diff --git a/lib/file_document.php b/lib/file_document.php
index dc9199f..6e7ab98 100644
--- a/lib/file_document.php
+++ b/lib/file_document.php
@@ -1,781 +1,778 @@
 <?php
 /**
  +--------------------------------------------------------------------------+
  | This file is part of the Kolab File API                                  |
  |                                                                          |
  | Copyright (C) 2012-2016, Kolab Systems AG                                |
  |                                                                          |
  | 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/>      |
  +--------------------------------------------------------------------------+
  | Author: Aleksander Machniak <machniak@kolabsys.com>                      |
  +--------------------------------------------------------------------------+
 */
 
 /**
  * Document editing sessions handling
  */
 class file_document
 {
     protected $api;
     protected $rc;
     protected $user;
     protected $sessions_table    = 'chwala_sessions';
     protected $invitations_table = 'chwala_invitations';
     protected $icache            = array();
 
     const STATUS_INVITED   = 'invited';
     const STATUS_REQUESTED = 'requested';
     const STATUS_ACCEPTED  = 'accepted';
     const STATUS_DECLINED  = 'declined';
     const STATUS_DECLINED_OWNER = 'declined-owner'; // same as 'declined' but done by the session owner
     const STATUS_ACCEPTED_OWNER = 'accepted-owner'; // same as 'accepted' but done by the session owner
 
 
     /**
      * Class constructor
      *
      * @param file_api Chwala API app instance
      */
     public function __construct($api)
     {
         $this->rc   = rcube::get_instance();
         $this->api  = $api;
         $this->user = $_SESSION['user'];
 
         $db = $this->rc->get_dbh();
         $this->sessions_table    = $db->table_name($this->sessions_table);
         $this->invitations_table = $db->table_name($this->invitations_table);
     }
 
     /**
      * Return viewer URI for specified file/session. This creates
      * a new collaborative editing session when needed.
      *
      * @param string $file        File path
      * @param string &$mimetype   File type
      * @param string &$session_id Optional session ID to join to
      * @param string $readonly    Create readonly (one-time) session
      *
      * @return string An URI for specified file/session
      * @throws Exception
      */
     public function session_start($file, &$mimetype, &$session_id = null, $readonly = false)
     {
         if ($file !== null) {
             $uri = $this->path2uri($file, $driver);
         }
 
         $backend = $this->api->get_backend();
 
         if ($session_id) {
             $session = $this->session_info($session_id);
 
             if (empty($session)) {
                 throw new Exception("Document session not found.", file_api_core::ERROR_CODE);
             }
 
             // check session ownership
             if ($session['owner'] != $this->user) {
                 // check if the user was invited
                 $invitations = $this->invitations_find(array('session_id' => $session_id, 'user' => $this->user));
                 $states      = array(self::STATUS_INVITED, self::STATUS_ACCEPTED, self::STATUS_ACCEPTED_OWNER);
 
                 if (empty($invitations) || !in_array($invitations[0]['status'], $states)) {
                     throw new Exception("No permission to join the editing session.", file_api_core::ERROR_CODE);
                 }
 
                 // automatically accept the invitation, if not done yet
                 if ($invitations[0]['status'] == self::STATUS_INVITED) {
                     $this->invitation_update($session_id, $this->user, self::STATUS_ACCEPTED);
                 }
             }
 
             $mimetype = $session['type'];
         }
         else if (!empty($uri)) {
             // To prevent from creating new sessions for the same file+user
             // (e.g. when user uses F5 to refresh the page), we check first
             // if such a session exist and continue with it
-            $db  = $this->rc->get_dbh();
+            $db = $this->rc->get_dbh();
 
-            if (!$readonly) {
-                $res = $db->query("SELECT `id` FROM `{$this->sessions_table}`"
-                    . " WHERE `owner` = ? AND `uri` = ? AND `readonly` = 0",
-                    $this->user, $uri);
+            $res = $db->query("SELECT `id` FROM `{$this->sessions_table}`"
+                . " WHERE `owner` = ? AND `uri` = ? AND `readonly` = ?",
+                $this->user, $uri, intval($readonly));
 
