diff --git a/plugins/kolab_addressbook/drivers/carddav/carddav_contacts_driver.php b/plugins/kolab_addressbook/drivers/carddav/carddav_contacts_driver.php
index 1a656be7..006a54e2 100644
--- a/plugins/kolab_addressbook/drivers/carddav/carddav_contacts_driver.php
+++ b/plugins/kolab_addressbook/drivers/carddav/carddav_contacts_driver.php
@@ -1,202 +1,214 @@
 <?php
 
 /**
  * Backend class for a custom address book using CardDAV service.
  *
  * @author Aleksander Machniak <machniak@apheleia-it.chm>
  *
  * Copyright (C) 2011-2022, Apheleia IT AG <contact@apheleia-it.ch>
  *
  * 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/>.
  *
  * @see rcube_addressbook
  */
 
 class carddav_contacts_driver
 {
     protected $plugin;
     protected $rc;
+    protected $sources;
 
     public function __construct($plugin)
     {
         $this->plugin = $plugin;
         $this->rc     = rcube::get_instance();
     }
 
     /**
      * List addressbook sources (folders)
      */
-    public static function list_folders()
+    public function list_folders()
     {
+        if (isset($this->sources)) {
+            return $this->sources;
+        }
+
         $storage = self::get_storage();
-        $sources = [];
+        $this->sources = [];
 
         // get all folders that have "contact" type
         foreach ($storage->get_folders('contact') as $folder) {
-            $sources[$folder->id] = new carddav_contacts($folder);
+            $this->sources[$folder->id] = new carddav_contacts($folder);
         }
 
-        return $sources;
+        return $this->sources;
     }
 
     /**
      * Getter for the rcube_addressbook instance
      *
      * @param string $id Addressbook (folder) ID
      *
      * @return ?carddav_contacts
      */
-    public static function get_address_book($id)
+    public function get_address_book($id)
     {
+        if (isset($this->sources[$id])) {
+            return $this->sources[$id];
+        }
+
         $storage = self::get_storage();
         $folder = $storage->get_folder($id, 'contact');
 
         if ($folder) {
             return new carddav_contacts($folder);
         }
     }
 
     /**
      * Initialize kolab_storage_dav instance
      */
     protected static function get_storage()
     {
         $rcube = rcube::get_instance();
         $url   = $rcube->config->get('kolab_addressbook_carddav_server', 'http://localhost');
 
         return new kolab_storage_dav($url);
     }
 
     /**
      * Delete address book folder
      *
      * @param string $source Addressbook identifier
      *
      * @return bool
      */
     public function folder_delete($folder)
     {
         $storage = self::get_storage();
 
+        $this->sources = null;
+
         return $storage->folder_delete($folder, 'contact');
     }
 
     /**
      * Address book folder form content for book create/edit
      *
      * @param string $action Action name (edit, create)
      * @param string $source Addressbook identifier
      *
      * @return string HTML output
      */
     public function folder_form($action, $source)
     {
         $name = '';
 
         if ($source && ($book = $this->get_address_book($source))) {
             $name = $book->get_name();
         }
 
         $foldername = new html_inputfield(['name' => '_name', 'id' => '_name', 'size' => 30]);
         $foldername = $foldername->show($name);
 
         // General tab
         $form = [
             'properties' => [
                 'name'   => $this->rc->gettext('properties'),
                 'fields' => [
                     'name' => [
                         'label' => $this->plugin->gettext('bookname'),
                         'value' => $foldername,
                         'id'    => '_name',
                     ],
                 ],
             ],
         ];
 
         $hidden_fields = [['name' => '_source', 'value' => $source]];
 
         return kolab_utils::folder_form($form, '', 'contacts', $hidden_fields, false);
     }
 
     /**
      * Handler for address book create/edit form submit
      */
     public function folder_save()
     {
         $storage = self::get_storage();
 
         $prop  = [
             'id'   => trim(rcube_utils::get_input_value('_source', rcube_utils::INPUT_POST)),
             'name' => trim(rcube_utils::get_input_value('_name', rcube_utils::INPUT_POST)),
             'type' => 'contact',
             'subscribed' => true,
         ];
 
         $type = !empty($prop['id']) ? 'update' : 'create';
 
