Properly catch whether a share is `null`

Despite it's PHPDoc the function might return `null` which was not properly catched and thus in some situations the share was resolved to the sharing users root directory.

To test this perform the following steps:

* Share file in owncloud 7 (7.0.4.2)
* Delete the parent folder of the shared file
* The share stays is in the DB and the share via the sharelink is inaccessible. (which is good)
* Upgrade to owncloud 8 (8.0.2) (This step is crucial. The bug is not reproduceable without upgrading from 7 to 8. It seems like the old tokens are handled different than the newer ones)
* Optional Step: Logout, Reset Browser Session, etc.
* Access the share via the old share url: almost empty page, but there is a dowload button which adds a "/download" to the URL.
* Upon clicking, a download.zip is downloaded which contains EVERYTHING from the owncloud directory (of the user who shared the file)
* No exception is thrown and no error is logged.

This will add a check whether the share is a valid one and also adds unit tests to prevent further regressions in the future. Needs to be backported to ownCloud 8.

Adding a proper clean-up of the orphaned shares is out-of-scope and would probably require some kind of FK or so.

Fixes https://github.com/owncloud/core/issues/15097

1 files changed, 43 insertions, 0 deletions

diff --git a/lib/public/appframework/http/notfoundresponse.php b/lib/public/appframework/http/notfoundresponse.php
new file mode 100644
index 00000000000..21f0461f5e6
--- /dev/null
+++ b/lib/public/appframework/http/notfoundresponse.php
@@ -0,0 +1,43 @@
+<?php
+/**
+ * @author Lukas Reschke <lukas@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/>
+ *
+ */
+
+namespace OCP\AppFramework\Http;
+
+use OCP\AppFramework\Http;
+use OCP\Template;
+
+/**
+ * A generic 404 response showing an 404 error page as well to the end-user
+ */
+class NotFoundResponse extends Response {
+
+	public function __construct() {
+		$this->setStatus(404);
+	}
+
+	/**
+	 * @return string
+	 */
+	public function render() {
+		$template = new Template('core', '404', 'guest');
+		return $template->fetchPage();
+	}
+}