-                if ($row = $db->fetch_assoc($res)) {
-                    $session_id = $row['id'];
-                    $res = true;
-                }
+            if ($row = $db->fetch_assoc($res)) {
+                $session_id = $row['id'];
+                $res = true;
             }
-
-            if (empty($res) && !$db->is_error($res)) {
+            else if (!$db->is_error($res)) {
                 $session_id = rcube_utils::bin2ascii(md5(time() . $uri, true));
                 $data       = array('type' => $mimetype);
                 $owner      = $this->user;
 
                 // we'll store user credentials if the file comes from
                 // an external source that requires authentication
                 if ($backend != $driver) {
                     $auth = $driver->auth_info();
                     $auth['password']  = $this->rc->encrypt($auth['password']);
                     $data['auth_info'] = $auth;
                 }
 
                 $res = $this->session_create($session_id, $uri, $owner, $data, $readonly);
             }
 
             if (!$res) {
                 throw new Exception("Failed creating document editing session", file_api_core::ERROR_CODE);
             }
         }
         else {
             throw new Exception("Failed creating document editing session (unknown file)", file_api_core::ERROR_CODE);
         }
 
         // Implementations should return real URI
         return '';
     }
 
     /**
      * Get file path (not URI) from session.
      *
      * @param string $id        Session ID
      * @param bool   $join_mode Throw exception only if session does not exist
      *
      * @return string File path
      * @throws Exception
      */
     public function session_file($id, $join_mode = false)
     {
         $session = $this->session_info($id);
 
         if (empty($session)) {
             throw new Exception("Document session not found.", file_api_core::ERROR_CODE);
         }
 
         $path = $this->uri2path($session['uri']);
 
         if (empty($path) && (!$join_mode || $session['owner'] == $this->user)) {
             throw new Exception("Document session not found.", file_api_core::ERROR_CODE);
         }
 
         // check permissions to the session
         if ($session['owner'] != $this->user) {
             $invitations = $this->invitations_find(array('session_id' => $id, 'user' => $this->user));
             $states      = array(self::STATUS_INVITED, self::STATUS_ACCEPTED, self::STATUS_ACCEPTED_OWNER);
 
             if (empty($invitations) || !in_array($invitations[0]['status'], $states)) {
                 throw new Exception("No permission to join the editing session.", file_api_core::ERROR_CODE);
             }
         }
 
         return $path;
     }
 
     /**
      * Get editing session info
      *
      * @param string $id               Session identifier
      * @param bool   $with_invitations Return invitations list
      *
      * @return array Session data
      */
     public function session_info($id, $with_invitations = false)
     {
         $session = $this->icache["session:$id"];
 
         if (!$session) {
             $db     = $this->rc->get_dbh();
             $result = $db->query("SELECT * FROM `{$this->sessions_table}`"
                 . " WHERE `id` = ?", $id);
 
             if ($row = $db->fetch_assoc($result)) {
                 $session = $this->session_info_parse($row);
 
                 $this->icache["session:$id"] = $session;
             }
         }
 
         if ($session) {
             if ($session['owner'] == $this->user) {
                 $session['is_owner'] = true;
             }
 
             if ($with_invitations && $session['is_owner']) {
                 $session['invitations'] = $this->invitations_find(array('session_id' => $id));
             }
         }
 
         return $session;
     }
 
     /**
      * Find editing sessions for specified path
      */
     public function session_find($path, $invitations = true)
     {
         // create an URI for specified path
         $uri = trim($this->path2uri($path), '/') . '/';
 
         // get existing sessions
         $sessions = array();
         $filter   = array('file', 'owner', 'owner_name', 'is_owner');
         $db       = $this->rc->get_dbh();
         $result   = $db->query("SELECT * FROM `{$this->sessions_table}`"
             . " WHERE `readonly` = 0 AND `uri` LIKE '" . $db->escape($uri) . "%'");
 
         while ($row = $db->fetch_assoc($result)) {
             if ($path = $this->uri2path($row['uri'])) {
                 $sessions[$row['id']] = $this->session_info_parse($row, $path, $filter);
             }
         }
 
