Support null CONTENT_ORIGIN

[dralley]

As per pulp/pulpcore#5931, Pulp plugins need to support the possibility of the value provided for CONTENT_ORIGIN being None

[dralley]

https://issues.redhat.com/browse/PULP-277

[ggainey]

The place where we're affected is when we try to auto-generate the config.repo file - baseurl wants to be a full URL, not relative.

We can do one of a few things here :

1. just return relative-urls in config.repo and let the user Figure It Out
2. refuse to generate config.repo if you don't set CONTENT_ORIGIN - user has to "supply their own" rather than rely on us to set it. DOCUMENT THIS.
3. build the URL based on the incoming request (assuming we even have that?) ("path" is the filename, not the URL)

See https://github.com/pulp/pulp_rpm/blob/main/pulp_rpm/app/models/repository.py#L526 for the code that's affected

[dralley]

re: 3, It would likely be an API breaking change to the content_handler() function, but it could be done.

I think I'm partial to option 2 personally

[mdellweg]

IMHO the feature is described as if content origin is not set, the base url is the same as from the incoming request. So ideally pulpcore would come with a helper function to extract that from the request so we can do a simple search and replace for settings.CONTENT_ORIGIN to content_origin(request). That should enable option 3 (least surprising one?).

edit: AFTER some discussion (e.g. that the request may not know the original URL in all deployments) I agree with 2: Explicitly telling the user it's impossible and maybe bring more scenarios back later when we know it's possible. Existing installations will have the setting anyway, so nothing changes for them.