#!/usr/bin/perl
use strict;
#
# Upon start, starts sending UDP messages to $dest_ip on $data_port
# The initial data packets are:
#         DATA1: 1234567890\n
#         DATA2: ABCDEFGHIJ\n
#         DATA3: abcdefghij\n

# Then checks port $cmd_port for any commands.
# If a command is received on $cmd_port, 
#      cmd = DIGITS ; DATA1 is replaced by "111111111111\n"
#                     DATA2 is replaced by "222222222222\n"
#                     DATA3 is replaced by "333333333333\n"
#      cmd = LETTERS; DATA1 is replaced by "AAAAAAAAAAAA\n"
#                     DATA2 is replaced by "BBBBBBBBBBBB\n"
#                     DATA3 is replaced by "CCCCCCCCCCCC\n"
#      cmd = DEFAULT; DATA1 is replaced by "1234567890\n"
#                     DATA2 is replaced by "ABCDEFGHIJ\n"
#                     DATA3 is replaced by "abcdefghij\n"
#      cmd = STOP;    Data broadcast is stopped
#      cmd = EXIT;    This program terminates
#      cmd = RESUME;  Previously stopped broadcast is resumed
#
#      any other value for cmd is ignored

#      Commands can be sent to this process by the program "cmd.pl"
#
# and loops forever

# Sent packets can ve verified by 
#         "tcpdump  dst port 7777"
# on remote host

my $dest_ip   = "139.179.10.6";
my $data_port = 7777;
my $cmd_port  = 7778;
#
use IO::Socket;
use IO::Select;

##use Socket;
my ($hostname, $sockaddr, $name, $aliases, $proto, $type, $len, $myaddr);
my ($broadaddr, $me, $them);

my @dest_addr = split(/\./, $dest_ip);
chop($hostname = `hostname`);

# prepare socket for outbound data transfer
$sockaddr = "S n a4 x8";
($name,$aliases,$proto) = getprotobyname('udp');
($name,$aliases,$type,$len,$myaddr) = gethostbyname($hostname);

my @my_ip = unpack("C4", $myaddr);
my $my_ip_addr  = join(".", @my_ip);
print "$my_ip_addr $hostname\n";

$broadaddr=pack("C4",@dest_addr);

$me   = pack($sockaddr,&AF_INET, 0,     $myaddr);
$them = pack($sockaddr,&AF_INET, $data_port, $broadaddr);
 
socket(S, &AF_INET, &SOCK_DGRAM, $proto) || die $!;
setsockopt(S,&SOL_SOCKET,&SO_BROADCAST,1) || die $1;
bind(S, $me) || die $!;

# prepare socket for inbound command transfer (if any)
# Use IO::Select to check if there is any data to read in the socket
# IO::Select (see cpan.org) provides a library for NON-BLOCKING I/O

my $s = new IO::Select;
my $ip1 = IO::Socket::INET->new(LocalPort => $cmd_port, Proto=>'udp',
                                LocalAddr => $my_ip_addr)
	        or die "error creating UDP server for $my_ip_addr  $@\n";

$s -> add($ip1);  # sockets to check for pending data

#
# default $data
my $default_data = " 1234567890 ABCDEFGHIJ abcdefghij\n",
my $letter_data = "AAAAAAAAAAA BBBBBBBBBBB CCCCCCCCCCC\n";
my $digit_data =  "11111111111 22222222222 33333333333\n";

my $data = $default_data;
my ($server, $remote_port, $remote_ipaddr, $cmd, $local_port, $local_ipaddr);
my @available_clients;
my $seq_no = 0;
my $actual_data;
my $stop_broadcast = 0;       # Broadcast on by default

while (1) {    # LOOP INDEFINITELY
  if ($stop_broadcast == 0) {

          $actual_data = "SeqNo: $seq_no-".$data;
          send(S,$actual_data,0,$them) || die $!;
          $seq_no++;
  
          sleep (1);
  }
  #
  # Check if any command has arrived
  @available_clients = $s -> can_read(0);  
  foreach $server ( @available_clients) {
	  $server -> recv($cmd, 1024);
	  # 
	  # You cna use the following functions to gather info on host that
	  # has sent the command

	  ##($remote_port, $remote_ipaddr) = sockaddr_in($server -> peername);
	  ##($local_port, $local_ipaddr) = sockaddr_in($server -> sockname);
	  $data = $letter_data if ($cmd =~ /^LETTERS/);
	  $data = $digit_data if ($cmd =~ /^DIGITS/);
	  $data = $default_data if ($cmd =~ /^DEFAULT/);

	  $stop_broadcast = 1 if ($cmd =~ /^STOP/);
	  $stop_broadcast = 0 if ($cmd =~ /^RESUME/);

	  exit if ($cmd =~ /^EXIT/);
  }
  # Give up some cycles if not in broadcast mode
  sleep (2) if ($stop_broadcast == 1); 
  
}