Drupal 8: Intercepting a 404 route and setting to code to 200 - drupal-8

Question

In a Drupal 8 site, /some/random/path will return "404 not found". At runtime, I need to intercept some of these paths and set them to return something valid.
I added a file called MYMODULE.services.yml:
services:
mymodule.route_subscriber:
class: Drupal\MYMODULE\Routing\RouteSubscriber
tags:
- { name: event_subscriber }
Then, in ./src/Routing/RouteSubscriber.php, I have:
<?php
namespace Drupal\MYMODULE\Routing;
use Drupal\Core\Routing\RouteSubscriberBase;
use Symfony\Component\Routing\RouteCollection;
class RouteSubscriber extends RouteSubscriberBase {
protected function alterRoutes(RouteCollection $collection) {
if ($route = $collection->get('system.404')) {
$route->setDefault('_controller', '\Drupal\MYMODULE\Controller\MyController::load');
}
}
}
Then in ./src/Controller/SpokeController.php, I have:
class SpokeController extends ControllerBase {
public function load() {
$path = \Drupal::service('path.current')->getPath();
if (path_is_valid()) { // I can only do this at runtime.
// Is there a way to add something here like:
// $this->setResponseCode(200);
// return a render array for the content.
}
else {
// return a render array like "page not found".
}
}
}
In my controller, can I change the response code from 404 to 200? (I am expecting something like $this->setResponseCode(200) to exist, but I can't find it.)

Answer 1

This change record explains how to achieve this:
In SpokeController::load(), we can return a render array which contains the following:
$render['#attached']['http_header'][] = ['Status', "200"];
That changes the status code.
To change the title dynamically, you can add the following line to alterRoutes():
$route->setDefault('_title_callback', '\Drupal\steward_spoke\Controller\SpokeController::title');
Then, return a title in SpokeController::title(). All this together lets you return a title, content, and status code for a route dynamically.