Merge pull request #1197 from nextcloud/oc-public-sharing

CalDAV calendar public sharing

5 files changed, 593 insertions, 1 deletions

diff --git a/apps/dav/lib/CalDAV/CalDavBackend.php b/apps/dav/lib/CalDAV/CalDavBackend.php
index 17479c490a9..440188c13ca 100644
--- a/apps/dav/lib/CalDAV/CalDavBackend.php
+++ b/apps/dav/lib/CalDAV/CalDavBackend.php
@@ -29,9 +29,11 @@ use OCA\DAV\DAV\Sharing\IShareable;
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCA\DAV\Connector\Sabre\Principal;
 use OCA\DAV\DAV\Sharing\Backend;
+use OCP\IConfig;
 use OCP\IDBConnection;
 use OCP\IUser;
 use OCP\IUserManager;
+use OCP\Security\ISecureRandom;
 use Sabre\CalDAV\Backend\AbstractBackend;
 use Sabre\CalDAV\Backend\SchedulingSupport;
 use Sabre\CalDAV\Backend\SubscriptionSupport;
@@ -41,6 +43,7 @@ use Sabre\CalDAV\Xml\Property\ScheduleCalendarTransp;
 use Sabre\CalDAV\Xml\Property\SupportedCalendarComponentSet;
 use Sabre\DAV;
 use Sabre\DAV\Exception\Forbidden;
+use Sabre\DAV\Exception\NotFound;
 use Sabre\DAV\PropPatch;
 use Sabre\HTTP\URLUtil;
 use Sabre\VObject\DateTimeParser;
@@ -66,6 +69,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 */
 	const MAX_DATE = '2038-01-01';
 
+	const ACCESS_PUBLIC = 4;
 	const CLASSIFICATION_PUBLIC = 0;
 	const CLASSIFICATION_PRIVATE = 1;
 	const CLASSIFICATION_CONFIDENTIAL = 2;
@@ -117,6 +121,12 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 
 	/** @var IUserManager */
 	private $userManager;
+	
+	/** @var IConfig */
+	private $config;
+
+	/** @var ISecureRandom */
+	private $random;
 
 	/**
 	 * CalDavBackend constructor.
@@ -124,12 +134,20 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param IDBConnection $db
 	 * @param Principal $principalBackend
 	 * @param IUserManager $userManager
+	 * @param IConfig $config
+	 * @param ISecureRandom $random
 	 */
-	public function __construct(IDBConnection $db, Principal $principalBackend, IUserManager $userManager) {
+	public function __construct(IDBConnection $db,
+								Principal $principalBackend,
+								IUserManager $userManager,
+								IConfig $config,
+								ISecureRandom $random) {
 		$this->db = $db;
 		$this->principalBackend = $principalBackend;
 		$this->userManager = $userManager;
 		$this->sharingBackend = new Backend($this->db, $principalBackend, 'calendar');
+		$this->config = $config;
+		$this->random = $random;
 	}
 
