Add abstract class to extract previews from files that are zip archives

Signed-off-by: Julius Härtl <jus@bitgrid.net>

lib/private/Preview/Bundled.php

+<?php
+/**
+ * @copyright Copyright (c) 2020 Julius Härtl <jus@bitgrid.net>
+ *
+ * @author Julius Härtl <jus@bitgrid.net>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OC\Preview;
+
+use OCP\Files\File;
+use OCP\Files\NotPermittedException;
+use OCP\IImage;
+use OCP\Lock\LockedException;
+
+/**
+ * Extracts a preview from files that embed them in an ZIP archive
+ */
+abstract class Bundled extends ProviderV2 {
+
+	protected function extractThumbnail(File $file, $path): ?IImage {
+		$sourceTmp = \OC::$server->getTempManager()->getTemporaryFile();
+		$targetTmp = \OC::$server->getTempManager()->getTemporaryFile();
+
+		try {
+			$content = $file->fopen('r');
+			$content = stream_get_contents($content);
+			file_put_contents($sourceTmp, $content);
+
+			$zip = new \OC\Archive\ZIP($sourceTmp);
+			$zip->extractFile($path, $targetTmp);
+
+			$image = new \OC_Image();
+			$image->loadFromFile($targetTmp);
+			$image->fixOrientation();
+
+			return $image;
+		} catch (\Exception $e) {
+			return null;
+		}
+	}
+
+}