diff --git a/plugins/libkolab/lib/kolab_storage_cache.php b/plugins/libkolab/lib/kolab_storage_cache.php
index 7f206e55..2581a592 100644
--- a/plugins/libkolab/lib/kolab_storage_cache.php
+++ b/plugins/libkolab/lib/kolab_storage_cache.php
@@ -1,1065 +1,1065 @@
 <?php
 
 /**
  * Kolab storage cache class providing a local caching layer for Kolab groupware objects.
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2012-2013, Kolab Systems AG <contact@kolabsys.com>
  *
  * 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_storage_cache
 {
     const DB_DATE_FORMAT = 'Y-m-d H:i:s';
 
     protected $db;
     protected $imap;
     protected $folder;
     protected $uid2msg;
     protected $objects;
     protected $index = null;
     protected $metadata = array();
     protected $folder_id;
     protected $resource_uri;
     protected $enabled = true;
     protected $synched = false;
     protected $synclock = false;
     protected $ready = false;
     protected $cache_table;
     protected $cache_refresh = 3600;
     protected $folders_table;
     protected $max_sql_packet;
     protected $max_sync_lock_time = 600;
     protected $binary_items = array();
     protected $extra_cols = array();
     protected $order_by = null;
     protected $limit = null;
     protected $error = 0;
 
 
     /**
      * Factory constructor
      */
     public static function factory(kolab_storage_folder $storage_folder)
     {
         $subclass = 'kolab_storage_cache_' . $storage_folder->type;
         if (class_exists($subclass)) {
             return new $subclass($storage_folder);
         }
         else {
             rcube::raise_error(array(
                 'code' => 900,
                 'type' => 'php',
                 'message' => "No kolab_storage_cache class found for folder '$storage_folder->name' of type '$storage_folder->type'"
             ), true);
 
             return new kolab_storage_cache($storage_folder);
         }
     }
 
 
     /**
      * Default constructor
      */
     public function __construct(kolab_storage_folder $storage_folder = null)
     {
         $rcmail = rcube::get_instance();
         $this->db = $rcmail->get_dbh();
         $this->imap = $rcmail->get_storage();
         $this->enabled = $rcmail->config->get('kolab_cache', false);
         $this->folders_table = $this->db->table_name('kolab_folders');
         $this->cache_refresh = get_offset_sec($rcmail->config->get('kolab_cache_refresh', '12h'));
 
         if ($this->enabled) {
             // always read folder cache and lock state from DB master
             $this->db->set_table_dsn('kolab_folders', 'w');
             // remove sync-lock on script termination
             $rcmail->add_shutdown_function(array($this, '_sync_unlock'));
         }
 
         if ($storage_folder)
             $this->set_folder($storage_folder);
     }
 
     /**
      * Direct access to cache by folder_id
      * (only for internal use)
      */
     public function select_by_id($folder_id)
     {
         $sql_arr = $this->db->fetch_assoc($this->db->query("SELECT * FROM {$this->folders_table} WHERE folder_id=?", $folder_id));
         if ($sql_arr) {
             $this->metadata = $sql_arr;
             $this->folder_id = $sql_arr['folder_id'];
             $this->folder = new StdClass;
             $this->folder->type = $sql_arr['type'];
             $this->resource_uri = $sql_arr['resource'];
             $this->cache_table = $this->db->table_name('kolab_cache_' . $sql_arr['type']);
             $this->ready = true;
         }
     }
 
     /**
      * Connect cache with a storage folder
      *
      * @param kolab_storage_folder The storage folder instance to connect with
      */
     public function set_folder(kolab_storage_folder $storage_folder)
     {
         $this->folder = $storage_folder;
 
         if (empty($this->folder->name) || !$this->folder->valid) {
             $this->ready = false;
             return;
         }
 
         // compose fully qualified ressource uri for this instance
         $this->resource_uri = $this->folder->get_resource_uri();
         $this->cache_table = $this->db->table_name('kolab_cache_' . $this->folder->type);
         $this->ready = $this->enabled && !empty($this->folder->type);
         $this->folder_id = null;
     }
 
