Support apc cache

how about this totally untested code idea?

its missing code to cache messages as they are read, and to put a user object in APC with a list of the chat's they have access to, but they would both be pretty simple. on a windoze machine, so no patch yet...

/**
 * Whether or not we have APC functionality.
 */
define('CHATROOM_APC_ENABLED', function_exists('apc_fetch'));

/**
 * @file
 * Process chatroom polling requests.
 *
 * This file is a performance hack, aimed at making moderately sized rooms
 * possible with this module.
 * 
 * The intent is to handle the polling requests from chatrooms without doing 
 * a full Drupal bootstrap unless absolutely necessary. All simple polling 
 * requests are handled by this script, as they are by far the most common 
 * type of request, and are very easy to check against a cache.
 *
 * First, we check to see if the last message seen in a given chat client-side
 * is older than the latest message in that chat server-side. 
 *
 * Only if the chat being polled has messages newer than what the requesting
 * client has seen do we bootstrap Drupal. 
 */

// We need the $latest_msg_id, $chat_id and $chat_cache_file to check the
// cache for this chat. 
if (!isset($_POST['latest_msg_id']) || !preg_match('/^\d+$/', $_POST['latest_msg_id'])) {
  exit;
}
$client_latest_msg_id = $_POST['latest_msg_id'];
$server_latest_message_id = FALSE;

if (!isset($_POST['chat_id']) || !preg_match('/^\d+$/', $_POST['chat_id'])) {
  exit;
}
$chat_id = $_POST['chat_id'];

if (!isset($_POST['chat_cache_directory']) || !is_dir($_POST['chat_cache_directory'])) {
  exit;
}
$chat_cache_file = $_POST['chat_cache_directory'] . '/chatroom.chat.' . $chat_id . '.cache';

if (!isset($_POST['skip_cache'])) {
  exit;
}
$skip_cache = $_POST['skip_cache'] == 1 ? TRUE : FALSE;

// We let the client signal that we should skip the cache. Right now we're 
// using this to make sure users last-seen time is updated, and there may 
// be more uses for it down the track.
if (!$skip_cache && file_exists($chat_cache_file)) {

  // Do a quick DoS check - we don't validate the path, so we have to make
  // sure we're not reading arbitrarily big files into memory. Our cache file 
  // should contain a single numeric id. So, if the file is bigger than 25 
  // bytes, something is fishy, and we should just bail out.
  $file_stats = stat($chat_cache_file);
  if ($file_stats['size'] > 25) {
    exit;
  }

  $server_latest_msg_id = trim(file_get_contents($chat_cache_file));
  if ($server_latest_msg_id == $client_latest_msg_id) {
    print json_encode(array('data' => array('cacheHit' => 1, 'messages' => array())));
    exit;
  }
}

if ($chat_user = chatroom_get_cached_user()) {
  if (in_array($chat_id, $chat_user->allowed_chats)) {
    // Try to get messages from our cache.
    if ($cached_messages = chatroom_get_cached_messages($chat_id, $client_latest_message_id)) {
      print json_encode(array('data' => array('cacheHit' => 1, 'messages' => $cached_messages)));
      exit;
    }
  }
}

/**
 * Get a cached user object to check access for the given chat.
 */
function chatroom_get_cached_user() {  
  if (!CHATROOM_APC_ENABLED) {
    return FALSE;
  }
  require_once './includes/bootstrap.php';
  drupal_bootstrap(DRUPAL_BOOTSTRAP_CONFIGURATION);
  return apc_fetch('chatroom_user_cache_' . $_COOKIE[session_name()]);
}

/**
 * Get cached messages for the given chat newer than $client_latest_message_id.
 */
function chatroom_get_cached_messages($chat_id, $client_latest_message_id) {
  if (!CHATROOM_APC_ENABLED) {
    return FALSE;
  }
  $valid_cached_messages = array();
  if ($cached_messages = apc_fetch('chatroom_message_cache_' . $chat_id)) {
    foreach ($cached_messages as $message) {      
      if ($message->id > $client_latest_message_id) {
        $valid_cached_messages[] = $message;
      } 
    }
  }
  return $valid_cached_messages;
}

// Make this look like a normal request to Drupal, then execute index.php.
$_GET['q'] = "chatroom/chat/get/latest/messages/$chat_id/$client_latest_msg_id";
require_once './index.php';

working on this, patch coming soon. *much* faster now.

i've committed early support for this:

http://drupal.org/cvs?commit=341232

much faster, please test.

closing, as i've released 6.x-2.8 with this feature included.

@miro_dietiker yep, sorry for the confusion. are you using the dev branch? have you tried the new cache setup?