code: func ParseCallbacks(msg *Message, sender func(id uint64, args []interface{}) error) error {
  	// Parse callbacks field and create callback functions.
  	for methodID, path := range msg.Callbacks {
  		id, err := strconv.ParseUint(methodID, 10, 64)
  		if err != nil {
  			return err
  		}
  
  		f := func(args ...interface{}) error { return sender(id, args) }
  		spec := CallbackSpec{path, Function{functionReceived(f)}}
  		msg.Arguments.CallbackSpecs = append(msg.Arguments.CallbackSpecs, spec)
  	}
  
  	return nil
  }
docs: // parseCallbacks parses the message's "callbacks" field and prepares
  // callback functions in "arguments" field.