 	/**
@@ -295,6 +313,120 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 
 		return $this->userDisplayNames[$uid];
 	}
+	
+	/**
+	 * @return array
+	 */
+	public function getPublicCalendars() {
+		$fields = array_values($this->propertyMap);
+		$fields[] = 'a.id';
+		$fields[] = 'a.uri';
+		$fields[] = 'a.synctoken';
+		$fields[] = 'a.components';
+		$fields[] = 'a.principaluri';
+		$fields[] = 'a.transparent';
+		$fields[] = 's.access';
+		$fields[] = 's.publicuri';
+		$calendars = [];
+		$query = $this->db->getQueryBuilder();
+		$result = $query->select($fields)
+			->from('dav_shares', 's')
+			->join('s', 'calendars', 'a', $query->expr()->eq('s.resourceid', 'a.id'))
+			->where($query->expr()->in('s.access', $query->createNamedParameter(self::ACCESS_PUBLIC)))
+			->andWhere($query->expr()->eq('s.type', $query->createNamedParameter('calendar')))
+			->execute();
+
+		while($row = $result->fetch()) {
+			list(, $name) = URLUtil::splitPath($row['principaluri']);
+			$row['displayname'] = $row['displayname'] . "($name)";
+			$components = [];
+			if ($row['components']) {
+				$components = explode(',',$row['components']);
+			}
+			$calendar = [
+				'id' => $row['id'],
+				'uri' => $row['publicuri'],
+				'principaluri' => $row['principaluri'],
+				'{' . Plugin::NS_CALENDARSERVER . '}getctag' => 'http://sabre.io/ns/sync/' . ($row['synctoken']?$row['synctoken']:'0'),
+				'{http://sabredav.org/ns}sync-token' => $row['synctoken']?$row['synctoken']:'0',
+				'{' . Plugin::NS_CALDAV . '}supported-calendar-component-set' => new SupportedCalendarComponentSet($components),
+				'{' . Plugin::NS_CALDAV . '}schedule-calendar-transp' => new ScheduleCalendarTransp($row['transparent']?'transparent':'opaque'),
+				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal' => $row['principaluri'],
+				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}read-only' => (int)$row['access'] === Backend::ACCESS_READ,
+				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}public' => (int)$row['access'] === self::ACCESS_PUBLIC,
+			];
+
+			foreach($this->propertyMap as $xmlName=>$dbName) {
+				$calendar[$xmlName] = $row[$dbName];
+			}
+
+			if (!isset($calendars[$calendar['id']])) {
+				$calendars[$calendar['id']] = $calendar;
+			}
+		}
+		$result->closeCursor();
+
+		return array_values($calendars);
+	}
+
+	/**
+	 * @param string $uri
+	 * @return array
+	 * @throws NotFound
+	 */
+	public function getPublicCalendar($uri) {
+		$fields = array_values($this->propertyMap);
+		$fields[] = 'a.id';
+		$fields[] = 'a.uri';
+		$fields[] = 'a.synctoken';
+		$fields[] = 'a.components';
+		$fields[] = 'a.principaluri';
+		$fields[] = 'a.transparent';
+		$fields[] = 's.access';
+		$fields[] = 's.publicuri';
+		$query = $this->db->getQueryBuilder();
+		$result = $query->select($fields)
+			->from('dav_shares', 's')
+			->join('s', 'calendars', 'a', $query->expr()->eq('s.resourceid', 'a.id'))
+			->where($query->expr()->in('s.access', $query->createNamedParameter(self::ACCESS_PUBLIC)))
+			->andWhere($query->expr()->eq('s.type', $query->createNamedParameter('calendar')))
+			->andWhere($query->expr()->eq('s.publicuri', $query->createNamedParameter($uri)))
+			->execute();
+
+		$row = $result->fetch(\PDO::FETCH_ASSOC);
+
+		$result->closeCursor();
+
+		if ($row === false) {
+			throw new NotFound('Node with name \'' . $uri . '\' could not be found');
+		}
+
+		list(, $name) = URLUtil::splitPath($row['principaluri']);
+		$row['displayname'] = $row['displayname'] . ' ' . "($name)";
+		$components = [];
+		if ($row['components']) {
+			$components = explode(',',$row['components']);
+		}
+		$calendar = [
+			'id' => $row['id'],
+			'uri' => $row['publicuri'],
+			'principaluri' => $row['principaluri'],
+			'{' . Plugin::NS_CALENDARSERVER . '}getctag' => 'http://sabre.io/ns/sync/' . ($row['synctoken']?$row['synctoken']:'0'),
+			'{http://sabredav.org/ns}sync-token' => $row['synctoken']?$row['synctoken']:'0',
+			'{' . Plugin::NS_CALDAV . '}supported-calendar-component-set' => new SupportedCalendarComponentSet($components),
+			'{' . Plugin::NS_CALDAV . '}schedule-calendar-transp' => new ScheduleCalendarTransp($row['transparent']?'transparent':'opaque'),
+			'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal' => $row['principaluri'],
+			'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}read-only' => (int)$row['access'] === Backend::ACCESS_READ,
+			'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}public' => (int)$row['access'] === self::ACCESS_PUBLIC,
+		];
+
+		foreach($this->propertyMap as $xmlName=>$dbName) {
+			$calendar[$xmlName] = $row[$dbName];
+		}
+
+		return $calendar;
+
+	}
 
