fqdn.go

// Package net contains helper function for handling
// e.g. ip addresses or domain names
package net

import (
	"errors"
	"fmt"
	"strings"

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

// IsFQDN (fqdn) returns true if fqdn is a FQDN (Fully Qualified Domain Name) hostname + domainname + tld, otherwise false
func IsFQDN(fqdn string) bool {
	fqdn = strings.ToLower(strings.TrimSpace(fqdn))

	if IsIPAddr(fqdn) || IsDomain(fqdn) || strings.Contains(fqdn, "/") || strings.Contains(fqdn, "@") || strings.Contains(fqdn, ":") || strings.Contains(fqdn, "\\") {
		return false
	}

	if domain := DomainFromFqdn(fqdn); domain != "" {
		i := strings.LastIndex(fqdn, domain)
		if fqdn[:i] != "" {
			return true
		}
	}

	return false
}

// DomainFromFqdn returns domain name or empty string
func DomainFromFqdn(fqdn string) string {
	fqdn = strings.TrimSpace(fqdn)
	fqdn = strings.ToLower(fqdn)
	domain := ""

	if !IsIPAddr(fqdn) && !IsDomain(fqdn) {
		for _, s := range PublicSuffix {
			s = fmt.Sprintf(".%s", s)
			if strings.HasSuffix(fqdn, s) {
				if i := strings.LastIndex(fqdn, s); i != -1 {
					if j := strings.LastIndex(fqdn[:i], "."); j != -1 {
						domain = fqdn[j+1:]
					}
				}
			}
		}
	}

	return domain
}

// FQDNToUnicode returns  domain name as Unicode
func FQDNToUnicode(fqdn string) (string, error) {
	fqdn = strings.TrimSpace(fqdn)
	fqdn = strings.ToLower(fqdn)

	if !IsFQDN(fqdn) {
		return "", errors.New("invalid FQDN")
	}

	return idna.ToUnicode(fqdn)
}

// FQDNToPunycode returns domain name as Punycode
func FQDNToPunycode(fqdn string) (string, error) {
	fqdn = strings.TrimSpace(fqdn)
	fqdn = strings.ToLower(fqdn)

	if !IsFQDN(fqdn) {
		return "", errors.New("invalid FQDN")
	}

	return idna.ToASCII(fqdn)
}