You might not know this, but PHP comes with a very capable socketprogramming API. These socket functions now include almost everything youwould need for socket-based client-server communication over TCP/IP, andcan be easily deployed to build simple network applications. Find out more,inside.
Now, how about seeing it in action? Since this script generates an "always-on" socket, it isn't a good idea to run it via your Web server; instead, you might prefer to run it from the command line via the PHP binary:
$ /usr/local/bin/php -q server.php
In case you don't have a PHP binary, it's fairly easy to
compile one - just follow the installation instructions for compiling a static Apache module (these instructions are available in the PHP distribution), but omit the "--with-apache" parameter to the "configure" script.
Note the additional -q parameter to PHP - this tells the program to suppress the "Content-Type: text/html" header that it usually adds when executing a script (I don't need this header here because the output of this script isn't going to a browser).
Once the script has been executed and the socket server is active, you can simply telnet to it using any standard telnet application, and send it a string of characters as input. The server should respond with the reversed string, and then terminate the connection. Here's what it looks like:
$ telnet 192.168.1.99 1234
Connected to medusa.
Escape character is '^]'.
jack and the beanstalk
klatsnaeb eht dna kcaj
Connection closed by foreign host.