<?php
/**
 * @file
 * session_cache.module
 *
 * A pluggable user session access facility for programmers who want a simple
 * two-function API that is independent of the actual storage mechanism.
 * Used in particular to avoid $_SESSION as the storage mechanism, so that
 * anonymous user sessions can be used in the context of Varnish.
 *
 * The database storage mechanism uses core's cache.inc.
 *
 * See README.txt for details.
 */

define('SESSION_CACHE_STORAGE_COOKIE', 3);
define('SESSION_CACHE_STORAGE_DB_CORE', 2);
define('SESSION_CACHE_STORAGE_SESSION', 1);

define('SESSION_CACHE_COOKIE_FOR_SID', 0);
define('SESSION_CACHE_UID_FOR_SID', 1);
define('SESSION_CACHE_IP_ADDRESS_FOR_SID', 2);

define('SESSION_CACHE_DEFAULT_EXPIRATION_DAYS', 7);

// See [#2119579]
require_once DRUPAL_ROOT . '/includes/unicode.inc';

/**
 * Write data to the user session, whatever the storage mechanism may be.
 *
 * @param string $bin
 *   Unique id, eg a string prefixed by the module name.
 * @param mixed $data
 *   A number or string, an object, a multi-dimensional array etc.
 *   $bin is the identifier you choose for the data you want to store. To
 *   guarante uniqueness, you could prefix it with the name of the module that
 *   you use this API with.
 *   Use NULL to erase the bin; it may be recreated and refilled at any time by
 *   calling the function with a non-NULL data argument.
 */
function session_cache_set($bin, $data) {

  if (!isset($bin)) {
    return;
  }
  $method = variable_get('session_cache_storage_method', SESSION_CACHE_STORAGE_SESSION);
  switch ($method) {

    case SESSION_CACHE_STORAGE_COOKIE:
      $serialized_data = ($data == NULL) ? NULL : json_encode($data);

      // For $cookie_domain see also: drupal_settings_initialize()
      global $cookie_domain;
      // .localhost causes problems
      $cdom = ($cookie_domain == '.localhost') ? ini_get('session.cookie_domain') : $cookie_domain;

      // Tell the browser to return the cookie only via HTTP or HTTPS, to any
      // path under the root of this server.
      setcookie("Drupal.session_cache.$bin", $serialized_data,
        // If no data make it a cookie that expires when the browser is closed.
        ($data == NULL) ? 0 : session_cache_expiration_time(),
        '/', $cdom, NULL, TRUE);
      // Make sure that subsequent session_cache_get() calls get the data
      // updated here, not what was in the cookie at the start of the request!
      // Note that in array indices '.' are converted to '_'
      $_COOKIE["Drupal_session_cache_$bin"] = $serialized_data;
      return;

    case SESSION_CACHE_STORAGE_DB_CORE:
      $sid = session_cache_get_sid();
      if ($data == NULL) {
        cache_clear_all("$bin:$sid", 'cache_session_cache');
      }
      else {
        cache_set("$bin:$sid", $data, 'cache_session_cache', session_cache_expiration_time());
      }
      return;

    case SESSION_CACHE_STORAGE_SESSION:
      // $data == NULL means unset().
      $_SESSION[$bin] = $data;
      return;

    default:
      module_invoke_all('session_cache_set', $method, $bin, $data);
  }
}

/**
 * Read data from the user session, given its bin id.
 *
 * @param string $bin
 *   unique id eg a string prefixed by the module name
 */
function session_cache_get($bin) {

  if (!isset($bin)) {
    return NULL;
  }
  $method = variable_get('session_cache_storage_method', SESSION_CACHE_STORAGE_SESSION);
  switch ($method) {

    case SESSION_CACHE_STORAGE_COOKIE:
      // Note that in array indices '.' are converted to '_'
      return isset($_COOKIE["Drupal_session_cache_$bin"]) ? json_decode($_COOKIE["Drupal_session_cache_$bin"], TRUE) : NULL;

    case SESSION_CACHE_STORAGE_DB_CORE:
      $sid = session_cache_get_sid();
      $cache = cache_get("$bin:$sid", 'cache_session_cache');
      return is_object($cache) ? $cache->data : NULL;

    case SESSION_CACHE_STORAGE_SESSION:
      return isset($_SESSION) && isset($_SESSION[$bin]) ? $_SESSION[$bin] : NULL;

    default:
      return module_invoke_all('session_cache_get', $method, $bin);
  }
}

/**
 * Implements hook_flush_caches().
 */
function session_cache_flush_caches() {
  if (variable_get('session_cache_storage_method') == SESSION_CACHE_STORAGE_DB_CORE) {
    return array('cache_session_cache');
  }
}

/**
 * Returns an identifier for the current user session.
 *
 * Typically only called when a database or file-based storage mechanism is
 * employd.
 *
 * @return int
 *   session cache id
 */
function session_cache_get_sid() {
  global $user;

  $sid_source = variable_get('session_cache_sid_source', SESSION_CACHE_COOKIE_FOR_SID);
  
  if ($sid_source == SESSION_CACHE_IP_ADDRESS_FOR_SID) {
    // Do we want '::1' for localhost or dots in file names?
    $sid = ip_address();
    return ($sid == '::1') ? 'localhost' : $sid;
  }

  // SESSION_CACHE_UID_FOR_SID falls back on cookie for anonymous users.
  if ($sid_source == SESSION_CACHE_UID_FOR_SID && !empty($user->uid)) {
    // Fine if concurrent sessions for the same auth. user are NOT required.
    return 'user' . $user->uid;
  }

  if (empty($_COOKIE['Drupal_session_cache_sid'])) {

    // Don't use core's session id. Security not a problem, so keep it short.
    $sid = drupal_substr(session_id(), 0, 12);

    global $cookie_domain;
    // .localhost causes problems
    $cdom = ($cookie_domain == '.localhost') ? ini_get('session.cookie_domain') : $cookie_domain;

    // If setcookie() fails, then everything still works, but a new session will
    // be created when logging in or out.
    setcookie('Drupal.session_cache.sid', $sid, session_cache_expiration_time(), '/', $cdom, NULL, TRUE);
    // Need to also set $_COOKIE explicitly, see [#2210329].
    $_COOKIE['Drupal_session_cache_sid'] = $sid;
  }
  else {
    $sid = $_COOKIE['Drupal_session_cache_sid'];
  }
  return $sid;
}

/**
 * Returns the date/time that the session cache will expire.
 *
 * @return int
 *   UNIX time stamp
 */
function session_cache_expiration_time() {
  return REQUEST_TIME + 24 * 60 * 60 * variable_get('session_cache_expire_period', SESSION_CACHE_DEFAULT_EXPIRATION_DAYS);
}

/**
 * Implements hook_menu().
 */
function session_cache_menu() {
  $items['admin/config/development/session_cache'] = array(
    'title' => 'Session Cache API',
    'description' => 'Select the session storage mechanism.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('session_cache_admin_config'),
    'access arguments' => array('administer site configuration'),
    'file' => 'session_cache.admin.inc',
  );
  return $items;
}