#!/usr/athena/bin/perl # Filename: autopilot.pl # Set a variable to the file name of the file with the # list of URLs $filename = "/var/www/data/autopilot/urllist"; # Set a variable to the number of lines in the file. # Our file has 7250 lines in it. $num_lines = `cat /var/www/data/autopilot/count`; # Figure out the browser type for the client $client_type = $ENV{'HTTP_USER_AGENT'}; # Break the client type into the program name and the version # number. $client_type =~ /^([^\/]*)\/([\d\.]*)/; $client_program = $1; $client_version = $2; # Initialize the random seed (don't worry about this) srand; # Find a random variable between 0 and the number of lines in # the file. This will be the line of the file that we return. $which_line = int( rand( $num_lines ) ); # Open the file that has the list of URLs. Check to make sure it # opened properly. if (open (LIST, $filename)) { # The file opened fine. Now find the line corresponding to # $which_line. # In order to do this, set up a loop to read in $which_line # lines. while( $current_line = ) { $line_no++; if ($line_no == $which_line) { last; } } if ($line_no < $which_line) { &return_error(); } # Once we get to the end, close the file. close(LIST); if($ENV{'QUERY_STRING'} =~ /(\d+)/){ $n = $1; } else { $n = 10; } # $current_line should now contain the last line read. # If the client is Netscape 1.1 or higher, tell the client # to make the request every 10 seconds. print("HTTP/1.0 302 Go here\n"); print("Refresh: $n; URL=http://stuff.mit.edu/cgi/autopilot?$n\n"); # Regardless of the browser type being used, return a # redirection print ("Location: $current_line"); # Send the blank line to end the response. print "\n"; exit; } &return_error(); sub return_error { # If there was an error, return an error status code. print "Status: 500 Internal Server Error\n"; # Return a Content Type along with the error. print "Content-Type: text/html\n"; # Print the blank line to end the response; print "\n"; # Print an error message print "\n"; print "\n"; print "Autopilot Error\n"; print "\n"; print "\n"; print "

Autopilot was unable to retrieve a URL to return.

\n"; print "\n"; print "\n"; } exit;