     /**
      * Returns true if this cache supports query by type
      */
     public function has_type_col()
     {
         return in_array('type', $this->extra_cols);
     }
 
     /**
      * Getter for the numeric ID used in cache tables
      */
     public function get_folder_id()
     {
         $this->_read_folder_data();
         return $this->folder_id;
     }
 
     /**
      * Returns code of last error
      *
      * @return int Error code
      */
     public function get_error()
     {
         return $this->error;
     }
 
     /**
      * Synchronize local cache data with remote
      */
     public function synchronize()
     {
         // only sync once per request cycle
         if ($this->synched)
             return;
 
         // increase time limit
         @set_time_limit($this->max_sync_lock_time);
 
         if (!$this->ready) {
             // kolab cache is disabled, synchronize IMAP mailbox cache only
             $this->imap->folder_sync($this->folder->name);
         }
         else {
             // read cached folder metadata
             $this->_read_folder_data();
 
             // check cache status ($this->metadata is set in _read_folder_data())
             if (  empty($this->metadata['ctag']) ||
                   empty($this->metadata['changed']) ||
                   $this->metadata['objectcount'] === null ||
                   $this->metadata['changed'] < date(self::DB_DATE_FORMAT, time() - $this->cache_refresh) ||
                   $this->metadata['ctag'] != $this->folder->get_ctag() ||
                   intval($this->metadata['objectcount']) !== $this->count()
                 ) {
                 // lock synchronization for this folder or wait if locked
                 $this->_sync_lock();
 
                 // disable messages cache if configured to do so
                 $this->bypass(true);
 
                 // synchronize IMAP mailbox cache
                 $this->imap->folder_sync($this->folder->name);
 
                 // compare IMAP index with object cache index
                 $imap_index = $this->imap->index($this->folder->name, null, null, true, true);
                 $this->index = $imap_index->get();
 
                 // determine objects to fetch or to invalidate
-                if ($imap_index->is_error()) {
+                if (!$imap_index->is_error()) {
                     // read cache index
                     $sql_result = $this->db->query(
                         "SELECT msguid, uid FROM $this->cache_table WHERE folder_id=?",
                         $this->folder_id
                     );
 
                     $old_index = array();
                     while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                         $old_index[] = $sql_arr['msguid'];
                         $this->uid2msg[$sql_arr['uid']] = $sql_arr['msguid'];
                     }
 
                     // fetch new objects from imap
                     foreach (array_diff($this->index, $old_index) as $msguid) {
                         if ($object = $this->folder->read_object($msguid, '*')) {
                             $this->_extended_insert($msguid, $object);
                         }
                     }
                     $this->_extended_insert(0, null);
 
                     // delete invalid entries from local DB
                     $del_index = array_diff($old_index, $this->index);
                     if (!empty($del_index)) {
                         $quoted_ids = join(',', array_map(array($this->db, 'quote'), $del_index));
                         $this->db->query(
                             "DELETE FROM $this->cache_table WHERE folder_id=? AND msguid IN ($quoted_ids)",
                             $this->folder_id
                         );
                     }
 
                     // update ctag value (will be written to database in _sync_unlock())
                     $this->metadata['ctag'] = $this->folder->get_ctag();
                     $this->metadata['changed'] = date(self::DB_DATE_FORMAT, time());
                     // remember the number of cache entries linked to this folder
                     $this->metadata['objectcount'] = $this->count();
                 }
 
                 $this->bypass(false);
 
                 // remove lock
                 $this->_sync_unlock();
             }
         }
 
         $this->check_error();
         $this->synched = time();
     }
 
 
     /**
      * Read a single entry from cache or from IMAP directly
      *
      * @param string Related IMAP message UID
      * @param string Object type to read
      * @param string IMAP folder name the entry relates to
      * @param array  Hash array with object properties or null if not found
      */
     public function get($msguid, $type = null, $foldername = null)
     {
         // delegate to another cache instance
         if ($foldername && $foldername != $this->folder->name) {
             $success = false;
             if ($targetfolder = kolab_storage::get_folder($foldername)) {
                 $success = $targetfolder->cache->get($msguid, $type);
                 $this->error = $targetfolder->cache->get_error();
             }
             return $success;
         }
 
