NSWI142: Web Applications

Exercise: Front Controller

The idea is to have a single file that will handle all requests.

Implement a /index.php file that prints (using var_dump is fine for now) event details based on the URL. For example, /events/{event-id} should show details for an event with the specified id.

We need to properly configure our web server. See the next slides.

Update your README.md with instructions on how to run your server locally.

Not required right now: Add .htaccess files for Apache.

Configuring PHP built-in server

Static files (e.g., .css, .js) are served from the /public/ directory. Everything else is passed to /index.php. You can still access files in ../ via require/include.

php -S 127.0.0.1:8888 -t ./public/

To test it, you can try the following script:

<?php
  var_dump($_SERVER['REQUEST_URI']);

Configuring Apache

The Apache server must be configured to allow for use of .htaccess and rewrites. webik.ms.mff.cuni.cz is configured this way. We need two files to make it work.

The first /.htaccess file is located in the src of your project. It passes all requests to the public directory.

RewriteEngine on
RewriteRule ^$ public/ [L]
RewriteRule (.*) public/$1 [L]

The second /public/.htaccess file is in the public directory. It redirects requests to /public/index.php if the requested file does not exist.

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^ index.php [QSA,L]

Keep in mind that files starting with a dot (for example .htaccess) are hidden by default on some systems.

If nothing works... 💀

Instead of nice URLs, use query parameters such as ?page=event/42.

Instead of $_SERVER['REQUEST_URI'] use $_GET['page'].

Front Controller vs. Presenters

Front Controller is a single centralized part that does:

• Request handling: Parses URL and request methods.
• Routing: Based on URL, calls appropriate Presenter and delegates the work.

Presenter is responsible for handling specific requests:

• Interacts with Models to get data.
• Prepares data for the View (template).
• Renders the View.

Project structure:

/public/index.php usually only calls the Front Controller and does not contain much logic.

/src/FrontController.php contains the FrontController class.

/src/presenters/ contains Presenter classes that handle specific requests.

Exercise: Building better Front Controller with Presenters

Implement a simple Front Controller that delegates work to an EventPresenter based on the URL /events/{event-id}.

Final code example 1/3

src/Container.php

<?php
/**
 * Simple services container. Provides access to services such as Database.
 */
class Container
{
  public function getDatabase() {}
}

/public/index.php

<?php
$fc = new FrontController();

$container = new Container();
$fc->injectContainer($container);

$fc->routeAndDispatch($_SERVER);

Final code example 2/3

/**
 * This exception is thrown when a requested resource is not found.
 */
class NotFoundException extends Exception {}

interface Presenter
{
  /**
   * @param $url array URL chunks after the presenter name
   * @param $method string HTTP method (e.g., 'GET', 'POST')
   * @param $data mixed Data sent with the request (e.g., $_POST)
   * @throws NotFoundException
   */
  function process(array $url, string $method, mixed $data);

  /**
   * Renders the template with data prepared in process().
   */
  function render();

  /**
   * Injects the container with access to services such as Database.
   */
  function injectContainer(Container $container);
}

Final code example 3/3

/**
 * FrontController is responsible for routing requests to appropriate presenters.
 */
class FrontController
{
  private $container;

  /**
   * Injects the container with access to services such as Database.
   */
  public function injectContainer(Container $container)
  {
    $this->container = $container;
  }

  public function routeAndDispatch($serverData)
  {
    $chunks = explode('/', $serverData['REQUEST_URI']);
    $presenter = $this->route($chunks[1]);
    $this->dispatch($presenter, array_slice($chunks, 2), $serverData['REQUEST_METHOD'], $_POST);
  }

  private function route($chunk)
  {
    switch ($chunk) {
      case 'home':
        $presenter = new HomePresenter();
        break;
      case 'about':
        $presenter = new AboutPresenter();
        break;
      default:
        $presenter = new NotFoundPresenter();
        break;
    }
    $presenter->injectContainer($this->container);
    return $presenter;
  }

  private function dispatch($presenter, array $chunks, $method, $data)
  {
    try {
      $presenter->process($chunks, $method, $data);
    } catch (NotFoundException $e) {
      $presenter = new NotFoundPresenter();
      $presenter->injectContainer($this->container);
      $presenter->process([], 'GET', null);
    } catch (Exception $e) {
      http_response_code(500);
      die("Internal server error.");
    }

    $presenter->render();
  }
}