Add support for overwrite when adding content

[daviddavis]

Plumb the new pulpcore overwrite parameter to sign_and_create and signed_add_and_remove and override AptRepository.check_content_overwrite to exempt incoming packages already in the version that were produced by the signing workflow (tracked via DebPackageSigningResult).

[daviddavis]

This PR includes the changes from the package signing PR. Only the last commit is new.

[quba42]

If you rebase to latest main branch, the deprecations test should turn green.

[daviddavis]

Thanks, looks like it's green now.

[quba42]

I had to look up what overwrite is and does. As I understand it, what it does is the following: Where in the past a upload content to repository might have failed on repo uniqueness constraints, with overwrite=True it instead succeeds by kicking out the content it collides with. Did I get this right?

Some more questions for my comprehension:

• It looks like this is making use of something in pulpcore. I don't see the check_content_overwrite method getting invoked anywhere in these changes, so I am guessing something in pulpcore will use it. Am I getting this right?
• It looks like this PR is disabling this overwrite mechanism only for cases where package signing is on and packages have already been signed in the caching mechanism? I am not sure I fully understand why this is needed. Are the overwrite mechanism and the "cached signed package" mechanisms clashing somehow for cases where they are both active?

[daviddavis]

Mostly right. Before the overwrite feature, duplicate content was always quietly replaced in Pulp. This is what happens now when overwrite=True. True is the default value for overwrite so it's backwards compatible.

Now with overwrite, you can set overwrite=False, which will call check_content_overwrite in a few different places like when uploading content into a repo or modifying a repo's content via add_and_remove. When overwrite=False, this method will raise a ContentOverwriteError if it detects that content would be overwritten/replaced.

This method check_content_overwrite can be overriden to add custom logic. Here we are overriding it to prevent ContentOverwriteError from being raised if the code detects that a signed version of the package being added to a repo already exists. This is to deal with the case that a user adds a package to a repo and it gets signed (producing a signed version of the package), and then they tried to add the package again with overwrite=True.

Without this custom logic, they would hit a ContentOverwriteError. Ideally this would just be a noop even if overwrite=True and that's what this code does--it uses DebPackageSigningResult to link the package being added to the repo to the signed version in the repo.

[quba42]

Based on my code review and my cost-benefit-risk intuition, I think we should go ahead and merge this, so we can release it as part of 3.10.0!