cache webcal calendars on server

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

20 files changed, 2379 insertions, 116 deletions

diff --git a/apps/dav/appinfo/app.php b/apps/dav/appinfo/app.php
index 089aaeb6c78..36b3a39ab17 100644
--- a/apps/dav/appinfo/app.php
+++ b/apps/dav/appinfo/app.php
@@ -48,6 +48,34 @@ $eventDispatcher->addListener('OCP\Federation\TrustedServerEvent::remove',
 	}
 );
 
+$eventDispatcher->addListener('\OCA\DAV\CalDAV\CalDavBackend::createSubscription',
+	function(GenericEvent $event) use ($app) {
+		$jobList = $app->getContainer()->getServer()->getJobList();
+		$subscriptionData = $event->getArgument('subscriptionData');
+
+		$jobList->add(\OCA\DAV\BackgroundJob\RefreshWebcalJob::class, [
+			'principaluri' => $subscriptionData['principaluri'],
+			'uri' => $subscriptionData['uri']
+		]);
+	}
+);
+
+$eventDispatcher->addListener('\OCA\DAV\CalDAV\CalDavBackend::deleteSubscription',
+	function(GenericEvent $event) use ($app) {
+		$jobList = $app->getContainer()->getServer()->getJobList();
+		$subscriptionData = $event->getArgument('subscriptionData');
+
+		$jobList->remove(\OCA\DAV\BackgroundJob\RefreshWebcalJob::class, [
+			'principaluri' => $subscriptionData['principaluri'],
+			'uri' => $subscriptionData['uri']
+		]);
+
+		/** @var \OCA\DAV\CalDAV\CalDavBackend $calDavBackend */
+		$calDavBackend = $app->getContainer()->query(\OCA\DAV\CalDAV\CalDavBackend::class);
+		$calDavBackend->purgeAllCachedEventsForSubscription($subscriptionData['id']);
+	}
+);
+
 $eventHandler = function() use ($app) {
 	try {
 		$job = $app->getContainer()->query(\OCA\DAV\BackgroundJob\UpdateCalendarResourcesRoomsBackgroundJob::class);
diff --git a/apps/dav/appinfo/info.xml b/apps/dav/appinfo/info.xml
index f4fc58e230c..47b6a77c109 100644
--- a/apps/dav/appinfo/info.xml
+++ b/apps/dav/appinfo/info.xml
@@ -30,6 +30,7 @@
 			<step>OCA\DAV\Migration\FixBirthdayCalendarComponent</step>
 			<step>OCA\DAV\Migration\CalDAVRemoveEmptyValue</step>
 			<step>OCA\DAV\Migration\BuildCalendarSearchIndex</step>
+			<step>OCA\DAV\Migration\RefreshWebcalJobRegistrar</step>
 		</post-migration>
 	</repair-steps>
 
