Laravel CIDR validation rule

Cidr.php

<?php

namespace App\Rules;

use Closure;
use Illuminate\Contracts\Validation\ValidationRule;

use const FILTER_FLAG_IPV4;
use const FILTER_FLAG_IPV6;
use const FILTER_VALIDATE_INT;
use const FILTER_VALIDATE_IP;

class Cidr implements ValidationRule
{
    /** @var bool whether or not the rule has been called with network constraints */
    private bool $has_bits;

    /**
     * @param int|null $ipv4minbits The minimum number of bits allowed in an IPv4 network
     * @param int|null $ipv4maxbits The maximum number of bits allowed in an IPv4 network
     * @param int|null $ipv6minbits The minimum number of bits allowed in an IPv6 network
     * @param int|null $ipv6maxbits The maximum number of bits allowed in an IPv6 network
     */
    public function __construct(
        public ?int $ipv4minbits = null,
        public ?int $ipv4maxbits = null,
        public ?int $ipv6minbits = null,
        public ?int $ipv6maxbits = null,
    )
    {
        $this->has_bits = func_num_args() > 0;
    }

    /**
     * @param string $attribute The attribute being validated
     * @param mixed $value The current value of the attribute
     * @param Closure $fail Closure to be run in case of failure
     * @return void
     */
    public function validate(string $attribute, mixed $value, Closure $fail): void
    {
        $mask = null;
        $valid_mask = true;

        if (str_contains($value, "/")) {
            [$value, $mask] = explode("/", $value);
        } elseif ($this->has_bits) {
            // if we specify a bit constraint, assume the bits are required
            $fail($this->message());
        }

        if (str_contains($value, ":")) {
            // ipv6
            if ($mask !== null) {
                $valid_mask = filter_var(
                    $mask,
                    FILTER_VALIDATE_INT,
                    ["options" => ["min_range" => $this->ipv6minbits ?? 0, "max_range" => $this->ipv6maxbits ?? 128]]
                );
            }
            $valid_address = filter_var($value, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6);
        } else {
            // ipv4
            if ($mask !== null) {
                $valid_mask = filter_var(
                    $mask,
                    FILTER_VALIDATE_INT,
                    ["options" => ["min_range" => $this->ipv4minbits ?? 0, "max_range" => $this->ipv4maxbits ?? 32]]
                );
                if ($valid_mask) {
                    $long = ip2long($value);
                    $mask = -1 << (32 - $mask);
                    $valid_mask = long2ip($long & $mask) === $value;
                }
            }
            $valid_address = filter_var($value, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4);
        }
        if (!$valid_address ||  !$valid_mask) {
            $fail($this->message());
        }
    }

    public function message(): string
    {
        return !$this->has_bits
            ? __("The :attribute must be a valid IP address or CIDR subnet.")
            : sprintf(
                __("The :attribute must be a valid CIDR subnet with a mask of %d-%d (IPv4) or %d-%d (IPv6) bits."),
                $this->ipv4minbits ?? 0,
                $this->ipv4maxbits ?? 32,
                $this->ipv6minbits ?? 0,
                $this->ipv6maxbits ?? 128
            );
    }
}

@miken32 brilliant! thank you very much

Very excited for this!