--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/program/lib/Roundcube/rcube_imap_cache.php	Thu Jan 04 15:52:31 2018 -0500
@@ -0,0 +1,1297 @@
+<?php
+
+/**
+ +-----------------------------------------------------------------------+
+ | This file is part of the Roundcube Webmail client                     |
+ | Copyright (C) 2005-2012, The Roundcube Dev Team                       |
+ |                                                                       |
+ | Licensed under the GNU General Public License version 3 or            |
+ | any later version with exceptions for skins & plugins.                |
+ | See the README file for a full license statement.                     |
+ |                                                                       |
+ | PURPOSE:                                                              |
+ |   Caching of IMAP folder contents (messages and index)                |
+ +-----------------------------------------------------------------------+
+ | Author: Thomas Bruederli <roundcube@gmail.com>                        |
+ | Author: Aleksander Machniak <alec@alec.pl>                            |
+ +-----------------------------------------------------------------------+
+*/
+
+/**
+ * Interface class for accessing Roundcube messages cache
+ *
+ * @package    Framework
+ * @subpackage Storage
+ * @author     Thomas Bruederli <roundcube@gmail.com>
+ * @author     Aleksander Machniak <alec@alec.pl>
+ */
+class rcube_imap_cache
+{
+    const MODE_INDEX   = 1;
+    const MODE_MESSAGE = 2;
+
+    /**
+     * Instance of rcube_imap
+     *
+     * @var rcube_imap
+     */
+    private $imap;
+
+    /**
+     * Instance of rcube_db
+     *
+     * @var rcube_db
+     */
+    private $db;
+
+    /**
+     * User ID
+     *
+     * @var int
+     */
+    private $userid;
+
+    /**
+     * Expiration time in seconds
+     *
+     * @var int
+     */
+    private $ttl;
+
+    /**
+     * Maximum cached message size
+     *
+     * @var int
+     */
+    private $threshold;
+
+    /**
+     * Internal (in-memory) cache
+     *
+     * @var array
+     */
+    private $icache = array();
+
+    private $skip_deleted = false;
+    private $mode;
+
+    /**
+     * List of known flags. Thanks to this we can handle flag changes
+     * with good performance. Bad thing is we need to know used flags.
+     */
+    public $flags = array(
+        1       => 'SEEN',          // RFC3501
+        2       => 'DELETED',       // RFC3501
+        4       => 'ANSWERED',      // RFC3501
+        8       => 'FLAGGED',       // RFC3501
+        16      => 'DRAFT',         // RFC3501
+        32      => 'MDNSENT',       // RFC3503
+        64      => 'FORWARDED',     // RFC5550
+        128     => 'SUBMITPENDING', // RFC5550
+        256     => 'SUBMITTED',     // RFC5550
+        512     => 'JUNK',
+        1024    => 'NONJUNK',
+        2048    => 'LABEL1',
+        4096    => 'LABEL2',
+        8192    => 'LABEL3',
+        16384   => 'LABEL4',
+        32768   => 'LABEL5',
+    );
+
+
+    /**
+     * Object constructor.
+     *
+     * @param rcube_db   $db           DB handler
+     * @param rcube_imap $imap         IMAP handler
+     * @param int        $userid       User identifier
+     * @param bool       $skip_deleted skip_deleted flag
+     * @param string     $ttl          Expiration time of memcache/apc items
+     * @param int        $threshold    Maximum cached message size
+     */
+    function __construct($db, $imap, $userid, $skip_deleted, $ttl=0, $threshold=0)
+    {
+        // convert ttl string to seconds
+        $ttl = get_offset_sec($ttl);
+        if ($ttl > 2592000) $ttl = 2592000;
+
+        $this->db           = $db;
+        $this->imap         = $imap;
+        $this->userid       = $userid;
+        $this->skip_deleted = $skip_deleted;
+        $this->ttl          = $ttl;
+        $this->threshold    = $threshold;
+
+        // cache all possible information by default
+        $this->mode = self::MODE_INDEX | self::MODE_MESSAGE;
+
+        // database tables
+        $this->index_table    = $db->table_name('cache_index', true);
+        $this->thread_table   = $db->table_name('cache_thread', true);
+        $this->messages_table = $db->table_name('cache_messages', true);
+    }
+
+    /**
+     * Cleanup actions (on shutdown).
+     */
+    public function close()
+    {
+        $this->save_icache();
+        $this->icache = null;
+    }
+
+    /**
+     * Set cache mode
+     *
+     * @param int $mode Cache mode
+     */
+    public function set_mode($mode)
+    {
+        $this->mode = $mode;
+    }
+
+    /**
+     * Return (sorted) messages index (UIDs).
+     * If index doesn't exist or is invalid, will be updated.
