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From Timothy Partee <timothy.par...@gmail.com>
Subject Re: [users@httpd] Apache/Perl CGI intermittent missing POST data
Date Mon, 09 Aug 2010 07:32:23 GMT
   Okay, so for the last few days now I've been trying to repro the
intermittent POST data issues on my Apache servers through a test POST
form script and thus far I've had a zero repro rate out of over 40,000
POST submissions from the test script - however I've added error
logging for every time a POST form processor receives an empty set of
CGI params and it's gone off a half dozen to couple dozen times per
day out of a few thousand POST processings per day. Seems negligible,
but we commonly receive user complaints and bug reports abut this
issue nonetheless, and we're getting very tired of it, to say the
least.
   Since we cannot repro the issue in a controlled sense, and
therefore can't get mod_dumpio in on the investigation, we need some
new direction. One 'professional' on this list contacted us privately
and mentioned that mod_rewrite is the likely culprit and we are indeed
using mod_rewrite for some redirects from troublesome referrer sources
and people who attempt to host images from our site in off-site pages.
It was suggested that we exclude the CGI folders from the mod_rewrite
rules and processing, however we could find no info in Apache
documentation on how to exclude mod_rewrite rules/operation from any
specific directories. Any pointers in the right direction would be
appreciated, thanks!

- Tim Partee


On Fri, Aug 6, 2010 at 3:55 AM, Jeff Trawick <trawick@gmail.com> wrote:
> On Fri, Aug 6, 2010 at 2:50 AM, Timothy Partee <timothy.partee@gmail.com> wrote:
>>   Basically what's happening is I have a small horde of Perl (not
>> mod_perl, just plain Perl) scripts which use the CGI.pm module to
>> parse out incoming CGI parameters and cookies, and about 2% of the
>> time when I get the POST data params from CGI they are a completely
>> empty collection. I can consistently reproduce this with a simple POST
>> form page to a simple Perl CGI script which dumps a set of static form
>> data (as in the form fields are hidden and therefore no data entry is
>> needed so I can just hit the submit button over and over again for
>> rapid testing) to the browser. Everything runs fine, no errors on the
>> server being reported, no error in the Perl script reported, just a
>> blank params collection about 2% of the time, seemingly completely at
>> random. Under high load and under low load there seems to be no
>> difference.
>
> First, confirm exactly what the browser is sending when you encounter
> the problem symptom:
>
> a) Content-Length non-zero + POST data
> b) Content-Length zero
> c) Content-Length non-zero but no post data (we'd expect the web
> server to wait for Timeout seconds before giving up on the POST data)
>
> You can easily log the incoming Content-Length in the access log.  You
> can log the incoming headers/POST data with mod_dumpio.  You can step
> outside of the web server process itself and use a packet trace tool
> such as Wireshark.  You can use something like the ieHttpHeaders
> plug-in for IE, or equivalent for Firefox, to see the perspective of
> the browser process.
>
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