diff --git a/apps/dav/composer/composer/autoload_classmap.php b/apps/dav/composer/composer/autoload_classmap.php
index 11da32fb3a2..6bbd2cf27d4 100644
--- a/apps/dav/composer/composer/autoload_classmap.php
+++ b/apps/dav/composer/composer/autoload_classmap.php
@@ -14,6 +14,7 @@ return array(
     'OCA\\DAV\\BackgroundJob\\CleanupDirectLinksJob' => $baseDir . '/../lib/BackgroundJob/CleanupDirectLinksJob.php',
     'OCA\\DAV\\BackgroundJob\\CleanupInvitationTokenJob' => $baseDir . '/../lib/BackgroundJob/CleanupInvitationTokenJob.php',
     'OCA\\DAV\\BackgroundJob\\GenerateBirthdayCalendarBackgroundJob' => $baseDir . '/../lib/BackgroundJob/GenerateBirthdayCalendarBackgroundJob.php',
+    'OCA\\DAV\\BackgroundJob\\RefreshWebcalJob' => $baseDir . '/../lib/BackgroundJob/RefreshWebcalJob.php',
     'OCA\\DAV\\BackgroundJob\\UpdateCalendarResourcesRoomsBackgroundJob' => $baseDir . '/../lib/BackgroundJob/UpdateCalendarResourcesRoomsBackgroundJob.php',
     'OCA\\DAV\\CalDAV\\Activity\\Backend' => $baseDir . '/../lib/CalDAV/Activity/Backend.php',
     'OCA\\DAV\\CalDAV\\Activity\\Filter\\Calendar' => $baseDir . '/../lib/CalDAV/Activity/Filter/Calendar.php',
@@ -27,6 +28,8 @@ return array(
     'OCA\\DAV\\CalDAV\\Activity\\Setting\\Todo' => $baseDir . '/../lib/CalDAV/Activity/Setting/Todo.php',
     'OCA\\DAV\\CalDAV\\BirthdayCalendar\\EnablePlugin' => $baseDir . '/../lib/CalDAV/BirthdayCalendar/EnablePlugin.php',
     'OCA\\DAV\\CalDAV\\BirthdayService' => $baseDir . '/../lib/CalDAV/BirthdayService.php',
+    'OCA\\DAV\\CalDAV\\CachedSubscription' => $baseDir . '/../lib/CalDAV/CachedSubscription.php',
+    'OCA\\DAV\\CalDAV\\CachedSubscriptionObject' => $baseDir . '/../lib/CalDAV/CachedSubscriptionObject.php',
     'OCA\\DAV\\CalDAV\\CalDavBackend' => $baseDir . '/../lib/CalDAV/CalDavBackend.php',
     'OCA\\DAV\\CalDAV\\Calendar' => $baseDir . '/../lib/CalDAV/Calendar.php',
     'OCA\\DAV\\CalDAV\\CalendarHome' => $baseDir . '/../lib/CalDAV/CalendarHome.php',
@@ -57,6 +60,7 @@ return array(
     'OCA\\DAV\\CalDAV\\Search\\Xml\\Filter\\PropFilter' => $baseDir . '/../lib/CalDAV/Search/Xml/Filter/PropFilter.php',
     'OCA\\DAV\\CalDAV\\Search\\Xml\\Filter\\SearchTermFilter' => $baseDir . '/../lib/CalDAV/Search/Xml/Filter/SearchTermFilter.php',
     'OCA\\DAV\\CalDAV\\Search\\Xml\\Request\\CalendarSearchReport' => $baseDir . '/../lib/CalDAV/Search/Xml/Request/CalendarSearchReport.php',
+    'OCA\\DAV\\CalDAV\\WebcalCaching\\Plugin' => $baseDir . '/../lib/CalDAV/WebcalCaching/Plugin.php',
     'OCA\\DAV\\Capabilities' => $baseDir . '/../lib/Capabilities.php',
     'OCA\\DAV\\CardDAV\\AddressBook' => $baseDir . '/../lib/CardDAV/AddressBook.php',
     'OCA\\DAV\\CardDAV\\AddressBookImpl' => $baseDir . '/../lib/CardDAV/AddressBookImpl.php',
@@ -149,6 +153,7 @@ return array(
     'OCA\\DAV\\Migration\\BuildCalendarSearchIndexBackgroundJob' => $baseDir . '/../lib/Migration/BuildCalendarSearchIndexBackgroundJob.php',
     'OCA\\DAV\\Migration\\CalDAVRemoveEmptyValue' => $baseDir . '/../lib/Migration/CalDAVRemoveEmptyValue.php',
     'OCA\\DAV\\Migration\\FixBirthdayCalendarComponent' => $baseDir . '/../lib/Migration/FixBirthdayCalendarComponent.php',
+    'OCA\\DAV\\Migration\\RefreshWebcalJobRegistrar' => $baseDir . '/../lib/Migration/RefreshWebcalJobRegistrar.php',
     'OCA\\DAV\\Migration\\Version1004Date20170825134824' => $baseDir . '/../lib/Migration/Version1004Date20170825134824.php',
     'OCA\\DAV\\Migration\\Version1004Date20170919104507' => $baseDir . '/../lib/Migration/Version1004Date20170919104507.php',
     'OCA\\DAV\\Migration\\Version1004Date20170924124212' => $baseDir . '/../lib/Migration/Version1004Date20170924124212.php',
@@ -156,6 +161,7 @@ return array(
     'OCA\\DAV\\Migration\\Version1005Date20180413093149' => $baseDir . '/../lib/Migration/Version1005Date20180413093149.php',
     'OCA\\DAV\\Migration\\Version1005Date20180530124431' => $baseDir . '/../lib/Migration/Version1005Date20180530124431.php',
     'OCA\\DAV\\Migration\\Version1006Date20180619154313' => $baseDir . '/../lib/Migration/Version1006Date20180619154313.php',
+    'OCA\\DAV\\Migration\\Version1006Date20180628111625' => $baseDir . '/../lib/Migration/Version1006Date20180628111625.php',
     'OCA\\DAV\\Migration\\Version1007Date20181007225117' => $baseDir . '/../lib/Migration/Version1007Date20181007225117.php',
     'OCA\\DAV\\Migration\\Version1008Date20181030113700' => $baseDir . '/../lib/Migration/Version1008Date20181030113700.php',
     'OCA\\DAV\\RootCollection' => $baseDir . '/../lib/RootCollection.php',
diff --git a/apps/dav/composer/composer/autoload_static.php b/apps/dav/composer/composer/autoload_static.php
index c73db57a703..61f6966170e 100644
--- a/apps/dav/composer/composer/autoload_static.php
+++ b/apps/dav/composer/composer/autoload_static.php
@@ -29,6 +29,7 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\BackgroundJob\\CleanupDirectLinksJob' => __DIR__ . '/..' . '/../lib/BackgroundJob/CleanupDirectLinksJob.php',
         'OCA\\DAV\\BackgroundJob\\CleanupInvitationTokenJob' => __DIR__ . '/..' . '/../lib/BackgroundJob/CleanupInvitationTokenJob.php',
         'OCA\\DAV\\BackgroundJob\\GenerateBirthdayCalendarBackgroundJob' => __DIR__ . '/..' . '/../lib/BackgroundJob/GenerateBirthdayCalendarBackgroundJob.php',
+        'OCA\\DAV\\BackgroundJob\\RefreshWebcalJob' => __DIR__ . '/..' . '/../lib/BackgroundJob/RefreshWebcalJob.php',
         'OCA\\DAV\\BackgroundJob\\UpdateCalendarResourcesRoomsBackgroundJob' => __DIR__ . '/..' . '/../lib/BackgroundJob/UpdateCalendarResourcesRoomsBackgroundJob.php',
         'OCA\\DAV\\CalDAV\\Activity\\Backend' => __DIR__ . '/..' . '/../lib/CalDAV/Activity/Backend.php',
         'OCA\\DAV\\CalDAV\\Activity\\Filter\\Calendar' => __DIR__ . '/..' . '/../lib/CalDAV/Activity/Filter/Calendar.php',
@@ -42,6 +43,8 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\CalDAV\\Activity\\Setting\\Todo' => __DIR__ . '/..' . '/../lib/CalDAV/Activity/Setting/Todo.php',
         'OCA\\DAV\\CalDAV\\BirthdayCalendar\\EnablePlugin' => __DIR__ . '/..' . '/../lib/CalDAV/BirthdayCalendar/EnablePlugin.php',
         'OCA\\DAV\\CalDAV\\BirthdayService' => __DIR__ . '/..' . '/../lib/CalDAV/BirthdayService.php',
+        'OCA\\DAV\\CalDAV\\CachedSubscription' => __DIR__ . '/..' . '/../lib/CalDAV/CachedSubscription.php',
+        'OCA\\DAV\\CalDAV\\CachedSubscriptionObject' => __DIR__ . '/..' . '/../lib/CalDAV/CachedSubscriptionObject.php',
         'OCA\\DAV\\CalDAV\\CalDavBackend' => __DIR__ . '/..' . '/../lib/CalDAV/CalDavBackend.php',
         'OCA\\DAV\\CalDAV\\Calendar' => __DIR__ . '/..' . '/../lib/CalDAV/Calendar.php',
         'OCA\\DAV\\CalDAV\\CalendarHome' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarHome.php',
@@ -72,6 +75,7 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\CalDAV\\Search\\Xml\\Filter\\PropFilter' => __DIR__ . '/..' . '/../lib/CalDAV/Search/Xml/Filter/PropFilter.php',
         'OCA\\DAV\\CalDAV\\Search\\Xml\\Filter\\SearchTermFilter' => __DIR__ . '/..' . '/../lib/CalDAV/Search/Xml/Filter/SearchTermFilter.php',
         'OCA\\DAV\\CalDAV\\Search\\Xml\\Request\\CalendarSearchReport' => __DIR__ . '/..' . '/../lib/CalDAV/Search/Xml/Request/CalendarSearchReport.php',
+        'OCA\\DAV\\CalDAV\\WebcalCaching\\Plugin' => __DIR__ . '/..' . '/../lib/CalDAV/WebcalCaching/Plugin.php',
         'OCA\\DAV\\Capabilities' => __DIR__ . '/..' . '/../lib/Capabilities.php',
         'OCA\\DAV\\CardDAV\\AddressBook' => __DIR__ . '/..' . '/../lib/CardDAV/AddressBook.php',
         'OCA\\DAV\\CardDAV\\AddressBookImpl' => __DIR__ . '/..' . '/../lib/CardDAV/AddressBookImpl.php',
@@ -164,6 +168,7 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\Migration\\BuildCalendarSearchIndexBackgroundJob' => __DIR__ . '/..' . '/../lib/Migration/BuildCalendarSearchIndexBackgroundJob.php',
         'OCA\\DAV\\Migration\\CalDAVRemoveEmptyValue' => __DIR__ . '/..' . '/../lib/Migration/CalDAVRemoveEmptyValue.php',
         'OCA\\DAV\\Migration\\FixBirthdayCalendarComponent' => __DIR__ . '/..' . '/../lib/Migration/FixBirthdayCalendarComponent.php',
+        'OCA\\DAV\\Migration\\RefreshWebcalJobRegistrar' => __DIR__ . '/..' . '/../lib/Migration/RefreshWebcalJobRegistrar.php',
         'OCA\\DAV\\Migration\\Version1004Date20170825134824' => __DIR__ . '/..' . '/../lib/Migration/Version1004Date20170825134824.php',
         'OCA\\DAV\\Migration\\Version1004Date20170919104507' => __DIR__ . '/..' . '/../lib/Migration/Version1004Date20170919104507.php',
         'OCA\\DAV\\Migration\\Version1004Date20170924124212' => __DIR__ . '/..' . '/../lib/Migration/Version1004Date20170924124212.php',
@@ -171,6 +176,7 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\Migration\\Version1005Date20180413093149' => __DIR__ . '/..' . '/../lib/Migration/Version1005Date20180413093149.php',
         'OCA\\DAV\\Migration\\Version1005Date20180530124431' => __DIR__ . '/..' . '/../lib/Migration/Version1005Date20180530124431.php',
         'OCA\\DAV\\Migration\\Version1006Date20180619154313' => __DIR__ . '/..' . '/../lib/Migration/Version1006Date20180619154313.php',
+        'OCA\\DAV\\Migration\\Version1006Date20180628111625' => __DIR__ . '/..' . '/../lib/Migration/Version1006Date20180628111625.php',
         'OCA\\DAV\\Migration\\Version1007Date20181007225117' => __DIR__ . '/..' . '/../lib/Migration/Version1007Date20181007225117.php',
         'OCA\\DAV\\Migration\\Version1008Date20181030113700' => __DIR__ . '/..' . '/../lib/Migration/Version1008Date20181030113700.php',
         'OCA\\DAV\\RootCollection' => __DIR__ . '/..' . '/../lib/RootCollection.php',
diff --git a/apps/dav/lib/BackgroundJob/RefreshWebcalJob.php b/apps/dav/lib/BackgroundJob/RefreshWebcalJob.php
new file mode 100644
index 00000000000..871734aab55
--- /dev/null
+++ b/apps/dav/lib/BackgroundJob/RefreshWebcalJob.php
@@ -0,0 +1,438 @@
+<?php
+declare(strict_types=1);
+/**
+ * @copyright 2018 Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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 OCA\DAV\BackgroundJob;
+
+use GuzzleHttp\HandlerStack;
+use GuzzleHttp\Middleware;
+use OC\BackgroundJob\Job;
+use OCA\DAV\CalDAV\CalDavBackend;
+use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\Http\Client\IClientService;
+use OCP\IConfig;
+use OCP\ILogger;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+use Sabre\DAV\Exception\BadRequest;
+use Sabre\DAV\PropPatch;
+use Sabre\DAV\Xml\Property\Href;
+use Sabre\VObject\Component;
+use Sabre\VObject\DateTimeParser;
+use Sabre\VObject\InvalidDataException;
+use Sabre\VObject\ParseException;
+use Sabre\VObject\Reader;
+use Sabre\VObject\Splitter\ICalendar;
+
+class RefreshWebcalJob extends Job {
+
+	/** @var CalDavBackend */
+	private $calDavBackend;
+
+	/** @var IClientService */
+	private $clientService;
+
+	/** @var IConfig */
+	private $config;
+
+	/** @var ILogger */
+	private $logger;
+
+	/** @var ITimeFactory */
+	private $timeFactory;
+
+	/** @var array */
+	private $subscription;
+
+	/**
+	 * RefreshWebcalJob constructor.
+	 *
+	 * @param CalDavBackend $calDavBackend
+	 * @param IClientService $clientService
+	 * @param IConfig $config
+	 * @param ILogger $logger
+	 * @param ITimeFactory $timeFactory
+	 */
+	public function __construct(CalDavBackend $calDavBackend, IClientService $clientService, IConfig $config, ILogger $logger, ITimeFactory $timeFactory) {
+		$this->calDavBackend = $calDavBackend;
+		$this->clientService = $clientService;
+		$this->config = $config;
+		$this->logger = $logger;
+		$this->timeFactory = $timeFactory;
+	}
+
+	/**
+	 * this function is called at most every hour
+	 *
+	 * @inheritdoc
+	 */
+	public function execute($jobList, ILogger $logger = null) {
+		$subscription = $this->getSubscription($this->argument['principaluri'], $this->argument['uri']);
+		if (!$subscription) {
+			return;
+		}
+
+		// if no refresh rate was configured, just refresh once a week
+		$subscriptionId = $subscription['id'];
+		$refreshrate = $subscription['refreshrate'] ?? 'P1W';
+
+		try {
+			/** @var \DateInterval $dateInterval */
+			$dateInterval = DateTimeParser::parseDuration($refreshrate);
+		} catch(InvalidDataException $ex) {
+			$this->logger->logException($ex);
+			$this->logger->warning("Subscription $subscriptionId could not be refreshed, refreshrate in database is invalid");
+			return;
+		}
+
+		$interval = $this->getIntervalFromDateInterval($dateInterval);
+		if (($this->timeFactory->getTime() - $this->lastRun) <= $interval) {
+			return;
+		}
+
+		parent::execute($jobList, $logger);
+	}
+
+	/**
+	 * @param array $argument
+	 */
+	protected function run($argument) {
+		$subscription = $this->getSubscription($argument['principaluri'], $argument['uri']);
+		$mutations = [];
+		if (!$subscription) {
+			return;
+		}
+
+		$webcalData = $this->queryWebcalFeed($subscription, $mutations);
+		if (!$webcalData) {
+			return;
+		}
+
+		$stripTodos = $subscription['striptodos'] ?? 1;
+		$stripAlarms = $subscription['stripalarms'] ?? 1;
+		$stripAttachments = $subscription['stripattachments'] ?? 1;
+
+		try {
+			$splitter = new ICalendar($webcalData, Reader::OPTION_FORGIVING);
+
+			// we wait with deleting all outdated events till we parsed the new ones
+			// in case the new calendar is broken and `new ICalendar` throws a ParseException
+			// the user will still see the old data
+			$this->calDavBackend->purgeAllCachedEventsForSubscription($subscription['id']);
+
+			while ($vObject = $splitter->getNext()) {
+				/** @var Component $vObject */
+				$uid = null;
+				$compName = null;
+
+				foreach ($vObject->getComponents() as $component) {
+					if ($component->name === 'VTIMEZONE') {
+						continue;
+					}
+
+					$uid = $component->{'UID'}->getValue();
+					$compName = $component->name;
+
+					if ($stripAlarms) {
+						unset($component->{'VALARM'});
+					}
+					if ($stripAttachments) {
+						unset($component->{'ATTACH'});
+					}
+				}
+
+				if ($stripTodos && $compName === 'VTODO') {
+					continue;
+				}
+
+				$uri = $uid . '.ics';
+				$calendarData = $vObject->serialize();
+				try {
+					$this->calDavBackend->createCalendarObject($subscription['id'], $uri, $calendarData, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+				} catch(BadRequest $ex) {
+					$this->logger->logException($ex);
+				}
+			}
+
+			$newRefreshRate = $this->checkWebcalDataForRefreshRate($subscription, $webcalData);
+			if ($newRefreshRate) {
+				$mutations['{http://apple.com/ns/ical/}refreshrate'] = $newRefreshRate;
+			}
+
+			$this->updateSubscription($subscription, $mutations);
+		} catch(ParseException $ex) {
