cas

type Driver interface {
	// Supported returns whether the resource at the given URI is supported by
	// the driver (used for auto-detection). If two drivers support the same
	// URI, then the earliest registered driver takes precedence.
	//
	// Note that this is _not_ a validation of the URI -- if the URI refers to
	// an invalid or non-existent resource it is expected that the URI is
	// "supported".
	Supported(uri string) bool

	// Open "opens" a new CAS engine accessor for the given URI.
	Open(uri string) (Engine, error)

	// Create creates a new image at the provided URI.
	Create(uri string) error
}

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)

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

	// PutIndex sets the index of the OCI image to the given index, replacing
	// the previously existing index. This operation is atomic; any readers
	// attempting to access the OCI image while it is being modified will only
	// ever see the new or old index.
	PutIndex(ctx context.Context, index ispec.Index) (err error)

	// GetIndex returns the index of the OCI image. Return ErrNotExist if the
	// digest is not found. If the image doesn't have an index, ErrInvalid is
	// returned (a valid OCI image MUST have an image index).
	//
	// It is not recommended that users of cas.Engine use this interface
	// directly, due to the complication of properly handling references as
	// well as correctly handling nested indexes. casext.Engine provides a
	// wrapper for cas.Engine that implements various reference resolution
	// functions that should work for most users.
	GetIndex(ctx context.Context) (index ispec.Index, ierr 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)

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

	// Clean 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.
	Clean(ctx context.Context) (err error)

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