PSR-7 and Value Objects

Slim supports PSR-7 interfaces for its Request and Response objects. This makes Slim flexible because it can use any PSR-7 implementation. For example, you could return an instance of GuzzleHttp\Psr7\CachingStream or any instance returned by the GuzzleHttp\Psr7\stream_for() function.

Slim provides its own PSR-7 implementation. However, you are free to install a third-party implementation.

Value objects

Request and Response objects are immutable value objects. They can be “changed” only by requesting a cloned version that has updated property values. Value objects have a nominal overhead because they must be cloned when their properties are updated. This overhead does not affect performance in any meaningful way.

You can request a copy of a value object by invoking any of its PSR-7 interface methods (these methods typically have a with prefix). For example, a PSR-7 Response object has a withHeader($name, $value) method that returns a cloned value object with the new HTTP header.

use Psr\Http\Message\ResponseInterface as Response;
use Psr\Http\Message\ServerRequestInterface as Request;
use Slim\Factory\AppFactory;

require __DIR__ . '/../vendor/autoload.php';

$app = AppFactory::create();

$app->get('/foo', function (Request $request, Response $response, array $args) {
    $payload = json_encode(['hello' => 'world'], JSON_PRETTY_PRINT);
    return $response->withHeader('Content-Type', 'application/json');


The PSR-7 interface provides these methods to transform Request and Response objects:

  • withProtocolVersion($version)
  • withHeader($name, $value)
  • withAddedHeader($name, $value)
  • withoutHeader($name)
  • withBody(StreamInterface $body)

The PSR-7 interface provides these methods to transform Request objects:

  • withMethod($method)
  • withUri(UriInterface $uri, $preserveHost = false)
  • withCookieParams(array $cookies)
  • withQueryParams(array $query)
  • withUploadedFiles(array $uploadedFiles)
  • withParsedBody($data)
  • withAttribute($name, $value)
  • withoutAttribute($name)

The PSR-7 interface provides these methods to transform Response objects:

  • withStatus($code, $reasonPhrase = '')

Refer to the PSR-7 documentation for more information about these methods.