code: func GetEnvelopeFromBlock(data []byte) (*common.Envelope, error) {
  	// Block always begins with an envelope
  	var err error
  	env := &common.Envelope{}
  	if err = proto.Unmarshal(data, env); err != nil {
  		return nil, errors.Wrap(err, "error unmarshaling Envelope")
  	}
  
  	return env, nil
  }
docs: // GetEnvelopeFromBlock gets an envelope from a block's Data field.