您正确地将函数作为参数传递，但是它们与预期的签名不匹配.将您的功能更改为:

You are passing the function as an argument correctly but they do not match the expected signature. Change your functions to:

func UpperCaseHandler(md busboy.MessageDelivery) (interface{}, error} {
     s.Reply(MessageTest{strings.ToUpper(md.Message.(string))}, md.Delivery)
     return nil, nil
}

func RepeatHandler(md busboy.MessageDelivery) (interface{}, error} {
     s.Reply(MessageTest{strings.Repeat(md.Message.(string), 5)}, md.Delivery)
     return nil, nil
}