-        if (
-            ($result = $storage->folder_update($prop))
-            && ($abook = $this->get_address_book($prop['id'] ?: $result))
-        ) {
+        $this->sources = null;
+
+        $result = $storage->folder_update($prop);
+
+        if ($result && ($abook = $this->get_address_book($prop['id'] ?: $result))) {
             $abook->id = $prop['id'] ?: $result;
             $props = $this->abook_prop($abook->id, $abook);
 
             $this->rc->output->show_message('kolab_addressbook.book'.$type.'d', 'confirmation');
             $this->rc->output->command('book_update', $props, $prop['id']);
         }
         else {
             $this->rc->output->show_message('kolab_addressbook.book'.$type.'error', 'error');
         }
     }
 
     /**
      * Helper method to build a hash array of address book properties
      */
     public function abook_prop($id, $abook)
     {
 /*
         if ($abook->virtual) {
             return [
                 'id'       => $id,
                 'name'     => $abook->get_name(),
                 'listname' => $abook->get_foldername(),
                 'group'    => $abook instanceof kolab_storage_folder_user ? 'user' : $abook->get_namespace(),
                 'readonly' => true,
                 'rights'   => 'l',
                 'kolab'    => true,
                 'virtual'  => true,
                 'carddav'  => true,
             ];
         }
 */
         return [
             'id'         => $id,
             'name'       => $abook->get_name(),
             'listname'   => $abook->get_foldername(),
             'readonly'   => $abook->readonly,
             'rights'     => $abook->rights,
             'groups'     => $abook->groups,
             'undelete'   => $abook->undelete && $this->rc->config->get('undo_timeout'),
             'realname'   => rcube_charset::convert($abook->get_realname(), 'UTF7-IMAP'), // IMAP folder name
             'group'      => $abook->get_namespace(),
             'subscribed' => $abook->is_subscribed(),
             'carddavurl' => $abook->get_carddav_url(),
             'removable'  => true,
             'kolab'      => true,
             'carddav'    => true,
             'audittrail' => false, // !empty($this->plugin->bonnie_api),
         ];
     }
 }
diff --git a/plugins/libkolab/lib/kolab_dav_client.php b/plugins/libkolab/lib/kolab_dav_client.php
index 79c23be8..1659372b 100644
--- a/plugins/libkolab/lib/kolab_dav_client.php
+++ b/plugins/libkolab/lib/kolab_dav_client.php
@@ -1,776 +1,802 @@
 <?php
 
 /**
  * A *DAV client.
  *
  * @author Aleksander Machniak <machniak@apheleia-it.ch>
  *
  * Copyright (C) 2022, Apheleia IT AG <contact@apheleia-it.ch>
  *
  * 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/>.
  */
 
 class kolab_dav_client
 {
     public $url;
 
     protected $user;
     protected $password;
     protected $rc;
     protected $responseHeaders = [];
 
     /**
      * Object constructor
      */
     public function __construct($url)
     {
         $this->rc = rcube::get_instance();
 
         $parsedUrl = parse_url($url);
 
         if (!empty($parsedUrl['user']) && !empty($parsedUrl['pass'])) {
             $this->user     = rawurldecode($parsedUrl['user']);
             $this->password = rawurldecode($parsedUrl['pass']);
 
             $url = str_replace(rawurlencode($this->user) . ':' . rawurlencode($this->password) . '@', '', $url);
         }
         else {
             $this->user     = $this->rc->user->get_username();
             $this->password = $this->rc->decrypt($_SESSION['password']);
         }
 
         $this->url = $url;
     }
 
     /**
      * Execute HTTP request to a DAV server
      */
     protected function request($path, $method, $body = '', $headers = [])
     {
         $rcube = rcube::get_instance();
         $debug = (array) $rcube->config->get('dav_debug');
 
         $request_config = [
             'store_body'       => true,
             'follow_redirects' => true,
         ];
 
         $this->responseHeaders = [];
 
         if ($path && ($rootPath = parse_url($this->url, PHP_URL_PATH)) && strpos($path, $rootPath) === 0) {
             $path = substr($path, strlen($rootPath));
         }
 
         try {
             $request = $this->initRequest($this->url . $path, $method, $request_config);
 
