bootstrap.inc

<?php

use Drupal\Component\Utility\Crypt;
use Drupal\Component\Utility\NestedArray;
use Drupal\Component\Utility\Settings;
use Drupal\Component\Utility\String;
use Drupal\Component\Utility\Timer;
use Drupal\Component\Utility\Unicode;
use Drupal\Component\Utility\Url;
use Drupal\Core\DrupalKernel;
use Drupal\Core\Database\Database;
use Drupal\Core\DependencyInjection\ContainerBuilder;
use Drupal\Core\Utility\Title;
use Symfony\Component\ClassLoader\ApcClassLoader;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\DependencyInjection\Container;
use Symfony\Component\DependencyInjection\Reference;
use Symfony\Component\DependencyInjection\Exception\RuntimeException as DependencyInjectionRuntimeException;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Drupal\Core\Language\Language;
use Drupal\Core\Lock\DatabaseLockBackend;
use Drupal\Core\Lock\LockBackendInterface;
use Drupal\Core\Session\UserSession;

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

/**
 * Minimum supported version of PHP.
 */
const DRUPAL_MINIMUM_PHP = '5.3.10';

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

/**
 * Error reporting level: display no errors.
 */
const ERROR_REPORTING_HIDE = 'hide';

/**
 * Error reporting level: display errors and warnings.
 */
const ERROR_REPORTING_DISPLAY_SOME = 'some';

/**
 * Error reporting level: display all messages.
 */
const ERROR_REPORTING_DISPLAY_ALL = 'all';

/**
 * Error reporting level: display all messages, plus backtrace information.
 */
const ERROR_REPORTING_DISPLAY_VERBOSE = 'verbose';

/**
 * @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, initalize a kernel.
 */
const DRUPAL_BOOTSTRAP_KERNEL = 1;

/**
 * Third bootstrap phase: try to serve a cached page.
 */
const DRUPAL_BOOTSTRAP_PAGE_CACHE = 2;

/**
 * Fourth bootstrap phase: initialize database layer.
 */
const DRUPAL_BOOTSTRAP_DATABASE = 3;

/**
 * Fifth bootstrap phase: initialize the variable system.
 */
const DRUPAL_BOOTSTRAP_VARIABLES = 4;

/**
 * Sixth bootstrap phase: load code for subsystems and modules.
 */
const DRUPAL_BOOTSTRAP_CODE = 5;

/**
 * Final bootstrap phase: initialize language, path, theme, and modules.
 */
const DRUPAL_BOOTSTRAP_FULL = 6;

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

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

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

/**
 * The maximum number of characters in a module or theme name.
 */
const DRUPAL_EXTENSION_NAME_MAX_LENGTH = 50;

/**
 * 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 has already been sanitized.
 *
 * @todo Move to the Title class.
 */
const PASS_THROUGH = -1;

/**
 * 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]*';

/**
 * $config_directories key for active directory.
 *
 * @see config_get_config_directory()
 */
const CONFIG_ACTIVE_DIRECTORY = 'active';

/**
 * $config_directories key for staging directory.
 *
 * @see config_get_config_directory()
 */
const CONFIG_STAGING_DIRECTORY = 'staging';

/**
 * Defines the root directory of the Drupal installation.
 *
 * This strips two levels of directories off the current directory.
 */
define('DRUPAL_ROOT', dirname(dirname(__DIR__)));

/**
 * @deprecated as of Drupal 8.0.
 * @see \Drupal\Component\Utility\Timer::start
 */
function timer_start($name) {
  Timer::start($name);
}

/**
 * @deprecated as of Drupal 8.0.
 * @see \Drupal\Component\Utility\Timer::read
 */
function timer_read($name) {
  return Timer::read($name);
}

/**
 * @deprecated as of Drupal 8.0.
 * @see \Drupal\Component\Utility\Timer::stop
 */
function timer_stop($name) {
  return Timer::stop($name);
}