+			$subscriptionId = $subscription['id'];
+
+			$this->logger->logException($ex);
+			$this->logger->warning("Subscription $subscriptionId could not be refreshed due to a parsing error");
+		}
+	}
+
+	/**
+	 * gets webcal feed from remote server
+	 *
+	 * @param array $subscription
+	 * @param array &$mutations
+	 * @return null|string
+	 */
+	private function queryWebcalFeed(array $subscription, array &$mutations) {
+		$client = $this->clientService->newClient();
+
+		$didBreak301Chain = false;
+		$latestLocation = null;
+
+		$handlerStack = HandlerStack::create();
+		$handlerStack->push(Middleware::mapRequest(function (RequestInterface $request) {
+			return $request
+				->withHeader('Accept', 'text/calendar, application/calendar+json, application/calendar+xml')
+				->withHeader('User-Agent', 'Nextcloud Webcal Crawler');
+		}));
+		$handlerStack->push(Middleware::mapResponse(function(ResponseInterface $response) use (&$didBreak301Chain, &$latestLocation) {
+			if (!$didBreak301Chain) {
+				if ($response->getStatusCode() !== 301) {
+					$didBreak301Chain = true;
+				} else {
+					$latestLocation = $response->getHeader('Location');
+				}
+			}
+			return $response;
+		}));
+
+		$allowLocalAccess = $this->config->getAppValue('dav', 'webcalAllowLocalAccess', 'no');
+		$subscriptionId = $subscription['id'];
+		$url = $this->cleanURL($subscription['source']);
+		if ($url === null) {
+			return null;
+		}
+
+		if ($allowLocalAccess !== 'yes') {
+			$host = parse_url($url, PHP_URL_HOST);
+			// remove brackets from IPv6 addresses
+			if (strpos($host, '[') === 0 && substr($host, -1) === ']') {
+				$host = substr($host, 1, -1);
+			}
+
+			if ($host === 'localhost' || substr($host, -6) === '.local' || substr($host, -10) === '.localhost' ||
+				preg_match('/(^127\.)|(^192\.168\.)|(^10\.)|(^172\.1[6-9]\.)|(^172\.2[0-9]\.)|(^172\.3[0-1]\.)|(^::1$)|(^[fF][cCdD])/', $host)) {
+				$this->logger->warning("Subscription $subscriptionId was not refreshed because it violates local access rules");
+				return null;
+			}
+		}
+
+		try {
+			$params = [
+				'allow_redirects' => [
+					'redirects' => 10
+				],
+				'handler' => $handlerStack,
+			];
+
+			$user = parse_url($subscription['source'], PHP_URL_USER);
+			$pass = parse_url($subscription['source'], PHP_URL_PASS);
+			if ($user !== null && $pass !== null) {
+				$params['auth'] = [$user, $pass];
+			}
+
+			$response = $client->get($url, $params);
+			$body = $response->getBody();
+
+			if ($latestLocation) {
+				$mutations['{http://calendarserver.org/ns/}source'] = new Href($latestLocation);
+			}
+
+			$contentType = $response->getHeader('Content-Type');
+			$contentType = explode(';', $contentType, 2)[0];
+			switch($contentType) {
+				case 'application/calendar+json':
+					try {
+						$jCalendar = Reader::readJson($body, Reader::OPTION_FORGIVING);
+					} catch(\Exception $ex) {
+						// In case of a parsing error return null
+						$this->logger->debug("Subscription $subscriptionId could not be parsed");
+						return null;
+					}
+					return $jCalendar->serialize();
+
+				case 'application/calendar+xml':
+					try {
+						$xCalendar = Reader::readXML($body);
+					} catch(\Exception $ex) {
+						// In case of a parsing error return null
+						$this->logger->debug("Subscription $subscriptionId could not be parsed");
+						return null;
+					}
+					return $xCalendar->serialize();
+
+				case 'text/calendar':
+				default:
+					try {
+						$vCalendar = Reader::read($body);
+					} catch(\Exception $ex) {
+						// In case of a parsing error return null
+						$this->logger->debug("Subscription $subscriptionId could not be parsed");
+						return null;
+					}
+					return $vCalendar->serialize();
+			}
+		} catch(\Exception $ex) {
+			$this->logger->logException($ex);
+			$this->logger->warning("Subscription $subscriptionId could not be refreshed due to a network error");
+
+			return null;
+		}
+	}
+
+	/**
+	 * loads subscription from backend
+	 *
+	 * @param string $principalUri
+	 * @param string $uri
+	 * @return array|null
+	 */
+	private function getSubscription(string $principalUri, string $uri) {
+		$subscriptions = array_values(array_filter(
+			$this->calDavBackend->getSubscriptionsForUser($principalUri),
+			function($sub) use ($uri) {
+				return $sub['uri'] === $uri;
+			}
+		));
+
+		if (\count($subscriptions) === 0) {
+			return null;
+		}
+
+		$this->subscription = $subscriptions[0];
+		return $this->subscription;
+	}
+
+	/**
+	 * get total number of seconds from DateInterval object
+	 *
+	 * @param \DateInterval $interval
+	 * @return int
+	 */
+	private function getIntervalFromDateInterval(\DateInterval $interval):int {
+		return $interval->s
+			+ ($interval->i * 60)
+			+ ($interval->h * 60 * 60)
+			+ ($interval->d * 60 * 60 * 24)
+			+ ($interval->m * 60 * 60 * 24 * 30)
+			+ ($interval->y * 60 * 60 * 24 * 365);
+	}
+
+	/**
+	 * check if:
+	 *  - current subscription stores a refreshrate
+	 *  - the webcal feed suggests a refreshrate
+	 *  - return suggested refreshrate if user didn't set a custom one
+	 *
+	 * @param array $subscription
+	 * @param string $webcalData
+	 * @return string|null
+	 */
+	private function checkWebcalDataForRefreshRate($subscription, $webcalData) {
+		// if there is no refreshrate stored in the database, check the webcal feed
+		// whether it suggests any refresh rate and store that in the database
+		if (isset($subscription['refreshrate']) && $subscription['refreshrate'] !== null) {
+			return null;
+		}
+
+		/** @var Component\VCalendar $vCalendar */
+		$vCalendar = Reader::read($webcalData);
+
+		$newRefreshrate = null;
+		if (isset($vCalendar->{'X-PUBLISHED-TTL'})) {
+			$newRefreshrate = $vCalendar->{'X-PUBLISHED-TTL'}->getValue();
+		}
+		if (isset($vCalendar->{'REFRESH-INTERVAL'})) {
+			$newRefreshrate = $vCalendar->{'REFRESH-INTERVAL'}->getValue();
+		}
+
+		if (!$newRefreshrate) {
+			return null;
+		}
+
+		// check if new refresh rate is even valid
+		try {
+			DateTimeParser::parseDuration($newRefreshrate);
+		} catch(InvalidDataException $ex) {
+			return null;
+		}
+
+		return $newRefreshrate;
+	}
+
+	/**
+	 * update subscription stored in database
+	 * used to set:
+	 *  - refreshrate
+	 *  - source
+	 *
+	 * @param array $subscription
+	 * @param array $mutations
+	 */
+	private function updateSubscription(array $subscription, array $mutations) {
+		if (empty($mutations)) {
+			return;
+		}
+
+		$propPatch = new PropPatch($mutations);
+		$this->calDavBackend->updateSubscription($subscription['id'], $propPatch);
+		$propPatch->commit();
+	}
+
+	/**
+	 * This method will strip authentication information and replace the
+	 * 'webcal' or 'webcals' protocol scheme
+	 *
+	 * @param string $url
+	 * @return string|null
+	 */
+	private function cleanURL(string $url) {
+		$parsed = parse_url($url);
+		if ($parsed === false) {
+			return null;
+		}
+
+		if (isset($parsed['scheme']) && $parsed['scheme'] === 'http') {
+			$scheme = 'http';
+		} else {
+			$scheme = 'https';
+		}
+
+		$host = $parsed['host'] ?? '';
+		$port = isset($parsed['port']) ? ':' . $parsed['port'] : '';
+		$path = $parsed['path'] ?? '';
+		$query = isset($parsed['query']) ? '?' . $parsed['query'] : '';
+		$fragment = isset($parsed['fragment']) ? '#' . $parsed['fragment'] : '';
+
+		$cleanURL = "$scheme://$host$port$path$query$fragment";
+		// parse_url is giving some weird results if no url and no :// is given,
+		// so let's test the url again
+		$parsedClean = parse_url($cleanURL);
+		if ($parsedClean === false || !isset($parsedClean['host'])) {
+			return null;
+		}
+
+		return $cleanURL;
+	}
+}
diff --git a/apps/dav/lib/CalDAV/CachedSubscription.php b/apps/dav/lib/CalDAV/CachedSubscription.php
new file mode 100644
index 00000000000..a95ee15bbe5
--- /dev/null
+++ b/apps/dav/lib/CalDAV/CachedSubscription.php
@@ -0,0 +1,198 @@
+<?php
+declare(strict_types=1);
+/**
+ * @copyright 2018 Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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 OCA\DAV\CalDAV;
+
+use Sabre\CalDAV\Backend\BackendInterface;
+use Sabre\DAV\Exception\MethodNotAllowed;
+use Sabre\DAV\Exception\NotFound;
+use Sabre\DAV\PropPatch;
+
+/**
+ * Class CachedSubscription
+ *
+ * @package OCA\DAV\CalDAV
+ * @property BackendInterface|CalDavBackend $caldavBackend
+ */
+class CachedSubscription extends \Sabre\CalDAV\Calendar {
+
+	/**
+	 * @return string
+	 */
+	public function getPrincipalURI():string {
+		return $this->calendarInfo['principaluri'];
+	}
+
+	/**
+	 * @return array
+	 */
+	public function getACL():array {
+		return [
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => $this->getOwner(),
+				'protected' => true,
+			],
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => $this->getOwner() . '/calendar-proxy-write',
+				'protected' => true,
+			],
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => $this->getOwner() . '/calendar-proxy-read',
+				'protected' => true,
+			],
+			[
+				'privilege' => '{' . Plugin::NS_CALDAV . '}read-free-busy',
+				'principal' => '{DAV:}authenticated',
+				'protected' => true,
+			],
+		];
+	}
+
+	/**
+	 * @return array
+	 */
+	public function getChildACL():array {
+		return [
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => $this->getOwner(),
+				'protected' => true,
+			],
+
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => $this->getOwner() . '/calendar-proxy-write',
+				'protected' => true,
+			],
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => $this->getOwner() . '/calendar-proxy-read',
+				'protected' => true,
+			],
+
+		];
+	}
+
+	/**
+	 * @return null|string
+	 */
+	public function getOwner() {
+		if (isset($this->calendarInfo['{http://owncloud.org/ns}owner-principal'])) {
+			return $this->calendarInfo['{http://owncloud.org/ns}owner-principal'];
+		}
+		return parent::getOwner();
+	}
+
+	/**
+	 *
+	 */
+	public function delete() {
+		$this->caldavBackend->deleteSubscription($this->calendarInfo['id']);
+	}
+
+	/**
+	 * @param PropPatch $propPatch
+	 */
+	public function propPatch(PropPatch $propPatch) {
+		$this->caldavBackend->updateSubscription($this->calendarInfo['id'], $propPatch);
+	}
+
+	/**
+	 * @param string $name
+	 * @return CalendarObject|\Sabre\CalDAV\ICalendarObject
+	 * @throws NotFound
+	 */
+	public function getChild($name) {
+		$obj = $this->caldavBackend->getCalendarObject($this->calendarInfo['id'], $name, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+		if (!$obj) {
+			throw new NotFound('Calendar object not found');
+		}
+
+		$obj['acl'] = $this->getChildACL();
+		return new CachedSubscriptionObject	($this->caldavBackend, $this->calendarInfo, $obj);
+
+	}
+
+	/**
+	 * @return array
+	 */
+	public function getChildren():array {
+		$objs = $this->caldavBackend->getCalendarObjects($this->calendarInfo['id'], CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+
+		$children = [];
+		foreach($objs as $obj) {
+			$children[] = new CachedSubscriptionObject($this->caldavBackend, $this->calendarInfo, $obj);
+		}
+
+		return $children;
+	}
+
+	/**
+	 * @param array $paths
+	 * @return array
+	 */
+	public function getMultipleChildren(array $paths):array {
+		$objs = $this->caldavBackend->getMultipleCalendarObjects($this->calendarInfo['id'], $paths, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+
+		$children = [];
+		foreach($objs as $obj) {
+			$children[] = new CachedSubscriptionObject($this->caldavBackend, $this->calendarInfo, $obj);
+		}
+
+		return $children;
+	}
+
+	/**
+	 * @param string $name
+	 * @param null $calendarData
+	 * @return null|string|void
+	 * @throws MethodNotAllowed
+	 */
+	public function createFile($name, $calendarData = null) {
+		throw new MethodNotAllowed('Creating objects in cached subscription is not allowed');
+	}
+
+	/**
+	 * @param string $name
+	 * @return bool
+	 */
+	public function childExists($name):bool {
+		$obj = $this->caldavBackend->getCalendarObject($this->calendarInfo['id'], $name, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+		if (!$obj) {
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * @param array $filters
+	 * @return array
+	 */
+	public function calendarQuery(array $filters):array {
+		return $this->caldavBackend->calendarQuery($this->calendarInfo['id'], $filters, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+	}
+}
diff --git a/apps/dav/lib/CalDAV/CachedSubscriptionObject.php b/apps/dav/lib/CalDAV/CachedSubscriptionObject.php
new file mode 100644
index 00000000000..c2f7eeabf41
--- /dev/null
+++ b/apps/dav/lib/CalDAV/CachedSubscriptionObject.php
@@ -0,0 +1,64 @@
+<?php
+declare(strict_types=1);
+/**
+ * @copyright 2018 Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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 OCA\DAV\CalDAV;
+
+use Sabre\DAV\Exception\MethodNotAllowed;
+
+/**
+ * Class CachedSubscriptionObject
+ *
+ * @package OCA\DAV\CalDAV
+ * @property CalDavBackend $caldavBackend
+ */
+class CachedSubscriptionObject extends \Sabre\CalDAV\CalendarObject {
+
+	/**
+	 * @inheritdoc
+	 */
+	public function get() {
+		// Pre-populating the 'calendardata' is optional, if we don't have it
+		// already we fetch it from the backend.
+		if (!isset($this->objectData['calendardata'])) {
+			$this->objectData = $this->caldavBackend->getCalendarObject($this->calendarInfo['id'], $this->objectData['uri'], CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+		}
+
+		return $this->objectData['calendardata'];
+	}
+
+	/**
+	 * @param resource|string $calendarData
+	 * @return string|void
+	 * @throws MethodNotAllowed
+	 */
+	public function put($calendarData) {
+		throw new MethodNotAllowed('Creating objects in a cached subscription is not allowed');
+	}
+
+	/**
+	 * @throws MethodNotAllowed
+	 */
+	public function delete() {
+		throw new MethodNotAllowed('Deleting objects in a cached subscription is not allowed');
+	}
+}
diff --git a/apps/dav/lib/CalDAV/CalDavBackend.php b/apps/dav/lib/CalDAV/CalDavBackend.php
index df10b62fc5b..60f163abcbf 100644
--- a/apps/dav/lib/CalDAV/CalDavBackend.php
+++ b/apps/dav/lib/CalDAV/CalDavBackend.php
@@ -1,7 +1,7 @@
 <?php
 /**
  * @copyright Copyright (c) 2016, ownCloud, Inc.
- * @copyright Copyright (c) 2017 Georg Ehrke
+ * @copyright Copyright (c) 2018 Georg Ehrke
  *
  * @author Georg Ehrke <oc.list@georgehrke.com>
  * @author Joas Schilling <coding@schilljs.com>
@@ -73,6 +73,9 @@ use Symfony\Component\EventDispatcher\GenericEvent;
  */
 class CalDavBackend extends AbstractBackend implements SyncSupport, SubscriptionSupport, SchedulingSupport {
 
