path: root/program/include/rcube_imap.php

<?php

/*
 +-----------------------------------------------------------------------+
 | program/include/rcube_imap.php                                        |
 |                                                                       |
 | This file is part of the RoundCube Webmail client                     |
 | Copyright (C) 2005-2010, RoundCube Dev. - Switzerland                 |
 | Licensed under the GNU GPL                                            |
 |                                                                       |
 | PURPOSE:                                                              |
 |   IMAP Engine                                                         |
 |                                                                       |
 +-----------------------------------------------------------------------+
 | Author: Thomas Bruederli <roundcube@gmail.com>                        |
 | Author: Aleksander Machniak <alec@alec.pl>                            |
 +-----------------------------------------------------------------------+

 $Id$

*/


/**
 * Interface class for accessing an IMAP server
 *
 * @package    Mail
 * @author     Thomas Bruederli <roundcube@gmail.com>
 * @author     Aleksander Machniak <alec@alec.pl>
 * @version    2.0
 */
class rcube_imap
{
    public $debug_level = 1;
    public $error_code = 0;
    public $skip_deleted = false;
    public $root_dir = '';
    public $page_size = 10;
    public $list_page = 1;
    public $delimiter = NULL;
    public $threading = false;
    public $fetch_add_headers = '';
    public $conn; // rcube_imap_generic object

    private $db;
    private $root_ns = '';
    private $mailbox = 'INBOX';
    private $sort_field = '';
    private $sort_order = 'DESC';
    private $caching_enabled = false;
    private $default_charset = 'ISO-8859-1';
    private $struct_charset = NULL;
    private $default_folders = array('INBOX');
    private $icache = array();
    private $cache = array();
    private $cache_keys = array();
    private $cache_changes = array();
    private $uid_id_map = array();
    private $msg_headers = array();
    public  $search_set = NULL;
    public  $search_string = '';
    private $search_charset = '';
    private $search_sort_field = '';
    private $search_threads = false;
    private $db_header_fields = array('idx', 'uid', 'subject', 'from', 'to', 'cc', 'date', 'size');
    private $options = array('auth_method' => 'check');
    private $host, $user, $pass, $port, $ssl;


    /**
     * Object constructor
     *
     * @param object DB Database connection
     */
    function __construct($db_conn)
    {
        $this->db = $db_conn;
        $this->conn = new rcube_imap_generic();
    }


    /**
     * Connect to an IMAP server
     *
     * @param  string   Host to connect
     * @param  string   Username for IMAP account
     * @param  string   Password for IMAP account
     * @param  number   Port to connect to
     * @param  string   SSL schema (either ssl or tls) or null if plain connection
     * @return boolean  TRUE on success, FALSE on failure
     * @access public
     */
    function connect($host, $user, $pass, $port=143, $use_ssl=null)
    {
        // check for OpenSSL support in PHP build
        if ($use_ssl && extension_loaded('openssl'))
            $this->options['ssl_mode'] = $use_ssl == 'imaps' ? 'ssl' : $use_ssl;
        else if ($use_ssl) {
            raise_error(array('code' => 403, 'type' => 'imap',
                'file' => __FILE__, 'line' => __LINE__,
                'message' => "OpenSSL not available"), true, false);
            $port = 143;
        }

        $this->options['port'] = $port;

        $attempt = 0;
        do {
            $data = rcmail::get_instance()->plugins->exec_hook('imap_connect',
                array('host' => $host, 'user' => $user, 'attempt' => ++$attempt));

            if (!empty($data['pass']))
                $pass = $data['pass'];

            $this->conn->connect($data['host'], $data['user'], $pass, $this->options);
        } while(!$this->conn->connected() && $data['retry']);

        $this->host = $data['host'];
        $this->user = $data['user'];
        $this->pass = $pass;
        $this->port = $port;
        $this->ssl  = $use_ssl;

        // print trace messages
        if ($this->conn->connected()) {
            if ($this->conn->message && ($this->debug_level & 8)) {
                console($this->conn->message);
            }

            // get server properties
            if (!empty($this->conn->rootdir))
                $this->set_rootdir($this->conn->rootdir);
            if (empty($this->delimiter))
	            $this->get_hierarchy_delimiter();

            return true;
        }
        // write error log
        else if ($this->conn->error) {
            $this->error_code = $this->conn->errornum;
            raise_error(array('code' => 403, 'type' => 'imap',
                'file' => __FILE__, 'line' => __LINE__,
                'message' => $this->conn->error), true, false);
        }

        return false;
    }


    /**
     * Close IMAP connection
     * Usually done on script shutdown
     *
     * @access public
     */
    function close()
    {
        if ($this->conn && $this->conn->connected())
            $this->conn->close();
        $this->write_cache();
    }


    /**
     * Close IMAP connection and re-connect
     * This is used to avoid some strange socket errors when talking to Courier IMAP
     *
     * @access public
     */
    function reconnect()
    {
        $this->close();
        $this->connect($this->host, $this->user, $this->pass, $this->port, $this->ssl);

        // issue SELECT command to restore connection status
        if ($this->mailbox)
            $this->conn->select($this->mailbox);
    }

    /**
     * Set options to be used in rcube_imap_generic::connect()
     */
    function set_options($opt)
    {
        $this->options = array_merge($this->options, (array)$opt);
    }

    /**
     * Set a root folder for the IMAP connection.
     *
     * Only folders within this root folder will be displayed
     * and all folder paths will be translated using this folder name
     *
     * @param  string   Root folder
     * @access public
     */
    function set_rootdir($root)
    {
        if (preg_match('/[.\/]$/', $root)) //(substr($root, -1, 1)==='/')
            $root = substr($root, 0, -1);

        $this->root_dir = $root;
        $this->options['rootdir'] = $root;

        if (empty($this->delimiter))
            $this->get_hierarchy_delimiter();
    }


    /**
     * Set default message charset
     *
     * This will be used for message decoding if a charset specification is not available
     *
     * @param  string   Charset string
     * @access public
     */
    function set_charset($cs)
    {
        $this->default_charset = $cs;
    }


    /**
     * This list of folders will be listed above all other folders
     *
     * @param  array  Indexed list of folder names
     * @access public
     */
    function set_default_mailboxes($arr)
    {
        if (is_array($arr)) {
            $this->default_folders = $arr;

            // add inbox if not included
            if (!in_array('INBOX', $this->default_folders))
                array_unshift($this->default_folders, 'INBOX');
        }
    }


    /**
     * Set internal mailbox reference.
     *
     * All operations will be perfomed on this mailbox/folder
     *
     * @param  string  Mailbox/Folder name
     * @access public
     */
    function set_mailbox($new_mbox)
    {
        $mailbox = $this->mod_mailbox($new_mbox);

        if ($this->mailbox == $mailbox)
            return;

        $this->mailbox = $mailbox;

        // clear messagecount cache for this mailbox
        $this->_clear_messagecount($mailbox);
    }


    /**
     * Set internal list page
     *
     * @param  number  Page number to list
     * @access public
     */
    function set_page($page)
    {
        $this->list_page = (int)$page;
    }


    /**
     * Set internal page size
     *
     * @param  number  Number of messages to display on one page
     * @access public
     */
    function set_pagesize($size)
    {
        $this->page_size = (int)$size;
    }


    /**
     * Save a set of message ids for future message listing methods
     *
     * @param  string  IMAP Search query
     * @param  array   List of message ids or NULL if empty
     * @param  string  Charset of search string
     * @param  string  Sorting field
     */
    function set_search_set($str=null, $msgs=null, $charset=null, $sort_field=null, $threads=false)
    {
        if (is_array($str) && $msgs == null)
            list($str, $msgs, $charset, $sort_field, $threads) = $str;
        if ($msgs === false)
            $msgs = array();
        else if ($msgs != null && !is_array($msgs))
            $msgs = explode(',', $msgs);

        $this->search_string     = $str;
        $this->search_set        = $msgs;
        $this->search_charset    = $charset;
        $this->search_sort_field = $sort_field;
        $this->search_threads    = $threads;
    }


    /**
     * Return the saved search set as hash array
     * @return array Search set
     */
    function get_search_set()
    {
        return array($this->search_string,
	        $this->search_set,
        	$this->search_charset,
        	$this->search_sort_field,
        	$this->search_threads,
	    );
    }


    /**
     * Returns the currently used mailbox name
     *
     * @return  string Name of the mailbox/folder
     * @access  public
     */
    function get_mailbox_name()
    {
        return $this->conn->connected() ? $this->mod_mailbox($this->mailbox, 'out') : '';
    }


    /**
     * Returns the IMAP server's capability
     *
     * @param   string  Capability name
     * @return  mixed   Capability value or TRUE if supported, FALSE if not
     * @access  public
     */
    function get_capability($cap)
    {
        return $this->conn->getCapability(strtoupper($cap));
    }


    /**
     * Sets threading flag to the best supported THREAD algorithm
     *
     * @param  boolean  TRUE to enable and FALSE
     * @return string   Algorithm or false if THREAD is not supported
     * @access public
     */
    function set_threading($enable=false)
    {
        $this->threading = false;

        if ($enable) {
            if ($this->get_capability('THREAD=REFS'))
                $this->threading = 'REFS';
            else if ($this->get_capability('THREAD=REFERENCES'))
                $this->threading = 'REFERENCES';
            else if ($this->get_capability('THREAD=ORDEREDSUBJECT'))
                $this->threading = 'ORDEREDSUBJECT';
        }

        return $this->threading;
    }


    /**
     * Checks the PERMANENTFLAGS capability of the current mailbox
     * and returns true if the given flag is supported by the IMAP server
     *
     * @param   string  Permanentflag name
     * @return  mixed   True if this flag is supported
     * @access  public
     */
    function check_permflag($flag)
    {
        $flag = strtoupper($flag);
        $imap_flag = $this->conn->flags[$flag];
        return (in_array_nocase($imap_flag, $this->conn->permanentflags));
    }


    /**
     * Returns the delimiter that is used by the IMAP server for folder separation
     *
     * @return  string  Delimiter string
     * @access  public
     */
    function get_hierarchy_delimiter()
    {
        if ($this->conn && empty($this->delimiter))
            $this->delimiter = $this->conn->getHierarchyDelimiter();

        if (empty($this->delimiter))
            $this->delimiter = '/';

        return $this->delimiter;
    }


    /**
     * Get message count for a specific mailbox
     *
     * @param  string  Mailbox/folder name
     * @param  string  Mode for count [ALL|THREADS|UNSEEN|RECENT]
     * @param  boolean Force reading from server and update cache
     * @param  boolean Enables storing folder status info (max UID/count),
     *                 required for mailbox_status()
     * @return int     Number of messages
     * @access public
     */
    function messagecount($mbox_name='', $mode='ALL', $force=false, $status=true)
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        return $this->_messagecount($mailbox, $mode, $force, $status);
    }


    /**
     * Private method for getting nr of messages
     *
     * @access  private
     * @see     rcube_imap::messagecount()
     */
    private function _messagecount($mailbox='', $mode='ALL', $force=false, $status=true)
    {
        $mode = strtoupper($mode);

        if (empty($mailbox))
            $mailbox = $this->mailbox;

        // count search set
        if ($this->search_string && $mailbox == $this->mailbox && ($mode == 'ALL' || $mode == 'THREADS') && !$force) {
            if ($this->search_threads)
                return $mode == 'ALL' ? count((array)$this->search_set['depth']) : count((array)$this->search_set['tree']);
            else
                return count((array)$this->search_set);
        }

        $a_mailbox_cache = $this->get_cache('messagecount');

        // return cached value
        if (!$force && is_array($a_mailbox_cache[$mailbox]) && isset($a_mailbox_cache[$mailbox][$mode]))
            return $a_mailbox_cache[$mailbox][$mode];

        if (!is_array($a_mailbox_cache[$mailbox]))
            $a_mailbox_cache[$mailbox] = array();

        if ($mode == 'THREADS') {
            $count = $this->_threadcount($mailbox, $msg_count);
            if ($status) {
                $this->set_folder_stats($mailbox, 'cnt', $msg_count);
                $this->set_folder_stats($mailbox, 'maxuid', $msg_count ? $this->_id2uid($msg_count, $mailbox) : 0);
            }
        }
        // RECENT count is fetched a bit different
        else if ($mode == 'RECENT') {
            $count = $this->conn->checkForRecent($mailbox);
        }
        // use SEARCH for message counting
        else if ($this->skip_deleted) {
            $search_str = "ALL UNDELETED";

            // get message count and store in cache
            if ($mode == 'UNSEEN')
                $search_str .= " UNSEEN";
            // get message count using SEARCH
            // not very performant but more precise (using UNDELETED)
            $index = $this->conn->search($mailbox, $search_str);

            $count = is_array($index) ? count($index) : 0;

            if ($mode == 'ALL' && $status) {
                $this->set_folder_stats($mailbox, 'cnt', $count);
                $this->set_folder_stats($mailbox, 'maxuid', $index ? $this->_id2uid(max($index), $mailbox) : 0);
            }
        }
        else {
            if ($mode == 'UNSEEN')
                $count = $this->conn->countUnseen($mailbox);
            else {
                $count = $this->conn->countMessages($mailbox);
                if ($status) {
                    $this->set_folder_stats($mailbox,'cnt', $count);
                    $this->set_folder_stats($mailbox, 'maxuid', $count ? $this->_id2uid($count, $mailbox) : 0);
                }
            }
        }

        $a_mailbox_cache[$mailbox][$mode] = (int)$count;

        // write back to cache
        $this->update_cache('messagecount', $a_mailbox_cache);

        return (int)$count;
    }


    /**
     * Private method for getting nr of threads
     *
     * @access  private
     * @see     rcube_imap::messagecount()
     */
    private function _threadcount($mailbox, &$msg_count)
    {
        if (!empty($this->icache['threads']))
            return count($this->icache['threads']['tree']);

        list ($thread_tree, $msg_depth, $has_children) = $this->_fetch_threads($mailbox);

        $msg_count = count($msg_depth);

//    $this->update_thread_cache($mailbox, $thread_tree, $msg_depth, $has_children);
        return count($thread_tree);
    }


    /**
     * Public method for listing headers
     * convert mailbox name with root dir first
     *
     * @param   string   Mailbox/folder name
     * @param   int      Current page to list
     * @param   string   Header field to sort by
     * @param   string   Sort order [ASC|DESC]
     * @param   boolean  Number of slice items to extract from result array
     * @return  array    Indexed array with message header objects
     * @access  public
     */
    function list_headers($mbox_name='', $page=NULL, $sort_field=NULL, $sort_order=NULL, $slice=0)
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        return $this->_list_headers($mailbox, $page, $sort_field, $sort_order, false, $slice);
    }


