cas

type Blob struct {
	// MediaType is the OCI media type of Data.
	MediaType string

	// Digest is the digest of the parsed image. Note that this does not update
	// if Data is changed (it is the digest that this blob was parsed *from*).
	Digest digest.Digest

	// Data is the "parsed" blob taken from the OCI image's blob store, and is
	// typed according to the media type. The mapping from MIME => type is as
	// follows.
	//
	// ispec.MediaTypeDescriptor => *ispec.Descriptor
	// ispec.MediaTypeImageManifest => *ispec.Manifest
	// ispec.MediaTypeImageManifestList => *ispec.ManifestList
	// ispec.MediaTypeImageLayer => io.ReadCloser
	// ispec.MediaTypeImageLayerGzip => io.ReadCloser
	// ispec.MediaTypeImageLayerNonDistributable => io.ReadCloser
	// ispec.MediaTypeImageLayerNonDistributableGzip => io.ReadCloser
	// ispec.MediaTypeImageConfig => *ispec.Image
	Data interface{}
}

type Engine interface {
	// PutBlob adds a new blob to the image. This is idempotent; a nil error
	// means that "the content is stored at DIGEST" without implying "because
	// of this PutBlob() call".
	PutBlob(ctx context.Context, reader io.Reader) (digest digest.Digest, size int64, err error)

	// PutBlobJSON adds a new JSON blob to the image (marshalled from the given
	// interface). This is equivalent to calling PutBlob() with a JSON payload
	// as the reader. Note that due to intricacies in the Go JSON
	// implementation, we cannot guarantee that two calls to PutBlobJSON() will
	// return the same digest.
	PutBlobJSON(ctx context.Context, data interface{}) (digest digest.Digest, size int64, err error)

	// PutReference adds a new reference descriptor blob to the image. This is
	// idempotent; a nil error means that "the descriptor is stored at NAME"
	// without implying "because of this PutReference() call". ErrClobber is
	// returned if there is already a descriptor stored at NAME, but does not
	// match the descriptor requested to be stored.
	PutReference(ctx context.Context, name string, descriptor *ispec.Descriptor) (err error)

	// GetBlob returns a reader for retrieving a blob from the image, which the
	// caller must Close(). Returns os.ErrNotExist if the digest is not found.
	GetBlob(ctx context.Context, digest digest.Digest) (reader io.ReadCloser, err error)

	// GetReference returns a reference from the image. Returns os.ErrNotExist
	// if the name was not found.
	GetReference(ctx context.Context, name string) (descriptor *ispec.Descriptor, err error)

	// DeleteBlob removes a blob from the image. This is idempotent; a nil
	// error means "the content is not in the store" without implying "because
	// of this DeleteBlob() call".
	DeleteBlob(ctx context.Context, digest digest.Digest) (err error)

	// DeleteReference removes a reference from the image. This is idempotent;
	// a nil error means "the content is not in the store" without implying
	// "because of this DeleteReference() call".
	DeleteReference(ctx context.Context, name string) (err error)

	// ListBlobs returns the set of blob digests stored in the image.
	ListBlobs(ctx context.Context) (digests []digest.Digest, err error)

	// ListReferences returns the set of reference names stored in the image.
	ListReferences(ctx context.Context) (names []string, err error)

	// GC executes a garbage collection of any non-blob garbage in the store
	// (this includes temporary files and directories not reachable from the
	// CAS interface). This MUST NOT remove any blobs or references in the
	// store.
	GC(ctx context.Context) (err error)

	// Close releases all references held by the engine. Subsequent operations
	// may fail.
	Close() (err error)
}