Laravel 4.2 Extending The Framework

Introduction

Laravel offers many extension points for you to customize the behavior of the framework's core components, or even replace them entirely. For example, the hashing facilities are defined by a HasherInterface contract, which you may implement based on your application's requirements. You may also extend the Request object, allowing you to add your own convenient "helper" methods. You may even add entirely new authentication, cache, and session drivers!

Laravel components are generally extended in two ways: binding new implementations in the IoC container, or registering an extension with a Manager class, which are implementations of the "Factory" design pattern. In this chapter we'll explore the various methods of extending the framework and examine the necessary code.

Note: Remember, Laravel components are typically extended in one of two ways: IoC bindings and the Manager classes. The manager classes serve as an implementation of the "factory" design pattern, and are responsible for instantiating driver based facilities such as cache and session.

Managers & Factories

Laravel has several Manager classes that manage the creation of driver-based components. These include the cache, session, authentication, and queue components. The manager class is responsible for creating a particular driver implementation based on the application's configuration. For example, the CacheManager class can create APC, Memcached, File, and various other implementations of cache drivers.

Each of these managers includes an extend method which may be used to easily inject new driver resolution functionality into the manager. We'll cover each of these managers below, with examples of how to inject custom driver support into each of them.

Note: Take a moment to explore the various Manager classes that ship with Laravel, such as the CacheManager and SessionManager. Reading through these classes will give you a more thorough understanding of how Laravel works under the hood. All manager classes extend the Illuminate\Support\Manager base class, which provides some helpful, common functionality for each manager.

Where To Extend

This documentation covers how to extend a variety of Laravel's components, but you may be wondering where to place your extension code. Like most other bootstrapping code, you are free to place some extensions in your start files. Cache and Auth extensions are good candidates for this approach. Other extensions, like Session, must be placed in the register method of a service provider since they are needed very early in the request life-cycle.

Cache

To extend the Laravel cache facility, we will use the extend method on the CacheManager, which is used to bind a custom driver resolver to the manager, and is common across all manager classes. For example, to register a new cache driver named "mongo", we would do the following:

Cache::extend('mongo', function($app)
{
    // Return Illuminate\Cache\Repository instance...
});

The first argument passed to the extend method is the name of the driver. This will correspond to your driver option in the app/config/cache.php configuration file. The second argument is a Closure that should return an Illuminate\Cache\Repository instance. The Closure will be passed an $app instance, which is an instance of Illuminate\Foundation\Application and an IoC container.

To create our custom cache driver, we first need to implement the Illuminate\Cache\StoreInterface contract. So, our MongoDB cache implementation would look something like this:

class MongoStore implements Illuminate\Cache\StoreInterface {

    public function get($key) {}
    public function put($key, $value, $minutes) {}
    public function increment($key, $value = 1) {}
    public function decrement($key, $value = 1) {}
    public function forever($key, $value) {}
    public function forget($key) {}
    public function flush() {}

}

We just need to implement each of these methods using a MongoDB connection. Once our implementation is complete, we can finish our custom driver registration:

use Illuminate\Cache\Repository;

Cache::extend('mongo', function($app)
{
    return new Repository(new MongoStore);
});

As you can see in the example above, you may use the base Illuminate\Cache\Repository when creating custom cache drivers. There is typically no need to create your own repository class.

If you're wondering where to put your custom cache driver code, consider making it available on Packagist! Or, you could create an Extensions namespace within your application's primary folder. For example, if the application is named Snappy, you could place the cache extension in app/Snappy/Extensions/MongoStore.php. However, keep in mind that Laravel does not have a rigid application structure and you are free to organize your application according to your preferences.

Note: If you're ever wondering where to put a piece of code, always consider a service provider. As we've discussed, using a service provider to organize framework extensions is a great way to organize your code.

Session

Extending Laravel with a custom session driver is just as easy as extending the cache system. Again, we will use the extend method to register our custom code:

Session::extend('mongo', function($app)
{
    // Return implementation of SessionHandlerInterface
});

Where To Extend The Session

Session extensions need to be registered differently than other extensions like Cache and Auth. Since sessions are started very early in the request-lifecycle, registering the extensions in a start file will happen too late. Instead, a service provider will be needed. You should place your session extension code in the register method of your service provider, and the provider should be placed below the default Illuminate\Session\SessionServiceProvider in the providers configuration array.

Writing The Session Extension

Note that our custom session driver should implement the SessionHandlerInterface. This interface is included in the PHP 5.4+ core. If you are using PHP 5.3, the interface will be defined for you by Laravel so you have forward-compatibility. This interface contains just a few simple methods we need to implement. A stubbed MongoDB implementation would look something like this:

class MongoHandler implements SessionHandlerInterface {

    public function open($savePath, $sessionName) {}
    public function close() {}
    public function read($sessionId) {}
    public function write($sessionId, $data) {}
    public function destroy($sessionId) {}
    public function gc($lifetime) {}

}

Since these methods are not as readily understandable as the cache StoreInterface, let's quickly cover what each of the methods do:

• The open method would typically be used in file based session store systems. Since Laravel ships with a file session driver, you will almost never need to put anything in this method. You can leave it as an empty stub. It is simply a fact of poor interface design (which we'll discuss later) that PHP requires us to implement this method.
• The close method, like the open method, can also usually be disregarded. For most drivers, it is not needed.
• The read method should return the string version of the session data associated with the given $sessionId. There is no need to do any serialization or other encoding when retrieving or storing session data in your driver, as Laravel will perform the serialization for you.
• The write method should write the given $data string associated with the $sessionId to some persistent storage system, such as MongoDB, Dynamo, etc.
• The destroy method should remove the data associated with the $sessionId from persistent storage.
• The gc method should destroy all session data that is older than the given $lifetime, which is a UNIX timestamp. For self-expiring systems like Memcached and Redis, this method may be left empty.