    /**
     * Private method for listing message headers
     *
     * @access  private
     * @see     rcube_imap::list_headers
     */
    private function _list_headers($mailbox='', $page=NULL, $sort_field=NULL, $sort_order=NULL, $recursive=false, $slice=0)
    {
        if (!strlen($mailbox))
            return array();

        // use saved message set
        if ($this->search_string && $mailbox == $this->mailbox)
            return $this->_list_header_set($mailbox, $page, $sort_field, $sort_order, $slice);

        if ($this->threading)
            return $this->_list_thread_headers($mailbox, $page, $sort_field, $sort_order, $recursive, $slice);

        $this->_set_sort_order($sort_field, $sort_order);

        $page         = $page ? $page : $this->list_page;
        $cache_key    = $mailbox.'.msg';
        $cache_status = $this->check_cache_status($mailbox, $cache_key);

        // cache is OK, we can get all messages from local cache
        if ($cache_status>0) {
            $start_msg = ($page-1) * $this->page_size;
            $a_msg_headers = $this->get_message_cache($cache_key, $start_msg,
                $start_msg+$this->page_size, $this->sort_field, $this->sort_order);
            $result = array_values($a_msg_headers);
            if ($slice)
                $result = array_slice($result, -$slice, $slice);
            return $result;
        }
        // cache is dirty, sync it
        else if ($this->caching_enabled && $cache_status==-1 && !$recursive) {
            $this->sync_header_index($mailbox);
            return $this->_list_headers($mailbox, $page, $this->sort_field, $this->sort_order, true, $slice);
        }

        // retrieve headers from IMAP
        $a_msg_headers = array();

        // use message index sort as default sorting (for better performance)
        if (!$this->sort_field) {
            if ($this->skip_deleted) {
                // @TODO: this could be cached
                if ($msg_index = $this->_search_index($mailbox, 'ALL UNDELETED')) {
                    $max = max($msg_index);
                    list($begin, $end) = $this->_get_message_range(count($msg_index), $page);
                    $msg_index = array_slice($msg_index, $begin, $end-$begin);
                }
            }
            else if ($max = $this->conn->countMessages($mailbox)) {
                list($begin, $end) = $this->_get_message_range($max, $page);
                $msg_index = range($begin+1, $end);
            }
            else
                $msg_index = array();

            if ($slice && $msg_index)
                $msg_index = array_slice($msg_index, ($this->sort_order == 'DESC' ? 0 : -$slice), $slice);

            // fetch reqested headers from server
            if ($msg_index)
                $this->_fetch_headers($mailbox, join(",", $msg_index), $a_msg_headers, $cache_key);
        }
        // use SORT command
        else if ($this->get_capability('SORT')) {
            if ($msg_index = $this->conn->sort($mailbox, $this->sort_field, $this->skip_deleted ? 'UNDELETED' : '')) {
                list($begin, $end) = $this->_get_message_range(count($msg_index), $page);
                $max = max($msg_index);
                $msg_index = array_slice($msg_index, $begin, $end-$begin);

                if ($slice)
                    $msg_index = array_slice($msg_index, ($this->sort_order == 'DESC' ? 0 : -$slice), $slice);

                // fetch reqested headers from server
                $this->_fetch_headers($mailbox, join(',', $msg_index), $a_msg_headers, $cache_key);
            }
        }
        // fetch specified header for all messages and sort
        else if ($a_index = $this->conn->fetchHeaderIndex($mailbox, "1:*", $this->sort_field, $this->skip_deleted)) {
            asort($a_index); // ASC
            $msg_index = array_keys($a_index);
            $max = max($msg_index);
            list($begin, $end) = $this->_get_message_range(count($msg_index), $page);
            $msg_index = array_slice($msg_index, $begin, $end-$begin);

            if ($slice)
                $msg_index = array_slice($msg_index, ($this->sort_order == 'DESC' ? 0 : -$slice), $slice);

            // fetch reqested headers from server
            $this->_fetch_headers($mailbox, join(",", $msg_index), $a_msg_headers, $cache_key);
        }

        // delete cached messages with a higher index than $max+1
        // Changed $max to $max+1 to fix this bug : #1484295
        $this->clear_message_cache($cache_key, $max + 1);

        // kick child process to sync cache
        // ...

        // return empty array if no messages found
        if (!is_array($a_msg_headers) || empty($a_msg_headers))
            return array();

        // use this class for message sorting
        $sorter = new rcube_header_sorter();
        $sorter->set_sequence_numbers($msg_index);
        $sorter->sort_headers($a_msg_headers);

        if ($this->sort_order == 'DESC')
            $a_msg_headers = array_reverse($a_msg_headers);

        return array_values($a_msg_headers);
    }


    /**
     * Private method for listing message headers using threads
     *
     * @access  private
     * @see     rcube_imap::list_headers
     */
    private function _list_thread_headers($mailbox, $page=NULL, $sort_field=NULL, $sort_order=NULL, $recursive=false, $slice=0)
    {
        $this->_set_sort_order($sort_field, $sort_order);

        $page = $page ? $page : $this->list_page;
//    $cache_key = $mailbox.'.msg';
//    $cache_status = $this->check_cache_status($mailbox, $cache_key);

        // get all threads (default sort order)
        list ($thread_tree, $msg_depth, $has_children) = $this->_fetch_threads($mailbox);

        if (empty($thread_tree))
            return array();

        $msg_index = $this->_sort_threads($mailbox, $thread_tree);

        return $this->_fetch_thread_headers($mailbox,
            $thread_tree, $msg_depth, $has_children, $msg_index, $page, $slice);
    }


    /**
     * Private method for fetching threads data
     *
     * @param   string   Mailbox/folder name
     * @return  array    Array with thread data
     * @access  private
     */
    private function _fetch_threads($mailbox)
    {
        if (empty($this->icache['threads'])) {
            // get all threads
            list ($thread_tree, $msg_depth, $has_children) = $this->conn->thread(
                $mailbox, $this->threading, $this->skip_deleted ? 'UNDELETED' : '');

            // add to internal (fast) cache
            $this->icache['threads'] = array();
            $this->icache['threads']['tree'] = $thread_tree;
            $this->icache['threads']['depth'] = $msg_depth;
            $this->icache['threads']['has_children'] = $has_children;
        }

        return array(
            $this->icache['threads']['tree'],
            $this->icache['threads']['depth'],
            $this->icache['threads']['has_children'],
        );
    }


    /**
     * Private method for fetching threaded messages headers
     *
     * @access  private
     */
    private function _fetch_thread_headers($mailbox, $thread_tree, $msg_depth, $has_children, $msg_index, $page, $slice=0)
    {
        $cache_key = $mailbox.'.msg';
        // now get IDs for current page
        list($begin, $end) = $this->_get_message_range(count($msg_index), $page);
        $msg_index = array_slice($msg_index, $begin, $end-$begin);

        if ($slice)
            $msg_index = array_slice($msg_index, ($this->sort_order == 'DESC' ? 0 : -$slice), $slice);

        if ($this->sort_order == 'DESC')
            $msg_index = array_reverse($msg_index);

        // flatten threads array
        // @TODO: fetch children only in expanded mode (?)
        $all_ids = array();
        foreach($msg_index as $root) {
            $all_ids[] = $root;
            if (!empty($thread_tree[$root]))
                $all_ids = array_merge($all_ids, array_keys_recursive($thread_tree[$root]));
        }

        // fetch reqested headers from server
        $this->_fetch_headers($mailbox, $all_ids, $a_msg_headers, $cache_key);

        // return empty array if no messages found
        if (!is_array($a_msg_headers) || empty($a_msg_headers))
            return array();

        // use this class for message sorting
        $sorter = new rcube_header_sorter();
        $sorter->set_sequence_numbers($all_ids);
        $sorter->sort_headers($a_msg_headers);

        // Set depth, has_children and unread_children fields in headers
        $this->_set_thread_flags($a_msg_headers, $msg_depth, $has_children);

        return array_values($a_msg_headers);
    }


    /**
     * Private method for setting threaded messages flags:
     * depth, has_children and unread_children
     *
     * @param  array   Reference to headers array indexed by message ID
     * @param  array   Array of messages depth indexed by message ID
     * @param  array   Array of messages children flags indexed by message ID
     * @return array   Message headers array indexed by message ID
     * @access private
     */
    private function _set_thread_flags(&$headers, $msg_depth, $msg_children)
    {
        $parents = array();

        foreach ($headers as $idx => $header) {
            $id = $header->id;
            $depth = $msg_depth[$id];
            $parents = array_slice($parents, 0, $depth);

            if (!empty($parents)) {
                $headers[$idx]->parent_uid = end($parents);
                if (!$header->seen)
                    $headers[$parents[0]]->unread_children++;
            }
            array_push($parents, $header->uid);

            $headers[$idx]->depth = $depth;
            $headers[$idx]->has_children = $msg_children[$id];
        }
    }


    /**
     * Private method for listing a set of message headers (search results)
     *
     * @param   string   Mailbox/folder name
     * @param   int      Current page to list
     * @param   string   Header field to sort by
     * @param   string   Sort order [ASC|DESC]
     * @param   boolean  Number of slice items to extract from result array
     * @return  array    Indexed array with message header objects
     * @access  private
     * @see     rcube_imap::list_header_set()
     */
    private function _list_header_set($mailbox, $page=NULL, $sort_field=NULL, $sort_order=NULL, $slice=0)
    {
        if (!strlen($mailbox) || empty($this->search_set))
            return array();

        // use saved messages from searching
        if ($this->threading)
            return $this->_list_thread_header_set($mailbox, $page, $sort_field, $sort_order, $slice);

        // search set is threaded, we need a new one
        if ($this->search_threads) {
            if (empty($this->search_set['tree']))
                return array();
            $this->search('', $this->search_string, $this->search_charset, $sort_field);
        }

        $msgs = $this->search_set;
        $a_msg_headers = array();
        $page = $page ? $page : $this->list_page;
        $start_msg = ($page-1) * $this->page_size;

        $this->_set_sort_order($sort_field, $sort_order);

        // quickest method (default sorting)
        if (!$this->search_sort_field && !$this->sort_field) {
            if ($sort_order == 'DESC')
                $msgs = array_reverse($msgs);

            // get messages uids for one page
            $msgs = array_slice(array_values($msgs), $start_msg, min(count($msgs)-$start_msg, $this->page_size));

            if ($slice)
                $msgs = array_slice($msgs, -$slice, $slice);

            // fetch headers
            $this->_fetch_headers($mailbox, join(',',$msgs), $a_msg_headers, NULL);

            // I didn't found in RFC that FETCH always returns messages sorted by index
            $sorter = new rcube_header_sorter();
            $sorter->set_sequence_numbers($msgs);
            $sorter->sort_headers($a_msg_headers);

            return array_values($a_msg_headers);
        }

        // sorted messages, so we can first slice array and then fetch only wanted headers
        if ($this->get_capability('SORT')) { // SORT searching result
            // reset search set if sorting field has been changed
            if ($this->sort_field && $this->search_sort_field != $this->sort_field)
                $msgs = $this->search('', $this->search_string, $this->search_charset, $this->sort_field);

            // return empty array if no messages found
            if (empty($msgs))
                return array();

            if ($sort_order == 'DESC')
                $msgs = array_reverse($msgs);

            // get messages uids for one page
            $msgs = array_slice(array_values($msgs), $start_msg, min(count($msgs)-$start_msg, $this->page_size));

            if ($slice)
                $msgs = array_slice($msgs, -$slice, $slice);

            // fetch headers
            $this->_fetch_headers($mailbox, join(',',$msgs), $a_msg_headers, NULL);

            $sorter = new rcube_header_sorter();
            $sorter->set_sequence_numbers($msgs);
            $sorter->sort_headers($a_msg_headers);

            return array_values($a_msg_headers);
        }
        else { // SEARCH result, need sorting
            $cnt = count($msgs);
            // 300: experimantal value for best result
            if (($cnt > 300 && $cnt > $this->page_size) || !$this->sort_field) {
                // use memory less expensive (and quick) method for big result set
                $a_index = $this->message_index('', $this->sort_field, $this->sort_order);
                // get messages uids for one page...
                $msgs = array_slice($a_index, $start_msg, min($cnt-$start_msg, $this->page_size));
                if ($slice)
                    $msgs = array_slice($msgs, -$slice, $slice);
                // ...and fetch headers
                $this->_fetch_headers($mailbox, join(',', $msgs), $a_msg_headers, NULL);

                // return empty array if no messages found
                if (!is_array($a_msg_headers) || empty($a_msg_headers))
                    return array();

                $sorter = new rcube_header_sorter();
                $sorter->set_sequence_numbers($msgs);
                $sorter->sort_headers($a_msg_headers);

                return array_values($a_msg_headers);
            }
            else {
                // for small result set we can fetch all messages headers
                $this->_fetch_headers($mailbox, join(',', $msgs), $a_msg_headers, NULL);

                // return empty array if no messages found
                if (!is_array($a_msg_headers) || empty($a_msg_headers))
                    return array();

                // if not already sorted
                $a_msg_headers = $this->conn->sortHeaders(
                    $a_msg_headers, $this->sort_field, $this->sort_order);

                // only return the requested part of the set
                $a_msg_headers = array_slice(array_values($a_msg_headers),
                    $start_msg, min($cnt-$start_msg, $this->page_size));

                if ($slice)
                    $a_msg_headers = array_slice($a_msg_headers, -$slice, $slice);

                return $a_msg_headers;
            }
        }
    }


    /**
     * Private method for listing a set of threaded message headers (search results)
     *
     * @param   string   Mailbox/folder name
     * @param   int      Current page to list
     * @param   string   Header field to sort by
     * @param   string   Sort order [ASC|DESC]
     * @param   boolean  Number of slice items to extract from result array
     * @return  array    Indexed array with message header objects
     * @access  private
     * @see     rcube_imap::list_header_set()
     */
    private function _list_thread_header_set($mailbox, $page=NULL, $sort_field=NULL, $sort_order=NULL, $slice=0)
    {
        // update search_set if previous data was fetched with disabled threading
        if (!$this->search_threads) {
            if (empty($this->search_set))
                return array();
            $this->search('', $this->search_string, $this->search_charset, $sort_field);
        }