 	/**
 	 * @param string $principal
@@ -1473,6 +1605,50 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	}
 
 	/**
+	 * @param boolean $value
+	 * @param \OCA\DAV\CalDAV\Calendar $calendar
+	 * @return string|null
+	 */
+	public function setPublishStatus($value, $calendar) {
+		$query = $this->db->getQueryBuilder();
+		if ($value) {
+			$publicUri = $this->random->generate(16, ISecureRandom::CHAR_UPPER.ISecureRandom::CHAR_DIGITS);
+			$query->insert('dav_shares')
+				->values([
+					'principaluri' => $query->createNamedParameter($calendar->getPrincipalURI()),
+					'type' => $query->createNamedParameter('calendar'),
+					'access' => $query->createNamedParameter(self::ACCESS_PUBLIC),
+					'resourceid' => $query->createNamedParameter($calendar->getResourceId()),
+					'publicuri' => $query->createNamedParameter($publicUri)
+				]);
+			$query->execute();
+			return $publicUri;
+		}
+		$query->delete('dav_shares')
+			->where($query->expr()->eq('resourceid', $query->createNamedParameter($calendar->getResourceId())))
+			->andWhere($query->expr()->eq('access', $query->createNamedParameter(self::ACCESS_PUBLIC)));
+		$query->execute();
+		return null;
+	}
+
+	/**
+	 * @param \OCA\DAV\CalDAV\Calendar $calendar
+	 * @return mixed
+	 */
+	public function getPublishStatus($calendar) {
+		$query = $this->db->getQueryBuilder();
+		$result = $query->select('publicuri')
+			->from('dav_shares')
+			->where($query->expr()->eq('resourceid', $query->createNamedParameter($calendar->getResourceId())))
+			->andWhere($query->expr()->eq('access', $query->createNamedParameter(self::ACCESS_PUBLIC)))
+			->execute();
+
+		$row = $result->fetch();
+		$result->closeCursor();
+		return $row ? reset($row) : false;
+	}
+
+	/**
 	 * @param int $resourceId
 	 * @param array $acl
 	 * @return array
diff --git a/apps/dav/lib/CalDAV/Calendar.php b/apps/dav/lib/CalDAV/Calendar.php
index 821a71babb1..3fbcd87acc0 100644
--- a/apps/dav/lib/CalDAV/Calendar.php
+++ b/apps/dav/lib/CalDAV/Calendar.php
@@ -89,6 +89,13 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 		return $this->calendarInfo['id'];
 	}
 
+	/**
+	 * @return string
+	 */
+	public function getPrincipalURI() {
+		return $this->calendarInfo['principaluri'];
+	}
+
 	function getACL() {
 		$acl =  [
 			[
@@ -117,6 +124,13 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 				];
 			}
 		}
+		if ($this->isPublic()) {
+			$acl[] = [
+				'privilege' => '{DAV:}read',
+				'principal' => 'principals/system/public',
+				'protected' => true,
+			];
+		}
 
 		/** @var CalDavBackend $calDavBackend */
 		$calDavBackend = $this->caldavBackend;
@@ -236,6 +250,23 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 		return $uris;
 	}
 
