Basic CGI in C with Merecat httpd

- 2 mins read

This post is a writeup of how to use basic CGI programs in Merecat httpd v2.32.

Downloads:

Build Merecat httpd according to the instructions in the README. This document assumes the directory ~/merecat/. Then create a config file, ~/test.conf, with the following content:

port = 8080

cgi "**.cgi|cgi-bin/*" {
    enabled = true
}

In this example we’ve chosen port 8080 so we can start the server as a regular user. For production systems you likely want to use the default (80), or set up proper HTTPS, see Let’s Encrypt Merecat for help with that.

The classic cgic used here is just an example. A CGI program can be written in just about any programming language, or plain shell script. Merecat actually ships with a /cgi-bin/printenv, which is a plain Bourne shell script.

Download, unpack and build cgic:

mkdir temp; cd temp/
wget http://www.boutell.com/cgic/cgic207.tar.gz
tar xf cgic207.tar.gz
cd cgic207/
make

A stand-alone example program is built which we can install into the Merecat web root. Notice the name change to index.cgi, we don’t have to use the cgi-bin/ due to the CGI pattern we set up previously:

cp cgictest.cgi ~/merecat/www/index.cgi

Now we can start the web server and test the CGI program out.

cd ~/merecat/
./src/merecat -f ~/test.conf www

We can now open our browser at http://127.0.0.1:8080/ and there is the CGI! Remember to check out http://127.0.0.1:8080/cgi-bin/printenv too.