Bug#677086: apache2-mpm-prefork: apache2 sends "400 bad request" on POST from some firefox browsers

[Stefan Fritsch <sf@sfritsch.de>]

On Sunday 17 June 2012, Thomas Voelkl wrote:
> I have collected some statistical data (by analysing the apache
> logs) on how often this problem occurs on our webserver:
> ~38% of our users upload files by using a firefox browser
> ~6% of these firefox users get the error (400 bad request) when
> uploading a file
> 
> bash-command:
> cat access.log | egrep '"POST .+" 400 ' | cut -d ' ' -f 2 | sort -u
> | wc -l
> 
> By using this command you see the amount of unique users having
> that problem. And I think 6 out of 100 firefox-users are too much
> users to ignore that problem.
> 
> Remember: When changing apache from 2.2.16 (squeeze) to 2.2.22
> (wheezy) that problem does NOT occur anymore. So, what changes in
> apache from 16 to 22 can be responsible for that strange behavior?

Nothing seems to be relevant besides the "send 408 instead of 400 on 
timeout". Maybe firefox automatically retries on 408, but doesn't on 
400?

You could try:

- create a tcpdump of a large upload to 2.2.22 and compare to what's 
going on with 2.2.16

- Apply this patch to 2.2.16 and see if it helps:
http://svn.apache.org/viewvc?view=revision&revision=1100200

From the dump you uploaded, increasing mod_reqtimeout's timeouts could 
also help as a workaround. But the > 20 second delay is clearly a 
problem on the client side, because it happens before the server sends 
anything on that connection.