         // set 'is_invited' flag
         if ($invitations && !empty($sessions)) {
             $invitations = $this->invitations_find(array('user' => $this->user));
             $states      = array(self::STATUS_INVITED, self::STATUS_ACCEPTED, self::STATUS_ACCEPTED_OWNER);
 
             foreach ($invitations as $invitation) {
                 if (!empty($sessions[$invitation['session_id']]) && in_array($invitation['status'], $states)) {
                     $sessions[$invitation['session_id']]['is_invited'] = true;
                 }
             }
         }
 
         return $sessions;
     }
 
     /**
      * Delete editing session (only owner can do that)
      *
      * @param string $id Session identifier
      */
     public function session_delete($id)
     {
         $db     = $this->rc->get_dbh();
         $result = $db->query("DELETE FROM `{$this->sessions_table}`"
             . " WHERE `id` = ? AND `owner` = ?",
             $id, $this->user);
 
         return $db->affected_rows($result) > 0;
     }
 
     /**
      * Create editing session
      */
     protected function session_create($id, $uri, $owner, $data, $readonly = false)
     {
         // get user name
         $owner_name = $this->api->resolve_user($owner) ?: '';
 
         $db     = $this->rc->get_dbh();
         $result = $db->query("INSERT INTO `{$this->sessions_table}`"
             . " (`id`, `uri`, `owner`, `owner_name`, `data`, `readonly`)"
             . " VALUES (?, ?, ?, ?, ?, ?)",
             $id, $uri, $owner, $owner_name, json_encode($data), intval($readonly));
 
         $success = $db->affected_rows($result) > 0;
 
         if ($success) {
 
             // @TODO
         }
 
         return $success;
     }
 
     /**
      * Find sessions, including:
      *   1. to which the user has access (is a creator or has been invited)
      *   2. to which the user is considered eligible to request authorization
      *     to participate in the session by already having access to the file
      * Note: Readonly sessions are ignored here.
      *
      * @param array $param List parameters
      *
      * @return array Sessions list
      */
     public function sessions_list($param = array())
     {
         $db       = $this->rc->get_dbh();
         $sessions = array();
 
         // 1. Get sessions user has access to
         $result = $db->query("SELECT * FROM `{$this->sessions_table}` s"
             . " WHERE s.`readonly` = 0 AND (s.`owner` = ? OR s.`id` IN ("
                 . "SELECT i.`session_id` FROM `{$this->invitations_table}` i"
                 . " WHERE i.`user` = ?"
             . "))",
             $this->user, $this->user);
 
         if ($db->is_error($result)) {
             throw new Exception("Internal error.", file_api_core::ERROR_CODE);
         }
 
         while ($row = $db->fetch_assoc($result)) {
             if ($path = $this->uri2path($row['uri'], true)) {
                 $sessions[$row['id']] = $this->session_info_parse($row, $path);
             }
         }
 
         // 2. Get sessions user is eligible
         // - get list of all folder URIs and find sessions for files in these locations
         // @FIXME: in corner cases (user has many folders) this may produce a big query,
         // maybe fetching all sessions and then comparing with list of locations would be faster?
         $uris  = $this->all_folder_locations();
         $where = array_map(function($uri) use ($db) {
                 return 's.`uri` LIKE ' . $db->quote(str_replace('%', '_', $uri) . '/%');
             }, $uris);
 
         $result = $db->query("SELECT * FROM `{$this->sessions_table}` s"
             . " WHERE s.`readonly` = 0 AND (" . join(' OR ', $where) . ")");
 
         if ($db->is_error($result)) {
             throw new Exception("Internal error.", file_api_core::ERROR_CODE);
         }
 
         while ($row = $db->fetch_assoc($result)) {
             if (empty($sessions[$row['id']])) {
                 // remove filename (and anything after it) so we have the folder URI
                 // to check if it's on the folders list we have
                 $uri = substr($row['uri'], 0, strrpos($row['uri'], '/'));
                 if (in_array($uri, $uris) && ($path = $this->uri2path($row['uri'], true))) {
                     $sessions[$row['id']] = $this->session_info_parse($row, $path);
                 }
             }
         }
 
