Lesson 12	Clearing cookies
Objective	Identify the steps involved in clearing a cookie

Clearing Cookies in Perl

In order to clear a cookie, you simply expire it. In Netscape cookies, that means setting the Expires date to a date in the past:

Set cookie: UserID=007; Expires=Mon, 01-Jan-1990 00:00:00 GMT

In RFC-2109 cookies, you set the Max-Age value to zero:

Set cookie: UserID=007; Max-Age=0; Version=1

This does not work in the current beta of Netscape 4. As of this writing, RFC-2109 is still being debated by the members of the Internet Engineering Task Force, HTTP Working Group. For that reason, all the examples in this module use the Netscape cookies which are supported by a large number of browsers currently available.

Simple Perl Cookie example

This Perl code can be used to clear cookies by setting the `expires` attribute of the cookie to a date in the past, which tells the browser to delete the cookie. The following code is functional but could benefit from both simplification and modernization. Here's a breakdown of areas that can be improved:

Simplification:
- Global Variables: Perl allows using lexical variables (my) instead of global variables, which is a better practice for avoiding unwanted side effects.
- Removing `CRLF`: Instead of manually defining CRLF, you can use \n, which is more readable.
- Hardcoding Date: A hardcoded expiration date for cookies can be made more flexible by using Perlâs date handling modules.
- `each` Loop: The each loop can be avoided by using more modern techniques for hash iteration.
Modernization:
- Use of `strict` and `warnings`: It's common practice to include these pragmas in modern Perl to catch common mistakes and encourage better coding habits.
- CGI Module: Perlâs CGI module can handle query strings and cookies more elegantly. This avoids manually parsing the query string and cookie headers.
- Lexical Filehandles: Modern Perl uses lexical filehandles (i.e., open my $fh) instead of global filehandles.
- Template::Toolkit or Other Templating Modules: Instead of embedding Perl code directly into HTML, you could use templating engines to separate concerns better.

Revised Code with Improvements:

#!/usr/bin/perl
use strict;
use warnings;
use CGI;
use CGI::Cookie;

# Create a new CGI object
my $cgi = CGI->new;

# Get server information
my $servername = $cgi->server_name();
my $scriptname = $cgi->script_name();
my $callback = "http://$servername$scriptname";

# Expired date for clearing cookies
my $expdate = "Mon, 01-Jan-1990 00:00:00 GMT";

# Get query parameters
my %query = $cgi->Vars();
my $state = $query{'state'} // 'first';  # Default to 'first' state

# Parse cookies
my %cookies = CGI::Cookie->fetch;
my $cookie_value = $cookies{'cookie_name'} ? $cookies{'cookie_name'}->value : undef;

# Print HTTP header
print $cgi->header(-type => 'text/html');

# Main logic
if ($state eq 'first') {
    first();
} elsif ($state eq 'setcookie') {
    setcookie();
} else {
    unknown();
}

exit;

# STATE SCREENS
sub first {
    print $cgi->start_html("First State");
    print "You are in the first state. Current cookie: " . ($cookie_value // 'No cookie') . "";
    print $cgi->end_html;
}

sub setcookie {
    if ($cgi->param('cookie') && $cgi->param('value')) {
        my $cookie = CGI::Cookie->new(
            -name    => 'cookie_name',
            -value   => $cgi->param('value'),
            -expires => '+1h'  # Set cookie to expire in 1 hour
        );
        print $cgi->header(-cookie => $cookie);
        print "Cookie set with value: " . $cgi->param('value') . "";
    } else {
        print "Cookie not set";
    }
}

sub unknown {
    print $cgi->start_html("Unknown State");
    print "Unknown state encountered.";
    print $cgi->end_html;
}

Key Changes:

Use of `CGI` module: This module simplifies the handling of query parameters, headers, and cookies. It removes the need to manually parse query strings and cookies.
Lexical variables: Replaced global variables with lexical (my) variables to avoid unintended global scope.
Simplified cookie handling: Using CGI::Cookie makes setting and clearing cookies easier and more readable.
Better filehandle usage: Replaced old-style filehandles with modern lexical filehandles.
Removed hardcoded headers: The CGI->header method handles headers more robustly.

This version is more maintainable, readable, and secure, while making use of modern Perl practices.

ClearPerl - Cookie - Exercise