use strict;
use warnings;

use FileHandle;
use Socket qw( SOCK_DGRAM SOCK_STREAM SOCK_RAW PF_INET SOL_SOCKET SO_ERROR inet_aton inet_ntoa sockaddr_in );;

use Data::Dumper;

use constant ICMP_PROTO      => 1;
use constant ICMP_STRUCT     => "C2 n3 C4";  # icmp address-mask request packet format
use constant ICMP_TYPE       => 17;             # icmp address-mask request type
use constant ICMP_IDENT      => $$ & 0xffff; # icmp identity field (build from current pid and stripped to lower 16 bits)
use constant ICMP_MASK_REPLY => 18;          # icmp address-mask reply type (answer is not checked against by now)
use constant ICMP_CODE       => 0;           # icmp code field (should be set to 0)
use constant ICMP_PORT       => 0;           # port to use with icmp
use constant ICMP_FLAGS      => 0;           # icmp flags

my $FH = FileHandle->new(); # create FileHandle to use with socket
socket($FH, PF_INET, SOCK_RAW, ICMP_PROTO) || croak ("icmp socket error - $!"); # open socket

my $host = shift;
my $timeout = shift;
print get_network_mask($host);

# code below is based on code from package Perl.pm
sub get_network_mask {
    my $ip = inet_aton(shift); # trx dest address
    my ($seq,           # packet sequence number    
        $checksum,         # packet checksum
        $msg,              # trx message
        $msg_len,          # trx message length
        $saddr,            # trx socket address
      $from_ip,        # rcv src ip address
      $from_type,      # rcv icmp packet type field (to match request it must be set to 18)
      $from_code,      # rcv icmp packet code field (must be set to 0)
      $from_addr_msk,  # rcv icmp packet mask field (contains the requested address mask)
      $from_saddr,     # rcv socket address
      $from_port,      # rcv socket port
      $from_id,        # rcv icmp packet identity field (should contain the same value as set for ICMP_IDENT)
      $from_seq,       # rcv icmp packet sequence flied (should contain the same value as set for $seq
      $from_crc,       # rcv icmp packet checksum (could be tested to ensure message integrity)
      $recv_msg,       # rcv message
      $finish_time,    # var to measure the timeout
      $done,           # var telling that packet rcvd or timout reached
      $nfound,         # for timing issues
      $rbits           # bits send over socket
      );
  $seq = 0;
  $seq = ($seq + 256) % 65536;
  $checksum = 0;
  $msg = pack(ICMP_STRUCT, ICMP_TYPE, ICMP_CODE, $checksum, ICMP_IDENT, $seq, 0x0, 0x0, 0x0, 0x0);
  $checksum = checksum($msg);
  $msg = pack(ICMP_STRUCT, ICMP_TYPE, ICMP_CODE, $checksum, ICMP_IDENT, $seq, 0x0, 0x0, 0x0, 0x0);
  $msg_len = length($msg);
  $saddr = sockaddr_in(ICMP_PORT, $ip);
  send($FH, $msg, ICMP_FLAGS, $saddr);
  $rbits = "";
  vec($rbits, $FH->fileno(), 1) = 1;
  $done = $from_ip = $from_type = $from_code = $from_addr_msk = $from_id = 0;
  $finish_time = time() + $timeout;
  while(!$done && $timeout > 0) {
    $nfound = mselect((my $rout=$rbits), undef, undef, $timeout); # Wait for packet
    $timeout = $finish_time - time();    # Get remaining time
    if (!defined($nfound)) {             # Hmm, a strange error
      $from_addr_msk = undef;
      $done = 1;
    }
    elsif ($nfound) {                    # Got a packet from somewhere
      $recv_msg = "";
      $from_saddr = recv($FH, $recv_msg, 1500, ICMP_FLAGS);
      ($from_port, $from_ip) = sockaddr_in($from_saddr);
      print "IP". Dumper inet_ntoa $from_ip;
      ($from_type, $from_code, $from_crc, $from_id, $from_seq) = unpack("C2 n3", substr $recv_msg, 20, 8);
      $from_addr_msk = join ".", unpack("C4", substr $recv_msg, 28, 4);
      $done = 1;
    } 
    else {     # Oops, timed out
      $done = 1;
      $from_addr_msk = undef;
    }
  }
  return $from_addr_msk;
}

# Below this line code is taken from package Ping.pm
sub checksum {
  my $msg = shift;
  my ($len_msg,       # Length of the message
      $num_short,     # The number of short words in the message
      $short,         # One short word
      $chk            # The checksum
      );
  $len_msg = length($msg);
  $num_short = int($len_msg / 2);
  $chk = 0;
  foreach $short (unpack("n$num_short", $msg)) {
    $chk += $short;
  }                                           # Add the odd byte in
  $chk += (unpack("C", substr($msg, $len_msg - 1, 1)) << 8) if $len_msg % 2;
  $chk = ($chk >> 16) + ($chk & 0xffff);      # Fold high into low
  return(~(($chk >> 16) + $chk) & 0xffff);    # Again and complement
}

# Description: A select() wrapper that compensates for platform
# peculiarities.
sub mselect {
  if ($_[3] > 0 and $^O eq 'MSWin32') {
  # On windows, select() doesn't process the message loop,
  # but sleep() will, allowing alarm() to interrupt the latter.
  # So we chop up the timeout into smaller pieces and interleave
  # select() and sleep() calls.
  my $t = $_[3];
  my $gran = 0.5;  # polling granularity in seconds
  my @args = @_;
  while (1) {
      $gran = $t if $gran > $t;
      my $nfound = select($_[0], $_[1], $_[2], $gran);
      $t -= $gran;
    return $nfound if $nfound or !defined($nfound) or $t <= 0;
      sleep(0);
      ($_[0], $_[1], $_[2]) = @args;
    }
  }
  else {
    return select($_[0], $_[1], $_[2], $_[3]);
  }
}