/**
 * Returns the appropriate configuration directory.
 *
 * Returns the configuration path based on the site's hostname, port, and
 * pathname. Uses find_conf_path() to find the current configuration directory.
 * See default.settings.php for examples on how the URL is converted to a
 * directory.
 *
 * @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 $reset
 *   Force a full search for matching directories even if one had been
 *   found previously. Defaults to FALSE.
 *
 * @return
 *   The path of the matching directory.
 *
 * @see default.settings.php
 */
function conf_path($require_settings = TRUE, $reset = FALSE) {
  $conf_path = &drupal_static(__FUNCTION__, '');

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

  // Check for a simpletest override.
  if ($simpletest_conf_path = _drupal_simpletest_conf_path()) {
    $conf_path = $simpletest_conf_path;
    return $conf_path;
  }

  // Otherwise, use the normal $conf_path.
  $script_name = $_SERVER['SCRIPT_NAME'];
  if (!$script_name) {
    $script_name = $_SERVER['SCRIPT_FILENAME'];
  }
  $http_host = $_SERVER['HTTP_HOST'];
  $conf_path = find_conf_path($http_host, $script_name, $require_settings);
  return $conf_path;
}

/**
 * Determines whether to use an overridden value for conf_path().
 *
 * Simpletest may provide a secondary, test-specific settings.php file to load
 * after the primary one used by the parent site and override its variables.
 * - If the child settings.php does not override $conf_path, then this function
 * returns FALSE and conf_path() returns the directory of the primary
 * settings.php.
 * - If the child settings.php does override $conf_path, then
 * _drupal_load_test_overrides() sets the 'simpletest_conf_path' setting, and
 * this function returns that to conf_path(), causing installations and
 * upgrades to act on that one.
 *
 * @return string|false
 *   The overridden $conf_path, or FALSE if the $conf_path should not currently
 *   be overridden.
 *
 * @see conf_path()
 * @see _drupal_load_test_overrides()
 */
function _drupal_simpletest_conf_path() {
  // Ensure that the settings object is available. conf_path() is called once
  // before the Settings class is included, and at that point it should still
  // load the primary $conf_path. See drupal_settings_initialize().
  if (!class_exists('Drupal\Component\Utility\Settings', FALSE)) {
    return FALSE;
  }

  // If no $simpletest_conf_path is set, use the normal $conf_path.
  if (!($simpletest_conf_path = settings()->get('simpletest_conf_path'))) {
    return FALSE;
  }

  // Ensure that this is actually a simpletest request. We can't check this
  // before settings.php is loaded.
  if (!drupal_valid_test_ua()) {
    return FALSE;
  }

  // When the $simpletest_conf_path is set in a valid test request,
  // return that path.
  return $simpletest_conf_path;
}

/**
 * Finds the appropriate configuration directory for a given host and path.
 *
 * Finds a matching configuration directory file by stripping the website's
 * hostname from left to right and pathname from right to left. By default,
 * the directory must contain a 'settings.php' file for it to match. If the
 * parameter $require_settings is set to FALSE, then a directory without a
 * 'settings.php' file will match as well. The first configuration
 * file found will be used and the remaining ones will be ignored. If no
 * configuration file is found, returns a default value '$confdir/default'. See
 * default.settings.php for examples on how the URL is converted to a directory.
 *
 * If a file named sites.php is present in the $confdir, it will be loaded
 * prior to scanning for directories. That file can define aliases in an
 * associative array named $sites. The array is written in the format
 * '<port>.<domain>.<path>' => 'directory'. As an example, to create a
 * directory alias for http://www.drupal.org:8080/mysite/test whose configuration
 * file is in sites/example.com, the array should be defined as:
 * @code
 * $sites = array(
 *   '8080.www.drupal.org.mysite.test' => 'example.com',
 * );
 * @endcode
 *
 * @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.
 * @param $require_settings
 *   Defaults to TRUE. If TRUE, then only match directories with a
 *   'settings.php' file. Otherwise match any directory.
 *
 * @return
 *   The path of the matching configuration directory.
 *
 * @see default.settings.php
 * @see example.sites.php
 * @see conf_path()
 */
function find_conf_path($http_host, $script_name, $require_settings = TRUE) {
  // Determine whether multi-site functionality is enabled.
  if (!file_exists(DRUPAL_ROOT . '/sites/sites.php')) {
    return 'sites/default';
  }