+	/**
+	 * @param boolean $value
+	 * @return string|null
+	 */
+	function setPublishStatus($value) {
+		$publicUri = $this->caldavBackend->setPublishStatus($value, $this);
+		$this->calendarInfo['publicuri'] = $publicUri;
+		return $publicUri;
+	}
+
+	/**
+	 * @return mixed $value
+	 */
+	function getPublishStatus() {
+		return $this->caldavBackend->getPublishStatus($this);
+	}
+
 	private function canWrite() {
 		if (isset($this->calendarInfo['{http://owncloud.org/ns}read-only'])) {
 			return !$this->calendarInfo['{http://owncloud.org/ns}read-only'];
@@ -243,8 +274,16 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 		return true;
 	}
 
+	private function isPublic() {
+		return isset($this->calendarInfo['{http://owncloud.org/ns}public']);
+	}
+
 	private function isShared() {
 		return isset($this->calendarInfo['{http://owncloud.org/ns}owner-principal']);
 	}
 
+	public function isSubscription() {
+		return isset($this->calendarInfo['{http://calendarserver.org/ns/}source']);
+	}
+
 }
diff --git a/apps/dav/lib/CalDAV/PublicCalendarRoot.php b/apps/dav/lib/CalDAV/PublicCalendarRoot.php
new file mode 100644
index 00000000000..6d74b97f96e
--- /dev/null
+++ b/apps/dav/lib/CalDAV/PublicCalendarRoot.php
@@ -0,0 +1,67 @@
+<?php
+/**
+ * @author Thomas Müller <thomas.mueller@tmit.eu>
+ *
+ * @copyright Copyright (c) 2016, 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 OCA\DAV\CalDAV;
+
+use Sabre\DAV\Collection;
+use Sabre\DAV\Exception\NotFound;
+
+class PublicCalendarRoot extends Collection {
+
+	/** @var CalDavBackend */
+	protected $caldavBackend;
+
+	/** @var \OCP\IL10N */
+	protected $l10n;
+
+	function __construct(CalDavBackend $caldavBackend) {
+		$this->caldavBackend = $caldavBackend;
+		$this->l10n = \OC::$server->getL10N('dav');
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	function getName() {
+		return 'public-calendars';
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	function getChild($name) {
+		$calendar = $this->caldavBackend->getPublicCalendar($name);
+		return new Calendar($this->caldavBackend, $calendar, $this->l10n);
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	function getChildren() {
+		$calendars = $this->caldavBackend->getPublicCalendars();
+		$children = [];
+		foreach ($calendars as $calendar) {
+			// TODO: maybe implement a new class PublicCalendar ???
+			$children[] = new Calendar($this->caldavBackend, $calendar, $this->l10n);
+		}
+
+		return $children;
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Publishing/PublishPlugin.php b/apps/dav/lib/CalDAV/Publishing/PublishPlugin.php
new file mode 100644
index 00000000000..199bc67e615
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Publishing/PublishPlugin.php
@@ -0,0 +1,227 @@
+<?php
+/**
+ * @author Thomas Citharel <tcit@tcit.fr>
+ *
+ * @copyright Copyright (c) 2016 Thomas Citharel <tcit@tcit.fr>
+ * @license GNU AGPL version 3 or any later version
+ *
+ * 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 OCA\DAV\CalDAV\Publishing;
+
+use Sabre\DAV\PropFind;
+use Sabre\DAV\INode;
+use Sabre\DAV\Server;
+use Sabre\DAV\ServerPlugin;
+use Sabre\DAV\Exception\NotFound;
+use Sabre\HTTP\RequestInterface;
+use Sabre\HTTP\ResponseInterface;
+use Sabre\CalDAV\Xml\Property\AllowedSharingModes;
+use OCA\DAV\CalDAV\Publishing\Xml\Publisher;
+use OCA\DAV\CalDAV\Calendar;
+use OCP\IURLGenerator;
+use OCP\IConfig;
+
+class PublishPlugin extends ServerPlugin {
+	const NS_CALENDARSERVER = 'http://calendarserver.org/ns/';
+
+	/**
