Issue #2843420 by deviantintegral, bstan: Support embedding the cache subscriber as a middleware

README.md

+# Guzzle Cache for Drupal
+
+Provides a Drupal cache backend for
+[Kevinrob/guzzle-cache-middleware](https://github.com/Kevinrob/guzzle-cache-middleware).
+
+## Automatic caching for all HTTP requests
+
+To enable the caching layer for all HTTP requests automatically, enable the `guzzle_cache_middleware` sub-module.

modules/guzzle_cache_middleware/guzzle_cache_middleware.info.yml

+name: Guzzle Cache Backend Middleware
+description: 'Provides a default middleware for the DrupalGuzzleCache.'
+package: Caching
+type: module
+core: 8.x
+core_version_requirement: ^8 || ^9
\ No newline at end of file

modules/guzzle_cache_middleware/guzzle_cache_middleware.services.yml

+services:
+  guzzle_cache.middleware:
+    class: \Drupal\guzzle_cache\DrupalGuzzleCache
+    arguments: ['@cache.default']
+    tags:
+      - { name: http_client_middleware }
\ No newline at end of file

src/DrupalGuzzleCache.php

@@ -2,9 +2,13 @@
 
 namespace Drupal\guzzle_cache;
 
+use Drupal\Core\Cache\BackendChain;
+use Drupal\Core\Cache\MemoryBackend;
+use Kevinrob\GuzzleCache\CacheMiddleware;
 use Kevinrob\GuzzleCache\Storage\CacheStorageInterface;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Kevinrob\GuzzleCache\CacheEntry;
+use Kevinrob\GuzzleCache\Strategy\PrivateCacheStrategy;
 
 /**
  * Provides a Drupal cache backend for the Guzzle caching middleware.
@@ -48,6 +52,22 @@ class DrupalGuzzleCache implements CacheStorageInterface {
     $this->tags = $tags;
   }
 
+  /**
+   * Implements invoke() so this class can be used as a middleware.
+   *
+   * @return \Kevinrob\GuzzleCache\CacheMiddleware
+   *   The middleware to cache data.
+   */
+  public function __invoke(): CacheMiddleware {
+    $cache = new BackendChain('default');
+    $cache->appendBackend(new MemoryBackend());
+    $cache->appendBackend($this->cache);
+
+    $cache = new DrupalGuzzleCache($cache);
+    $middleware = new CacheMiddleware(new PrivateCacheStrategy($cache));
+    return $middleware;
+  }
+
   /**
    * Set the cache key prefix.
    *

tests/src/Unit/DrupalGuzzleCacheTest.php

@@ -8,6 +8,7 @@ use Drupal\Tests\UnitTestCase;
 use GuzzleHttp\Psr7\Request;
 use GuzzleHttp\Psr7\Response;
 use Kevinrob\GuzzleCache\CacheEntry;
+use Kevinrob\GuzzleCache\CacheMiddleware;
 
 /**
  * Tests Guzzle cache integration.
@@ -120,4 +121,16 @@ class DrupalGuzzleCacheTest extends UnitTestCase {
     new DrupalGuzzleCache($backend, $prefix);
   }
 
+  /**
+   * Test invoking for a middleware.
+   *
+   * @covers ::__invoke
+   */
+  public function testInvoke() {
+    /** @var \Drupal\Core\Cache\CacheBackendInterface $backend */
+    $backend = $this->createMock(CacheBackendInterface::class);
+    $cache = new DrupalGuzzleCache($backend);
+    $this->assertInstanceOf(CacheMiddleware::class, $cache());
+  }
+
 }