Cache: do not inherit last_modified and etag from stale response. When replacing a stale cache entry, its last_modified and etag could be inherited from the old entry if the response code is not 200 or 206. Moreover, etag could be inherited with any response code if it's missing in the new response. As a result, the cache entry is left with invalid last_modified or etag which could lead to broken revalidation. For example, when a file is deleted from backend, its last_modified is copied to the new 404 cache entry and is used later for revalidation. Once the old file appears again with its original timestamp, revalidation succeeds and the cached 404 response is sent to client instead of the file. The problem appeared with etags in 44b9ab7752e3 (1.7.3) and affected last_modified in 1573fc7875fa (1.7.9).

uwsgi_param  QUERY_STRING       $query_string;
uwsgi_param  REQUEST_METHOD     $request_method;
uwsgi_param  CONTENT_TYPE       $content_type;
uwsgi_param  CONTENT_LENGTH     $content_length;

uwsgi_param  REQUEST_URI        $request_uri;
uwsgi_param  PATH_INFO          $document_uri;
uwsgi_param  DOCUMENT_ROOT      $document_root;
uwsgi_param  SERVER_PROTOCOL    $server_protocol;
uwsgi_param  HTTPS              $https if_not_empty;

uwsgi_param  REMOTE_ADDR        $remote_addr;
uwsgi_param  REMOTE_PORT        $remote_port;
uwsgi_param  SERVER_PORT        $server_port;
uwsgi_param  SERVER_NAME        $server_name;