getEffectiveUrl() replacement for Guzzle 6.*

_usage.php

<?php
/*

    $response->getEffectiveUrl() solution for Guzzle 6

  --------------------------------------------------------------
 
  In Guzzle 3, 4 and 5 one could use $response->getEffectiveUrl() to retrieve
  the last URL in a chain of HTTP redirects.

  Guzzle 6 uses PSR7 interfaces which do not support this use case, however
  we can still manipulate response headers to store additional information.
  This is a standard practice among proxies, caches, authentication gateways
  and other internet services.
  
  The effective URL is stored in response header X-GUZZLE-EFFECTIVE-URL

  @link http://stackoverflow.com/questions/30682307/how-to-read-the-response-effective-url-in-guzzle-6-0/31962446#31962446

*/

use GuzzleHttp\Client;
use Thinkscape\Guzzle\EffectiveUrlMiddleware;

// Add the middleware to stack and create guzzle client
$stack = HandlerStack::create();
$stack->push(EffectiveUrlMiddleware::middleware());
$client = new Client(['handler' => $stack]);

// Test it out!
$response = $client->get('http://bit.ly/1N2DZdP');
echo $response->getHeaderLine('X-GUZZLE-EFFECTIVE-URL');

EffectiveUrlMiddleware.php

<?php
namespace Thinkscape\Guzzle;

use Psr\Http\Message\RequestInterface;
use Psr\Http\Message\ResponseInterface;

class EffectiveUrlMiddleware
{
    /**
     * @var Callable
     */
    protected $nextHandler;

    /**
     * @var string
     */
    protected $headerName;

    /**
     * @param callable $nextHandler
     * @param string   $headerName  The header name to use for storing effective url
     */
    public function __construct(
        callable $nextHandler,
        $headerName = 'X-GUZZLE-EFFECTIVE-URL'
    ) {
        $this->nextHandler = $nextHandler;
        $this->headerName = $headerName;
    }

    /**
     * Inject effective-url header into response.
     *
     * @param RequestInterface $request
     * @param array            $options
     *
     * @return RequestInterface
     */
    public function __invoke(RequestInterface $request, array $options)
    {
        $fn = $this->nextHandler;

        return $fn($request, $options)->then(function (ResponseInterface $response) use ($request, $options) {
            return $response->withAddedHeader($this->headerName, $request->getUri()->__toString());
        });
    }

    /**
     * Prepare a middleware closure to be used with HandlerStack
     *
     * @param string $headerName The header name to use for storing effective url
     *
     * @return \Closure
     */
    public static function middleware($headerName = 'X-GUZZLE-EFFECTIVE-URL')
    {
        return function (callable $handler) use (&$headerName) {
            return new static($handler, $headerName);
        };
    }
}

@Thinkscape Have you ever thought of turning this into something that can easily be installed using composer? :)