feat: adds media type detection when loading OCI descriptors

[jpower432]

Closes #14

Signed-off-by: Jennifer Power barnabei.jennifer@gmail.com

[afflom]

The warning was confusing:

WARN[0000] reference for unknown type: text/plain; charset=utf-8 
WARN[0000] reference for unknown type: image/jpeg       
WARN[0000] reference for unknown type: text/plain; charset=utf-8 
WARN[0000] reference for unknown type: application/vnd.uor.config.v1+json 
WARN[0000] reference for unknown type: application/json 
WARN[0000] reference for unknown type: image/jpeg       
WARN[0000] reference for unknown type: image/jpeg  

But the code runs as advertised!

[jpower432]

The warning was confusing:

WARN[0000] reference for unknown type: text/plain; charset=utf-8 
WARN[0000] reference for unknown type: image/jpeg       
WARN[0000] reference for unknown type: text/plain; charset=utf-8 
WARN[0000] reference for unknown type: application/vnd.uor.config.v1+json 
WARN[0000] reference for unknown type: application/json 
WARN[0000] reference for unknown type: image/jpeg       
WARN[0000] reference for unknown type: image/jpeg  

But the code runs as advertised!

This seems to come from the containerd library used by oras. Looks like it appears anytime the media type is outside of the OCI Spec which for this purpose is expected. I think if the CopyOptions for oras were appended to allow these as allowedMediaTypes this warning may go away. It's worth trying.

[sabre1041]

Is there a specific need to bring in a 3rd party library when http.DetectContentType is available?

[jpower432]

@sabre1041 http.DetectContentType does not recognize JSON. We originally pulled this import in to detected content types in the parser package; so detected format types are more important here. Just decided to use the already imported library in this instance as well. https://github.com/uor-framework/client/blob/3c715c563642f7542e70799b4afcb43c1018c5e8/builder/parser/parser.go#L37.