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

src/Forum/ForumServiceProvider.php

@@ -31,8 +31,10 @@
 use Flarum\Settings\Event\Saved;
 use Flarum\Settings\Event\Saving;
 use Flarum\Settings\SettingsRepositoryInterface;
+use Flarum\Settings\SettingsValidator;
 use Illuminate\Contracts\Container\Container;
 use Illuminate\Contracts\Events\Dispatcher;
+use Illuminate\Contracts\Validation\Factory as ValidatorFactory;
 use Illuminate\Contracts\View\Factory;
 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 +174,10 @@ function (Saved $event) use ($container) {
 
         $events->listen(
             Saving::class,
-            function (Saving $event) use ($container) {
+            function (Saving $event) use ($container, $validatorFactory) {
+                $settingsValidator = new SettingsValidator($validatorFactory, $event->settings);
+                $settingsValidator->validate();
+
                 $validator = new ValidateCustomLess(
                     $container->make('flarum.assets.forum'),
                     $container->make('flarum.locales'),

src/Settings/SettingsValidator.php

@@ -0,0 +1,46 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Settings;
+
+use Illuminate\Contracts\Validation\Factory;
+use Illuminate\Validation\ValidationException;
+
+class SettingsValidator
+{
+    /**
+     * @var Factory
+     */
+    protected $validatorFactory;
+
+    /**
+     * @var array
+     */
+    protected $settings;
+
+    public function __construct(Factory $validatorFactory, array $settings)
+    {
+        $this->validatorFactory = $validatorFactory;
+        $this->settings = $settings;
+    }
+
+    public function validate()
+    {
+        $validator = $this->validatorFactory->make(
+            $this->settings,
+            array_map(function ($value) {
+                return 'max:65000';
+            }, $this->settings),
+        );
+
+        if ($validator->fails()) {
+            throw new ValidationException($validator);
+        }
+    }
+}