[6.x] Fix memory usage on downloading large files (#31163)

* fix memory usage on downloading large files

* Update FilesystemAdapter.php

Co-authored-by: Taylor Otwell <taylor@laravel.com>

src/Illuminate/Filesystem/FilesystemAdapter.php

@@ -162,7 +162,11 @@ public function response($path, $name = null, array $headers = [], $disposition
 
         $response->setCallback(function () use ($path) {
             $stream = $this->readStream($path);
-            fpassthru($stream);
+
+            while (! feof($stream)) {
+                echo fread($stream, 2048);
+            }
+
             fclose($stream);
         });