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From "Manni Wood" <mw...@digitas.com>
Subject RE: mod_usertrack bugfix patch
Date Tue, 25 Feb 2003 20:13:00 GMT
I suppose I should have put more details at http://www.manniwood.net/mod_usertrack_patch.html
about my results running a patched vs. unpatched version of my code through a JMeter test,
but as my web page says, the patch adds a couple of milliseconds to the request time. Is there
any standard way the Apache group tests new code for performance? I will happily run more
tests for you if you'd like.

The patch that I sent is the best balance I could find between correctness and speed. (The
current mod_usertrack is fast but incorrect, unfortunately.) Remember that in my patch, I
compile the regexp only once (at config time), so running the compiled regexp on the cookie
header is really quite fast.

As a matter of fact, the use of regexps in mod_alias is what inspired me to use a regexp in
my mod_usertrack patch. I figured if the performance hit of mod_alias was deemed worthwhile
in the pursuit of correctness, a corrected mod_usertrack would also be permitted the same
indulgence. (But I *am* new to this, so is my assumption incorrect?)

Finally, the use of strstr to find the cookie name and substr to find the cookie value is,
unfortunately, what leads to the bug in the current code. A more refined use of strstr might
look for the cookiename proceeded by a space and followed by the '=' sign. However there's
no reason why the space separating cookienames can't actually be a tab, as the RFC only calls
for "whitespace" between cookie/value pairs. Also, the whitespace is not going to be present
if the cookiename happens to be the first cookie in the header, so one would have to handle
that exception. Finally, one has to deal with the fact that the cookiename could actually
have a space in it, as long as it is in quotation marks, so that would break the algorithm
I just discussed. In the end, as with mod_alias, a regexp starts to make a whole lot of sense
for mod_usertrack instead of coding a baroque usage of strstr and substr to take care of all
these exceptions.

What do you think?

As I said, I'm willing to run more tests and give you numbers, if you'd like (and encourage
you to do the same, naturally). Is there a standard way the Apache Group runs tests on new
code to see if it meets performance guidelines? I'm sure the performance hit won't be any
worse than for mod_alias.

-Manni

--------------------------------------------
Manni Wood, Programmer, Digitas
800 Boylston Street, Boston, MA, 02199
617 867 1881 mwood@digitas.com

"Most men would rather die than think. Many do."    --Bertrand Russell
 

-----Original Message-----
From: Jeff Trawick [mailto:trawick@attglobal.net]
Sent: Tuesday, February 25, 2003 6:29 AM
To: dev@httpd.apache.org
Subject: Re: mod_usertrack bugfix patch


Manni Wood wrote:

> I am submitting a patch to mod_usertrack for both Apache 2.0 and 1.3 
> for your consideration.

> The patch fixes a bug where the use of strstr() to find the name of 
> the cookie in the cookieheader can accidentally "find" the name of the 
> cookie in what is actually the contents of a cookie if the contents 
> happen to contain the name of the user tracking cookie.
>
> The patch relies on a robust regexp to find the cookiename in the 
> header instead of strstr().

performance concern a.k.a. dumb question...  is a regexp required for 
fixing this problem?

> More details are at http://www.manniwood.net/mod_usertrack_patch.html.


excellent resource...  I applaud you for taking the initiative to deal 
with this so carefully



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