#!/usr/bin/perl

use IPC::Open2;
use IO::Socket;

my $server = IO::Socket::INET->new(
        LocalPort => 8000,
        Listen => 1,
        Reuse => 1,
        Proto => 'tcp'
) or die $@;
my $client = $server->accept;

my ($output, $input);
my $pid = open2($output, $input, '/usr/bin/bc');

my $length = 80;

my $readable;
vec($readable, fileno($output), 1) = 1;
vec($readable, fileno($client), 1) = 1;
while (select($readable, undef, undef, undef)) {
        if (vec($readable, fileno($output), 1)) {
                my $data;
                sysread $output, $data, $length;                # Read output from program
                syswrite $client, $data;                        # Forward to client
                print 'PROGRAM:', "\t", $data;
        }

        if (vec($readable, fileno($client), 1)) {
                my $data;
                sysread $client, $data, $length;                # Read input from client
                syswrite $input, $data;                         # Forward to program
                print 'CLIENT:', "\t", $data;
        }

        unless ($server and $client and $input and $output) {
                close $_ for $input, $output, $client, $server; # Exit if program handles closed
                waitpid $pid, 0;
                exit;
        }
}