Practical mod_perl, from O'Reilly.

Transition from mod_cgi Scripts to Apache Handlers

If you don't need to preserve backward compatibility with mod_cgi, you can port mod_cgi scripts to use mod_perl-specific APIs. This allows you to benefit from features not available under mod_cgi and gives you better performance for the features available under both. We have already seen how easily Apache::Registry turns scripts into handlers before they get executed. The transition to handlers is straightforward in most cases.

Let's see a transition example. We will start with a mod_cgi-compatible script running under Apache::Registry, transpose it into a Perl content handler without using any mod_perl-specific modules, and then convert it to use the Apache::Request and Apache::Cookie modules that are available only in the mod_perl environment.

Starting with a mod_cgi-Compatible Script

Example 6-18 shows the original script's code.

Example 6-18: cookie_script.pl

use strict; use CGI; use CGI::Cookie; use vars qw($q $switch $status $sessionID); init( ); print_header( ); print_status( ); sub init { $q = new CGI; $switch = $q->param("switch") ? 1 : 0; my %cookies = CGI::Cookie->fetch; $sessionID = exists $cookies{'sessionID'} ? $cookies{'sessionID'}->value : ''; # 0 = not running, 1 = running $status = $sessionID ? 1 : 0; # switch status if asked to $status = !$status if $switch; if ($status) { # preserve sessionID if it exists or create a new one $sessionID ||= generate_sessionID( ) if $status; } else { # delete the sessionID $sessionID = ''; } } sub print_header { my $c = CGI::Cookie->new( -name => 'sessionID', -value => $sessionID, -expires => '+1h' ); print $q->header( -type => 'text/html', -cookie => $c ); } # print the current Session status and a form to toggle the status sub print_status { print qq{<html><head><title>Cookie</title></head><body>}; print "<B>Status:</B> ", $status ? "Session is running with ID: $sessionID" : "No session is running"; # change status form my $button_label = $status ? "Stop" : "Start"; print qq{<hr> <form> <input type=submit name=switch value=" $button_label "> </form> }; print qq{</body></html>}; } # A dummy ID generator # Replace with a real session ID generator ######################## sub generate_sessionID { return scalar localtime; }

The code is very simple. It creates a session when you press the Start button and deletes it when you pressed the Stop button. The session is stored and retrieved using cookies.

We have split the code into three subroutines.

init( 
  )

initializes global variables and parses incoming data.

print_header( 
  )

prints the HTTP headers, including the cookie header. Finally,

print_status( 
  )

generates the output. Later, we will see that this logical separation will allow an easy conversion to Perl content-handler code.

We have used a few global variables, since we didn't want to pass them from function to function. In a big project, you should be very restrictive about what variables are allowed to be global, if any. In any case, the

init( 
  )

subroutine makes sure all these variables are reinitialized for each code reinvocation.

We have used a very simple

generate_sessionID( 
  )

function that returns a current date-time string (e.g., Wed Apr 12 15:02:23 2000) as a session ID. You'll want to replace this with code that generates a unique and unpredictable session ID each time it is called.