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Apache2-ClickPath-1.3
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/ Apache2::ClickPath

NAME

Apache2::ClickPath - Apache WEB Server User Tracking

SYNOPSIS

LoadModule perl_module ".../mod_perl.so"
PerlLoadModule Apache2::ClickPath
<ClickPathUAExceptions>
  Google     Googlebot
  MSN        msnbot
  Mirago     HeinrichderMiragoRobot
  Yahoo      Yahoo-MMCrawler
  Seekbot    Seekbot
  Picsearch  psbot
  Globalspec Ocelli
  Naver      NaverBot
  Turnitin   TurnitinBot
  dir.com    Pompos
  search.ch  search\.ch
  IBM        http://www\.almaden\.ibm\.com/cs/crawler/
</ClickPathUAExceptions>
ClickPathSessionPrefix "-S:"
ClickPathMaxSessionAge 18000
PerlTransHandler Apache2::ClickPath
PerlOutputFilterHandler Apache2::ClickPath::OutputFilter
LogFormat "%h %l %u %t \"%m %U%q %H\" %>s %b \"%{Referer}i\" \"%{User-agent}i\" \"%{SESSION}e\""

ABSTRACT

Apache2::ClickPath can be used to track user activity on your web server and gather click streams. Unlike mod_usertrack it does not use a cookie. Instead the session identifier is transferred as the first part on an URI.

Furthermore, in conjunction with a load balancer it can be used to direct all requests belonging to a session to the same server.

DESCRIPTION

Apache2::ClickPath adds a PerlTransHandler and an output filter to Apache's request cycle. The transhandler inspects the requested URI to decide if an existing session is used or a new one has to be created.

The Translation Handler

If the requested URI starts with a slash followed by the session prefix (see "ClickPathSessionPrefix" below) the rest of the URI up to the next slash is treated as session identifier. If for example the requested URI is /-S:s9NNNd:doBAYNNNiaNQOtNNNNNM/index.html then assuming ClickPathSessionPrefix is set to -S: the session identifier would be s9NNNd:doBAYNNNiaNQOtNNNNNM.

If no session identifier is found a new one is created.

Then the session prefix and identifier are stripped from the current URI. Also a potentially existing session is stripped from the incoming Referer header.

There are several exceptions to this scheme. Even if the incoming URI contains a session a new one is created if it is too old. This is done to prevent link collections, bookmarks or search engines generating endless click streams.

If the incoming UserAgent header matches a configurable regular expression neither session identifier is generated nor output filtering is done. That way search engine crawlers will not create sessions and links to your site remain readable (without the session stuff).

The translation handler sets the following environment variables that can be used in CGI programms or template systems (eg. SSI):

SESSION

the session identifier itself. In the example above s9NNNd:doBAYNNNiaNQOtNNNNNM is assigned. If the UserAgent prevents session generation the name of the matching regular expression is assigned, (see "ClickPathUAExceptions").

CGI_SESSION

the session prefix + the session identifier. In the example above /-S:s9NNNd:doBAYNNNiaNQOtNNNNNM is assigned. If the UserAgent prevents session generation CGI_SESSION is empty.

SESSION_START

the request time of the request starting a session in seconds since 1/1/1970.

CGI_SESSION_AGE

the session age in seconds, i.e. CURRENT_TIME - SESSION_START.

REMOTE_SESSION

in case a friendly session was caught this variable contains it, see below.

REMOTE_SESSION_HOST

in case a friendly session was caught this variable contains the host it belongs to, see below.

The Output Filter

The output filter is entirely skipped if the translation handler had not set the CGI_SESSION environment variable.

It prepends the session prefix and identifier to any Location an Refresh output headers.

If the output Content-Type is text/html the body part is modified. In this case the filter patches the following HTML tags:

<a ... href="LINK" ...>
<area ... href="LINK" ...>
<form ... action="LINK" ...>
<frame ... src="LINK" ...>
<iframe ... src="LINK" ...>
<meta ... http-equiv="refresh" ... content="N; URL=LINK" ...>

In all cases if LINK starts with a slash the current value of CGI_SESSION is prepended. If LINK starts with http://HOST/ (or https:) where HOST matches the incoming Host header CGI_SESSION is inserted right after HOST. If LINK is relative and the incoming request URI had contained a session then LINK is left unmodified. Otherwize it is converted to a link starting with a slash and CGI_SESSION is prepended.

Configuration Directives

All directives are valid only in server config or virtual host contexts.

ClickPathSessionPrefix

specifies the session prefix without the leading slash.

ClickPathMaxSessionAge

if a session gets older than this value (in seconds) a new one is created instead of continuing the old. Values of about a few hours should be good, eg. 18000 = 5 h.

ClickPathMachine

set this machine's name. The name is used with load balancers. Each machine of a farm is assigned a unique name. That makes session identifiers unique across the farm.

If this directive is omitted a compressed form (6 Bytes) of the server's IP address is used. Thus the session is unique across the Internet.

In environments with only one server this directive can be given without an argument. Then an empty name is used and the session is unique on the server.

If possible use short or empty names. It saves bandwidth.

A name consists of letters, digits and underscores (_).

The generated session identifier contains the name in a slightly scrambled form to slightly hide your infrastructure.