        // empty result
        if (empty($this->search_set['tree']))
            return array();

        $thread_tree = $this->search_set['tree'];
        $msg_depth = $this->search_set['depth'];
        $has_children = $this->search_set['children'];
        $a_msg_headers = array();

        $page = $page ? $page : $this->list_page;
        $start_msg = ($page-1) * $this->page_size;

        $this->_set_sort_order($sort_field, $sort_order);

        $msg_index = $this->_sort_threads($mailbox, $thread_tree, array_keys($msg_depth));

        return $this->_fetch_thread_headers($mailbox,
            $thread_tree, $msg_depth, $has_children, $msg_index, $page, $slice=0);
    }


    /**
     * Helper function to get first and last index of the requested set
     *
     * @param  int     message count
     * @param  mixed   page number to show, or string 'all'
     * @return array   array with two values: first index, last index
     * @access private
     */
    private function _get_message_range($max, $page)
    {
        $start_msg = ($page-1) * $this->page_size;

        if ($page=='all') {
            $begin  = 0;
            $end    = $max;
        }
        else if ($this->sort_order=='DESC') {
            $begin  = $max - $this->page_size - $start_msg;
            $end    = $max - $start_msg;
        }
        else {
            $begin  = $start_msg;
            $end    = $start_msg + $this->page_size;
        }

        if ($begin < 0) $begin = 0;
        if ($end < 0) $end = $max;
        if ($end > $max) $end = $max;

        return array($begin, $end);
    }


    /**
     * Fetches message headers
     * Used for loop
     *
     * @param  string  Mailbox name
     * @param  string  Message index to fetch
     * @param  array   Reference to message headers array
     * @param  array   Array with cache index
     * @return int     Messages count
     * @access private
     */
    private function _fetch_headers($mailbox, $msgs, &$a_msg_headers, $cache_key)
    {
        // fetch reqested headers from server
        $a_header_index = $this->conn->fetchHeaders(
            $mailbox, $msgs, false, false, $this->fetch_add_headers);

        if (empty($a_header_index))
            return 0;

        // cache is incomplete
        $cache_index = $this->get_message_cache_index($cache_key);

        foreach ($a_header_index as $i => $headers) {
            if ($this->caching_enabled && $cache_index[$headers->id] != $headers->uid) {
                // prevent index duplicates
                if ($cache_index[$headers->id]) {
                    $this->remove_message_cache($cache_key, $headers->id, true);
                    unset($cache_index[$headers->id]);
                }
                // add message to cache
                $this->add_message_cache($cache_key, $headers->id, $headers, NULL,
                    !in_array($headers->uid, $cache_index));
            }

            $a_msg_headers[$headers->uid] = $headers;
        }

        return count($a_msg_headers);
    }


    /**
     * Returns current status of mailbox
     *
     * We compare the maximum UID to determine the number of
     * new messages because the RECENT flag is not reliable.
     *
     * @param string Mailbox/folder name
     * @return int   Folder status
     */
    function mailbox_status($mbox_name = null)
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        $old = $this->get_folder_stats($mailbox);

        // refresh message count -> will update
        $this->_messagecount($mailbox, 'ALL', true);

        $result = 0;
        $new = $this->get_folder_stats($mailbox);

        // got new messages
        if ($new['maxuid'] > $old['maxuid'])
            $result += 1;
        // some messages has been deleted
        if ($new['cnt'] < $old['cnt'])
            $result += 2;

        // @TODO: optional checking for messages flags changes (?)
        // @TODO: UIDVALIDITY checking

        return $result;
    }


    /**
     * Stores folder statistic data in session
     * @TODO: move to separate DB table (cache?)
     *
     * @param string Mailbox name
     * @param string Data name
     * @param mixed  Data value
     */
    private function set_folder_stats($mbox_name, $name, $data)
    {
        $_SESSION['folders'][$mbox_name][$name] = $data;
    }


    /**
     * Gets folder statistic data
     *
     * @param string Mailbox name
     * @return array Stats data
     */
    private function get_folder_stats($mbox_name)
    {
        if ($_SESSION['folders'][$mbox_name])
            return (array) $_SESSION['folders'][$mbox_name];
        else
            return array();
    }


    /**
     * Return sorted array of message IDs (not UIDs)
     *
     * @param string Mailbox to get index from
     * @param string Sort column
     * @param string Sort order [ASC, DESC]
     * @return array Indexed array with message ids
     */
    function message_index($mbox_name='', $sort_field=NULL, $sort_order=NULL)
    {
        if ($this->threading)
            return $this->thread_index($mbox_name, $sort_field, $sort_order);

        $this->_set_sort_order($sort_field, $sort_order);

        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        $key = "{$mailbox}:{$this->sort_field}:{$this->sort_order}:{$this->search_string}.msgi";

        // we have a saved search result, get index from there
        if (!isset($this->cache[$key]) && $this->search_string
            && !$this->search_threads && $mailbox == $this->mailbox) {
            // use message index sort as default sorting
            if (!$this->sort_field) {
                $msgs = $this->search_set;

                if ($this->search_sort_field != 'date')
                    sort($msgs);

                if ($this->sort_order == 'DESC')
                    $this->cache[$key] = array_reverse($msgs);
                else
                    $this->cache[$key] = $msgs;
            }
            // sort with SORT command
            else if ($this->get_capability('SORT')) {
                if ($this->sort_field && $this->search_sort_field != $this->sort_field)
                    $this->search('', $this->search_string, $this->search_charset, $this->sort_field);

                if ($this->sort_order == 'DESC')
                    $this->cache[$key] = array_reverse($this->search_set);
                else
                    $this->cache[$key] = $this->search_set;
            }
            else {
                $a_index = $this->conn->fetchHeaderIndex($mailbox,
	                join(',', $this->search_set), $this->sort_field, $this->skip_deleted);

                if (is_array($a_index)) {
                    if ($this->sort_order=="ASC")
                        asort($a_index);
                    else if ($this->sort_order=="DESC")
                        arsort($a_index);

                    $this->cache[$key] = array_keys($a_index);
                }
                else {
                    $this->cache[$key] = array();
                }
            }
        }

        // have stored it in RAM
        if (isset($this->cache[$key]))
            return $this->cache[$key];

        // check local cache
        $cache_key = $mailbox.'.msg';
        $cache_status = $this->check_cache_status($mailbox, $cache_key);

        // cache is OK
        if ($cache_status>0) {
            $a_index = $this->get_message_cache_index($cache_key,
                true, $this->sort_field, $this->sort_order);
            return array_keys($a_index);
        }

        // use message index sort as default sorting
        if (!$this->sort_field) {
            if ($this->skip_deleted) {
                $a_index = $this->_search_index($mailbox, 'ALL');
            } else if ($max = $this->_messagecount($mailbox)) {
                $a_index = range(1, $max);
            }

            if ($a_index !== false && $this->sort_order == 'DESC')
                $a_index = array_reverse($a_index);

            $this->cache[$key] = $a_index;
        }
        // fetch complete message index
        else if ($this->get_capability('SORT')) {
            $a_index = $this->conn->sort($mailbox,
                $this->sort_field, $this->skip_deleted ? 'UNDELETED' : '');

            if ($a_index !== false && $this->sort_order == 'DESC')
                $a_index = array_reverse($a_index);

            $this->cache[$key] = $a_index;
        }
        else if ($a_index = $this->conn->fetchHeaderIndex(
            $mailbox, "1:*", $this->sort_field, $this->skip_deleted)) {
            if ($this->sort_order=="ASC")
                asort($a_index);
            else if ($this->sort_order=="DESC")
                arsort($a_index);

            $this->cache[$key] = array_keys($a_index);
        }

        return $this->cache[$key] !== false ? $this->cache[$key] : array();
    }


    /**
     * Return sorted array of threaded message IDs (not UIDs)
     *
     * @param string Mailbox to get index from
     * @param string Sort column
     * @param string Sort order [ASC, DESC]
     * @return array Indexed array with message IDs
     */
    function thread_index($mbox_name='', $sort_field=NULL, $sort_order=NULL)
    {
        $this->_set_sort_order($sort_field, $sort_order);

        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        $key = "{$mailbox}:{$this->sort_field}:{$this->sort_order}:{$this->search_string}.thi";

        // we have a saved search result, get index from there
        if (!isset($this->cache[$key]) && $this->search_string
            && $this->search_threads && $mailbox == $this->mailbox) {
            // use message IDs for better performance
            $ids = array_keys_recursive($this->search_set['tree']);
            $this->cache[$key] = $this->_flatten_threads($mailbox, $this->search_set['tree'], $ids);
        }

        // have stored it in RAM
        if (isset($this->cache[$key]))
            return $this->cache[$key];
/*
        // check local cache
        $cache_key = $mailbox.'.msg';
        $cache_status = $this->check_cache_status($mailbox, $cache_key);

        // cache is OK
        if ($cache_status>0) {
            $a_index = $this->get_message_cache_index($cache_key, true, $this->sort_field, $this->sort_order);
            return array_keys($a_index);
        }
*/
        // get all threads (default sort order)
        list ($thread_tree) = $this->_fetch_threads($mailbox);

        $this->cache[$key] = $this->_flatten_threads($mailbox, $thread_tree);

        return $this->cache[$key];
    }


    /**
     * Return array of threaded messages (all, not only roots)
     *
     * @param string Mailbox to get index from
     * @param array  Threaded messages array (see _fetch_threads())
     * @param array  Message IDs if we know what we need (e.g. search result)
     *               for better performance
     * @return array Indexed array with message IDs
     *
     * @access private
     */
    private function _flatten_threads($mailbox, $thread_tree, $ids=null)
    {
        if (empty($thread_tree))
            return array();

        $msg_index = $this->_sort_threads($mailbox, $thread_tree, $ids);

        if ($this->sort_order == 'DESC')
            $msg_index = array_reverse($msg_index);

        // flatten threads array
        $all_ids = array();
        foreach($msg_index as $root) {
            $all_ids[] = $root;
            if (!empty($thread_tree[$root])) {
                foreach (array_keys_recursive($thread_tree[$root]) as $val)
                    $all_ids[] = $val;
            }
        }

        return $all_ids;
    }


    /**
     * @access private
     */
    private function sync_header_index($mailbox)
    {
        $cache_key = $mailbox.'.msg';
        $cache_index = $this->get_message_cache_index($cache_key);

        // fetch complete message index
        $a_message_index = $this->conn->fetchHeaderIndex($mailbox, "1:*", 'UID', $this->skip_deleted);

        if ($a_message_index === false)
            return false;

        foreach ($a_message_index as $id => $uid) {
            // message in cache at correct position
            if ($cache_index[$id] == $uid) {
                unset($cache_index[$id]);
                continue;
            }

            // message in cache but in wrong position
            if (in_array((string)$uid, $cache_index, true)) {
                unset($cache_index[$id]);
            }

            // other message at this position
            if (isset($cache_index[$id])) {
                $for_remove[] = $cache_index[$id];
                unset($cache_index[$id]);
            }

            $for_update[] = $id;
        }

        // clear messages at wrong positions and those deleted that are still in cache_index
        if (!empty($for_remove))
            $cache_index = array_merge($cache_index, $for_remove);

        if (!empty($cache_index))
            $this->remove_message_cache($cache_key, $cache_index);

        // fetch complete headers and add to cache
        if (!empty($for_update)) {
            if ($headers = $this->conn->fetchHeader($mailbox,
                    join(',', $for_update), false, $this->fetch_add_headers)) {
                foreach ($headers as $header) {
                    $this->add_message_cache($cache_key, $header->id, $header, NULL,
                        in_array($header->uid, (array)$for_remove));
                }
            }
        }
    }


    /**
     * Invoke search request to IMAP server
     *
     * @param  string  mailbox name to search in
     * @param  string  search string
     * @param  string  search string charset
     * @param  string  header field to sort by
     * @return array   search results as list of message ids
     * @access public
     */
    function search($mbox_name='', $str=NULL, $charset=NULL, $sort_field=NULL)
    {
        if (!$str)
            return false;

        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;

        $results = $this->_search_index($mailbox, $str, $charset, $sort_field);

        $this->set_search_set($str, $results, $charset, $sort_field, (bool)$this->threading);

        return $results;
    }


    /**
     * Private search method
     *
     * @return array   search results as list of message ids
     * @access private
     * @see rcube_imap::search()
     */
    private function _search_index($mailbox, $criteria='ALL', $charset=NULL, $sort_field=NULL)
    {
        $orig_criteria = $criteria;

        if ($this->skip_deleted && !preg_match('/UNDELETED/', $criteria))
            $criteria = 'UNDELETED '.$criteria;

        if ($this->threading) {
            $a_messages = $this->conn->thread($mailbox, $this->threading, $criteria, $charset);

            // Error, try with US-ASCII (RFC5256: SORT/THREAD must support US-ASCII and UTF-8,
            // but I've seen that Courier doesn't support UTF-8)
            if ($a_messages === false && $charset && $charset != 'US-ASCII')
                $a_messages = $this->conn->thread($mailbox, $this->threading,
                    $this->convert_criteria($criteria, $charset), 'US-ASCII');

            if ($a_messages !== false) {
                list ($thread_tree, $msg_depth, $has_children) = $a_messages;
                $a_messages = array(
                    'tree' 	=> $thread_tree,
	                'depth'	=> $msg_depth,
	                'children' => $has_children
                );
            }
        }
        else if ($sort_field && $this->get_capability('SORT')) {
            $charset = $charset ? $charset : $this->default_charset;
            $a_messages = $this->conn->sort($mailbox, $sort_field, $criteria, false, $charset);

            // Error, try with US-ASCII (RFC5256: SORT/THREAD must support US-ASCII and UTF-8,
            // but I've seen that Courier doesn't support UTF-8)
            if ($a_messages === false && $charset && $charset != 'US-ASCII')
                $a_messages = $this->conn->sort($mailbox, $sort_field,
                    $this->convert_criteria($criteria, $charset), false, 'US-ASCII');
        }
        else {
            if ($orig_criteria == 'ALL') {
                $max = $this->_messagecount($mailbox);
                $a_messages = $max ? range(1, $max) : array();
            }
            else {
                $a_messages = $this->conn->search($mailbox,
                    ($charset ? "CHARSET $charset " : '') . $criteria);

                // Error, try with US-ASCII (some servers may support only US-ASCII)
                if ($a_messages === false && $charset && $charset != 'US-ASCII')
                    $a_messages = $this->conn->search($mailbox,
                        'CHARSET US-ASCII ' . $this->convert_criteria($criteria, $charset));

