added part 4

book/part4.rst

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+Create your own framework... on top of the Symfony2 Components (part 4)
+=======================================================================
+
+Before we start with today's topic, let's refactor our current framework just
+a little to make templates even more readable::
+
+    <?php
+
+    // example.com/web/front.php
+
+    require_once __DIR__.'/../src/autoload.php';
+
+    use Symfony\Component\HttpFoundation\Request;
+    use Symfony\Component\HttpFoundation\Response;
+
+    $request = Request::createFromGlobals();
+
+    $map = array(
+        '/hello' => 'hello',
+        '/bye'   => 'bye',
+    );
+
+    $path = $request->getPathInfo();
+    if (isset($map[$path])) {
+        ob_start();
+        extract($request->query->all());
+        include sprintf(__DIR__.'/../src/pages/%s.php', $map[$path]);
+        $response = new Response(ob_get_clean());
+    } else {
+        $response = new Response('Not Found', 404);
+    }
+
+    $response->send();
+
+As we now extract the request query parameters, simplify the ``hello.php``
+template as follows::
+
+    <!-- example.com/src/pages/hello.php -->
+
+    Hello <?php echo htmlspecialchars($name, ENT_QUOTES, 'UTF-8') ?>
+
+Now, we are in good shape to add new features.
+
+One very important aspect of any website is the form of its URLs. Thanks to
+the URL map, we have decoupled the URL from the code that generates the
+associated response, but it is not yet flexible enough. For instance, we might
+want to support dynamic paths to allow embedding data directly into the URL
+instead of relying on a query string:
+
+    # Before
+    /hello?name=Fabien
+
+    # After
+    /hello/Fabien
+
+To support this feature, we are going to use the Symfony2 Routing component.
+As always, add it to ``composer.json`` and run the ``php composer.phar
+update`` command to install it::
+
+.. code-block:: json
+
+    {
+        "require": {
+            "symfony/class-loader": "2.1.*",
+            "symfony/http-foundation": "2.1.*",
+            "symfony/routing": "2.1.*"
+        }
+    }
+
+From now on, we are going to use the generated Composer autoloader instead of
+our own ``autoload.php``. Remove the ``autoload.php`` file and replace its
+reference in ``front.php``::
+
+    <?php
+
+    // example.com/web/front.php
+
+    require_once __DIR__.'/../vendor/.composer/autoload.php';
+
+    // ...
+
+Instead of an array for the URL map, the Routing component relies on a
+``RouteCollection`` instance::
+
+    use Symfony\Component\Routing\RouteCollection;
+
+    $routes = new RouteCollection();
+
+Let's add a route that describe the ``/hello/SOMETHING`` URL and add another
+one for the simple ``/bye`` one::
+
+    use Symfony\Component\Routing\Route;
+
+    $routes->add('hello', new Route('/hello/{name}', array('name' => 'World')));
+    $routes->add('bye', new Route('/bye'));
+
+Each entry in the collection is defined by a name (``hello``) and a ``Route``
+instance, which is defined by a route pattern (``/hello/{name}``) and an array
+of default values for route attributes (``array('name' => 'World')``).
+
+.. note::
+
+    Read the official `documentation`_ for the Routing component to learn more
+    about its many features like URL generation, attribute requirements, HTTP
+    method enforcements, loaders for YAML or XML files, dumpers to PHP or
+    Apache rewrite rules for enhanced performance, and much more.
+
+Based on the information stored in the ``RouteCollection`` instance, a
+``UrlMatcher`` instance can match URL paths::
+
+    use Symfony\Component\Routing\RequestContext;
+    use Symfony\Component\Routing\Matcher\UrlMatcher;
+
+    $context = new RequestContext();
+    $context->fromRequest($request);
+    $matcher = new UrlMatcher($routes, $context);
+
+    $attributes = $matcher->match($request->getPathInfo());
+
+The ``match()`` method takes a request path and returns an array of attributes
+(notice that the matched route is automatically stored under the special
+``_route`` attribute)::
+
+    print_r($matcher->match('/bye'));
+    array (
+      '_route' => 'bye',
+    );
+
+    print_r($matcher->match('/hello/Fabien'));
+    array (
+      'name' => 'Fabien',
+      '_route' => 'hello',
+    );
+
+    print_r($matcher->match('/hello'));
+    array (
+      'name' => 'World',
+      '_route' => 'hello',
+    );
+
+.. note::
+
+    Even if we don't strictly need the request context in our examples, it is
+    used in real-world applications to enforce method requirements and more.
