######################  UDP Datagram Socket Demo  #######################
#!/usr/bin/perl -w

#  This is the client!!
use IO::Socket;      
use constant MAXBYTES => scalar 80;

$socket = IO::Socket::INET->new( PeerPort  => 3711,
                                 PeerAddr  => "challenger.atc.fhda.edu",
                                 Type      => SOCK_DGRAM,
                                 Proto     => 'udp')
             or
die "Could not open socket!\n";


while (1)
{
      print "Want the time (y/n)?  ";
      $line = <STDIN>;
      if ($line !~ /^\s*(y(es)?|no?)\s*$/i)
      {
            print "Illegal response!  Try again!\n";
            next;
      }
      last if $line =~ /^\s*no?\s*$/i;

#  Wake up the server by satisfying the recv on its end.
      $socket->send("junk") or die "Client send: $!\n"; 

#  We want the receive to die if we don't get the time within 5 seconds.
#  It illustrates how to make one request attempt die without killing the
#  entire client.  Most useful in a UDP client.
      eval
      {
           local $SIG{ALRM} = sub {die "No response from server!\n"};
           alarm 5;
           $socket->recv($inline, MAXBYTES);
           print "Got \"$inline\" from server!\n";
           alarm 0;
           1;    #  Value for eval code block on normal exit.
      }
}

#  Note:  A die statement in an eval makes the eval block die, *not* the
#         entire client.


#   This is the server!!
#!/usr/bin/perl -w

use IO::Socket;      
use constant MAXBYTES => scalar 80;

$socket = IO::Socket::INET->new(LocalPort => 3711,
                                Type      => SOCK_DGRAM,
                                Proto     => 'udp')
             or
die "Could not open socket!\n";
#  Notice that there are no processes created and no signals handled!
#  UDP is a *much* easier protocol which is used to supply quick, short
#  services.  It is not as reliable as TCP.  However, since it is a
#  connectionless protocol, there is no need to trap SIGPIPE.  Since
#  there are no processes, there's no need to trap delinquent clients 
#  with SIGALRM and no need for zombie clearance with SIGCHLD. 
  
while (1)
{
      eval{
              $socket->recv($data, MAXBYTES) or die "Server recv: $!\n";
              1; 
      };

      next if $@;   #  If eval error variable set, skip the send.
      chomp($data = localtime); 

      eval{
              $socket->send($data) or die "Server send: $!\n";
              1;
      }
}
##############################  UDP Sessions Below  ###########################

$ userv.pl&
[1]     22952

$ uclient.pl
Want the time (y/n)?    dfdfdf
Illegal response!  Try again!
Want the time (y/n)?  
Illegal response!  Try again!
Want the time (y/n)?    yES
Got "Mon Aug 30 18:44:08 1999" from server!
Want the time (y/n)?   y
Got "Mon Aug 30 18:44:10 1999" from server!
Want the time (y/n)?  noe
Illegal response!  Try again!
Want the time (y/n)?  nO

$ uclient.pl
Want the time (y/n)?   y
Got "Mon Aug 30 18:44:43 1999" from server!
Want the time (y/n)?  n
$