Add server-side APCu caching for guest API responses

Author: pierres

extend.php

@@ -14,6 +14,7 @@
 use App\Console\PruneHiddenContent;
 use App\Console\PurgeSuspendedUsers;
 use App\Middleware\ContentSecurityPolicy;
+use App\Middleware\GuestApiCacheHeader;
 use App\Middleware\NoCacheHeader;
 use App\ServiceProvider\ApcuCacheProvider;
 use App\ServiceProvider\ErrorLogProvider;
@@ -47,6 +48,7 @@
     (new Extend\ServiceProvider())->register(SessionServiceProvider::class),
     (new Extend\Middleware('forum'))->add(ContentSecurityPolicy::class),
     (new Extend\Middleware('forum'))->add(NoCacheHeader::class),
+    (new Extend\Middleware('api'))->add(GuestApiCacheHeader::class),
     (new Extend\Formatter())
         ->configure(function (Configurator $config) {
             // Emoticons used to be provided by flarum/emoji

src/Middleware/GuestApiCacheHeader.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace App\Middleware;
+
+use Flarum\Http\RequestUtil;
+use Illuminate\Contracts\Cache\Repository as Cache;
+use Laminas\Diactoros\Response\JsonResponse;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+
+class GuestApiCacheHeader implements MiddlewareInterface
+{
+    private const TTL = 60;
+    private const PREFIX = 'api_';
+
+    public function __construct(private Cache $cache)
+    {
+    }
+
+    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
+    {
+        if ($request->getMethod() !== 'GET' || !RequestUtil::getActor($request)->isGuest()) {
+            return $handler->handle($request);
+        }
+
+        $cacheKey = self::PREFIX . md5($request->getUri()->getPath() . '?' . $request->getUri()->getQuery());
+
+        /** @var ?string $cached */
+        $cached = $this->cache->get($cacheKey);
+        if ($cached !== null) {
+            return new JsonResponse(
+                json_decode($cached, true, 512, JSON_THROW_ON_ERROR),
+                200,
+                ['content-type' => 'application/vnd.api+json', 'X-Cache' => 'HIT']
+            );
+        }
+
+        $response = $handler->handle($request);
+
+        if ($response->getStatusCode() === 200) {
+            $this->cache->put($cacheKey, (string) $response->getBody(), self::TTL);
+        }
+
+        return $response->withHeader('X-Cache', 'MISS');
+    }
+}

tests/e2e/cypress/e2e/CacheHeaders.cy.js

@@ -0,0 +1,17 @@
+describe('Cache headers', () => {
+  it('caches guest API responses', () => {
+    cy.request('/api').should((response) => {
+      expect(response.headers['x-cache']).to.equal('MISS')
+    })
+
+    cy.request('/api').should((response) => {
+      expect(response.headers['x-cache']).to.equal('HIT')
+    })
+  })
+
+  it('does not set cache header on forum HTML', () => {
+    cy.request('/').should((response) => {
+      expect(response.headers['cache-control']).to.contain('no-store')
+    })
+  })
+})