func (s *dirImageSource) GetManifest(ctx context.Context, instanceDigest *digest.Digest) ([]byte, string, error) {
	if instanceDigest != nil {
		return nil, "", errors.Errorf(`Getting target manifest not supported by "dir:"`)
	}
	m, err := ioutil.ReadFile(s.ref.manifestPath())
	if err != nil {
		return nil, "", err
	}
	return m, manifest.GuessMIMEType(m), err
}
func (s *dirImageSource) GetManifest(ctx context.Context, instanceDigest *digest.Digest) ([]byte, string, error) {
	if instanceDigest != nil {
		return nil, "", errors.Errorf(`Getting target manifest not supported by "dir:"`)
	}
	m, err := ioutil.ReadFile(s.ref.manifestPath())
	if err != nil {
		return nil, "", err
	}
	return m, manifest.GuessMIMEType(m), err
}
// GetManifest returns the image's manifest along with its MIME type (which may be empty when it can't be determined but the manifest is available).
// It may use a remote (= slow) service.
// If instanceDigest is not nil, it contains a digest of the specific manifest instance to retrieve (when the primary manifest is a manifest list);
// this never happens if the primary manifest is not a manifest list (e.g. if the source never returns manifest lists).