                // I didn't found that SEARCH should return sorted IDs
	            if (is_array($a_messages) && !$this->sort_field)
                    sort($a_messages);
            }
        }

        // update messagecount cache ?
//      $a_mailbox_cache = get_cache('messagecount');
//      $a_mailbox_cache[$mailbox][$criteria] = sizeof($a_messages);
//      $this->update_cache('messagecount', $a_mailbox_cache);

        return $a_messages;
    }


    /**
     * Direct (real and simple) SEARCH request to IMAP server,
     * without result sorting and caching
     *
     * @param  string  Mailbox name to search in
     * @param  string  Search string
     * @param  boolean True if UIDs should be returned
     * @return array   Search results as list of message IDs or UIDs
     * @access public
     */
    function search_once($mbox_name='', $str=NULL, $ret_uid=false)
    {
        if (!$str)
            return false;

        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;

        return $this->conn->search($mailbox, $str, $ret_uid);
    }


    /**
     * Converts charset of search criteria string
     *
     * @param  string  Search string
     * @param  string  Original charset
     * @param  string  Destination charset (default US-ASCII)
     * @return string  Search string
     * @access private
     */
    private function convert_criteria($str, $charset, $dest_charset='US-ASCII')
    {
        // convert strings to US_ASCII
        if (preg_match_all('/\{([0-9]+)\}\r\n/', $str, $matches, PREG_OFFSET_CAPTURE)) {
            $last = 0; $res = '';
            foreach ($matches[1] as $m) {
                $string_offset = $m[1] + strlen($m[0]) + 4; // {}\r\n
                $string = substr($str, $string_offset - 1, $m[0]);
                $string = rcube_charset_convert($string, $charset, $dest_charset);
                if (!$string)
                    continue;
                $res .= sprintf("%s{%d}\r\n%s", substr($str, $last, $m[1] - $last - 1), strlen($string), $string);
                $last = $m[0] + $string_offset - 1;
            }
            if ($last < strlen($str))
                $res .= substr($str, $last, strlen($str)-$last);
        }
        else // strings for conversion not found
            $res = $str;

        return $res;
    }


    /**
     * Sort thread
     *
     * @param string Mailbox name
     * @param  array Unsorted thread tree (rcube_imap_generic::thread() result)
     * @param  array Message IDs if we know what we need (e.g. search result)
     * @return array Sorted roots IDs
     * @access private
     */
    private function _sort_threads($mailbox, $thread_tree, $ids=NULL)
    {
        // THREAD=ORDEREDSUBJECT: 	sorting by sent date of root message
        // THREAD=REFERENCES: 	sorting by sent date of root message
        // THREAD=REFS: 		sorting by the most recent date in each thread
        // default sorting
        if (!$this->sort_field || ($this->sort_field == 'date' && $this->threading == 'REFS')) {
            return array_keys((array)$thread_tree);
          }
        // here we'll implement REFS sorting, for performance reason
        else { // ($sort_field == 'date' && $this->threading != 'REFS')
            // use SORT command
            if ($this->get_capability('SORT')) {
                $a_index = $this->conn->sort($mailbox, $this->sort_field,
	                !empty($ids) ? $ids : ($this->skip_deleted ? 'UNDELETED' : ''));

	            // return unsorted tree if we've got no index data
	            if (!$a_index)
	                return array_keys((array)$thread_tree);
            }
            else {
                // fetch specified headers for all messages and sort them
                $a_index = $this->conn->fetchHeaderIndex($mailbox, !empty($ids) ? $ids : "1:*",
	                $this->sort_field, $this->skip_deleted);

	            // return unsorted tree if we've got no index data
	            if (!$a_index)
	                return array_keys((array)$thread_tree);

                asort($a_index); // ASC
	            $a_index = array_values($a_index);
            }

	        return $this->_sort_thread_refs($thread_tree, $a_index);
        }
    }


    /**
     * THREAD=REFS sorting implementation
     *
     * @param  array   Thread tree array (message identifiers as keys)
     * @param  array   Array of sorted message identifiers
     * @return array   Array of sorted roots messages
     * @access private
     */
    private function _sort_thread_refs($tree, $index)
    {
        if (empty($tree))
            return array();

        $index = array_combine(array_values($index), $index);

        // assign roots
        foreach ($tree as $idx => $val) {
            $index[$idx] = $idx;
            if (!empty($val)) {
                $idx_arr = array_keys_recursive($tree[$idx]);
                foreach ($idx_arr as $subidx)
                    $index[$subidx] = $idx;
            }
        }

        $index = array_values($index);

        // create sorted array of roots
        $msg_index = array();
        if ($this->sort_order != 'DESC') {
            foreach ($index as $idx)
                if (!isset($msg_index[$idx]))
                    $msg_index[$idx] = $idx;
            $msg_index = array_values($msg_index);
        }
        else {
            for ($x=count($index)-1; $x>=0; $x--)
                if (!isset($msg_index[$index[$x]]))
                    $msg_index[$index[$x]] = $index[$x];
            $msg_index = array_reverse($msg_index);
        }

        return $msg_index;
    }


    /**
     * Refresh saved search set
     *
     * @return array Current search set
     */
    function refresh_search()
    {
        if (!empty($this->search_string))
            $this->search_set = $this->search('', $this->search_string, $this->search_charset,
    	        $this->search_sort_field, $this->search_threads);

        return $this->get_search_set();
    }


    /**
     * Check if the given message ID is part of the current search set
     *
     * @return boolean True on match or if no search request is stored
     */
    function in_searchset($msgid)
    {
        if (!empty($this->search_string)) {
            if ($this->search_threads)
                return isset($this->search_set['depth']["$msgid"]);
            else
                return in_array("$msgid", (array)$this->search_set, true);
        }
        else
            return true;
    }


    /**
     * Return message headers object of a specific message
     *
     * @param int     Message ID
     * @param string  Mailbox to read from
     * @param boolean True if $id is the message UID
     * @param boolean True if we need also BODYSTRUCTURE in headers
     * @return object Message headers representation
     */
    function get_headers($id, $mbox_name=NULL, $is_uid=true, $bodystr=false)
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        $uid = $is_uid ? $id : $this->_id2uid($id, $mailbox);

        // get cached headers
        if ($uid && ($headers = &$this->get_cached_message($mailbox.'.msg', $uid)))
            return $headers;

        $headers = $this->conn->fetchHeader(
            $mailbox, $id, $is_uid, $bodystr, $this->fetch_add_headers);

        // write headers cache
        if ($headers) {
            if ($headers->uid && $headers->id)
                $this->uid_id_map[$mailbox][$headers->uid] = $headers->id;

            $this->add_message_cache($mailbox.'.msg', $headers->id, $headers, NULL);
        }

        return $headers;
    }


    /**
     * Fetch body structure from the IMAP server and build
     * an object structure similar to the one generated by PEAR::Mail_mimeDecode
     *
     * @param int Message UID to fetch
     * @param string Message BODYSTRUCTURE string (optional)
     * @return object rcube_message_part Message part tree or False on failure
     */
    function &get_structure($uid, $structure_str='')
    {
        $cache_key = $this->mailbox.'.msg';
        $headers = &$this->get_cached_message($cache_key, $uid);

        // return cached message structure
        if (is_object($headers) && is_object($headers->structure)) {
            return $headers->structure;
        }

        if (!$structure_str) {
            $structure_str = $this->conn->fetchStructureString($this->mailbox, $uid, true);
        }
        $structure = rcube_mime_struct::parseStructure($structure_str);
        $struct = false;

        // parse structure and add headers
        if (!empty($structure)) {
            $headers = $this->get_headers($uid);
            $this->_msg_id = $headers->id;

        // set message charset from message headers
        if ($headers->charset)
            $this->struct_charset = $headers->charset;
        else
            $this->struct_charset = $this->_structure_charset($structure);

        // Here we can recognize malformed BODYSTRUCTURE and
        // 1. [@TODO] parse the message in other way to create our own message structure
        // 2. or just show the raw message body.
        // Example of structure for malformed MIME message:
        // ("text" "plain" ("charset" "us-ascii") NIL NIL "7bit" 2154 70 NIL NIL NIL)
        if ($headers->ctype && $headers->ctype != 'text/plain'
            && $structure[0] == 'text' && $structure[1] == 'plain') {
            return false;
        }

        $struct = &$this->_structure_part($structure);
        $struct->headers = get_object_vars($headers);

        // don't trust given content-type
        if (empty($struct->parts) && !empty($struct->headers['ctype'])) {
            $struct->mime_id = '1';
            $struct->mimetype = strtolower($struct->headers['ctype']);
            list($struct->ctype_primary, $struct->ctype_secondary) = explode('/', $struct->mimetype);
        }

        // write structure to cache
        if ($this->caching_enabled)
            $this->add_message_cache($cache_key, $this->_msg_id, $headers, $struct);
        }

        return $struct;
    }


    /**
     * Build message part object
     *
     * @access private
     */
    function &_structure_part($part, $count=0, $parent='', $mime_headers=null, $raw_headers=null)
    {
        $struct = new rcube_message_part;
        $struct->mime_id = empty($parent) ? (string)$count : "$parent.$count";

        // multipart
        if (is_array($part[0])) {
            $struct->ctype_primary = 'multipart';

            // find first non-array entry
            for ($i=1; $i<count($part); $i++) {
                if (!is_array($part[$i])) {
                    $struct->ctype_secondary = strtolower($part[$i]);
                    break;
                }
            }

            $struct->mimetype = 'multipart/'.$struct->ctype_secondary;

            // build parts list for headers pre-fetching
            for ($i=0, $count=0; $i<count($part); $i++) {
                if (is_array($part[$i]) && count($part[$i]) > 4) {
                    // fetch message headers if message/rfc822
                    // or named part (could contain Content-Location header)
                    if (!is_array($part[$i][0])) {
                        $tmp_part_id = $struct->mime_id ? $struct->mime_id.'.'.($i+1) : $i+1;
                        if (strtolower($part[$i][0]) == 'message' && strtolower($part[$i][1]) == 'rfc822') {
                            $raw_part_headers[] = $tmp_part_id;
                            $mime_part_headers[] = $tmp_part_id;
                        }
                        else if (in_array('name', (array)$part[$i][2]) && (empty($part[$i][3]) || $part[$i][3]=='NIL')) {
                            $mime_part_headers[] = $tmp_part_id;
                        }
                    }
                }
            }

            // pre-fetch headers of all parts (in one command for better performance)
            // @TODO: we could do this before _structure_part() call, to fetch
            // headers for parts on all levels
            if ($mime_part_headers) {
                $mime_part_headers = $this->conn->fetchMIMEHeaders($this->mailbox,
                    $this->_msg_id, $mime_part_headers);
            }
            // we'll need a real content-type of message/rfc822 part
            if ($raw_part_headers) {
                $raw_part_headers = $this->conn->fetchMIMEHeaders($this->mailbox,
                    $this->_msg_id, $raw_part_headers, false);
            }
            $struct->parts = array();
            for ($i=0, $count=0; $i<count($part); $i++) {
                if (is_array($part[$i]) && count($part[$i]) > 4) {
                    $tmp_part_id = $struct->mime_id ? $struct->mime_id.'.'.($i+1) : $i+1;
                    $struct->parts[] = $this->_structure_part($part[$i], ++$count, $struct->mime_id,
                    $mime_part_headers[$tmp_part_id], $raw_part_headers[$tmp_part_id]);
                }
            }

            return $struct;
        }

        // regular part
        $struct->ctype_primary = strtolower($part[0]);
        $struct->ctype_secondary = strtolower($part[1]);
        $struct->mimetype = $struct->ctype_primary.'/'.$struct->ctype_secondary;

        // read content type parameters
        if (is_array($part[2])) {
            $struct->ctype_parameters = array();
            for ($i=0; $i<count($part[2]); $i+=2)
                $struct->ctype_parameters[strtolower($part[2][$i])] = $part[2][$i+1];

            if (isset($struct->ctype_parameters['charset']))
                $struct->charset = $struct->ctype_parameters['charset'];
        }

        // read content encoding
        if (!empty($part[5]) && $part[5]!='NIL') {
            $struct->encoding = strtolower($part[5]);
            $struct->headers['content-transfer-encoding'] = $struct->encoding;
        }

        // get part size
        if (!empty($part[6]) && $part[6]!='NIL')
            $struct->size = intval($part[6]);

        // read part disposition
        $di = count($part) - 2;
        if ((is_array($part[$di]) && count($part[$di]) == 2 && is_array($part[$di][1])) ||
            (is_array($part[--$di]) && count($part[$di]) == 2)) {
            $struct->disposition = strtolower($part[$di][0]);

            if (is_array($part[$di][1]))
                for ($n=0; $n<count($part[$di][1]); $n+=2)
                    $struct->d_parameters[strtolower($part[$di][1][$n])] = $part[$di][1][$n+1];
        }

        // get child parts
        if (is_array($part[8]) && $di != 8) {
            $struct->parts = array();
            for ($i=0, $count=0; $i<count($part[8]); $i++)
                if (is_array($part[8][$i]) && count($part[8][$i]) > 5)
                    $struct->parts[] = $this->_structure_part($part[8][$i], ++$count, $struct->mime_id);
        }

        // get part ID
        if (!empty($part[3]) && $part[3]!='NIL') {
            $struct->content_id = $part[3];
            $struct->headers['content-id'] = $part[3];

            if (empty($struct->disposition))
                $struct->disposition = 'inline';
        }

        // fetch message headers if message/rfc822 or named part (could contain Content-Location header)
        if ($struct->ctype_primary == 'message' || ($struct->ctype_parameters['name'] && !$struct->content_id)) {
            if (empty($mime_headers)) {
                $mime_headers = $this->conn->fetchPartHeader(
                    $this->mailbox, $this->_msg_id, false, $struct->mime_id);
            }
            $struct->headers = $this->_parse_headers($mime_headers) + $struct->headers;

            // get real headers for message of type 'message/rfc822'
            if ($struct->mimetype == 'message/rfc822') {
                if (empty($raw_headers)) {
                    $raw_headers = $this->conn->fetchMIMEHeaders(
                        $this->mailbox, $this->_msg_id, (array)$struct->mime_id, false);
                }
                $struct->real_headers = $this->_parse_headers($raw_headers);

