Enforce 65k character limit when attempting to update setting values.

src/Forum/ForumServiceProvider.php

@@ -33,7 +33,9 @@
 use Flarum\Settings\SettingsRepositoryInterface;
 use Illuminate\Contracts\Container\Container;
 use Illuminate\Contracts\Events\Dispatcher;
+use Illuminate\Contracts\Validation\Factory as ValidatorFactory;
 use Illuminate\Contracts\View\Factory;
+use Illuminate\Validation\ValidationException;
 use Laminas\Stratigility\MiddlewarePipe;
 use Symfony\Contracts\Translation\TranslatorInterface;
 
@@ -131,7 +133,7 @@ public function register()
         });
     }
 
-    public function boot(Container $container, Dispatcher $events, Factory $view)
+    public function boot(Container $container, Dispatcher $events, Factory $view, ValidatorFactory $validatorFactory)
     {
         $this->loadViewsFrom(__DIR__.'/../../views', 'flarum.forum');
 
@@ -172,7 +174,18 @@ function (Saved $event) use ($container) {
 
         $events->listen(
             Saving::class,
-            function (Saving $event) use ($container) {
+            function (Saving $event) use ($container, $validatorFactory) {
+                $validator = $validatorFactory->make(
+                    $event->settings,
+                    array_map(function ($value) {
+                        return 'max:65000';
+                    }, $event->settings),
+                );
+
+                if ($validator->fails()) {
+                    throw new ValidationException($validator);
+                }
+
                 $validator = new ValidateCustomLess(
                     $container->make('flarum.assets.forum'),
                     $container->make('flarum.locales'),