Test adding oras command for shpc

[vsoch]

@alecbcs SHPC recently had the oras directive added to the container.yaml, meaning that a user can pull a singularity SIF directly from an OCI registry! Since it's an OCI registry entry and just a different artifact type, I'm thinking we can first try parsing it the same as docker. If that does not work we can skip for now. Should I use this branch to test shpc and verify if this works or not (I think this would be a good idea over blindly merging it!)

Signed-off-by: vsoch vsoch@users.noreply.github.com

[vsoch]

okay I've tested:

1. treating oras like Docker hoping it would use the same OCI registry API (did not work)
2. current implementation - allowing return of an empty string result given no match (assuming passing on to lookout will return found false)

This turned out not to work - lookout (or cuppa?) seemed to try and look for the reference and exit on error:

[Parsing Container Blueprints]
2022/01/30 23:36:48 reference not found
Error

I couldn't find anywhere in either lookout or cuppa with this error message so I suspect it's coming from a dependency library. I tried returning false for found and an empty result, but that didn't work. @alecbcs what would you suggest? We likely want to get in a quick fix here so oras isn't removed from the recipe, but we also don't want the entire parsing to fail. Does oras need to be added to lookout?

[vsoch]

okay I'm debugging and testing in autamus/cuppa now (I always forgot about this fork!) and I'll update if I learn anything! It does look like the code here would have trouble parsing oras.

[vsoch]

okay I got pretty close - the registry (GitHub packages) will return tags for an oras artifact, but it doesn't seem to be able to return the image config, e.g., https://crane.ggcr.dev/config/ghcr.io/singularityhub/github-ci is empty.

[vsoch]

huzzah! I got the manifest to work! So this might work - going to take a break for dinner and back after.