bootstrap.inc

<?php

use Drupal\Core\Database\Database;
use Symfony\Component\ClassLoader\UniversalClassLoader;
use Symfony\Component\ClassLoader\ApcUniversalClassLoader;
use Symfony\Component\DependencyInjection\ContainerBuilder;

/**
 * @file
 * Functions that need to be loaded on every Drupal request.
 */

/**
 * The current system version.
 */
const VERSION = '8.0-dev';

/**
 * Core API compatibility.
 */
const DRUPAL_CORE_COMPATIBILITY = '8.x';

/**
 * Minimum supported version of PHP.
 */
const DRUPAL_MINIMUM_PHP = '5.3.3';

/**
 * Minimum recommended value of PHP memory_limit.
 */
const DRUPAL_MINIMUM_PHP_MEMORY_LIMIT = '32M';

/**
 * Indicates that the item should never be removed unless explicitly selected.
 *
 * The item may be removed using cache()->delete() with a cache ID.
 */
const CACHE_PERMANENT = 0;

/**
 * Indicates that the item should be removed at the next general cache wipe.
 */
const CACHE_TEMPORARY = -1;

/**
 * @defgroup logging_severity_levels Logging severity levels
 * @{
 * Logging severity levels as defined in RFC 3164.
 *
 * The WATCHDOG_* constant definitions correspond to the logging severity levels
 * defined in RFC 3164, section 4.1.1. PHP supplies predefined LOG_* constants
 * for use in the syslog() function, but their values on Windows builds do not
 * correspond to RFC 3164. The associated PHP bug report was closed with the
 * comment, "And it's also not a bug, as Windows just have less log levels,"
 * and "So the behavior you're seeing is perfectly normal."
 *
 * @see http://www.faqs.org/rfcs/rfc3164.html
 * @see http://bugs.php.net/bug.php?id=18090
 * @see http://php.net/manual/function.syslog.php
 * @see http://php.net/manual/network.constants.php
 * @see watchdog()
 * @see watchdog_severity_levels()
 */

/**
 * Log message severity -- Emergency: system is unusable.
 */
const WATCHDOG_EMERGENCY = 0;

/**
 * Log message severity -- Alert: action must be taken immediately.
 */
const WATCHDOG_ALERT = 1;

/**
 * Log message severity -- Critical conditions.
 */
const WATCHDOG_CRITICAL = 2;

/**
 * Log message severity -- Error conditions.
 */
const WATCHDOG_ERROR = 3;

/**
 * Log message severity -- Warning conditions.
 */
const WATCHDOG_WARNING = 4;

/**
 * Log message severity -- Normal but significant conditions.
 */
const WATCHDOG_NOTICE = 5;

/**
 * Log message severity -- Informational messages.
 */
const WATCHDOG_INFO = 6;

/**
 * Log message severity -- Debug-level messages.
 */
const WATCHDOG_DEBUG = 7;

/**
 * @} End of "defgroup logging_severity_levels".
 */

/**
 * First bootstrap phase: initialize configuration.
 */
const DRUPAL_BOOTSTRAP_CONFIGURATION = 0;

/**
 * Second bootstrap phase: try to serve a cached page.
 */
const DRUPAL_BOOTSTRAP_PAGE_CACHE = 1;

/**
 * Third bootstrap phase: initialize database layer.
 */
const DRUPAL_BOOTSTRAP_DATABASE = 2;

/**
 * Fourth bootstrap phase: initialize the variable system.
 */
const DRUPAL_BOOTSTRAP_VARIABLES = 3;

/**
 * Fifth bootstrap phase: initialize session handling.
 */
const DRUPAL_BOOTSTRAP_SESSION = 4;

/**
 * Sixth bootstrap phase: set up the page header.
 */
const DRUPAL_BOOTSTRAP_PAGE_HEADER = 5;

/**
 * Seventh bootstrap phase: find out language of the page.
 */
const DRUPAL_BOOTSTRAP_LANGUAGE = 6;

/**
 * Final bootstrap phase: Drupal is fully loaded; validate and fix input data.
 */
const DRUPAL_BOOTSTRAP_FULL = 7;

/**
 * Role ID for anonymous users; should match what's in the "role" table.
 */
const DRUPAL_ANONYMOUS_RID = 1;