+
+The URL matcher throws an exception when none of the routes match::
+
+    $matcher->match('/not-found');
+
+    // throws a Symfony\Component\Routing\Exception\ResourceNotFoundException
+
+With this knowledge in mind, let's write the new version of our framework::
+
+    <?php
+
+    // example.com/web/front.php
+
+    require_once __DIR__.'/../vendor/.composer/autoload.php';
+
+    use Symfony\Component\HttpFoundation\Request;
+    use Symfony\Component\HttpFoundation\Response;
+    use Symfony\Component\Routing;
+
+    $request = Request::createFromGlobals();
+    $routes = include __DIR__.'/../src/app.php';
+
+    $context = new Routing\RequestContext();
+    $context->fromRequest($request);
+    $matcher = new Routing\Matcher\UrlMatcher($routes, $context);
+
+    try {
+        extract($matcher->match($request->getPathInfo()));
+        ob_start();
+        include sprintf(__DIR__.'/../src/pages/%s.php', $_route);
+
+        $response = new Response(ob_get_clean());
+    } catch (Routing\Exception\ResourceNotFoundException $e) {
+        $response = new Response('Not Found', 404);
+    } catch (Exception $e) {
+        $response = new Response('An error occurred', 500);
+    }
+
+    $response->send();
+
+There are a few new things in the code::
+
+* Route names are used for template names;
+
+* ``500`` errors are now managed correctly;
+
+* Request attributes are extracted to keep our templates simple::
+
+      <!-- example.com/src/pages/hello.php -->
+
+      Hello <?php echo htmlspecialchars($name, ENT_QUOTES, 'UTF-8') ?>
+
+* Routes configuration has been moved to its own file:
+
+  .. code-block:: php
+
+      <?php
+
+      // example.com/src/app.php
+
+      use Symfony\Component\Routing;
+
+      $routes = new Routing\RouteCollection();
+      $routes->add('hello', new Routing\Route('/hello/{name}', array('name' => 'World')));
+      $routes->add('bye', new Routing\Route('/bye'));
+
+  We now have a clear separation between the configuration (everything
+  specific to our application in ``app.php``) and the framework (the generic
+  code that powers our application in ``front.php``).
+
+With less than 30 lines of code, we have a new framework, more powerful and
+more flexible than the previous one. Enjoy!
+
+Using the Routing component has one big additional benefit: the ability to
+generate URLs based on Route definitions. When using both URL matching and URL
+generation in your code, changing the URL patterns should have no other
+impact. Want to know how to use the generator? Insanely easy::
+
+    use Symfony\Component\Routing;
+
+    $generator = new Routing\Generator\UrlGenerator($routes, $context);
+
+    echo $generator->generate('hello', array('name' => 'Fabien));
+    // outputs /hello/Fabien
+
+The code should be self-explanatory; and thanks to the context, you can even
+generate absolute URLs::
+
+    echo $generator->generate('hello', array('name' => 'Fabien), true);
+    // outputs something like http://example.com/somewhere/hello/Fabien
+
+.. tip::
+
+    Concerned about performance? Based on your route definitions, create a
+    highly optimized URL matcher class that can replace the default
+    ``UrlMatcher``::
+
+        $dumper = new Routing\Matcher\Dumper\PhpMatcherDumper($routes);
+
+        echo $dumper->dump();
+
+    Want even more performance? Dump your routes as a set of Apache rewrite
+    rules::
+
+        $dumper = new Routing\Matcher\Dumper\ApacheMatcherDumper($routes);
+
+        echo $dumper->dump();
+
+.. _`documentation`: http://symfony.com/doc/current/components/routing.html