simple IPv4 checker (CIDR included)

IPv4.php

<?php

declare(strict_types=1);

class IPv4
{
    /**
     * Check if input is a valid IPv4 address
     *
     * A valid IPv4 address is presents like `192.168.1.1`
     *
     * @param string $input
     * @return bool true if address is valid, false if not
     */
    public static function isIpAddress(string $input): bool
    {
        $res = preg_match('/^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/', $input);

        if (1 !== $res) {
            return false;
        }

        $class = explode('.', $input);
        foreach ($class as $num) {
            if ($num > 255) {
                return false;
            }
        }
        return true;
    }

    /**
     * Check input is a valid CIDR expression
     *
     * CIDR is present as `196.168.0.0/16`
     *
     * @param string $input
     * @return bool true if CIDR is valid, false if not
     */
    public static function isCidr($input): bool
    {
        if (1 !== preg_match("/^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\/[0-9]{1,2}?$/", $input)) {
            return false;
        }

        // mask check
        list($ip, $mask) = explode('/', $input);
        if (32 < intval($mask)) {
            return false;
        }

        // class number check
        foreach (explode('.', $ip) as $num) {
            if ($num > 255) {
                return false;
            }
        }
        return true;
    }

    /**
     * Check input is a valid hostname
     *
     * A valid hostname can be reverse to an IP address
     *
     * @param string $input
     * @return bool true if valid, false if not
     */
    public static function isHostname($input): bool
    {
        $ip = gethostbyname($input);

        if ($ip === $input) {
            // 正解失敗，或是原本就是 IP address
            return false;
        }
        if (!static::isIpAddress($ip)) {
            // 正解出來的不是正常的 IP
            return false;
        }
        return true;
    }
}

IPv4Test.php

<?php

require 'IPv4.php';

use PHPUnit\Framework\TestCase;

class IPv4Test extends TestCase
{
    public function setUp()
    {
    }

    public function tearDown()
    {
    }

    /**
     * @dataProvider ipAddressProvider
     */
    public function testIpChecker($input, $expected)
    {
        $this->assertSame($expected, IPv4::isIpAddress($input));
    }

    public function ipAddressProvider()
    {
        return [
            ['127.0.0.1', true],
            ['192.168.2.255', true],
            ['172.16.200.1', true],
            ['10.0.0.1', true],
            ['8.8.8.8', true],

            ['192.168.1.300', false],
            ['10.0.0.1/24', false], // do not support CIDR
            ['www.hermes.com.tw', false], // IPv4 address only
        ];
    }

    /**
     * @dataProvider cidrProvider
     */
    public function testCidrChecker($input, $expected)
    {
        $this->assertSame($expected, IPv4::isCidr($input));
    }

    public function cidrProvider()
    {
        return [
            ['192.168.1.1/24', true],
            ['10.0.0.0/8', true],
            ['172.16.0.0/16', true],
            ['10.1.0.0/24', true],
            ['10.2.3.0/30', true],

            ['192.168.1.1', false],  // CIDR only
            ['192.168.1.1/', false], // wrong format
            ['192.168.300.1/32', false], // 300 is invalid
            ['www.hermes.com.tw', false],
        ];
    }
  
    /**
     * @dataProvider hostnameProvider
     */
    public function testHostnameChecker($input, $expected)
    {
        $this->assertSame($expected, IPv4::isHostname($input));
    }

    public function hostnameProvider()
    {
        return [
            ['www.google.com', true],
            ['mail.google.com', true],
            ['php.net', true],
            ['www.netflix.com', true],

            ['this-is-not-domain', false],
            ['10.0.0.1', false],
        ];
    }
}