Issue #2473113 by znerol, dpovshed, Wim Leers, Fabianx, dawehner,...

Issue #2473113 by znerol, dpovshed, Wim Leers, Fabianx, dawehner, effulgentsia: All stack middlewares are constructed at the same time even for cached pages

core/lib/Drupal/Core/DependencyInjection/Compiler/StackedKernelPass.php

@@ -14,6 +14,40 @@
 /**
  * Provides a compiler pass for stacked HTTP kernels.
  *
+ * Builds the HTTP kernel by collecting all services tagged 'http_middleware'
+ * and assembling them into a StackedKernel. The middleware with the lowest
+ * priority ends up as the outermost while the highest priority middleware
+ * wraps the actual HTTP kernel defined by the http_kernel.basic service.
+ *
+ * The 'http_middleware' service tag additionally accepts a 'responder'
+ * parameter. It should be set to TRUE if many or most requests will be handled
+ * directly by the middleware. Any underlying middleware and the HTTP kernel are
+ * then flagged as 'lazy'. As a result those low priority services and their
+ * dependencies are only initialized if the 'responder' middleware fails to
+ * generate a response and the request is delegated to the underlying kernel.
+ *
+ * In general middlewares should not have heavy dependencies. This is especially
+ * important for high-priority services which need to run before the internal
+ * page cache.
+ *
+ * An example of a high priority middleware.
+ * @code
+ * http_middleware.reverse_proxy:
+ *   class: Drupal\Core\StackMiddleware\ReverseProxyMiddleware
+ *   arguments: ['@settings']
+ *   tags:
+ *     - { name: http_middleware, priority: 300 }
+ * @endcode
+ *
+ * An example of a responder middleware:
+ * @code
+ * http_middleware.page_cache:
+ *   class: Drupal\page_cache\StackMiddleware\PageCache
+ *   arguments: ['@cache.render', '@page_cache_request_policy', '@page_cache_response_policy']
+ *   tags:
+ *     - { name: http_middleware, priority: 200, responder: true }
+ * @endcode
+ *
  * @see \Stack\Builder
  */
 class StackedKernelPass implements CompilerPassInterface {
@@ -36,16 +70,24 @@ public function process(ContainerBuilder $container) {
 
     $middlewares = [];
     $priorities = [];
+    $responders = [];
 
     foreach ($container->findTaggedServiceIds('http_middleware') as $id => $attributes) {
       $priorities[$id] = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
       $middlewares[$id] = $container->getDefinition($id);
+      $responders[$id] = !empty($attributes[0]['responder']);
     }
 
-    array_multisort($priorities, SORT_ASC, $middlewares);
+    array_multisort($priorities, SORT_ASC, $middlewares, $responders);
 
     $decorated_id = 'http_kernel.basic';
     $middlewares_param = [new Reference($decorated_id)];
+
+    $first_responder = array_search(TRUE, array_reverse($responders, TRUE), TRUE);
+    if ($first_responder) {
+      $container->getDefinition($decorated_id)->setLazy(TRUE);
+    }
+
     foreach ($middlewares as $id => $decorator) {
       // Prepend a reference to the middlewares container parameter.
       array_unshift($middlewares_param, new Reference($id));
@@ -55,6 +97,13 @@ public function process(ContainerBuilder $container) {
       array_unshift($arguments, new Reference($decorated_id));
       $decorator->setArguments($arguments);
 
+      if ($first_responder === $id) {
+        $first_responder = FALSE;
+      }
+      elseif ($first_responder) {
+        $decorator->setLazy(TRUE);
+      }
+
       $decorated_id = $id;
     }
 

core/modules/page_cache/page_cache.services.yml

@@ -3,4 +3,4 @@ services:
     class: Drupal\page_cache\StackMiddleware\PageCache
     arguments: ['@cache.render', '@page_cache_request_policy', '@page_cache_response_policy']
     tags:
-      - { name: http_middleware, priority: 200 }
+      - { name: http_middleware, priority: 200, responder: true }

core/modules/system/src/Tests/HttpKernel/StackKernelIntegrationTest.php

@@ -49,4 +49,23 @@ public function testRequest() {
     $this->assertEqual($request->attributes->get('_previous_optional_argument'), 'test_argument');
   }
 
+  /**
+   * Tests that late middlewares are automatically flagged lazy.
+   */
+  public function testLazyLateMiddlewares() {
+    $this->assertFalse($this->container->getDefinition('http_middleware.reverse_proxy')->isLazy(), 'lazy flag on http_middleware.reverse_proxy definition is not set');
+    $this->assertFalse($this->container->getDefinition('http_middleware.kernel_pre_handle')->isLazy(), 'lazy flag on http_middleware.kernel_pre_handle definition is not set');
+    $this->assertFalse($this->container->getDefinition('http_middleware.session')->isLazy(), 'lazy flag on http_middleware.session definition is not set');
+    $this->assertFalse($this->container->getDefinition('http_kernel.basic')->isLazy(), 'lazy flag on http_kernel.basic definition is not set');
+
+    \Drupal::service('module_installer')->install(['page_cache']);
+    $this->container = $this->kernel->rebuildContainer();
+
+    $this->assertFalse($this->container->getDefinition('http_middleware.reverse_proxy')->isLazy(), 'lazy flag on http_middleware.reverse_proxy definition is not set');
+    $this->assertFalse($this->container->getDefinition('http_middleware.page_cache')->isLazy(), 'lazy flag on http_middleware.page_cache definition is not set');
+    $this->assertTrue($this->container->getDefinition('http_middleware.kernel_pre_handle')->isLazy(), 'lazy flag on http_middleware.kernel_pre_handle definition is automatically set if page_cache is enabled.');
+    $this->assertTrue($this->container->getDefinition('http_middleware.session')->isLazy(), 'lazy flag on http_middleware.session definition is automatically set if page_cache is enabled.');
+    $this->assertTrue($this->container->getDefinition('http_kernel.basic')->isLazy(), 'lazy flag on http_kernel.basic definition is automatically set if page_cache is enabled.');
+  }
+
 }