+	 * Reference to SabreDAV server object.
+	 *
+	 * @var \Sabre\DAV\Server
+	 */
+	protected $server;
+
+	/**
+	 * Config instance to get instance secret.
+	 *
+	 * @var IConfig
+	 */
+	protected $config;
+
+	/**
+	 * URL Generator for absolute URLs.
+	 *
+	 * @var IURLGenerator
+	 */
+	protected $urlGenerator;
+
+	/**
+	 * PublishPlugin constructor.
+	 *
+	 * @param IConfig $config
+	 * @param IURLGenerator $urlGenerator
+	 */
+	public function __construct(IConfig $config, IURLGenerator $urlGenerator) {
+		$this->config = $config;
+		$this->urlGenerator = $urlGenerator;
+	}
+
+	/**
+	 * This method should return a list of server-features.
+	 *
+	 * This is for example 'versioning' and is added to the DAV: header
+	 * in an OPTIONS response.
+	 *
+	 * @return string[]
+	 */
+	public function getFeatures() {
+		// May have to be changed to be detected
+		return ['oc-calendar-publishing', 'calendarserver-sharing'];
+	}
+
+	/**
+	 * Returns a plugin name.
+	 *
+	 * Using this name other plugins will be able to access other plugins
+	 * using Sabre\DAV\Server::getPlugin
+	 *
+	 * @return string
+	 */
+	public function getPluginName()	{
+		return 'oc-calendar-publishing';
+	}
+
+	/**
+	 * 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 Server $server
+	 */
+	public function initialize(Server $server) {
+		$this->server = $server;
+
+		$this->server->on('method:POST', [$this, 'httpPost']);
+		$this->server->on('propFind',    [$this, 'propFind']);
+	}
+
+	public function propFind(PropFind $propFind, INode $node) {
+		if ($node instanceof Calendar) {
+			$propFind->handle('{'.self::NS_CALENDARSERVER.'}publish-url', function () use ($node) {
+				if ($node->getPublishStatus()) {
+					// We return the publish-url only if the calendar is published.
+					$token = $node->getPublishStatus();
+					$publishUrl = $this->urlGenerator->getAbsoluteURL($this->server->getBaseUri().'public-calendars/').$token;
+
+					return new Publisher($publishUrl, true);
+				}
+			});
+
+			$propFind->handle('{'.self::NS_CALENDARSERVER.'}allowed-sharing-modes', function() use ($node) {
+				return new AllowedSharingModes(!$node->isSubscription(), !$node->isSubscription());
+			});
+		}
+	}
+
+	/**
+	 * We intercept this to handle POST requests on calendars.
+	 *
+	 * @param RequestInterface $request
+	 * @param ResponseInterface $response
+	 *
+	 * @return void|bool
+	 */
+	public function httpPost(RequestInterface $request, ResponseInterface $response) {
+		$path = $request->getPath();
+
+		// Only handling xml
+		$contentType = $request->getHeader('Content-Type');
+		if (strpos($contentType, 'application/xml') === false && strpos($contentType, 'text/xml') === false) {
+			return;
+		}
+
+		// Making sure the node exists
+		try {
+			$node = $this->server->tree->getNodeForPath($path);
+		} catch (NotFound $e) {
+			return;
+		}
+
+		$requestBody = $request->getBodyAsString();
+
+		// If this request handler could not deal with this POST request, it
+		// will return 'null' and other plugins get a chance to handle the
+		// request.
+		//
+		// However, we already requested the full body. This is a problem,
+		// because a body can only be read once. This is why we preemptively
+		// re-populated the request body with the existing data.
+		$request->setBody($requestBody);
+
+		$this->server->xml->parse($requestBody, $request->getUrl(), $documentType);
+
+		switch ($documentType) {
+
+			case '{'.self::NS_CALENDARSERVER.'}publish-calendar' :
+
+			// We can only deal with IShareableCalendar objects
