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‎book/part5.rst

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Create your own framework... on top of the Symfony2 Components (part 5)
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=======================================================================
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The astute reader has noticed that our framework hardcodes the way specific
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"code" (the templates) is run. For simple pages like the ones we have created
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so far, that's not a problem, but if you want to add more logic, you would be
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forced to put the logic into the template itself, which is probably not a good
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idea, especially if you still have the separation of concerns principle in
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mind.
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Let's separate the template code from the logic by adding a new layer: the
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controller: *The controller mission is to generate a Response based on the
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information conveyed by the client Request.*
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Change the template rendering part of the framework to read as follows::
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<?php
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// example.com/web/front.php
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// ...
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try {
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$request->attributes->add($matcher->match($request->getPathInfo()));
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$response = call_user_func('render_template', $request);
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} catch (Routing\Exception\ResourceNotFoundException $e) {
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$response = new Response('Not Found', 404);
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} catch (Exception $e) {
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$response = new Response('An error occurred', 500);
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}
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As the rendering is now done by an external function (``render_template()``
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here), we need to pass to it the attributes extracted from the URL. We could
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have passed them as an additional argument to ``render_template()``, but
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instead, let's use another feature of the ``Request`` class called
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*attributes*: Request attributes lets you attach additional information about
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the Request that is not directly related to the HTTP Request data.
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You can now create the ``render_template()`` function, a generic controller
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that renders a template when there is no specific logic. To keep the same
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template as before, request attributes are extracted before the template is
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rendered::
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function render_template($request)
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{
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extract($request->attributes->all(), EXTR_SKIP);
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ob_start();
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include sprintf(__DIR__.'/../src/pages/%s.php', $_route);
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return new Response(ob_get_clean());
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}
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As ``render_template`` is used as an argument to the PHP ``call_user_func()``
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function, we can replace it with any valid PHP `callbacks`_. This allows us to
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use a function, an anonymous function, or a method of a class as a
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controller... your choice.
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As a convention, for each route, the associated controller is configured via
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the ``_controller`` route attribute::
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$routes->add('hello', new Routing\Route('/hello/{name}', array(
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'name' => 'World',
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'_controller' => 'render_template',
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)));
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try {
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$request->attributes->add($matcher->match($request->getPathInfo()));
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$response = call_user_func($request->attributes->get('_controller'), $request);
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} catch (Routing\Exception\ResourceNotFoundException $e) {
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$response = new Response('Not Found', 404);
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} catch (Exception $e) {
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$response = new Response('An error occurred', 500);
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}
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A route can now be associated with any controller and of course, within a
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controller, you can still use the ``render_template()`` to render a template::
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$routes->add('hello', new Routing\Route('/hello/{name}', array(
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'name' => 'World',
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'_controller' => function ($request) {
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return render_template($request);
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}
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)));
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This is rather flexible as you can change the Response object afterwards and
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you can even pass additional arguments to the template::
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$routes->add('hello', new Routing\Route('/hello/{name}', array(
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'name' => 'World',
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'_controller' => function ($request) {
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// $foo will be available in the template
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$request->attributes->set('foo', 'bar');
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$response = render_template($request);
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// change some header
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$response->headers->set('Content-Type', 'text/plain');
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return $response;
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}
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)));
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Here is the updated and improved version of our framework::
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<?php
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// example.com/web/front.php
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require_once __DIR__.'/../vendor/.composer/autoload.php';
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use Symfony\Component\HttpFoundation\Request;
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use Symfony\Component\HttpFoundation\Response;
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use Symfony\Component\Routing;
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function render_template($request)
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{
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extract($request->attributes->all(), EXTR_SKIP);
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ob_start();
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include sprintf(__DIR__.'/../src/pages/%s.php', $_route);
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return new Response(ob_get_clean());
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}
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$request = Request::createFromGlobals();
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$routes = include __DIR__.'/../src/app.php';
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$context = new Routing\RequestContext();
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$context->fromRequest($request);
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$matcher = new Routing\Matcher\UrlMatcher($routes, $context);
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try {
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$request->attributes->add($matcher->match($request->getPathInfo()));
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$response = call_user_func($request->attributes->get('_controller'), $request);
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} catch (Routing\Exception\ResourceNotFoundException $e) {
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$response = new Response('Not Found', 404);
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} catch (Exception $e) {
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$response = new Response('An error occurred', 500);
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}
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$response->send();
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To celebrate the birth of our new framework, let's create a brand new
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application that needs some simple logic. Our application has one page that
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says whether a given year is a leap year or not. When calling
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``/is_leap_year``, you get the answer for the current year, but the you can
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also specify a year like in ``/is_leap_year/2009``. Being generic, the
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framework does not need to be modified in any way, just create a new
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``app.php`` file::
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<?php
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// example.com/src/app.php
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use Symfony\Component\Routing;
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use Symfony\Component\HttpFoundation\Response;
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function is_leap_year($year = null) {
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if (null === $year) {
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$year = date('Y');
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}
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return 0 == $year % 400 || (0 == $year % 4 && 0 != $year % 100);
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}
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$routes = new Routing\RouteCollection();
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$routes->add('leap_year', new Routing\Route('/is_leap_year/{year}', array(
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'year' => null,
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'_controller' => function ($request) {
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if (is_leap_year($request->attributes->get('year'))) {
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return new Response('Yep, this is a leap year!');
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}
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return new Response('Nope, this is not a leap year.');
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}
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)));
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return $routes;
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The ``is_leap_year()`` function returns ``true`` when the given year is a leap
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year, ``false`` otherwise. If the year is null, the current year is tested.
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The controller is simple: it gets the year from the request attributes, pass
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it to the `is_leap_year()`` function, and according to the return value it
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creates a new Response object.
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As always, you can decide to stop here and use the framework as is; it's
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probably all you need to create simple websites like those fancy one-page
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`websites`_ and hopefully a few others.
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.. _`callbacks`: http://php.net/callback#language.types.callback
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.. _`websites`: http://kottke.org/08/02/single-serving-sites

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