             $request->setAuth($this->user, $this->password);
 
             if ($body) {
                 $request->setBody($body);
                 $request->setHeader(['Content-Type' => 'application/xml; charset=utf-8']);
             }
 
             if (!empty($headers)) {
                 $request->setHeader($headers);
             }
 
             if ($debug) {
                 rcube::write_log('dav', "C: {$method}: " . (string) $request->getUrl()
                      . "\n" . $this->debugBody($body, $request->getHeaders()));
             }
 
             $response = $request->send();
 
             $body = $response->getBody();
             $code = $response->getStatus();
 
             if ($debug) {
                 rcube::write_log('dav', "S: [{$code}]\n" . $this->debugBody($body, $response->getHeader()));
             }
 
             if ($code >= 300) {
                 throw new Exception("DAV Error ($code):\n{$body}");
             }
 
             $this->responseHeaders = $response->getHeader();
 
             return $this->parseXML($body);
         }
         catch (Exception $e) {
             rcube::raise_error($e, true, false);
             return false;
         }
     }
 
     /**
      * Discover DAV home (root) collection of specified type.
      *
      * @param string $component Component to filter by (VEVENT, VTODO, VCARD)
      *
      * @return string|false Home collection location or False on error
      */
     public function discover($component = 'VEVENT')
     {
+        if ($cache = $this->get_cache()) {
+            $cache_key = "discover.{$component}." . md5($this->url);
+
+            if ($response = $cache->get($cache_key)) {
+                return $response;
+            }
+        }
+
         $roots = [
             'VEVENT' => 'calendars',
             'VTODO' => 'calendars',
             'VCARD' => 'addressbooks',
         ];
 
         $path = parse_url($this->url, PHP_URL_PATH);
 
         $body = '<?xml version="1.0" encoding="utf-8"?>'
             . '<d:propfind xmlns:d="DAV:">'
                 . '<d:prop>'
                     . '<d:current-user-principal />'
                 . '</d:prop>'
             . '</d:propfind>';
 
         // Note: Cyrus CardDAV service requires Depth:1 (CalDAV works without it)
         $response = $this->request('/' . $roots[$component], 'PROPFIND', $body, ['Depth' => 1, 'Prefer' => 'return-minimal']);
 
         if (empty($response)) {
             return false;
         }
 
         $elements = $response->getElementsByTagName('response');
 
         foreach ($elements as $element) {
             foreach ($element->getElementsByTagName('prop') as $prop) {
                 $principal_href = $prop->nodeValue;
                 break;
             }
         }
 
         if ($path && strpos($principal_href, $path) === 0) {
             $principal_href = substr($principal_href, strlen($path));
         }
 
         $homes = [
             'VEVENT' => 'calendar-home-set',
             'VTODO' => 'calendar-home-set',
             'VCARD' => 'addressbook-home-set',
         ];
 
         $ns = [
             'VEVENT' => 'caldav',
             'VTODO' => 'caldav',
             'VCARD' => 'carddav',
         ];
 
         $body = '<?xml version="1.0" encoding="utf-8"?>'
             . '<d:propfind xmlns:d="DAV:" xmlns:c="urn:ietf:params:xml:ns:' . $ns[$component] . '">'
                 . '<d:prop>'
                     . '<c:' . $homes[$component] . ' />'
                 . '</d:prop>'
             . '</d:propfind>';
 
         $response = $this->request($principal_href, 'PROPFIND', $body);
 
         if (empty($response)) {
             return false;
         }
 
         $elements = $response->getElementsByTagName('response');
 
         foreach ($elements as $element) {
             foreach ($element->getElementsByTagName('prop') as $prop) {
                 $root_href = $prop->nodeValue;
                 break;
             }
         }
 
         if (!empty($root_href)) {
             if ($path && strpos($root_href, $path) === 0) {
                 $root_href = substr($root_href, strlen($path));
             }
         }
         else {
             // Kolab iRony's calendar root
             $root_href = '/' . $roots[$component] . '/' . rawurlencode($this->user);
         }
 
+        if ($cache) {
+            $cache->set($cache_key, $root_href);
+        }
+
         return $root_href;
     }
 