+			if (!$node instanceof Calendar) {
+				return;
+			}
+			$this->server->transactionType = 'post-publish-calendar';
+
+			// Getting ACL info
+			$acl = $this->server->getPlugin('acl');
+
+			// If there's no ACL support, we allow everything
+			if ($acl) {
+				$acl->checkPrivileges($path, '{DAV:}write');
+			}
+
+			$node->setPublishStatus(true);
+
+			// iCloud sends back the 202, so we will too.
+			$response->setStatus(202);
+
+			// Adding this because sending a response body may cause issues,
+			// and I wanted some type of indicator the response was handled.
+			$response->setHeader('X-Sabre-Status', 'everything-went-well');
+
+			// Breaking the event chain
+			return false;
+
+			case '{'.self::NS_CALENDARSERVER.'}unpublish-calendar' :
+
+			// We can only deal with IShareableCalendar objects
+			if (!$node instanceof Calendar) {
+				return;
+			}
+			$this->server->transactionType = 'post-unpublish-calendar';
+
+			// Getting ACL info
+			$acl = $this->server->getPlugin('acl');
+
+			// If there's no ACL support, we allow everything
+			if ($acl) {
+				$acl->checkPrivileges($path, '{DAV:}write');
+			}
+
+			$node->setPublishStatus(false);
+
+			$response->setStatus(200);
+
+			// Adding this because sending a response body may cause issues,
+			// and I wanted some type of indicator the response was handled.
+			$response->setHeader('X-Sabre-Status', 'everything-went-well');
+
+			// Breaking the event chain
+			return false;
+
+		}
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Publishing/Xml/Publisher.php b/apps/dav/lib/CalDAV/Publishing/Xml/Publisher.php
new file mode 100644
index 00000000000..1fdba22e9e0
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Publishing/Xml/Publisher.php
@@ -0,0 +1,83 @@
+<?php
+/**
+ * @author Thomas Citharel <tcit@tcit.fr>
+ *
+ * @copyright Copyright (c) 2016 Thomas Citharel <tcit@tcit.fr>
+ * @license GNU AGPL version 3 or any later version
+ *
+ * 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 OCA\DAV\CalDAV\Publishing\Xml;
+
+use OCA\DAV\CalDAV\Publishing\PublishPlugin as Plugin;
+use Sabre\Xml\Writer;
+use Sabre\Xml\XmlSerializable;
+
+class Publisher implements XmlSerializable {
+
+	/**
+	 * @var string $publishUrl
+	 */
+	protected $publishUrl;
+
+	/**
+	 * @var boolean $isPublished
+	 */
+	protected $isPublished;
+
+	/**
+	 * @param string $publishUrl
+	 * @param boolean $isPublished
+	 */
+	function __construct($publishUrl, $isPublished) {
+		$this->publishUrl = $publishUrl;
+		$this->isPublished = $isPublished;
+	}
+
+	/**
+	 * @return string
+	 */
+	function getValue() {
+		return $this->publishUrl;
+	}
+
+	/**
+	 * The xmlSerialize metod is called during xml writing.
+	 *
+	 * Use the $writer argument to write its own xml serialization.
+	 *
+	 * An important note: do _not_ create a parent element. Any element
+	 * implementing XmlSerializble should only ever write what's considered
+	 * its 'inner xml'.
+	 *
+	 * The parent of the current element is responsible for writing a
+	 * containing element.
+	 *
+	 * This allows serializers to be re-used for different element names.
+	 *
+	 * If you are opening new elements, you must also close them again.
+	 *
+	 * @param Writer $writer
+	 * @return void
+	 */
+	function xmlSerialize(Writer $writer) {
+		if (!$this->isPublished) {
+			// for pre-publish-url
+			$writer->write($this->publishUrl);
+		} else {
+			// for publish-url
+			$writer->writeElement('{DAV:}href', $this->publishUrl);
+		}
+	}
+}