+     *
+     * @param string  $mailbox     Folder name
+     * @param string  $sort_field  Sorting column
+     * @param string  $sort_order  Sorting order (ASC|DESC)
+     * @param bool    $exiting     Skip index initialization if it doesn't exist in DB
+     *
+     * @return array Messages index
+     */
+    function get_index($mailbox, $sort_field = null, $sort_order = null, $existing = false)
+    {
+        if (empty($this->icache[$mailbox])) {
+            $this->icache[$mailbox] = array();
+        }
+
+        $sort_order = strtoupper($sort_order) == 'ASC' ? 'ASC' : 'DESC';
+
+        // Seek in internal cache
+        if (array_key_exists('index', $this->icache[$mailbox])) {
+            // The index was fetched from database already, but not validated yet
+            if (empty($this->icache[$mailbox]['index']['validated'])) {
+                $index = $this->icache[$mailbox]['index'];
+            }
+            // We've got a valid index
+            else if ($sort_field == 'ANY' || $this->icache[$mailbox]['index']['sort_field'] == $sort_field) {
+                $result = $this->icache[$mailbox]['index']['object'];
+                if ($result->get_parameters('ORDER') != $sort_order) {
+                    $result->revert();
+                }
+                return $result;
+            }
+        }
+
+        // Get index from DB (if DB wasn't already queried)
+        if (empty($index) && empty($this->icache[$mailbox]['index_queried'])) {
+            $index = $this->get_index_row($mailbox);
+
+            // set the flag that DB was already queried for index
+            // this way we'll be able to skip one SELECT, when
+            // get_index() is called more than once
+            $this->icache[$mailbox]['index_queried'] = true;
+        }
+
+        $data = null;
+
+        // @TODO: Think about skipping validation checks.
+        // If we could check only every 10 minutes, we would be able to skip
+        // expensive checks, mailbox selection or even IMAP connection, this would require
+        // additional logic to force cache invalidation in some cases
+        // and many rcube_imap changes to connect when needed
+
+        // Entry exists, check cache status
+        if (!empty($index)) {
+            $exists = true;
+
+            if ($sort_field == 'ANY') {
+                $sort_field = $index['sort_field'];
+            }
+
+            if ($sort_field != $index['sort_field']) {
+                $is_valid = false;
+            }
+            else {
+                $is_valid = $this->validate($mailbox, $index, $exists);
+            }
+
+            if ($is_valid) {
+                $data = $index['object'];
+                // revert the order if needed
+                if ($data->get_parameters('ORDER') != $sort_order) {
+                    $data->revert();
+                }
+            }
+        }
+        else {
+            if ($existing) {
+                return null;
+            }
+            else if ($sort_field == 'ANY') {
+                $sort_field = '';
+            }
+
+            // Got it in internal cache, so the row already exist
+            $exists = array_key_exists('index', $this->icache[$mailbox]);
+        }
+
+        // Index not found, not valid or sort field changed, get index from IMAP server
+        if ($data === null) {
+            // Get mailbox data (UIDVALIDITY, counters, etc.) for status check
+            $mbox_data = $this->imap->folder_data($mailbox);
+            $data      = $this->get_index_data($mailbox, $sort_field, $sort_order, $mbox_data);
+
+            // insert/update
+            $this->add_index_row($mailbox, $sort_field, $data, $mbox_data, $exists, $index['modseq']);
+        }
+
+        $this->icache[$mailbox]['index'] = array(
+            'validated'  => true,
+            'object'     => $data,
+            'sort_field' => $sort_field,
+            'modseq'     => !empty($index['modseq']) ? $index['modseq'] : $mbox_data['HIGHESTMODSEQ']
+        );
+
+        return $data;
+    }
+
+    /**
+     * Return messages thread.
+     * If threaded index doesn't exist or is invalid, will be updated.
+     *
+     * @param string $mailbox Folder name
+     *
+     * @return array Messages threaded index
+     */
+    function get_thread($mailbox)
+    {
+        if (empty($this->icache[$mailbox])) {
+            $this->icache[$mailbox] = array();
+        }
+
+        // Seek in internal cache
+        if (array_key_exists('thread', $this->icache[$mailbox])) {
+            return $this->icache[$mailbox]['thread']['object'];
+        }
+
+        // Get thread from DB (if DB wasn't already queried)
+        if (empty($this->icache[$mailbox]['thread_queried'])) {
+            $index = $this->get_thread_row($mailbox);
+
+            // set the flag that DB was already queried for thread
+            // this way we'll be able to skip one SELECT, when
+            // get_thread() is called more than once or after clear()
+            $this->icache[$mailbox]['thread_queried'] = true;
+        }
+
+        // Entry exist, check cache status
+        if (!empty($index)) {
+            $exists   = true;
+            $is_valid = $this->validate($mailbox, $index, $exists);
+
+            if (!$is_valid) {
+                $index = null;
+            }
+        }
+
+        // Index not found or not valid, get index from IMAP server
+        if ($index === null) {
+            // Get mailbox data (UIDVALIDITY, counters, etc.) for status check
+            $mbox_data = $this->imap->folder_data($mailbox);
+            // Get THREADS result
+            $index['object'] = $this->get_thread_data($mailbox, $mbox_data);
+
+            // insert/update
+            $this->add_thread_row($mailbox, $index['object'], $mbox_data, $exists);
+        }
+
+        $this->icache[$mailbox]['thread'] = $index;
+
+        return $index['object'];
+    }
+
+    /**
+     * Returns list of messages (headers). See rcube_imap::fetch_headers().