+	const CALENDAR_TYPE_CALENDAR = 0;
+	const CALENDAR_TYPE_SUBSCRIPTION = 1;
+
 	const PERSONAL_CALENDAR_URI = 'personal';
 	const PERSONAL_CALENDAR_NAME = 'Personal';
 
@@ -145,7 +148,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	private $db;
 
 	/** @var Backend */
-	private $sharingBackend;
+	private $calendarSharingBackend;
 
 	/** @var Principal */
 	private $principalBackend;
@@ -191,7 +194,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		$this->db = $db;
 		$this->principalBackend = $principalBackend;
 		$this->userManager = $userManager;
-		$this->sharingBackend = new Backend($this->db, $this->userManager, $groupManager, $principalBackend, 'calendar');
+		$this->calendarSharingBackend = new Backend($this->db, $this->userManager, $groupManager, $principalBackend, 'calendar');
 		$this->random = $random;
 		$this->logger = $logger;
 		$this->dispatcher = $dispatcher;
@@ -372,6 +375,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		return array_values($calendars);
 	}
 
+	/**
+	 * @param $principalUri
+	 * @return array
+	 */
 	public function getUsersOwnCalendars($principalUri) {
 		$principalUri = $this->convertPrincipal($principalUri, true);
 		$fields = array_values($this->propertyMap);
@@ -417,6 +424,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	}
 
 
+	/**
+	 * @param $uid
+	 * @return string
+	 */
 	private function getUserDisplayName($uid) {
 		if (!isset($this->userDisplayNames[$uid])) {
 			$user = $this->userManager->get($uid);
@@ -601,6 +612,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		return $calendar;
 	}
 
+	/**
+	 * @param $calendarId
+	 * @return array|null
+	 */
 	public function getCalendarById($calendarId) {
 		$fields = array_values($this->propertyMap);
 		$fields[] = 'id';
@@ -648,6 +663,50 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	}
 
 	/**
+	 * @param $subscriptionId
+	 */
+	public function getSubscriptionById($subscriptionId) {
+		$fields = array_values($this->subscriptionPropertyMap);
+		$fields[] = 'id';
+		$fields[] = 'uri';
+		$fields[] = 'source';
+		$fields[] = 'synctoken';
+		$fields[] = 'principaluri';
+		$fields[] = 'lastmodified';
+
+		$query = $this->db->getQueryBuilder();
+		$query->select($fields)
+			->from('calendarsubscriptions')
+			->where($query->expr()->eq('id', $query->createNamedParameter($subscriptionId)))
+			->orderBy('calendarorder', 'asc');
+		$stmt =$query->execute();
+
+		$row = $stmt->fetch(\PDO::FETCH_ASSOC);
+		$stmt->closeCursor();
+		if ($row === false) {
+			return null;
+		}
+
+		$subscription = [
+			'id'           => $row['id'],
+			'uri'          => $row['uri'],
+			'principaluri' => $row['principaluri'],
+			'source'       => $row['source'],
+			'lastmodified' => $row['lastmodified'],
+			'{' . Plugin::NS_CALDAV . '}supported-calendar-component-set' => new SupportedCalendarComponentSet(['VTODO', 'VEVENT']),
+			'{http://sabredav.org/ns}sync-token' => $row['synctoken']?$row['synctoken']:'0',
+		];
+
+		foreach($this->subscriptionPropertyMap as $xmlName=>$dbName) {
+			if (!is_null($row[$dbName])) {
+				$subscription[$xmlName] = $row[$dbName];
+			}
+		}
+
+		return $subscription;
+	}
+
+	/**
 	 * Creates a new calendar for a principal.
 	 *
 	 * If the creation was a success, an id must be returned that can be used to reference
@@ -783,20 +842,21 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				'shares' => $this->getShares($calendarId),
 		]));
 
-		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ?');
-		$stmt->execute([$calendarId]);
+		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ? AND `calendartype` = ?');
+		$stmt->execute([$calendarId, self::CALENDAR_TYPE_CALENDAR]);
 
 		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendars` WHERE `id` = ?');
 		$stmt->execute([$calendarId]);
 
-		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarchanges` WHERE `calendarid` = ?');
-		$stmt->execute([$calendarId]);
+		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarchanges` WHERE `calendarid` = ? AND `calendartype` = ?');
+		$stmt->execute([$calendarId, self::CALENDAR_TYPE_CALENDAR]);
 
-		$this->sharingBackend->deleteAllShares($calendarId);
+		$this->calendarSharingBackend->deleteAllShares($calendarId);
 
 		$query = $this->db->getQueryBuilder();
 		$query->delete($this->dbObjectPropertiesTable)
 			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_CALENDAR)))
 			->execute();
 	}
 
@@ -807,7 +867,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @return void
 	 */
 	function deleteAllSharesByUser($principaluri) {
-		$this->sharingBackend->deleteAllSharesByUser($principaluri);
+		$this->calendarSharingBackend->deleteAllSharesByUser($principaluri);
 	}
 
 	/**
@@ -838,27 +898,29 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * used/fetched to determine these numbers. If both are specified the
 	 * amount of times this is needed is reduced by a great degree.
 	 *
-	 * @param mixed $calendarId
+	 * @param mixed $id
+	 * @param int $calendarType
 	 * @return array
 	 */
-	function getCalendarObjects($calendarId) {
+	public function getCalendarObjects($id, $calendarType=self::CALENDAR_TYPE_CALENDAR):array {
 		$query = $this->db->getQueryBuilder();
 		$query->select(['id', 'uri', 'lastmodified', 'etag', 'calendarid', 'size', 'componenttype', 'classification'])
 			->from('calendarobjects')
-			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)));
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($id)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)));
 		$stmt = $query->execute();
 
