Serve locally stored fbc content via a server

[everettraven]

As part of implementing the RFC for catalogd's content storage and serving mechanism we should import the RukPak storage library (dependent on operator-framework/rukpak#656). Once imported we will need to create a custom implementation of the Storage interface.

The custom Storage implementation should:

• Store all FBC JSON blobs in a singular {catalogName}/all.json file
• Serve the {catalogName}/all.json file via a go http.FileServer handler

Note If operator-framework/rukpak#656 is not accepted by the RukPak maintainers it would be acceptable to copy the Storage interface to a catalogd package. This is not ideal but is rather a last resort if RukPak maintainers deny the request to externalize the storage package.

Acceptance Criteria

• Storage interface implementation that:
  • Store all FBC JSON blobs in a singular {catalogName}/all.json file
  • Serve the {catalogName}/all.json file via a go http.FileServer handler
• Unit tests

[everettraven]

/assign @anik120

[anik120]

@everettraven what's the motivation for implementing rukpak's storage interface again?

type Storage interface {
	Loader
	Storer
}

type Loader interface {
	Load(ctx context.Context, owner client.Object) (fs.FS, error)
}

type Storer interface {
	Store(ctx context.Context, owner client.Object, bundle fs.FS) error
	Delete(ctx context.Context, owner client.Object) error

	http.Handler
	URLFor(ctx context.Context, owner client.Object) (string, error)
}

Looks like rukpak's storage interface is specialized for storing/loading a filesystem (like an operator bundle, which has multiple files containing multiple Kubernetes CRs), but for catalogd, we want something like

type Storage interface {
	Loader
	Storer
}

type Loader interface {
	Load(ctx context.Context, owner client.Object) (*declaritiveConfig, error)
}

type Storer interface {
	Store(ctx context.Context, owner client.Object, fbc *declarativeConfig) error
	Delete(ctx context.Context, owner client.Object) error

	http.Handler
	URLFor(ctx context.Context, owner client.Object) (string, error)
}

I.e that ☝🏽 is an interface that's for loading and storing fbc files, whereas the first one, is an interface to store and load bundles (two different interfaces with separate purpose).

If we were to store the catalog as a tar.gz file, it'd probably still make sense to implement the rukpak storage. But looks like we decided to store the catalogs as json files, and not compress them like we have to for bundle content.
It's doable if there's a very good reason why we must implement rukpak's interface, but thinking about implementing storing, it's evident that it's not exactly a natural fit:

func Store(ctx context.Context, owner client.Object, catalog fs.FS) error {
         fbc := dclcfg.LoadFS(catalog)
         declcfg.WriteJSON(fbc, writer)
}

There's an extra step of loading the fs into declarativeConfig there, that'll just be done just to fit into the rukpak bundle storing/loading interface

dclcfg.LoadFS