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Bob Stocker and Carol Taylor

Common Gateway Interface Programs

What are they?

Programs that run on the server to generate web pages or process data from forms.

What are the pros and cons?

Benefits

Adds interactivity, flexibility and currency to your pages. For example, a CGI program can be used to extract current information from a database.
For many CGI programs nothing special like the ability to run java programs is required of the browser.
Programs do not have to be downloaded to the browser.

Disadvantages

Potential security risks. A program that anyone in the world can run on your system better be carefully written!
Increased load on the server -- especially if a buggy program gets stuck in an infinite loop.

Do they require server or client software?

Yes. CGI programs are special-purpose server software.
A CGI-wrapper to create a safer environment for executing CGI programs is highly recommended.
Generally no special client software is required.

Can you use it with DU's central Web server?

Yes. In March 1998 we installed a CGI wrapper that will allow designated individuals to maintain their own CGI programs.

Technical discussion and examples

The two basic methods for transmitting data to a CGI program are GET and POST.
It is also possible to pass a PATH_INFO environment variable to a CGI program by appending its value to the URL. For example, cgiemail program that we use at DU to send forms-based electronic mail uses PATH_INFO to determine the location of a text file used for formating messages.

Useful Tools

Lincoln D. Stein's sbox program.: We are using a customized version of this program to wrap user-supported CGI programs. CGI programs are checked for potential security risks and then executed by the program's owner with resource limitations in a restricted file space. Authorization from webmaster@du.edu is required to run CGI programs wrapped by sbox.

Basic Documentation

The Common Gateway Interface: National Center for Supercomputing Applications played a major role in the early development of the World Wide Web. This is their brief introduction to CGIs. Be sure to look at the security tips!

Revised November 11, 1998.