         // load object if not in memory
         if (!isset($this->objects[$msguid])) {
             if ($this->ready) {
                 $this->_read_folder_data();
 
                 $sql_result = $this->db->query(
                     "SELECT * FROM $this->cache_table ".
                     "WHERE folder_id=? AND msguid=?",
                     $this->folder_id,
                     $msguid
                 );
 
                 if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                     $this->objects = array($msguid => $this->_unserialize($sql_arr));  // store only this object in memory (#2827)
                 }
             }
 
             // fetch from IMAP if not present in cache
             if (empty($this->objects[$msguid])) {
                 $result = $this->_fetch(array($msguid), $type, $foldername);
                 $this->objects = array($msguid => $result[0]);  // store only this object in memory (#2827)
             }
         }
 
         $this->check_error();
         return $this->objects[$msguid];
     }
 
 
     /**
      * Insert/Update a cache entry
      *
      * @param string Related IMAP message UID
      * @param mixed  Hash array with object properties to save or false to delete the cache entry
      * @param string IMAP folder name the entry relates to
      */
     public function set($msguid, $object, $foldername = null)
     {
         if (!$msguid) {
             return;
         }
 
         // delegate to another cache instance
         if ($foldername && $foldername != $this->folder->name) {
           if ($targetfolder = kolab_storage::get_folder($foldername)) {
               $targetfolder->cache->set($msguid, $object);
               $this->error = $targetfolder->cache->get_error();
           }
           return;
         }
 
         // remove old entry
         if ($this->ready) {
             $this->_read_folder_data();
             $this->db->query("DELETE FROM $this->cache_table WHERE folder_id=? AND msguid=?",
                 $this->folder_id, $msguid);
         }
 
         if ($object) {
             // insert new object data...
             $this->insert($msguid, $object);
         }
         else {
             // ...or set in-memory cache to false
             $this->objects[$msguid] = $object;
         }
 
         $this->check_error();
     }
 
 
     /**
      * Insert a cache entry
      *
      * @param string Related IMAP message UID
      * @param mixed  Hash array with object properties to save or false to delete the cache entry
      */
     public function insert($msguid, $object)
     {
         // write to cache
         if ($this->ready) {
             $this->_read_folder_data();
 
             $sql_data = $this->_serialize($object);
 
             $extra_cols   = $this->extra_cols ? ', ' . join(', ', $this->extra_cols) : '';
             $extra_fields = $this->extra_cols ? str_repeat(', ?', count($this->extra_cols)) : '';
 
             $args = array(
                 "INSERT INTO $this->cache_table ".
                 " (folder_id, msguid, uid, created, changed, data, xml, tags, words $extra_cols)".
                 " VALUES (?, ?, ?, " . $this->db->now() . ", ?, ?, ?, ?, ? $extra_fields)",
                 $this->folder_id,
                 $msguid,
                 $object['uid'],
                 $sql_data['changed'],
                 $sql_data['data'],
                 $sql_data['xml'],
                 $sql_data['tags'],
                 $sql_data['words'],
             );
 
             foreach ($this->extra_cols as $col) {
                 $args[] = $sql_data[$col];
             }
 
             $result = call_user_func_array(array($this->db, 'query'), $args);
 
             if (!$this->db->affected_rows($result)) {
                 rcube::raise_error(array(
                     'code' => 900, 'type' => 'php',
                     'message' => "Failed to write to kolab cache"
                 ), true);
             }
         }
 
         // keep a copy in memory for fast access
         $this->objects = array($msguid => $object);
         $this->uid2msg = array($object['uid'] => $msguid);
 
         $this->check_error();
     }
 
 
     /**
      * Move an existing cache entry to a new resource
      *
      * @param string Entry's IMAP message UID
      * @param string Entry's Object UID
      * @param object kolab_storage_folder Target storage folder instance
      */
     public function move($msguid, $uid, $target)
     {
         // clear cached uid mapping and force new lookup
         unset($target->cache->uid2msg[$uid]);
 
