src/http/ngx_http_upstream.c:2543: error: Uninitialized Value
  The value read from do_write was never initialized.

src/http/ngx_http_upstream.c:2543:13: 
2541.     for ( ;; ) {
2542. 
2543.         if (do_write) {
                  ^
2544. 
2545.             size = b->last - b->pos;
