how do i validate the body structure of rest api request in golang

I am trying to ensure the body of a post request for example contains exact structure of the body and if not ahould throw an error

for example i have the following function

func UpdatePassword(c *fiber.Ctx) error {

	type UpdatePasswordData struct {
		Password  string `json:"password" form:"password"`
		NewPassword string `json:"new_password" form:"new_password"`
		NewPasswordConfirm string `json:"new_password_confirm" form:"new_password_confirm"`
	}
	
	data := UpdatePasswordData{}

	if err := c.BodyParser(&data); err != nil {
		return err
	}

	var user models.User
	
	if data.NewPassword != data.NewPasswordConfirm {
		c.Status(400)
		return c.JSON(fiber.Map{
			"message": "passwords do not match",
		})
	}

	email, _ := middlewares.GetUserEmail(c)

	newPassword := models.HashPassword(data.NewPassword)

	database.DB.Model(&user).Select("Password").Where("email = ?", email).Updates(map[string]interface{}{"Password": newPassword})

	return c.JSON(user)
}

the POST request should be looking for body with this structure

{
    "password": "oldpassword",
    "new_password": "newpassword",
    "new_password_confirm": "newpassword",
}

but currently this endpoint accepts body that does not have this exact structure. So how do i enforce the structure in the body of request, so that if structure does not match, i throw an error?

do not like gin, fiber has not builtin validate package

use go-playground/validator

go get github.com/go-playground/validator

example

type UpdatePasswordData struct {
        Password  string `json:"password" validate:"required,min=8,max=32"`
        NewPassword string `json:"new_password" validate:"required,min=8,max=32"`
        NewPasswordConfirm string `json:"new_password_confirm" validate:"eqfield=NewPassword"`
}

func UpdatePassword(c *fiber.Ctx) error {
  var body UpdatePasswordData
  if err := c.BodyParser(&body); err != nil {
    return err
  }

  validate := validator.New()
  if err := validate.Struct(body); err != nil {
    return err
  }

  // do others
  // get current user, check password == hash(body.password)
  // save new passworld
}

or you can see fiber office docs https://docs.gofiber.io/guide/validation#validator-package

We can use struct tag

`validate:"required"`

to ensure that all the mandatory fields are there in the request payload.

Moreover we can validate the fields with the provided tags of the validator package and for additional validations we can implement custom validators and register them like this:

validate := validator.New()
validate.RegisterValidation("password-validator", PasswordValidator)