Implementation of a URL router

Question

I was wondering if you could provide some feedback on this Router class I built. Worth noting that it relies on an Apache rewrite rule that always redirects to this file, but passes the path into $_GET['url'] as a string (e.g. A request to http://foo.com/foo/bar) goes into $_GET['url] => 'foo/bar'.

You can then define routes that match against this path string, and the function defined with the route can execute any aribtrary code, like handing off to a controller.

Mainly I would like to know if I should be sanitizing any strings? How could I handle paths that don't match any defined routes?

class Router
{
    private $routes = null;
    private $req_path = null;

    function __construct()
    {
        if (isset($_GET['url']))
            $this->req_path = $_GET['url'];

        // Build the requested path.
        $this->req_path = is_null($this->req_path) ? "/" : "/" . $this->req_path;
    }

    // Create a route with a path and a function associated with that path that we
    // can call.
    function route($path, $handler)
    {
        $this->routes[] = array('path' => $path, 'handler' => $handler);
    }

    // Run the router to compare the request against any defined routes, run the 
    // associated function.
    function run()
    {
        if (is_null($this->routes))
            throw new RuntimeException("No routes have been defined");

        foreach($this->routes as $route) {
            if ($route['path'] == $this->req_path) {
                $route['handler']();
                return;
            }
        }
    }
}

$router = new Router();

$router->route("/steve", function() { 
    echo "steve"; 
});

$router->run();

Answer 1

Mainly I would like to know if I should be sanitizing any strings?

Assuming that the only unsafe input is in $_GET['url'], you're safe: junk that doesn't match a defined route will be ignored. The routes work effectively like a white list.

How could I handle paths that don't match any defined routes?

Return a 404 error page (and correctly set status code in the header).

---

This seems quite redundant:

function __construct()
{
    if (isset($_GET['url']))
        $this->req_path = $_GET['url'];

    // Build the requested path.
    $this->req_path = is_null($this->req_path) ? "/" : "/" . $this->req_path;
}

This should be equivalent and shorter:

function __construct()
{
    // Build the requested path.
    $this->req_path = '/' . @$_GET['url'];
}

---

Instead of iterating over the list of routes and stop when you find a match, why not use an associative array instead? Like this:

function route($path, $handler)
{
    $this->routes[$path] = $handler;
}

function run()
{
    if (is_null($this->routes))
        throw new RuntimeException("No routes have been defined");

    if (isset($this->routes[$this->req_path])) {
        $this->routes[$this->req_path]();
        return;
    }
}