+     *
+     * @param string $mailbox  Folder name
+     * @param array  $msgs     Message UIDs
+     *
+     * @return array The list of messages (rcube_message_header) indexed by UID
+     */
+    function get_messages($mailbox, $msgs = array())
+    {
+        if (empty($msgs)) {
+            return array();
+        }
+
+        $result = array();
+
+        if ($this->mode & self::MODE_MESSAGE) {
+            // Fetch messages from cache
+            $sql_result = $this->db->query(
+                "SELECT `uid`, `data`, `flags`"
+                ." FROM {$this->messages_table}"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?"
+                    ." AND `uid` IN (".$this->db->array2list($msgs, 'integer').")",
+                $this->userid, $mailbox);
+
+            $msgs = array_flip($msgs);
+
+            while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
+                $uid          = intval($sql_arr['uid']);
+                $result[$uid] = $this->build_message($sql_arr);
+
+                if (!empty($result[$uid])) {
+                    // save memory, we don't need message body here (?)
+                    $result[$uid]->body = null;
+
+                    unset($msgs[$uid]);
+                }
+            }
+
+            $this->db->reset();
+
+            $msgs = array_flip($msgs);
+        }
+
+        // Fetch not found messages from IMAP server
+        if (!empty($msgs)) {
+            $messages = $this->imap->fetch_headers($mailbox, $msgs, false, true);
+
+            // Insert to DB and add to result list
+            if (!empty($messages)) {
+                foreach ($messages as $msg) {
+                    if ($this->mode & self::MODE_MESSAGE) {
+                        $this->add_message($mailbox, $msg, !array_key_exists($msg->uid, $result));
+                    }
+
+                    $result[$msg->uid] = $msg;
+                }
+            }
+        }
+
+        return $result;
+    }
+
+    /**
+     * Returns message data.
+     *
+     * @param string $mailbox  Folder name
+     * @param int    $uid      Message UID
+     * @param bool   $update   If message doesn't exists in cache it will be fetched
+     *                         from IMAP server
+     * @param bool   $no_cache Enables internal cache usage
+     *
+     * @return rcube_message_header Message data
+     */
+    function get_message($mailbox, $uid, $update = true, $cache = true)
+    {
+        // Check internal cache
+        if ($this->icache['__message']
+            && $this->icache['__message']['mailbox'] == $mailbox
+            && $this->icache['__message']['object']->uid == $uid
+        ) {
+            return $this->icache['__message']['object'];
+        }
+
+        if ($this->mode & self::MODE_MESSAGE) {
+            $sql_result = $this->db->query(
+                "SELECT `flags`, `data`"
+                ." FROM {$this->messages_table}"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?"
+                    ." AND `uid` = ?",
+                    $this->userid, $mailbox, (int)$uid);
+
+            if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
+                $message = $this->build_message($sql_arr);
+                $found   = true;
+            }
+        }
+
+        // Get the message from IMAP server
+        if (empty($message) && $update) {
+            $message = $this->imap->get_message_headers($uid, $mailbox, true);
+            // cache will be updated in close(), see below
+        }
+
+        if (!($this->mode & self::MODE_MESSAGE)) {
+            return $message;
+        }
+
+        // Save the message in internal cache, will be written to DB in close()
+        // Common scenario: user opens unseen message
+        // - get message (SELECT)
+        // - set message headers/structure (INSERT or UPDATE)
+        // - set \Seen flag (UPDATE)
+        // This way we can skip one UPDATE
+        if (!empty($message) && $cache) {
+            // Save current message from internal cache
+            $this->save_icache();
+
+            $this->icache['__message'] = array(
+                'object'  => $message,
+                'mailbox' => $mailbox,
+                'exists'  => $found,
+                'md5sum'  => md5(serialize($message)),
+            );
+        }
+
+        return $message;
+    }
+
+    /**
+     * Saves the message in cache.
+     *
+     * @param string               $mailbox  Folder name
+     * @param rcube_message_header $message  Message data
+     * @param bool                 $force    Skips message in-cache existence check
+     */
+    function add_message($mailbox, $message, $force = false)
+    {
+        if (!is_object($message) || empty($message->uid)) {
+            return;
+        }
+
+        if (!($this->mode & self::MODE_MESSAGE)) {
+            return;
+        }
+
+        $flags = 0;
+        $msg   = clone $message;
+
+        if (!empty($message->flags)) {
+            foreach ($this->flags as $idx => $flag) {
+                if (!empty($message->flags[$flag])) {
+                    $flags += $idx;
+                }
+            }
+        }
+
+        unset($msg->flags);
+        $msg = $this->db->encode($msg, true);
+
+        // update cache record (even if it exists, the update
+        // here will work as select, assume row exist if affected_rows=0)
+        if (!$force) {
+            $res = $this->db->query(
+                "UPDATE {$this->messages_table}"
+                ." SET `flags` = ?, `data` = ?, `expires` = " . ($this->ttl ? $this->db->now($this->ttl) : 'NULL')
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?"
