NGX_HTTP_LEVEL_400  112 http/ngx_http_header_filter_module.c #define NGX_HTTP_LEVEL_400       (NGX_HTTP_LAST_LEVEL_400 - 400)
NGX_HTTP_LEVEL_400  326 http/ngx_http_special_response.c #define NGX_HTTP_LEVEL_400       (NGX_HTTP_LAST_LEVEL_400 - 400)