Why are $_Files and/or HTTPFoundationFileBag invalid in custom module Controller?

I have noticed a very strange issue with accessing an individual file from the $_FILES object or the Symfony derived SymfonyComponentHTTPFoundationFileBag from within a custom module controller.

The exact location of the issue seems to be in SymfonyComponentHttpKernelHttpKernel -> handleRaw

Specifically, the file exists prior dispatching the KernelEvent::REQUEST but it does not after.

// request $event = new GetResponseEvent($this, $request, $type);  // THE FILE EXISTS HERE // file_exists( $request->files->get(0)->getRealPath()) == TRUE  $this->dispatcher->dispatch(KernelEvents::REQUEST, $event);  // THE FILE DOES NOT EXISTS HERE // file_exists( $request->files->get(0)->getRealPath()) == FALSE 

Here is the entire method for reference also including some code to move the file, which works as expected as long as it is before the event dispatch.

  /**  * Handles a request to convert it to a response.  *  * Exceptions are not caught.  *  * @param Request $request A Request instance  * @param int     $type    The type of the request (one of HttpKernelInterface::MASTER_REQUEST or HttpKernelInterface::SUB_REQUEST)  *  * @return Response A Response instance  *  * @throws LogicException       If one of the listener does not behave as expected  * @throws NotFoundHttpException When controller cannot be found  */ private function handleRaw(Request $request, $type = self::MASTER_REQUEST) {     $this->requestStack->push($request);       $directory = Drupal::service('file_system')->realpath(file_default_scheme() . "://");      /* @var SymfonyComponentHttpFoundationFileUploadedFile $uploadedFile*/     $uploadedFile = $request->files->get(0);      if (is_uploaded_file($uploadedFile->getRealPath())){       $success = $uploadedFile->move($directory);     }      // request     $event = new GetResponseEvent($this, $request, $type);     $this->dispatcher->dispatch(KernelEvents::REQUEST, $event);      if ($event->hasResponse()) {         return $this->filterResponse($event->getResponse(), $request, $type);     }      // load controller     if (false === $controller = $this->resolver->getController($request)) {         throw new NotFoundHttpException(sprintf('Unable to find the controller for path "%s". The route is wrongly configured.', $request->getPathInfo()));     }      $event = new FilterControllerEvent($this, $controller, $request, $type);     $this->dispatcher->dispatch(KernelEvents::CONTROLLER, $event);     $controller = $event->getController();      // controller arguments     $arguments = $this->argumentResolver->getArguments($request, $controller);      $event = new FilterControllerArgumentsEvent($this, $controller, $arguments, $request, $type);     $this->dispatcher->dispatch(KernelEvents::CONTROLLER_ARGUMENTS, $event);     $controller = $event->getController();     $arguments = $event->getArguments();      // call controller     $response = call_user_func_array($controller, $arguments);      // view     if (!$response instanceof Response) {         $event = new GetResponseForControllerResultEvent($this, $request, $type, $response);         $this->dispatcher->dispatch(KernelEvents::VIEW, $event);          if ($event->hasResponse()) {             $response = $event->getResponse();         }          if (!$response instanceof Response) {             $msg = sprintf('The controller must return a response (%s given).', $this->varToString($response));              // the user may have forgotten to return something             if (null === $response) {                 $msg .= ' Did you forget to add a return statement somewhere in your controller?';             }             throw new LogicException($msg);         }     }      return $this->filterResponse($response, $request, $type); } 

I am trying to write a custom GraphQL module mutation plugin that handles file uploads and unless I can get access to the file object from the POST request, I don’t think this will be possible.

Any thoughts are greatly appreciated.

I believe this may be a core issue or an upstream issue with Symfony or at the very least a side effect of the assumptions of how new requests are created.

https://www.drupal.org/project/drupal/issues/2934486#comment-12406531