README

NegotiationMiddleware provides content negotiation middleware for PHP applications using a middleware signature that requires a request object, a response object, and the next callable in the middleware stack.

This library depends on willdurand/negotiation for content negotiation. It allows you to add negotiation to a middleware stack that:

1. Identifies and matches against a list of acceptable media types.
2. Supplies a default media type in the absence of an Accept request header.
3. Enriches the request object with the negotiated media type.

If the negotiator cannot determine which media type to use in response to the request, it will return a response with a 406 Not Acceptable status.

Installation

Use Composer to install NegotiationMiddleware:

$ composer require cn-tools/negotiation-middleware

This will install the library and its dependencies. NegotiationMiddleware requires PHP 8.0 or newer.

Usage - POSSIBLY WRONG

Add an instance of NegotiationMiddleware\Negotiator to an application or route level middleware stack, passing two arguments to the constructor: an array of acceptable media types to be matched against and a boolean indicating whether or not the middleware should simply match the first acceptable media type in the absence of an Accept header in the request.

Example from Slim 4.x:

<?php

require 'vendor/autoload.php';

use \NegotiationMiddleware\Negotiator;

$app = new \Slim\App();

$app
    ->get('/hello', function(Slim\Http\Request $request, Slim\Http\Response $response, $args) {
        return $response->write('Hello, world!');
    })
    ->add(new Negotiator(['text/html', 'application/json'], TRUE));

$app->run();

In this case, a request to /hello from a web browser will more than likely match the text/html media type specified as an acceptable media type for this route (which is just as well, given our response isn't valid JSON). However, if the server received a request that did not have an Accept header, it will still match to text/html since we instructed the object to supply a default media type.

Note that the Slim\Http\Request object implements PSR-7's ServerRequestInterface. Negotiator::__invoke() requires an instance of this interface to store the negotiated media type in the request object using an attribute named mediaType.

Thus, the route closure could print the negotiated media type like so:

$app
    ->get('/hello', function(Slim\Http\Request $request, Slim\Http\Response $response, $args) {
        $mediaType = $request->getAttribute('mediaType')->getValue();
        return $response->write($mediaType);
    })
    ->add(new Negotiator(['text/html', 'application/json'], TRUE));

The mediaType attribute is an instance of \Negotiation\Accept, which contains a variety of methods for inspecting the actual matched media type from the request header. Refer to the class documentation of willdurand/negotiation for more information.

Middleware Signature - POSSIBLY WRONG

NegotiationMiddleware uses the middleware signature required by Slim 4.x, that of a callable that accepts two arguments: a PSR-7 request object, a PSR-15 response object, and a callable that represents the next middleware in the stack.

This pattern and its usefulness thanks to the adoption of PSR-7 are discussed in a helpful blog post by Matthew O'Phinney, including a similar example:

<?php

use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Message\ResponseInterface;

class Middleware {
    public function function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface {
      // Execute code before calling the next middleware.
      $response = $handler->handle($request);
      // Execute code after calling the next middleware.
      return $response;
    }
    ...
}

Since this implementation is not specific to Slim (or any other framework), it can be reused by any application that uses the same middleware signature or adapted to work with other middleware patterns that still make use of PSR-7 request and response objects.

License

NegotiationMiddleware is licensed under the MIT license. See LICENSE for more information.