                // get real content-type of message/rfc822
                if (preg_match('/^([a-z0-9_\/-]+)/i', $struct->real_headers['content-type'], $matches)) {
                    $struct->real_mimetype = strtolower($matches[1]);
                }
            }
        }

        if ($struct->ctype_primary=='message') {
            if (is_array($part[8]) && $di != 8 && empty($struct->parts))
                $struct->parts[] = $this->_structure_part($part[8], ++$count, $struct->mime_id);
        }

        // normalize filename property
        $this->_set_part_filename($struct, $mime_headers);

        return $struct;
    }


    /**
     * Set attachment filename from message part structure
     *
     * @access private
     * @param  object rcube_message_part Part object
     * @param  string Part's raw headers
     */
    private function _set_part_filename(&$part, $headers=null)
    {
        if (!empty($part->d_parameters['filename']))
            $filename_mime = $part->d_parameters['filename'];
        else if (!empty($part->d_parameters['filename*']))
            $filename_encoded = $part->d_parameters['filename*'];
        else if (!empty($part->ctype_parameters['name*']))
            $filename_encoded = $part->ctype_parameters['name*'];
        // RFC2231 value continuations
        // TODO: this should be rewrited to support RFC2231 4.1 combinations
        else if (!empty($part->d_parameters['filename*0'])) {
            $i = 0;
            while (isset($part->d_parameters['filename*'.$i])) {
                $filename_mime .= $part->d_parameters['filename*'.$i];
                $i++;
            }
            // some servers (eg. dovecot-1.x) have no support for parameter value continuations
            // we must fetch and parse headers "manually"
            if ($i<2) {
                if (!$headers) {
                    $headers = $this->conn->fetchPartHeader(
                        $this->mailbox, $this->_msg_id, false, $part->mime_id);
                }
                $filename_mime = '';
                $i = 0;
                while (preg_match('/filename\*'.$i.'\s*=\s*"*([^"\n;]+)[";]*/', $headers, $matches)) {
                    $filename_mime .= $matches[1];
                    $i++;
                }
            }
        }
        else if (!empty($part->d_parameters['filename*0*'])) {
            $i = 0;
            while (isset($part->d_parameters['filename*'.$i.'*'])) {
                $filename_encoded .= $part->d_parameters['filename*'.$i.'*'];
                $i++;
            }
            if ($i<2) {
                if (!$headers) {
                    $headers = $this->conn->fetchPartHeader(
                            $this->mailbox, $this->_msg_id, false, $part->mime_id);
                }
                $filename_encoded = '';
                $i = 0; $matches = array();
                while (preg_match('/filename\*'.$i.'\*\s*=\s*"*([^"\n;]+)[";]*/', $headers, $matches)) {
                    $filename_encoded .= $matches[1];
                    $i++;
                }
            }
        }
        else if (!empty($part->ctype_parameters['name*0'])) {
            $i = 0;
            while (isset($part->ctype_parameters['name*'.$i])) {
                $filename_mime .= $part->ctype_parameters['name*'.$i];
                $i++;
            }
            if ($i<2) {
                if (!$headers) {
                    $headers = $this->conn->fetchPartHeader(
                        $this->mailbox, $this->_msg_id, false, $part->mime_id);
                }
                $filename_mime = '';
                $i = 0; $matches = array();
                while (preg_match('/\s+name\*'.$i.'\s*=\s*"*([^"\n;]+)[";]*/', $headers, $matches)) {
                    $filename_mime .= $matches[1];
                    $i++;
                }
            }
        }
        else if (!empty($part->ctype_parameters['name*0*'])) {
            $i = 0;
            while (isset($part->ctype_parameters['name*'.$i.'*'])) {
                $filename_encoded .= $part->ctype_parameters['name*'.$i.'*'];
                $i++;
            }
            if ($i<2) {
                if (!$headers) {
                    $headers = $this->conn->fetchPartHeader(
                        $this->mailbox, $this->_msg_id, false, $part->mime_id);
                }
                $filename_encoded = '';
                $i = 0; $matches = array();
                while (preg_match('/\s+name\*'.$i.'\*\s*=\s*"*([^"\n;]+)[";]*/', $headers, $matches)) {
                    $filename_encoded .= $matches[1];
                    $i++;
                }
            }
        }
        // read 'name' after rfc2231 parameters as it may contains truncated filename (from Thunderbird)
        else if (!empty($part->ctype_parameters['name']))
            $filename_mime = $part->ctype_parameters['name'];
        // Content-Disposition
        else if (!empty($part->headers['content-description']))
            $filename_mime = $part->headers['content-description'];
        else
            return;

        // decode filename
        if (!empty($filename_mime)) {
            $part->filename = rcube_imap::decode_mime_string($filename_mime,
                $part->charset ? $part->charset : ($this->struct_charset ? $this->struct_charset :
                rc_detect_encoding($filename_mime, $this->default_charset)));
        }
        else if (!empty($filename_encoded)) {
            // decode filename according to RFC 2231, Section 4
            if (preg_match("/^([^']*)'[^']*'(.*)$/", $filename_encoded, $fmatches)) {
                $filename_charset = $fmatches[1];
                $filename_encoded = $fmatches[2];
            }
            $part->filename = rcube_charset_convert(urldecode($filename_encoded), $filename_charset);
        }
    }


    /**
     * Get charset name from message structure (first part)
     *
     * @access private
     * @param  array  Message structure
     * @return string Charset name
     */
    function _structure_charset($structure)
    {
        while (is_array($structure)) {
            if (is_array($structure[2]) && $structure[2][0] == 'charset')
                return $structure[2][1];
            $structure = $structure[0];
        }
    }


    /**
     * Fetch message body of a specific message from the server
     *
     * @param  int    Message UID
     * @param  string Part number
     * @param  object rcube_message_part Part object created by get_structure()
     * @param  mixed  True to print part, ressource to write part contents in
     * @param  resource File pointer to save the message part
     * @return string Message/part body if not printed
     */
    function &get_message_part($uid, $part=1, $o_part=NULL, $print=NULL, $fp=NULL)
    {
        // get part encoding if not provided
        if (!is_object($o_part)) {
            $structure_str = $this->conn->fetchStructureString($this->mailbox, $uid, true);
            $structure = new rcube_mime_struct();
            // error or message not found
            if (!$structure->loadStructure($structure_str)) {
                return false;
            }

            $o_part = new rcube_message_part;
            $o_part->ctype_primary = strtolower($structure->getPartType($part));
            $o_part->encoding      = strtolower($structure->getPartEncoding($part));
            $o_part->charset       = $structure->getPartCharset($part);
        }

        // TODO: Add caching for message parts

        if (!$part) $part = 'TEXT';

        $body = $this->conn->handlePartBody($this->mailbox, $uid, true, $part,
            $o_part->encoding, $print, $fp);

        if ($fp || $print)
            return true;

        // convert charset (if text or message part)
        if ($body && ($o_part->ctype_primary == 'text' || $o_part->ctype_primary == 'message')) {
            // assume default if no charset specified
            if (empty($o_part->charset) || strtolower($o_part->charset) == 'us-ascii')
                $o_part->charset = $this->default_charset;

            $body = rcube_charset_convert($body, $o_part->charset);
        }

        return $body;
    }


    /**
     * Fetch message body of a specific message from the server
     *
     * @param  int    Message UID
     * @return string Message/part body
     * @see    rcube_imap::get_message_part()
     */
    function &get_body($uid, $part=1)
    {
        $headers = $this->get_headers($uid);
        return rcube_charset_convert($this->get_message_part($uid, $part, NULL),
            $headers->charset ? $headers->charset : $this->default_charset);
    }


    /**
     * Returns the whole message source as string
     *
     * @param int  Message UID
     * @return string Message source string
     */
    function &get_raw_body($uid)
    {
        return $this->conn->handlePartBody($this->mailbox, $uid, true);
    }


    /**
     * Returns the message headers as string
     *
     * @param int  Message UID
     * @return string Message headers string
     */
    function &get_raw_headers($uid)
    {
        return $this->conn->fetchPartHeader($this->mailbox, $uid, true);
    }


    /**
     * Sends the whole message source to stdout
     *
     * @param int  Message UID
     */
    function print_raw_body($uid)
    {
        $this->conn->handlePartBody($this->mailbox, $uid, true, NULL, NULL, true);
    }


    /**
     * Set message flag to one or several messages
     *
     * @param mixed   Message UIDs as array or comma-separated string, or '*'
     * @param string  Flag to set: SEEN, UNDELETED, DELETED, RECENT, ANSWERED, DRAFT, MDNSENT
     * @param string  Folder name
     * @param boolean True to skip message cache clean up
     * @return int    Number of flagged messages, -1 on failure
     */
    function set_flag($uids, $flag, $mbox_name=NULL, $skip_cache=false)
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;

        $flag = strtoupper($flag);
        list($uids, $all_mode) = $this->_parse_uids($uids, $mailbox);

        if (strpos($flag, 'UN') === 0)
            $result = $this->conn->unflag($mailbox, $uids, substr($flag, 2));
        else
            $result = $this->conn->flag($mailbox, $uids, $flag);

        if ($result >= 0) {
            // reload message headers if cached
            if ($this->caching_enabled && !$skip_cache) {
                $cache_key = $mailbox.'.msg';
                if ($all_mode)
                    $this->clear_message_cache($cache_key);
                else
                    $this->remove_message_cache($cache_key, explode(',', $uids));
            }
            // update counters
            if ($flag=='SEEN')
                $this->_set_messagecount($mailbox, 'UNSEEN', $result*(-1));
            else if ($flag=='UNSEEN')
                $this->_set_messagecount($mailbox, 'UNSEEN', $result);
            else if ($flag=='DELETED')
                $this->_set_messagecount($mailbox, 'ALL', $result*(-1));
        }

        return $result;
    }


    /**
     * Remove message flag for one or several messages
     *
     * @param mixed  Message UIDs as array or comma-separated string, or '*'
     * @param string Flag to unset: SEEN, DELETED, RECENT, ANSWERED, DRAFT, MDNSENT
     * @param string Folder name
     * @return int   Number of flagged messages, -1 on failure
     * @see set_flag
     */
    function unset_flag($uids, $flag, $mbox_name=NULL)
    {
        return $this->set_flag($uids, 'UN'.$flag, $mbox_name);
    }


    /**
     * Append a mail message (source) to a specific mailbox
     *
     * @param string   Target mailbox
     * @param string   The message source string or filename
     * @param string   Headers string if $message contains only the body
     * @param boolean  True if $message is a filename
     *
     * @return boolean True on success, False on error
     */
    function save_message($mbox_name, &$message, $headers='', $is_file=false)
    {
        $mailbox = $this->mod_mailbox($mbox_name);

        // make sure mailbox exists
        if ($this->mailbox_exists($mbox_name, true)) {
            if ($is_file) {
                $separator = rcmail::get_instance()->config->header_delimiter();
                $saved = $this->conn->appendFromFile($mailbox, $message,
                    $headers, $separator.$separator);
            }
            else
                $saved = $this->conn->append($mailbox, $message);
        }

        if ($saved) {
            // increase messagecount of the target mailbox
            $this->_set_messagecount($mailbox, 'ALL', 1);
        }

        return $saved;
    }


    /**
     * Move a message from one mailbox to another
     *
     * @param mixed  Message UIDs as array or comma-separated string, or '*'
     * @param string Target mailbox
     * @param string Source mailbox
     * @return boolean True on success, False on error
     */
    function move_message($uids, $to_mbox, $from_mbox='')
    {
        $fbox = $from_mbox;
        $tbox = $to_mbox;
        $to_mbox = $this->mod_mailbox($to_mbox);
        $from_mbox = $from_mbox ? $this->mod_mailbox($from_mbox) : $this->mailbox;

        list($uids, $all_mode) = $this->_parse_uids($uids, $from_mbox);

        // exit if no message uids are specified
        if (empty($uids))
            return false;

        // make sure mailbox exists
        if ($to_mbox != 'INBOX' && !$this->mailbox_exists($tbox, true)) {
            if (in_array($tbox, $this->default_folders))
                $this->create_mailbox($tbox, true);
            else
                return false;
        }

        // flag messages as read before moving them
        $config = rcmail::get_instance()->config;
        if ($config->get('read_when_deleted') && $tbox == $config->get('trash_mbox')) {
            // don't flush cache (4th argument)
            $this->set_flag($uids, 'SEEN', $fbox, true);
        }

        // move messages
        $move = $this->conn->move($uids, $from_mbox, $to_mbox);
        $moved = !($move === false || $move < 0);

        // send expunge command in order to have the moved message
        // really deleted from the source mailbox
        if ($moved) {
            $this->_expunge($from_mbox, false, $uids);
            $this->_clear_messagecount($from_mbox);
            $this->_clear_messagecount($to_mbox);
        }
        // moving failed
        else if ($config->get('delete_always', false) && $tbox == $config->get('trash_mbox')) {
            $moved = $this->delete_message($uids, $fbox);
        }

        if ($moved) {
            // unset threads internal cache
            unset($this->icache['threads']);

            // remove message ids from search set
            if ($this->search_set && $from_mbox == $this->mailbox) {
                // threads are too complicated to just remove messages from set
                if ($this->search_threads || $all_mode)
                    $this->refresh_search();
                else {
                    $uids = explode(',', $uids);
                    foreach ($uids as $uid)
                        $a_mids[] = $this->_uid2id($uid, $from_mbox);
                    $this->search_set = array_diff($this->search_set, $a_mids);
                }
            }

            // update cached message headers
            $cache_key = $from_mbox.'.msg';
            if ($all_mode || ($start_index = $this->get_message_cache_index_min($cache_key, $uids))) {
                // clear cache from the lowest index on
                $this->clear_message_cache($cache_key, $all_mode ? 1 : $start_index);
            }
        }

        return $moved;
    }


    /**
     * Copy a message from one mailbox to another
     *
     * @param mixed  Message UIDs as array or comma-separated string, or '*'
     * @param string Target mailbox
     * @param string Source mailbox
     * @return boolean True on success, False on error
     */
    function copy_message($uids, $to_mbox, $from_mbox='')
    {
        $fbox = $from_mbox;
        $tbox = $to_mbox;
        $to_mbox = $this->mod_mailbox($to_mbox);
        $from_mbox = $from_mbox ? $this->mod_mailbox($from_mbox) : $this->mailbox;

        list($uids, $all_mode) = $this->_parse_uids($uids, $from_mbox);

        // exit if no message uids are specified
        if (empty($uids))
            return false;

