Utility function to check if the domain is valid or not

isValidDomain.go

package main

import (
	"fmt"
	"regexp"

	"golang.org/x/net/publicsuffix"
)

func isRootDomain(domain string) (bool, error) {
	publicSuffix, icannManaged := publicsuffix.PublicSuffix(domain)
	if !icannManaged {
		return false, fmt.Errorf("the domain %s is not ICANN managed", domain)
	}
	return domain == publicSuffix, nil
}

func isValidSyntax(domain string) bool {
	// Regular expression for validating the domain syntax
	domainRegex := regexp.MustCompile(`^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,}$`)

	return domainRegex.MatchString(domain)
}

func isValidDomain(domain string) (bool, error) {
	if !isValidSyntax(domain) {
		return false, fmt.Errorf("invalid domain syntax")
	}
	isRoot, err := isRootDomain(domain)
	if err != nil {
		return false, err
	}
	if isRoot {
		return false, fmt.Errorf("%s is a root domain", domain)
	}
	return true, nil
}

func main() {
	domains := []string{
		"example.co.uk",
		"test.com",
		"c.gaa",
		"domainname",
		"com",
		"com.np",
	}

	for _, domain := range domains {
		valid, err := isValidDomain(domain)
		if valid {
			fmt.Printf("%s is valid domain.\n", domain)
		} else {
			fmt.Printf("invalid domain: %s , %v\n", domain, err)
		}
	}
}