  $sites = array();
  include DRUPAL_ROOT . '/sites/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 . '/sites/' . $sites[$dir])) {
        $dir = $sites[$dir];
      }
      if (file_exists(DRUPAL_ROOT . '/sites/' . $dir . '/settings.php') || (!$require_settings && file_exists(DRUPAL_ROOT . '/sites/' . $dir))) {
        return "sites/$dir";
      }
    }
  }
  return 'sites/default';
}

/**
 * Returns the path of a configuration directory.
 *
 * @param string $type
 *   (optional) The type of config directory to return. Drupal core provides
 *   'active' and 'staging'. Defaults to CONFIG_ACTIVE_DIRECTORY.
 *
 * @return string
 *   The configuration directory path.
 */
function config_get_config_directory($type = CONFIG_ACTIVE_DIRECTORY) {
  global $config_directories;

  if (!empty($config_directories[$type])) {
    // Allow a configuration directory path to be outside of webroot.
    if (empty($config_directories[$type]['absolute'])) {
      $path = conf_path() . '/files/' . $config_directories[$type]['path'];
    }
    else {
      $path = $config_directories[$type]['path'];
    }
  }
  else {
    throw new Exception(format_string('The configuration directory type %type does not exist.', array('%type' => $type)));
  }
  return $path;
}

/**
 * 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::request()->getClientIP()
 * 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 $variables
 *   (optional) An associative array of variables within
 *   \Drupal::request()->server that should be replaced. If the special element
 *   'url' is provided in this array, it will be used to populate some of the
 *   server defaults; it should be set to the URL of the current page request,
 *   excluding any GET request but including the script name
 *   (e.g., http://www.example.com/mysite/index.php).
 *
 * @see conf_path()
 * @see request_uri()
 * @see \Symfony\Component\HttpFoundation\Request::getClientIP()
 */
function drupal_override_server_variables($variables = array()) {
  $request = \Drupal::request();
  $server_vars = $request->server->all();
  // 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_vars['HTTP_HOST'] = $url['host'];
    }
    if (isset($url['path'])) {
      $server_vars['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.
  $request->server->replace($variables + $server_vars + $defaults);

  // @todo remove once conf_path() no longer uses $_SERVER.
  $_SERVER = $request->server->all();
}

/**
 * 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'] = '';
  }

  // @todo Refactor with the Symfony Request object.
  _current_path(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.

  // Deny execution with enabled "magic quotes" (both GPC and runtime).
  if (get_magic_quotes_gpc() || get_magic_quotes_runtime()) {
    header($_SERVER['SERVER_PROTOCOL'] . ' 500 Internal Server Error');
    print "PHP's 'magic_quotes_gpc' and 'magic_quotes_runtime' settings are not supported and must be disabled.";
    exit;
  }

  // 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, $script_path;

  // Export these settings.php variables to the global namespace.
  global $databases, $cookie_domain, $conf, $db_prefix, $drupal_hash_salt, $base_secure_url, $base_insecure_url, $config_directories;
  $conf = array();

  // Make conf_path() available as local variable in settings.php.
  $conf_path = conf_path();
  if (is_readable(DRUPAL_ROOT . '/' . $conf_path . '/settings.php')) {
    include_once DRUPAL_ROOT . '/' . $conf_path . '/settings.php';
  }
  require_once __DIR__ . '../../lib/Drupal/Component/Utility/Settings.php';

  new Settings(isset($settings) ? $settings : array());
  $is_https = isset($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) == 'on';

  if (isset($base_url)) {
    // Parse fixed base URL from settings.php.
    $parts = parse_url($base_url);
    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;

