Creating a variable of type from interface in golang

Question

I am trying to create validator/binder middleware in go using gin framework.

This is the model

type LoginForm struct{
    Email string `json:"email" form:"email" binding:"email,required"`
    Password string `json:"password" form:"password" binding:"required"`
}

Router

router.POST("/login",middlewares.Validator(LoginForm{}) ,controllers.Login)

Middleware

func Validator(v interface{}) gin.HandlerFunc{
    return func(c *gin.Context){
        a := reflect.New(reflect.TypeOf(v))
        err:=c.Bind(&a)
        if(err!=nil){
            respondWithError(401, "Login Error", c)
            return
        }
        c.Set("LoginForm",a)
        c.Next()
    }
}

I am very new to golang. I understand the problem is with the binding to the wrong variable. Is there any other way of solving this?

Answer 1

Clarify my comment,

Instead of having the signature func Validator(v interface{}) gin.HandlerFunc for the MW, use func Validator(f Viewfactory) gin.HandlerFunc

Where ViewFactory if a function type such as type ViewFactory func() interface{}

the MW can be changed so

type ViewFactory func() interface{}

func Validator(f ViewFactory) gin.HandlerFunc{
    return func(c *gin.Context){
        a := f()
        err:=c.Bind(a) // I don t think you need to send by ref here, to check by yourself
        if(err!=nil){
            respondWithError(401, "Login Error", c)
            return
        }
        c.Set("LoginForm",a)
        c.Next()
    }
}

You can write the router like this

type LoginForm struct{
    Email string `json:"email" form:"email" binding:"email,required"`
    Password string `json:"password" form:"password" binding:"required"`
}
func NewLoginForm() interface{} {
   return &LoginForm{}
}
router.POST("/login",middlewares.Validator(NewLoginForm) ,controllers.Login)

Going further, i think you may have to find out about this later, once you have an interface{} value, you can make it back a LoginForm like this v := some.(*LoginForm).

Or like this for more security

if v, ok := some.(*LoginForm); ok {
 // v is a *LoginForm
}

See golang type assertions for more in depth information.