Implementation process of laravel middleware

With the continuous development of the Internet and Web applications, Web development frameworks are also emerging. Among them, the Laravel framework has been widely recognized and used. The Laravel framework provides developers with the important function of middleware. Middleware is used to filter and process requests in applications, effectively improving development efficiency and security. This article will introduce the implementation process of Laravel middleware in detail to help developers better understand and apply this function.

1. What is middleware

In the Laravel framework, middleware (Middleware) refers to a mechanism for filtering and processing HTTP requests entering the application, similar to the code Common interceptor and filter concepts. Under normal circumstances, middleware will do some general processing work, such as:

• is responsible for authenticating requests;
• checks and limits the access frequency of requests;
• Maintain session status;
• Set the corresponding response header, etc. based on the header information in the request.

The Laravel framework provides some built-in middleware, such as authentication middleware, CSRF middleware, current limiting middleware, etc. Developers can also write custom middleware to meet the specific needs of the application. need.

2. Implementation Principle of Middleware

The middleware mechanism of the Laravel framework is implemented based on the PSR-15 standard. In Laravel, middleware generally consists of two parts: middleware class and middleware call. Next, we introduce these two parts in detail respectively.

1. Middleware class

The middleware class is the core part of implementing middleware logic. It generally needs to implement the process method in the MiddlewareInterface interface defined in PSR-15. This method accepts two parameters, the current request object and a callback function, which is responsible for passing the request to the next middleware or application.

The processing logic of middleware is generally implemented in the process method, which can read request data, modify response data, and perform other specific operations. The sample code is as follows:

<?php

namespace AppHttpMiddleware;

use Closure;
use IlluminateHttpRequest;

class MyMiddleware
{
    /**
     * Handle an incoming request.
     *
     * @param  IlluminateHttpRequest  $request
     * @param  Closure  $next
     * @return mixed
     */
    public function handle(Request $request, Closure $next)
    {
        // 判断当前请求是否携带token
        if (!$request->header('Authorization')) {
            return response()->json(['message' => 'Unauthorized'], 401);
        }

        // 执行下一个中间件或应用程序
        return $next($request);
    }
}

In the above code, we define a middleware class named MyMiddleware, which determines whether the request carries the Authorization header information. If it does not, an unauthorized response will be returned; if it has If carried, the next middleware or application is executed.

2. Middleware call

The way to introduce middleware in the Laravel framework is very flexible. Developers can introduce it according to different request paths, request methods, request types and other conditions. Different middleware can also be introduced in batches through middleware groups. Here are several common ways to introduce it:

• Introduce global middleware: Add the middleware to the $middleware attribute of the app/Http/Kernel.php file, and it will apply to all requests.

// app/Http/Kernel.php

protected $middleware = [
    AppHttpMiddlewareMyMiddleware::class,
];

• Introduce routing middleware: When defining routes in the routes/web.php file, you can introduce the specified middleware through the middleware method.

// routes/web.php

use AppHttpMiddlewareMyMiddleware;

Route::get('/user', function () {
    //
})->middleware(MyMiddleware::class);

In addition, you can also introduce multiple middleware in batches through middleware groups (Middleware Groups). Based on this, middleware can be flexibly applied and implemented in different scenarios. different functions.

3. Middleware execution process

When a request enters the Laravel application, the Laravel framework calls these middleware classes in the order in which the middleware is introduced, and then executes their process method. Due to the composition of the middleware chain, it is easy to operate before or after the request is processed.

The middleware scheduling process of the Laravel framework is as follows:

1. The request enters the application, is processed by the HttpKernel middleware, and the request object (IlluminateHttpRequest instance) is created.
2. Call global middleware. If there is the first middleware that needs to be executed, the process method of the middleware is executed.
3. Then the routing middleware is called. If there is the first middleware that needs to be executed, the process method of the middleware is executed.
4. The request finally reaches the routing closure function or controller method to complete specific business logic processing.
5. Return to the HttpKernel middleware via the process method of the routing middleware, and call the terminate methods of the routing middleware and global middleware in reverse order.
6. Finally generates an HTTP response and returns it to the browser.

Middleware of the Laravel framework is a very useful feature that can easily execute certain code or detect requests during request processing, thus adding flexibility and security to the application. Through the introduction and implementation principles of Laravel middleware, developers can have a deeper understanding and application of the role of middleware.

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