     /**
      * Get list of folders of specified type.
      *
      * @param string $component Component to filter by (VEVENT, VTODO, VCARD)
      *
      * @return false|array List of folders' metadata or False on error
      */
     public function listFolders($component = 'VEVENT')
     {
         $root_href = $this->discover($component);
 
         if ($root_href === false) {
             return false;
         }
 
         $ns    = 'xmlns:d="DAV:" xmlns:cs="http://calendarserver.org/ns/"';
         $props = '';
 
         if ($component != 'VCARD') {
             $ns .= ' xmlns:c="urn:ietf:params:xml:ns:caldav" xmlns:a="http://apple.com/ns/ical/" xmlns:k="Kolab:"';
             $props = '<c:supported-calendar-component-set />'
                 . '<a:calendar-color />'
                 . '<k:alarms />';
         }
 
         $body = '<?xml version="1.0" encoding="utf-8"?>'
             . '<d:propfind ' . $ns . '>'
                 . '<d:prop>'
                     . '<d:resourcetype />'
                     . '<d:displayname />'
                     // . '<d:sync-token />'
                     . '<cs:getctag />'
                     . $props
                 . '</d:prop>'
             . '</d:propfind>';
 
         // Note: Cyrus CardDAV service requires Depth:1 (CalDAV works without it)
         $response = $this->request($root_href, 'PROPFIND', $body, ['Depth' => 1, 'Prefer' => 'return-minimal']);
 
         if (empty($response)) {
             return false;
         }
 
         $folders = [];
         foreach ($response->getElementsByTagName('response') as $element) {
             $folder = $this->getFolderPropertiesFromResponse($element);
 
             // Note: Addressbooks don't have 'type' specified
             if (($component == 'VCARD' && in_array('addressbook', $folder['resource_type']))
                 || $folder['type'] === $component
             ) {
                 $folders[] = $folder;
             }
         }
 
         return $folders;
     }
 
     /**
      * Create a DAV object in a folder
      *
      * @param string $location  Object location
      * @param string $content   Object content
      * @param string $component Content type (VEVENT, VTODO, VCARD)
      *
      * @return false|string|null ETag string (or NULL) on success, False on error
      */
     public function create($location, $content, $component = 'VEVENT')
     {
         $ctype = [
             'VEVENT' => 'text/calendar',
             'VTODO' => 'text/calendar',
             'VCARD' => 'text/vcard',
         ];
 
         $headers = ['Content-Type' => $ctype[$component] . '; charset=utf-8'];
 
         $response = $this->request($location, 'PUT', $content, $headers);
 
         if ($response !== false) {
             $etag = $this->responseHeaders['etag'];
 
             if (preg_match('|^".*"$|', $etag)) {
                 $etag = substr($etag, 1, -1);
             }
 
             return $etag;
         }
 
         return false;
     }
 
     /**
      * Update a DAV object in a folder
      *
      * @param string $location  Object location
      * @param string $content   Object content
      * @param string $component Content type (VEVENT, VTODO, VCARD)
      *
      * @return false|string|null ETag string (or NULL) on success, False on error
      */
     public function update($location, $content, $component = 'VEVENT')
     {
         return $this->create($location, $content, $component);
     }
 
     /**
      * Delete a DAV object from a folder
      *
      * @param string $location Object location
      *
      * @return bool True on success, False on error
      */
     public function delete($location)
     {
         $response = $this->request($location, 'DELETE', '', ['Depth' => 1, 'Prefer' => 'return-minimal']);
 
         return $response !== false;
     }
 
     /**
      * Get folder properties.
      *
      * @param string $location Object location
      *
      * @return false|array Folder metadata or False on error
      */
     public function folderInfo($location)
     {
         $body = '<?xml version="1.0" encoding="utf-8"?>'
             . '<d:propfind xmlns:d="DAV:">'
                 . '<d:allprop/>'
             . '</d:propfind>';
 
         // Note: Cyrus CardDAV service requires Depth:1 (CalDAV works without it)
         $response = $this->request($location, 'PROPFIND', $body, ['Depth' => 1, 'Prefer' => 'return-minimal']);
 
         if (!empty($response)
             && ($element = $response->getElementsByTagName('response'))
             && ($folder = $this->getFolderPropertiesFromResponse($element))
         ) {
             return $folder;
         }
 
         return false;
     }
 
     /**
      * Create a DAV folder
      *
      * @param string $location   Object location (relative to the user home)
      * @param string $component  Content type (VEVENT, VTODO, VCARD)
      * @param array  $properties Object content
      *
      * @return bool True on success, False on error
      */
     public function folderCreate($location, $component, $properties = [])
     {
         // Create the collection
         $response = $this->request($location, 'MKCOL');
 
         if (empty($response)) {
             return false;
         }
 
         // Update collection properties
         return $this->folderUpdate($location, $component, $properties);
     }
 