         // resolve new message UID in target folder
         if ($this->ready && ($new_msguid = $target->cache->uid2msguid($uid))) {
             $this->_read_folder_data();
 
             $this->db->query(
                 "UPDATE $this->cache_table SET folder_id=?, msguid=? ".
                 "WHERE folder_id=? AND msguid=?",
                 $target->cache->get_folder_id(),
                 $new_msguid,
                 $this->folder_id,
                 $msguid
             );
         }
         else {
             // just clear cache entry
             $this->set($msguid, false);
         }
 
         unset($this->uid2msg[$uid]);
         $this->check_error();
     }
 
 
     /**
      * Remove all objects from local cache
      */
     public function purge($type = null)
     {
         $this->_read_folder_data();
 
         $result = $this->db->query(
             "DELETE FROM $this->cache_table WHERE folder_id=?",
             $this->folder_id
         );
 
         return $this->db->affected_rows($result);
     }
 
     /**
      * Update resource URI for existing cache entries
      *
      * @param string Target IMAP folder to move it to
      */
     public function rename($new_folder)
     {
         if ($target = kolab_storage::get_folder($new_folder)) {
             // resolve new message UID in target folder
             $this->db->query(
                 "UPDATE $this->folders_table SET resource=? ".
                 "WHERE resource=?",
                 $target->get_resource_uri(),
                 $this->resource_uri
             );
 
             $this->check_error();
         }
         else {
             $this->error = kolab_storage::ERROR_IMAP_CONN;
         }
     }
 
     /**
      * Select Kolab objects filtered by the given query
      *
      * @param array Pseudo-SQL query as list of filter parameter triplets
      *   triplet: array('<colname>', '<comparator>', '<value>')
      * @param boolean Set true to only return UIDs instead of complete objects
      * @return array List of Kolab data objects (each represented as hash array) or UIDs
      */
     public function select($query = array(), $uids = false)
     {
         $result = $uids ? array() : new kolab_storage_dataset($this);
 
         // read from local cache DB (assume it to be synchronized)
         if ($this->ready) {
             $this->_read_folder_data();
 
             // fetch full object data on one query if a small result set is expected
             $fetchall = !$uids && ($this->limit ? $this->limit[0] : $this->count($query)) < 500;
             $sql_query = "SELECT " . ($fetchall ? '*' : 'msguid AS _msguid, uid') . " FROM $this->cache_table ".
                          "WHERE folder_id=? " . $this->_sql_where($query);
             if (!empty($this->order_by)) {
                 $sql_query .= ' ORDER BY ' . $this->order_by;
             }
             $sql_result = $this->limit ?
                 $this->db->limitquery($sql_query, $this->limit[1], $this->limit[0], $this->folder_id) :
                 $this->db->query($sql_query, $this->folder_id);
 
             if ($this->db->is_error($sql_result)) {
                 if ($uids) {
                     return null;
                 }
                 $result->set_error(true);
                 return $result;
             }
 
             while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                 if ($uids) {
                     $this->uid2msg[$sql_arr['uid']] = $sql_arr['_msguid'];
                     $result[] = $sql_arr['uid'];
                 }
                 else if ($fetchall && ($object = $this->_unserialize($sql_arr))) {
                     $result[] = $object;
                 }
                 else if (!$fetchall) {
                     // only add msguid to dataset index
                     $result[] = $sql_arr;
                 }
             }
         }
         else {
             // extract object type from query parameter
             $filter = $this->_query2assoc($query);
 
             // use 'list' for folder's default objects
             if (is_array($this->index) && $filter['type'] == $this->type) {
                 $index = $this->index;
             }
             else {  // search by object type
                 $search = 'UNDELETED HEADER X-Kolab-Type ' . kolab_format::KTYPE_PREFIX . $filter['type'];
                 $index  = $this->imap->search_once($this->folder->name, $search)->get();
             }
 
             // fetch all messages in $index from IMAP
             $result = $uids ? $this->_fetch_uids($index, $filter['type']) : $this->_fetch($index, $filter['type']);
 
