How to bootstrap a custom script and retrieve the session object?

Question

I'm writing a custom script that requires a proper Drupal 8 user session to work. This is the current version:

<?php

use Drupal\Core\DrupalKernel;
use Symfony\Component\HttpFoundation\Request;

$drupal_root = __DIR__;
define('DRUPAL_DIR', $drupal_root);

// Specify relative path to the drupal root.
$autoloader = require_once DRUPAL_DIR . '/autoload.php';
$request = Request::createFromGlobals();

// Bootstrap drupal to different levels
$kernel = DrupalKernel::createFromRequest($request, $autoloader, 'prod');
$kernel->boot();
$kernel->handlePageCache($request);
$kernel->prepareLegacyRequest($request);

// get session handler and retrieve session details
$session_handler = \Drupal::getContainer()->get('session_handler.storage');
$session_id = $session_handler->getId();
$logged_in = (bool) $session_handler->read($session_id);

// inspect values
var_dump($request->getSession());
var_dump($session_id);
var_dump($logged_in); exit;

I'd expect $request->getSession() to return something, $session_id to be the Drupal's session id, and the $logged_in variable to be truthy. Instead I keep getting this output:

NULL string(0) "" bool(false)

---

Update 1: I executed this on a browser, which I have an active session with my Drupal. This script is placed in a subfolder of the Drupal installation, so it should not be a cookie path issue.

Update 2: Added var_dump($request->getSession()) to the script.

Answer 1

This is the code I came up with in the end. It works.

Feel free to suggest a more concise version :-)

<?php

use Drupal\Core\DrupalKernel;
use Symfony\Component\HttpFoundation\Request;

$drupal_root = realpath(__DIR__ . '/../');
$autoloader = require_once $drupal_root . '/autoload.php';

// Make sure Drupal operates correct when handle request instead of internal server error and twig error
chdir($drupal_root);

$kernel = new DrupalKernel('prod', $autoloader);

// Note: The session_name is generated from the string "{domain}/{script basepath}".
// Need to override the script filename and script name before creating request.
$_SERVER['SCRIPT_FILENAME'] = $drupal_root . '/index.php';
$_SERVER['SCRIPT_NAME'] = '/index.php';
$request = Request::createFromGlobals();
// Note: may restore script_name and script_filename after this line.

// This handle process would chain up and initialize all services
// in container, include the session handler.
$kernel->handle($request);

// now we can use session normally
$session_handler = \Drupal::getContainer()->get('session_handler.storage');
$session_id = $session_handler->getId();
$logged_in = (bool) $session_handler->read($session_id);

// restore app
chdir(__DIR__);