/**
 * Role ID for authenticated users; should match what's in the "role" table.
 */
const DRUPAL_AUTHENTICATED_RID = 2;

/**
 * The number of bytes in a kilobyte.
 *
 * For more information, visit http://en.wikipedia.org/wiki/Kilobyte.
 */
const DRUPAL_KILOBYTE = 1024;

/**
 * Special system language code (only applicable to UI language).
 *
 * Refers to the language used in Drupal and module/theme source code. Drupal
 * uses the built-in text for English by default, but if configured to allow
 * translation/customization of English, we need to differentiate between the
 * built-in language and the English translation.
 */
const LANGUAGE_SYSTEM = 'system';

/**
 * The language code used when no language is explicitly assigned (yet).
 *
 * Should be used when language information is not available or cannot be
 * determined. This special language code is useful when we know the data
 * might have linguistic information, but we don't know the language.
 *
 * See http://www.w3.org/International/questions/qa-no-language#undetermined.
 */
const LANGUAGE_NOT_SPECIFIED = 'und';

/**
 * The language code used when the marked object has no linguistic content.
 *
 * Should be used when we explicitly know that the data referred has no
 * linguistic content.
 *
 * See http://www.w3.org/International/questions/qa-no-language#nonlinguistic.
 */
const LANGUAGE_NOT_APPLICABLE = 'zxx';

/**
 * The language code used when multiple languages could be applied.
 *
 * Should be used when individual parts of the data cannot be marked with
 * language, but we know there are multiple languages involved. Such as a
 * PDF file for an electronic appliance, which has usage manuals in 8
 * languages but is uploaded as one file in Drupal.
 *
 * Defined by ISO639-2 for "Multiple languages".
 */
const LANGUAGE_MULTIPLE = 'mul';

/**
 * The type of language used to define the content language.
 */
const LANGUAGE_TYPE_CONTENT = 'language_content';

/**
 * The type of language used to select the user interface.
 */
const LANGUAGE_TYPE_INTERFACE = 'language_interface';

/**
 * The type of language used for URLs.
 */
const LANGUAGE_TYPE_URL = 'language_url';

/**
 * Language written left to right. Possible value of $language->direction.
 */
const LANGUAGE_LTR = 0;

/**
 * Language written right to left. Possible value of $language->direction.
 */
const LANGUAGE_RTL = 1;

/**
 * Time of the current request in seconds elapsed since the Unix Epoch.
 *
 * This differs from $_SERVER['REQUEST_TIME'], which is stored as a float
 * since PHP 5.4.0. Float timestamps confuse most PHP functions
 * (including date_create()).
 *
 * @see http://php.net/manual/reserved.variables.server.php
 * @see http://php.net/manual/function.time.php
 */
define('REQUEST_TIME', (int) $_SERVER['REQUEST_TIME']);

/**
 * Flag for drupal_set_title(); text is not sanitized, so run check_plain().
 */
const CHECK_PLAIN = 0;

/**
 * Flag for drupal_set_title(); text has already been sanitized.
 */
const PASS_THROUGH = -1;

/**
 * Signals that the registry lookup cache should be reset.
 */
const REGISTRY_RESET_LOOKUP_CACHE = 1;

/**
 * Signals that the registry lookup cache should be written to storage.
 */
const REGISTRY_WRITE_LOOKUP_CACHE = 2;

/**
 * Regular expression to match PHP function names.
 *
 * @see http://php.net/manual/language.functions.php
 */
const DRUPAL_PHP_FUNCTION_PATTERN = '[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*';

require_once DRUPAL_ROOT . '/core/includes/config.inc';

/**
 * Starts the timer with the specified name.
 *
 * If you start and stop the same timer multiple times, the measured intervals
 * will be accumulated.
 *
 * @param $name
 *   The name of the timer.
 */
function timer_start($name) {
  global $timers;

  $timers[$name]['start'] = microtime(TRUE);
  $timers[$name]['count'] = isset($timers[$name]['count']) ? ++$timers[$name]['count'] : 1;
}

