water/server/app/service/MqttTopic.php

<?php

namespace app\service;

final class MqttTopic
{
    public static function assertPublishable(string $topic): void
    {
        if ($topic === '' || strlen($topic) > 65535 || str_contains($topic, "\0") || strpbrk($topic, '+#') !== false) {
            throw new \InvalidArgumentException('MQTT topic is invalid.');
        }

        foreach (config('mqtt.publish_topics', []) as $filter) {
            if (self::matchesFilter($topic, $filter)) {
                return;
            }
        }

        throw new \InvalidArgumentException('MQTT topic is not permitted.');
    }

    private static function matchesFilter(string $topic, string $filter): bool
    {
        $pattern = preg_quote($filter, '/');
        $pattern = str_replace(['\\+', '\\#'], ['[^/]+', '.*'], $pattern);

        return (bool) preg_match('/^' . $pattern . '$/u', $topic);
    }
}