What is Routing?
Routing is the process of parsing a URI and determining the appropriate action to take.
For example, consider the following URI:
http://example.com/login
How does a request like the one above result in a response to the user?
Let’s break it down:
- The request is received by the application.
- The application breaks down the request into its components. Things like: the method (ex: GET), host, path, etc.
- The application looks for a defined route that matches this request.
- Once found, it takes the defined action and returns a response.
Example from Laravel
For a real-world example, here’s one way the above example could be implemented in Laravel.
Route::get('/login', function() {
return view('login');
});
We define a GET route for the /login URI.
When that route is requested we return a response – in this case, HTML for the login page.
How Routers Work
There are a number of routers in the PHP ecosystem.
They range from the more simplistic to feature-packed behemoths.
Although they differ in size and complexity, they generally employ the same fundamental steps: parse the request, match the pattern, run some code, return a response.
The Symfony router (probably the most widely used PHP router) does this.
As does this one.
And this one.
A Very Simple PHP Router
To demonstrate these concepts let’s create a stupid simple, not at all useful, PHP router.
<?php
/**
* First, let's define our Router object.
*/
class Router
{
/**
* The request we're working with.
*
* @var string
*/
public $request;
/**
* The $routes array will contain our URI's and callbacks.
* @var array
*/
public $routes = [];
/**
* For this example, the constructor will be responsible
* for parsing the request.
*
* @param array $request
*/
public function __construct(array $request)
{
/**
* This is a very (VERY) simple example of parsing
* the request. We use the $_SERVER superglobal to
* grab the URI.
*/
$this->request = basename($request['REQUEST_URI']);
}
/**
* Add a route and callback to our $routes array.
*
* @param string $uri
* @param Callable $fn
*/
public function addRoute(string $uri, \Closure $fn) : void
{
$this->routes[$uri] = $fn;
}
/**
* Determine is the requested route exists in our
* routes array.
*
* @param string $uri
* @return boolean
*/
public function hasRoute(string $uri) : bool
{
return array_key_exists($uri, $this->routes);
}
/**
* Run the router.
*
* @return mixed
*/
public function run()
{
if($this->hasRoute($this->request)) {
$this->routes[$this->request]->call($this);
}
}
}
/**
* Create a new router instance.
*/
$router = new Router($_SERVER);
/**
* Add a "hello" route that prints to the screen.
*/
$router->addRoute('hello', function() {
echo 'Well, hello there!!';
});
/**
* Run it!
*/
$router->run();
Run The Code
- Save this code locally as index.php.
- In your terminal navigate to the directory where you saved the script.
- Start the built-in PHP web server: php -S localhost:1234
- In your browser go to:
http://localhost:1234/hello
Conclusion
I’ve touched on the very basics of routing, shared some routing examples from the PHP world, and built a extremely simple router.
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