/**
 * Reads the current timer value without stopping the timer.
 *
 * @param $name
 *   The name of the timer.
 *
 * @return
 *   The current timer value in ms.
 */
function timer_read($name) {
  global $timers;

  if (isset($timers[$name]['start'])) {
    $stop = microtime(TRUE);
    $diff = round(($stop - $timers[$name]['start']) * 1000, 2);

    if (isset($timers[$name]['time'])) {
      $diff += $timers[$name]['time'];
    }
    return $diff;
  }
  return $timers[$name]['time'];
}

/**
 * Stops the timer with the specified name.
 *
 * @param $name
 *   The name of the timer.
 *
 * @return
 *   A timer array. The array contains the number of times the timer has been
 *   started and stopped (count) and the accumulated timer value in ms (time).
 */
function timer_stop($name) {
  global $timers;

  if (isset($timers[$name]['start'])) {
    $stop = microtime(TRUE);
    $diff = round(($stop - $timers[$name]['start']) * 1000, 2);
    if (isset($timers[$name]['time'])) {
      $timers[$name]['time'] += $diff;
    }
    else {
      $timers[$name]['time'] = $diff;
    }
    unset($timers[$name]['start']);
  }

  return $timers[$name];
}

/**
 * Finds the appropriate configuration directory.
 *
 * Finds a matching configuration directory by stripping the website's
 * hostname from left to right and pathname from right to left. The first
 * configuration file found will be used and the remaining ones will be ignored.
 * If no configuration file is found, return a default value '$confdir/default'.
 *
 * With a site located at http://www.example.com:8080/mysite/test/, the file,
 * settings.php, is searched for in the following directories:
 *
 * - $confdir/8080.www.example.com.mysite.test
 * - $confdir/www.example.com.mysite.test
 * - $confdir/example.com.mysite.test
 * - $confdir/com.mysite.test
 *
 * - $confdir/8080.www.example.com.mysite
 * - $confdir/www.example.com.mysite
 * - $confdir/example.com.mysite
 * - $confdir/com.mysite
 *
 * - $confdir/8080.www.example.com
 * - $confdir/www.example.com
 * - $confdir/example.com
 * - $confdir/com
 *
 * - $confdir/default
 *
 * If a file named sites.php is present in the $confdir, it will be loaded
 * prior to scanning for directories. It should define an associative array
 * named $sites, which maps domains to directories. It should be in the form
 * of:
 * @code
 * $sites = array(
 *   'The url to alias' => 'A directory within the sites directory'
 * );
 * @endcode
 * For example:
 * @code
 * $sites = array(
 *   'devexample.com' => 'example.com',
 *   'localhost.example' => 'example.com',
 * );
 * @endcode
 * The above array will cause Drupal to look for a directory named
 * "example.com" in the sites directory whenever a request comes from
 * "example.com", "devexample.com", or "localhost/example". That is useful
 * on development servers, where the domain name may not be the same as the
 * domain of the live server. Since Drupal stores file paths into the database
 * (files, system table, etc.) this will ensure the paths are correct while
 * accessed on development servers.
 *
 * @param bool $require_settings
 *   Only configuration directories with an existing settings.php file
 *   will be recognized. Defaults to TRUE. During initial installation,
 *   this is set to FALSE so that Drupal can detect a matching directory,
 *   then create a new settings.php file in it.
 * @param bool $reset
 *   Force a full search for matching directories even if one had been
 *   found previously. Defaults to FALSE.
 *
 * @return
 *   The path of the matching directory.
 */
function conf_path($require_settings = TRUE, $reset = FALSE) {
  $conf = &drupal_static(__FUNCTION__, '');

  if ($conf && !$reset) {
    return $conf;
  }

  $script_name = $_SERVER['SCRIPT_NAME'];
  if (!$script_name) {
    $script_name = $_SERVER['SCRIPT_FILENAME'];
  }
  $http_host = $_SERVER['HTTP_HOST'];
  $conf = find_conf_path($http_host, $script_name, $require_settings);
  return $conf;
}

/**
 * Finds the appropriate configuration directory for a given host and path.
 *
 * @param $http_host
 *   The hostname and optional port number, e.g. "www.example.com" or
 *   "www.example.com:8080".
 * @param $script_name
 *   The part of the url following the hostname, including the leading slash.
 *
 * @return
 *   The path of the matching configuration directory.
 *
 * @see conf_path()
 */
function find_conf_path($http_host, $script_name, $require_settings = TRUE) {
  $confdir = 'sites';

