Add support for pass-through publications.

[jortel]

https://pulp.plan.io/issues/4020

Adds support for pass-through publications.

Publishers would still use the Publication context and may (optionally) set pass-through=True. In combination with this, the publisher can (optionally) add PublishedMeta and possibly PublishedArtifacts to customize how the publication is composed.

I still need to run EXMPLAIN to see what django has translated the content-artifact query to be sure it's efficient and using the indexes.

I'm not sure where/how to update the docs. I'm inclined to capture pass-through in planned more comprehensive docs rewrite stores.

[pep8speaks]

Hello @jortel! Thanks for submitting the PR.

• There are no PEP8 issues in the file pulpcore/pulpcore/app/models/publication.py !

• There are no PEP8 issues in the file pulpcore/pulpcore/app/serializers/repository.py !

• There are no PEP8 issues in the file pulpcore/pulpcore/app/views/content.py !

• There are no PEP8 issues in the file pulpcore/pulpcore/app/viewsets/repository.py !

[codecov]

Codecov Report

Merging #3654 into master will decrease coverage by 0.2%.
The diff coverage is 27.77%.

@@            Coverage Diff            @@
##           master   #3654      +/-   ##
=========================================
- Coverage      56%   55.8%   -0.21%     
=========================================
  Files          61      61              
  Lines        2680    2695      +15     
=========================================
+ Hits         1501    1504       +3     
- Misses       1179    1191      +12

Impacted Files	Coverage Δ
pulpcore/pulpcore/app/serializers/repository.py	94.7% <100%> (+0.03%)	⬆️
pulpcore/pulpcore/app/models/publication.py	65% <100%> (+1.2%)	⬆️
pulpcore/pulpcore/app/views/content.py	23.52% <13.33%> (-2.64%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cebb5de...1c8ef71. Read the comment docs.

[daviddavis]

I was thinking that pass_through was going to only be available to plugin writers. I have two concerns about this option be managed by users. First, I wonder if users (as opposed to plugin writers) can understand the intricacies of pass-through vs not. How will they know whether they need to create a pass-through publication vs not? Also, what if I have plugin and I don't want to allow my content to be published via pass-through publications?

Edit: To give an example, in pulp_rpm we generate PublishedMetadata and probably don't want users to create publications via POST /pulp/api/v3/publications/ and bypass the publishing code.

[daviddavis]

I think to kind of address the concerns in my previous comment, we could remove the POST /pulp/api/v3/publications/ endpoint from core and instead let plugin writers define their own endpoints to utilize the pass_through option. So for example, the Ansible plugin might define its own POST /pulp/api/v3/ansible/publications endpoint that produces passthrough publications.

[bmbouter]

This PR is exactly as I imagined it, including the create that only allows pass_through=True. I hadn't considered what @daviddavis was saying though. Now I agree though that we should remove the ability to create Publications via the API and leave it for plugin writers to do via the plugin API. For me it's a safety issue. For plugins where its author expects to only use PublishedMetadata and/or PublishedArtifact, its users cannot use pass_through=True safely.

It's also not needed for the immediate use case. With pulp_ansible the plugin writer is making the Publication via plugin-code so the core API call isn't used there.

[jortel]

I will remove the publication POST endpoint and supporting changes.

[daviddavis]

LGTM

[bmbouter]

This also looks good to me. Thank you so much @jortel this unblocks a plugin writer w/ pulp_ansible!