 		$result = [];
 		foreach($stmt->fetchAll(\PDO::FETCH_ASSOC) as $row) {
 			$result[] = [
-					'id'           => $row['id'],
-					'uri'          => $row['uri'],
-					'lastmodified' => $row['lastmodified'],
-					'etag'         => '"' . $row['etag'] . '"',
-					'calendarid'   => $row['calendarid'],
-					'size'         => (int)$row['size'],
-					'component'    => strtolower($row['componenttype']),
-					'classification'=> (int)$row['classification']
+				'id'           => $row['id'],
+				'uri'          => $row['uri'],
+				'lastmodified' => $row['lastmodified'],
+				'etag'         => '"' . $row['etag'] . '"',
+				'calendarid'   => $row['calendarid'],
+				'size'         => (int)$row['size'],
+				'component'    => strtolower($row['componenttype']),
+				'classification'=> (int)$row['classification']
 			];
 		}
 
@@ -877,32 +939,35 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 *
 	 * This method must return null if the object did not exist.
 	 *
-	 * @param mixed $calendarId
+	 * @param mixed $id
 	 * @param string $objectUri
+	 * @param int $calendarType
 	 * @return array|null
 	 */
-	function getCalendarObject($calendarId, $objectUri) {
-
+	public function getCalendarObject($id, $objectUri, $calendarType=self::CALENDAR_TYPE_CALENDAR) {
 		$query = $this->db->getQueryBuilder();
 		$query->select(['id', 'uri', 'lastmodified', 'etag', 'calendarid', 'size', 'calendardata', 'componenttype', 'classification'])
-				->from('calendarobjects')
-				->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
-				->andWhere($query->expr()->eq('uri', $query->createNamedParameter($objectUri)));
+			->from('calendarobjects')
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($id)))
+			->andWhere($query->expr()->eq('uri', $query->createNamedParameter($objectUri)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)));
 		$stmt = $query->execute();
 		$row = $stmt->fetch(\PDO::FETCH_ASSOC);
 
-		if(!$row) return null;
+		if(!$row) {
+			return null;
+		}
 
 		return [
-				'id'            => $row['id'],
-				'uri'           => $row['uri'],
-				'lastmodified'  => $row['lastmodified'],
-				'etag'          => '"' . $row['etag'] . '"',
-				'calendarid'    => $row['calendarid'],
-				'size'          => (int)$row['size'],
-				'calendardata'  => $this->readBlob($row['calendardata']),
-				'component'     => strtolower($row['componenttype']),
-				'classification'=> (int)$row['classification']
+			'id'            => $row['id'],
+			'uri'           => $row['uri'],
+			'lastmodified'  => $row['lastmodified'],
+			'etag'          => '"' . $row['etag'] . '"',
+			'calendarid'    => $row['calendarid'],
+			'size'          => (int)$row['size'],
+			'calendardata'  => $this->readBlob($row['calendardata']),
+			'component'     => strtolower($row['componenttype']),
+			'classification'=> (int)$row['classification']
 		];
 	}
 
@@ -916,9 +981,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 *
 	 * @param mixed $calendarId
 	 * @param string[] $uris
+	 * @param int $calendarType
 	 * @return array
 	 */
-	function getMultipleCalendarObjects($calendarId, array $uris) {
+	public function getMultipleCalendarObjects($id, array $uris, $calendarType=self::CALENDAR_TYPE_CALENDAR):array {
 		if (empty($uris)) {
 			return [];
 		}
@@ -929,8 +995,9 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		$query = $this->db->getQueryBuilder();
 		$query->select(['id', 'uri', 'lastmodified', 'etag', 'calendarid', 'size', 'calendardata', 'componenttype', 'classification'])
 			->from('calendarobjects')
-			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
-			->andWhere($query->expr()->in('uri', $query->createParameter('uri')));
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($id)))
+			->andWhere($query->expr()->in('uri', $query->createParameter('uri')))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)));
 
 		foreach ($chunks as $uris) {
 			$query->setParameter('uri', $uris, IQueryBuilder::PARAM_STR_ARRAY);
@@ -951,6 +1018,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			}
 			$result->closeCursor();
 		}
+
 		return $objects;
 	}
 
@@ -970,16 +1038,18 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param mixed $calendarId
 	 * @param string $objectUri
 	 * @param string $calendarData
+	 * @param int $calendarType
 	 * @return string
 	 */
-	function createCalendarObject($calendarId, $objectUri, $calendarData) {
+	function createCalendarObject($calendarId, $objectUri, $calendarData, $calendarType=self::CALENDAR_TYPE_CALENDAR) {
 		$extraData = $this->getDenormalizedData($calendarData);
 
 		$q = $this->db->getQueryBuilder();
 		$q->select($q->createFunction('COUNT(*)'))
 			->from('calendarobjects')
 			->where($q->expr()->eq('calendarid', $q->createNamedParameter($calendarId)))
-			->andWhere($q->expr()->eq('uid', $q->createNamedParameter($extraData['uid'])));
+			->andWhere($q->expr()->eq('uid', $q->createNamedParameter($extraData['uid'])))
+			->andWhere($q->expr()->eq('calendartype', $q->createNamedParameter($calendarType)));
 
 		$result = $q->execute();
 		$count = (int) $result->fetchColumn();
@@ -1003,21 +1073,34 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				'lastoccurence' => $query->createNamedParameter($extraData['lastOccurence']),
 				'classification' => $query->createNamedParameter($extraData['classification']),
 				'uid' => $query->createNamedParameter($extraData['uid']),
+				'calendartype' => $query->createNamedParameter($calendarType),
 			])
 			->execute();
 
-		$this->updateProperties($calendarId, $objectUri, $calendarData);
+		$this->updateProperties($calendarId, $objectUri, $calendarData, $calendarType);
 
-		$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::createCalendarObject', new GenericEvent(
-			'\OCA\DAV\CalDAV\CalDavBackend::createCalendarObject',
-			[
-				'calendarId' => $calendarId,
-				'calendarData' => $this->getCalendarById($calendarId),
-				'shares' => $this->getShares($calendarId),
-				'objectData' => $this->getCalendarObject($calendarId, $objectUri),
-			]
-		));
-		$this->addChange($calendarId, $objectUri, 1);
+		if ($calendarType === self::CALENDAR_TYPE_CALENDAR) {
+			$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::createCalendarObject', new GenericEvent(
+				'\OCA\DAV\CalDAV\CalDavBackend::createCalendarObject',
+				[
+					'calendarId' => $calendarId,
+					'calendarData' => $this->getCalendarById($calendarId),
+					'shares' => $this->getShares($calendarId),
+					'objectData' => $this->getCalendarObject($calendarId, $objectUri),
+				]
+			));
+		} else {
+			$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::createCachedCalendarObject', new GenericEvent(
+				'\OCA\DAV\CalDAV\CalDavBackend::createCachedCalendarObject',
+				[
+					'subscriptionId' => $calendarId,
+					'calendarData' => $this->getCalendarById($calendarId),
+					'shares' => $this->getShares($calendarId),
+					'objectData' => $this->getCalendarObject($calendarId, $objectUri),
+				]
+			));
+		}
+		$this->addChange($calendarId, $objectUri, 1, $calendarType);
 
 		return '"' . $extraData['etag'] . '"';
 	}
@@ -1038,9 +1121,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param mixed $calendarId
 	 * @param string $objectUri
 	 * @param string $calendarData
+	 * @param int $calendarType
 	 * @return string
 	 */
-	function updateCalendarObject($calendarId, $objectUri, $calendarData) {
+	function updateCalendarObject($calendarId, $objectUri, $calendarData, $calendarType=self::CALENDAR_TYPE_CALENDAR) {
 		$extraData = $this->getDenormalizedData($calendarData);
 
 		$query = $this->db->getQueryBuilder();
@@ -1056,23 +1140,36 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				->set('uid', $query->createNamedParameter($extraData['uid']))
 			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
 			->andWhere($query->expr()->eq('uri', $query->createNamedParameter($objectUri)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)))
 			->execute();
 
-		$this->updateProperties($calendarId, $objectUri, $calendarData);
+		$this->updateProperties($calendarId, $objectUri, $calendarData, $calendarType);
 
 		$data = $this->getCalendarObject($calendarId, $objectUri);
 		if (is_array($data)) {
-			$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::updateCalendarObject', new GenericEvent(
-				'\OCA\DAV\CalDAV\CalDavBackend::updateCalendarObject',
-				[
-					'calendarId' => $calendarId,
-					'calendarData' => $this->getCalendarById($calendarId),
-					'shares' => $this->getShares($calendarId),
-					'objectData' => $data,
-				]
-			));
+			if ($calendarType === self::CALENDAR_TYPE_CALENDAR) {
+				$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::updateCalendarObject', new GenericEvent(
+					'\OCA\DAV\CalDAV\CalDavBackend::updateCalendarObject',
+					[
+						'calendarId' => $calendarId,
+						'calendarData' => $this->getCalendarById($calendarId),
+						'shares' => $this->getShares($calendarId),
+						'objectData' => $data,
+					]
+				));
+			} else {
+				$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::updateCachedCalendarObject', new GenericEvent(
+					'\OCA\DAV\CalDAV\CalDavBackend::updateCachedCalendarObject',
+					[
+						'subscriptionId' => $calendarId,
+						'calendarData' => $this->getCalendarById($calendarId),
+						'shares' => $this->getShares($calendarId),
+						'objectData' => $data,
+					]
+				));
+			}
 		}
-		$this->addChange($calendarId, $objectUri, 2);
+		$this->addChange($calendarId, $objectUri, 2, $calendarType);
 
 		return '"' . $extraData['etag'] . '"';
 	}
@@ -1101,28 +1198,41 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 *
 	 * @param mixed $calendarId
 	 * @param string $objectUri
+	 * @param int $calendarType
 	 * @return void
 	 */
-	function deleteCalendarObject($calendarId, $objectUri) {
-		$data = $this->getCalendarObject($calendarId, $objectUri);
+	function deleteCalendarObject($calendarId, $objectUri, $calendarType=self::CALENDAR_TYPE_CALENDAR) {
+		$data = $this->getCalendarObject($calendarId, $objectUri, $calendarType);
 		if (is_array($data)) {
-			$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::deleteCalendarObject', new GenericEvent(
-				'\OCA\DAV\CalDAV\CalDavBackend::deleteCalendarObject',
-				[
-					'calendarId' => $calendarId,
-					'calendarData' => $this->getCalendarById($calendarId),
-					'shares' => $this->getShares($calendarId),
-					'objectData' => $data,
-				]
-			));
+			if ($calendarType === self::CALENDAR_TYPE_CALENDAR) {
+				$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::deleteCalendarObject', new GenericEvent(
+					'\OCA\DAV\CalDAV\CalDavBackend::deleteCalendarObject',
+					[
+						'calendarId' => $calendarId,
+						'calendarData' => $this->getCalendarById($calendarId),
+						'shares' => $this->getShares($calendarId),
+						'objectData' => $data,
+					]
+				));
+			} else {
+				$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::deleteCachedCalendarObject', new GenericEvent(
+					'\OCA\DAV\CalDAV\CalDavBackend::deleteCachedCalendarObject',
+					[
+						'subscriptionId' => $calendarId,
+						'calendarData' => $this->getCalendarById($calendarId),
+						'shares' => $this->getShares($calendarId),
+						'objectData' => $data,
+					]
+				));
+			}
 		}
 
-		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ? AND `uri` = ?');
-		$stmt->execute([$calendarId, $objectUri]);
+		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ? AND `uri` = ? AND `calendartype` = ?');
+		$stmt->execute([$calendarId, $objectUri, $calendarType]);
 
-		$this->purgeProperties($calendarId, $data['id']);
+		$this->purgeProperties($calendarId, $data['id'], $calendarType);
 
-		$this->addChange($calendarId, $objectUri, 3);
+		$this->addChange($calendarId, $objectUri, 3, $calendarType);
 	}
 
 	/**
@@ -1170,11 +1280,12 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * as possible, so it gives you a good idea on what type of stuff you need
 	 * to think of.
 	 *
-	 * @param mixed $calendarId
+	 * @param mixed $id
 	 * @param array $filters
+	 * @param int $calendarType
 	 * @return array
 	 */
-	function calendarQuery($calendarId, array $filters) {
+	public function calendarQuery($id, array $filters, $calendarType=self::CALENDAR_TYPE_CALENDAR):array {
 		$componentType = null;
 		$requirePostFilter = true;
 		$timeRange = null;
@@ -1211,7 +1322,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		$query = $this->db->getQueryBuilder();
 		$query->select($columns)
 			->from('calendarobjects')
-			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)));
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($id)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)));
 
 		if ($componentType) {
 			$query->andWhere($query->expr()->eq('componenttype', $query->createNamedParameter($componentType)));
@@ -1236,13 +1348,13 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				} catch(ParseException $ex) {
 					$this->logger->logException($ex, [
 						'app' => 'dav',
-						'message' => 'Caught parsing exception for calendar data. This usually indicates invalid calendar data. calendar-id:'.$calendarId.' uri:'.$row['uri']
+						'message' => 'Caught parsing exception for calendar data. This usually indicates invalid calendar data. calendar-id:'.$id.' uri:'.$row['uri']
 					]);
 					continue;
 				} catch (InvalidDataException $ex) {
 					$this->logger->logException($ex, [
 						'app' => 'dav',
-						'message' => 'Caught invalid data exception for calendar data. This usually indicates invalid calendar data. calendar-id:'.$calendarId.' uri:'.$row['uri']
+						'message' => 'Caught invalid data exception for calendar data. This usually indicates invalid calendar data. calendar-id:'.$id.' uri:'.$row['uri']
 					]);
 					continue;
 				}
@@ -1260,6 +1372,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	/**
 	 * custom Nextcloud search extension for CalDAV
 	 *
+	 * TODO - this should optionally cover cached calendar objects as well
+	 *
 	 * @param string $principalUri
 	 * @param array $filters
 	 * @param integer|null $limit
@@ -1289,16 +1403,20 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		// Calendar id expressions
 		$calendarExpressions = [];
 		foreach($ownCalendars as $id) {
-			$calendarExpressions[] = $query->expr()
-				->eq('c.calendarid', $query->createNamedParameter($id));
+			$calendarExpressions[] = $query->expr()->andX(
+				$query->expr()->eq('c.calendarid',
+					$query->createNamedParameter($id)),
+				$query->expr()->eq('c.calendartype',
+						$query->createNamedParameter(self::CALENDAR_TYPE_CALENDAR)));
 		}
 		foreach($sharedCalendars as $id) {
 			$calendarExpressions[] = $query->expr()->andX(
 				$query->expr()->eq('c.calendarid',
 					$query->createNamedParameter($id)),
 				$query->expr()->eq('c.classification',
-					$query->createNamedParameter(self::CLASSIFICATION_PUBLIC))
-			);
+					$query->createNamedParameter(self::CLASSIFICATION_PUBLIC)),
+				$query->expr()->eq('c.calendartype',
+					$query->createNamedParameter(self::CALENDAR_TYPE_CALENDAR)));
 		}
 
 		if (count($calendarExpressions) === 1) {
@@ -1396,7 +1514,9 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		$innerQuery->selectDistinct('op.objectid')
 			->from($this->dbObjectPropertiesTable, 'op')
 			->andWhere($innerQuery->expr()->eq('op.calendarid',
-				$outerQuery->createNamedParameter($calendarInfo['id'])));
+				$outerQuery->createNamedParameter($calendarInfo['id'])))
+			->andWhere($innerQuery->expr()->eq('op.calendartype',
+				$outerQuery->createNamedParameter(self::CALENDAR_TYPE_CALENDAR)));
 
