New OCIStore

[shizhMSFT]

Resolves #107

Example usage:

func demo() error {
	ref := "localhost:5000/oras:test"
	ctx := context.Background()
	resolver := docker.NewResolver(docker.ResolverOptions{})

	store, err := content.NewOCIStore("store")
	if err != nil {
		return err
	}
	desc, _, err := oras.Pull(ctx, resolver, ref, nil,
		oras.WithContentProvideIngester(store),
		oras.WithPullEmptyNameAllowed(),
	)
	if err != nil {
		return err
	}

	store.AddReference(ref, desc)
	return store.SaveIndex()
}

It stores pulled content in the store folder as

store
├── blobs
│   └── sha256
│       ├── 03ba204e50d126e4674c005e04d82e84c21366780af1f43bd54a37816b6ab340
│       ├── 130c6b42d2ea0bbf0cc727aa2c2c193d1550e84b62202efbc1f24b5adddebd30
│       └── 44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a
├── index.json
├── ingest
└── oci-layout

where ingest is a folder generated by containerd.

The file contents are shown as follows:

• oci-layout after formatting:

{
    "imageLayoutVersion": "1.0.0"
}

• index.json after formatting:

{
    "schemaVersion": 2,
    "manifests": [
        {
            "mediaType": "application/vnd.oci.image.manifest.v1+json",
            "digest": "sha256:130c6b42d2ea0bbf0cc727aa2c2c193d1550e84b62202efbc1f24b5adddebd30",
            "size": 397,
            "annotations": {
                "org.opencontainers.image.ref.name": "localhost:5000/oras:test"
            }
        }
    ]
}

• The manifest blobs/sha256/130c6b42d2ea0bbf0cc727aa2c2c193d1550e84b62202efbc1f24b5adddebd30 after formatting:

{
    "schemaVersion": 2,
    "config": {
        "mediaType": "application/vnd.oci.image.config.v1+json",
        "digest": "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a",
        "size": 2
    },
    "layers": [
        {
            "mediaType": "application/vnd.oci.image.layer.v1.tar",
            "digest": "sha256:03ba204e50d126e4674c005e04d82e84c21366780af1f43bd54a37816b6ab340",
            "size": 13,
            "annotations": {
                "org.opencontainers.image.title": "hello.txt"
            }
        }
    ]
}

• The manifest config blobs/sha256/44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a:

{}

• The actual content blobs/sha256/03ba204e50d126e4674c005e04d82e84c21366780af1f43bd54a37816b6ab340:

Hello World!

---

The options

• oras.WithContentProvideIngester(store) allows pulling manifest or manifest index.
• oras.WithPullEmptyNameAllowed() allows pulling unnamed blobs.

If the option oras.WithAllowedMediaType() is not specified, setting both options basically dumps the remote image to the local file system. Try pull docker.io/library/hello-world:latest if interested.

[jdolitsky]

/test

[jdolitsky]

excellent shiwei!