+                    ." AND `uid` = ?",
+                $flags, $msg, $this->userid, $mailbox, (int) $message->uid);
+
+            if ($this->db->affected_rows($res)) {
+                return;
+            }
+        }
+
+        $this->db->set_option('ignore_key_errors', true);
+
+        // insert new record
+        $res = $this->db->query(
+            "INSERT INTO {$this->messages_table}"
+            ." (`user_id`, `mailbox`, `uid`, `flags`, `expires`, `data`)"
+            ." VALUES (?, ?, ?, ?, ". ($this->ttl ? $this->db->now($this->ttl) : 'NULL') . ", ?)",
+            $this->userid, $mailbox, (int) $message->uid, $flags, $msg);
+
+        // race-condition, insert failed so try update (#1489146)
+        // thanks to ignore_key_errors "duplicate row" errors will be ignored
+        if ($force && !$res && !$this->db->is_error($res)) {
+            $this->db->query(
+                "UPDATE {$this->messages_table}"
+                ." SET `expires` = " . ($this->ttl ? $this->db->now($this->ttl) : 'NULL')
+                    .", `flags` = ?, `data` = ?"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?"
+                    ." AND `uid` = ?",
+                $flags, $msg, $this->userid, $mailbox, (int) $message->uid);
+        }
+
+        $this->db->set_option('ignore_key_errors', false);
+    }
+
+    /**
+     * Sets the flag for specified message.
+     *
+     * @param string  $mailbox  Folder name
+     * @param array   $uids     Message UIDs or null to change flag
+     *                          of all messages in a folder
+     * @param string  $flag     The name of the flag
+     * @param bool    $enabled  Flag state
+     */
+    function change_flag($mailbox, $uids, $flag, $enabled = false)
+    {
+        if (empty($uids)) {
+            return;
+        }
+
+        if (!($this->mode & self::MODE_MESSAGE)) {
+            return;
+        }
+
+        $flag = strtoupper($flag);
+        $idx  = (int) array_search($flag, $this->flags);
+        $uids = (array) $uids;
+
+        if (!$idx) {
+            return;
+        }
+
+        // Internal cache update
+        if (($message = $this->icache['__message'])
+            && $message['mailbox'] === $mailbox
+            && in_array($message['object']->uid, $uids)
+        ) {
+            $message['object']->flags[$flag] = $enabled;
+
+            if (count($uids) == 1) {
+                return;
+            }
+        }
+
+        $binary_check = $this->db->db_provider == 'oracle' ? "BITAND(`flags`, %d)" : "(`flags` & %d)";
+
+        $this->db->query(
+            "UPDATE {$this->messages_table}"
+            ." SET `expires` = ". ($this->ttl ? $this->db->now($this->ttl) : 'NULL')
+            .", `flags` = `flags` ".($enabled ? "+ $idx" : "- $idx")
+            ." WHERE `user_id` = ?"
+                ." AND `mailbox` = ?"
+                .(!empty($uids) ? " AND `uid` IN (".$this->db->array2list($uids, 'integer').")" : "")
+                ." AND " . sprintf($binary_check, $idx) . ($enabled ? " = 0" : " = $idx"),
+            $this->userid, $mailbox);
+    }
+
+    /**
+     * Removes message(s) from cache.
+     *
+     * @param string $mailbox  Folder name
+     * @param array  $uids     Message UIDs, NULL removes all messages
+     */
+    function remove_message($mailbox = null, $uids = null)
+    {
+        if (!($this->mode & self::MODE_MESSAGE)) {
+            return;
+        }
+
+        if (!strlen($mailbox)) {
+            $this->db->query(
+                "DELETE FROM {$this->messages_table}"
+                ." WHERE `user_id` = ?",
+                $this->userid);
+        }
+        else {
+            // Remove the message from internal cache
+            if (!empty($uids) && ($message = $this->icache['__message'])
+                && $message['mailbox'] === $mailbox
+                && in_array($message['object']->uid, (array)$uids)
+            ) {
+                $this->icache['__message'] = null;
+            }
+
+            $this->db->query(
+                "DELETE FROM {$this->messages_table}"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?"
+                    .($uids !== null ? " AND `uid` IN (".$this->db->array2list((array)$uids, 'integer').")" : ""),
+                $this->userid, $mailbox);
+        }
+    }
+
+    /**
+     * Clears index cache.
+     *
+     * @param string  $mailbox     Folder name
+     * @param bool    $remove      Enable to remove the DB row
+     */
+    function remove_index($mailbox = null, $remove = false)
+    {
+        // The index should be only removed from database when
+        // UIDVALIDITY was detected or the mailbox is empty
+        // otherwise use 'valid' flag to not loose HIGHESTMODSEQ value
+        if ($remove) {
+            $this->db->query(
+                "DELETE FROM {$this->index_table}"
+                ." WHERE `user_id` = ?"
+                    .(strlen($mailbox) ? " AND `mailbox` = ".$this->db->quote($mailbox) : ""),
+                $this->userid
+            );
+        }
+        else {
+            $this->db->query(
+                "UPDATE {$this->index_table}"
+                ." SET `valid` = 0"
+                ." WHERE `user_id` = ?"
