fiber/docs/guide/validation.md

---
id: validation
title: 🔎 Validation
sidebar_position: 5
---

## Validator package

Fiber can make _great_ use of the validator package to ensure correct validation of data to store.

- [Official validator Github page \(Installation, use, examples..\).](https://github.com/go-playground/validator)

You can find the detailed descriptions of the _validations_ used in the fields contained on the structs below:

- [Detailed docs](https://pkg.go.dev/github.com/go-playground/validator?tab=doc)

```go title="Validation Example"
package main

import (
	"fmt"
	"log"
	"strings"

	"github.com/go-playground/validator/v10"
	"github.com/gofiber/fiber/v3"
)

type (
	User struct {
		Name string `validate:"required,min=5,max=20"` // Required field, min 5 char long max 20
		Age  int    `validate:"required,teener"`       // Required field, and client needs to implement our 'teener' tag format which we'll see later
	}

	ErrorResponse struct {
		Error       bool
		FailedField string
		Tag         string
		Value       any
	}

	XValidator struct {
		validator *validator.Validate
	}

	GlobalErrorHandlerResp struct {
		Success bool   `json:"success"`
		Message string `json:"message"`
	}
)

// This is the validator instance
// for more information see: https://github.com/go-playground/validator
var validate = validator.New()

func (v XValidator) Validate(data any) []ErrorResponse {
	validationErrors := []ErrorResponse{}

	errs := validate.Struct(data)
	if errs != nil {
		for _, err := range errs.(validator.ValidationErrors) {
			// In this case data object is actually holding the User struct
			var elem ErrorResponse

			elem.FailedField = err.Field() // Export struct field name
			elem.Tag = err.Tag()           // Export struct tag
			elem.Value = err.Value()       // Export field value
			elem.Error = true

			validationErrors = append(validationErrors, elem)
		}
	}

	return validationErrors
}

func main() {
	myValidator := &XValidator{
		validator: validate,
	}

	app := fiber.New(fiber.Config{
		// Global custom error handler
		ErrorHandler: func(c fiber.Ctx, err error) error {
			return c.Status(fiber.StatusBadRequest).JSON(GlobalErrorHandlerResp{
				Success: false,
				Message: err.Error(),
			})
		},
	})

	// Custom struct validation tag format
	myValidator.validator.RegisterValidation("teener", func(fl validator.FieldLevel) bool {
		// User.Age needs to fit our needs, 12-18 years old.
		return fl.Field().Int() >= 12 && fl.Field().Int() <= 18
	})

	app.Get("/", func(c fiber.Ctx) error {
		user := &User{
			Name: fiber.Query[string](c, "name"),
			Age:  fiber.Query[int](c, "age"),
		}

		// Validation
		if errs := myValidator.Validate(user); len(errs) > 0 && errs[0].Error {
			errMsgs := make([]string, 0)

			for _, err := range errs {
				errMsgs = append(errMsgs, fmt.Sprintf(
					"[%s]: '%v' | Needs to implement '%s'",
					err.FailedField,
					err.Value,
					err.Tag,
				))
			}

			return &fiber.Error{
				Code:    fiber.ErrBadRequest.Code,
				Message: strings.Join(errMsgs, " and "),
			}
		}

		// Logic, validated with success
		return c.SendString("Hello, World!")
	})

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

/**
OUTPUT

[1]
Request:

GET http://127.0.0.1:3000/

Response:

{"success":false,"message":"[Name]: '' | Needs to implement 'required' and [Age]: '0' | Needs to implement 'required'"}

[2]
Request:

GET http://127.0.0.1:3000/?name=efdal&age=9

Response:
{"success":false,"message":"[Age]: '9' | Needs to implement 'teener'"}

[3]
Request:

GET http://127.0.0.1:3000/?name=efdal&age=

Response:
{"success":false,"message":"[Age]: '0' | Needs to implement 'required'"}

[4]
Request:

GET http://127.0.0.1:3000/?name=efdal&age=18

Response:
Hello, World!

**/

```