Framework — Bootloaders

Spiral uses bootloader classes during the bootstrapping process to handle application configuration. One of the key features is that bootloaders are executed only once during the application bootstrapping, ensuring that adding additional code to them does not negatively impact runtime performance.

Bootloader classes play a crucial role in configuring various aspects of the application.

Here are some examples:

• Container Configuration: Bootloaders can be utilized to configure the dependency injection container. This includes tasks such as registering services and binding interfaces to their respective implementations.
• Application Configuration: Bootloaders are responsible for setting up various application-level settings, including the environment, debug mode, and error handling.
• Database Configuration: Bootloaders are involved in setting up and configuring the application's database connection. This includes specifying the database driver, connection details, and any necessary migrations.
• Routing Configuration: The bootloaders can be used to set up the application's routing rules, such as defining which controllers should handle which URLs.
• Services Initialization: Bootloaders take care of initializing any services required by the application, such as caching, logging, and event systems.

#Simple Bootloader

To create a simple bootloader effortlessly, use the scaffolding command:

php app.php create:bootloader GithubClient

Note
Read more about scaffolding in the Basics — Scaffolding section.

After executing this command, the following output will confirm the successful creation:

Declaration of 'GithubClientBootloader' has been successfully written into 'app/src/Application/Bootloader/GithubClientBootloader.php'.

Now you can find the GithubClientBootloader class in the app/src/Application/Bootloader directory.

Currently, a new Bootloader doesn't perform any actions. A little later, we will add some functionality to it.

#Registering bootloader

Every bootloader must be activated in your application kernel app/src/Application/Kernel.php.

In Spiral, you can register bootloaders in your kernel using two different approaches: constants and methods.

1. Constants: The kernel provides constants such as Kernel::SYSTEM, Kernel::LOAD, and Kernel::APP. These constants allow you to specify which bootloaders should be executed at different stages of the application's initialization process. By using these constants, you can achieve a clear separation of concerns and easily understand which bootloaders handle specific tasks.
2. Methods: The kernel also offers methods like defineBootloaders, defineAppBootloaders, and defineSystemBootloaders. These methods allow for more complex logic and registration of objects, anonymous classes, or other advanced use cases. With these methods, you have greater flexibility and control over the initialization process of your application.

Warning
You cannot use both methods and constants simultaneously. If you choose to use the method approach, the registration through constants will not take effect.

namespace App\Application;

use App\Application\Bootloader\RoutesBootloader;
use App\Application\Bootloader\LoggingBootloader;
use App\Application\Bootloader\MyBootloader;

class Kernel extends \Spiral\Framework\Kernel
{
    public function defineBootloaders(): array
    {
        return [
            // ...
           RoutesBootloader::class,
        ]
    }

    public function defineAppBootloaders(): array
    {
        return [
           LoggingBootloader::class,
           MyBootloader::class,
           
           // anonymous bootloader via object instance
           new class () extends Bootloader {
               public const BINDINGS = [
                 // ...
               ];
               public const SINGLETONS = [
                 // ...
               ];
               
               public function init(BinderInterface $binder): void
               {
                 // ...
               }
               
               public function boot(BinderInterface $binder): void
               {
                  // ...
               }
           },
       ];
    }
}

namespace App\Application;

use App\Application\Bootloader\RoutesBootloader;
use App\Application\Bootloader\LoggingBootloader;
use App\Application\Bootloader\MyBootloader;

class Kernel extends \Spiral\Framework\Kernel
{
    protected const LOAD = [
        // ...
        RoutesBootloader::class,
    ];

    protected const APP = [
        // ...
        LoggingBootloader::class,
        MyBootloader::class,
    ];
}

#Available methods

Bootloaders provide two methods init and boot that are executed when the application is initialized.

#Init method

This method will be run first.

It's a good idea to set default values for the config files before proceeding. You can use the special bootloader methods to modify the config files as needed. After that, you can go ahead and run any other logic that doesn't require reading the config files and isn't dependent on code execution in the init and boot methods of other bootloaders.

This is also a good time to add initialization callbacks and configure container bindings, as long as it doesn't require accessing the app config.

namespace App\Application\Bootloader;

use Spiral\Boot\Bootloader\Bootloader;
use Spiral\Boot\EnvironmentInterface;
use Spiral\Config\ConfiguratorInterface;
use App\Service\Github\GithubConfig;

final class GithubClientBootloader extends Bootloader
{
    public function __construct(
        private readonly ConfiguratorInterface $config
    ) {
    }

    public function init(EnvironmentInterface $env): void 
    {
        $this->config->setDefaults(
            GithubConfig::CONFIG,
            [
                'access_token' => $env->get('GITHUB_ACCESS_TOKEN'),
                'secret' => $env->get('GITHUB_SECRET'),
            ]
        );
    }
}

Note

1. Learn more about the Spiral\Boot\EnvironmentInterface, in the Configuration section.
2. Learn more about the Spiral\Boot\AbstractKernel class (also known as the 'Kernel'), in the Kernel and Environment section.
3. Learn more about the Spiral\Config\ConfiguratorInterface class, in the Config Objects section.

#Boot method

This method will be run after the init method in all the bootloaders have been executed. The reason for this is that you might need the results of bootloader initialization in order to proceed. For example, compiled configuration files.