+                    .(strlen($mailbox) ? " AND `mailbox` = ".$this->db->quote($mailbox) : ""),
+                $this->userid
+            );
+        }
+
+        if (strlen($mailbox)) {
+            unset($this->icache[$mailbox]['index']);
+            // Index removed, set flag to skip SELECT query in get_index()
+            $this->icache[$mailbox]['index_queried'] = true;
+        }
+        else {
+            $this->icache = array();
+        }
+    }
+
+    /**
+     * Clears thread cache.
+     *
+     * @param string  $mailbox     Folder name
+     */
+    function remove_thread($mailbox = null)
+    {
+        $this->db->query(
+            "DELETE FROM {$this->thread_table}"
+            ." WHERE `user_id` = ?"
+                .(strlen($mailbox) ? " AND `mailbox` = ".$this->db->quote($mailbox) : ""),
+            $this->userid
+        );
+
+        if (strlen($mailbox)) {
+            unset($this->icache[$mailbox]['thread']);
+            // Thread data removed, set flag to skip SELECT query in get_thread()
+            $this->icache[$mailbox]['thread_queried'] = true;
+        }
+        else {
+            $this->icache = array();
+        }
+    }
+
+    /**
+     * Clears the cache.
+     *
+     * @param string $mailbox  Folder name
+     * @param array  $uids     Message UIDs, NULL removes all messages in a folder
+     */
+    function clear($mailbox = null, $uids = null)
+    {
+        $this->remove_index($mailbox, true);
+        $this->remove_thread($mailbox);
+        $this->remove_message($mailbox, $uids);
+    }
+
+    /**
+     * Delete expired cache entries
+     */
+    static function gc()
+    {
+        $rcube = rcube::get_instance();
+        $db    = $rcube->get_dbh();
+        $now   = $db->now();
+
+        $db->query("DELETE FROM " . $db->table_name('cache_messages', true)
+              ." WHERE `expires` < $now");
+
+        $db->query("DELETE FROM " . $db->table_name('cache_index', true)
+              ." WHERE `expires` < $now");
+
+        $db->query("DELETE FROM ".$db->table_name('cache_thread', true)
+              ." WHERE `expires` < $now");
+    }
+
+    /**
+     * Fetches index data from database
+     */
+    private function get_index_row($mailbox)
+    {
+        // Get index from DB
+        $sql_result = $this->db->query(
+            "SELECT `data`, `valid`"
+            ." FROM {$this->index_table}"
+            ." WHERE `user_id` = ?"
+                ." AND `mailbox` = ?",
+            $this->userid, $mailbox);
+
+        if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
+            $data  = explode('@', $sql_arr['data']);
+            $index = $this->db->decode($data[0], true);
+            unset($data[0]);
+
+            if (empty($index)) {
+                $index = new rcube_result_index($mailbox);
+            }
+
+            return array(
+                'valid'      => $sql_arr['valid'],
+                'object'     => $index,
+                'sort_field' => $data[1],
+                'deleted'    => $data[2],
+                'validity'   => $data[3],
+                'uidnext'    => $data[4],
+                'modseq'     => $data[5],
+            );
+        }
+
+        return null;
+    }
+
+    /**
+     * Fetches thread data from database
+     */
+    private function get_thread_row($mailbox)
+    {
+        // Get thread from DB
+        $sql_result = $this->db->query(
+            "SELECT `data`"
+            ." FROM {$this->thread_table}"
+            ." WHERE `user_id` = ?"
+                ." AND `mailbox` = ?",
+            $this->userid, $mailbox);
+
+        if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
+            $data   = explode('@', $sql_arr['data']);
+            $thread = $this->db->decode($data[0], true);
+            unset($data[0]);
+
+            if (empty($thread)) {
+                $thread = new rcube_result_thread($mailbox);
+            }
+
+            return array(
+                'object'   => $thread,
+                'deleted'  => $data[1],
+                'validity' => $data[2],
+                'uidnext'  => $data[3],
+            );
+        }
+
+        return null;
+    }
+
+    /**
+     * Saves index data into database
+     */
+    private function add_index_row($mailbox, $sort_field,
+        $data, $mbox_data = array(), $exists = false, $modseq = null)
+    {
+        $data = array(
+            $this->db->encode($data, true),
+            $sort_field,
+            (int) $this->skip_deleted,
+            (int) $mbox_data['UIDVALIDITY'],
+            (int) $mbox_data['UIDNEXT'],
+            $modseq ? $modseq : $mbox_data['HIGHESTMODSEQ'],
+        );
+
+        $data    = implode('@', $data);
+        $expires = $this->ttl ? $this->db->now($this->ttl) : 'NULL';
+
+        if ($exists) {
+            $res = $this->db->query(
+                "UPDATE {$this->index_table}"
+                ." SET `data` = ?, `valid` = 1, `expires` = $expires"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?",
+                $data, $this->userid, $mailbox);
+
