#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11125685
use warnings;
use Tk;
use IO::Socket;

my $listen = new IO::Socket::INET (
    LocalHost => '127.0.0.1',
    LocalPort => '23456',
    Proto => 'tcp',
    Listen => 5,
    Reuse => 1
) or die "cannot create listen socket $@\n";
warn "server waiting for client connection on port 23456 \n";

my $val = 0;
my $client;
my $mw = MainWindow->new();
my $label = $mw->Label( -width => 50, -textvariable => \$val,)->pack();

my $button;
$button = $mw->Button( -text => 'Stop input', -command => sub 
  {
  $button->configure(-state=>'disabled');
  close $client;
  close $listen;
  }, )->pack();

$mw->fileevent( $listen, 'readable', \&newcon );

MainLoop;

sub newcon
  {
  $client = $listen->accept;
  $mw->fileevent($client, 'readable', \&getdata );
  }

sub getdata
  {
  if( sysread $client, my $buf, 1024 )
    {
    warn "received data: $buf\n";
    $val = $buf =~ tr/\n//dr;
    $client->send('ok'); # write response data to the connected client
    shutdown($client, 1); # notify client that response has been sent
    }
  else { close $client; }
  }