Simple debugging HTTP proxy in Perl

proxy.pl

#!/usr/bin/env perl

use Modern::Perl;
use HTTP::Proxy;
use HTTP::Proxy::HeaderFilter::simple;

my $proxy = HTTP::Proxy->new(host => undef, port => 3128);
my $filter = HTTP::Proxy::HeaderFilter::simple->new(sub
{
    my ($self, $headers, $message) = @_;
    my $is_response = (ref $message) =~ /Response/;
    my $leader = $is_response ? '<' : '>';
    print $leader x 80, "\n";
    print $message->as_string;
});

$proxy->push_filter(request => $filter, response => $filter);
$proxy->start;