         // set 'is_invited' flag
         if (!empty($sessions)) {
             $invitations = $this->invitations_find(array('user' => $this->user));
             $states      = array(self::STATUS_INVITED, self::STATUS_ACCEPTED, self::STATUS_ACCEPTED_OWNER);
 
             foreach ($invitations as $invitation) {
                 if (!empty($sessions[$invitation['session_id']]) && in_array($invitation['status'], $states)) {
                     $sessions[$invitation['session_id']]['is_invited'] = true;
                 }
             }
         }
 
         // Sorting
         $sort  = !empty($params['sort']) ? $params['sort'] : 'name';
         $index = array();
 
         if (in_array($sort, array('name', 'file', 'owner'))) {
             foreach ($sessions as $key => $val) {
                 if ($sort == 'name' || $sort == 'file') {
                     $path        = explode(file_storage::SEPARATOR, $val['file']);
                     $index[$key] = $path[count($path) - 1];
                     continue;
                 }
 
                 $index[$key] = $val[$sort];
             }
             array_multisort($index, SORT_ASC, SORT_LOCALE_STRING, $sessions);
         }
 
         if ($params['reverse']) {
             $sessions = array_reverse($sessions, true);
         }
 
         return $sessions;
     }
 
     /**
      * Retern extra editor parameters to post the the viewer iframe
      *
      * @param array $info File info
      *
      * @return array POST parameters
      */
     public function editor_post_params($info)
     {
         return array();
     }
 
     /**
      * Find invitations for current user. This will return all
      * invitations related to the user including his sessions.
      *
      * @param array $filter Search filter (see self::invitations_find())
      *
      * @return array Invitations list
      */
     public function invitations_list($filter = array())
     {
         $filter['user'] = $this->user;
 
         // list of invitations to the user or requested by him
         $result = $this->invitations_find($filter, true);
 
         unset($filter['user']);
         $filter['owner'] = $this->user;
 
         // other invitations that belong to the sessions owned by the user
         if ($other = $this->invitations_find($filter, true)) {
             $result = array_merge($result, $other);
         }
 
         return $result;
     }
 
     /**
      * Find invitations for specified filter
      *
      * @param array $filter Search filter (see self::invitations_find())
      *                      - session_id: session identifier
      *                      - timestamp: "changed > ?" filter
      *                      - user: Invitation user identifier
      *                      - owner: Session owner identifier
      * @param bool $extended Return session file names
      *
      * @return array Invitations list
      */
     public function invitations_find($filter, $extended = false)
     {
         $db     = $this->rc->get_dbh();
         $query  = '';
         $select = "i.*";
 
         foreach ($filter as $column => $value) {
             if ($column == 'timestamp') {
                 $where[] = "i.`changed` > " . $db->fromunixtime($value);
             }
             else if ($column == 'owner') {
                 $join[] = "`{$this->sessions_table}` s ON (i.`session_id` = s.`id`)";
                 $where[] = "s.`owner` = " . $db->quote($value);
             }
             else {
                 $where[] = "i.`$column` = " . $db->quote($value);
             }
         }
 
         if ($extended) {
             $select .= ", s.`uri`, s.`owner`, s.`owner_name`";
             $join[]  = "`{$this->sessions_table}` s ON (i.`session_id` = s.`id`)";
         }
 
         if (!empty($join)) {
             $query .= ' JOIN ' . implode(' JOIN ', array_unique($join));
         }
 
         if (!empty($where)) {
             $query .= ' WHERE ' . implode(' AND ', array_unique($where));
         }
 
         $result = $db->query("SELECT $select FROM `{$this->invitations_table}` i"
             . "$query ORDER BY i.`changed`");
 
         if ($db->is_error($result)) {
             throw new Exception("Internal error.", file_api_core::ERROR_CODE);
         }
 
         $invitations = array();
 
         while ($row = $db->fetch_assoc($result)) {
             if ($extended) {
                 try {
                     // add unix-timestamp of the `changed` date to the result
                     $dt = new DateTime($row['changed']);
                     $row['timestamp'] = $dt->format('U');
                 }
                 catch(Exception $e) { }
 