             // TODO: post-filter result according to query
         }
 
         // We don't want to cache big results in-memory, however
         // if we select only one object here, there's a big chance we will need it later
         if (!$uids && count($result) == 1) {
             if ($msguid = $result[0]['_msguid']) {
                 $this->uid2msg[$result[0]['uid']] = $msguid;
                 $this->objects = array($msguid => $result[0]);
             }
         }
 
         $this->check_error();
 
         return $result;
     }
 
 
     /**
      * Get number of objects mathing the given query
      *
      * @param array  $query Pseudo-SQL query as list of filter parameter triplets
      * @return integer The number of objects of the given type
      */
     public function count($query = array())
     {
         // cache is in sync, we can count records in local DB
         if ($this->ready) {
             $this->_read_folder_data();
 
             $sql_result = $this->db->query(
                 "SELECT COUNT(*) AS numrows FROM $this->cache_table ".
                 "WHERE folder_id=? " . $this->_sql_where($query),
                 $this->folder_id
             );
 
             if ($this->db->is_error($sql_result)) {
                 return null;
             }
 
             $sql_arr = $this->db->fetch_assoc($sql_result);
             $count   = intval($sql_arr['numrows']);
         }
         else {
             // search IMAP by object type
             $filter = $this->_query2assoc($query);
             $ctype  = kolab_format::KTYPE_PREFIX . $filter['type'];
             $index  = $this->imap->search_once($this->folder->name, 'UNDELETED HEADER X-Kolab-Type ' . $ctype);
 
             if ($index->is_error()) {
                 $this->check_error();
                 return null;
             }
 
             $count = $index->count();
         }
 
         $this->check_error();
         return $count;
     }
 
     /**
      * Define ORDER BY clause for cache queries
      */
     public function set_order_by($sortcols)
     {
         if (!empty($sortcols)) {
             $this->order_by = join(', ', (array)$sortcols);
         }
         else {
             $this->order_by = null;
         }
     }
 
     /**
      * Define LIMIT clause for cache queries
      */
     public function set_limit($length, $offset = 0)
     {
         $this->limit = array($length, $offset);
     }
 
     /**
      * Helper method to compose a valid SQL query from pseudo filter triplets
      */
     protected function _sql_where($query)
     {
         $sql_where = '';
         foreach ((array) $query as $param) {
             if (is_array($param[0])) {
                 $subq = array();
                 foreach ($param[0] as $q) {
                     $subq[] = preg_replace('/^\s*AND\s+/i', '', $this->_sql_where(array($q)));
                 }
                 if (!empty($subq)) {
                     $sql_where .= ' AND (' . implode($param[1] == 'OR' ? ' OR ' : ' AND ', $subq) . ')';
                 }
                 continue;
             }
             else if ($param[1] == '=' && is_array($param[2])) {
                 $qvalue = '(' . join(',', array_map(array($this->db, 'quote'), $param[2])) . ')';
                 $param[1] = 'IN';
             }
             else if ($param[1] == '~' || $param[1] == 'LIKE' || $param[1] == '!~' || $param[1] == '!LIKE') {
                 $not = ($param[1] == '!~' || $param[1] == '!LIKE') ? 'NOT ' : '';
                 $param[1] = $not . 'LIKE';
                 $qvalue = $this->db->quote('%'.preg_replace('/(^\^|\$$)/', ' ', $param[2]).'%');
             }
             else if ($param[0] == 'tags') {
                 $param[1] = ($param[1] == '!=' ? 'NOT ' : '' ) . 'LIKE';
                 $qvalue = $this->db->quote('% '.$param[2].' %');
             }
             else {
                 $qvalue = $this->db->quote($param[2]);
             }
 
             $sql_where .= sprintf(' AND %s %s %s',
                 $this->db->quote_identifier($param[0]),
                 $param[1],
                 $qvalue
             );
         }
 
         return $sql_where;
     }
 
     /**
      * Helper method to convert the given pseudo-query triplets into
      * an associative filter array with 'equals' values only
      */
     protected function _query2assoc($query)
     {
         // extract object type from query parameter
         $filter = array();
         foreach ($query as $param) {
             if ($param[1] == '=')
                 $filter[$param[0]] = $param[2];
         }
         return $filter;
     }
 