Once the SessionHandlerInterface has been implemented, we are ready to register it with the Session manager:

Session::extend('mongo', function($app)
{
    return new MongoHandler;
});

Once the session driver has been registered, we may use the mongo driver in our app/config/session.php configuration file.

Note: Remember, if you write a custom session handler, share it on Packagist!

Authentication

Authentication may be extended the same way as the cache and session facilities. Again, we will use the extend method we have become familiar with:

Auth::extend('riak', function($app)
{
    // Return implementation of Illuminate\Auth\UserProviderInterface
});

The UserProviderInterface implementations are only responsible for fetching a UserInterface implementation out of a persistent storage system, such as MySQL, Riak, etc. These two interfaces allow the Laravel authentication mechanisms to continue functioning regardless of how the user data is stored or what type of class is used to represent it.

Let's take a look at the UserProviderInterface:

interface UserProviderInterface {

    public function retrieveById($identifier);
    public function retrieveByToken($identifier, $token);
    public function updateRememberToken(UserInterface $user, $token);
    public function retrieveByCredentials(array $credentials);
    public function validateCredentials(UserInterface $user, array $credentials);

}

The retrieveById function typically receives a numeric key representing the user, such as an auto-incrementing ID from a MySQL database. The UserInterface implementation matching the ID should be retrieved and returned by the method.

The retrieveByToken function retrieves a user by their unique $identifier and "remember me" $token, stored in a field remember_token. As with with previous method, the UserInterface implementation should be returned.

The updateRememberToken method updates the $user field remember_token with the new $token. The new token can be either a fresh token, assigned on successfull "remember me" login attempt, or a null when user is logged out.

The retrieveByCredentials method receives the array of credentials passed to the Auth::attempt method when attempting to sign into an application. The method should then "query" the underlying persistent storage for the user matching those credentials. Typically, this method will run a query with a "where" condition on $credentials['username']. This method should not attempt to do any password validation or authentication.

The validateCredentials method should compare the given $user with the $credentials to authenticate the user. For example, this method might compare the $user->getAuthPassword() string to a Hash::make of $credentials['password'].

Now that we have explored each of the methods on the UserProviderInterface, let's take a look at the UserInterface. Remember, the provider should return implementations of this interface from the retrieveById and retrieveByCredentials methods:

interface UserInterface {

    public function getAuthIdentifier();
    public function getAuthPassword();

}

This interface is simple. The getAuthIdentifier method should return the "primary key" of the user. In a MySQL back-end, again, this would be the auto-incrementing primary key. The getAuthPassword should return the user's hashed password. This interface allows the authentication system to work with any User class, regardless of what ORM or storage abstraction layer you are using. By default, Laravel includes a User class in the app/models directory which implements this interface, so you may consult this class for an implementation example.

Finally, once we have implemented the UserProviderInterface, we are ready to register our extension with the Auth facade:

Auth::extend('riak', function($app)
{
    return new RiakUserProvider($app['riak.connection']);
});

After you have registered the driver with the extend method, you switch to the new driver in your app/config/auth.php configuration file.

IoC Based Extension

Almost every service provider included with the Laravel framework binds objects into the IoC container. You can find a list of your application's service providers in the app/config/app.php configuration file. As you have time, you should skim through each of these provider's source code. By doing so, you will gain a much better understanding of what each provider adds to the framework, as well as what keys are used to bind various services into the IoC container.

For example, the HashServiceProvider binds a hash key into the IoC container, which resolves into a Illuminate\Hashing\BcryptHasher instance. You can easily extend and override this class within your own application by overriding this IoC binding. For example:

class SnappyHashProvider extends Illuminate\Hashing\HashServiceProvider {

    public function boot()
    {
        App::bindShared('hash', function()
        {
            return new Snappy\Hashing\ScryptHasher;
        });

        parent::boot();
    }

}

Note that this class extends the HashServiceProvider, not the default ServiceProvider base class. Once you have extended the service provider, swap out the HashServiceProvider in your app/config/app.php configuration file with the name of your extended provider.

This is the general method of extending any core class that is bound in the container. Essentially every core class is bound in the container in this fashion, and can be overridden. Again, reading through the included framework service providers will familiarize you with where various classes are bound into the container, and what keys they are bound by. This is a great way to learn more about how Laravel is put together.

Request Extension

Because it is such a foundational piece of the framework and is instantiated very early in the request cycle, extending the Request class works a little differently than the previous examples.

First, extend the class like normal:

<?php namespace QuickBill\Extensions;

class Request extends \Illuminate\Http\Request {

    // Custom, helpful methods here...

}

Once you have extended the class, open the bootstrap/start.php file. This file is one of the very first files to be included on each request to your application. Note that the first action performed is the creation of the Laravel $app instance:

$app = new \Illuminate\Foundation\Application;

When a new application instance is created, it will create a new Illuminate\Http\Request instance and bind it to the IoC container using the request key. So, we need a way to specify a custom class that should be used as the "default" request type, right? And, thankfully, the requestClass method on the application instance does just this! So, we can add this line at the very top of our bootstrap/start.php file:

use Illuminate\Foundation\Application;

Application::requestClass('QuickBill\Extensions\Request');

Once you have specified the custom request class, Laravel will use this class anytime it creates a Request instance, conveniently allowing you to always have an instance of your custom request class available, even in unit tests!