 		// only return public items for shared calendars for now
 		if ($calendarInfo['principaluri'] !== $calendarInfo['{http://owncloud.org/ns}owner-principal']) {
@@ -1569,6 +1689,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			->from('calendarobjects', 'co')
 			->leftJoin('co', 'calendars', 'c', $query->expr()->eq('co.calendarid', 'c.id'))
 			->where($query->expr()->eq('c.principaluri', $query->createNamedParameter($principalUri)))
+			->andWhere($query->expr()->eq('co.uid', $query->createNamedParameter($uid)))
 			->andWhere($query->expr()->eq('co.uid', $query->createNamedParameter($uid)));
 
 		$stmt = $query->execute();
@@ -1634,9 +1755,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param string $syncToken
 	 * @param int $syncLevel
 	 * @param int $limit
+	 * @param int $calendarType
 	 * @return array
 	 */
-	function getChangesForCalendar($calendarId, $syncToken, $syncLevel, $limit = null) {
+	function getChangesForCalendar($calendarId, $syncToken, $syncLevel, $limit = null, $calendarType=self::CALENDAR_TYPE_CALENDAR) {
 		// Current synctoken
 		$stmt = $this->db->prepare('SELECT `synctoken` FROM `*PREFIX*calendars` WHERE `id` = ?');
 		$stmt->execute([ $calendarId ]);
@@ -1655,14 +1777,14 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 
 		if ($syncToken) {
 
-			$query = "SELECT `uri`, `operation` FROM `*PREFIX*calendarchanges` WHERE `synctoken` >= ? AND `synctoken` < ? AND `calendarid` = ? ORDER BY `synctoken`";
+			$query = "SELECT `uri`, `operation` FROM `*PREFIX*calendarchanges` WHERE `synctoken` >= ? AND `synctoken` < ? AND `calendarid` = ? AND `calendartype` = ? ORDER BY `synctoken`";
 			if ($limit>0) {
 				$query.= " LIMIT " . (int)$limit;
 			}
 
 			// Fetching all changes
 			$stmt = $this->db->prepare($query);
-			$stmt->execute([$syncToken, $currentToken, $calendarId]);
+			$stmt->execute([$syncToken, $currentToken, $calendarId, $calendarType]);
 
 			$changes = [];
 
@@ -1691,9 +1813,9 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			}
 		} else {
 			// No synctoken supplied, this is the initial sync.
-			$query = "SELECT `uri` FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ?";
+			$query = "SELECT `uri` FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ? AND `calendartype` = ?";
 			$stmt = $this->db->prepare($query);
-			$stmt->execute([$calendarId]);
+			$stmt->execute([$calendarId, $calendarType]);
 
 			$result['added'] = $stmt->fetchAll(\PDO::FETCH_COLUMN);
 		}
@@ -1740,6 +1862,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		$fields[] = 'source';
 		$fields[] = 'principaluri';
 		$fields[] = 'lastmodified';
+		$fields[] = 'synctoken';
 
 		$query = $this->db->getQueryBuilder();
 		$query->select($fields)
@@ -1759,6 +1882,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				'lastmodified' => $row['lastmodified'],
 
 				'{' . Plugin::NS_CALDAV . '}supported-calendar-component-set' => new SupportedCalendarComponentSet(['VTODO', 'VEVENT']),
+				'{http://sabredav.org/ns}sync-token' => $row['synctoken']?$row['synctoken']:'0',
 			];
 
 			foreach($this->subscriptionPropertyMap as $xmlName=>$dbName) {
@@ -1821,7 +1945,16 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			->values($valuesToInsert)
 			->execute();
 
-		return $this->db->lastInsertId('*PREFIX*calendarsubscriptions');
+		$subscriptionId = $this->db->lastInsertId('*PREFIX*calendarsubscriptions');
+
+		$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::createSubscription', new GenericEvent(
+			'\OCA\DAV\CalDAV\CalDavBackend::createSubscription',
+			[
+				'subscriptionId' => $subscriptionId,
+				'subscriptionData' => $this->getSubscriptionById($subscriptionId),
+			]));
+
+		return $subscriptionId;
 	}
 
 	/**
@@ -1869,6 +2002,14 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			$query->where($query->expr()->eq('id', $query->createNamedParameter($subscriptionId)))
 				->execute();
 
+			$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::updateSubscription', new GenericEvent(
+				'\OCA\DAV\CalDAV\CalDavBackend::updateSubscription',
+				[
+					'subscriptionId' => $subscriptionId,
+					'subscriptionData' => $this->getSubscriptionById($subscriptionId),
+					'propertyMutations' => $mutations,
+				]));
+
 			return true;
 
 		});
@@ -1881,10 +2022,33 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @return void
 	 */
 	function deleteSubscription($subscriptionId) {
+		$this->dispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::deleteSubscription', new GenericEvent(
+			'\OCA\DAV\CalDAV\CalDavBackend::deleteSubscription',
+			[
+				'subscriptionId' => $subscriptionId,
+				'subscriptionData' => $this->getSubscriptionById($subscriptionId),
+			]));
+
 		$query = $this->db->getQueryBuilder();
 		$query->delete('calendarsubscriptions')
 			->where($query->expr()->eq('id', $query->createNamedParameter($subscriptionId)))
 			->execute();
+
+		$query = $this->db->getQueryBuilder();
+		$query->delete('calendarobjects')
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))
+			->execute();
+
+		$query->delete('calendarchanges')
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))
+			->execute();
+
+		$query->delete($this->dbObjectPropertiesTable)
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))
+			->execute();
 	}
 
 	/**
@@ -2001,18 +2165,30 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param mixed $calendarId
 	 * @param string $objectUri
 	 * @param int $operation 1 = add, 2 = modify, 3 = delete.
+	 * @param int $calendarType
 	 * @return void
 	 */
-	protected function addChange($calendarId, $objectUri, $operation) {
+	protected function addChange($calendarId, $objectUri, $operation, $calendarType=self::CALENDAR_TYPE_CALENDAR) {
+		$table = $calendarType === self::CALENDAR_TYPE_CALENDAR ? 'calendars': 'calendarsubscriptions';
 
-		$stmt = $this->db->prepare('INSERT INTO `*PREFIX*calendarchanges` (`uri`, `synctoken`, `calendarid`, `operation`) SELECT ?, `synctoken`, ?, ? FROM `*PREFIX*calendars` WHERE `id` = ?');
-		$stmt->execute([
-			$objectUri,
-			$calendarId,
-			$operation,
-			$calendarId
-		]);
-		$stmt = $this->db->prepare('UPDATE `*PREFIX*calendars` SET `synctoken` = `synctoken` + 1 WHERE `id` = ?');
+		$query = $this->db->getQueryBuilder();
+		$query->select('synctoken')
+			->from($table)
+			->where($query->expr()->eq('id', $query->createNamedParameter($calendarId)));
+		$syncToken = (int)$query->execute()->fetchColumn();
+
+		$query = $this->db->getQueryBuilder();
+		$query->insert('calendarchanges')
+			->values([
+				'uri' => $query->createNamedParameter($objectUri),
+				'synctoken' => $query->createNamedParameter($syncToken),
+				'calendarid' => $query->createNamedParameter($calendarId),
+				'operation' => $query->createNamedParameter($operation),
+				'calendartype' => $query->createNamedParameter($calendarType),
+			])
+			->execute();
+
+		$stmt = $this->db->prepare("UPDATE `*PREFIX*$table` SET `synctoken` = `synctoken` + 1 WHERE `id` = ?");
 		$stmt->execute([
 			$calendarId
 		]);
@@ -2111,6 +2287,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 
 	}
 
+	/**
+	 * @param $cardData
+	 * @return bool|string
+	 */
 	private function readBlob($cardData) {
 		if (is_resource($cardData)) {
 			return stream_get_contents($cardData);
@@ -2135,15 +2315,16 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				'add' => $add,
 				'remove' => $remove,
 			]));
-		$this->sharingBackend->updateShares($shareable, $add, $remove);
+		$this->calendarSharingBackend->updateShares($shareable, $add, $remove);
 	}
 
 	/**
 	 * @param int $resourceId
+	 * @param int $calendarType
 	 * @return array
 	 */
-	public function getShares($resourceId) {
-		return $this->sharingBackend->getShares($resourceId);
+	public function getShares($resourceId, $calendarType=self::CALENDAR_TYPE_CALENDAR) {
+		return $this->calendarSharingBackend->getShares($resourceId);
 	}
 
 	/**
@@ -2206,7 +2387,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @return array
 	 */
 	public function applyShareAcl($resourceId, $acl) {
-		return $this->sharingBackend->applyShareAcl($resourceId, $acl);
+		return $this->calendarSharingBackend->applyShareAcl($resourceId, $acl);
 	}
 
 
@@ -2217,9 +2398,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param int $calendarId
 	 * @param string $objectUri
 	 * @param string $calendarData
+	 * @param int $calendarType
 	 */
-	public function updateProperties($calendarId, $objectUri, $calendarData) {
-		$objectId = $this->getCalendarObjectId($calendarId, $objectUri);
+	public function updateProperties($calendarId, $objectUri, $calendarData, $calendarType=self::CALENDAR_TYPE_CALENDAR) {
+		$objectId = $this->getCalendarObjectId($calendarId, $objectUri, $calendarType);
 
 		try {
 			$vCalendar = $this->readCalendarData($calendarData);
@@ -2234,6 +2416,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			->values(
 				[
 					'calendarid' => $query->createNamedParameter($calendarId),
+					'calendartype' => $query->createNamedParameter($calendarType),
 					'objectid' => $query->createNamedParameter($objectId),
 					'name' => $query->createParameter('name'),
 					'parameter' => $query->createParameter('parameter'),
@@ -2291,8 +2474,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	public function deleteAllBirthdayCalendars() {
 		$query = $this->db->getQueryBuilder();
 		$result = $query->select(['id'])->from('calendars')
-			->where($query->expr()->eq('uri',
-				$query->createNamedParameter(BirthdayService::BIRTHDAY_CALENDAR_URI)))
+			->where($query->expr()->eq('uri', $query->createNamedParameter(BirthdayService::BIRTHDAY_CALENDAR_URI)))
 			->execute();
 
 		$ids = $result->fetchAll();
@@ -2302,6 +2484,44 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	}
 
 	/**
+	 * @param $subscriptionId
+	 */
+	public function purgeAllCachedEventsForSubscription($subscriptionId) {
+		$query = $this->db->getQueryBuilder();
+		$query->select('uri')
+			->from('calendarobjects')
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)));
+		$stmt = $query->execute();
+
+		$uris = [];
+		foreach($stmt->fetchAll(\PDO::FETCH_ASSOC) as $row) {
+			$uris[] = $row['uri'];
+		}
+		$stmt->closeCursor();
+
+		$query = $this->db->getQueryBuilder();
+		$query->delete('calendarobjects')
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))
+			->execute();
+
+		$query->delete('calendarchanges')
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))
+			->execute();
+
+		$query->delete($this->dbObjectPropertiesTable)
+			->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))
+			->execute();
+
+		foreach($uris as $uri) {
+			$this->addChange($subscriptionId, $uri, 3, self::CALENDAR_TYPE_SUBSCRIPTION);
+		}
+	}
+
+	/**
 	 * read VCalendar data into a VCalendar object
 	 *
 	 * @param string $objectData
@@ -2330,13 +2550,16 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 *
 	 * @param int $calendarId
 	 * @param string $uri
+	 * @param int $calendarType
 	 * @return int
 	 */
-	protected function getCalendarObjectId($calendarId, $uri) {
+	protected function getCalendarObjectId($calendarId, $uri, $calendarType):int {
 		$query = $this->db->getQueryBuilder();
-		$query->select('id')->from('calendarobjects')
+		$query->select('id')
+			->from('calendarobjects')
 			->where($query->expr()->eq('uri', $query->createNamedParameter($uri)))
-			->andWhere($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)));
+			->andWhere($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)));
 
 		$result = $query->execute();
 		$objectIds = $result->fetch();
@@ -2349,6 +2572,13 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		return (int)$objectIds['id'];
 	}
 
+	/**
+	 * return legacy endpoint principal name to new principal name
+	 *
+	 * @param $principalUri
+	 * @param $toV2
+	 * @return string
+	 */
 	private function convertPrincipal($principalUri, $toV2) {
 		if ($this->principalBackend->getPrincipalPrefix() === 'principals') {
 			list(, $name) = Uri\split($principalUri);
@@ -2360,6 +2590,11 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		return $principalUri;
 	}
 
+	/**
+	 * adds information about an owner to the calendar data
+	 *
+	 * @param $calendarInfo
+	 */
 	private function addOwnerPrincipal(&$calendarInfo) {
 		$ownerPrincipalKey = '{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal';
 		$displaynameKey = '{' . \OCA\DAV\DAV\Sharing\Plugin::NS_NEXTCLOUD . '}owner-displayname';
diff --git a/apps/dav/lib/CalDAV/CalendarHome.php b/apps/dav/lib/CalDAV/CalendarHome.php
index 6700b1b2496..9ff71410f87 100644
--- a/apps/dav/lib/CalDAV/CalendarHome.php
+++ b/apps/dav/lib/CalDAV/CalendarHome.php
@@ -42,6 +42,9 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 	/** @var \OCP\IConfig */
 	private $config;
 
