Templating

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The astute reader has noticed that our framework hardcodes the way specific "code" (the templates) is run. For simple pages like the ones we have created so far, that's not a problem, but if you want to add more logic, you would be forced to put the logic into the template itself, which is probably not a good idea, especially if you still have the separation of concerns principle in mind.

Let's separate the template code from the logic by adding a new layer: the controller: The controller's mission is to generate a Response based on the information conveyed by the client's Request.

Change the template rendering part of the framework to read as follows:

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        // example.com/web/front.php

// ...
try {
    $request->attributes->add($matcher->match($request->getPathInfo()));
    $response = call_user_func('render_template', $request);
} catch (Routing\Exception\ResourceNotFoundException $exception) {
    $response = new Response('Not Found', 404);
} catch (Exception $exception) {
    $response = new Response('An error occurred', 500);
}
    

As the rendering is now done by an external function (render_template() here), we need to pass to it the attributes extracted from the URL. We could have passed them as an additional argument to render_template(), but instead, let's use another feature of the Request class called attributes: Request attributes is a way to attach additional information about the Request that is not directly related to the HTTP Request data.

You can now create the render_template() function, a generic controller that renders a template when there is no specific logic. To keep the same template as before, request attributes are extracted before the template is rendered:

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        function render_template(Request $request): Response
{
    extract($request->attributes->all(), EXTR_SKIP);
    ob_start();
    include sprintf(__DIR__.'/../src/pages/%s.php', $_route);

    return new Response(ob_get_clean());
}
    

As render_template is used as an argument to the PHP call_user_func() function, we can replace it with any valid PHP callbacks. This allows us to use a function, an anonymous function or a method of a class as a controller... your choice.

As a convention, for each route, the associated controller is configured via the _controller route attribute:

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        $routes->add('hello', new Routing\Route('/hello/{name}', [
    'name' => 'World',
    '_controller' => 'render_template',
]));

try {
    $request->attributes->add($matcher->match($request->getPathInfo()));
    $response = call_user_func($request->attributes->get('_controller'), $request);
} catch (Routing\Exception\ResourceNotFoundException $exception) {
    $response = new Response('Not Found', 404);
} catch (Exception $exception) {
    $response = new Response('An error occurred', 500);
}
    

A route can now be associated with any controller and within a controller, you can still use the render_template() to render a template:

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        $routes->add('hello', new Routing\Route('/hello/{name}', [
    'name' => 'World',
    '_controller' => function (Request $request): string {
        return render_template($request);
    }
]));
    

This is rather flexible as you can change the Response object afterwards and you can even pass additional arguments to the template:

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        $routes->add('hello', new Routing\Route('/hello/{name}', [
    'name' => 'World',
    '_controller' => function (Request $request): Response {
        // $foo will be available in the template
        $request->attributes->set('foo', 'bar');

        $response = render_template($request);

        // change some header
        $response->headers->set('Content-Type', 'text/plain');

        return $response;
    }
]));
    

Here is the updated and improved version of our framework:

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        // example.com/web/front.php
require_once __DIR__.'/../vendor/autoload.php';

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing;

function render_template(Request $request): Response
{
    extract($request->attributes->all(), EXTR_SKIP);
    ob_start();
    include sprintf(__DIR__.'/../src/pages/%s.php', $_route);

    return new Response(ob_get_clean());
}

$request = Request::createFromGlobals();
$routes = include __DIR__.'/../src/app.php';

$context = new Routing\RequestContext();
$context->fromRequest($request);
$matcher = new Routing\Matcher\UrlMatcher($routes, $context);

try {
    $request->attributes->add($matcher->match($request->getPathInfo()));
    $response = call_user_func($request->attributes->get('_controller'), $request);
} catch (Routing\Exception\ResourceNotFoundException $exception) {
    $response = new Response('Not Found', 404);
} catch (Exception $exception) {
    $response = new Response('An error occurred', 500);
}

$response->send();
    

To celebrate the birth of our new framework, let's create a brand new application that needs some simple logic. Our application has one page that says whether a given year is a leap year or not. When calling /is_leap_year, you get the answer for the current year, but you can also specify a year like in /is_leap_year/2009. Being generic, the framework does not need to be modified in any way, create a new app.php file:

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        // example.com/src/app.php
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing;

function is_leap_year(?int $year = null): bool
{
    if (null === $year) {
        $year = (int)date('Y');
    }

    return 0 === $year % 400 || (0 === $year % 4 && 0 !== $year % 100);
}

$routes = new Routing\RouteCollection();
$routes->add('leap_year', new Routing\Route('/is_leap_year/{year}', [
    'year' => null,
    '_controller' => function (Request $request): Response {
        if (is_leap_year($request->attributes->get('year'))) {
            return new Response('Yep, this is a leap year!');
        }

        return new Response('Nope, this is not a leap year.');
    }
]));

return $routes;
    

The is_leap_year() function returns true when the given year is a leap year, false otherwise. If the year is null, the current year is tested. The controller does little: it gets the year from the request attributes, pass it to the is_leap_year() function, and according to the return value it creates a new Response object.

As always, you can decide to stop here and use the framework as is; it's probably all you need to create simple websites like those fancy one-page websites and hopefully a few others.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.

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