    // For a request URI of '/index.php/foo', $_SERVER['SCRIPT_NAME'] is
    // '/index.php', whereas $_SERVER['PHP_SELF'] is '/index.php/foo'.
    if ($dir = rtrim(dirname($_SERVER['SCRIPT_NAME']), '\/')) {
      // Remove "core" directory if present, allowing install.php, update.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);

  // Determine the path of the script relative to the base path, and add a
  // trailing slash. This is needed for creating URLs to Drupal pages.
  if (!isset($script_path)) {
    $script_path = '';
    // We don't expect scripts outside of the base path, but sanity check
    // anyway.
    if (strpos($_SERVER['SCRIPT_NAME'], $base_path) === 0) {
      $script_path = substr($_SERVER['SCRIPT_NAME'], strlen($base_path)) . '/';
      // If the request URI does not contain the script name, then clean URLs
      // are in effect and the script path can be similarly dropped from URL
      // generation. For servers that don't provide $_SERVER['REQUEST_URI'], we
      // do not know the actual URI requested by the client, and request_uri()
      // returns a URI with the script name, resulting in non-clean URLs unless
      // there's other code that intervenes.
      if (strpos(request_uri(TRUE) . '/', $base_path . $script_path) !== 0) {
        $script_path = '';
      }
      // @todo Temporary BC for install.php, update.php, and other scripts.
      //   - http://drupal.org/node/1547184
      //   - http://drupal.org/node/1546082
      if ($script_path !== 'index.php/') {
        $script_path = '';
      }
    }
  }

  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 located
 * in any of these three places:
 *
 * core/modules/foo/foo.module
 * 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 (theme, theme_engine, module, profile).
 * @param $name
 *   The name of the item for which the filename is requested.
 * @param $filename
 *   The filename of the item if it is to be set explicitly rather
 *   than by consulting the database.
 *
 * @return
 *   The filename of the requested item or NULL if the item is not found.
 */
function drupal_get_filename($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 converted into modules in system_rebuild_module_data().
  // @todo Remove false-exposure of profiles as modules.
  $original_type = $type;
  if ($type == 'profile') {
    $type = 'module';
  }
  if (!isset($files[$type])) {
    $files[$type] = array();
  }

  if (!empty($filename)) {
    $files[$type][$name] = $filename;
  }
  elseif (isset($files[$type][$name])) {
    // nothing
  }
  else {
    // Verify that we have an keyvalue service before using it. This is required
    // because this function is called during installation.
    // @todo Inject database connection into KeyValueStore\DatabaseStorage.
    if (($container = \Drupal::getContainer()) && $container->has('keyvalue') && function_exists('db_query')) {
      if ($type == 'module') {
        if (empty($files[$type])) {
          $files[$type] = \Drupal::moduleHandler()->getModuleList();
        }
        if (isset($files[$type][$name])) {
          return $files[$type][$name];
        }
      }
      try {
        $file_list = \Drupal::state()->get('system.' . $type . '.files');
        if ($file_list && isset($file_list[$name]) && file_exists(DRUPAL_ROOT . '/' . $file_list[$name])) {
          $files[$type][$name] = $file_list[$name];
        }
      }
      catch (Exception $e) {
        // The keyvalue service raised an exception because the backend might
        // be down. We have a fallback for this case so we hide the error
        // completely.
      }
    }
    // Fallback to searching the filesystem if the database could not find the
    // file or the file returned by the database is not found.
    if (!isset($files[$type][$name])) {
      // We have consistent directory naming: modules, themes...
      $dir = $type . 's';
      if ($type == 'theme_engine') {
        $dir = 'themes/engines';
        $extension = 'engine';
      }
      elseif ($type == 'theme') {
        $extension = 'info.yml';
      }
      // Profiles are converted into modules in system_rebuild_module_data().
      // @todo Remove false-exposure of profiles as modules.
      elseif ($original_type == 'profile') {
        $dir = 'profiles';
        $extension = 'profile';
      }
      else {
        $extension = $type;
      }

      if (!isset($dirs[$dir][$extension])) {
        $dirs[$dir][$extension] = TRUE;
        if (!function_exists('drupal_system_listing')) {
          require_once __DIR__ . '/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$/", $dir);
        foreach ($matches as $matched_name => $file) {
          $files[$type][$matched_name] = $file->uri;
        }
      }
    }
  }

