proxy server,slice+limit_rate，keepalived connection will be delayed to receive

[kuninchengdu@…]

slice 512k;
limit_rate 512k;
proxy_pass ...

above configuration，ngx_http_write_filter will delay when sending last data，but request is main request which calling by ngx_http_writer as subrequest has finished before sending all the data，then ngx_http_slice_body_filter will exec ‘ngx_http_send_special(r, NGX_HTTP_LAST)’，and
ngx_http_write_filter will exec as following：

if (c->write->delayed) {
c->buffered |= NGX_HTTP_WRITE_BUFFERED;
return NGX_AGAIN;
}

then ngx_http_writer will return because c->buffered is not zero

if (r->buffered

r->postponed

(r == r->main && c->buffered)) {

if (!wev->delayed) {
ngx_add_timer(wev, clcf->send_timeout);
}
if (ngx_handle_write_event(wev, clcf->send_lowat) != NGX_OK) {
ngx_http_close_request(r, 0);
}
return;
}

now, client reuse this connection to send a new request，but
r->read_event_handler is ngx_http_test_reading，it only peek， after delay ms，old request will close, and exec
ngx_http_set_keepalive and ngx_http_process_request_line，then new request can be recived

[Maxim Dounin]

It looks like you are using a 3rd party fork of an outdated nginx version. Please make sure you are able to reproduce the issue with latest nginx version - nginx 1.17.1. If you are able to, please provide a self-contained configuration which demonstrates the issue.

[kuninchengdu@…]

although I use a 3rd module, but the process as above never enter it，I only use slice and limit_rate，
the result which I analysis is：
subrequest finilize firstly(set c->data to r->main),but data does not send completely.
this is a common process in nginx.
then ngx_http_writer will exec, but limit_rate will delay after sending all the data，
normally， ngx_http_finilize_request will delete timer and c->write->delay, but slice is a
subrequet, slice module will exec ngx_http_send_special(r, NGX_HTTP_LAST) in slice body filter, but
it will be delayed in ngx_http_write_filter becase c->write->delay is true, then
c->buffered |= NGX_HTTP_WRITE_BUFFERED;

then ngx_http_writer will abort not to exec ngx_http_finilize_request!

Replying to mdounin:

It looks like you are using a 3rd party fork of an outdated nginx version. Please make sure you are able to reproduce the issue with latest nginx version - nginx 1.17.1. If you are able to, please provide a self-contained configuration which demonstrates the issue.

[maxim]

Ticket retargeted after milestone closed

[Maxim Dounin]

Feedback timeout.

The description seems to suggest that limit_rate in certain edge cases can delay the request processing even if no further data is going to be sent in the response. It certainly can.