now that I think of it: I wonder if we ought to have a .removal to say that CHUNKED_UPLOAD_DIR should be a relative path now instead of an absolute path?

[dkliban]

Actually now that I think of it: I wonder if we ought to have a .removal to say that CHUNKED_UPLOAD_DIR should be a relative path now instead of an absolute path?

We could. We already had a .removal related to this setting for the 3.9.0 release.

https://docs.pulpproject.org/pulpcore/changes.html#removals

[mdellweg]

Two (green) approvals; all tests passed; no migration needed; last minute comments addressed
I am going to play merge bot now.