#!/usr/bin/perl -w

package IO::Socket::INET::Interceptor;

use base qw(IO::Socket::INET);


sub write
{
    my ($self, $buf, $len, $offset) = @_;
    $buf =~ s/cats/dogs/g;
    $self->SUPER::write($buf, $len, $offset);
}

package main;

my $sock = IO::Socket::INET::Interceptor->new("localhost:80") or die $!;

$sock->write("GET /cats/cats/cats.html HTTP/1.0\r\n\r\n");
print <$sock>;