+            if ($this->db->affected_rows($res)) {
+                return;
+            }
+        }
+
+        $this->db->set_option('ignore_key_errors', true);
+
+        $res = $this->db->query(
+            "INSERT INTO {$this->index_table}"
+            ." (`user_id`, `mailbox`, `valid`, `expires`, `data`)"
+            ." VALUES (?, ?, 1, $expires, ?)",
+            $this->userid, $mailbox, $data);
+
+        // race-condition, insert failed so try update (#1489146)
+        // thanks to ignore_key_errors "duplicate row" errors will be ignored
+        if (!$exists && !$res && !$this->db->is_error($res)) {
+            $res = $this->db->query(
+                "UPDATE {$this->index_table}"
+                ." SET `data` = ?, `valid` = 1, `expires` = $expires"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?",
+                $data, $this->userid, $mailbox);
+        }
+
+        $this->db->set_option('ignore_key_errors', false);
+    }
+
+    /**
+     * Saves thread data into database
+     */
+    private function add_thread_row($mailbox, $data, $mbox_data = array(), $exists = false)
+    {
+        $data = array(
+            $this->db->encode($data, true),
+            (int) $this->skip_deleted,
+            (int) $mbox_data['UIDVALIDITY'],
+            (int) $mbox_data['UIDNEXT'],
+        );
+
+        $data    = implode('@', $data);
+        $expires = $this->ttl ? $this->db->now($this->ttl) : 'NULL';
+
+        if ($exists) {
+            $res = $this->db->query(
+                "UPDATE {$this->thread_table}"
+                ." SET `data` = ?, `expires` = $expires"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?",
+                $data, $this->userid, $mailbox);
+
+            if ($this->db->affected_rows($res)) {
+                return;
+            }
+        }
+
+        $this->db->set_option('ignore_key_errors', true);
+
+        $res = $this->db->query(
+            "INSERT INTO {$this->thread_table}"
+            ." (`user_id`, `mailbox`, `expires`, `data`)"
+            ." VALUES (?, ?, $expires, ?)",
+            $this->userid, $mailbox, $data);
+
+        // race-condition, insert failed so try update (#1489146)
+        // thanks to ignore_key_errors "duplicate row" errors will be ignored
+        if (!$exists && !$res && !$this->db->is_error($res)) {
+            $this->db->query(
+                "UPDATE {$this->thread_table}"
+                ." SET `expires` = $expires, `data` = ?"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?",
+                $data, $this->userid, $mailbox);
+        }
+
+        $this->db->set_option('ignore_key_errors', false);
+    }
+
+    /**
+     * Checks index/thread validity
+     */
+    private function validate($mailbox, $index, &$exists = true)
+    {
+        $object    = $index['object'];
+        $is_thread = is_a($object, 'rcube_result_thread');
+
+        // sanity check
+        if (empty($object)) {
+            return false;
+        }
+
+        $index['validated'] = true;
+
+        // Get mailbox data (UIDVALIDITY, counters, etc.) for status check
+        $mbox_data = $this->imap->folder_data($mailbox);
+
+        // @TODO: Think about skipping validation checks.
+        // If we could check only every 10 minutes, we would be able to skip
+        // expensive checks, mailbox selection or even IMAP connection, this would require
+        // additional logic to force cache invalidation in some cases
+        // and many rcube_imap changes to connect when needed
+
+        // Check UIDVALIDITY
+        if ($index['validity'] != $mbox_data['UIDVALIDITY']) {
+            $this->clear($mailbox);
+            $exists = false;
+            return false;
+        }
+
+        // Folder is empty but cache isn't
+        if (empty($mbox_data['EXISTS'])) {
+            if (!$object->is_empty()) {
+                $this->clear($mailbox);
+                $exists = false;
+                return false;
+            }
+        }
+        // Folder is not empty but cache is
+        else if ($object->is_empty()) {
+            unset($this->icache[$mailbox][$is_thread ? 'thread' : 'index']);
+            return false;
+        }
+
+        // Validation flag
+        if (!$is_thread && empty($index['valid'])) {
+            unset($this->icache[$mailbox]['index']);
+            return false;
+        }
+
+        // Index was created with different skip_deleted setting
+        if ($this->skip_deleted != $index['deleted']) {
+            return false;
+        }
+
+        // Check HIGHESTMODSEQ
+        if (!empty($index['modseq']) && !empty($mbox_data['HIGHESTMODSEQ'])
+            && $index['modseq'] == $mbox_data['HIGHESTMODSEQ']
+        ) {
+            return true;
+        }
+
+        // Check UIDNEXT
+        if ($index['uidnext'] != $mbox_data['UIDNEXT']) {
+            unset($this->icache[$mailbox][$is_thread ? 'thread' : 'index']);
+            return false;
+        }
+
+        // @TODO: find better validity check for threaded index
+        if ($is_thread) {
+            // check messages number...