     /**
      * Fetch messages from IMAP
      *
      * @param array  List of message UIDs to fetch
      * @param string Requested object type or * for all
      * @param string IMAP folder to read from
      * @return array List of parsed Kolab objects
      */
     protected function _fetch($index, $type = null, $folder = null)
     {
         $results = new kolab_storage_dataset($this);
         foreach ((array)$index as $msguid) {
             if ($object = $this->folder->read_object($msguid, $type, $folder)) {
                 $results[] = $object;
                 $this->set($msguid, $object);
             }
         }
 
         return $results;
     }
 
 
     /**
      * Fetch object UIDs (aka message subjects) from IMAP
      *
      * @param array List of message UIDs to fetch
      * @param string Requested object type or * for all
      * @param string IMAP folder to read from
      * @return array List of parsed Kolab objects
      */
     protected function _fetch_uids($index, $type = null)
     {
         if (!$type)
             $type = $this->folder->type;
 
         $this->bypass(true);
 
         $results = array();
         $headers = $this->imap->fetch_headers($this->folder->name, $index, false);
 
         $this->bypass(false);
 
         foreach ((array)$headers as $msguid => $headers) {
             $object_type = kolab_format::mime2object_type($headers->others['x-kolab-type']);
 
             // check object type header and abort on mismatch
             if ($type != '*' && $object_type != $type)
                 return false;
 
             $uid = $headers->subject;
             $this->uid2msg[$uid] = $msguid;
             $results[] = $uid;
         }
 
         return $results;
     }
 
 
     /**
      * Helper method to convert the given Kolab object into a dataset to be written to cache
      */
     protected function _serialize($object)
     {
         $sql_data = array('changed' => null, 'xml' => '', 'tags' => '', 'words' => '');
 
         if ($object['changed']) {
             $sql_data['changed'] = date(self::DB_DATE_FORMAT, is_object($object['changed']) ? $object['changed']->format('U') : $object['changed']);
         }
 
         if ($object['_formatobj']) {
             $sql_data['xml']   = preg_replace('!(</?[a-z0-9:-]+>)[\n\r\t\s]+!ms', '$1', (string)$object['_formatobj']->write(3.0));
             $sql_data['tags']  = ' ' . join(' ', $object['_formatobj']->get_tags()) . ' ';  // pad with spaces for strict/prefix search
             $sql_data['words'] = ' ' . join(' ', $object['_formatobj']->get_words()) . ' ';
         }
 
         // extract object data
         $data = array();
         foreach ($object as $key => $val) {
             // skip empty properties
             if ($val === "" || $val === null) {
                 continue;
             }
             // mark binary data to be extracted from xml on unserialize()
             if (isset($this->binary_items[$key])) {
                 $data[$key] = true;
             }
             else if ($key[0] != '_') {
                 $data[$key] = $val;
             }
             else if ($key == '_attachments') {
                 foreach ($val as $k => $att) {
                     unset($att['content'], $att['path']);
                     if ($att['id'])
                         $data[$key][$k] = $att;
                 }
             }
         }
 
         // use base64 encoding (Bug #1912, #2662)
         $sql_data['data'] = base64_encode(serialize($data));
 
         return $sql_data;
     }
 
     /**
      * Helper method to turn stored cache data into a valid storage object
      */
     protected function _unserialize($sql_arr)
     {
         // check if data is a base64-encoded string, for backward compat.
         if (strpos(substr($sql_arr['data'], 0, 64), ':') === false) {
             $sql_arr['data'] = base64_decode($sql_arr['data']);
         }
 
         $object = unserialize($sql_arr['data']);
 
         // de-serialization failed
         if ($object === false) {
             rcube::raise_error(array(
                 'code' => 900, 'type' => 'php',
                 'message' => "Malformed data for {$this->resource_uri}/{$sql_arr['msguid']} object."
             ), true);
 
             return null;
         }
 
         // decode binary properties
         foreach ($this->binary_items as $key => $regexp) {
             if (!empty($object[$key]) && preg_match($regexp, $sql_arr['xml'], $m)) {
                 $object[$key] = base64_decode($m[1]);
             }
         }
 
