func (o *ObjectInfo) KMSKeyID() string { return kmsKeyIDFromMetadata(o.UserDefined) }

// KMSKeyID returns in AWS compatible KMS KeyID() format.
func (o *MultipartInfo) KMSKeyID() string { return kmsKeyIDFromMetadata(o.UserDefined) }

// kmsKeyIDFromMetadata returns any AWS S3 KMS key ID in the
// metadata, if any. It returns an empty ID if no key ID is
// present.
func kmsKeyIDFromMetadata(metadata map[string]string) string {