+            if (!$this->skip_deleted && $mbox_data['EXISTS'] != $object->count_messages()) {
+                return false;
+            }
+            return true;
+        }
+
+        // The rest of checks, more expensive
+        if (!empty($this->skip_deleted)) {
+            // compare counts if available
+            if (!empty($mbox_data['UNDELETED'])
+                && $mbox_data['UNDELETED']->count() != $object->count()
+            ) {
+                return false;
+            }
+            // compare UID sets
+            if (!empty($mbox_data['UNDELETED'])) {
+                $uids_new = $mbox_data['UNDELETED']->get();
+                $uids_old = $object->get();
+
+                if (count($uids_new) != count($uids_old)) {
+                    return false;
+                }
+
+                sort($uids_new, SORT_NUMERIC);
+                sort($uids_old, SORT_NUMERIC);
+
+                if ($uids_old != $uids_new)
+                    return false;
+            }
+            else {
+                // get all undeleted messages excluding cached UIDs
+                $ids = $this->imap->search_once($mailbox, 'ALL UNDELETED NOT UID '.
+                    rcube_imap_generic::compressMessageSet($object->get()));
+
+                if (!$ids->is_empty()) {
+                    return false;
+                }
+            }
+        }
+        else {
+            // check messages number...
+            if ($mbox_data['EXISTS'] != $object->count()) {
+                return false;
+            }
+            // ... and max UID
+            if ($object->max() != $this->imap->id2uid($mbox_data['EXISTS'], $mailbox)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Synchronizes the mailbox.
+     *
+     * @param string $mailbox Folder name
+     */
+    function synchronize($mailbox)
+    {
+        // RFC4549: Synchronization Operations for Disconnected IMAP4 Clients
+        // RFC4551: IMAP Extension for Conditional STORE Operation
+        //          or Quick Flag Changes Resynchronization
+        // RFC5162: IMAP Extensions for Quick Mailbox Resynchronization
+
+        // @TODO: synchronize with other methods?
+        $qresync   = $this->imap->get_capability('QRESYNC');
+        $condstore = $qresync ? true : $this->imap->get_capability('CONDSTORE');
+
+        if (!$qresync && !$condstore) {
+            return;
+        }
+
+        // Get stored index
+        $index = $this->get_index_row($mailbox);
+
+        // database is empty
+        if (empty($index)) {
+            // set the flag that DB was already queried for index
+            // this way we'll be able to skip one SELECT in get_index()
+            $this->icache[$mailbox]['index_queried'] = true;
+            return;
+        }
+
+        $this->icache[$mailbox]['index'] = $index;
+
+        // no last HIGHESTMODSEQ value
+        if (empty($index['modseq'])) {
+            return;
+        }
+
+        if (!$this->imap->check_connection()) {
+            return;
+        }
+
+        // Enable QRESYNC
+        $res = $this->imap->conn->enable($qresync ? 'QRESYNC' : 'CONDSTORE');
+        if ($res === false) {
+            return;
+        }
+
+        // Close mailbox if already selected to get most recent data
+        if ($this->imap->conn->selected == $mailbox) {
+            $this->imap->conn->close();
+        }
+
+        // Get mailbox data (UIDVALIDITY, HIGHESTMODSEQ, counters, etc.)
+        $mbox_data = $this->imap->folder_data($mailbox);
+
+        if (empty($mbox_data)) {
+             return;
+        }
+
+        // Check UIDVALIDITY
+        if ($index['validity'] != $mbox_data['UIDVALIDITY']) {
+            $this->clear($mailbox);
+            return;
+        }
+
+        // QRESYNC not supported on specified mailbox
+        if (!empty($mbox_data['NOMODSEQ']) || empty($mbox_data['HIGHESTMODSEQ'])) {
+            return;
+        }
+
+        // Nothing new
+        if ($mbox_data['HIGHESTMODSEQ'] == $index['modseq']) {
+            return;
+        }
+
+        $uids    = array();
+        $removed = array();
+
+        // Get known UIDs
+        if ($this->mode & self::MODE_MESSAGE) {
+            $sql_result = $this->db->query(
+                "SELECT `uid`"
+                ." FROM {$this->messages_table}"
+                ." WHERE `user_id` = ?"
+                    ." AND `mailbox` = ?",
+                $this->userid, $mailbox);
+
+            while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
+                $uids[] = $sql_arr['uid'];
+            }
+        }
+
+        // Synchronize messages data
+        if (!empty($uids)) {
+            // Get modified flags and vanished messages
+            // UID FETCH 1:* (FLAGS) (CHANGEDSINCE 0123456789 VANISHED)
+            $result = $this->imap->conn->fetch($mailbox,
+                $uids, true, array('FLAGS'), $index['modseq'], $qresync);
+
+            if (!empty($result)) {
+                foreach ($result as $msg) {
+                    $uid = $msg->uid;
+                    // Remove deleted message
+                    if ($this->skip_deleted && !empty($msg->flags['DELETED'])) {
+                        $removed[] = $uid;
+                        // Invalidate index
+                        $index['valid'] = false;
+                        continue;
+                    }
+
+                    $flags = 0;
+                    if (!empty($msg->flags)) {
+                        foreach ($this->flags as $idx => $flag) {
+                            if (!empty($msg->flags[$flag])) {
+                                $flags += $idx;
+                            }
+                        }
+                    }
+
+                    $this->db->query(
+                        "UPDATE {$this->messages_table}"
+                        ." SET `flags` = ?, `expires` = " . ($this->ttl ? $this->db->now($this->ttl) : 'NULL')
+                        ." WHERE `user_id` = ?"
