manifest/manifest.go
func Digest(manifest []byte) (digest.Digest, error) {
	if GuessMIMEType(manifest) == DockerV2Schema1SignedMediaType {
		sig, err := libtrust.ParsePrettySignature(manifest, "signatures")
		if err != nil {
			return "", err
		}
		manifest, err = sig.Payload()
		if err != nil {
			// Coverage: This should never happen, libtrust's Payload() can fail only if joseBase64UrlDecode() fails, on a string
			// that libtrust itself has josebase64UrlEncode()d
			return "", err
		}
	}

	return digest.FromBytes(manifest), nil
}
func Digest(manifest []byte) (digest.Digest, error) {
	if GuessMIMEType(manifest) == DockerV2Schema1SignedMediaType {
		sig, err := libtrust.ParsePrettySignature(manifest, "signatures")
		if err != nil {
			return "", err
		}
		manifest, err = sig.Payload()
		if err != nil {
			// Coverage: This should never happen, libtrust's Payload() can fail only if joseBase64UrlDecode() fails, on a string
			// that libtrust itself has josebase64UrlEncode()d
			return "", err
		}
	}

	return digest.FromBytes(manifest), nil
}
// Digest returns the a digest of a docker manifest, with any necessary implied transformations like stripping v1s1 signatures.