        // make sure mailbox exists
        if ($to_mbox != 'INBOX' && !$this->mailbox_exists($tbox, true)) {
            if (in_array($tbox, $this->default_folders))
                $this->create_mailbox($tbox, true);
            else
                return false;
        }

        // copy messages
        $copy = $this->conn->copy($uids, $from_mbox, $to_mbox);
        $copied = !($copy === false || $copy < 0);

        if ($copied) {
            $this->_clear_messagecount($to_mbox);
        }

        return $copied;
    }


    /**
     * Mark messages as deleted and expunge mailbox
     *
     * @param mixed  Message UIDs as array or comma-separated string, or '*'
     * @param string Source mailbox
     * @return boolean True on success, False on error
     */
    function delete_message($uids, $mbox_name='')
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;

        list($uids, $all_mode) = $this->_parse_uids($uids, $mailbox);

        // exit if no message uids are specified
        if (empty($uids))
            return false;

        $deleted = $this->conn->delete($mailbox, $uids);

        if ($deleted) {
            // send expunge command in order to have the deleted message
            // really deleted from the mailbox
            $this->_expunge($mailbox, false, $uids);
            $this->_clear_messagecount($mailbox);
            unset($this->uid_id_map[$mailbox]);

            // unset threads internal cache
            unset($this->icache['threads']);

            // remove message ids from search set
            if ($this->search_set && $mailbox == $this->mailbox) {
                // threads are too complicated to just remove messages from set
                if ($this->search_threads || $all_mode)
                    $this->refresh_search();
                else {
                    $uids = explode(',', $uids);
                    foreach ($uids as $uid)
                        $a_mids[] = $this->_uid2id($uid, $mailbox);
                    $this->search_set = array_diff($this->search_set, $a_mids);
                }
            }

            // remove deleted messages from cache
            $cache_key = $mailbox.'.msg';
            if ($all_mode || ($start_index = $this->get_message_cache_index_min($cache_key, $uids))) {
                // clear cache from the lowest index on
                $this->clear_message_cache($cache_key, $all_mode ? 1 : $start_index);
            }
        }

        return $deleted;
    }


    /**
     * Clear all messages in a specific mailbox
     *
     * @param string Mailbox name
     * @return int Above 0 on success
     */
    function clear_mailbox($mbox_name=NULL)
    {
        $mailbox = !empty($mbox_name) ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        $msg_count = $this->_messagecount($mailbox, 'ALL');

        if (!$msg_count) {
            return 0;
        }

        $cleared = $this->conn->clearFolder($mailbox);

        // make sure the message count cache is cleared as well
        if ($cleared) {
            $this->clear_message_cache($mailbox.'.msg');
            $a_mailbox_cache = $this->get_cache('messagecount');
            unset($a_mailbox_cache[$mailbox]);
            $this->update_cache('messagecount', $a_mailbox_cache);
        }

        return $cleared;
    }


    /**
     * Send IMAP expunge command and clear cache
     *
     * @param string Mailbox name
     * @param boolean False if cache should not be cleared
     * @return boolean True on success
     */
    function expunge($mbox_name='', $clear_cache=true)
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        return $this->_expunge($mailbox, $clear_cache);
    }


    /**
     * Send IMAP expunge command and clear cache
     *
     * @param string 	 Mailbox name
     * @param boolean  False if cache should not be cleared
     * @param mixed    Message UIDs as array or comma-separated string, or '*'
     * @return boolean True on success
     * @access private
     * @see rcube_imap::expunge()
     */
    private function _expunge($mailbox, $clear_cache=true, $uids=NULL)
    {
        if ($uids && $this->get_capability('UIDPLUS'))
            $a_uids = is_array($uids) ? join(',', $uids) : $uids;
        else
            $a_uids = NULL;

        $result = $this->conn->expunge($mailbox, $a_uids);

        if ($result>=0 && $clear_cache) {
            $this->clear_message_cache($mailbox.'.msg');
            $this->_clear_messagecount($mailbox);
        }

        return $result;
    }


    /**
     * Parse message UIDs input
     *
     * @param mixed  UIDs array or comma-separated list or '*' or '1:*'
     * @param string Mailbox name
     * @return array Two elements array with UIDs converted to list and ALL flag
     * @access private
     */
    private function _parse_uids($uids, $mailbox)
    {
        if ($uids === '*' || $uids === '1:*') {
            if (empty($this->search_set)) {
                $uids = '1:*';
                $all = true;
            }
            // get UIDs from current search set
            // @TODO: skip fetchUIDs() and work with IDs instead of UIDs (?)
            else {
                if ($this->search_threads)
                    $uids = $this->conn->fetchUIDs($mailbox, array_keys($this->search_set['depth']));
                else
                    $uids = $this->conn->fetchUIDs($mailbox, $this->search_set);

                // save ID-to-UID mapping in local cache
                if (is_array($uids))
                    foreach ($uids as $id => $uid)
                        $this->uid_id_map[$mailbox][$uid] = $id;

                $uids = join(',', $uids);
            }
        }
        else {
            if (is_array($uids))
                $uids = join(',', $uids);

            if (preg_match('/[^0-9,]/', $uids))
                $uids = '';
        }

        return array($uids, (bool) $all);
    }


    /**
     * Translate UID to message ID
     *
     * @param int    Message UID
     * @param string Mailbox name
     * @return int   Message ID
     */
    function get_id($uid, $mbox_name=NULL)
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        return $this->_uid2id($uid, $mailbox);
    }


    /**
     * Translate message number to UID
     *
     * @param int    Message ID
     * @param string Mailbox name
     * @return int   Message UID
     */
    function get_uid($id,$mbox_name=NULL)
    {
        $mailbox = $mbox_name ? $this->mod_mailbox($mbox_name) : $this->mailbox;
        return $this->_id2uid($id, $mailbox);
    }



    /* --------------------------------
     *        folder managment
     * --------------------------------*/

    /**
     * Public method for listing subscribed folders
     *
     * Converts mailbox name with root dir first
     *
     * @param   string  Optional root folder
     * @param   string  Optional filter for mailbox listing
     * @return  array   List of mailboxes/folders
     * @access  public
     */
    function list_mailboxes($root='', $filter='*')
    {
        $a_out = array();
        $a_mboxes = $this->_list_mailboxes($root, $filter);

        foreach ($a_mboxes as $idx => $mbox_row) {
            if ($name = $this->mod_mailbox($mbox_row, 'out'))
                $a_out[] = $name;
            unset($a_mboxes[$idx]);
        }

        // INBOX should always be available
        if (!in_array('INBOX', $a_out))
            array_unshift($a_out, 'INBOX');

        // sort mailboxes
        $a_out = $this->_sort_mailbox_list($a_out);

        return $a_out;
    }


    /**
     * Private method for mailbox listing
     *
     * @return  array   List of mailboxes/folders
     * @see     rcube_imap::list_mailboxes()
     * @access  private
     */
    private function _list_mailboxes($root='', $filter='*')
    {
        // get cached folder list
        $a_mboxes = $this->get_cache('mailboxes');
        if (is_array($a_mboxes))
            return $a_mboxes;

        $a_defaults = $a_out = array();

        // Give plugins a chance to provide a list of mailboxes
        $data = rcmail::get_instance()->plugins->exec_hook('mailboxes_list',
            array('root' => $root, 'filter' => $filter, 'mode' => 'LSUB'));

        if (isset($data['folders'])) {
            $a_folders = $data['folders'];
        }
        else {
            // retrieve list of folders from IMAP server
            $a_folders = $this->conn->listSubscribed($this->mod_mailbox($root), $filter);
        }

        if (!is_array($a_folders) || !sizeof($a_folders))
            $a_folders = array();

        // write mailboxlist to cache
        $this->update_cache('mailboxes', $a_folders);

        return $a_folders;
    }


    /**
     * Get a list of all folders available on the IMAP server
     *
     * @param string IMAP root dir
     * @param string Optional filter for mailbox listing
     * @return array Indexed array with folder names
     */
    function list_unsubscribed($root='', $filter='*')
    {
        // Give plugins a chance to provide a list of mailboxes
        $data = rcmail::get_instance()->plugins->exec_hook('mailboxes_list',
            array('root' => $root, 'filter' => $filter, 'mode' => 'LIST'));

        if (isset($data['folders'])) {
            $a_mboxes = $data['folders'];
        }
        else {
            // retrieve list of folders from IMAP server
            $a_mboxes = $this->conn->listMailboxes($this->mod_mailbox($root), $filter);
        }

        $a_folders = array();
        if (!is_array($a_mboxes))
            $a_mboxes = array();

        // modify names with root dir
        foreach ($a_mboxes as $idx => $mbox_name) {
            if ($name = $this->mod_mailbox($mbox_name, 'out'))
                $a_folders[] = $name;
            unset($a_mboxes[$idx]);
        }

        // INBOX should always be available
        if (!in_array('INBOX', $a_folders))
            array_unshift($a_folders, 'INBOX');

        // filter folders and sort them
        $a_folders = $this->_sort_mailbox_list($a_folders);
        return $a_folders;
    }


    /**
     * Get mailbox quota information
     * added by Nuny
     *
     * @return mixed Quota info or False if not supported
     */
    function get_quota()
    {
        if ($this->get_capability('QUOTA'))
            return $this->conn->getQuota();

        return false;
    }


    /**
     * Subscribe to a specific mailbox(es)
     *
     * @param array Mailbox name(s)
     * @return boolean True on success
     */
    function subscribe($a_mboxes)
    {
        if (!is_array($a_mboxes))
            $a_mboxes = array($a_mboxes);

        // let this common function do the main work
        return $this->_change_subscription($a_mboxes, 'subscribe');
    }


    /**
     * Unsubscribe mailboxes
     *
     * @param array Mailbox name(s)
     * @return boolean True on success
     */
    function unsubscribe($a_mboxes)
    {
        if (!is_array($a_mboxes))
            $a_mboxes = array($a_mboxes);

        // let this common function do the main work
        return $this->_change_subscription($a_mboxes, 'unsubscribe');
    }


    /**
     * Create a new mailbox on the server and register it in local cache
     *
     * @param string  New mailbox name (as utf-7 string)
     * @param boolean True if the new mailbox should be subscribed
     * @param string  Name of the created mailbox, false on error
     */
    function create_mailbox($name, $subscribe=false)
    {
        $result = false;

        // reduce mailbox name to 100 chars
        $name = substr($name, 0, 100);
        $abs_name = $this->mod_mailbox($name);
        $result = $this->conn->createFolder($abs_name);

        // try to subscribe it
        if ($result && $subscribe)
            $this->subscribe($name);

        return $result ? $name : false;
    }


    /**
     * Set a new name to an existing mailbox
     *
     * @param string Mailbox to rename (as utf-7 string)
     * @param string New mailbox name (as utf-7 string)
     * @return string Name of the renames mailbox, False on error
     */
    function rename_mailbox($mbox_name, $new_name)
    {
        $result = false;

        // encode mailbox name and reduce it to 100 chars
        $name = substr($new_name, 0, 100);

        // make absolute path
        $mailbox = $this->mod_mailbox($mbox_name);
        $abs_name = $this->mod_mailbox($name);

        // check if mailbox is subscribed
        $a_subscribed = $this->_list_mailboxes();
        $subscribed = in_array($mailbox, $a_subscribed);

        // unsubscribe folder
        if ($subscribed)
            $this->conn->unsubscribe($mailbox);

        if (strlen($abs_name))
            $result = $this->conn->renameFolder($mailbox, $abs_name);

        if ($result) {
            $delm = $this->get_hierarchy_delimiter();

            // check if mailbox children are subscribed
            foreach ($a_subscribed as $c_subscribed)
                if (preg_match('/^'.preg_quote($mailbox.$delm, '/').'/', $c_subscribed)) {
                    $this->conn->unsubscribe($c_subscribed);
                    $this->conn->subscribe(preg_replace('/^'.preg_quote($mailbox, '/').'/',
                        $abs_name, $c_subscribed));
                }

            // clear cache
            $this->clear_message_cache($mailbox.'.msg');
            $this->clear_cache('mailboxes');
        }

        // try to subscribe it
        if ($result && $subscribed)
            $this->conn->subscribe($abs_name);

        return $result ? $name : false;
    }


    /**
     * Remove mailboxes from server
     *
     * @param string Mailbox name(s) string/array
     * @return boolean True on success
     */
    function delete_mailbox($mbox_name)
    {
        $deleted = false;

        if (is_array($mbox_name))
            $a_mboxes = $mbox_name;
        else if (is_string($mbox_name) && strlen($mbox_name))
            $a_mboxes = explode(',', $mbox_name);

        if (is_array($a_mboxes)) {
            foreach ($a_mboxes as $mbox_name) {
                $mailbox = $this->mod_mailbox($mbox_name);
                $sub_mboxes = $this->conn->listMailboxes($this->mod_mailbox(''),
	                $mbox_name . $this->delimiter . '*');

                // unsubscribe mailbox before deleting
                $this->conn->unsubscribe($mailbox);

                // send delete command to server
                $result = $this->conn->deleteFolder($mailbox);
                if ($result) {
                    $deleted = true;
                    $this->clear_message_cache($mailbox.'.msg');
	            }

                foreach ($sub_mboxes as $c_mbox) {
                    if ($c_mbox != 'INBOX') {
                        $this->conn->unsubscribe($c_mbox);
                        $result = $this->conn->deleteFolder($c_mbox);
                        if ($result) {
                            $deleted = true;
    	                    $this->clear_message_cache($c_mbox.'.msg');
                        }
                    }
                }
            }
        }

        // clear mailboxlist cache
        if ($deleted)
            $this->clear_cache('mailboxes');

        return $deleted;
    }


    /**
     * Create all folders specified as default
     */
    function create_default_folders()
    {
        // create default folders if they do not exist
        foreach ($this->default_folders as $folder) {
            if (!$this->mailbox_exists($folder))
                $this->create_mailbox($folder, true);
            else if (!$this->mailbox_exists($folder, true))
                $this->subscribe($folder);
        }
    }


    /**
     * Checks if folder exists and is subscribed
     *
     * @param string   Folder name
     * @param boolean  Enable subscription checking
     * @return boolean TRUE or FALSE
     */
    function mailbox_exists($mbox_name, $subscription=false)
    {
        if ($mbox_name) {
            if ($mbox_name == 'INBOX')
                return true;

