ColdFusion Tips and Tutorials

I. Comments:

Keep Coding,
Nathan Stanford
http://www.cftipsplus.com

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Overview
The overall technique presented here is to designate a ColdFusion page as the source for an image or sound, have that page do something useful in the background, and then have that page send content that it has marked as an image or sound as appropriate. You'll turn off all output except ColdFusion output, do your business, use the cfcontent tag to pass this non-text content, and enable normal output again. Everything useful must be accomplished prior to the cfcontent tag; because, the browser stops caring after the image has been received. Its job is done.

Log
Here's some simple code - call it log.cfm - that can be used to track the progress of sessions from the time an individual enters a site unthe profile of sessions an individual's progress through a site. Because no expiration date is given to the cookie, it will vanish when the user closes the browser, but a logical session can be inferred from the data, nevertheless. (Commercial applications typically set a "permanent" cookie which they eventually associate with a userid if a user actually logs into your site.)
It performs the functions named in the overview. First, it enables ColdFusion output only. Then, it checks to see if the cookie identifying a session exists. If not, it sets it to a unique value using the createUUID function. It then gathers information for the log: this ID, the IP address, the full name by which this link was called, any more information following a question mark in that URL (if anything), and the current date and time. In determining the current date/time, it sets a variable to the current date and time first so that the time won't be seconds behind the date. It spits all this information into a log, displays an image, and turns normal output back on. Note that the content type must be appropriate for the content: gif for gif, jpeg for jpg, and so forth.

<cfsetting enablecfoutputonly="yes">
<cfif not isDefined("cookie.webbug")>
<cfcookie name="webbug" value="#createUUID()#">
</cfif>
<cfset id="#cookie.webbug#">
<cfset ip="#cgi.remote_addr#">
<cfset link="#cgi.script_name#">
<cfset more="#cgi.query_string#">
<cfset dt=now()>
<cfset when="#dateformat(dt)# #timeformat(dt)#">
<cfset doline="#id#:#ip#:#link#:#more#:#when#">
<cffile action="append" file="d:\mysite\webbug\log.txt" output="#doline#" addnewline attributes="normal">
<cfcontent type="image/jpeg" file="d:\mysite\webbug\world3.jpg">
<cfsetting enablecfoutputonly="no">

Embed
Now embed calls to this log as "image" requests in normal pages. Each call will look something like this. It looks quite ordinary except that the URL ends in .cfm instead of .gif or .jpg.

<img src="http://mysite.com/webbug/log.cfm">

Mysteries
The idea behind logging the URL (with extra path information) and the query string (everything after the question mark) is to let the calling site provide more information if desired. For example, the query string or extra path information (or both) could be deliberately varied by the maintainer when adding the call. (A call to log.cfm?page=home would work just as well as a plain call to log.cfm.)

When you run this code, it works. However, it winds up creating a cookie that is only noticed by log.cfm, and then only in the context of the call. If you try to see the cookie from the page that called log.cfm, it won't be there. If you try to see the cookie from the site that hosts log.cfm, it won't be there, either. It is as if this cookie can only be seen in the cross-domain context in which it was set. If a user browses multiple sites containing this call to log.cfm, log.cfm will give each site a separate cookie. This quirk makes it hard to envision more useful roles for this Web bug. It can track sessions for a single site, but it doesn't lend itself yet to tracking the same user across different sites.

Determine workarounds for its apparent limitations, and then let us know what you've done.

=Marty=