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typo3/sysext/backend/Classes/Controller/FlashMessageController.php

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+<?php
+declare(strict_types = 1);
+namespace TYPO3\CMS\Backend\Controller;
+
+/*
+ * This file is part of the TYPO3 CMS project.
+ *
+ * It is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License, either version 2
+ * of the License, or any later version.
+ *
+ * For the full copyright and license information, please read the
+ * LICENSE.txt file that was distributed with this source code.
+ *
+ * The TYPO3 project - inspiring people to share!
+ */
+
+use Psr\Http\Message\ResponseInterface;
+use TYPO3\CMS\Core\Http\JsonResponse;
+use TYPO3\CMS\Core\Messaging\FlashMessageService;
+use TYPO3\CMS\Core\Utility\GeneralUtility;
+
+/**
+ * Render FlashMessages
+ * @internal This class is a specific Backend controller implementation and is not considered part of the Public TYPO3 API.
+ */
+class FlashMessageController
+{
+    /**
+     * Renders the FlashMessages from queue and returns them as JSON.
+     *
+     * @return ResponseInterface
+     */
+    public function getQueuedFlashMessagesAction(): ResponseInterface
+    {
+        $flashMessageService = GeneralUtility::makeInstance(FlashMessageService::class);
+        $defaultFlashMessageQueue = $flashMessageService->getMessageQueueByIdentifier();
+        $flashMessages = $defaultFlashMessageQueue->getAllMessagesAndFlush();
+
+        $messages = [];
+        foreach ($flashMessages as $flashMessage) {
+            $messages[] = [
+                'title' => $flashMessage->getTitle(),
+                'message' => $flashMessage->getMessage(),
+                'severity' => $flashMessage->getSeverity()
+            ];
+        }
+
+        return (new JsonResponse())->setPayload($messages);
+    }
+}