Validator struct

type RegisterValidator struct {
    Name              string     `form:"name" json:"name" binding:"required,min=4,max=50"`
    Email             string     `form:"email" json:"email" binding:"required,email,min=4,max=50"`
    Password          string     `form:"password" json:"password" binding:"required,min=8,max=50"`
    MobileCountryCode int        `form:"mobile_country_code" json:"mobile_country_code" binding:"required,gte=2,lt=5"`
    Mobile            int        `form:"mobile" json:"mobile" binding:"required,gte=5,lt=15"`
    UserModel         users.User `json:"-"`
}

Formatting a custom error as below:

type CustomError struct {
    Errors map[string]interface{} `json:"errors"`
}

func NewValidatorError(err error) CustomError {
    res := CustomError{}
    res.Errors = make(map[string]interface{})
    errs := err.(validator.ValidationErrors)

    for _, v := range errs {
        param := v.Param()
        field := v.Field()
        tag := v.Tag()

        if param != "" {
            res.Errors[field] = fmt.Sprintf("{%v: %v}", tag, param)
        } else {
            res.Errors[field] = fmt.Sprintf("{key: %v}", tag)
        }
    }

    return res
}

works when data sent is

{
    "email": "[email protected]",
    "name": "John Doe",
    "mobile_country_code": 1,
    "mobile": 1234567
}

but sending an invalid type

{
    "email": "[email protected]",
    "name": "John Doe",
    "mobile_country_code": "1",
    "mobile": 1234567
}

throws the error interface conversion: error is *json.UnmarshalTypeError, not validator.ValidationErrors

This question is related to this one: How to assert error type json.UnmarshalTypeError when caught by gin c.BindJSON however the answers do not make sense.

CodePudding user response：

As the exception suggests, the following line failed type conversion

    errs := err.(validator.ValidationErrors)

A different type of error must have got passed into the function that is not validator.ValidationErrors.

So either make sure other errors won't be passed into NewValidatorError. Or do a safer type check like:

errs, ok := err.(validator.ValidationErrors)
if !ok {
  // handles other err type
}

More info: A Tour of Go - type assertions, A Tour of Go - type switches

CodePudding user response：

I added a check for the UnmarshalTypeError as below:

    if reflect.TypeOf(err).Elem().String() == "json.UnmarshalTypeError" {
        errs := err.(*json.UnmarshalTypeError)
        res.Errors[errs.Field] = fmt.Sprintf("{key: %v}", errs.Error())

        return res
    }

    errs := err.(validator.ValidationErrors)

I guess Golang is strict when json is type-hinted. It has to be the exact type otherwise it will throw an UnmarshalTypeError error.