Bootstrapping

\TYPO3\CMS\Frontend\Http\Application

This class handles all incoming web requests coming through index.php in the public web directory. It handles all regular page (TSFE) and eID requests.

It checks if all configuration is set, otherwise redirects to the TYPO3 Install Tool.

\TYPO3\CMS\Backend\Http\Application

This class handles all incoming web requests for any regular backend call inside typo3/*.

Its \TYPO3\CMS\Backend\Http\RequestHandler is used for all backend requests, including Ajax routes. If a get/post parameter "route" is set, the backend routing is called by the RequestHandler and searches for a matching route inside the router. The corresponding controller / action is called then which returns the response.

The Application checks if all configuration is set, otherwise it redirects to the TYPO3 Install Tool.

\TYPO3\CMS\Core\Console\CommandApplication

This class is the entry point for the TYPO3 command line for console commands. In addition to registering all available commands, this also sets up a CLI user.

\TYPO3\CMS\Install\Http\Application

The install tool Application only runs with a very limited bootstrap set up. The failsafe package manager does not take the ext_localconf.php of installed extensions into account.

Example of bootstrapping the TYPO3 Backend:

// Set up the application for the backend
call_user_func(function () {
    $classLoader = require dirname(__DIR__) . '/vendor/autoload.php';
    \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::run(1, \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::REQUESTTYPE_BE);
    \TYPO3\CMS\Core\Core\Bootstrap::init($classLoader)->get(\TYPO3\CMS\Backend\Http\Application::class)->run();
});

1. Initialize the class loader

This defines which autoloader to use.

2. Run SystemEnvironmentBuilder

The \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder is responsible for setting up a system environment that is shared by all contexts (FE, BE, Install Tool and CLI). This class defines a large number of constants and global variables. If you want to have an overview of these base values, it is worth taking a look into the following methods:

• SystemEnvironmentBuilder::defineTypo3RequestTypes() defines the different constants for determining if the current request is a frontend, backend, CLI, Ajax or Install Tool request.
• SystemEnvironmentBuilder::defineBaseConstants() defines constants containing values such as the current version number, blank character codes and error codes related to services.
• SystemEnvironmentBuilder::initializeEnvironment() initializes the Environment class that points to various parts of the TYPO3 installation like the absolute path to the typo3 directory or the absolute path to the installation root.
• SystemEnvironmentBuilder::calculateScriptPath() calculates the script path. This is the absolute path to the entry script. This can be something like '.../public/index.php' or '.../public/typo3/index.php' for web calls, or '.../bin/typo3' or similar for CLI calls.
• SystemEnvironmentBuilder::initializeGlobalVariables() sets some global variables as empty arrays.
• SystemEnvironmentBuilder::initializeGlobalTimeTrackingVariables() defines special variables which contain, for example, the current time or a simulated time as may be set using the Admin Panel.

3. Initialize bootstrap

\TYPO3\CMS\Core\Core\Bootstrap boots up TYPO3 and returns a container that is later used to run an application. As a basic overview it does the following:

• Bootstrap::initializeClassLoader() processes all the information available to be able to determine where to load classes from, including class alias maps which are used to map legacy class names to new class names.
• Bootstrap::checkIfEssentialConfigurationExists() checks if crucial configuration elements have been set. If that is not the case, the installation is deemed incomplete and the user is redirected to the Install Tool.
• Bootstrap::createConfigurationManager() creates the Configuration Manager which is then populated with the the main configuration ("TYPO3_CONF_VARS").
• $builder->createDependencyInjectionContainer() creates a dependency injection container which is later returned by Bootstrap::init().
• The caching framework and the package management are set up.
• All configuration items from extensions are loaded
• The database connection is established

4. Dispatch

After all that the, the newly created container receives the application object and Application::run() method is called, which basically dispatches the request to the right handler.

5. Initialization of the TYPO3 backend

The backend request handler then calls the MiddlewareDispatcher which then manages and dispatches a PSR-15 middleware stack. In the backend context this will typically go through such important steps like:

• checking backend access: Is it locked? Does it have proper SSL setup?
• loading the full TCA
• verifying and initializing the backend user

Custom contexts

In certain situations, more specific contexts are desirable:

• a staging system may run in a Production context, but requires a different set of credentials than the production server.
• developers working on a project may need different application specific settings but prefer to maintain all configuration files in a common Git repository.

By defining custom contexts which inherit from one of the three base contexts, more specific configuration sets can be realized.

While it is not possible to add new "top-level" contexts at the same level like Production and Testing, you can create arbitrary sub-contexts, just by specifying them like <MainContext>/<SubContext>.

For a staging environment a custom context Production/Staging may provide the necessary settings while the Production/Live context is used on the live instance.

switch (\TYPO3\CMS\Core\Core\Environment::getContext()) {
   case 'Development':
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 1;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '*';
      break;
   case 'Production/Staging':
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 0;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '192.168.1.*';
      break;
   default:
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 0;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '127.0.0.1';
}