zero size buf in output

[Carlos Eduardo Ferreira Rodrigues]

Hi,

Another issue I started seeing after moving to 1.8.0 is messages like these in the error log:

    2015/05/29 09:29:40 [alert] 16116#0: *82677257 zero size buf in output t:0 r:0 f:0 00007FF33C18F6D0 00007FF33C18F6D0-00007FF33C19F2B6 0000000000000000 0-0 while sending to client [...]

I've seen a mention of this as having been fixed a few versions ago, but it seems to have returned.

Best regards,

--
Carlos Rodrigues
________________________________________
From: nginx-devel-bounces at nginx.org [nginx-devel-bounces at nginx.org]
Sent: Wednesday, May 27, 2015 18:05
To: nginx-devel at nginx.org
Subject: Strange status 500 with empty response

Hi,

Since upgrading to nginx 1.8.0, we started seeing some requests being logged with status 500 and a response of 0 bytes ($bytes_sent). Not many, only one for about 36000 requests.
I've been trying to reliably reproduce this and/or figure out the cause without success, at least to know if this is an nginx bug or some module's. Any ideas or suggestions of how I can go about doing this?

These requests use proxy_pass (with cache) and header_filter_by_lua, so I've been able to figure out some things for these failed requests:

   * They are always a cache hit;
   * Headers created by the Lua code are correctly logged with $sent_http_*;
   * Errors in Lua code result in status 500 with a non-empty response (our custom error page);

Also, the error log shows nothing along with these errors.

Thanks in advance,

--
Carlos Rodrigues