librenms-librenms/LibreNMS/Util/Validate.php

<?php
/**
 * Validate.php
 *
 * -Description-
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @link       http://librenms.org
 * @copyright  2019 Tony Murray
 * @author     Tony Murray <murraytony@gmail.com>
 */

namespace LibreNMS\Util;

class Validate
{
    /**
     * Checks if the give string is a valid hostname
     * @param string $hostname
     * @return bool
     */
    public static function hostname($hostname)
    {
        // The Internet standards (Request for Comments) for protocols mandate that
        // component hostname labels may contain only the ASCII letters 'a' through 'z'
        // (in a case-insensitive manner), the digits '0' through '9', and the hyphen
        // ('-'). The original specification of hostnames in RFC 952, mandated that
        // labels could not start with a digit or with a hyphen, and must not end with
        // a hyphen. However, a subsequent specification (RFC 1123) permitted hostname
        // labels to start with digits. No other symbols, punctuation characters, or
        // white space are permitted. While a hostname may not contain other characters,
        // such as the underscore character (_), other DNS names may contain the underscore
        // maximum length is 253 characters, maximum segment size is 63

        return
            preg_match("/^([a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*\.?$/i", $hostname) //valid chars check
            && preg_match('/^.{1,253}$/', $hostname) //overall length check
            && preg_match("/^[^\.]{1,63}(\.[^\.]{1,63})*\.?$/", $hostname);
    }
}