code: func ExtractPayload(envelope *cb.Envelope) (*cb.Payload, error) {
  	payload := &cb.Payload{}
  	err := proto.Unmarshal(envelope.Payload, payload)
  	err = errors.Wrap(err, "no payload in envelope")
  	return payload, err
  }
docs: // ExtractPayload retrieves the payload of a given envelope and unmarshals it.