                 // add filename to the result
                 $filename = parse_url($row['uri'], PHP_URL_PATH);
                 $filename = pathinfo($filename, PATHINFO_BASENAME);
                 $filename = rawurldecode($filename);
 
                 $row['filename'] = $filename;
 
                 if ($path = $this->uri2path($row['uri'])) {
                     $row['file'] = $path;
                 }
 
                 unset($row['uri']);
             }
 
             $invitations[] = $row;
         }
 
         return $invitations;
     }
 
     /**
      * Create an invitation
      *
      * @param string $session_id Document session identifier
      * @param string $user       User identifier (use null for current user)
      * @param string $status     Invitation status (invited, requested)
      * @param string $comment    Invitation description/comment
      * @param string &$user_name Optional user name
      *
      * @throws Exception
      */
     public function invitation_create($session_id, $user, $status = 'invited', $comment = '', &$user_name = '')
     {
         if (empty($user)) {
             $user = $this->user;
         }
 
         if ($status != self::STATUS_INVITED && $status != self::STATUS_REQUESTED) {
             throw new Exception("Invalid invitation status.", file_api_core::ERROR_CODE);
         }
 
         // get session information
         $session = $this->session_info($session_id);
 
         if (empty($session)) {
             throw new Exception("Document session not found.", file_api_core::ERROR_CODE);
         }
 
         // check session ownership, only owner can create 'new' invitations
         if ($status == self::STATUS_INVITED && $session['owner'] != $this->user) {
             throw new Exception("No permission to create an invitation.", file_api_core::ERROR_CODE);
         }
 
         if ($session['owner'] == $user) {
             throw new Exception("Not possible to create an invitation for the session creator.", file_api_core::ERROR_CODE);
         }
 
         // get user name
         if (empty($user_name)) {
             $user_name = $this->api->resolve_user($user) ?: '';
         }
 
         // insert invitation
         $db     = $this->rc->get_dbh();
         $result = $db->query("INSERT INTO `{$this->invitations_table}`"
             . " (`session_id`, `user`, `user_name`, `status`, `comment`, `changed`)"
             . " VALUES (?, ?, ?, ?, ?, " . $db->now() . ")",
             $session_id, $user, $user_name, $status, $comment ?: '');
 
         if (!$db->affected_rows($result)) {
             throw new Exception("Failed to create an invitation.", file_api_core::ERROR_CODE);
         }
     }
 
     /**
      * Delete an invitation (only session owner can do that)
      *
      * @param string $session_id Session identifier
      * @param string $user       User identifier
      * @param bool   $local      Remove invitation only from local database
      *
      * @throws Exception
      */
     public function invitation_delete($session_id, $user, $local = false)
     {
         $db     = $this->rc->get_dbh();
         $result = $db->query("DELETE FROM `{$this->invitations_table}`"
             . " WHERE `session_id` = ? AND `user` = ?"
                 . " AND EXISTS (SELECT 1 FROM `{$this->sessions_table}` WHERE `id` = ? AND `owner` = ?)",
             $session_id, $user, $session_id, $this->user);
 
         if (!$db->affected_rows($result)) {
             throw new Exception("Failed to delete an invitation.", file_api_core::ERROR_CODE);
         }
     }
 
     /**
      * Update an invitation status
      *
      * @param string $session_id Session identifier
      * @param string $user       User identifier (use null for current user)
      * @param string $status     Invitation status (accepted, declined)
      * @param string $comment    Invitation description/comment
      *
      * @throws Exception
      */
     public function invitation_update($session_id, $user, $status, $comment = '')
     {
         if (empty($user)) {
             $user = $this->user;
         }
 
         if ($status != self::STATUS_ACCEPTED && $status != self::STATUS_DECLINED) {
             throw new Exception("Invalid invitation status.", file_api_core::ERROR_CODE);
         }
 
         // get session information
         $session = $this->session_info($session_id);
 
         if (empty($session)) {
             throw new Exception("Document session not found.", file_api_core::ERROR_CODE);
         }
 
         // check session ownership
         if ($user != $this->user && $session['owner'] != $this->user) {
             throw new Exception("No permission to update an invitation.", file_api_core::ERROR_CODE);
         }
 
         if ($session['owner'] == $this->user) {
             $status = $status . '-owner';
         }
 
