🐛 [Bug]: Validator using Fiber v3 or v2 is not using json tags for field names.

[daibertdiego]

Bug Description

I'm using validator v10 with fiber v3 (but also tested on v2), and when I intercept validation errors, my custom messages are not using the json tag names, but the property names.
For example:

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

func NewValidatorError(err error) ValidatorError {
	e := ValidatorError{}
	e.Errors = make(map[string]interface{})
	errs := err.(validator.ValidationErrors)
	for _, v := range errs {
		e.Errors[v.Field()] = fmt.Sprintf("%v", v.Tag())
	}
	return e
}

type UserStatsCreateDTO struct {
	FirstName string `json:"first_name" validate:"required"`
	Age       int    `json:"age" validate:"required,gt=5"`
	BirthDate string `json:"birth_date" validate:"required,datetime=2006/01/02"`
}

			// Override default error handler
			ErrorHandler: func(ctx fiber.Ctx, err error) error {
				// Status code defaults to 500
				code := fiber.StatusInternalServerError

				// Set Content-Type: text/application-json; charset=utf-8
				ctx.Set(fiber.HeaderContentType, fiber.MIMEApplicationJSON)

				// Retrieve the custom status code if it's a *fiber.Error
				var e *fiber.Error
				if errors.As(err, &e) {
					if errors.Is(err, fiber.ErrUnprocessableEntity) {
						code = fiber.ErrBadRequest.Code
					} else {
						code = e.Code
					}
				}

				if vldt, ok := err.(validator.ValidationErrors); ok {
					validationErrors := settings.NewValidatorError(vldt)
					// Return status code with error message
					return ctx.Status(fiber.ErrBadRequest.Code).JSON(validationErrors)
				}

				// Return status code with error message
				return ctx.Status(code).JSON(err.Error())
			},
		}),
	}

    func (h userStatsHandler) TestPost(c fiber.Ctx) error {
    	var userDTO UserStatsCreateDTO
    	// if err := c.BodyParser(&userDTO); err != nil {
    	if err := c.Bind().Body(&userDTO); err != nil {
    		return err
    	}
    
    	return c.JSON(userDTO)
    }

When I try to send an invalid request using this DTO, this is my response.

How to Reproduce

Steps to reproduce the behavior:

1. Go to '....'
2. Click on '....'
3. Do '....'
4. See '....'

Expected Behavior

Receive the error msg using the json tag name like :

{
errors:[
"first_name": required,
"age": gt,
"birth_date": datetime
]
}

Fiber Version

v3

Code Snippet (optional)

package main

import "github.com/gofiber/fiber/v3"
import "log"

func main() {
  app := fiber.New()

  // Steps to reproduce

  log.Fatal(app.Listen(":3000"))
}

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my problem prior to opening this one.
• I understand that improperly formatted bug reports may be closed without explanation.

[welcome]

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[JIeJaitt]

Take a look at this code you wrote below, Field() method returns the structure field name, not the JSON tag name.

func NewValidatorError(err error) ValidatorError {
	e := ValidatorError{}
	e.Errors = make(map[string]interface{})
	errs := err.(validator.ValidationErrors)
	for _, v := range errs {
		e.Errors[v.Field()] = fmt.Sprintf("%v", v.Tag())
	}
	return e
}

like this photos, u can debug it in u local

This issue has nothing to do with fiber, maybe you should go to validator to post an issue.

my test code:

package main

import (
	"fmt"
	"testing"

	"github.com/go-playground/validator/v10"
)

// test main func
func Test_NewValidatorError(t *testing.T) {
	userDTO := UserStatsCreateDTO{
		FirstName: "John",
		Age:       10,
		BirthDate: "2024-01-01 12:00:00",
	}

	validate := validator.New()
	err := validate.Struct(userDTO)

	validationErrors := err.(validator.ValidationErrors)

	fmt.Println(validationErrors[0].Field())
	// fmt.Println(validationErrors[1].Field())
	// fmt.Println(validationErrors[2].Field())

	// fmt.Println(validationErrors[0].ActualTag())
	// fmt.Println(validationErrors[1].ActualTag())
	// fmt.Println(validationErrors[2].ActualTag())

	fmt.Println(validationErrors[0].Tag())
	// fmt.Println(validationErrors[1].Tag())
	// fmt.Println(validationErrors[2].Tag())
}

Couldn't using gin return different results than fiber? If so this discussion needs to be continued

[daibertdiego]

From the documentation:

Field returns the fields name with the tag name taking precedence over the field's actual name.

eq. JSON name "fname" see StructField for comparison

And Tag() returns the tag that failed the validation. So, using Field() function should return the json tags from the struct properties. And this is not happening.

[JIeJaitt]

@daibertdiego I also see this comment, but that's not what is actually shown in the test code. Do you think this has something to do with the fiber framework? Maybe I can try experimenting on the gin framework

[daibertdiego]

Yeah, it's related to Fiber framework. Using the validator out of the framework, shows the json tag for the Field() function.

[ReneWerner87]

type UserStatsCreateDTO struct {
	FirstName string `json:"first_name" validate:"required"`
	Age       int    `json:"age" validate:"required,gt=5"`
	BirthDate string `json:"birth_date" validate:"required,datetime=2006/01/02"`
}

func Test_NewValidatorError(t *testing.T) {
	userDTO := UserStatsCreateDTO{
		FirstName: "John",
		Age:       10,
		BirthDate: "2024-01-01 12:00:00",
	}

	validate := validator.New()
	err := validate.Struct(userDTO)

	validationErrors := err.(validator.ValidationErrors)

	fmt.Println(validationErrors[0].Field())
	require.Equal(t, "BirthDate", validationErrors[0].Field())
	require.Equal(t, "datetime", validationErrors[0].Tag())
}

https://pkg.go.dev/github.com/go-playground/validator/v10#FieldError

i have tested it in a setup without fiber, should be an error in the validation package
normally I would assume that the json tag name at Field

@gaby @efectn can someone confirm

[ReneWerner87]

go-playground/validator#935
you should follow this
its a bug inside of the lhttps://github.com/go-playground/validator lib