nginx silently drops response body of POST depending on its length

[Maxim Dounin]

Hello!

On Sun, May 08, 2011 at 03:15:28PM -0400, zildjohn01 wrote:

> I've come across an incredibly weird problem with POST responses using
> nginx 1.0.1 and uWSGI 0.9.7.2 on CentOS 5.6.
> 
> uWSGI successfully sends the response body to nginx, but nginx seems to
> ignore it if both (1) the request method is POST, and (2) the response
> length is less than 4052 bytes. The issue doesn't occur when serving
> directly using `uwsgi --http`, so I'm pretty sure the problem is
> something to do with nginx.
> 
> To explain things in code, this Python results in the desired response:
> 
> ....def app_uwsgi(environ, start_response):
> ........start_response('200 OK', [('Content-type', 'text/html')])
> ........return [b'x' * 4052]
> 
> while this results in zero bytes being sent to the client for POST
> requests:
> 
> ....def app_uwsgi(environ, start_response):
> ........start_response('200 OK', [('Content-type', 'text/html')])
> ........return [b'x' * 4051]
> 
> I stripped down to a minimal nginx.conf, and the issue still occurs:
> 
> ....events {
> ........worker_connections  1024;
> ....}
> 
> ....http {
> ........upstream uwsgi_connect {
> ............server  127.0.0.1:39275;
> ........}
> 
> ........server {
> ............listen       20101;
> ............server_name  domain.net;
> 
> ............location / {
> ................uwsgi_pass  uwsgi_connect;
> ................include     uwsgi_params;
> ............}
> ........}
> ....}
> 
> Does anyone have any clue what could be causing this behavior?

As it was already said - you have to read body of POST before 
sending reply.  Else you'll get something like

... readv() failed (54: Connection reset by peer) while reading 
upstream ...

in nginx error log and possibly incorrect reply (depending on various 
factors, including sizes and event method used).

Maxim Dounin