Add name support to OCI outputter

[chrisdostert]

The OCI image spec has standardized the org.opencontainers.image.ref.name attribute for including an image name in an image layout.

I would like the ability to include name in my oci image output argument as in --output type=oci,dest=/image.tar,name=$imageName and have it add this attribute.

[chrisdostert]

it looks like if we get a release including 6153472#diff-da065b99f35d8e4d9cba814afea2b8a7L196 this will be supported?

[chrisdostert]

Actually to answer my own question, even after building against master I still get the same error

> exporting to oci image format:
------
error: failed to solve: rpc error: code = Unknown desc = oci exporter cannot export named image

so no that PR doesn't seem to have added support.

[tonistiigi]

Afaik OCI has "stardardized" org.opencontainers.image.ref.name key but has provided no spec about what value it should contain. There were discussions about this when this was added, some projects use this annotation for normalized name and some use it as a tag in oci index. If containerd chooses a specific way to start using this annotation we can do the same thing. When I last discussed it, the most supported idea was to ignore it completely and start putting annotation like com.docker.image.ref.name instead, where we at least can agree on what it should mean.

[tonistiigi]

@chrisdostert https://github.com/opencontainers/image-spec/blob/master/image-layout.md#indexjson-file

[chrisdostert]

@tonistiigi thanks for the fast response. Why does buildkit need to care? It seems like the desired behavior would be to just treat it as opaque and set as specified. An alternative to allowing specifying name would be to allow specifying annotations which would be a map of keys/values.

[tonistiigi]

We don't want to make images that are broken in some other tools that claim OCI compatibility. If another tool expects a tagname for that annotation they will fail miserably if we fill it in with a full name.

[chrisdostert]

The other tool wouldn't be behaving in OCI compliant fashion if they assumed a certain value for that annotation per spec https://github.com/opencontainers/image-spec/blob/master/annotations.md

[tonistiigi]

It's a vague and unfortunate situation. Obviously the reason why it is defined as a special key is for the different implementations to reuse the key. Otherwise we would just put buildkit.name there if we just need a label. And the spec does list a "common use case" and example how to use this annotation that strictly contradicts on what you are asking (although I agree that this would be the much better use case for it). #227

[chrisdostert]

After our conversation and thinking on it more I feel like the best way is to expose annotations and let the consumer decide. I can either close this issue and open new, or rename, to reflect the request being for allowing specifying annotations. Do you have a preference?

[tonistiigi]

I'm ok with allowing to set raw annotations. Suggested the same in #227 (comment)

[chrisdostert]

Great, thanks. Opened new and referenced this. Will see you over there.