+	/** @var bool */
+	private $returnCachedSubscriptions=false;
+
 	public function __construct(BackendInterface $caldavBackend, $principalInfo) {
 		parent::__construct($caldavBackend, $principalInfo);
 		$this->l10n = \OC::$server->getL10N('dav');
@@ -91,7 +94,11 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 		// If the backend supports subscriptions, we'll add those as well,
 		if ($this->caldavBackend instanceof SubscriptionSupport) {
 			foreach ($this->caldavBackend->getSubscriptionsForUser($this->principalInfo['uri']) as $subscription) {
-				$objects[] = new Subscription($this->caldavBackend, $subscription);
+				if ($this->returnCachedSubscriptions) {
+					$objects[] = new CachedSubscription($this->caldavBackend, $subscription);
+				} else {
+					$objects[] = new Subscription($this->caldavBackend, $subscription);
+				}
 			}
 		}
 
@@ -123,6 +130,10 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 		if ($this->caldavBackend instanceof SubscriptionSupport) {
 			foreach ($this->caldavBackend->getSubscriptionsForUser($this->principalInfo['uri']) as $subscription) {
 				if ($subscription['uri'] === $name) {
+					if ($this->returnCachedSubscriptions) {
+						return new CachedSubscription($this->caldavBackend, $subscription);
+					}
+
 					return new Subscription($this->caldavBackend, $subscription);
 				}
 			}
@@ -141,4 +152,11 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 		$principalUri = $this->principalInfo['uri'];
 		return $this->caldavBackend->calendarSearch($principalUri, $filters, $limit, $offset);
 	}
+
+	/**
+	 *
+	 */
+	public function enableCachedSubscriptionsForThisRequest() {
+		$this->returnCachedSubscriptions = true;
+	}
 }
diff --git a/apps/dav/lib/CalDAV/WebcalCaching/Plugin.php b/apps/dav/lib/CalDAV/WebcalCaching/Plugin.php
new file mode 100644
index 00000000000..de2ff5a8e8b
--- /dev/null
+++ b/apps/dav/lib/CalDAV/WebcalCaching/Plugin.php
@@ -0,0 +1,145 @@
+<?php
+declare(strict_types=1);
+/**
+ * @copyright 2018 Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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 OCA\DAV\CalDAV\WebcalCaching;
+
+use OCA\DAV\CalDAV\CalendarHome;
+use OCP\IRequest;
+use Sabre\DAV\Exception\NotFound;
+use Sabre\DAV\Server;
+use Sabre\DAV\ServerPlugin;
+use Sabre\HTTP\RequestInterface;
+use Sabre\HTTP\ResponseInterface;
+
+class Plugin extends ServerPlugin {
+
+	/**
+	 * list of regular expressions for calendar user agents,
+	 * that do not support subscriptions on their own
+	 *
+	 * @var string[]
+	 */
+	const ENABLE_FOR_CLIENTS = [];
+
+	/**
+	 * @var bool
+	 */
+	private $enabled=false;
+
+	/**
+	 * @var Server
+	 */
+	private $server;
+
+	/**
+	 * Plugin constructor.
+	 *
+	 * @param IRequest $request
+	 */
+	public function __construct(IRequest $request) {
+		if ($request->isUserAgent(self::ENABLE_FOR_CLIENTS)) {
+			$this->enabled = true;
+		}
+
+		$magicHeader = $request->getHeader('X-NC-CalDAV-Webcal-Caching');
+		if ($magicHeader === 'On') {
+			$this->enabled = true;
+		}
+	}
+
+	/**
+	 * 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;
+		$server->on('beforeMethod', [$this, 'beforeMethod']);
+	}
+
+	/**
+	 * @param RequestInterface $request
+	 * @param ResponseInterface $response
+	 */
+	public function beforeMethod(RequestInterface $request, ResponseInterface $response) {
+		if (!$this->enabled) {
+			return;
+		}
+
+		$path = $request->getPath();
+		$pathParts = explode('/', ltrim($path, '/'));
+		if (\count($pathParts) < 2) {
+			return;
+		}
+
+		// $calendarHomePath will look like: calendars/username
+		$calendarHomePath = $pathParts[0] . '/' . $pathParts[1];
+		try {
+			$calendarHome = $this->server->tree->getNodeForPath($calendarHomePath);
+			if (!($calendarHome instanceof CalendarHome)) {
+				//how did we end up here?
+				return;
+			}
+
+			$calendarHome->enableCachedSubscriptionsForThisRequest();
+		} catch(NotFound $ex) {
+			return;
+		}
+	}
+
+	/**
+	 * @return bool
+	 */
+	public function isCachingEnabledForThisRequest():bool {
+		return $this->enabled;
+	}
+
+	/**
+	 * 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():array {
+		return ['nc-calendar-webcal-cache'];
+	}
+
+	/**
+	 * 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():string {
+		return 'nc-calendar-webcal-cache';
+	}
+}
diff --git a/apps/dav/lib/Migration/RefreshWebcalJobRegistrar.php b/apps/dav/lib/Migration/RefreshWebcalJobRegistrar.php
new file mode 100644
index 00000000000..912e0aec98e
--- /dev/null
+++ b/apps/dav/lib/Migration/RefreshWebcalJobRegistrar.php
@@ -0,0 +1,83 @@
+<?php
+declare(strict_types=1);
+/**
+ * @copyright 2018 Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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 OCA\DAV\Migration;
+
+use OCA\DAV\BackgroundJob\RefreshWebcalJob;
+use OCP\BackgroundJob\IJobList;
+use OCP\IDBConnection;
+use OCP\Migration\IOutput;
+use OCP\Migration\IRepairStep;
+
+class RefreshWebcalJobRegistrar implements IRepairStep {
+
+	/** @var IDBConnection */
+	private $connection;
+
+	/** @var IJobList */
+	private $jobList;
+
+	/**
+	 * FixBirthdayCalendarComponent constructor.
+	 *
+	 * @param IDBConnection $connection
+	 * @param IJobList $jobList
+	 */
+	public function __construct(IDBConnection $connection, IJobList $jobList) {
+		$this->connection = $connection;
+		$this->jobList = $jobList;
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	public function getName() {
+		return 'Registering background jobs to update cache for webcal calendars';
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	public function run(IOutput $output) {
+		$query = $this->connection->getQueryBuilder();
+		$query->select(['principaluri', 'uri'])
+			->from('calendarsubscriptions');
+		$stmt = $query->execute();
+
+		$count = 0;
+		while($row = $stmt->fetch(\PDO::FETCH_ASSOC)) {
+			$args = [
+				'principaluri' => $row['principaluri'],
+				'uri' => $row['uri'],
+			];
+
+			if (!$this->jobList->has(RefreshWebcalJob::class, $args)) {
+				$this->jobList->add(RefreshWebcalJob::class, $args);
+				$count++;
+			}
+		}
+
+		$output->info("Added $count background jobs to update webcal calendars");
+	}
+}
diff --git a/apps/dav/lib/Migration/Version1006Date20180628111625.php b/apps/dav/lib/Migration/Version1006Date20180628111625.php
new file mode 100644
index 00000000000..8113b4c69bf
--- /dev/null
+++ b/apps/dav/lib/Migration/Version1006Date20180628111625.php
@@ -0,0 +1,105 @@
+<?php
+declare(strict_types=1);
+/**
+ * @copyright 2018 Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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 OCA\DAV\Migration;
+
+use Doctrine\DBAL\Types\Type;
+use OCP\DB\ISchemaWrapper;
+use OCP\Migration\SimpleMigrationStep;
+use OCP\Migration\IOutput;
+
+class Version1006Date20180628111625 extends SimpleMigrationStep {
+
+	/**
+	 * @param IOutput $output
+	 * @param \Closure $schemaClosure The `\Closure` returns a `ISchemaWrapper`
+	 * @param array $options
+	 * @return null|ISchemaWrapper
+	 */
+	public function changeSchema(IOutput $output, \Closure $schemaClosure, array $options) {
+		/** @var ISchemaWrapper $schema */
+		$schema = $schemaClosure();
+
+		if ($schema->hasTable('calendarchanges')) {
+			$calendarChangesTable = $schema->getTable('calendarchanges');
+			$calendarChangesTable->addColumn('calendartype', Type::INTEGER, [
+				'notnull' => true,
+				'default' => 0,
+			]);
+
+			if ($calendarChangesTable->hasIndex('calendarid_synctoken')) {
+				$calendarChangesTable->dropIndex('calendarid_synctoken');
+			}
+			$calendarChangesTable->addIndex(['calendarid', 'calendartype', 'synctoken'], 'calendarid_calendartype_synctoken');
+		}
+
+		if ($schema->hasTable('calendarobjects')) {
+			$calendarObjectsTable = $schema->getTable('calendarobjects');
+			$calendarObjectsTable->addColumn('calendartype', Type::INTEGER, [
+				'notnull' => true,
+				'default' => 0,
+			]);
+
+			if ($calendarObjectsTable->hasIndex('calobjects_index')) {
+				$calendarObjectsTable->dropIndex('calobjects_index');
+			}
+			$calendarObjectsTable->addUniqueIndex(['calendarid', 'calendartype', 'uri'], 'calobjects_index');
+		}
+
+		if ($schema->hasTable('calendarobjects_props')) {
+			$calendarObjectsPropsTable = $schema->getTable('calendarobjects_props');
+			$calendarObjectsPropsTable->addColumn('calendartype', Type::INTEGER, [
+				'notnull' => true,
+				'default' => 0,
+			]);
+
+
+			if ($calendarObjectsPropsTable->hasIndex('calendarobject_index')) {
+				$calendarObjectsPropsTable->dropIndex('calendarobject_index');
+			}
+			if ($calendarObjectsPropsTable->hasIndex('calendarobject_name_index')) {
+				$calendarObjectsPropsTable->dropIndex('calendarobject_name_index');
+			}
+			if ($calendarObjectsPropsTable->hasIndex('calendarobject_value_index')) {
+				$calendarObjectsPropsTable->dropIndex('calendarobject_value_index');
+			}
+
+			$calendarObjectsPropsTable->addIndex(['objectid', 'calendartype'], 'calendarobject_index');
+			$calendarObjectsPropsTable->addIndex(['name', 'calendartype'], 'calendarobject_name_index');
+			$calendarObjectsPropsTable->addIndex(['value', 'calendartype'], 'calendarobject_value_index');
+		}
+
+		if ($schema->hasTable('calendarsubscriptions')) {
+			$calendarSubscriptionsTable = $schema->getTable('calendarsubscriptions');
+			$calendarSubscriptionsTable->addColumn('synctoken', 'integer', [
+				'notnull' => true,
+				'default' => 1,
+				'length' => 10,
+				'unsigned' => true,
+			]);
+		}
+
+		return $schema;
+	}
+}
diff --git a/apps/dav/lib/Server.php b/apps/dav/lib/Server.php
index c8d223b18b8..dac2fa102b3 100644
--- a/apps/dav/lib/Server.php
+++ b/apps/dav/lib/Server.php
@@ -149,7 +149,10 @@ class Server {
 			if (\OC::$server->getConfig()->getAppValue('dav', 'sendInvitations', 'yes') === 'yes') {
 				$this->server->addPlugin(\OC::$server->query(\OCA\DAV\CalDAV\Schedule\IMipPlugin::class));
 			}
+
+			$this->server->addPlugin(new CalDAV\WebcalCaching\Plugin($request));
 			$this->server->addPlugin(new \Sabre\CalDAV\Subscriptions\Plugin());
+
 			$this->server->addPlugin(new \Sabre\CalDAV\Notifications\Plugin());
 			$this->server->addPlugin(new DAV\Sharing\Plugin($authBackend, \OC::$server->getRequest()));
 			$this->server->addPlugin(new \OCA\DAV\CalDAV\Publishing\PublishPlugin(
diff --git a/apps/dav/tests/unit/BackgroundJob/RefreshWebcalJobTest.php b/apps/dav/tests/unit/BackgroundJob/RefreshWebcalJobTest.php
new file mode 100644
index 00000000000..b7cee2c884d
--- /dev/null
+++ b/apps/dav/tests/unit/BackgroundJob/RefreshWebcalJobTest.php
@@ -0,0 +1,242 @@
+<?php
+/**
+ * @copyright Copyright (c) 2018, Georg Ehrke
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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\Tests\unit\BackgroundJob;
+
+use GuzzleHttp\HandlerStack;
+use OCA\DAV\BackgroundJob\RefreshWebcalJob;
+use OCA\DAV\CalDAV\CalDavBackend;
+use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\BackgroundJob\IJobList;
+use OCP\Http\Client\IClient;
+use OCP\Http\Client\IClientService;
+use OCP\Http\Client\IResponse;
+use OCP\IConfig;
+use OCP\ILogger;
+use Test\TestCase;
+
+use Sabre\VObject;
+
+class RefreshWebcalJobTest extends TestCase {
+
+	/** @var CalDavBackend | \PHPUnit_Framework_MockObject_MockObject */
+	private $caldavBackend;
+
+	/** @var IClientService | \PHPUnit_Framework_MockObject_MockObject */
+	private $clientService;
+
+	/** @var IConfig | \PHPUnit_Framework_MockObject_MockObject */
+	private $config;
+
+	/** @var ILogger | \PHPUnit_Framework_MockObject_MockObject */
+	private $logger;
+
+	/** @var ITimeFactory | \PHPUnit_Framework_MockObject_MockObject */
+	private $timeFactory;
+
+	/** @var IJobList | \PHPUnit_Framework_MockObject_MockObject */
+	private $jobList;
+
+	protected function setUp() {
+		parent::setUp();
+
+		$this->caldavBackend = $this->createMock(CalDavBackend::class);
+		$this->clientService = $this->createMock(IClientService::class);
+		$this->config = $this->createMock(IConfig::class);
+		$this->logger = $this->createMock(ILogger::class);
+		$this->timeFactory = $this->createMock(ITimeFactory::class);
+
+		$this->jobList = $this->createMock(IJobList::class);
+	}
+
+	/**
+	 * @param string $body
+	 * @param string $contentType
+	 * @param string $result
+	 *
+	 * @dataProvider runDataProvider
+	 */
+	public function testRun(string $body, string $contentType, string $result) {
+		$backgroundJob = new RefreshWebcalJob($this->caldavBackend,
+			$this->clientService, $this->config, $this->logger, $this->timeFactory);
+
+		$backgroundJob->setArgument([
+			'principaluri' => 'principals/users/testuser',
+			'uri' => 'sub123',
+		]);
+		$backgroundJob->setLastRun(0);
+
+		$this->timeFactory->expects($this->once())
+			->method('getTime')
+			->with()
+			->will($this->returnValue(1000000000));
+
+		$this->caldavBackend->expects($this->exactly(2))
+			->method('getSubscriptionsForUser')
+			->with('principals/users/testuser')
+			->will($this->returnValue([
+				[
+					'id' => 99,
+					'uri' => 'sub456',
+					'refreshreate' => 'P1D',
+					'striptodos' => 1,
+					'stripalarms' => 1,
+					'stripattachments' => 1,
+					'source' => 'webcal://foo.bar/bla'
+				],
+				[
+					'id' => 42,
+					'uri' => 'sub123',
+					'refreshreate' => 'P1H',
+					'striptodos' => 1,
+					'stripalarms' => 1,
+					'stripattachments' => 1,
+					'source' => 'webcal://foo.bar/bla2'
+				],
+			]));
+
+		$client = $this->createMock(IClient::class);
+		$response = $this->createMock(IResponse::class);
+		$this->clientService->expects($this->once())
+			->method('newClient')
+			->with()
+			->will($this->returnValue($client));
+
+		$this->config->expects($this->once())
+			->method('getAppValue')
+			->with('dav', 'webcalAllowLocalAccess', 'no')
+			->will($this->returnValue('no'));
+
+		$client->expects($this->once())
+			->method('get')
+			->with('https://foo.bar/bla2', $this->callback(function($obj) {
+				return $obj['allow_redirects']['redirects'] === 10 && $obj['handler'] instanceof HandlerStack;
+			}))
+			->will($this->returnValue($response));
+
+		$response->expects($this->once())
+			->method('getBody')
+			->with()
+			->will($this->returnValue($body));
+		$response->expects($this->once())
+			->method('getHeader')
+			->with('Content-Type')
+			->will($this->returnValue($contentType));
+
+		$this->caldavBackend->expects($this->once())
+			->method('purgeAllCachedEventsForSubscription')
+			->with(42);
+
+		$this->caldavBackend->expects($this->once())
+			->method('createCalendarObject')
+			->with(42, '12345.ics', $result, 1);
+
+		$backgroundJob->execute($this->jobList, $this->logger);
+	}
+
+	/**
+	 * @return array
+	 */
+	public function runDataProvider():array {
+		return [
+			[
+				"BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Sabre//Sabre VObject 4.1.1//EN\r\nCALSCALE:GREGORIAN\r\nBEGIN:VEVENT\r\nUID:12345\r\nDTSTAMP:20160218T133704Z\r\nDTSTART;VALUE=DATE:19000101\r\nDTEND;VALUE=DATE:19000102\r\nRRULE:FREQ=YEARLY\r\nSUMMARY:12345's Birthday (1900)\r\nTRANSP:TRANSPARENT\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n",
+				'text/calendar;charset=utf8',
+				"BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Sabre//Sabre VObject " . VObject\Version::VERSION . "//EN\r\nCALSCALE:GREGORIAN\r\nBEGIN:VEVENT\r\nUID:12345\r\nDTSTAMP:20160218T133704Z\r\nDTSTART;VALUE=DATE:19000101\r\nDTEND;VALUE=DATE:19000102\r\nRRULE:FREQ=YEARLY\r\nSUMMARY:12345's Birthday (1900)\r\nTRANSP:TRANSPARENT\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n",
+			],
+			[
+				'["vcalendar",[["prodid",{},"text","-//Example Corp.//Example Client//EN"],["version",{},"text","2.0"]],[["vtimezone",[["last-modified",{},"date-time","2004-01-10T03:28:45Z"],["tzid",{},"text","US/Eastern"]],[["daylight",[["dtstart",{},"date-time","2000-04-04T02:00:00"],["rrule",{},"recur",{"freq":"YEARLY","byday":"1SU","bymonth":4}],["tzname",{},"text","EDT"],["tzoffsetfrom",{},"utc-offset","-05:00"],["tzoffsetto",{},"utc-offset","-04:00"]],[]],["standard",[["dtstart",{},"date-time","2000-10-26T02:00:00"],["rrule",{},"recur",{"freq":"YEARLY","byday":"1SU","bymonth":10}],["tzname",{},"text","EST"],["tzoffsetfrom",{},"utc-offset","-04:00"],["tzoffsetto",{},"utc-offset","-05:00"]],[]]]],["vevent",[["dtstamp",{},"date-time","2006-02-06T00:11:21Z"],["dtstart",{"tzid":"US/Eastern"},"date-time","2006-01-02T14:00:00"],["duration",{},"duration","PT1H"],["recurrence-id",{"tzid":"US/Eastern"},"date-time","2006-01-04T12:00:00"],["summary",{},"text","Event #2"],["uid",{},"text","12345"]],[]]]]',
+				'application/calendar+json',
+				"BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Sabre//Sabre VObject " . VObject\Version::VERSION . "//EN\r\nCALSCALE:GREGORIAN\r\nBEGIN:VTIMEZONE\r\nLAST-MODIFIED:20040110T032845Z\r\nTZID:US/Eastern\r\nBEGIN:DAYLIGHT\r\nDTSTART:20000404T020000\r\nRRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4\r\nTZNAME:EDT\r\nTZOFFSETFROM:-0500\r\nTZOFFSETTO:-0400\r\nEND:DAYLIGHT\r\nBEGIN:STANDARD\r\nDTSTART:20001026T020000\r\nRRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=10\r\nTZNAME:EST\r\nTZOFFSETFROM:-0400\r\nTZOFFSETTO:-0500\r\nEND:STANDARD\r\nEND:VTIMEZONE\r\nBEGIN:VEVENT\r\nDTSTAMP:20060206T001121Z\r\nDTSTART;TZID=US/Eastern:20060102T140000\r\nDURATION:PT1H\r\nRECURRENCE-ID;TZID=US/Eastern:20060104T120000\r\nSUMMARY:Event #2\r\nUID:12345\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n"
+			],
+			[
+				'<?xml version="1.0" encoding="utf-8" ?><icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0"><vcalendar><properties><prodid><text>-//Example Inc.//Example Client//EN</text></prodid><version><text>2.0</text></version></properties><components><vevent><properties><dtstamp><date-time>2006-02-06T00:11:21Z</date-time></dtstamp><dtstart><parameters><tzid><text>US/Eastern</text></tzid></parameters><date-time>2006-01-04T14:00:00</date-time></dtstart><duration><duration>PT1H</duration></duration><recurrence-id><parameters><tzid><text>US/Eastern</text></tzid></parameters><date-time>2006-01-04T12:00:00</date-time></recurrence-id><summary><text>Event #2 bis</text></summary><uid><text>12345</text></uid></properties></vevent></components></vcalendar></icalendar>',
+				'application/calendar+xml',
+				"BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Sabre//Sabre VObject " . VObject\Version::VERSION . "//EN\r\nCALSCALE:GREGORIAN\r\nBEGIN:VEVENT\r\nDTSTAMP:20060206T001121Z\r\nDTSTART;TZID=US/Eastern:20060104T140000\r\nDURATION:PT1H\r\nRECURRENCE-ID;TZID=US/Eastern:20060104T120000\r\nSUMMARY:Event #2 bis\r\nUID:12345\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n"
+			]
+		];
+	}
+
+	/**
+	 * @dataProvider runLocalURLDataProvider
+	 *
+	 * @param string $source
+	 */
+	public function testRunLocalURL($source) {
+		$backgroundJob = new RefreshWebcalJob($this->caldavBackend,
+			$this->clientService, $this->config, $this->logger, $this->timeFactory);
+
+		$backgroundJob->setArgument([
+			'principaluri' => 'principals/users/testuser',
+			'uri' => 'sub123',
+		]);
+		$backgroundJob->setLastRun(0);
+
+		$this->timeFactory->expects($this->once())
+			->method('getTime')
+			->with()
+			->will($this->returnValue(1000000000));
+
+		$this->caldavBackend->expects($this->exactly(2))
+			->method('getSubscriptionsForUser')
+			->with('principals/users/testuser')
+			->will($this->returnValue([
+				[
+					'id' => 42,
+					'uri' => 'sub123',
+					'refreshreate' => 'P1H',
+					'striptodos' => 1,
+					'stripalarms' => 1,
+					'stripattachments' => 1,
+					'source' => $source
+				],
+			]));
+
+		$client = $this->createMock(IClient::class);
+		$this->clientService->expects($this->once())
+			->method('newClient')
+			->with()
+			->will($this->returnValue($client));
+
+		$this->config->expects($this->once())
+			->method('getAppValue')
+			->with('dav', 'webcalAllowLocalAccess', 'no')
+			->will($this->returnValue('no'));
+
+		$client->expects($this->never())
+			->method('get');
+
+		$backgroundJob->execute($this->jobList, $this->logger);
+	}
+
+	public function runLocalURLDataProvider():array {
+		return [
+			['localhost/foo.bar'],
+			['[::1]/bla.blub'],
+			['192.168.0.1'],
+			['10.0.0.1'],
+			['another-host.local'],
+			['service.localhost'],
+			['!@#$'], // test invalid url
+		];
+	}
+}
diff --git a/apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php b/apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php
index d49e3bdc778..63d48910f8b 100644
--- a/apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php
+++ b/apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php
@@ -35,6 +35,7 @@ use OCP\IUserSession;
 use OCP\Security\ISecureRandom;
 use OCP\Share\IManager as ShareManager;
 use Sabre\CalDAV\Xml\Property\SupportedCalendarComponentSet;
+use Sabre\DAV\Xml\Property\Href;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Test\TestCase;
 
