how to validate a struct field of type null.v4 package with validator v10?

Question

I have a struct that i'm trying to validate a struct using validator v10 for which field can be of type null.XX from null.v4 package.

type FooStruct struct {
    Foo null.Int `json:"foo" binding:"nullIntMin=1"`
}

it's (obviously ) not working out of the box so i'm trying to make a custom validator.

var validateNullIntMin validator.Func = func(fl validator.FieldLevel) bool {
    number, ok := fl.Field().Interface().(null.Int)
    min := cToInt(fl.Param())
    if ok {
        if number.Value > min && number.Valid {
            return false
        }
    }
    return true
}

func cToInt(param string) int64 {

    i, err := strconv.ParseInt(param, 0, 64)
    panic(err)

    return i
}

The problem is that the data is never validated. Is never even entering the function and i can't understand why.

example to reproduce :

package main

import (
    "log"
    "net/http"
    "strconv"

    "github.com/gin-gonic/gin"
    "github.com/gin-gonic/gin/binding"
    "github.com/go-playground/validator"
    "gopkg.in/guregu/null.v4"
)

type FooStruct struct {
    Foo null.Int `json:"foo" binding:"nullIntMin=3"`
}

var validateNullIntMin validator.Func = func(fl validator.FieldLevel) bool {
    log.Println("inside validator")
    number, ok := fl.Field().Interface().(null.Int)
    min := cToInt(fl.Param())
    if ok {
        if number.Valid && number.Int64 > min {
            return false
        }
    }
    return true
}

func cToInt(param string) int64 {

    i, err := strconv.ParseInt(param, 0, 64)
    panic(err)

    return i
}

func main() {
    route := gin.Default()

    // Custom validator

    if v, ok := binding.Validator.Engine().(*validator.Validate); ok {
        v.RegisterValidation("nullIntMin", validateNullIntMin)
    }

    route.POST("/foo", postFoo)
    route.Run(":5000")
}

func postFoo(c *gin.Context) {
    var f FooStruct
    err := c.BindJSON(&f)
    if err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"status": http.StatusText(http.StatusBadRequest)})
        return
    }
    c.JSON(http.StatusOK, gin.H{"status": http.StatusText(http.StatusOK), "data": f.Foo.Int64})

}

if you call it with

{"foo":1}

you'll get { "data": 1, "status": "OK" }

when i'm expecting Error:Field validation for 'Foo' failed on the 'nullIntMin' tag

Answer 1

You dont need to unparse the field inside the validator and make a custom case just for the special type.

Instead just create a new type then you can just use the normal bindings.

if v, ok := binding.Validator.Engine().(*validator.Validate); ok {
    v.RegisterCustomTypeFunc(nullIntValidator, null.Int{})
}

func nullIntValidator(field reflect.Value) interface{} {
    if valuer, ok := field.Interface().(null.Int); ok {
        if valuer.Valid {
            return valuer.Int64
        }
    }
    return nil
}

type FooStruct struct {
    Foo  null.Int  `json:"foo" binding:"min=3"`
}