Custom validators (regex and callback) with the Symfony HTTP Foundation component

gistfile1.php

<?php
require_once __DIR__.'/vendor/autoload.php';

use Symfony\Component\HttpFoundation\Request;

// Real request data
// $request = Request::createFromGlobals();

// Or fake it (for testing)
// e.g. http://example.com/script.php?page=home

$request = Request::create('/script.php', 'GET', array(
    'page'   => 'home',
    'search' => 'grumpycat',
));

/* e.g. script.php?search=grumpycat
 * If 'search' contains anything that isn't letters, numbers, or spaces this
 * validator will return false. If search is empty, it returns 'default'.
 */
$query = $request->query->filter('search', 'default', false, FILTER_VALIDATE_REGEXP, 
    array('options' => array(
        'regexp' => '/^[a-z0-9 ]+$/i',
    )
);

/* e.g. script.php?page=home
 * Check if the page exists
 * This could be a database lookup instead, and instead of returning
 * the value or false, it could load your page object and return it. 
 * The callback shown here is an anonymous function, but you could also
 * use 'trim' or array($pageHandler, 'load') to call the 'load' method 
 * on the $pageHandler object. 
 */
 $contentDir = __DIR__.'/content';
 $page = $request->query->filter('page', 'default', false, FILTER_CALLBACK, array('options' => function($input) use ($contentDir) {
    
     // Resolve any sneaky ../ stuff
     $path = realpath($contentDir.DIRECTORY_SEPARATOR.$input.'.html');
    
     // Make sure the path still points to your content directory
     // And check the file exists
     if ((strpos($path, $contentDir) === 0) && is_file($path)) {
         return $path;
     }
    
     // File doesn't exist or is invalid
     return false;
 }));