server/apps/files_trashbin/ajax/preview.php

<?php
/**
 * @author Björn Schießle <schiessle@owncloud.com>
 * @author Georg Ehrke <georg@owncloud.com>
 * @author Lukas Reschke <lukas@owncloud.com>
 * @author Morris Jobke <hey@morrisjobke.de>
 * @author Vincent Petry <pvince81@owncloud.com>
 *
 * @copyright Copyright (c) 2015, ownCloud, Inc.
 * @license AGPL-3.0
 *
 * This code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * 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, version 3,
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 *
 */
\OC_Util::checkLoggedIn();
\OC::$server->getSession()->close();

if(!\OC_App::isEnabled('files_trashbin')){
	exit;
}

$file = array_key_exists('file', $_GET) ? (string) $_GET['file'] : '';
$maxX = array_key_exists('x', $_GET) ? (int) $_GET['x'] : '44';
$maxY = array_key_exists('y', $_GET) ? (int) $_GET['y'] : '44';
$scalingUp = array_key_exists('scalingup', $_GET) ? (bool) $_GET['scalingup'] : true;

if($file === '') {
	\OC_Response::setStatus(400); //400 Bad Request
	\OC_Log::write('core-preview', 'No file parameter was passed', \OC_Log::DEBUG);
	exit;
}

if($maxX === 0 || $maxY === 0) {
	\OC_Response::setStatus(400); //400 Bad Request
	\OC_Log::write('core-preview', 'x and/or y set to 0', \OC_Log::DEBUG);
	exit;
}

try{
	$preview = new \OC\Preview(\OC_User::getUser(), 'files_trashbin/files', $file);
	$view = new \OC\Files\View('/'.\OC_User::getUser(). '/files_trashbin/files');
	if ($view->is_dir($file)) {
		$mimetype = 'httpd/unix-directory';
	} else {
		$pathInfo = pathinfo(ltrim($file, '/'));
		$fileName = $pathInfo['basename'];
		// if in root dir
		if ($pathInfo['dirname'] === '.') {
			// cut off the .d* suffix
			$i = strrpos($fileName, '.');
			if ($i !== false) {
				$fileName = substr($fileName, 0, $i);
			}
		}
		$mimetype = \OC_Helper::getFileNameMimeType($fileName);
	}
	$preview->setMimetype($mimetype);
	$preview->setMaxX($maxX);
	$preview->setMaxY($maxY);
	$preview->setScalingUp($scalingUp);

	$preview->showPreview();
}catch(\Exception $e) {
	\OC_Response::setStatus(500);
	\OC_Log::write('core', $e->getmessage(), \OC_Log::DEBUG);
}