PSR-15 basics
Learn the PSR-15 middleware interface and the MiddlewareInterface.
PSR-15 MiddlewareInterface
PSR-15 is the standard middleware interface defined by PHP-FIG. MiddlewareInterface has a single method: process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface.
This standard lets middlewares written for different frameworks be used interchangeably. Every class has the same signature, so chaining is easy.
$request is a PSR-7 request, and $handler is the next request handler. Calling $handler->handle($request) continues the flow; the return value is a PSR-7 response.
How PSR-15 works
In a PSR-15 middleware class, the process method inspects the request, optionally logs or validates, then continues to the next step with $handler->handle($request).
The RequestHandlerInterface defines a single handle method. It represents either the next middleware or the innermost handler. Each call chains to the next.
In this lesson we mimic the PSR-15 structure with simplified classes: process and handle follow the same signature pattern without a PSR-7 dependency.
Exercise Write a PSR-15 style class
Define a LoggingMiddleware class that mimics the PSR-15 structure. Give it a public function process($request, $handler) method. First print echo "[LOG] Request received", then obtain the response with $response = $handler->handle($request), print echo "[LOG] Response produced" and return $response. FinalHandler is already defined. Instantiate the class, call process and print the response.
Show example solution
Write class LoggingMiddleware { public function process($request, $handler) { echo "[LOG] Request received\n"; $response = $handler->handle($request); echo "[LOG] Response produced\n"; return $response; } }. Then $mw = new LoggingMiddleware(); echo $mw->process("istek", new FinalHandler()) . "\n";.
Example solution:
<?php
class LoggingMiddleware {
public function process($request, $handler) {
echo "[LOG] Request received\n";
$response = $handler->handle($request);
echo "[LOG] Response produced\n";
return $response;
}
}
class FinalHandler {
public function handle($request) {
return "TAMAM";
}
}
$mw = new LoggingMiddleware();
echo $mw->process("istek", new FinalHandler()) . "\n";Test yourself
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The process method signature
public function process(ServerRequestInterface $request, ____ $handler): ResponseInterface { return $handler->handle($request); }Show answer
public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface { return $handler->handle($request); } -
What does the PSR-15 process method return?
- ResponseInterface
- void
- bool
- array
Show answer
ResponseInterface — Correct. process returns a ResponseInterface, the PSR-7 response.
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Match the PSR-15 concepts
- MiddlewareInterface
- process() method
- RequestHandlerInterface
- handle() method
- ServerRequestInterface
- PSR-7 request
- ResponseInterface
- PSR-7 response