ClickPathUAExceptions

this is a container directive like <Location> or <Directory>. The container content lines consist of a name and a regular expression. For example

1   <ClickPathUAExceptions>
2     Google     Googlebot
3     MSN        (?i:msnbot)
4   </ClickPathUAExceptions>

Line 2 maps each UserAgent containing the word Googlebot to the name Google. Now if a request comes in with an UserAgent header containing Googlebot no session is generated. Instead the environment variable SESSION is set to Google and CGI_SESSION is emtpy.

ClickPathUAExceptionsFile

this directive takes a filename as argument. The file's syntax and semantic are the same as for ClickPathUAExceptions. The file is reread every time is has been changed avoiding server restarts after configuration changes at the prize of memory consumption.

ClickPathFriendlySessions

this is also a container directive. It describes friendly sessions. What is a friendly session? Well, suppose you have a WEB shop running on shop.tld.org and your company site running on www.tld.org. The shop does it's own URL based session management but there are links from the shop to the company site and back. Wouldn't it be nice if a customer once he has stepped into the shop could click links to the company without loosing the shopping session? This is where friendly sessions come in.

Since your shop's session management is URL based the Referer seen by www.tld.org will be something like

https://shop.tld.org/cgi-bin/shop.pl?session=sdafsgr;clusterid=25

(if session and clusterid are passed as CGI parameters) or

https://shop.tld.org/C:25/S:sdafsgr/cgi-bin/shop.pl

(if session and clusterid are passed as URL parts) or something mixed.

Assuming that clusterid and session both identify the session on shop.tld.org Apache2::ClickPath can extract them, encode them in it's own session and place them in environment variables.

Each line in the ClickPathFriendlySessions section decribes one friendly site. The line consists of the friendly hostname, a list of URL parts or CGI parameters identifying the friendly session and an optional short name for this friend, eg:

shop.tld.org uri(1) param(session) shop

This means sessions at shop.tld.org are identified by the combination of 1st URL part after the leading slash (/) and a CGI parameter named session.

If now a request comes in with a Referer of http://shop.tld.org/25/bin/shop.pl?action=showbasket;session=213 the REMOTE_SESSION environment variable will contain 2 lines:

25
session=213

Their order is determined by the order of uri() and param() statements in the configuration section between the hostname and the short name. The REMOTE_SESSION_HOST environment variable will contain the host name the session belongs to.

Now a CGI script or a modperl handler or something similar can fetch the environment and build links back to shop.tld.org. Instead of directly linking back to the shop your links then point to that script. The script then puts out an appropriate redirect.

ClickPathFriendlySessionsFile

this directive takes a filename as argument. The file's syntax and semantic are the same as for ClickPathFriendlySessions. The file is reread every time is has been changed avoiding server restarts after configuration changes at the prize of memory consumption.

Working with a load balancer

Most load balancers are able to map a request to a particular machine based on a part of the request URI. They look for a prefix followed by a given number of characters or until a suffix is found. The string between identifies the machine to route the request to.

The name set with ClickPathMachine can be used by a load balancer. It is immediately following the session prefix and finished by a single colon. The default name is always 6 bytes long.

Logging

The most important part of user tracking and clickstreams is logging. With Apache2::ClickPath many request URIs contain an initial session part. Thus, for logfile analyzers most requests are unique which leads to useless results. Normally Apache's common logfile format starts with

%h %l %u %t \"%r\"

%r stands for the request. It is the first line a browser sends to a server. For use with Apache2::ClickPath %r is better changed to %m %U%q %H. Since Apache2::ClickPath strips the session part from the current URI %U appears without the session. With this modification logfile analyzers will produce meaningful results again.

The session can be logged as %{SESSION}e at end of a logfile line.

A word about proxies

Depending on your content and your users community HTTP proxies can serve a significant part of your traffic. With Apache2::ClickPath almost all request have to be served by your server.

Using with SSI

Server Side Includes are also implemented as an output filter. Normally Perl output filters are called before mod_include leading to unexpected results if an SSI statement generated links. On the other hand one can configure the INCLUDES filter with PerlSetOutputFilter which preserves the order given in the configuration file. Unfortunately there is no PerlSetOutputFilterByType directive and and the INCLUDES filter processes everything independend of the Content-Type. Thus, also images and other stuff is scanned for SSI statements.

With Apache 2.2 there will be a filter dispatcher module that can maybe address this problem.

Currently my only solution to this problem is a little module Apache2::RemoveNextFilterIfNotTextHtml and setting up the filter chain with PerlOutputFilterHandler and PerlSetOutputFilter:

PerlOutputFilterHandler Apache2::RemoveNextFilterIfNotTextHtml
PerlSetOutputFilter INCLUDES
PerlOutputFilterHandler Apache2::ClickPath::OutputFilter

Don't hesitate to contact me if you are interested in this little module.

Debugging

Sometimes it is useful to know the information encoded in a session identifier. This is why Apache2::ClickPath::Decode exists.

SEE ALSO

Apache2::ClickPath::Decode(3) http://perl.apache.org, http://httpd.apache.org

AUTHOR

Torsten Foertsch, <torsten.foertsch@gmx.net>

COPYRIGHT AND LICENSE

Copyright (C) 2004-2005 by Torsten Foertsch

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.