  $sites = array();
  if (file_exists(DRUPAL_ROOT . '/' . $confdir . '/sites.php')) {
    // This will overwrite $sites with the desired mappings.
    include(DRUPAL_ROOT . '/' . $confdir . '/sites.php');
  }

  $uri = explode('/', $script_name);
  $server = explode('.', implode('.', array_reverse(explode(':', rtrim($http_host, '.')))));
  for ($i = count($uri) - 1; $i > 0; $i--) {
    for ($j = count($server); $j > 0; $j--) {
      $dir = implode('.', array_slice($server, -$j)) . implode('.', array_slice($uri, 0, $i));
      if (isset($sites[$dir]) && file_exists(DRUPAL_ROOT . '/' . $confdir . '/' . $sites[$dir])) {
        $dir = $sites[$dir];
      }
      if (file_exists(DRUPAL_ROOT . '/' . $confdir . '/' . $dir . '/settings.php') || (!$require_settings && file_exists(DRUPAL_ROOT . '/' . $confdir . '/' . $dir))) {
        $conf = "$confdir/$dir";
        return $conf;
      }
    }
  }
  $conf = "$confdir/default";
  return $conf;
}

/**
 * Sets appropriate server variables needed for command line scripts to work.
 *
 * This function can be called by command line scripts before bootstrapping
 * Drupal, to ensure that the page loads with the desired server parameters.
 * This is because many parts of Drupal assume that they are running in a web
 * browser and therefore use information from the global PHP $_SERVER variable
 * that does not get set when Drupal is run from the command line.
 *
 * In many cases, the default way in which this function populates the $_SERVER
 * variable is sufficient, and it can therefore be called without passing in
 * any input. However, command line scripts running on a multisite installation
 * (or on any installation that has settings.php stored somewhere other than
 * the sites/default folder) need to pass in the URL of the site to allow
 * Drupal to detect the correct location of the settings.php file. Passing in
 * the 'url' parameter is also required for functions like request_uri() to
 * return the expected values.
 *
 * Most other parameters do not need to be passed in, but may be necessary in
 * some cases; for example, if Drupal's ip_address() function needs to return
 * anything but the standard localhost value ('127.0.0.1'), the command line
 * script should pass in the desired value via the 'REMOTE_ADDR' key.
 *
 * @param $variables
 *   (optional) An associative array of variables within $_SERVER that should
 *   be replaced. If the special element 'url' is provided in this array, it
 *   will be used to populate some of the server defaults; it should be set to
 *   the URL of the current page request, excluding any $_GET request but
 *   including the script name (e.g., http://www.example.com/mysite/index.php).
 *
 * @see conf_path()
 * @see request_uri()
 * @see ip_address()
 */
function drupal_override_server_variables($variables = array()) {
  // Allow the provided URL to override any existing values in $_SERVER.
  if (isset($variables['url'])) {
    $url = parse_url($variables['url']);
    if (isset($url['host'])) {
      $_SERVER['HTTP_HOST'] = $url['host'];
    }
    if (isset($url['path'])) {
      $_SERVER['SCRIPT_NAME'] = $url['path'];
    }
    unset($variables['url']);
  }
  // Define default values for $_SERVER keys. These will be used if $_SERVER
  // does not already define them and no other values are passed in to this
  // function.
  $defaults = array(
    'HTTP_HOST' => 'localhost',
    'SCRIPT_NAME' => NULL,
    'REMOTE_ADDR' => '127.0.0.1',
    'REQUEST_METHOD' => 'GET',
    'SERVER_NAME' => NULL,
    'SERVER_SOFTWARE' => NULL,
    'HTTP_USER_AGENT' => NULL,
  );
  // Replace elements of the $_SERVER array, as appropriate.
  $_SERVER = $variables + $_SERVER + $defaults;
}

