minor #28907 [Messenger] make middlewares truly lazy on a bus (nicola…

…s-grekas)

This PR was merged into the 4.2-dev branch.

Discussion
----------

[Messenger] make middlewares truly lazy on a bus

| Q             | A
| ------------- | ---
| Branch?       | 4.2
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Right now, as soon as a message is dispatched on a bus, all its handlers are instantiated.
This PR fixes it by leveraging `IteratorAggregate` when possible (implemented by DI's `RewindableGenerator`).

Commits
-------

6a5d7a1 [Messenger] make middlewares truly lazy on a bus

src/Symfony/Component/Messenger/MessageBus.php

@@ -11,28 +11,39 @@
 
 namespace Symfony\Component\Messenger;
 
-use Symfony\Component\Messenger\Exception\InvalidArgumentException;
 use Symfony\Component\Messenger\Middleware\MiddlewareInterface;
 
 /**
  * @author Samuel Roze <samuel.roze@gmail.com>
  * @author Matthias Noback <matthiasnoback@gmail.com>
+ * @author Nicolas Grekas <p@tchwork.com>
  */
 class MessageBus implements MessageBusInterface
 {
-    private $middlewareHandlers;
-
-    /**
-     * @var MiddlewareInterface[]|null
-     */
-    private $indexedMiddlewareHandlers;
+    private $middlewareAggregate;
 
     /**
      * @param MiddlewareInterface[]|iterable $middlewareHandlers
      */
     public function __construct(iterable $middlewareHandlers = array())
     {
-        $this->middlewareHandlers = $middlewareHandlers;
+        if ($middlewareHandlers instanceof \IteratorAggregate) {
+            $this->middlewareAggregate = $middlewareHandlers;
+        } elseif (\is_array($middlewareHandlers)) {
+            $this->middlewareAggregate = new \ArrayObject($middlewareHandlers);
+        } else {
+            $this->middlewareAggregate = new class() {
+                public $aggregate;
+                public $iterator;
+
+                public function getIterator()
+                {
+                    return $this->aggregate = new \ArrayObject(iterator_to_array($this->iterator, false));
+                }
+            };
+            $this->middlewareAggregate->aggregate = &$this->middlewareAggregate;
+            $this->middlewareAggregate->iterator = $middlewareHandlers;
+        }
     }
 
     /**
@@ -41,24 +52,26 @@ public function __construct(iterable $middlewareHandlers = array())
     public function dispatch($message): void
     {
         if (!\is_object($message)) {
-            throw new InvalidArgumentException(sprintf('Invalid type for message argument. Expected object, but got "%s".', \gettype($message)));
+            throw new \TypeError(sprintf('Invalid argument provided to "%s()": expected object, but got %s.', __METHOD__, \gettype($message)));
         }
+        $middlewareIterator = $this->middlewareAggregate->getIterator();
 
-        $this->callableForNextMiddleware(0)($message instanceof Envelope ? $message : new Envelope($message));
-    }
-
-    private function callableForNextMiddleware(int $index): callable
-    {
-        if (null === $this->indexedMiddlewareHandlers) {
-            $this->indexedMiddlewareHandlers = \is_array($this->middlewareHandlers) ? array_values($this->middlewareHandlers) : iterator_to_array($this->middlewareHandlers, false);
+        while ($middlewareIterator instanceof \IteratorAggregate) {
+            $middlewareIterator = $middlewareIterator->getIterator();
         }
+        $middlewareIterator->rewind();
 
-        if (!isset($this->indexedMiddlewareHandlers[$index])) {
-            return static function () {};
+        if (!$middlewareIterator->valid()) {
+            return;
         }
+        $next = static function (Envelope $envelope) use ($middlewareIterator, &$next) {
+            $middlewareIterator->next();
 
-        return function (Envelope $envelope) use ($index) {
-            $this->indexedMiddlewareHandlers[$index]->handle($envelope, $this->callableForNextMiddleware($index + 1));
+            if ($middlewareIterator->valid()) {
+                $middlewareIterator->current()->handle($envelope, $next);
+            }
         };
+
+        $middlewareIterator->current()->handle($message instanceof Envelope ? $message : new Envelope($message), $next);
     }
 }

src/Symfony/Component/Messenger/Tests/DependencyInjection/MessengerPassTest.php

@@ -90,10 +90,10 @@ public function testProcessHandlersByBus()
             ->setAbstract(true)
         ;
 
-        $middlewares = array(array('id' => 'call_message_handler'));
+        $middlewareHandlers = array(array('id' => 'call_message_handler'));
 
-        $container->setParameter($commandBusId.'.middleware', $middlewares);
-        $container->setParameter($queryBusId.'.middleware', $middlewares);
+        $container->setParameter($commandBusId.'.middleware', $middlewareHandlers);
+        $container->setParameter($queryBusId.'.middleware', $middlewareHandlers);
 
         $container->register(DummyCommandHandler::class)->addTag('messenger.message_handler', array('bus' => $commandBusId));
         $container->register(DummyQueryHandler::class)->addTag('messenger.message_handler', array('bus' => $queryBusId));
@@ -607,10 +607,10 @@ public function testItRegistersTheDebugCommand()
 
         $container->register('console.command.messenger_debug', DebugCommand::class)->addArgument(array());
 
-        $middlewares = array(array('id' => 'call_message_handler'));
+        $middlewareHandlers = array(array('id' => 'call_message_handler'));
 
-        $container->setParameter($commandBusId.'.middleware', $middlewares);
-        $container->setParameter($queryBusId.'.middleware', $middlewares);
+        $container->setParameter($commandBusId.'.middleware', $middlewareHandlers);
+        $container->setParameter($queryBusId.'.middleware', $middlewareHandlers);
 
         $container->register(DummyCommandHandler::class)->addTag('messenger.message_handler', array('bus' => $commandBusId));
         $container->register(DummyQueryHandler::class)->addTag('messenger.message_handler', array('bus' => $queryBusId));

src/Symfony/Component/Messenger/Tests/MessageBusTest.php

@@ -30,8 +30,8 @@ public function testItHasTheRightInterface()
     }
 
     /**
-     * @expectedException \Symfony\Component\Messenger\Exception\InvalidArgumentException
-     * @expectedExceptionMessage Invalid type for message argument. Expected object, but got "string".
+     * @expectedException \TypeError
+     * @expectedExceptionMessage Invalid argument provided to "Symfony\Component\Messenger\MessageBus::dispatch()": expected object, but got string.
      */
     public function testItDispatchInvalidMessageType()
     {