Prolem with Middleware

1

Hey there guys, I have this middleware:

<?php

declare(strict_types=1);

namespace Masoretic\Middlewares;

use Psr\Http\Message\ResponseInterface as Response;
use Psr\Http\Message\ServerRequestInterface as Request;
use Psr\Http\Server\RequestHandlerInterface as RequestHandler;

class ContentTypeJsonMiddleware
{
    public function __invoke(
        Request $request,
        RequestHandler $handler
    ): Response
    {
        header('Content-Type: application/json');
        $response = $handler->handle($request);
        $response = new Response();
        return $response;
    }
}

But, I’m receiving this error message:
“Cannot instantiate interface Psr\Http\Message\ResponseInterface”
Any one knows why?

2

use Psr\Http\Message\ResponseInterface as Response;
$response = new Response();

It is not possible to create an instance from an interface.

To fix this, either create an Response from your PSR-7 package (slim or nyholm)
or use the ResponseFactory.

header(‘Content-Type: application/json’);

This (header) function should not be used in a PSR-7 application. To change the response header, better use the the response object instead.

Example:

$response = $response->withHeader('Content-Type', 'application/json');
3

Hi odan! Thanks for your answer, could you give me a example code on how to create from the ResponseFactory or how to create from Response PSR-7/Slim, please? I’ve tried to findo some examples but couldn’t find it.

Thanks in advance.

4

Just an update, I’ve tried to do this:

<?php

declare(strict_types=1);

namespace Masoretic\Middlewares;

use Psr\Http\Message\ResponseInterface as Response;
use Psr\Http\Message\ServerRequestInterface as Request;
use Psr\Http\Server\RequestHandlerInterface as RequestHandler;

class ContentTypeJsonMiddleware
{
    public function __invoke(
        Request $request,
        RequestHandler $handler
    ): Response
    {
        header('Content-Type: application/json');
        $response = $handler->handle($request);
        $responseFactory = new \Slim\Psr7\ResponseFactory;
        $response = $responseFactory->createResponse();
        return $response;
    }
}

But it returned this: Class "Slim\Psr7\ResponseFactory" not found.
I cant import this class because my application simply cant find it to import.

5

Okay, found the solution, I was importing in an old way, if you change the:
new \Slim\Psr7\ResponseFactory
to:
new \Slim\Psr7\Factory\ResponseFactory
It will 100% work! Thanks Odan :slight_smile:

6

Note, that you have a $response returned to you from handle(), so do not need to create a new one.

It’s relatively rare for middleware to not return that $response instance from handle() as it represents a lot of processing that’s happened in other middleware and in the route handler itself.

1 Like
7

Thanks for your advice akrabat! I’ve removed the response creation and used only the handle instead, it worked smoothly!

8

Just a suggestion as PSR-15: HTTP Server Request Handlers - PHP-FIG mentioned

image
image797×373 26.7 KB

If you’re in a company. Maybe it would be better to use some standard.
Like this example

<?php

declare(strict_types=1);

namespace Masoretic\Middlewares;

use Psr\Http\Message\ResponseInterface as Response;
use Psr\Http\Message\ServerRequestInterface as Request;
use Psr\Http\Server\RequestHandlerInterface as RequestHandler;
use Psr\Http\Server\MiddlewareInterface;

final class ContentTypeJsonMiddleware implements MiddlewareInterface
{
    public function process(Request $request, RequestHandler $handler): Response
    {
        header('Content-Type: application/json');
        
        return $handler->handle($request);
    }
}
9

Note: While this approach might work in some scenarios, it’s more robust to PSR-7 standards to use the Response object provided by the PSR interfaces for modifying headers.