OCI image source about image

[alexlarsson]

I was just experimenting with skopeo, but the command above is copying from one OCI directory (which skopeo created) to another directory. Why should this not work?

[runcom]

Because we didn't implement that yet. Can't you just cp the directory? Do you have any hard requirement to do that here?

[alexlarsson]

I was going to use skopeo to test OCI support for flatpak use, and this was just the minimal test i could come up with. What I really wanted was to take an OCI directory i've created and round-trip it to a docker registry and back to see how well that worked.

[mtrmac]

Yeah, it makes sense that containers/image should support this. I don’t personally know about priorities/timing though.

[runcom]

@mtrmac do you mean you're ok having an OCI image source based on directories? (and maybe later support remote images for OCI as well).
Implementing this for directories should be trivial afaict and I have some spare cycles if this is needed.

[mtrmac]

Well, to be precise: I haven’t paid enough attention to OCI to say how much (or whether) the OCI directory transport is useful. But it seems to me that if it is useful, both reading and writing is probably useful.

(I’d also like OCI to switch to the manifest support in c/i/image instead of hiding the conversions if possible; the write path was an useful stopgap but it would be nice not propagate that further.)

[runcom]

@mtrmac what do you mean by switch to the manifest support in c/i/image? Link to code?

[mtrmac]

• Copy image/manifest_schema2.go to image/manifest_oci.go, edit suitably.
• Implement types.Image.UpdatedImage(&types.ManifestUpdateOptions{ManifestMIMEType:} to convert at least between s2 and OCI, both ways, based on the existing oci_dest.go:createManifest code; then combine with existing s1<->s2 conversions to support any conversion between all three of s1, s2, OCI.
• Drop the now redundant ad-hoc conversion in oci_dest.go:createManifest

[hustcat]

@runcom @mtrmac I want to copy image from OCI layout directories to docker daemon after docker #26369.
So OCI image source based on directories is very useful. I'd like to implement it:)