Services

Silex is not only a microframework. It is also a micro service container. It does this by extending Pimple which provides service goodness in just 44 NCLOC.

Dependency Injection

Note

You can skip this if you already know what Dependency Injection is.

Dependency Injection is a design pattern where you pass dependencies to services instead of creating them from within the service or relying on globals. This generally leads to code that is decoupled, re-usable, flexible and testable.

Here is an example of a class that takes a User object and stores it as a file in JSON format:

class JsonUserPersister
{
    private $basePath;

    public function __construct($basePath)
    {
        $this->basePath = $basePath;
    }

    public function persist(User $user)
    {
        $data = $user->getAttributes();
        $json = json_encode($data);
        $filename = $this->basePath.'/'.$user->id.'.json';
        file_put_contents($filename, $json, LOCK_EX);
    }
}

In this simple example the dependency is the basePath property. It is passed to the constructor. This means you can create several independent instances with different base paths. Of course dependencies do not have to be simple strings. More often they are in fact other services.

Container

A DIC or service container is responsible for creating and storing services. It can recursively create dependencies of the requested services and inject them. It does so lazily, which means a service is only created when you actually need it.

Most containers are quite complex and are configured through XML or YAML files.

Pimple is different.

Pimple

Pimple is probably the simplest service container out there. It makes strong use of closures and implements the ArrayAccess interface.

We will start off by creating a new instance of Pimple – and because Silex\Application extends Pimple all of this applies to Silex as well:

$container = new Pimple();

or:

$app = new Silex\Application();

Parameters

You can set parameters (which are usually strings) by setting an array key on the container:

$app['some_parameter'] = 'value';

The array key can be anything, by convention periods are used for namespacing:

$app['asset.host'] = 'http://cdn.mysite.com/';

Reading parameter values is possible with the same syntax:

echo $app['some_parameter'];

Service definitions

Defining services is no different than defining parameters. You just set an array key on the container to be a closure. However, when you retrieve the service, the closure is executed. This allows for lazy service creation:

$app['some_service'] = function () {
    return new Service();
};

And to retrieve the service, use:

$service = $app['some_service'];

Every time you call $app['some_service'], a new instance of the service is created.

Shared services

You may want to use the same instance of a service across all of your code. In order to do that you can make a shared service:

$app['some_service'] = $app->share(function () {
    return new Service();
});

This will create the service on first invocation, and then return the existing instance on any subsequent access.

Access container from closure

In many cases you will want to access the service container from within a service definition closure. For example when fetching services the current service depends on.

Because of this, the container is passed to the closure as an argument:

$app['some_service'] = function ($app) {
    return new Service($app['some_other_service'], $app['some_service.config']);
};

Here you can see an example of Dependency Injection. some_service depends on some_other_service and takes some_service.config as configuration options. The dependency is only created when some_service is accessed, and it is possible to replace either of the dependencies by simply overriding those definitions.

Note

This also works for shared services.

Protected closures

Because the container sees closures as factories for services, it will always execute them when reading them.

In some cases you will however want to store a closure as a parameter, so that you can fetch it and execute it yourself – with your own arguments.

This is why Pimple allows you to protect your closures from being executed, by using the protect method:

$app['closure_parameter'] = $app->protect(function ($a, $b) {
    return $a + $b;
});

// will not execute the closure
$add = $app['closure_parameter'];

// calling it now
echo $add(2, 3);

Note that protected closures do not get access to the container.

Core services

Silex defines a range of services which can be used or replaced. You probably don’t want to mess with most of them.

• request: Contains the current request object, which is an instance of Request. It gives you access to GET, POST parameters and lots more!

  Example usage:

  $id = $app['request']->get('id');
  

  This is only available when a request is being served, you can only access it from within a controller, an application before/after middlewares, or an error handler.

• routes: The RouteCollection that is used internally. You can add, modify, read routes.

• controllers: The Silex\ControllerCollection that is used internally. Check the Internals chapter for more information.

• dispatcher: The EventDispatcher that is used internally. It is the core of the Symfony2 system and is used quite a bit by Silex.

• resolver: The ControllerResolver that is used internally. It takes care of executing the controller with the right arguments.

• kernel: The HttpKernel that is used internally. The HttpKernel is the heart of Symfony2, it takes a Request as input and returns a Response as output.

• request_context: The request context is a simplified representation of the request that is used by the Router and the UrlGenerator.

• exception_handler: The Exception handler is the default handler that is used when you don’t register one via the error() method or if your handler does not return a Response. Disable it with $app['exception_handler']->disable().

• logger: A LoggerInterface instance. By default, logging is disabled as the value is set to null. When the Symfony2 Monolog bridge is installed, Monolog is automatically used as the default logger.

Note

All of these Silex core services are shared.

Core parameters

• request.http_port (optional): Allows you to override the default port for non-HTTPS URLs. If the current request is HTTP, it will always use the current port.

  Defaults to 80.

  This parameter can be used by the UrlGeneratorProvider.

• request.https_port (optional): Allows you to override the default port for HTTPS URLs. If the current request is HTTPS, it will always use the current port.

  Defaults to 443.

  This parameter can be used by the UrlGeneratorProvider.

• locale (optional): The locale of the user. When set before any request handling, it defines the default locale (en by default). When a request is being handled, it is automatically set according to the _locale request attribute of the current route.

• debug (optional): Returns whether or not the application is running in debug mode.

  Defaults to false.

• charset (optional): The charset to use for Responses.

  Defaults to UTF-8.