[2.x] Fix resolving StreamResponse callback (laravel#1042)

* [2.x] Fix resolving `StreamResponse` callback

fix laravel#1040

Signed-off-by: Mior Muhammad Zaki <crynobone@gmail.com>

* Apply fixes from StyleCI

* formatting

---------

Signed-off-by: Mior Muhammad Zaki <crynobone@gmail.com>
Co-authored-by: StyleCI Bot <bot@styleci.io>
Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: 3 people

src/RoadRunner/RoadRunnerClient.php

@@ -49,11 +49,8 @@ public function respond(RequestContext $context, OctaneResponse $octaneResponse)
             );
         }
 
-        if (
-            ($octaneResponse->response instanceof StreamedResponse) &&
-            ($responseCallback = $octaneResponse->response->getCallback()) &&
-            ((new ReflectionFunction($responseCallback))->getReturnType()?->getName() === Generator::class)
-        ) {
+        if (($octaneResponse->response instanceof StreamedResponse) &&
+            ! is_null($responseCallback = static::resolveStreamResponseCallback($octaneResponse->response))) {
             $this->client->getHttpWorker()->respond(
                 $octaneResponse->response->getStatusCode(),
                 $responseCallback(),
@@ -66,6 +63,28 @@ public function respond(RequestContext $context, OctaneResponse $octaneResponse)
         $this->client->respond($this->toPsr7Response($octaneResponse->response));
     }
 
+    /**
+     * Resolve the stream response callback from the given response.
+     *
+     * @param  \Symfony\Component\HttpFoundation\StreamedResponse  $response
+     * @return \Closure|null
+     */
+    public static function resolveStreamResponseCallback(StreamedResponse $response)
+    {
+        if (is_null($responseCallback = $response->getCallback())) {
+            return null;
+        }
+
+        $reflection = new ReflectionFunction($responseCallback);
+
+        if ($reflection->hasReturnType() === true &&
+            in_array($reflection->getReturnType()?->getName(), [Generator::class, 'string'])) {
+            return $responseCallback;
+        }
+
+        return null;
+    }
+
     /**
      * Send an error message to the server.
      */