The File maxSize Constraint does not seem to work when post_max_size has been reached. The request method is post, but the rest of all variables (including $files) is empty.

When the post is too big, the form will try to get validated via $form->isValid() but since there are no values this goes wrong. Or to be more precise, nothing happens because the form was not marked as submitted.

Currently I did fix this by calling the following snippet before calling $form->isValid():

    // First check or the filesize was too large, because in that case files global is empty
    $params = new ServerParams();
    if ($params->getContentLength() > $params->getPostMaxSize()) {
        $form->get('file')->addError(
            new FormError($this->get('translator')->trans('form.msg_max_post',
                array(
                    '%contentSize%' => $document->formatFilesize($params->getContentLength()),
                    '%maxSize%'     => '20 MB',
                ),
                'validators'
            ))
        );
    }

Symfony has a FormValidator, which even has a similar check like the above snippet.

My above snippet does work properly, but after commenting it, for the same request FormValidator->validate() is not executed when the post is too large.

It seems to go wrong in the HttpFoundationRequestHandler where $request->request and $request->files are both empty.