@@ -151,6 +152,20 @@ abstract class AbstractCalDavBackend extends TestCase {
 		return $calendarId;
 	}
 
+	protected function createTestSubscription() {
+		$this->backend->createSubscription(self::UNIT_TEST_USER, 'Example', [
+			'{http://apple.com/ns/ical/}calendar-color' => '#1C4587FF',
+			'{http://calendarserver.org/ns/}source' => new Href(['foo']),
+		]);
+		$calendars = $this->backend->getSubscriptionsForUser(self::UNIT_TEST_USER);
+		$this->assertEquals(1, count($calendars));
+		$this->assertEquals(self::UNIT_TEST_USER, $calendars[0]['principaluri']);
+		$this->assertEquals('Example', $calendars[0]['uri']);
+		$calendarId = $calendars[0]['id'];
+
+		return $calendarId;
+	}
+
 	protected function createEvent($calendarId, $start = '20130912T130000Z', $end = '20130912T140000Z') {
 
 		$randomPart = self::getUniqueID();
diff --git a/apps/dav/tests/unit/CalDAV/CachedSubscriptionObjectTest.php b/apps/dav/tests/unit/CalDAV/CachedSubscriptionObjectTest.php
new file mode 100644
index 00000000000..131c3011e46
--- /dev/null
+++ b/apps/dav/tests/unit/CalDAV/CachedSubscriptionObjectTest.php
@@ -0,0 +1,95 @@
+<?php
+/**
+ * @copyright Copyright (c) 2018 Georg Ehrke
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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\Tests\unit\CalDAV;
+
+use OCA\DAV\CalDAV\CachedSubscriptionObject;
+use OCA\DAV\CalDAV\CalDavBackend;
+use OCA\DAV\CalDAV\Calendar;
+use OCA\DAV\CalDAV\CalendarImpl;
+
+class CachedSubscriptionObjectTest extends \Test\TestCase {
+
+	public function testGet() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+		$objectData = [
+			'uri' => 'foo123'
+		];
+
+		$backend->expects($this->once())
+			->method('getCalendarObject')
+			->with(666, 'foo123', 1)
+			->will($this->returnValue([
+				'calendardata' => 'BEGIN...',
+			]));
+
+		$calendarObject = new CachedSubscriptionObject($backend, $calendarInfo, $objectData);
+		$this->assertEquals('BEGIN...', $calendarObject->get());
+	}
+
+	/**
+	 * @expectedException \Sabre\DAV\Exception\MethodNotAllowed
+	 * @expectedExceptionMessage Creating objects in a cached subscription is not allowed
+	 */
+	public function testPut() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+		$objectData = [
+			'uri' => 'foo123'
+		];
+
+		$calendarObject = new CachedSubscriptionObject($backend, $calendarInfo, $objectData);
+		$calendarObject->put('');
+	}
+
+	/**
+	 * @expectedException \Sabre\DAV\Exception\MethodNotAllowed
+	 * @expectedExceptionMessage Deleting objects in a cached subscription is not allowed
+	 */
+	public function testDelete() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+		$objectData = [
+			'uri' => 'foo123'
+		];
+
+		$calendarObject = new CachedSubscriptionObject($backend, $calendarInfo, $objectData);
+		$calendarObject->delete();
+	}
+
+}
\ No newline at end of file
diff --git a/apps/dav/tests/unit/CalDAV/CachedSubscriptionTest.php b/apps/dav/tests/unit/CalDAV/CachedSubscriptionTest.php
new file mode 100644
index 00000000000..82f9af364da
--- /dev/null
+++ b/apps/dav/tests/unit/CalDAV/CachedSubscriptionTest.php
@@ -0,0 +1,300 @@
+<?php
+/**
+ * @copyright Copyright (c) 2018 Georg Ehrke
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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\Tests\unit\CalDAV;
+
+use OCA\DAV\CalDAV\CachedSubscription;
+use OCA\DAV\CalDAV\CachedSubscriptionObject;
+use OCA\DAV\CalDAV\CalDavBackend;
+use Sabre\DAV\PropPatch;
+
+class CachedSubscriptionTest extends \Test\TestCase {
+
+	public function testGetACL() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+		$this->assertEquals([
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => 'user1',
+				'protected' => true,
+			],
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => 'user1/calendar-proxy-write',
+				'protected' => true,
+			],
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => 'user1/calendar-proxy-read',
+				'protected' => true,
+			],
+			[
+				'privilege' => '{urn:ietf:params:xml:ns:caldav}read-free-busy',
+				'principal' => '{DAV:}authenticated',
+				'protected' => true,
+			],
+		], $calendar->getACL());
+	}
+
+	public function testGetChildACL() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+		$this->assertEquals([
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => 'user1',
+				'protected' => true,
+			],
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => 'user1/calendar-proxy-write',
+				'protected' => true,
+			],
+			[
+				'privilege' => '{DAV:}read',
+				'principal' => 'user1/calendar-proxy-read',
+				'protected' => true,
+			]
+		], $calendar->getChildACL());
+	}
+
+	public function testGetOwner() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+		$this->assertEquals('user1', $calendar->getOwner());
+	}
+
+	public function testDelete() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$backend->expects($this->once())
+			->method('deleteSubscription')
+			->with(666);
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+		$calendar->delete();
+	}
+
+	public function testPropPatch() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+		$propPatch = $this->createMock(PropPatch::class);
+
+		$backend->expects($this->once())
+			->method('updateSubscription')
+			->with(666, $propPatch);
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+		$calendar->propPatch($propPatch);
+	}
+
+	/**
+	 * @expectedException \Sabre\DAV\Exception\NotFound
+	 * @expectedExceptionMessage Calendar object not found
+	 */
+	public function testGetChild() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$backend->expects($this->at(0))
+			->method('getCalendarObject')
+			->with(666, 'foo1', 1)
+			->will($this->returnValue([
+				'id' => 99,
+				'uri' => 'foo1'
+			]));
+		$backend->expects($this->at(1))
+			->method('getCalendarObject')
+			->with(666, 'foo2', 1)
+			->will($this->returnValue(null));
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+
+		$first = $calendar->getChild('foo1');
+		$this->assertInstanceOf(CachedSubscriptionObject::class, $first);
+
+		$calendar->getChild('foo2');
+	}
+
+	public function testGetChildren() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$backend->expects($this->at(0))
+			->method('getCalendarObjects')
+			->with(666, 1)
+			->will($this->returnValue([
+				[
+					'id' => 99,
+					'uri' => 'foo1'
+				],
+				[
+					'id' => 100,
+					'uri' => 'foo2'
+				],
+			]));
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+
+		$res = $calendar->getChildren();
+		$this->assertCount(2, $res);
+		$this->assertInstanceOf(CachedSubscriptionObject::class, $res[0]);
+		$this->assertInstanceOf(CachedSubscriptionObject::class, $res[1]);
+	}
+
+	public function testGetMultipleChildren() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$backend->expects($this->at(0))
+			->method('getMultipleCalendarObjects')
+			->with(666, ['foo1', 'foo2'], 1)
+			->will($this->returnValue([
+				[
+					'id' => 99,
+					'uri' => 'foo1'
+				],
+				[
+					'id' => 100,
+					'uri' => 'foo2'
+				],
+			]));
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+
+		$res = $calendar->getMultipleChildren(['foo1', 'foo2']);
+		$this->assertCount(2, $res);
+		$this->assertInstanceOf(CachedSubscriptionObject::class, $res[0]);
+		$this->assertInstanceOf(CachedSubscriptionObject::class, $res[1]);
+	}
+
+	/**
+	 * @expectedException \Sabre\DAV\Exception\MethodNotAllowed
+	 * @expectedExceptionMessage Creating objects in cached subscription is not allowed
+	 */
+	public function testCreateFile() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+		$calendar->createFile('foo', []);
+	}
+
+	public function testChildExists() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$backend->expects($this->at(0))
+			->method('getCalendarObject')
+			->with(666, 'foo1', 1)
+			->will($this->returnValue([
+				'id' => 99,
+				'uri' => 'foo1'
+			]));
+		$backend->expects($this->at(1))
+			->method('getCalendarObject')
+			->with(666, 'foo2', 1)
+			->will($this->returnValue(null));
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+
+		$this->assertEquals(true, $calendar->childExists('foo1'));
+		$this->assertEquals(false, $calendar->childExists('foo2'));
+	}
+
+	public function testCalendarQuery() {
+		$backend = $this->createMock(CalDavBackend::class);
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666,
+			'uri' => 'cal',
+		];
+
+		$backend->expects($this->once())
+			->method('calendarQuery')
+			->with(666, ['foo'], 1)
+			->will($this->returnValue([99]));
+
+		$calendar = new CachedSubscription($backend, $calendarInfo);
+
+		$this->assertEquals([99], $calendar->calendarQuery(['foo']));
+	}
+}
diff --git a/apps/dav/tests/unit/CalDAV/CalDavBackendTest.php b/apps/dav/tests/unit/CalDAV/CalDavBackendTest.php
index 26439df4a01..44609f2ca6c 100644
--- a/apps/dav/tests/unit/CalDAV/CalDavBackendTest.php
+++ b/apps/dav/tests/unit/CalDAV/CalDavBackendTest.php
@@ -911,4 +911,76 @@ EOD;
 			[true, 2],
 		];
 	}
+
+	public function testSameUriSameIdForDifferentCalendarTypes() {
+		$calendarId = $this->createTestCalendar();
+		$subscriptionId = $this->createTestSubscription();
+
+		$uri = static::getUniqueID('calobj');
+		$calData = <<<EOD
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:ownCloud Calendar
+BEGIN:VEVENT
+CREATED;VALUE=DATE-TIME:20130910T125139Z
+UID:47d15e3ec8
+LAST-MODIFIED;VALUE=DATE-TIME:20130910T125139Z
+DTSTAMP;VALUE=DATE-TIME:20130910T125139Z
+SUMMARY:Test Event
+DTSTART;VALUE=DATE-TIME:20130912T130000Z
+DTEND;VALUE=DATE-TIME:20130912T140000Z
+CLASS:PUBLIC
+END:VEVENT
+END:VCALENDAR
+EOD;
+
+		$calData2 = <<<EOD
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:ownCloud Calendar
+BEGIN:VEVENT
+CREATED;VALUE=DATE-TIME:20130910T125139Z
+UID:47d15e3ec8
+LAST-MODIFIED;VALUE=DATE-TIME:20130910T125139Z
+DTSTAMP;VALUE=DATE-TIME:20130910T125139Z
+SUMMARY:Test Event 123
+DTSTART;VALUE=DATE-TIME:20130912T130000Z
+DTEND;VALUE=DATE-TIME:20130912T140000Z
+CLASS:PUBLIC
+END:VEVENT
+END:VCALENDAR
+EOD;
+
+		$this->backend->createCalendarObject($calendarId, $uri, $calData);
+		$this->backend->createCalendarObject($subscriptionId, $uri, $calData2, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+
+		$this->assertEquals($calData, $this->backend->getCalendarObject($calendarId, $uri, CalDavBackend::CALENDAR_TYPE_CALENDAR)['calendardata']);
+		$this->assertEquals($calData2, $this->backend->getCalendarObject($subscriptionId, $uri, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION)['calendardata']);
+	}
+
+	public function testPurgeAllCachedEventsForSubscription() {
+		$subscriptionId = $this->createTestSubscription();
+		$uri = static::getUniqueID('calobj');
+		$calData = <<<EOD
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:ownCloud Calendar
+BEGIN:VEVENT
+CREATED;VALUE=DATE-TIME:20130910T125139Z
+UID:47d15e3ec8
+LAST-MODIFIED;VALUE=DATE-TIME:20130910T125139Z
+DTSTAMP;VALUE=DATE-TIME:20130910T125139Z
+SUMMARY:Test Event
+DTSTART;VALUE=DATE-TIME:20130912T130000Z
+DTEND;VALUE=DATE-TIME:20130912T140000Z
+CLASS:PUBLIC
+END:VEVENT
+END:VCALENDAR
+EOD;
+
+		$this->backend->createCalendarObject($subscriptionId, $uri, $calData, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+		$this->backend->purgeAllCachedEventsForSubscription($subscriptionId);
+
+		$this->assertEquals(null, $this->backend->getCalendarObject($subscriptionId, $uri, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION));
+	}
 }
diff --git a/apps/dav/tests/unit/CalDAV/WebcalCaching/PluginTest.php b/apps/dav/tests/unit/CalDAV/WebcalCaching/PluginTest.php
new file mode 100644
index 00000000000..87f11a5c29d
--- /dev/null
+++ b/apps/dav/tests/unit/CalDAV/WebcalCaching/PluginTest.php
@@ -0,0 +1,63 @@
+<?php
+/**
+ * @copyright Copyright (c) 2018 Georg Ehrke
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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\Tests\unit\CalDAV\WebcalCaching;
+
+use OCA\DAV\CalDAV\WebcalCaching\Plugin;
+use OCP\IRequest;
+
+class PluginTest extends \Test\TestCase {
+
+	public function testDisabled() {
+		$request = $this->createMock(IRequest::class);
+		$request->expects($this->at(0))
+			->method('isUserAgent')
+			->with([])
+			->will($this->returnValue(false));
+
+		$request->expects($this->at(1))
+			->method('getHeader')
+			->with('X-NC-CalDAV-Webcal-Caching')
+			->will($this->returnValue(''));
+
+		$plugin = new Plugin($request);
+
+		$this->assertEquals(false, $plugin->isCachingEnabledForThisRequest());
+	}
+
+	public function testEnabled() {
+		$request = $this->createMock(IRequest::class);
+		$request->expects($this->at(0))
+			->method('isUserAgent')
+			->with([])
+			->will($this->returnValue(false));
+
+		$request->expects($this->at(1))
+			->method('getHeader')
+			->with('X-NC-CalDAV-Webcal-Caching')
+			->will($this->returnValue('On'));
+
+		$plugin = new Plugin($request);
+
+		$this->assertEquals(true, $plugin->isCachingEnabledForThisRequest());
+	}
+}
diff --git a/apps/dav/tests/unit/Migration/RefreshWebcalJobRegistrarTest.php b/apps/dav/tests/unit/Migration/RefreshWebcalJobRegistrarTest.php
new file mode 100644
index 00000000000..1bd7ab4e232
--- /dev/null
+++ b/apps/dav/tests/unit/Migration/RefreshWebcalJobRegistrarTest.php
@@ -0,0 +1,146 @@
+<?php
+/**
+ * @copyright Copyright (c) 2018, Georg Ehrke
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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\Tests\unit\DAV\Migration;
+
+use OCA\DAV\BackgroundJob\RefreshWebcalJob;
+use OCA\DAV\Migration\RefreshWebcalJobRegistrar;
+use OCP\BackgroundJob\IJobList;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+use OCP\Migration\IOutput;
+use Test\TestCase;
+
+class RefreshWebcalJobRegistrarTest extends TestCase {
+
+	/** @var IDBConnection | \PHPUnit_Framework_MockObject_MockObject */
+	private $db;
+
+	/** @var IJobList | \PHPUnit_Framework_MockObject_MockObject */
+	private $jobList;
+
+	/** @var RefreshWebcalJobRegistrar */
+	private $migration;
+
+	protected function setUp() {
+		parent::setUp();
+
+		$this->db = $this->createMock(IDBConnection::class);
+		$this->jobList = $this->createMock(IJobList::class);
+
+		$this->migration = new RefreshWebcalJobRegistrar($this->db, $this->jobList);
+	}
+
+	public function testGetName() {
+		$this->assertEquals($this->migration->getName(), 'Registering background jobs to update cache for webcal calendars');
+	}
+
+	public function testRun() {
+		$output = $this->createMock(IOutput::class);
+
+		$queryBuilder = $this->createMock(IQueryBuilder::class);
+		$statement = $this->createMock(\Doctrine\DBAL\Driver\Statement::class);
+
+		$this->db->expects($this->once())
+			->method('getQueryBuilder')
+			->will($this->returnValue($queryBuilder));
+
+		$queryBuilder->expects($this->at(0))
+			->method('select')
+			->with(['principaluri', 'uri'])
+			->will($this->returnValue($queryBuilder));
+		$queryBuilder->expects($this->at(1))
+			->method('from')
+			->with('calendarsubscriptions')
+			->will($this->returnValue($queryBuilder));
+		$queryBuilder->expects($this->at(2))
+			->method('execute')
+			->will($this->returnValue($statement));
+
+		$statement->expects($this->at(0))
+			->method('fetch')
+			->with(\PDO::FETCH_ASSOC)
+			->will($this->returnValue([
+				'principaluri' => 'foo1',
+				'uri' => 'bar1',
+			]));
+		$statement->expects($this->at(1))
+			->method('fetch')
+			->with(\PDO::FETCH_ASSOC)
+			->will($this->returnValue([
+				'principaluri' => 'foo2',
+				'uri' => 'bar2',
+			]));
+		$statement->expects($this->at(2))
+			->method('fetch')
+			->with(\PDO::FETCH_ASSOC)
+			->will($this->returnValue([
+				'principaluri' => 'foo3',
+				'uri' => 'bar3',
+			]));
+		$statement->expects($this->at(0))
+			->method('fetch')
+			->with(\PDO::FETCH_ASSOC)
+			->will($this->returnValue(null));
+
+		$this->jobList->expects($this->at(0))
+			->method('has')
+			->with(RefreshWebcalJob::class, [
+				'principaluri' => 'foo1',
+				'uri' => 'bar1',
+			])
+			->will($this->returnValue(false));
+		$this->jobList->expects($this->at(1))
+			->method('add')
+			->with(RefreshWebcalJob::class, [
+				'principaluri' => 'foo1',
+				'uri' => 'bar1',
+			]);
+		$this->jobList->expects($this->at(2))
+			->method('has')
+			->with(RefreshWebcalJob::class, [
+				'principaluri' => 'foo2',
+				'uri' => 'bar2',
+			])
+			->will($this->returnValue(true));
+		$this->jobList->expects($this->at(3))
+			->method('has')
+			->with(RefreshWebcalJob::class, [
+				'principaluri' => 'foo3',
+				'uri' => 'bar3',
+			])
+			->will($this->returnValue(false));
+		$this->jobList->expects($this->at(4))
+			->method('add')
+			->with(RefreshWebcalJob::class, [
+				'principaluri' => 'foo3',
+				'uri' => 'bar3',
+			]);
+
+		$output->expects($this->once())
+			->method('info')
+			->with('Added 2 background jobs to update webcal calendars');
+
+		$this->migration->run($output);
+	}
+
+}