/**
 * Initializes the PHP environment.
 */
function drupal_environment_initialize() {
  if (!isset($_SERVER['HTTP_REFERER'])) {
    $_SERVER['HTTP_REFERER'] = '';
  }
  if (!isset($_SERVER['SERVER_PROTOCOL']) || ($_SERVER['SERVER_PROTOCOL'] != 'HTTP/1.0' && $_SERVER['SERVER_PROTOCOL'] != 'HTTP/1.1')) {
    $_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.0';
  }

  if (isset($_SERVER['HTTP_HOST'])) {
    // As HTTP_HOST is user input, ensure it only contains characters allowed
    // in hostnames. See RFC 952 (and RFC 2181).
    // $_SERVER['HTTP_HOST'] is lowercased here per specifications.
    $_SERVER['HTTP_HOST'] = strtolower($_SERVER['HTTP_HOST']);
    if (!drupal_valid_http_host($_SERVER['HTTP_HOST'])) {
      // HTTP_HOST is invalid, e.g. if containing slashes it may be an attack.
      header($_SERVER['SERVER_PROTOCOL'] . ' 400 Bad Request');
      exit;
    }
  }
  else {
    // Some pre-HTTP/1.1 clients will not send a Host header. Ensure the key is
    // defined for E_ALL compliance.
    $_SERVER['HTTP_HOST'] = '';
  }

  // When clean URLs are enabled, emulate ?q=foo/bar using REQUEST_URI. It is
  // not possible to append the query string using mod_rewrite without the B
  // flag (this was added in Apache 2.2.8), because mod_rewrite unescapes the
  // path before passing it on to PHP. This is a problem when the path contains
  // e.g. "&" or "%" that have special meanings in URLs and must be encoded.
  $_GET['q'] = request_path();

  // Enforce E_STRICT, but allow users to set levels not part of E_STRICT.
  error_reporting(E_STRICT | E_ALL | error_reporting());

  // Override PHP settings required for Drupal to work properly.
  // sites/default/default.settings.php contains more runtime settings.
  // The .htaccess file contains settings that cannot be changed at runtime.

  // Don't escape quotes when reading files from the database, disk, etc.
  ini_set('magic_quotes_runtime', '0');
  // Use session cookies, not transparent sessions that puts the session id in
  // the query string.
  ini_set('session.use_cookies', '1');
  ini_set('session.use_only_cookies', '1');
  ini_set('session.use_trans_sid', '0');
  // Don't send HTTP headers using PHP's session handler.
  // Send an empty string to disable the cache limiter.
  ini_set('session.cache_limiter', '');
  // Use httponly session cookies.
  ini_set('session.cookie_httponly', '1');

  // Set sane locale settings, to ensure consistent string, dates, times and
  // numbers handling.
  setlocale(LC_ALL, 'C');
}

/**
 * Validates that a hostname (for example $_SERVER['HTTP_HOST']) is safe.
 *
 * @return
 *  TRUE if only containing valid characters, or FALSE otherwise.
 */
function drupal_valid_http_host($host) {
  return preg_match('/^\[?(?:[a-zA-Z0-9-:\]_]+\.?)+$/', $host);
}

/**
 * Sets the base URL, cookie domain, and session name from configuration.
 */
function drupal_settings_initialize() {
  global $base_url, $base_path, $base_root;

  // Export the following settings.php variables to the global namespace
  global $databases, $cookie_domain, $conf, $installed_profile, $update_free_access, $db_url, $db_prefix, $drupal_hash_salt, $is_https, $base_secure_url, $base_insecure_url, $config_directory_name, $config_signature_key;
  $conf = array();

  if (file_exists(DRUPAL_ROOT . '/' . conf_path() . '/settings.php')) {
    include_once DRUPAL_ROOT . '/' . conf_path() . '/settings.php';
  }
  $is_https = isset($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) == 'on';

  if (isset($base_url)) {
    // Parse fixed base URL from settings.php.
    $parts = parse_url($base_url);
    $http_protocol = $parts['scheme'];
    if (!isset($parts['path'])) {
      $parts['path'] = '';
    }
    $base_path = $parts['path'] . '/';
    // Build $base_root (everything until first slash after "scheme://").
    $base_root = substr($base_url, 0, strlen($base_url) - strlen($parts['path']));
  }
  else {
    // Create base URL
    $http_protocol = $is_https ? 'https' : 'http';
    $base_root = $http_protocol . '://' . $_SERVER['HTTP_HOST'];

    $base_url = $base_root;

