… And to do it on the app side, you can use preg_match while iterating over all items. You may narrow them down with other allowed criteria if you want (e.g. search for only tcp connections that come from a known interface) to optimize the performance somewhat.
e.g. (without such criteria)
foreach ($util->setMenu('/ip firewall connection')->getAll() as $connection) {
if (preg_match('/\:80$/', $connection->getProperty('src-address'))) {
//Connection matches. Deal with it here
}
}