            $key = $subscription ? 'subscribed' : 'existing';
            if (is_array($this->icache[$key]) && in_array($mbox_name, $this->icache[$key]))
                return true;

            if ($subscription) {
                $a_folders = $this->conn->listSubscribed($this->mod_mailbox(''), $mbox_name);
            }
            else {
                $a_folders = $this->conn->listMailboxes($this->mod_mailbox(''), $mbox_name);
	        }

            if (is_array($a_folders) && in_array($this->mod_mailbox($mbox_name), $a_folders)) {
                $this->icache[$key][] = $mbox_name;
                return true;
            }
        }

        return false;
    }


    /**
     * Modify folder name for input/output according to root dir and namespace
     *
     * @param string  Folder name
     * @param string  Mode
     * @return string Folder name
     */
    function mod_mailbox($mbox_name, $mode='in')
    {
        if ($mbox_name == 'INBOX')
            return $mbox_name;

        if (!empty($this->root_dir)) {
            if ($mode=='in')
                $mbox_name = $this->root_dir.$this->delimiter.$mbox_name;
            else if (!empty($mbox_name)) // $mode=='out'
                $mbox_name = substr($mbox_name, strlen($this->root_dir)+1);
        }

        return $mbox_name;
    }


    /* --------------------------------
     *   internal caching methods
     * --------------------------------*/

    /**
     * @access public
     */
    function set_caching($set)
    {
        if ($set && is_object($this->db))
            $this->caching_enabled = true;
        else
            $this->caching_enabled = false;
    }

    /**
     * @access public
     */
    function get_cache($key)
    {
        // read cache (if it was not read before)
        if (!count($this->cache) && $this->caching_enabled) {
            return $this->_read_cache_record($key);
        }

        return $this->cache[$key];
    }

    /**
     * @access private
     */
    private function update_cache($key, $data)
    {
        $this->cache[$key] = $data;
        $this->cache_changed = true;
        $this->cache_changes[$key] = true;
    }

    /**
     * @access private
     */
    private function write_cache()
    {
        if ($this->caching_enabled && $this->cache_changed) {
            foreach ($this->cache as $key => $data) {
                if ($this->cache_changes[$key])
                    $this->_write_cache_record($key, serialize($data));
            }
        }
    }

    /**
     * @access public
     */
    function clear_cache($key=NULL)
    {
        if (!$this->caching_enabled)
            return;

        if ($key===NULL) {
            foreach ($this->cache as $key => $data)
                $this->_clear_cache_record($key);

            $this->cache = array();
            $this->cache_changed = false;
            $this->cache_changes = array();
        }
        else {
            $this->_clear_cache_record($key);
            $this->cache_changes[$key] = false;
            unset($this->cache[$key]);
        }
    }

    /**
     * @access private
     */
    private function _read_cache_record($key)
    {
        if ($this->db) {
            // get cached data from DB
            $sql_result = $this->db->query(
                "SELECT cache_id, data, cache_key ".
                "FROM ".get_table_name('cache').
                " WHERE user_id=? ".
	            "AND cache_key LIKE 'IMAP.%'",
                $_SESSION['user_id']);

            while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
	            $sql_key = preg_replace('/^IMAP\./', '', $sql_arr['cache_key']);
                $this->cache_keys[$sql_key] = $sql_arr['cache_id'];
	            if (!isset($this->cache[$sql_key]))
	                $this->cache[$sql_key] = $sql_arr['data'] ? unserialize($sql_arr['data']) : false;
            }
        }

        return $this->cache[$key];
    }

    /**
     * @access private
     */
    private function _write_cache_record($key, $data)
    {
        if (!$this->db)
            return false;

        // update existing cache record
        if ($this->cache_keys[$key]) {
            $this->db->query(
                "UPDATE ".get_table_name('cache').
                " SET created=". $this->db->now().", data=? ".
                "WHERE user_id=? ".
                "AND cache_key=?",
                $data,
                $_SESSION['user_id'],
                'IMAP.'.$key);
        }
        // add new cache record
        else {
            $this->db->query(
                "INSERT INTO ".get_table_name('cache').
                " (created, user_id, cache_key, data) ".
                "VALUES (".$this->db->now().", ?, ?, ?)",
                $_SESSION['user_id'],
                'IMAP.'.$key,
                $data);

            // get cache entry ID for this key
            $sql_result = $this->db->query(
                "SELECT cache_id ".
                "FROM ".get_table_name('cache').
                " WHERE user_id=? ".
                "AND cache_key=?",
                $_SESSION['user_id'],
                'IMAP.'.$key);

            if ($sql_arr = $this->db->fetch_assoc($sql_result))
                $this->cache_keys[$key] = $sql_arr['cache_id'];
        }
    }

    /**
     * @access private
     */
    private function _clear_cache_record($key)
    {
        $this->db->query(
            "DELETE FROM ".get_table_name('cache').
            " WHERE user_id=? ".
            "AND cache_key=?",
            $_SESSION['user_id'],
            'IMAP.'.$key);

        unset($this->cache_keys[$key]);
    }



    /* --------------------------------
     *   message caching methods
     * --------------------------------*/

    /**
     * Checks if the cache is up-to-date
     *
     * @param string Mailbox name
     * @param string Internal cache key
     * @return int   Cache status: -3 = off, -2 = incomplete, -1 = dirty, 1 = OK
     */
    private function check_cache_status($mailbox, $cache_key)
    {
        if (!$this->caching_enabled)
            return -3;

        $cache_index = $this->get_message_cache_index($cache_key);
        $msg_count = $this->_messagecount($mailbox);
        $cache_count = count($cache_index);

        // empty mailbox
        if (!$msg_count)
            return $cache_count ? -2 : 1;

        // @TODO: We've got one big performance problem in cache status checking method
        // E.g. mailbox contains 1000 messages, in cache table we've got first 100
        // of them. Now if we want to display only that 100 (which we've got)
        // check_cache_status returns 'incomplete' and messages are fetched
        // from IMAP instead of DB.

        if ($cache_count==$msg_count) {
            if ($this->skip_deleted) {
	            $h_index = $this->conn->fetchHeaderIndex($mailbox, "1:*", 'UID', $this->skip_deleted);

                if (empty($h_index))
                    return -2;

	            if (sizeof($h_index) == $cache_count) {
	                $cache_index = array_flip($cache_index);
	                foreach ($h_index as $idx => $uid)
                        unset($cache_index[$uid]);

	                if (empty($cache_index))
	                    return 1;
	            }
	            return -2;
            } else {
                // get UID of message with highest index
                $uid = $this->conn->ID2UID($mailbox, $msg_count);
                $cache_uid = array_pop($cache_index);

                // uids of highest message matches -> cache seems OK
                if ($cache_uid == $uid)
                    return 1;
            }
            // cache is dirty
            return -1;
        }
        // if cache count differs less than 10% report as dirty
        else if (abs($msg_count - $cache_count) < $msg_count/10)
            return -1;
        else
            return -2;
    }

    /**
     * @access private
     */
    private function get_message_cache($key, $from, $to, $sort_field, $sort_order)
    {
        $cache_key = "$key:$from:$to:$sort_field:$sort_order";

        // use idx sort as default sorting
        if (!$sort_field || !in_array($sort_field, $this->db_header_fields)) {
            $sort_field = 'idx';
        }

        if ($this->caching_enabled && !isset($this->cache[$cache_key])) {
            $this->cache[$cache_key] = array();
            $sql_result = $this->db->limitquery(
                "SELECT idx, uid, headers".
                " FROM ".get_table_name('messages').
                " WHERE user_id=?".
                " AND cache_key=?".
                " ORDER BY ".$this->db->quoteIdentifier($sort_field)." ".strtoupper($sort_order),
                $from,
                $to - $from,
                $_SESSION['user_id'],
                $key);

            while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                $uid = $sql_arr['uid'];
                $this->cache[$cache_key][$uid] =  $this->db->decode(unserialize($sql_arr['headers']));

                // featch headers if unserialize failed
                if (empty($this->cache[$cache_key][$uid]))
                    $this->cache[$cache_key][$uid] = $this->conn->fetchHeader(
                            preg_replace('/.msg$/', '', $key), $uid, true, $this->fetch_add_headers);
            }
        }

        return $this->cache[$cache_key];
    }

    /**
     * @access private
     */
    private function &get_cached_message($key, $uid)
    {
        $internal_key = 'message';

        if ($this->caching_enabled && !isset($this->icache[$internal_key][$uid])) {
            $sql_result = $this->db->query(
                "SELECT idx, headers, structure".
                " FROM ".get_table_name('messages').
                " WHERE user_id=?".
                " AND cache_key=?".
                " AND uid=?",
                $_SESSION['user_id'],
                $key,
                $uid);

            if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
	            $this->uid_id_map[preg_replace('/\.msg$/', '', $key)][$uid] = $sql_arr['idx'];
                $this->icache[$internal_key][$uid] = $this->db->decode(unserialize($sql_arr['headers']));
                if (is_object($this->icache[$internal_key][$uid]) && !empty($sql_arr['structure']))
                    $this->icache[$internal_key][$uid]->structure = $this->db->decode(unserialize($sql_arr['structure']));
            }
        }

        return $this->icache[$internal_key][$uid];
    }

    /**
     * @access private
     */
    private function get_message_cache_index($key, $force=false, $sort_field='idx', $sort_order='ASC')
    {
        static $sa_message_index = array();

        // empty key -> empty array
        if (!$this->caching_enabled || empty($key))
            return array();

        if (!empty($sa_message_index[$key]) && !$force)
            return $sa_message_index[$key];

        // use idx sort as default
        if (!$sort_field || !in_array($sort_field, $this->db_header_fields))
            $sort_field = 'idx';

        $sa_message_index[$key] = array();
        $sql_result = $this->db->query(
            "SELECT idx, uid".
            " FROM ".get_table_name('messages').
            " WHERE user_id=?".
            " AND cache_key=?".
            " ORDER BY ".$this->db->quote_identifier($sort_field)." ".$sort_order,
            $_SESSION['user_id'],
            $key);

        while ($sql_arr = $this->db->fetch_assoc($sql_result))
            $sa_message_index[$key][$sql_arr['idx']] = $sql_arr['uid'];

        return $sa_message_index[$key];
    }

    /**
     * @access private
     */
    private function add_message_cache($key, $index, $headers, $struct=null, $force=false)
    {
        if (empty($key) || !is_object($headers) || empty($headers->uid))
            return;

        // add to internal (fast) cache
        $this->icache['message'][$headers->uid] = clone $headers;
        $this->icache['message'][$headers->uid]->structure = $struct;

        // no further caching
        if (!$this->caching_enabled)
            return;

        // check for an existing record (probably headers are cached but structure not)
        if (!$force) {
            $sql_result = $this->db->query(
                "SELECT message_id".
                " FROM ".get_table_name('messages').
                " WHERE user_id=?".
                " AND cache_key=?".
                " AND uid=?",
                $_SESSION['user_id'],
                $key,
                $headers->uid);

            if ($sql_arr = $this->db->fetch_assoc($sql_result))
                $message_id = $sql_arr['message_id'];
        }

        // update cache record
        if ($message_id) {
            $this->db->query(
                "UPDATE ".get_table_name('messages').
                " SET idx=?, headers=?, structure=?".
                " WHERE message_id=?",
                $index,
                serialize($this->db->encode(clone $headers)),
                is_object($struct) ? serialize($this->db->encode(clone $struct)) : NULL,
                $message_id
            );
        }
        else { // insert new record
            $this->db->query(
                "INSERT INTO ".get_table_name('messages').
                " (user_id, del, cache_key, created, idx, uid, subject, ".
                $this->db->quoteIdentifier('from').", ".
                $this->db->quoteIdentifier('to').", ".
                "cc, date, size, headers, structure)".
                " VALUES (?, 0, ?, ".$this->db->now().", ?, ?, ?, ?, ?, ?, ".
                $this->db->fromunixtime($headers->timestamp).", ?, ?, ?)",
                $_SESSION['user_id'],
                $key,
                $index,
                $headers->uid,
                (string)mb_substr($this->db->encode($this->decode_header($headers->subject, true)), 0, 128),
                (string)mb_substr($this->db->encode($this->decode_header($headers->from, true)), 0, 128),
                (string)mb_substr($this->db->encode($this->decode_header($headers->to, true)), 0, 128),
                (string)mb_substr($this->db->encode($this->decode_header($headers->cc, true)), 0, 128),
                (int)$headers->size,
                serialize($this->db->encode(clone $headers)),
                is_object($struct) ? serialize($this->db->encode(clone $struct)) : NULL
            );
        }
    }

    /**
     * @access private
     */
    private function remove_message_cache($key, $ids, $idx=false)
    {
        if (!$this->caching_enabled)
            return;

        $this->db->query(
            "DELETE FROM ".get_table_name('messages').
            " WHERE user_id=?".
            " AND cache_key=?".
            " AND ".($idx ? "idx" : "uid")." IN (".$this->db->array2list($ids, 'integer').")",
            $_SESSION['user_id'],
            $key);
    }

    /**
     * @access private
     */
    private function clear_message_cache($key, $start_index=1)
    {
        if (!$this->caching_enabled)
            return;

        $this->db->query(
            "DELETE FROM ".get_table_name('messages').
            " WHERE user_id=?".
            " AND cache_key=?".
            " AND idx>=?",
            $_SESSION['user_id'], $key, $start_index);
    }

    /**
     * @access private
     */
    private function get_message_cache_index_min($key, $uids=NULL)
    {
        if (!$this->caching_enabled)
            return;

        if (!empty($uids) && !is_array($uids)) {
            if ($uids == '*' || $uids == '1:*')
                $uids = NULL;
            else
                $uids = explode(',', $uids);
        }

        $sql_result = $this->db->query(
            "SELECT MIN(idx) AS minidx".
            " FROM ".get_table_name('messages').
            " WHERE  user_id=?".
            " AND    cache_key=?"
            .(!empty($uids) ? " AND uid IN (".$this->db->array2list($uids, 'integer').")" : ''),
            $_SESSION['user_id'],
            $key);

        if ($sql_arr = $this->db->fetch_assoc($sql_result))
            return $sql_arr['minidx'];
        else
            return 0;
    }


    /* --------------------------------
     *   encoding/decoding methods
     * --------------------------------*/

    /**
     * Split an address list into a structured array list
     *
     * @param string  Input string
     * @param int     List only this number of addresses
     * @param boolean Decode address strings
     * @return array  Indexed list of addresses
     */
    function decode_address_list($input, $max=null, $decode=true)
    {
        $a = $this->_parse_address_list($input, $decode);
        $out = array();
        // Special chars as defined by RFC 822 need to in quoted string (or escaped).
        $special_chars = '[\(\)\<\>\\\.\[\]@,;:"]';

        if (!is_array($a))
            return $out;