    // $_SERVER['SCRIPT_NAME'] can, in contrast to $_SERVER['PHP_SELF'], not
    // be modified by a visitor.
    if ($dir = rtrim(dirname($_SERVER['SCRIPT_NAME']), '\/')) {
      // Remove "core" directory if present, allowing install.php, update.php,
      // cron.php and others to auto-detect a base path.
      $core_position = strrpos($dir, '/core');
      if ($core_position !== FALSE && strlen($dir) - 5 == $core_position) {
        $base_path = substr($dir, 0, $core_position);
      }
      else {
        $base_path = $dir;
      }
      $base_url .= $base_path;
      $base_path .= '/';
    }
    else {
      $base_path = '/';
    }
  }
  $base_secure_url = str_replace('http://', 'https://', $base_url);
  $base_insecure_url = str_replace('https://', 'http://', $base_url);

  if ($cookie_domain) {
    // If the user specifies the cookie domain, also use it for session name.
    $session_name = $cookie_domain;
  }
  else {
    // Otherwise use $base_url as session name, without the protocol
    // to use the same session identifiers across http and https.
    list( , $session_name) = explode('://', $base_url, 2);
    // HTTP_HOST can be modified by a visitor, but we already sanitized it
    // in drupal_settings_initialize().
    if (!empty($_SERVER['HTTP_HOST'])) {
      $cookie_domain = $_SERVER['HTTP_HOST'];
      // Strip leading periods, www., and port numbers from cookie domain.
      $cookie_domain = ltrim($cookie_domain, '.');
      if (strpos($cookie_domain, 'www.') === 0) {
        $cookie_domain = substr($cookie_domain, 4);
      }
      $cookie_domain = explode(':', $cookie_domain);
      $cookie_domain = '.' . $cookie_domain[0];
    }
  }
  // Per RFC 2109, cookie domains must contain at least one dot other than the
  // first. For hosts such as 'localhost' or IP Addresses we don't set a cookie domain.
  if (count(explode('.', $cookie_domain)) > 2 && !is_numeric(str_replace('.', '', $cookie_domain))) {
    ini_set('session.cookie_domain', $cookie_domain);
  }
  // To prevent session cookies from being hijacked, a user can configure the
  // SSL version of their website to only transfer session cookies via SSL by
  // using PHP's session.cookie_secure setting. The browser will then use two
  // separate session cookies for the HTTPS and HTTP versions of the site. So we
  // must use different session identifiers for HTTPS and HTTP to prevent a
  // cookie collision.
  if ($is_https) {
    ini_set('session.cookie_secure', TRUE);
  }
  $prefix = ini_get('session.cookie_secure') ? 'SSESS' : 'SESS';
  session_name($prefix . substr(hash('sha256', $session_name), 0, 32));
}

/**
 * Returns and optionally sets the filename for a system resource.
 *
 * The filename, whether provided, cached, or retrieved from the database, is
 * only returned if the file exists.
 *
 * This function plays a key role in allowing Drupal's resources (modules
 * and themes) to be located in different places depending on a site's
 * configuration. For example, a module 'foo' may legally be be located
 * in any of these three places:
 *
 * modules/foo/foo.module
 * sites/all/modules/foo/foo.module
 * sites/example.com/modules/foo/foo.module
 *
 * Calling drupal_get_filename('module', 'foo') will give you one of
 * the above, depending on where the module is located.
 *
 * @param $type
 *   The type of the item (i.e. theme, theme_engine, module, profile).
 * @param $name
 *   The name of the item for which the filename is requested.
 * @param $filename
 *   The filename of the item if it is to be set explicitly rather
 *   than by consulting the database.
 *
 * @return
 *   The filename of the requested item.
 */
function drupal_get_filename($type, $name, $filename = NULL) {
  // The location of files will not change during the request, so do not use
  // drupal_static().
  static $files = array(), $dirs = array();

