Nginx 499错误码

/*
* HTTP does not define the code for the case when a client closed
* the connection while we are processing its request so we introduce
* own code to log such situation when a client has closed the connection
* before we even try to send the HTTP header to it
*/
#define NGX_HTTP_CLIENT_CLOSED_REQUEST 499

    if (c->error) { //connecttion错误
　　　　 ……
        if (!u->cacheable) { //upstream的cacheable为false，这个值跟http_cache模块的设置有关。指示内容是否缓存。
            ngx_http_upstream_finalize_request(r, u, NGX_HTTP_CLIENT_CLOSED_REQUEST);
        }
}