use strict;
use Socket;
#use FileHandle;

my $ICMP_PORT = 0;  #ICMP, no port !
my $ICMP_FLAGS = 0; #No special flag
my $ICMP_SUBCODE = 0; 
my $SEQ = 1; #cuz we're going to send single packet
my $pid = $$ & 0xffff; #get the PID
my $checksum = 0; #starter

if(!defined $ARGV[0] || !defined $ARGV[1] || !defined $ARGV[2]) { usage(); }

my $ip = inet_aton($ARGV[0]);
length($ip) or die "$ARGV[0] is not valid or $ARGV[0] is Unreachable\n";

my $time_out = 10;

if(defined $ARGV[3] && defined $ARGV[4]) {
  die "Unknown options $ARGV[3] - You should try with -t \n" if ($ARGV[3] ne "-t") ;
  $time_out = $ARGV[4];
  }
  
socket(SOCK,PF_INET,SOCK_RAW,getprotobyname('icmp')) || die "Can not create socket $! \n";
my $saddr = sockaddr_in($ICMP_PORT,$ip);

if(defined $ARGV[1]) {
  if($ARGV[2] eq 'ec') { 
    print "send icmp echo request \n"; 
    ping_icmp_echo_req();
    }
  elsif($ARGV[2] eq 'ts') { 
    print "send timestamp request \n";
    ping_icmp_timestamp_req();
  }
  elsif($ARGV[2] eq 'in') {
    print "send information request \n";
    ping_icmp_information_req();
  }
  elsif($ARGV[2] eq 'am') {
    print "send address mask request \n";
    ping_icmp_addressmask_req();
  }
  else {
     print "unknown request type \n";
     kill_sock();
     exit(1); 
    }
  }
else { usage(); kill_sock(); }

sub ping_icmp_echo_req {
  my $msg =  pack("C2 n3",8,0,$checksum,$pid,$SEQ);
  #someone said i must pack the minimum of icmp packet 
  #with this -> "C2 S3", but it's work with "C2" n3", 
  #what do you think ?
  $checksum = checksum($msg);
  $msg = pack("C2 n3",8,0,$checksum,$pid,$SEQ);
  send(SOCK,$msg,$ICMP_FLAGS,$saddr) || die "error sending : $! \n";
  #$socket->autoflush(1); 
  #im not sure to add this line to this code, any advices ? 

  my $buff = timing();
  my($icmp_type, $icmp_subcode,$icmp_cksum,$icmp_pid,$icmp_seq) = unpack("C2 n3",substr($buff,20,8));
  alive($icmp_type);
  kill_sock();
}

sub ping_icmp_timestamp_req {
  my $msg = pack("C2 n3 N3",13,$ICMP_SUBCODE,$checksum,$pid,$SEQ,0,0,0);
  $checksum = checksum($msg);  
  $msg = pack("C2 n3 N3",13,$ICMP_SUBCODE,$checksum,$pid,$SEQ,0,0,0);
  send(SOCK,$msg,$ICMP_FLAGS,$saddr);
  #SOCK->autoflush(1); #hmmm ?
  
  my $buff = timing();
 my($icmp_type,$icmp_subcode) = unpack("C2",substr($buff,20,2)) ;
  alive($icmp_type);
  kill_sock();
}

sub ping_icmp_information_req {
  my $ICMP_STRUCT_INFORM = "C2 n3 N"; 
  my $ICMP_INFORM_REQ = 15;
  my $ICMP_INFORM_REPLY = 16; #echo req code
  my $msg = pack("C2 n3 N",15,$ICMP_SUBCODE,$checksum,$pid,$SEQ,0);
  $checksum = checksum($msg);
  $msg = pack("C2 n3 N",15,$ICMP_SUBCODE,$checksum,$pid,$SEQ,0);
  send(SOCK,$msg,$ICMP_FLAGS,$saddr) || die "error sending : $! \n";
  #$socket->autoflush(1); #im not sure to add this line to this code, any advices ? 

  my $buff= timing();
  my($icmp_type, $icmp_subcode) = unpack("C2",substr($buff,20,2));
  kill_sock();
}

sub ping_icmp_addressmask_req {
  my $msg = pack("C2 n3 N",17,$ICMP_SUBCODE,$checksum,$pid,$SEQ,0);
  $checksum = checksum($msg);
  $msg = pack("C2 n3 N",17,$ICMP_SUBCODE,$checksum,$pid,$SEQ,0);
  send(SOCK,$msg,$ICMP_FLAGS,$saddr) || die "error sending : $! \n";
  #$socket->autoflush(1);  

  my $buff = timing();
  my($icmp_type, $icmp_subcode) = unpack("C2 n3 N",substr($buff,20,2));
  alive($icmp_type);
  kill_sock();
}


sub alive {
  my ($type) = @_;
  # 0 = icmp echo reply, 
  # 14 = icmp timestamp reply
  # 16 = icmp infoemation reply
  # 18 = icmp address mask reply
  if($type == 0) { print "Received ICMP echo reply from $ARGV[0], alive ! \n" }
  elsif($type == 14) { print "Received ICMP timestamp reply from $ARGV[0], alive ! \n" }
  elsif($type == 16) { print "Received ICMP information reply from $ARGV[0], alive ! \n"}
  elsif($type == 18) { print "Received ICMP address mask reply from $ARGV[0], alive ! \n"}
  else { print "I never expect to received this kind of ICMP reply, Uknown type ! \n"
    } 
  }

sub kill_sock { 
  close(SOCK) || warn "Can not close socket $! \n";
}

sub timing {
  my $buff="";
  print "time out set to $time_out\n";
  $SIG{ALRM} = sub { die "TIMED OUT \n" };
  eval {
    alarm($time_out);
    recv(SOCK,$buff,1500,$ICMP_FLAGS);
    alarm(0);
  };
  kill_sock() if (length($buff) == 0);
  die "timed out \n" if (length($buff) == 0);
  return $buff;
}

sub checksum  {
  my ($msg) = @_;
  my ($len_msg, $num_short, $short, $chk);
  $len_msg = length($msg);
  $num_short = int($len_msg / 2);
  $chk = 0;
  foreach $short (unpack("n$num_short", $msg)){
    $chk += $short;
  } 
  $chk += (unpack("C", substr($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
}

sub usage {
  print "Usage $0 : <host ip> -c <request type[ec/ts/in/am]> -t <timeout>\n";
  exit(1);
  }