  // Profiles are a special case: they have a fixed location and naming.
  if ($type == 'profile') {
    $profile_filename = "profiles/$name/$name.profile";
    $files[$type][$name] = file_exists($profile_filename) ? $profile_filename : FALSE;
  }
  if (!isset($files[$type])) {
    $files[$type] = array();
  }

  if (!empty($filename) && file_exists($filename)) {
    $files[$type][$name] = $filename;
  }
  elseif (isset($files[$type][$name])) {
    // nothing
  }
  // Verify that we have an active database connection, before querying
  // the database. This is required because this function is called both
  // before we have a database connection (i.e. during installation) and
  // when a database connection fails.
  else {
    try {
      if (function_exists('db_query')) {
        $file = db_query("SELECT filename FROM {system} WHERE name = :name AND type = :type", array(':name' => $name, ':type' => $type))->fetchField();
        if (file_exists(DRUPAL_ROOT . '/' . $file)) {
          $files[$type][$name] = $file;
        }
      }
    }
    catch (Exception $e) {
      // The database table may not exist because Drupal is not yet installed,
      // or the database might be down. We have a fallback for this case so we
      // hide the error completely.
    }
    // Fallback to searching the filesystem if the database could not find the
    // file or the file returned by the database is not found.
    if (!isset($files[$type][$name])) {
      // We have a consistent directory naming: modules, themes...
      $dir = $type . 's';
      if ($type == 'theme_engine') {
        $dir = 'themes/engines';
        $extension = 'engine';
      }
      elseif ($type == 'theme') {
        $extension = 'info';
      }
      else {
        $extension = $type;
      }

      if (!isset($dirs[$dir][$extension])) {
        $dirs[$dir][$extension] = TRUE;
        if (!function_exists('drupal_system_listing')) {
          require_once DRUPAL_ROOT . '/core/includes/common.inc';
        }
        // Scan the appropriate directories for all files with the requested
        // extension, not just the file we are currently looking for. This
        // prevents unnecessary scans from being repeated when this function is
        // called more than once in the same page request.
        $matches = drupal_system_listing("/^" . DRUPAL_PHP_FUNCTION_PATTERN . "\.$extension$/", $dir, 'name', 0);
        foreach ($matches as $matched_name => $file) {
          $files[$type][$matched_name] = $file->uri;
        }
      }
    }
  }

  if (isset($files[$type][$name])) {
    return $files[$type][$name];
  }
}

/**
 * Loads the persistent variable table.
 *
 * The variable table is composed of values that have been saved in the table
 * with variable_set() as well as those explicitly specified in the
 * configuration file.
 */
function variable_initialize($conf = array()) {
  // NOTE: caching the variables improves performance by 20% when serving
  // cached pages.
  if ($cached = cache('bootstrap')->get('variables')) {
    $variables = $cached->data;
  }
  else {
    // Cache miss. Avoid a stampede.
    $name = 'variable_init';
    if (!lock_acquire($name, 1)) {
      // Another request is building the variable cache.
      // Wait, then re-run this function.
      lock_wait($name);
      return variable_initialize($conf);
    }
    else {
      // Proceed with variable rebuild.
      $variables = array_map('unserialize', db_query('SELECT name, value FROM {variable}')->fetchAllKeyed());
      cache('bootstrap')->set('variables', $variables);
      lock_release($name);
    }
  }

  foreach ($conf as $name => $value) {
    $variables[$name] = $value;
  }

  return $variables;
}

/**
 * Returns a persistent variable.
 *
 * Case-sensitivity of the variable_* functions depends on the database
 * collation used. To avoid problems, always use lower case for persistent
 * variable names.
 *
 * @param $name
 *   The name of the variable to return.
 * @param $default
 *   The default value to use if this variable has never been set.
 *
 * @return
 *   The value of the variable. Unserialization is taken care of as necessary.
 *
 * @see variable_del()
 * @see variable_set()
 */
function variable_get($name, $default = NULL) {
  global $conf;

  return isset($conf[$name]) ? $conf[$name] : $default;
}

/**
 * Sets a persistent variable.
 *
 * Case-sensitivity of the variable_* functions depends on the database
 * collation used. To avoid problems, always use lower case for persistent
 * variable names.
 *
 * @param $name
 *   The name of the variable to set.
 * @param $value
 *   The value to set. This can be any PHP data type; these functions take care
 *   of serialization as necessary.
 *
 * @see variable_del()
 * @see variable_get()
 */
function variable_set($name, $value) {
  global $conf;

  db_merge('variable')->key(array('name'