         $db     = $this->rc->get_dbh();
         $result = $db->query("UPDATE `{$this->invitations_table}`"
             . " SET `status` = ?, `comment` = ?, `changed` = " . $db->now()
             . " WHERE `session_id` = ? AND `user` = ?",
             $status, $comment ?: '', $session_id, $user);
 
         if (!$db->affected_rows($result)) {
             throw new Exception("Failed to update an invitation status.", file_api_core::ERROR_CODE);
         }
     }
 
     /**
      * Update a session URI (e.g. on file/folder move)
      *
      * @param string $from      Source file/folder path
      * @param string $to        Destination file/folder path
      * @param bool   $is_folder True if the path is a folder
      */
     public function session_uri_update($from, $to, $is_folder = false)
     {
         $db = $this->rc->get_dbh();
 
         // Resolve paths
         $from = $this->path2uri($from);
         $to   = $this->path2uri($to);
 
         if ($is_folder) {
             $set = "`uri` = REPLACE(`uri`, " . $db->quote($from . '/') . ", " . $db->quote($to .'/') . ")";
             $where = "`uri` LIKE " . $db->quote(str_replace('%', '_', $from) . '/%');
         }
         else {
             $set = "`uri` = " . $db->quote($to);
             $where = "`uri` = " . $db->quote($from);
         }
 
         $db->query("UPDATE `{$this->sessions_table}` SET $set WHERE $where");
     }
 
     /**
      * Parse session info data
      */
     protected function session_info_parse($record, $path = null, $filter = array())
     {
         $session = array();
         $fields  = array('id', 'uri', 'owner', 'owner_name');
 
         foreach ($fields as $field) {
             if (isset($record[$field])) {
                 $session[$field] = $record[$field];
             }
         }
 
         if ($path) {
             $session['file'] = $path;
         }
 
         if (!empty($record['data']) && (empty($filter) || in_array('type', $filter))) {
             $data = json_decode($record['data'], true);
             $session['type'] = $data['type'];
         }
 
         // @TODO: is_invited?, last_modified?
 
         if ($session['owner'] == $this->user) {
             $session['is_owner'] = true;
         }
 
         if (!empty($filter)) {
             $session = array_intersect_key($session, array_flip($filter));
         }
 
         return $session;
     }
 
     /**
      * Get file URI from path
      */
     protected function path2uri($path, &$driver = null)
     {
         list($driver, $path) = $this->api->get_driver($path);
 
         return $driver->path2uri($path);
     }
 
     /**
      * Get file path from the URI
      */
     protected function uri2path($uri, $use_fallback = false)
     {
         $backend = $this->api->get_backend();
 
         try {
             return $backend->uri2path($uri);
         }
         catch (Exception $e) {
                 // do nothing
         }
 
         foreach ($this->api->get_drivers(true) as $driver) {
             try {
                 $path  = $driver->uri2path($uri);
                 $title = $driver->title();
 
                 if ($title) {
                     $path = $title . file_storage::SEPARATOR . $path;
                 }
 
                 return $path;
             }
             catch (Exception $e) {
                 // do nothing
             }
         }
 
         // likely user has no access to the file, but has been invited,
         // extract filename from the URI
         if ($use_fallback && $uri) {
             $path = parse_url($uri, PHP_URL_PATH);
             $path = explode('/', $path);
             $path = $path[count($path) - 1];
 
             return $path;
         }
     }
 
     /**
      * Get URI of all user folders (with shared locations)
      */
     protected function all_folder_locations()
     {
         $locations = array();
 
         foreach (array_merge(array($this->api->get_backend()), $this->api->get_drivers(true)) as $driver) {
             // Performance optimization: We're interested here in shared folders,
             // Kolab is the only driver that currently supports them, ignore others
             if (get_class($driver) != 'kolab_file_storage') {
                 continue;
             }
 
             try {
                 foreach ($driver->folder_list() as $folder) {
                     if ($uri = $driver->path2uri($folder)) {
                         $locations[] = $uri;
                     }
                 }
             }
             catch (Exception $e) {
                // do nothing
             }
         }
 
         return $locations;
     }
 }