Automating the $baseURL configuration value between test and production servers or when moving public/index.php saves time and potential headaches. Follow this guide to define a DYNAMIC_BASE_URL for use in your CodeIgniter 4 application.

Edit app/Config/Constants.php

<?php

/*
 | --------------------------------------------------------------------
 | Dynamic Base URL
 | --------------------------------------------------------------------
 | 
 | Generate absolute URL based on request scheme, host and script path.
 */
defined('DYNAMIC_BASE_URL') || define('DYNAMIC_BASE_URL', sprintf('%s://%s%s', (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] != 'off') ? 'https' : 'http', isset($_SERVER['HTTP_HOST']) ? $_SERVER['HTTP_HOST'] : 'localhost', str_replace(basename($_SERVER['SCRIPT_NAME']), '', $_SERVER['SCRIPT_NAME'])));

Update app/Config/App.php

public string $baseURL = DYNAMIC_BASE_URL;

So far, that reliably automates Config\App::$baseURL in all tested environments 🙂

---

Single-File Approach

DYNAMIC_BASE_URL can be defined directly in app/Config/App.php limiting changes to a single file, but doing so ignores intended architecture.

<?php

namespace Config;

use CodeIgniter\Config\BaseConfig;

defined('DYNAMIC_BASE_URL') || define('DYNAMIC_BASE_URL', sprintf('%s://%s%s', (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] != 'off') ? 'https' : 'http', isset($_SERVER['HTTP_HOST']) ? $_SERVER['HTTP_HOST'] : 'localhost', str_replace(basename($_SERVER['SCRIPT_NAME']), '', $_SERVER['SCRIPT_NAME'])));

class App extends BaseConfig
{
    /**
     * --------------------------------------------------------------------------
     * Base Site URL
     * --------------------------------------------------------------------------
     *
     * URL to your CodeIgniter root. Typically, this will be your base URL,
     * WITH a trailing slash:
     *
     * E.g., http://example.com/
     */
    public string $baseURL = DYNAMIC_BASE_URL;