     /**
      * Delete a DAV folder
      *
      * @param string $location Folder location
      *
      * @return bool True on success, False on error
      */
     public function folderDelete($location)
     {
         $response = $this->request($location, 'DELETE');
 
         return $response !== false;
     }
 
     /**
      * Update a DAV folder
      *
      * @param string $location   Object location
      * @param string $component  Content type (VEVENT, VTODO, VCARD)
      * @param array  $properties Object content
      *
      * @return bool True on success, False on error
      */
     public function folderUpdate($location, $component, $properties = [])
     {
         $ns    = 'xmlns:d="DAV:"';
         $props = '';
 
         if ($component == 'VCARD') {
             $ns .= ' xmlns:c="urn:ietf:params:xml:ns:carddav"';
             // Resourcetype property is protected
             // $props = '<d:resourcetype><d:collection/><c:addressbook/></d:resourcetype>';
         }
         else {
             $ns .= ' xmlns:c="urn:ietf:params:xml:ns:caldav"';
             // Resourcetype property is protected
             // $props = '<d:resourcetype><d:collection/><c:calendar/></d:resourcetype>';
             /*
                 // Note: These are set by Cyrus automatically for calendars
                 . '<c:supported-calendar-component-set>'
                     . '<c:comp name="VEVENT"/>'
                     . '<c:comp name="VTODO"/>'
                     . '<c:comp name="VJOURNAL"/>'
                     . '<c:comp name="VFREEBUSY"/>'
                     . '<c:comp name="VAVAILABILITY"/>'
                 . '</c:supported-calendar-component-set>';
             */
         }
 
         foreach ($properties as $name => $value) {
             if ($name == 'name') {
                 $props .= '<d:displayname>' . htmlspecialchars($value, ENT_XML1, 'UTF-8') . '</d:displayname>';
             }
             else if ($name == 'color' && strlen($value)) {
                 if ($value[0] != '#') {
                     $value = '#' . $value;
                 }
 
                 $ns .= ' xmlns:a="http://apple.com/ns/ical/"';
                 $props .= '<a:calendar-color>' . htmlspecialchars($value, ENT_XML1, 'UTF-8') . '</a:calendar-color>';
             }
             else if ($name == 'alarms') {
                 if (!strpos($ns, 'Kolab:')) {
                     $ns .= ' xmlns:k="Kolab:"';
                 }
 
                 $props .= "<k:{$name}>" . ($value ? 'true' : 'false') . "</k:{$name}>";
             }
         }
 
         if (empty($props)) {
             return true;
         }
 
         $body = '<?xml version="1.0" encoding="utf-8"?>'
             . '<d:propertyupdate ' . $ns . '>'
                 . '<d:set>'
                     . '<d:prop>' . $props . '</d:prop>'
                 . '</d:set>'
             . '</d:propertyupdate>';
 
         $response = $this->request($location, 'PROPPATCH', $body);
 
         // TODO: Should we make sure "200 OK" status is set for all requested properties?
 
         return $response !== false;
     }
 
     /**
      * Fetch DAV objects metadata (ETag, href) a folder
      *
      * @param string $location  Folder location
      * @param string $component Object type (VEVENT, VTODO, VCARD)
      *
      * @return false|array Objects metadata on success, False on error
      */
     public function getIndex($location, $component = 'VEVENT')
     {
         $queries = [
             'VEVENT' => 'calendar-query',
             'VTODO' => 'calendar-query',
             'VCARD' => 'addressbook-query',
         ];
 
         $ns = [
             'VEVENT' => 'caldav',
             'VTODO' => 'caldav',
             'VCARD' => 'carddav',
         ];
 
         $filter = '';
         if ($component != 'VCARD') {
             $filter = '<c:comp-filter name="VCALENDAR">'
                     . '<c:comp-filter name="' . $component . '" />'
                 . '</c:comp-filter>';
         }
 
         $body = '<?xml version="1.0" encoding="utf-8"?>'
             .' <c:' . $queries[$component] . ' xmlns:d="DAV:" xmlns:c="urn:ietf:params:xml:ns:' . $ns[$component]. '">'
                 . '<d:prop>'
                     . '<d:getetag />'
                 . '</d:prop>'
                 . ($filter ? "<c:filter>$filter</c:filter>" : '')
             . '</c:' . $queries[$component] . '>';
 