Just keep in mind that it should be run after all those init methods have completed.

namespace App\Application\Bootloader;

// ...
use App\Service\Github\GithubConfig;

final class GithubClientBootloader extends Bootloader
{
    // See code above ...
    
    public function boot(GithubConfig $config): void 
    {
        $token = $config->getAccessToken();
        // ...
    }
}

#Configuring Container

Bootloaders are usually used to set up a container, like if we want to link multiple implementations to their interfaces or create some service. We can use both init or boot method for this, which lets us request any services we need using method injection.

namespace App\Application\Bootloader;

// ...
use Spiral\Core\BinderInterface;
use App\Service\Github\GithubConfig;
use App\Service\Github\ClinetInterface;
use App\Service\Github\Clinet;

final class GithubClientBootloader extends Bootloader
{
    // See code above ...
    
    public function boot(BinderInterface $binder): void 
    {
        $binder->bindSingleton(ClinetInterface::class, function (GithubConfig $config) {
            return new Clinet(
                $config->getAccessToken(),
                $config->getSecret(),
            );
        });
    }
}

Note
The closure is provided as an argument to the bindSingleton method will be called by the dependency injection (DI) container when it needs to create an instance of MyService. When the closure is called, the DI container will automatically resolve and inject any dependencies that are required by the closure.

If you want to learn more about DI, you can check out the Container and Factories section of the documentation. It should have all the info you need.

Bootloaders provide the ability to simplify container binding definition using constants BINDINGS and SINGLETONS.

namespace App\Application\Bootloader;

// ...
use Spiral\Core\BinderInterface;
use App\Service\Github\GithubConfig;
use App\Service\Github\ClientInterface;
use App\Service\Github\Client;

final class GithubClientBootloader extends Bootloader
{
    const BINDINGS = [
        MyInterface::class => MyClass::class
    ];
    
    const SINGLETONS = [
        ClientInterface::class => [self::class, 'createClient'],
    ];
    
    // See code above ...
    
    public function createClient(GithubConfig $config): ClinetInterface 
    {
        return new Clinet(
            $config->getAccessToken(),
            $config->getSecret(),
        );
    }
}

#Configuring Application

Another common use case of bootloaders is to configure the framework before the application launch. For example, we can declare a new route for our application or module:

namespace App\Application\Bootloader;

use Spiral\Router\RouterInterface;
use Spiral\Router\Target\Controller;
use Spiral\Router\Route;

final class RoutesBootloader extends Bootloader 
{
    public function boot(RouterInterface $router): void
    {
        $router->setRoute(
            'my-route',
            new Route('/<action>', new Controller(MyController::class))
        );
    }
}

Note
You are only able to use bootloaders to configure your components during the bootstrap phase (a.k.a. via another bootloader). The framework would not allow you to change any configuration value after component initialization.

#Depending on other Bootloaders

Depending on other bootloaders can be really useful in certain situations. For example, if you want to make sure a certain bootloader is initialized before yours, you can use one of two main approaches: injecting the bootloader class into the init or boot method as an argument, or using the Bootloader::DEPENDENCIES constant in your bootloader class.

This can be a good way to manage the initialization of your app and make sure all the necessary resources and dependencies are available when you need them. Just keep in mind that dependent bootloaders will only be initialized once, even if they are depended on by multiple other bootloaders.

Some framework bootloaders can be used as a simple way to configure application settings. For example, we can use Spiral\Bootloader\Http\HttpBootloader to add global PSR-15 middleware:

There are two ways to define dependent bootloaders:

1. Injecting the bootloader class into the init or boot method as an argument of your bootloader class

For example:

namespace App\Application\Bootloader;

use Spiral\Bootloader\Http\HttpBootloader;
use App\Middleware\MyMiddleware;

class MyBootloader extends Bootloader 
{
    public function boot(HttpBootloader $http): void
    {
        $http->addMiddleware(MyMiddleware::class);
    }
}

2. Using the Bootloader::DEPENDENCIES constant in your bootloader class. This can be a convenient way to define dependent bootloaders when you don't need to access them directly in your bootloader class.

For example:

namespace App\Application\Bootloader;

class MyBootloader extends Bootloader 
{
    protected const DEPENDENCIES = [
        \Spiral\Bootloader\Http\HttpBootloader::class
    ];
    
    public function boot(): void
    {
        // ...
    }
}

Spiral will automatically resolve and initialize the dependent bootloader before the depending bootloader is initialized.

Both of these approaches allow you to define dependent bootloaders in a declarative way, which can make it easier to manage the initialization of your application and ensure that all necessary resources and dependencies are available when they are needed.

Note
Dependent bootloaders will be only initialized once, even if multiple other bootloaders depend on them.

#Cascade bootloading

You can control the bootload process using Bootloader itself, simply request Spiral\Boot\BootloadManager:

namespace App\Application\Bootloader;

use Spiral\Boot\Bootloader\Bootloader;
use Spiral\Boot\BootloadManager;
use Spiral\Bootloader\DebugBootloader;
use Spiral\Boot\EnvironmentInterface;

class AppBootloader extends Bootloader
{
    public function boot(BootloadManager $bootloadManager, EnvironmentInterface $env): void
    {
        if ($env->get('DEBUG')) {
            $bootloadManager->bootload([
                DebugBootloader::class
            ]);
        }
    }
}

#What's Next?

Now, dive deeper into the fundamentals by reading some articles:

• HTTP — Interceptors
• Scaffolding