added part 3

Author: fabpot

book/part3.rst

@@ -0,0 +1,248 @@
+Create your own framework... on top of the Symfony2 Components (part 3)
+=======================================================================
+
+Up until now, our application is simplistic as there is only one page. To
+spice things up a little bit, let's go crazy and add another page that says
+goodbye::
+
+    <?php
+
+    // framework/bye.php
+
+    require_once __DIR__.'/autoload.php';
+
+    use Symfony\Component\HttpFoundation\Request;
+    use Symfony\Component\HttpFoundation\Response;
+
+    $request = Request::createFromGlobals();
+
+    $response = new Response('Goodbye!');
+    $response->send();
+
+As you can see for yourself, much of the code is exactly the same as the one
+we have written for the first page. Let's extract the common code that we can
+share between all our pages. Code sharing sounds like a good plan to create
+our first "real" framework!
+
+The PHP way of doing the refactoring would probably be the creation of an
+include file::
+
+    <?php
+
+    // framework/init.php
+
+    require_once __DIR__.'/autoload.php';
+
+    use Symfony\Component\HttpFoundation\Request;
+    use Symfony\Component\HttpFoundation\Response;
+
+    $request = Request::createFromGlobals();
+    $response = new Response();
+
+Let's see it in action::
+
+    <?php
+
+    // framework/index.php
+
+    require_once __DIR__.'/init.php';
+
+    $input = $request->get('name', 'World');
+
+    $response->setContent(sprintf('Hello %s', htmlspecialchars($input, ENT_QUOTES, 'UTF-8')));
+    $response->send();
+
+And for the "Goodbye" page::
+
+    <?php
+
+    // framework/bye.php
+
+    require_once __DIR__.'/init.php';
+
+    $response->setContent('Goodbye!');
+    $response->send();
+
+We have indeed moved most of the shared code into a central place, but it does
+not feel like a good abstraction, doesn't it? First, we still have the
+``send()`` method in all pages, then our pages does not look like templates,
+and we are still not able to test this code properly.
+
+Moreover, adding a new page means that we need to create a new PHP script,
+which name is exposed to the end user via the URL
+(``http://example.com/goodbye.php``): there is a direct mapping between the PHP
+script name and the client URL. This is because the dispatching of the request
+is done by the web server directly. It might be a good idea to move this
+dispatching to our code for better flexibility. This can be easily achieved by
+routing all client requests to a single PHP script.
+
+.. tip::
+
+    Exposing a single PHP script to the end user is a design pattern called
+    the "`front controller`_".
+
+Such a script might look like the following::
+
+    <?php
+
+    // framework/front.php
+
+    require_once __DIR__.'/autoload.php';
+
+    use Symfony\Component\HttpFoundation\Request;
+    use Symfony\Component\HttpFoundation\Response;
+
+    $request = Request::createFromGlobals();
+    $response = new Response();
+
+    $map = array(
+        '/hello' => __DIR__.'/hello.php',
+        '/bye'   => __DIR__.'/bye.php',
+    );
+
+    $path = $request->getPathInfo();
+    if (isset($map[$path])) {
+        require $map[$path];
+    } else {
+        $response->setStatusCode(404);
+        $response->setContent('Not Found');
+    }
+
+    $response->send();
+
+And here is for instance the new ``hello.php`` script::
+
+    <?php
+
+    // framework/hello.php
+
+    $input = $request->get('name', 'World');
+    $response->setContent(sprintf('Hello %s', htmlspecialchars($input, ENT_QUOTES, 'UTF-8')));
+
+In the ``front.php`` script, ``$map`` associates URL paths with their
+corresponding PHP script paths.
+
+As a bonus, if the client ask for a path that is not defined in the URL map,
+we return a custom 404 page; you are now in control of your website.
+
+To access a page, you must now use the ``front.php`` script:
+
+* ``http://example.com/front.php/hello?name=Fabien``
+
+* ``http://example.com/front.php/bye``
+
+``/hello`` and ``/bye`` are the page *path*s.
+
+.. tip::
+
+    Most web servers like Apache or nginx are able to rewrite the incoming
+    URLs and remove the front controller script so that your users will be
+    able to type ``http://example.com/hello?name=Fabien``, which looks much
+    better.
+
+So, the trick is the usage of the ``Request::getPathInfo()`` method which
+returns the path of the Request by removing the front controller script name
+including its sub-directories (only if needed -- see above tip).
+
+.. tip::
+
+    You don't even need to setup a web server to test the code. Instead,
+    replace the ``$request = Request::createFromGlobals();`` call to something
+    like ``$request = Request::create('/hello?name=Fabien');`` where the
+    argument is the URL path you want to simulate.
+
+Now that the web server always access the same script (``front.php``) for all
+our pages, we can secure our code further by moving all other PHP files
+outside the web root directory:
+
+    example.com
+    ├── composer.json
+    │   src
+    │   ├── autoload.php
+    │   └── pages
+    │       ├── hello.php
+    │       └── bye.php
+    ├── vendor
+    └── web
+        └── front.php
+
+Now, configure your web server root directory to point to ``web/`` and all
+other files won't be accessible from the client anymore.
+
+.. note::
+
+    For this new structure to work, you will have to adjust some paths in
+    various PHP files; the changes are left as an exercise for the reader.
+
+The last thing that is repeated in each page is the call to ``setContent()``.
+We can convert all pages to "templates" by just echoing the content and
+calling the ``setContent()`` directly from the front controller script::
+
+    <?php
+
+    // example.com/web/front.php
+
+    // ...
+
+    $path = $request->getPathInfo();
+    if (isset($map[$path])) {
+        ob_start();
+        include $map[$path];
+        $response->setContent(ob_get_clean());
+    } else {
+        $response->setStatusCode(404);
+        $response->setContent('Not Found');
+    }
+
+    // ...
+
+And the ``hello.php`` script can now be converted to a template::
+
+    <!-- example.com/src/pages/hello.php -->
+
+    <?php $name = $request->get('name', 'World') ?>
+
+    Hello <?php echo htmlspecialchars($name, ENT_QUOTES, 'UTF-8') ?>
+
+We have our framework for today::
+
+    <?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();
+    $response = new Response();
+
+    $map = array(
+        '/hello' => __DIR__.'/../src/pages/hello.php',
+        '/bye'   => __DIR__.'/../src/pages/bye.php',
+    );
+
+    $path = $request->getPathInfo();
+    if (isset($map[$path])) {
+        ob_start();
+        include $map[$path];
+        $response->setContent(ob_get_clean());
+    } else {
+        $response->setStatusCode(404);
+        $response->setContent('Not Found');
+    }
+
+    $response->send();
+
+Adding a new page is a two step process: add an entry in the map and create a
+PHP template in ``src/pages/``. From a template, get the Request data via the
+``$request`` variable and tweak the Response headers via the ``$response``
+variable.
+
+.. note::
+
+    If you decide to stop here, you can probably enhance your framework by
+    extracting the URL map to a configuration file.
+
+.. _`front controller`: http://symfony.com/doc/current/book/from_flat_php_to_symfony2.html#a-front-controller-to-the-rescue