        $c = count($a);
        $j = 0;

        foreach ($a as $val) {
            $j++;
            $address = trim($val['address']);
            $name = trim($val['name']);

            if (preg_match('/^[\'"]/', $name) && preg_match('/[\'"]$/', $name))
                $name = preg_replace(array('/^[\'"]/', '/[\'"]$/'), '', $name);

            if ($name && $address && $name != $address)
                $string = sprintf('%s <%s>', preg_match("/$special_chars/", $name) ? '"'.addcslashes($name, '"').'"' : $name, $address);
            else if ($address)
                $string = $address;
            else if ($name)
                $string = $name;

            $out[$j] = array('name' => $name,
                'mailto' => $address,
                'string' => $string
            );

            if ($max && $j==$max)
                break;
        }

        return $out;
    }


    /**
     * Decode a message header value
     *
     * @param string  Header value
     * @param boolean Remove quotes if necessary
     * @return string Decoded string
     */
    function decode_header($input, $remove_quotes=false)
    {
        $str = rcube_imap::decode_mime_string((string)$input, $this->default_charset);
        if ($str{0}=='"' && $remove_quotes)
            $str = str_replace('"', '', $str);

        return $str;
    }


    /**
     * Decode a mime-encoded string to internal charset
     *
     * @param string $input    Header value
     * @param string $fallback Fallback charset if none specified
     *
     * @return string Decoded string
     * @static
     */
    public static function decode_mime_string($input, $fallback=null)
    {
        // Initialize variable
        $out = '';

        // Iterate instead of recursing, this way if there are too many values we don't have stack overflows
        // rfc: all line breaks or other characters not found
        // in the Base64 Alphabet must be ignored by decoding software
        // delete all blanks between MIME-lines, differently we can
        // receive unnecessary blanks and broken utf-8 symbols
        $input = preg_replace("/\?=\s+=\?/", '?==?', $input);

        // Check if there is stuff to decode
        if (strpos($input, '=?') !== false) {
            // Loop through the string to decode all occurences of =? ?= into the variable $out
            while(($pos = strpos($input, '=?')) !== false) {
                // Append everything that is before the text to be decoded
                $out .= substr($input, 0, $pos);

                // Get the location of the text to decode
                $end_cs_pos = strpos($input, "?", $pos+2);
                $end_en_pos = strpos($input, "?", $end_cs_pos+1);
                $end_pos = strpos($input, "?=", $end_en_pos+1);

                // Extract the encoded string
                $encstr = substr($input, $pos+2, ($end_pos-$pos-2));
                // Extract the remaining string
                $input = substr($input, $end_pos+2);

                // Decode the string fragement
                $out .= rcube_imap::_decode_mime_string_part($encstr);
            }

            // Deocde the rest (if any)
            if (strlen($input) != 0)
                $out .= rcube_imap::decode_mime_string($input, $fallback);

            // return the results
            return $out;
        }

        // no encoding information, use fallback
        return rcube_charset_convert($input,
            !empty($fallback) ? $fallback : rcmail::get_instance()->config->get('default_charset', 'ISO-8859-1'));
    }


    /**
     * Decode a part of a mime-encoded string
     *
     * @access private
     */
    private function _decode_mime_string_part($str)
    {
        $a = explode('?', $str);
        $count = count($a);

        // should be in format "charset?encoding?base64_string"
        if ($count >= 3) {
            for ($i=2; $i<$count; $i++)
                $rest .= $a[$i];

            if (($a[1]=='B') || ($a[1]=='b'))
                $rest = base64_decode($rest);
            else if (($a[1]=='Q') || ($a[1]=='q')) {
                $rest = str_replace('_', ' ', $rest);
                $rest = quoted_printable_decode($rest);
            }

            return rcube_charset_convert($rest, $a[0]);
        }

        // we dont' know what to do with this
        return $str;
    }


    /**
     * Decode a mime part
     *
     * @param string Input string
     * @param string Part encoding
     * @return string Decoded string
     */
    function mime_decode($input, $encoding='7bit')
    {
        switch (strtolower($encoding)) {
        case 'quoted-printable':
            return quoted_printable_decode($input);
        case 'base64':
            return base64_decode($input);
        case 'x-uuencode':
        case 'x-uue':
        case 'uue':
        case 'uuencode':
            return convert_uudecode($input);
        case '7bit':
        default:
            return $input;
        }
    }


    /**
     * Convert body charset to RCMAIL_CHARSET according to the ctype_parameters
     *
     * @param string Part body to decode
     * @param string Charset to convert from
     * @return string Content converted to internal charset
     */
    function charset_decode($body, $ctype_param)
    {
        if (is_array($ctype_param) && !empty($ctype_param['charset']))
            return rcube_charset_convert($body, $ctype_param['charset']);

        // defaults to what is specified in the class header
        return rcube_charset_convert($body,  $this->default_charset);
    }


    /* --------------------------------
     *         private methods
     * --------------------------------*/

    /**
     * Validate the given input and save to local properties
     * @access private
     */
    private function _set_sort_order($sort_field, $sort_order)
    {
        if ($sort_field != null)
            $this->sort_field = asciiwords($sort_field);
        if ($sort_order != null)
            $this->sort_order = strtoupper($sort_order) == 'DESC' ? 'DESC' : 'ASC';
    }

    /**
     * Sort mailboxes first by default folders and then in alphabethical order
     * @access private
     */
    private function _sort_mailbox_list($a_folders)
    {
        $a_out = $a_defaults = $folders = array();

        $delimiter = $this->get_hierarchy_delimiter();

        // find default folders and skip folders starting with '.'
        foreach ($a_folders as $i => $folder) {
            if ($folder[0] == '.')
                continue;

            if (($p = array_search($folder, $this->default_folders)) !== false && !$a_defaults[$p])
                $a_defaults[$p] = $folder;
            else
                $folders[$folder] = rcube_charset_convert($folder, 'UTF7-IMAP');
        }

        // sort folders and place defaults on the top
        asort($folders, SORT_LOCALE_STRING);
        ksort($a_defaults);
        $folders = array_merge($a_defaults, array_keys($folders));

        // finally we must rebuild the list to move
        // subfolders of default folders to their place...
        // ...also do this for the rest of folders because
        // asort() is not properly sorting case sensitive names
        while (list($key, $folder) = each($folders)) {
            // set the type of folder name variable (#1485527)
            $a_out[] = (string) $folder;
            unset($folders[$key]);
            $this->_rsort($folder, $delimiter, $folders, $a_out);
        }

        return $a_out;
    }


    /**
     * @access private
     */
    private function _rsort($folder, $delimiter, &$list, &$out)
    {
        while (list($key, $name) = each($list)) {
	        if (strpos($name, $folder.$delimiter) === 0) {
	            // set the type of folder name variable (#1485527)
    	        $out[] = (string) $name;
	            unset($list[$key]);
	            $this->_rsort($name, $delimiter, $list, $out);
	        }
        }
        reset($list);
    }


    /**
     * @access private
     */
    private function _uid2id($uid, $mbox_name=NULL)
    {
        if (!$mbox_name)
            $mbox_name = $this->mailbox;

        if (!isset($this->uid_id_map[$mbox_name][$uid]))
            $this->uid_id_map[$mbox_name][$uid] = $this->conn->UID2ID($mbox_name, $uid);

        return $this->uid_id_map[$mbox_name][$uid];
    }

    /**
     * @access private
     */
    private function _id2uid($id, $mbox_name=NULL)
    {
        if (!$mbox_name)
            $mbox_name = $this->mailbox;

        if ($uid = array_search($id, (array)$this->uid_id_map[$mbox_name]))
            return $uid;

        $uid = $this->conn->ID2UID($mbox_name, $id);
        $this->uid_id_map[$mbox_name][$uid] = $id;

        return $uid;
    }


    /**
     * Subscribe/unsubscribe a list of mailboxes and update local cache
     * @access private
     */
    private function _change_subscription($a_mboxes, $mode)
    {
        $updated = false;

        if (is_array($a_mboxes))
            foreach ($a_mboxes as $i => $mbox_name) {
                $mailbox = $this->mod_mailbox($mbox_name);
                $a_mboxes[$i] = $mailbox;

                if ($mode=='subscribe')
                    $updated = $this->conn->subscribe($mailbox);
                else if ($mode=='unsubscribe')
                    $updated = $this->conn->unsubscribe($mailbox);
            }

        // get cached mailbox list
        if ($updated) {
            $a_mailbox_cache = $this->get_cache('mailboxes');
            if (!is_array($a_mailbox_cache))
                return $updated;

            // modify cached list
            if ($mode=='subscribe')
                $a_mailbox_cache = array_merge($a_mailbox_cache, $a_mboxes);
            else if ($mode=='unsubscribe')
                $a_mailbox_cache = array_diff($a_mailbox_cache, $a_mboxes);

            // write mailboxlist to cache
            $this->update_cache('mailboxes', $this->_sort_mailbox_list($a_mailbox_cache));
        }

        return $updated;
    }


    /**
     * Increde/decrese messagecount for a specific mailbox
     * @access private
     */
    private function _set_messagecount($mbox_name, $mode, $increment)
    {
        $a_mailbox_cache = false;
        $mailbox = $mbox_name ? $mbox_name : $this->mailbox;
        $mode = strtoupper($mode);

        $a_mailbox_cache = $this->get_cache('messagecount');

        if (!is_array($a_mailbox_cache[$mailbox]) || !isset($a_mailbox_cache[$mailbox][$mode]) || !is_numeric($increment))
            return false;

        // add incremental value to messagecount
        $a_mailbox_cache[$mailbox][$mode] += $increment;

        // there's something wrong, delete from cache
        if ($a_mailbox_cache[$mailbox][$mode] < 0)
            unset($a_mailbox_cache[$mailbox][$mode]);

        // write back to cache
        $this->update_cache('messagecount', $a_mailbox_cache);

        return true;
    }


    /**
     * Remove messagecount of a specific mailbox from cache
     * @access private
     */
    private function _clear_messagecount($mbox_name='')
    {
        $a_mailbox_cache = false;
        $mailbox = $mbox_name ? $mbox_name : $this->mailbox;

        $a_mailbox_cache = $this->get_cache('messagecount');

        if (is_array($a_mailbox_cache[$mailbox])) {
            unset($a_mailbox_cache[$mailbox]);
            $this->update_cache('messagecount', $a_mailbox_cache);
        }
    }


    /**
     * Split RFC822 header string into an associative array
     * @access private
     */
    private function _parse_headers($headers)
    {
        $a_headers = array();
        $headers = preg_replace('/\r?\n(\t| )+/', ' ', $headers);
        $lines = explode("\n", $headers);
        $c = count($lines);

        for ($i=0; $i<$c; $i++) {
            if ($p = strpos($lines[$i], ': ')) {
                $field = strtolower(substr($lines[$i], 0, $p));
                $value = trim(substr($lines[$i], $p+1));
                if (!empty($value))
                    $a_headers[$field] = $value;
            }
        }

        return $a_headers;
    }


    /**
     * @access private
     */
    private function _parse_address_list($str, $decode=true)
    {
        // remove any newlines and carriage returns before
        $a = rcube_explode_quoted_string('[,;]', preg_replace( "/[\r\n]/", " ", $str));
        $result = array();

        foreach ($a as $key => $val) {
            $val = preg_replace("/([\"\w])</", "$1 <", $val);
            $sub_a = rcube_explode_quoted_string(' ', $decode ? $this->decode_header($val) : $val);
            $result[$key]['name'] = '';

            foreach ($sub_a as $k => $v) {
	            // use angle brackets in regexp to not handle names with @ sign
                if (preg_match('/^<\S+@\S+>$/', $v))
                    $result[$key]['address'] = trim($v, '<>');
                else
                    $result[$key]['name'] .= (empty($result[$key]['name'])?'':' ').str_replace("\"",'',stripslashes($v));
            }

            if (empty($result[$key]['name']))
                $result[$key]['name'] = $result[$key]['address'];
            elseif (empty($result[$key]['address']))
                $result[$key]['address'] = $result[$key]['name'];
        }

        return $result;
    }

}  // end class rcube_imap


/**
 * Class representing a message part
 *
 * @package Mail
 */
class rcube_message_part
{
    var $mime_id = '';
    var $ctype_primary = 'text';
    var $ctype_secondary = 'plain';
    var $mimetype = 'text/plain';
    var $disposition = '';
    var $filename = '';
    var $encoding = '8bit';
    var $charset = '';
    var $size = 0;
    var $headers = array();
    var $d_parameters = array();
    var $ctype_parameters = array();

    function __clone()
    {
        if (isset($this->parts))
            foreach ($this->parts as $idx => $part)
                if (is_object($part))
	                $this->parts[$idx] = clone $part;
    }
}


/**
 * Class for sorting an array of rcube_mail_header objects in a predetermined order.
 *
 * @package Mail
 * @author Eric Stadtherr
 */
class rcube_header_sorter
{
    var $sequence_numbers = array();

    /**
     * Set the predetermined sort order.
     *
     * @param array Numerically indexed array of IMAP message sequence numbers
     */
    function set_sequence_numbers($seqnums)
    {
        $this->sequence_numbers = array_flip($seqnums);
    }

    /**
     * Sort the array of header objects
     *
     * @param array Array of rcube_mail_header objects indexed by UID
     */
    function sort_headers(&$headers)
    {
        /*
        * uksort would work if the keys were the sequence number, but unfortunately
        * the keys are the UIDs.  We'll use uasort instead and dereference the value
        * to get the sequence number (in the "id" field).
        *
        * uksort($headers, array($this, "compare_seqnums"));
        */
        uasort($headers, array($this, "compare_seqnums"));
    }

    /**
     * Sort method called by uasort()
     */
    function compare_seqnums($a, $b)
    {
        // First get the sequence number from the header object (the 'id' field).
        $seqa = $a->id;
        $seqb = $b->id;

        // then find each sequence number in my ordered list
        $posa = isset($this->sequence_numbers[$seqa]) ? intval($this->sequence_numbers[$seqa]) : -1;
        $posb = isset($this->sequence_numbers[$seqb]) ? intval($this->sequence_numbers[$seqb]) : -1;

        // return the relative position as the comparison value
        return $posa - $posb;
    }
}