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

/**
 * Returns a setting.
 *
 * Settings can be set in settings.php in the $settings array and requested
 * by this function. Settings should be used over configuration for read-only,
 * possibly low bootstrap configuration that is environment specific.
 *
 * @return \Drupal\Component\Utility\Settings
 *   The settings object.
 */
function settings() {
  return Settings::getSingleton();
}

/**
 * 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';
    $lock = \Drupal::lock();
    if (!$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 $default
 *   The default value to use if this variable has never been set.
 *
 * @return
 *   The value of the variable. Unserialization is taken care of as necessary.
 *
 * @deprecated This will be removed in Drupal 8.0. Instead, use the
 *   configuration API.
 *
 * @see \Drupal\Core\Config::get()
 */
function variable_get($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 $value
 *   The value to set. This can be any PHP data type; these functions take care
 *   of serialization as necessary.
 *
 * @deprecated This will be removed in Drupal 8.0. Instead, use the
 *   configuration API.
 *
 * @see \Drupal\Core\Config::set()
 */
function variable_set($name, $value) {
  global $conf;

  db_merge('variable')->key(array('name' => $name))->fields(array('value' => serialize($value)))->execute();

  cache('bootstrap')->delete('variables');

  $conf[$name] = $value;
}

/**
 * Unsets 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 $name
 *   The name of the variable to undefine.
 *
 * @deprecated This will be removed in Drupal 8.0. Instead, use the
 *   configuration API.
 *
 * @see \Drupal\Core\Config::clear()
 */
function variable_del($name) {
  global $conf;

  db_delete('variable')
    ->condition('name', $name)
    ->execute();
  cache('bootstrap')->delete('variables');

  unset($conf[$name]);
}

/**
 * Gets the page cache cid for this request.
 *
 * @param \Symfony\Component\HttpFoundation\Request $request
 *   The request for this page.
 *
 * @return string
 *   The cid for this request.
 */
function drupal_page_cache_get_cid(Request $request) {
  $cid_parts = array(
    $request->getUri(),
    \Drupal::service('content_negotiation')->getContentType($request),
  );
  return sha1(implode(':', $cid_parts));
}

/**
 * Retrieves the current page from the cache.
 *
 * Note: we do not serve cached pages to authenticated users, or to anonymous
 * users when $_SESSION is non-empty. $_SESSION may contain status messages
 * from a form submission, the contents of a shopping cart, or other user-
 * specific content that should not be cached and displayed to other users.
 *
 * @param \Symfony\Component\HttpFoundation\Request $request
 *   The request for this page.
 *
 * @return
 *   The cache object, if the page was found in the cache, NULL otherwise.
 */
function drupal_page_get_cache(Request $request) {
  if (drupal_page_is_cacheable()) {
    return \Drupal::cache('page')->get(drupal_page_cache_get_cid($request));
  }
}

/**
 * Determines the cacheability of the current page.
 *
 * @param $allow_caching
 *   Set to FALSE if you want to prevent this page to get cached.
 *
 * @return
 *   TRUE if the current page can be cached, FALSE otherwise.
 */
function drupal_page_is_cacheable($allow_caching = NULL) {
  $allow_caching_static = &drupal_static(__FUNCTION__, TRUE);
  if (isset($allow_caching)) {
    $allow_caching_static = $allow_caching;
  }

  return $allow_caching_static && ($_SERVER['REQUEST_METHOD'] == 'GET' || $_SERVER['REQUEST_METHOD'] == 'HEAD')
    && !drupal_is_cli();
}

/**
 * Includes a file with the provided type and name.
 *
 * This prevents including a theme, engine, module, etc., more than once.
 *
 * @param $type
 *   The type of item to load (i.e. theme, theme_engine, module).
 * @param $name
 *   The name of the item to load.
 *
 * @return
 *   TRUE if the item is loaded or has already been loaded.
 */
function drupa