Hello!

On Fri, May 20, 2011 at 11:58:20AM +0800, Wu Bingzheng wrote:

> Hi Maxim,
>
> 1.
> I am so sorry that I made a big mistake on question 1.
> Nginx didn't detect the downstream breaking, because I use "proxy_ignore_client_abort on;".
> So Nginx works correctlly. I am so sorry about it.

I believe the problem may still appear with normal usage once
upstream connection terminates, EPOLLHUP handling in epoll event
module doesn't look correct for me. This should be investigated
further.

> 2.
> For question 2.
> You said that :
> >Note also that in debug log you provided nginx correctly times out
> >after 20s from last send.
>
> That's because I set the send_timeout as 10s. I am sorry that I did not make clear of that.
>
> You can reproduce the doubled timeout easy:

Ok, I was able to reproduce this and see the problem. Indeed,
when upstream module detects client timeout it doesn't finalize
request properly, and as a result http core thinks it should
continue sending data in buffers and hence waits for another
timeout.

Quick fix for this particular problem would be something like

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2320,7 +2320,7 @@ ngx_http_upstream_process_non_buffered_d
if (wev->timedout) {
c->timedout = 1;
ngx_connection_error(c, NGX_ETIMEDOUT, "client timed out");
- ngx_http_upstream_finalize_request(r, u, 0);
+ ngx_http_upstream_finalize_request(r, u, NGX_HTTP_REQUEST_TIME_OUT);
return;
}

@@ -3013,6 +3013,7 @@ ngx_http_upstream_finalize_request(ngx_h
#endif

if (u->header_sent
+ && rc != NGX_HTTP_REQUEST_TIME_OUT
&& (rc == NGX_ERROR || rc >= NGX_HTTP_SPECIAL_RESPONSE))
{
rc = 0;


Though upstream module certainly requires larger cleanup of error
handling. This is not the first time I've been bitten by upstream
not finalizing requests properly.

Maxim Dounin

>
> [server] using nginx-1.0.0, without any addon module. in nginx.conf:
>
> server {
> listen 5821;
> proxy_buffering off; #must in non-buffering mode
> send_timeout 10;
>
> location / {
> proxy_pass http://sourceserver;
> }
> }
>
>
>
> [client] you can run this simple python script:
>
> #!/usr/bin/python
> import socket
> import time
> s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
> s.connect((127.0.0.1, 5821))
> s.send("GET /data/something HTTP/1.0\r\n\r\n")
> buf = s.recv(100)
> print buf
> time.sleep(100)
>
>
>
> Then, in access.log, you will find that the request is finished in 20s.
>
>
> Best Regads,
> Wu
>
>
>
>
>
>
>
>
> At 2011-05-19 19:38:42，"Maxim Dounin" <mdounin@mdounin.ru> wrote:
>
> >Hello!
> >
> >On Thu, May 19, 2011 at 10:39:43AM +0800, Wu Bingzheng wrote:
> >
> >> Hi Maxim,
> >>
> >> Thanks for your answer. But I am still confused.
> >>
> >>
> >> At 2011-05-18 21:35:07，"Maxim Dounin" <mdounin@mdounin.ru> wrote:
> >>
> >> >Hello!
> >> >
> >> >On Wed, May 18, 2011 at 05:15:00PM +0800, Wu Bingzheng wrote:
> >> >
> >> >> hi all,
> >> >>
> >> >>
> >> >> I meet 2 question when using nginx 1.0.0.
> >> >>
> >> >>
> >> >> Question1.
> >> >>
> >> >> what happens if the downstream connection breaks, before all
> >> >> data sent to the client?
> >> >>
> >> >> 1. get client's request
> >> >> 2. set handler: r->read_event_handle=ngx_http_block_reading
> >> >> 3. send data to client, and blocked (
> >> >> write_filter.c:c->send_chain() returns non-NULL or non-error),
> >> >> and go back to epoll_wait
> >> >> 4. HERE, the downstream breaks
> >> >> 5. epoll detect the breaking, so epoll_wait() continues in
> >> >> ngx_epoll_process_events(), where the revents==EPOLL_IN |
> >> >> EPOLL_ERR | EPOLL_HUP. So we call rev->handler(), which calls
> >> >> r->read_event_handle, which dose nothing. AS A RESULT, the
> >> >> downstream breaking was not detected by nginx !!!
> >> >
> >> >Here write event handler will be called. While standard
> >> >ngx_http_writer() is in use - it will call output filter chain and
> >> >detect error. Else it's up to active handler to correctly handle
> >> >this, e.g. standard upstream modules (proxy/fastcgi/...) may
> >> >either terminate request immediately or wait for full upstream
> >> >response depending on various settings (proxy_ignore_client_abort,
> >> >proxy_cache/proxy_store enabled).
> >> >
> >>
> >> You said the write handler will be called. But if a connection
> >> is break, revents returned by epoll_wait() is 'EPOLL_IN |
> >> EPOLL_ERR | EPOLL_HUP', and no EPOLL_OUT in revents. So I think
> >> the write-handler will NOT be called.
> >
> >Ah, ok, it looks like I was wrong here. Write handler will be
> >only called if there are no EPOLLIN flag in revents, and this is
> >probably wrong assuming EPOLLHUP follows the same semantics as
> >POLLHUP[1], i.e.
> >
> >POLLHUP
> >... This event and POLLOUT are mutually-exclusive; a stream can
> >never be writable if a hangup has occurred. ...
> >
> >Could you please provide detailed instructions to reproduce the
> >problem, preferably with standard modules involved?
> >
> >[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/poll.html
> >
> >> The FACT is, in my server, there are many many access logs whose
> >> time-taken are 40.001s. (send_timeout is 20s, and this is a
> >> music online server, so many people re-choose a song before the
> >> current song finishs, which means the downstream breaks before
> >> nginx sends all data).
> >>
> >> I add 2 debug log in ngx_epoll_process_events(), and copy part
> >> of the debug log here.
> >
> >Just a side note: mostly same information may be seen at global
> >level debug log.
> >
> >[...]
> >
> >> >> I set 'send_timeout' as 20s, but nginx timeouts in 40s actually.
> >> >>
> >> >> 1. in
> >> >> src/http/ngx_http_upstream.c[line2448]:ngx_http_upstream_process_non_buffered_request(),
> >> >> a timer is added;
> >> >> 2. after that timer timeout, in
> >> >> src/http/ngx_http_request.c[line2179]:ngx_http_set_write_handler(),
> >> >> another timer is added again.
> >> >>
> >> >> so the send_timeout is doubled.
> >> >
> >> >Timeout is re-set on each send operation, and expected to be
> >> >triggered when nothing happens during send_timeout.
> >>
> >> So, you think that, I set 'send_timeout' as 20s, but nginx
> >> actually timeout in 40s is right and expected?
> >
> >It should timeout in 20s after last send. Whether request time
> >of 40s is wrong or not depends on many factors, but the code you
> >pointed out looks fine.
> >
> >Note also that in debug log you provided nginx correctly times out
> >after 20s from last send.
> >
> >Maxim Dounin
>
>
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