Golang Custom Validator examples

validators.go

package main 

import (
	"fmt"
	"github.com/satori/go.uuid"		//for uuid
	"gopkg.in/validator.v2"
	"reflect"
	"regexp"
	"time"
)

const regexEmail string = `(?m)^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$`

type Data struct {
	Token 		string 		`json:"token" validate:"tokenvalidator"`
	Email		string		`json:"email" validate:"nonzero,emailvalidator"`
	CreatedOn	time.Time  	`json:"created_on" validate:"datevalidator"`	
}

//EmailValidator checks if email is valid using regex defined globally
func EmailValidator(v interface{}, param string) error {
	st := reflect.ValueOf(v)
	if st.Kind() != reflect.String {
		return validator.ErrBadParameter
	}
	re := regexp.MustCompile(regexEmail)
	if  re.MatchString(v.(string)) == false {
		return validator.ErrRegexp
	}
	return nil
}

//TokenValidator checks if token is valid UUID
func TokenValidator(v interface{}, param string) error {
	st := reflect.ValueOf(v)
	if st.Kind() != reflect.String {
		return validator.ErrBadParameter
	}
	_, err := uuid.FromString(v.(string))
	if err != nil {
		return validator.ErrInvalid
	}
	return nil
}


//DateValidator checks if date provided is not less than today's date
func DateValidator(v interface{}, param string) error {
	st := reflect.ValueOf(v)
	if date, ok:= st.Interface().(time.Time); ok {
		today := time.Now()
		if today.Year() > date.Year() || today.YearDay() > date.YearDay(){
			return validator.ErrInvalid
		}
	} else {
		return validator.ErrUnsupported
	}
	return nil
}


func main() {
	validator.SetValidationFunc("emailvalidator", EmailValidator)
	validator.SetValidationFunc("tokenvalidator", TokenValidator)
	validator.SetValidationFunc("datevalidator", DateValidator)

	test := &Data{Token:"b85d3fe4-aaac-11e8-96b2-74d4354af7d2", Email:"example@xyz.com", CreatedOn:time.Now()}

	if err := validator.Validate(test); err == nil {
		fmt.Println("Validated.")
	} else {
		fmt.Println(err.Error())
	}
}