rust/rpmostree-client: parse OCI deployment manifest

[jbtrystram]

When the deployment is an OCI image, the base_commit_meta field contains nested escaped JSON.

Add a method to get the base oci manifest deserialized into an ImageManifest from the oci-spec rust crate.

Fixes #5196

Re-openning a new PR after #5208 was closed, given coreos/zincati#1241 (comment)

[openshift-ci]

@jbtrystram: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/kola-upgrade	b0fb8b0	link	true	/test kola-upgrade
ci/prow/images	b0fb8b0	link	true	/test images

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[jlebon]

Hmm, did you mean to also update status --json with this?

But anyway, I think I'd rather just have that code in Zincati and parse ostree.manifest there? Anyway, we'll need that crate too there to be able to deserialize it, and that'll be useful too for when we get that info from bootc instead of rpm-ostree.

[cgwalters]

I think it'd be cleaner to do something like:

if let Some(serde_json::Value::String(inner))) {
            let manifest: oci_spec::image::ImageManifest = serde_json::from_str(&inner)?;
            return Ok(Some(manifest));
}

or so, this String::deserialize is duplicating the value unnecessarily.

[cgwalters]

Hmm, did you mean to also update status --json with this?

In theory that'd be a compatibility break right?

But anyway, I think I'd rather just have that code in Zincati and parse ostree.manifest there? Anyway, we'll need that crate too there to be able to deserialize it, and that'll be useful too for when we get that info from bootc instead of rpm-ostree.

Yes we still have the practical issue that zincati isn't using this code ref coreos/zincati#491

[jbtrystram]

But anyway, I think I'd rather just have that code in Zincati and parse ostree.manifest there?

Yes, that's my plan. I simply thought i'd share the patch in this repo as well in case that can help someone :)

Yes we still have the practical issue that zincati isn't using this code ref coreos/zincati#491

I'll try to pick up this one at some point !