         $object_type = $sql_arr['type'] ?: $this->folder->type;
         $format_type = $this->folder->type == 'configuration' ? 'configuration' : $object_type;
 
         // add meta data
         $object['_type']      = $object_type;
         $object['_msguid']    = $sql_arr['msguid'];
         $object['_mailbox']   = $this->folder->name;
         $object['_size']      = strlen($sql_arr['xml']);
         $object['_formatobj'] = kolab_format::factory($format_type, 3.0, $sql_arr['xml']);
 
         return $object;
     }
 
     /**
      * Write records into cache using extended inserts to reduce the number of queries to be executed
      *
      * @param int  Message UID. Set 0 to commit buffered inserts
      * @param array Kolab object to cache
      */
     protected function _extended_insert($msguid, $object)
     {
         static $buffer = '';
 
         $line = '';
         if ($object) {
             $sql_data = $this->_serialize($object);
             $values = array(
                 $this->db->quote($this->folder_id),
                 $this->db->quote($msguid),
                 $this->db->quote($object['uid']),
                 $this->db->now(),
                 $this->db->quote($sql_data['changed']),
                 $this->db->quote($sql_data['data']),
                 $this->db->quote($sql_data['xml']),
                 $this->db->quote($sql_data['tags']),
                 $this->db->quote($sql_data['words']),
             );
             foreach ($this->extra_cols as $col) {
                 $values[] = $this->db->quote($sql_data[$col]);
             }
             $line = '(' . join(',', $values) . ')';
         }
 
         if ($buffer && (!$msguid || (strlen($buffer) + strlen($line) > $this->max_sql_packet()))) {
             $extra_cols = $this->extra_cols ? ', ' . join(', ', $this->extra_cols) : '';
             $result = $this->db->query(
                 "INSERT INTO $this->cache_table ".
                 " (folder_id, msguid, uid, created, changed, data, xml, tags, words $extra_cols)".
                 " VALUES $buffer"
             );
             if (!$this->db->affected_rows($result)) {
                 rcube::raise_error(array(
                     'code' => 900, 'type' => 'php',
                     'message' => "Failed to write to kolab cache"
                 ), true);
             }
 
             $buffer = '';
         }
 
         $buffer .= ($buffer ? ',' : '') . $line;
     }
 
     /**
      * Returns max_allowed_packet from mysql config
      */
     protected function max_sql_packet()
     {
         if (!$this->max_sql_packet) {
             // mysql limit or max 4 MB
             $value = $this->db->get_variable('max_allowed_packet', 1048500);
             $this->max_sql_packet = min($value, 4*1024*1024) - 2000;
         }
 
         return $this->max_sql_packet;
     }
 
     /**
      * Read this folder's ID and cache metadata
      */
     protected function _read_folder_data()
     {
         // already done
         if (!empty($this->folder_id))
             return;
 
         $sql_arr = $this->db->fetch_assoc($this->db->query("SELECT folder_id, synclock, ctag, changed, objectcount"
             . " FROM $this->folders_table WHERE resource=?", $this->resource_uri));
 
         if ($sql_arr) {
             $this->metadata = $sql_arr;
             $this->folder_id = $sql_arr['folder_id'];
         }
         else {
             $this->db->query("INSERT INTO $this->folders_table (resource, type) VALUES (?, ?)", $this->resource_uri, $this->folder->type);
             $this->folder_id = $this->db->insert_id('kolab_folders');
             $this->metadata = array();
         }
     }
 
     /**
      * Check lock record for this folder and wait if locked or set lock
      */
     protected function _sync_lock()
     {
         if (!$this->ready)
             return;
 
         $this->_read_folder_data();
         $sql_query = "SELECT synclock, ctag FROM $this->folders_table WHERE folder_id=?";
 
         // abort if database is not set-up
         if ($this->db->is_error()) {
             $this->check_error();
             $this->ready = false;
             return;
         }
 
         $this->synclock = true;
 
