Developing Web Applications - Part II

    As I promised, I was going to give you guys another example of a php3 program. This program is a very simple program, and yet somewhat useful.

    One night, I was at the university working and I tried to call home to talk to my wife. Unfortunately, I had left my computer connected that day, and could not get through. So, since my computer was running Apache, I decided to scan through the IPs of my ISP , and find out which computer was my computer, so I could telnet to it, and remotely disconnect it.

    The fastest, and simplest way to do this was either through php3 or java, but since I am not very fond of java applets, I decided to do it in php3.

    And here is how it goes:

<?

    //Author: Anderson Silva

    //Date: September, 1999

    //Opens socket and goes through a bunch of sequential IPs, and

    //it returns all the address that have a web server running.

    // This loop will go through all addresses in the block 10.0.0.x

    // The 10.0.0.x series is a fictional example, these IPs are normally

    // for intranet addresses, I am just trying to keep my ISP safe from

    // all of you guys :-)

    for($i=1; $i < 256; $i++)

    {

       // $path is the variable that will hold the URL you are testing.

       $path = "http://10.0.0.".$i;

       // Opens socket on server PAI, port 80.

       $fp = fsockopen("pai", 80, &$errno, &$errstr);

       // Sends the HTTP request that returns the info we need to know.

       fputs($fp,"GET $path HTTP/1.0\n\n");

       set_socket_blocking($fp, false);

       // This is the string we wait for as a reply to the HTTP request.

       $str2 = "HTTP/1.0 200 OK";

       // Gives the program 2 seconds to try to connect to the server.

       Sleep(2);

 
       // Captures the line from the HTTP request.

       $line = fgets($fp, 16);

       // If str2 is the same line, then we have a match, and there is a web

       // server running. Then go ahead and show me the name of the server with

       // a link to it.

       if (strcmp($line, $str2) == 0)

            echo "<A HREF=".$path.">".gethostbyaddr($pathhost)."</a><br>\n";

       fclose($fp);

    }

?>

    One important observation, this process is very simple, but it is very inefficient, since for every IP you check you will wait a maximum of 2 seconds. So, don't abuse this script, because you will probably get a time out operation from your web server, or you will be stuck waiting for all the iterations for a long time.

    But still, it is a good example of what you as a home user can do with php3.

    Next month, I will write yet another example of php3 program, this time I will show you how to create your own guest book, using php3 and mySQL.