define HTTP Middleware

Answer

HTTP middleware provide a convenient mechanism for filtering HTTP requests entering your application. For example, Laravel includes a middleware that verifies the user of your application is authenticated. If the user is not authenticated, the middleware will redirect the user to the login screen. However, if the user is authenticated, the middleware will allow the request to proceed further into the application.

Of course, middleware can be written to perform a variety of tasks besides authentication. A CORS middleware might be responsible for adding the proper headers to all responses leaving your application. A logging middleware might log all incoming requests to your application.

There are several middleware included in the Laravel framework, including middleware for maintenance, authentication, CSRF protection, and more. All of these middleware are located in the app/Http/Middleware directory.

Defining Middleware

To create a new middleware, use the make:middleware Artisan command:

php artisan make:middleware OldMiddleware

This command will place a new OldMiddleware class within your app/Http/Middleware directory. In this middleware, we will only allow access to the route if the supplied age is greater than 200. Otherwise, we will redirect the users back to the "home" URI.

<?php namespace App\Http\Middleware;

use Closure;

class OldMiddleware {

    /**
     * Run the request filter.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        if ($request->input('age') < 200)
        {
            return redirect('home');
        }

        return $next($request);
    }

}

As you can see, if the given age is less than 200, the middleware will return an HTTP redirect to the client; otherwise, the request will be passed further into the application. To pass the request deeper into the application (allowing the middleware to "pass"), simply call the $next callback with the $request.

It's best to envision middleware as a series of "layers" HTTP requests must pass through before they hit your application. Each layer can examine the request and even reject it entirely.

Before / After Middleware

Whether a middleware runs before or after a request depends on the middleware itself. This middleware would perform some task before the request is handled by the application:

<?php namespace App\Http\Middleware;

use Closure;

class BeforeMiddleware implements Middleware {

    public function handle($request, Closure $next)
    {
        // Perform action

        return $next($request);
    }
}

However, this middleware would perform its task after the request is handled by the application:

<?php namespace App\Http\Middleware;

use Closure;

class AfterMiddleware implements Middleware {

    public function handle($request, Closure $next)
    {
        $response = $next($request);

        // Perform action

        return $response;
    }
}