webdav returns "503 Service Unavailable" in case the ownCloud server is currently in maintenance mode.

apps/files/appinfo/remote.php

@@ -45,6 +45,7 @@ $server->addPlugin(new Sabre_DAV_Auth_Plugin($authBackend, 'ownCloud'));
 $server->addPlugin(new Sabre_DAV_Locks_Plugin($lockBackend));
 $server->addPlugin(new Sabre_DAV_Browser_Plugin(false)); // Show something in the Browser, but no upload
 $server->addPlugin(new OC_Connector_Sabre_QuotaPlugin());
+$server->addPlugin(new OC_Connector_Sabre_MaintenancePlugin());
 
 // And off we go!
 $server->exec();

lib/connector/sabre/ServiceUnavailable.php

@@ -0,0 +1,22 @@
+<?php
+/**
+ * ownCloud
+ *
+ * @author Thomas Müller
+ * @copyright 2013 Thomas Müller <thomas.mueller@tmit.eu>
+ *
+ * @license AGPL3
+ */
+
+class Sabre_DAV_Exception_ServiceUnavailable extends Sabre_DAV_Exception {
+
+	/**
+	 * Returns the HTTP statuscode for this exception
+	 *
+	 * @return int
+	 */
+	public function getHTTPCode() {
+
+		return 503;
+	}
+}

lib/connector/sabre/maintenanceplugin.php

@@ -0,0 +1,56 @@
+<?php
+
+/**
+ * ownCloud
+ *
+ * @author Thomas Müller
+ * @copyright 2013 Thomas Müller <thomas.mueller@tmit.eu>
+ *
+ * @license AGPL3
+ */
+
+require 'ServiceUnavailable.php';
+
+class OC_Connector_Sabre_MaintenancePlugin extends Sabre_DAV_ServerPlugin
+{
+
+	/**
+	 * Reference to main server object
+	 *
+	 * @var Sabre_DAV_Server
+	 */
+	private $server;
+
+	/**
+	 * This initializes the plugin.
+	 *
+	 * This function is called by Sabre_DAV_Server, after
+	 * addPlugin is called.
+	 *
+	 * This method should set up the required event subscriptions.
+	 *
+	 * @param Sabre_DAV_Server $server
+	 * @return void
+	 */
+	public function initialize(Sabre_DAV_Server $server) {
+
+		$this->server = $server;
+		$this->server->subscribeEvent('beforeMethod', array($this, 'checkMaintenanceMode'), 10);
+	}
+
+	/**
+	 * This method is called before any HTTP method and returns http status code 503
+	 * in case the system is in maintenance mode.
+	 *
+	 * @throws Sabre_DAV_Exception_ServiceUnavailable
+	 * @internal param string $method
+	 * @return bool
+	 */
+	public function checkMaintenanceMode() {
+		if (OC_Config::getValue('maintenance', false)) {
+			throw new Sabre_DAV_Exception_ServiceUnavailable();
+		}
+
+		return true;
+	}
+}