         // wait if locked (expire locks after 10 minutes)
         while ($this->metadata && intval($this->metadata['synclock']) > 0 && $this->metadata['synclock'] + $this->max_sync_lock_time > time()) {
             usleep(500000);
             $this->metadata = $this->db->fetch_assoc($this->db->query($sql_query, $this->folder_id));
         }
 
         // set lock
         $this->db->query("UPDATE $this->folders_table SET synclock = ? WHERE folder_id = ?", time(), $this->folder_id);
     }
 
     /**
      * Remove lock for this folder
      */
     public function _sync_unlock()
     {
         if (!$this->ready || !$this->synclock)
             return;
 
         $this->db->query(
             "UPDATE $this->folders_table SET synclock = 0, ctag = ?, changed = ?, objectcount = ? WHERE folder_id = ?",
             $this->metadata['ctag'],
             $this->metadata['changed'],
             $this->metadata['objectcount'],
             $this->folder_id
         );
 
         $this->synclock = false;
     }
 
     /**
      * Check IMAP connection error state
      */
     protected function check_error()
     {
         if (($err_code = $this->imap->get_error_code()) < 0) {
             $this->error = kolab_storage::ERROR_IMAP_CONN;
             if (($res_code = $this->imap->get_response_code()) !== 0 && in_array($res_code, array(rcube_storage::NOPERM, rcube_storage::READONLY))) {
                 $this->error = kolab_storage::ERROR_NO_PERMISSION;
             }
         }
         else if ($this->db->is_error()) {
             $this->error = kolab_storage::ERROR_CACHE_DB;
         }
     }
 
     /**
      * Resolve an object UID into an IMAP message UID
      *
      * @param string  Kolab object UID
      * @param boolean Include deleted objects
      * @return int The resolved IMAP message UID
      */
     public function uid2msguid($uid, $deleted = false)
     {
         if (!isset($this->uid2msg[$uid])) {
             // use IMAP SEARCH to get the right message
             $index = $this->imap->search_once($this->folder->name, ($deleted ? '' : 'UNDELETED ') .
                 'HEADER SUBJECT ' . rcube_imap_generic::escape($uid));
             $results = $index->get();
             $this->uid2msg[$uid] = end($results);
         }
 
         return $this->uid2msg[$uid];
     }
 
     /**
      * Getter for protected member variables
      */
     public function __get($name)
     {
         if ($name == 'folder_id') {
             $this->_read_folder_data();
         }
 
         return $this->$name;
     }
 
     /**
      * Bypass Roundcube messages cache.
      * Roundcube cache duplicates information already stored in kolab_cache.
      *
      * @param bool $disable True disables, False enables messages cache
      */
     public function bypass($disable = false)
     {
         // if kolab cache is disabled do nothing
         if (!$this->enabled) {
             return;
         }
 
         static $messages_cache, $cache_bypass;
 
         if ($messages_cache === null) {
             $rcmail = rcube::get_instance();
             $messages_cache = (bool) $rcmail->config->get('messages_cache');
             $cache_bypass   = (int) $rcmail->config->get('kolab_messages_cache_bypass');
         }
 
         if ($messages_cache) {
             // handle recurrent (multilevel) bypass() calls
             if ($disable) {
                 $this->cache_bypassed += 1;
                 if ($this->cache_bypassed > 1) {
                     return;
                 }
             }
             else {
                 $this->cache_bypassed -= 1;
                 if ($this->cache_bypassed > 0) {
                     return;
                 }
             }
 
             switch ($cache_bypass) {
                 case 2:
                     // Disable messages cache completely
                     $this->imap->set_messages_caching(!$disable);
                     break;
 
                 case 1:
                     // We'll disable messages cache, but keep index cache.
                     // Default mode is both (MODE_INDEX | MODE_MESSAGE)
                     $mode = rcube_imap_cache::MODE_INDEX;
 
                     if (!$disable) {
                         $mode |= rcube_imap_cache::MODE_MESSAGE;
                     }
 
                     $this->imap->set_messages_caching(true, $mode);
             }
         }
     }
 
 }