azure-storage-common\src\Common\Middlewares\MiddlewareBase.php

return function (
   RequestInterface $request,
   array $options
) use ($handler) {
   //do something prior to sending the request.
   $promise = $handler($request, $options);
   return $promise->then(
       function (ResponseInterface $response) use ($request, $options) {
           //do something
           return $response;
       },
       function ($reason) use ($request, $options) {
           //do something
           return new GuzzleHttp\Promise\RejectedPromise($reason);
       }
   );
};