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Extending ColdFusion

Extending ColdFusion

Welcome to another installment of Extending ColdFusion. This month I'm going to talk about a UDF (user-defined function) that will help deal with users. Users are wonderful. Without people visiting your site, your Web page may as well not exist. On the other hand, users have a way of doing the most stup... err crazy things that you can (or most likely cannot) imagine.

You should always assume that your site visitors will not do what you intend; in other words, you should build your Web site to handle every situation - a goal that is not easy to achieve. One of the (many) ways that users can "do the wrong thing" is when you give them a chance to enter information. Almost all Web sites allow users to enter information via forms. However, as soon as you let the user enter any kind of information, you need to make sure the information isn't something that will throw your site into a tailspin.

Consider forums. Many Web sites have a forum of some type that allows users to have threaded discussions. When posting to the forum, the Web application may ask for the user's name, the subject of his or her post, and then the body of the message. This information is then stored in a database and displayed on the Web page. However, what would happen if the user entered this for a name?

Jacob <b>Camden</b>

Instead of just entering his name, the user entered HTML as well. In this case, the user wrapped his last name with bold tags. This isn't horrible, but when the forum posting is viewed, his name will not appear in the same manner in which other forum postings appear. Next, consider this input:

Jacob <b>Camden

This time, the user entered incorrect HTML. When the Web page is viewed, the layout could be totally off from what it should be. If the user had entered a <table> tag instead, the entire page content may actually disappear in Netscape. In this case, the user just made a stupid mistake, but consider this input:

Jacob Camden<script>document.location.href=
"http://www.whitehouse.gov";</script>

This time the input will do something far worse. When the page is viewed, it will execute JavaScript code that will send visitors of your Web site to the official Web page of the U.S. president. However, if the ".gov" was switched to ".com", they would be sent to a porn site instead. Visitors may actually think that your site was the one hosting the porn.

So, how do we fix this? ColdFusion provides us with two functions that can easily and quickly "clean" HTML code input: HTMLCodeFormat and HTMLEditFormat. The only problem with these two functions is that they will remove all code. What if you want to allow some HTML like the bold or italics tags? The first UDF we will look at will allow you to specify the tags you don't want, and thereby allow other tags that are safe for your Web site.

The UDF, SafeText (www.cflib.org/udf.cfm?ID=56), was written by Nathan Dintenfass (who was featured in my last article as well; see CFDJ, Vol. 4, issue 10). The UDF takes one required argument, text (the text to be cleaned), and three optional arguments. You can specify if bad code should be escaped or removed (defaults to being removed). You can specify a list of bad tags, although the default list is intensive. Finally, you can create a list of bad "events". This allows you to remove JavaScript events like onClick or onMouseOver. Listing 1 contains the UDF.

The UDF begins with a set of var statements. These are variables that exist only in the UDF itself. The important ones are badTags and badEvents. These values are the defaults that define which tags and JavaScript events to strip from the string. After the var statements, we have a code branch that splits between replacing the bad tags or simply removing them. If we need to replace them, a while loop is used to search over the text. If bad tags should simply be removed, one regular expression call is used.

Why is it easier to just remove them? Replacing means calling htmlEditFormat on the particular tag that was matched. If this could be done with a simple regex, please e-mail the author (and me!). However, you can completely remove the bad tags with one call. Next, a regular expression call is used to remove the bad JavaScript events. Last, the cleaned text is removed. Listing 2 contains a simple example. I use <cfsavecontent> to store text into a variable. Notice how I use some good HTML, along with some bad HTML and JavaScript events. The good HTML will remain; the bad will be stripped out.

That's it for this installment. In the next one we'll look at another UDF that we can use to deal with user input. In the meantime, if you have any ideas for UDFs, custom tags, or CFCs that you would like to see discussed, please send them to me at [email protected].

More Stories By Ray Camden

A longtime ColdFusion user, Raymond is a co-author of the "Mastering ColdFusion" series published by Sybex Inc, as well as the lead author for the ColdFusion MX Developer's Handbook. He also presents at numerous conferences and contributes to online webzines. He and Rob Brooks-Bilson created and run the Common Function Library Project (www.cflib.org), an open source repository of ColdFusion UDFs. Raymond has helped form three ColdFusion User Groups and is the manager of the Acadiana MMUG.

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