+                            ." AND `mailbox` = ?"
+                            ." AND `uid` = ?"
+                            ." AND `flags` <> ?",
+                        $flags, $this->userid, $mailbox, $uid, $flags);
+                }
+            }
+
+            // VANISHED found?
+            if ($qresync) {
+                $mbox_data = $this->imap->folder_data($mailbox);
+
+                // Removed messages found
+                $uids = rcube_imap_generic::uncompressMessageSet($mbox_data['VANISHED']);
+                if (!empty($uids)) {
+                    $removed = array_merge($removed, $uids);
+                    // Invalidate index
+                    $index['valid'] = false;
+                }
+            }
+
+            // remove messages from database
+            if (!empty($removed)) {
+                $this->remove_message($mailbox, $removed);
+            }
+        }
+
+        $sort_field = $index['sort_field'];
+        $sort_order = $index['object']->get_parameters('ORDER');
+        $exists     = true;
+
+        // Validate index
+        if (!$this->validate($mailbox, $index, $exists)) {
+            // Invalidate (remove) thread index
+            // if $exists=false it was already removed in validate()
+            if ($exists) {
+                $this->remove_thread($mailbox);
+            }
+
+            // Update index
+            $data = $this->get_index_data($mailbox, $sort_field, $sort_order, $mbox_data);
+        }
+        else {
+            $data = $index['object'];
+        }
+
+        // update index and/or HIGHESTMODSEQ value
+        $this->add_index_row($mailbox, $sort_field, $data, $mbox_data, $exists);
+
+        // update internal cache for get_index()
+        $this->icache[$mailbox]['index']['object'] = $data;
+    }
+
+    /**
+     * Converts cache row into message object.
+     *
+     * @param array $sql_arr Message row data
+     *
+     * @return rcube_message_header Message object
+     */
+    private function build_message($sql_arr)
+    {
+        $message = $this->db->decode($sql_arr['data'], true);
+
+        if ($message) {
+            $message->flags = array();
+            foreach ($this->flags as $idx => $flag) {
+                if (($sql_arr['flags'] & $idx) == $idx) {
+                    $message->flags[$flag] = true;
+                }
+           }
+        }
+
+        return $message;
+    }
+
+    /**
+     * Saves message stored in internal cache
+     */
+    private function save_icache()
+    {
+        // Save current message from internal cache
+        if ($message = $this->icache['__message']) {
+            // clean up some object's data
+            $this->message_object_prepare($message['object']);
+
+            // calculate current md5 sum
+            $md5sum = md5(serialize($message['object']));
+
+            if ($message['md5sum'] != $md5sum) {
+                $this->add_message($message['mailbox'], $message['object'], !$message['exists']);
+            }
+
+            $this->icache['__message']['md5sum'] = $md5sum;
+        }
+    }
+
+    /**
+     * Prepares message object to be stored in database.
+     *
+     * @param rcube_message_header|rcube_message_part
+     */
+    private function message_object_prepare(&$msg, &$size = 0)
+    {
+        // Remove body too big
+        if (isset($msg->body)) {
+            $length = strlen($msg->body);
+
+            if ($msg->body_modified || $size + $length > $this->threshold * 1024) {
+                unset($msg->body);
+            }
+            else {
+                $size += $length;
+            }
+        }
+
+        // Fix mimetype which might be broken by some code when message is displayed
+        // Another solution would be to use object's copy in rcube_message class
+        // to prevent related issues, however I'm not sure which is better
+        if ($msg->mimetype) {
+            list($msg->ctype_primary, $msg->ctype_secondary) = explode('/', $msg->mimetype);
+        }
+
+        unset($msg->replaces);
+
+        if (is_object($msg->structure)) {
+            $this->message_object_prepare($msg->structure, $size);
+        }
+
+        if (is_array($msg->parts)) {
+            foreach ($msg->parts as $part) {
+                $this->message_object_prepare($part, $size);
+            }
+        }
+    }
+
+    /**
+     * Fetches index data from IMAP server
+     */
+    private function get_index_data($mailbox, $sort_field, $sort_order, $mbox_data = array())
+    {
+        if (empty($mbox_data)) {
+            $mbox_data = $this->imap->folder_data($mailbox);
+        }
+
+        if ($mbox_data['EXISTS']) {
+            // fetch sorted sequence numbers
+            $index = $this->imap->index_direct($mailbox, $sort_field, $sort_order);
+        }
+        else {
+            $index = new rcube_result_index($mailbox, '* SORT');
+        }
+
+        return $index;
+    }
+
+    /**
+     * Fetches thread data from IMAP server
+     */
+    private function get_thread_data($mailbox, $mbox_data = array())
+    {
+        if (empty($mbox_data)) {
+            $mbox_data = $this->imap->folder_data($mailbox);
+        }
+
+        if ($mbox_data['EXISTS']) {
+            // get all threads (default sort order)
+            return $this->imap->threads_direct($mailbox);
+        }
+
+        return new rcube_result_thread($mailbox, '* THREAD');
+    }
+}
+
+// for backward compat.
+class rcube_mail_header extends rcube_message_header { }