         $response = $this->request($location, 'REPORT', $body, ['Depth' => 1, 'Prefer' => 'return-minimal']);
 
         if (empty($response)) {
             return false;
         }
 
         $objects = [];
 
         foreach ($response->getElementsByTagName('response') as $element) {
             $objects[] = $this->getObjectPropertiesFromResponse($element);
         }
 
         return $objects;
     }
 
     /**
      * Fetch DAV objects data from a folder
      *
      * @param string $location  Folder location
      * @param string $component Object type (VEVENT, VTODO, VCARD)
      * @param array  $hrefs     List of objects' locations to fetch (empty for all objects)
      *
      * @return false|array Objects metadata on success, False on error
      */
     public function getData($location, $component = 'VEVENT', $hrefs = [])
     {
         if (empty($hrefs)) {
             return [];
         }
 
         $body = '';
         foreach ($hrefs as $href) {
             $body .= '<d:href>' . $href . '</d:href>';
         }
 
         $queries = [
             'VEVENT' => 'calendar-multiget',
             'VTODO' => 'calendar-multiget',
             'VCARD' => 'addressbook-multiget',
         ];
 
         $ns = [
             'VEVENT' => 'caldav',
             'VTODO' => 'caldav',
             'VCARD' => 'carddav',
         ];
 
         $types = [
             'VEVENT' => 'calendar-data',
             'VTODO' => 'calendar-data',
             'VCARD' => 'address-data',
         ];
 
         $body = '<?xml version="1.0" encoding="utf-8"?>'
             .' <c:' . $queries[$component] . ' xmlns:d="DAV:" xmlns:c="urn:ietf:params:xml:ns:' . $ns[$component] . '">'
                 . '<d:prop>'
                     . '<d:getetag />'
                     . '<c:' . $types[$component]. ' />'
                 . '</d:prop>'
                 . $body
             . '</c:' . $queries[$component] . '>';
 
         $response = $this->request($location, 'REPORT', $body, ['Depth' => 1, 'Prefer' => 'return-minimal']);
 
         if (empty($response)) {
             return false;
         }
 
         $objects = [];
 
         foreach ($response->getElementsByTagName('response') as $element) {
             $objects[] = $this->getObjectPropertiesFromResponse($element);
         }
 
         return $objects;
     }
 
     /**
      * Parse XML content
      */
     protected function parseXML($xml)
     {
         $doc = new DOMDocument('1.0', 'UTF-8');
 
         if (stripos($xml, '<?xml') === 0) {
             if (!$doc->loadXML($xml)) {
                 throw new Exception("Failed to parse XML");
             }
 
             $doc->formatOutput = true;
         }
 
         return $doc;
     }
 
     /**
      * Parse request/response body for debug purposes
      */
     protected function debugBody($body, $headers)
     {
         $head = '';
         foreach ($headers as $header_name => $header_value) {
             $head .= "{$header_name}: {$header_value}\n";
         }
 
         if (stripos($body, '<?xml') === 0) {
             $doc = new DOMDocument('1.0', 'UTF-8');
 
             $doc->formatOutput = true;
             $doc->preserveWhiteSpace = false;
 
             if (!$doc->loadXML($body)) {
                 throw new Exception("Failed to parse XML");
             }
 
             $body = $doc->saveXML();
         }
 
         return $head . "\n" . rtrim($body);
     }
 
     /**
      * Extract folder properties from a server 'response' element
      */
     protected function getFolderPropertiesFromResponse(DOMNode $element)
     {
 
         if ($href = $element->getElementsByTagName('href')->item(0)) {
             $href = $href->nodeValue;
 /*
             $path = parse_url($this->url, PHP_URL_PATH);
             if ($path && strpos($href, $path) === 0) {
                 $href = substr($href, strlen($path));
             }
 */
         }
 
         if ($color = $element->getElementsByTagName('calendar-color')->item(0)) {
             if (preg_match('/^#[0-9a-fA-F]{6,8}$/', $color->nodeValue)) {
                 $color = substr($color->nodeValue, 1);
             } else {
                 $color = null;
             }
         }
 
         if ($name = $element->getElementsByTagName('displayname')->item(0)) {
             $name = $name->nodeValue;
         }
 
         if ($ctag = $element->getElementsByTagName('getctag')->item(0)) {
             $ctag = $ctag->nodeValue;
         }
 
