Add middleware to check if feature is enabled

app/Exceptions/FeatureDisabledException.php

@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * SPDX-License-Identifier: MIT
+ * Copyright (c) 2017-2018 Tobias Reich
+ * Copyright (c) 2018-2026 LycheeOrg.
+ */
+
+namespace App\Exceptions;
+
+use Symfony\Component\HttpFoundation\Response;
+
+class FeatureDisabledException extends BaseLycheeException
+{
+	public function __construct(string $feature)
+	{
+		parent::__construct(Response::HTTP_NOT_IMPLEMENTED, sprintf("Feature '%s' is disabled", $feature), null);
+	}
+}

app/Http/Kernel.php

@@ -109,5 +109,6 @@ class Kernel extends HttpKernel
 		'response_cache' => \App\Http\Middleware\Caching\ResponseCache::class,
 		'album_cache_refresher' => \App\Http\Middleware\Caching\AlbumRouteCacheRefresher::class,
 		'legacy_id_redirect' => \App\Http\Middleware\LegacyLocalIdRedirect::class,
+		'feature' => \App\Http\Middleware\FeatureEnabled::class,
 	];
 }

app/Http/Middleware/FeatureEnabled.php

@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * SPDX-License-Identifier: MIT
+ * Copyright (c) 2017-2018 Tobias Reich
+ * Copyright (c) 2018-2026 LycheeOrg.
+ */
+
+namespace App\Http\Middleware;
+
+use App\Exceptions\ConfigurationKeyMissingException;
+use App\Exceptions\FeatureDisabledException;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Config;
+
+/**
+ * Class FeatureEnabled.
+ *
+ * This middleware checks whether a feature flag is enabled via the `features`
+ * config file. If the flag resolves to false, a 501 Not Implemented response
+ * is returned. Use as `feature:feature_name` in route definitions.
+ */
+class FeatureEnabled
+{
+	/**
+	 * Handle an incoming request.
+	 *
+	 * @param Request  $request      the incoming request to serve
+	 * @param \Closure $next         the next operation to be applied to the request
+	 * @param string   $feature_name the key to look up in config('features')
+	 *
+	 * @throws FeatureDisabledException
+	 */
+	public function handle(Request $request, \Closure $next, string $feature_name): mixed
+	{
+		$key = 'features.' . $feature_name;
+
+		if (!Config::has($key)) {
+			throw new ConfigurationKeyMissingException(sprintf("Feature key '%s' does not exist in config", $key));
+		}
+
+		if (config($key) !== true) {
+			throw new FeatureDisabledException($feature_name);
+		}
+
+		return $next($request);
+	}
+}

tests/Unit/Middleware/FeatureEnabledTest.php

@@ -0,0 +1,65 @@
+<?php
+
+/**
+ * SPDX-License-Identifier: MIT
+ * Copyright (c) 2017-2018 Tobias Reich
+ * Copyright (c) 2018-2026 LycheeOrg.
+ */
+
+/**
+ * We don't care for unhandled exceptions in tests.
+ * It is the nature of a test to throw an exception.
+ * Without this suppression we had 100+ Linter warning in this file which
+ * don't help anything.
+ *
+ * @noinspection PhpDocMissingThrowsInspection
+ * @noinspection PhpUnhandledExceptionInspection
+ */
+
+namespace Tests\Unit\Middleware;
+
+use App\Exceptions\ConfigurationKeyMissingException;
+use App\Exceptions\FeatureDisabledException;
+use App\Http\Middleware\FeatureEnabled;
+use Illuminate\Foundation\Testing\DatabaseTransactions;
+use Illuminate\Http\Request;
+use Tests\AbstractTestCase;
+
+class FeatureEnabledTest extends AbstractTestCase
+{
+	use DatabaseTransactions;
+
+	public function testFeatureEnabled(): void
+	{
+		config(['features.some_feature' => true]);
+
+		$request = $this->mock(Request::class);
+		$middleware = new FeatureEnabled();
+
+		self::assertEquals(1, $middleware->handle($request, fn () => 1, 'some_feature'));
+	}
+
+	public function testFeatureDisabled(): void
+	{
+		config(['features.some_feature' => false]);
+
+		$request = $this->mock(Request::class);
+		$middleware = new FeatureEnabled();
+
+		$this->assertThrows(
+			fn () => $middleware->handle($request, fn () => 1, 'some_feature'),
+			FeatureDisabledException::class
+		);
+	}
+
+	public function testFeatureNotDefined(): void
+	{
+		$request = $this->mock(Request::class);
+		$middleware = new FeatureEnabled();
+
+		$this->assertThrows(
+			fn () => $middleware->handle($request, fn () => 1, 'undefined_feature'),
+			ConfigurationKeyMissingException::class
+		);
+	}
+}