You make a few big errors in your client. 1. a different socket number from server. 2. No gtk2 main loop in client so it exits immediately. 3. No callback for the Gtk2->Helper to watch the socket. 4. Need to return 1 from Helper to keep it in play.

Try this, it works on linux.

#server
#!/usr/bin/perl
use warnings;
use strict;
use IO::Socket;

use Gtk2 -init;
use Glib qw/TRUE FALSE/;

my $main_window = Gtk2::Window->new("toplevel");
$main_window->signal_connect(delete_event => sub{Gtk2->main_quit});

my $buffer = Gtk2::TextBuffer->new;
my $table = Gtk2::Table->new(3, 2, FALSE);
my $label = Gtk2::Label->new("Chat Client Test");
my $textview = Gtk2::TextView->new_with_buffer($buffer);
my $swindow = Gtk2::ScrolledWindow->new( undef, undef);
$swindow->set_size_request (100, 150);
my $button = Gtk2::Button->new("Send");
my $entry = Gtk2::Entry->new();    
$textview->set_cursor_visible (FALSE);
$textview->set_editable(FALSE);
$buffer->create_mark ('end', $buffer->get_end_iter, FALSE);

$buffer->signal_connect (insert_text => sub {$textview->scroll_to_mark
+ ($buffer->get_mark ('end'),0.0, TRUE, 0, 0.5)});

$swindow->set_policy( 'automatic', 'automatic');
$swindow->set_shadow_type( 'etched-out');
    
$swindow->add( $textview);
    
$table->attach_defaults($label, 0, 1, 0, 1);
$table->attach_defaults($swindow, 0, 2, 1, 2);
$table->attach_defaults($entry, 0, 1, 2, 3);
$table->attach_defaults($button, 1, 2, 2, 3);
$main_window->add($table);

$main_window->show_all();
    


$button->signal_connect("clicked" =>sub {
  #get the contents of the entry
  my $msg_send = $entry->get_text;
  #clear the entry
  $entry->set_text("");
  #grab focus again for the next round of talks
  $entry->grab_focus;
  #if there was bogus input, ignore it!
  if ($msg_send !~ m/^\s*$/){
    #open up a UDP client connection
    my $SEND_PORT     = 5152;
        my $server_host = "localhost";
        my $sock = IO::Socket::INET->new(Proto => 'udp', PeerPort  => 
+$SEND_PORT, PeerAddr  => $server_host) or die "Creating socket: $!\n"
+;
    #send the message out on the socket
    $sock->send($msg_send."\n") or die "send: $!";
    #update the screen locally
    #&update_buffer($buffer,$msg_send,TRUE);    
            }
        });


Gtk2->main;
[download]

and the client

#!/usr/bin/perl -w

use strict;
use IO::Socket;

use Gtk2 -init;
use Glib qw/TRUE FALSE/;
use Gtk2::Helper;
 
 my($sock,$MAXLEN, 
 $LISTEN_PORT, $SEND_PORT,
 $tag,
 $tag_send,
 $tag_receive,$img_big,$img_send,$img_rec);

 $MAXLEN = 1024;
 $LISTEN_PORT     = 5152;
 
my $tview;

 #set up a udp server waiting for incomming messages
 $sock = IO::Socket::INET->new(LocalPort => $LISTEN_PORT, Proto => 'ud
+p')
 or die "socket: $@";
  
 #add a Gtk2::Helper watch on any incomming connections
 print "Awaiting UDP messages on port $LISTEN_PORT\n";

$tag = Gtk2::Helper->add_watch ( fileno($sock), 'in', sub {
     if (eof($sock)) {
        Gtk2::Helper->remove_watch ($tag);
        close($sock);
}
else {
   my $line = <$sock>;
   #$buffer->insert($buffer->get_end_iter,$line);
   print "$line";
}

return 1;
});

Gtk2->main;
[download]

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