what is php middleware

#php middleware (middleware) is a closure and returns a closure.

Middleware provides a convenient mechanism for filtering HTTP requests entering the application, which can be divided into pre-middleware and post-middleware. Commonly used to verify whether the user is authenticated, add response headers (cross-domain), record request logs, etc.(Recommended learning:PHP programming from entry to proficiency)

##Example

 $middleware) { $handler = $middleware($handler); } return $handler; } // 注册中间件 // 这里用的都是全局中间件，实际应用时还可以为指定路由注册局部中间件 $stack['log'] = $log; $stack['filter'] = $filter; $stack['auth'] = $auth; $run = pack_middleware($application, $stack); $run('Laravle');

Output ：

Laravle need a filter middleware Laravle need a auth middleware this is a Laravle application Laravle need a log middleware

Packaging program

The execution order of middleware is determined by the packaging function (pack_middleware). The closure returned here is actually equivalent to:

$run = $log($filter($auth($application))); $run('Laravle');

Writing specifications

Middleware must meet certain specifications: always return a closure, and always pass in the same parameters in the closure (determined by the main logic), The closure always returns the execution result of the handler;

If the logic of the middleware is completed before returning the handle return $handler($name), it is a pre-middleware, otherwise it is a post-middleware.

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