redaxo-extension-points

name	redaxo-extension-points
description	REDAXO Extension Points – the hook system for modifying core/addon behavior without patching files. Use when the user mentions rex_extension::register, hooks into events like ART_PRE_VIEW / OUTPUT_FILTER / PACKAGES_INCLUDED, or wants to extend backend pages and content.

Extension Points (EPs)

Extension Points are REDAXO's hook system. Instead of patching core or another addon, you register a callback that fires at a defined moment.

Registration goes in your addon's boot.php:

<?php
// boot.php
rex_extension::register('OUTPUT_FILTER', function (rex_extension_point $ep) {
    $content = $ep->getSubject();
    // modify $content...
    return $content;
});

The return value replaces the subject for downstream listeners. Returning null (or no return) keeps the subject unchanged.

Signature & priority

rex_extension::register(
    string $extensionPoint,
    callable $callback,
    int $level = rex_extension::NORMAL,  // EARLY, NORMAL, LATE
    array $params = []                    // extra data the EP receives
);

Lower level values run first. Use EARLY to run before the default behavior, LATE for cleanup or final adjustments.

Common extension points

Frontend rendering

EP	When	Subject	Use for
OUTPUT_FILTER	After full HTML is built	full page HTML	minify, inject scripts, replace tokens
OUTPUT_FILTER_CACHE	Before HTML is cached	full page HTML	sanitize before persisting cache
ART_PRE_VIEW	Before article renders	rendered article HTML	inject blocks, wrap content
ART_INIT	Article object created	rex_article_content	conditionally swap template

System lifecycle

EP	When	Use for
PACKAGES_INCLUDED	After all addons booted	cross-addon setup that needs siblings loaded
READY	After core+addons are ready, before request dispatch	last-chance configuration
RESPONSE_SHUTDOWN	After response was sent	async cleanup, stats

Backend / content

EP	When	Use for
STRUCTURE_CONTENT_HEADER	Backend article edit – above slices	warning banners, info
SLICE_SHOW	Each slice in edit mode	extra controls per slice
MEDIA_IS_IN_USE	Before media deletion	prevent deletion if you reference it elsewhere
CLANG_DELETED	A language was removed	clean up your clang-keyed data
ART_DELETED / CAT_DELETED	An article/category is removed	clean up references

The full list is documented at https://redaxo.org/doku/main/extension-points.

Reading params and subject

Inside the callback, the rex_extension_point instance carries:

• $ep->getSubject() – the value passed in (often what you'll modify)
• $ep->getParam('key', $default) – extra context (article ID, user, etc.)
• $ep->setParam('key', $value) – pass info to later listeners
• $ep->getName() – the EP name (useful for shared callbacks)

rex_extension::register('ART_PRE_VIEW', function (rex_extension_point $ep) {
    $articleId = $ep->getParam('article_id');
    $clang     = $ep->getParam('clang');
    $html      = $ep->getSubject();

    if ($articleId === rex_article::getNotfoundArticleId()) {
        return $html; // don't touch 404s
    }

    return preg_replace('/<\/body>/', '<!-- rendered -->\n</body>', $html);
});

Backend-only extension

Always guard backend-only logic:

rex_extension::register('PACKAGES_INCLUDED', function () {
    if (!rex::isBackend()) {
        return;
    }
    if (!rex::getUser() || !rex::getUser()->isAdmin()) {
        return;
    }
    // …admin-only setup
});

Defining your own EP

Lets other addons hook into your code:

$result = rex_extension::registerPoint(new rex_extension_point(
    'MY_ADDON_ITEM_SAVED',
    $itemHtml,                        // subject
    ['item_id' => $id, 'user' => rex::getUser()] // params
));

Subscribers can transform $result and your code continues with their version.

Common pitfalls

• Registering inside a function that isn't called (e.g. inside an if (rex::isFrontend()) that fires only on frontend). Register unconditionally in boot.php, then guard inside the callback.
• Forgetting to return $ep->getSubject() (or your modified version) – downstream listeners then see null.
• Using OUTPUT_FILTER for things that should be in the template – it runs on every uncached request and adds latency.
• Heavy work in PACKAGES_INCLUDED slows down every request. Cache results or move into a cronjob.