code: func makeBinaryContent(msg proto.Message) (string, error) {
  	d, err := proto.Marshal(msg)
  	if err != nil {
  		return "", errors.Annotate(err, "failed to marshal message").Err()
  	}
  
  	var buf bytes.Buffer
  	if _, err := cmpbin.WriteString(&buf, proto.MessageName(msg)); err != nil {
  		return "", errors.Annotate(err, "failed to write message name").Err()
  	}
  	if _, err := cmpbin.WriteBytes(&buf, d); err != nil {
  		return "", errors.Annotate(err, "failed to write binary message content").Err()
  	}
  	return buf.String(), nil
  }
docs: // makeBinaryContent constructs a binary content string from text protobuf
  // content.
  //
  // The binary content is formatted by concatenating two "cmpbin" binary values
  // together:
  // [Message Name] | [Marshaled Message Data]