如何编写golang验证功能，以便客户端能够优雅地处理？

Question

type Request struct{
  A string
  B string
  C string
  D string
  //...
}

func validator(req *Request)error{

  if req.A == "" && req.B != ""{
    return errors.New("Error 1 !!")
  }

  //...


}

I have some existing code like above which is already being used so I can not change the function signature.

I am writing a caller function which has to throttle some types of errors. All existing errors are created using either errors.New("some string") or fmt.Errorf("some string"). What I can do is

if err.Error() == "Error 1 !!" {
    return nil
  }

But this is not ideal. If on the server side, the message changes, client side breaks.

I thought about naming all the errors on the server side like:

const ErrorType1 =  "Error 1 !!"

But it's difficult to name each error.

Any better solutions?

Answer 1

error is an interface, so you can dynamically check - using type assertions - some specific types and act accordingly.

Here's a code snippet that may be useful (playground link):

package main

import (
    "errors"
    "fmt"
)

type MyError struct {
    msg string
    id  int
}

func (me MyError) Error() string {
    return me.msg
}

func checkErr(e error) {
    if me, ok := e.(MyError); ok {
        fmt.Println("found MyError", me)
    } else {
        fmt.Println("found error", e)
    }
}

func main() {
    checkErr(errors.New("something bad"))
    checkErr(MyError{msg: "MyError bad"})
}

The first line in checkErr is the ticket here - it checks if e is of some special underlying type.