Validate Handler and Input Params

validate.go

func validateFunc(handler interface{}, nArgs int) (interface{}, error) {
  method := reflect.ValueOf(handler)
	f := reflect.Indirect(method)

  // check type func
	if f.Kind() != reflect.Func {
		return f, fmt.Errorf("%T must be a Function ", f)
	}

	methodType := method.Type()
	numIn := methodType.NumIn()

  // check number of args 
	if nArgs < numIn {
		return nil, errors.New("Call with too few input arguments")
	} else if nArgs > numIn {
		return nil, errors.New("Call with too many input arguments")
	}
	return f, nil
}