         $component = null;
         if ($set_element = $element->getElementsByTagName('supported-calendar-component-set')->item(0)) {
             if ($comp_element = $set_element->getElementsByTagName('comp')->item(0)) {
                 $component = $comp_element->attributes->getNamedItem('name')->nodeValue;
             }
         }
 
         $types = [];
         if ($type_element = $element->getElementsByTagName('resourcetype')->item(0)) {
             foreach ($type_element->childNodes as $node) {
                 $_type = explode(':', $node->nodeName);
                 $types[] = count($_type) > 1 ? $_type[1] : $_type[0];
             }
         }
 
         $result = [
             'href' => $href,
             'name' => $name,
             'ctag' => $ctag,
             'color' => $color,
             'type' => $component,
             'resource_type' => $types,
         ];
 
         foreach (['alarms'] as $tag) {
             if ($el = $element->getElementsByTagName($tag)->item(0)) {
                 if (strlen($el->nodeValue) > 0) {
                     $result[$tag] = strtolower($el->nodeValue) === 'true';
                 }
             }
         }
 
         return $result;
     }
 
     /**
      * Extract object properties from a server 'response' element
      */
     protected function getObjectPropertiesFromResponse(DOMNode $element)
     {
         $uid = null;
         if ($href = $element->getElementsByTagName('href')->item(0)) {
             $href = $href->nodeValue;
 /*
             $path = parse_url($this->url, PHP_URL_PATH);
             if ($path && strpos($href, $path) === 0) {
                 $href = substr($href, strlen($path));
             }
 */
             // Extract UID from the URL
             $href_parts = explode('/', $href);
             $uid = preg_replace('/\.[a-z]+$/', '', $href_parts[count($href_parts)-1]);
         }
 
         if ($data = $element->getElementsByTagName('calendar-data')->item(0)) {
             $data = $data->nodeValue;
         }
         else if ($data = $element->getElementsByTagName('address-data')->item(0)) {
             $data = $data->nodeValue;
         }
 
         if ($etag = $element->getElementsByTagName('getetag')->item(0)) {
             $etag = $etag->nodeValue;
             if (preg_match('|^".*"$|', $etag)) {
                 $etag = substr($etag, 1, -1);
             }
         }
 
         return [
             'href' => $href,
             'data' => $data,
             'etag' => $etag,
             'uid' => $uid,
         ];
     }
 
     /**
      * Initialize HTTP request object
      */
     protected function initRequest($url = '', $method = 'GET', $config = array())
     {
         $rcube       = rcube::get_instance();
         $http_config = (array) $rcube->config->get('kolab_http_request');
 
         // deprecated configuration options
         if (empty($http_config)) {
             foreach (array('ssl_verify_peer', 'ssl_verify_host') as $option) {
                 $value = $rcube->config->get('kolab_' . $option, true);
                 if (is_bool($value)) {
                     $http_config[$option] = $value;
                 }
             }
         }
 
         if (!empty($config)) {
             $http_config = array_merge($http_config, $config);
         }
 
         // load HTTP_Request2 (support both composer-installed and system-installed package)
         if (!class_exists('HTTP_Request2')) {
             require_once 'HTTP/Request2.php';
         }
 
         try {
             $request = new HTTP_Request2();
             $request->setConfig($http_config);
 
             // proxy User-Agent string
             $request->setHeader('user-agent', $_SERVER['HTTP_USER_AGENT']);
 
             // cleanup
             $request->setBody('');
             $request->setUrl($url);
             $request->setMethod($method);
 
             return $request;
         }
         catch (Exception $e) {
             rcube::raise_error($e, true, true);
         }
     }
+
+    /**
+     * Return caching object if enabled
+     */
+    protected function get_cache()
+    {
+        $rcube = rcube::get_instance();
+        if ($cache_type = $rcube->config->get('dav_cache', 'db')) {
+            $cache_ttl  = $rcube->config->get('dav_cache_ttl', '10m');
+            $cache_name = 'DAV';
+
+            return $rcube->get_cache($cache_name, $cache_type, $cache_ttl);
+        }
+    }
 }