#! /usr/bin/perl
use IO::Socket::INET;
use Time::HiRes qw(gettimeofday sleep);
use Getopt::Long;
Getopt::Long::Configure("bundling");
Getopt::Long::Configure("pass_through");

$::USAGE = "Usage: detect_dhcpd -i interface [-m macaddress] [-t timeout] [-V]

This command can be used to detect the dhcp server in a network for a specific mac address.

Options:
    -i interface:  The interface which facing the target network.
    -m macaddress: The mac that will be used to detect dhcp server. Recommend to use the real mac of the node that will be netboot. If no specified, the mac of interface which specified by -i will be used.
    -t timeout:    The time to wait to detect the dhcp messages. The default value is 10s.

Author:  Wang, Xiao Peng\n";
if (!GetOptions(
    'i=s'       => \$::IF,
    'm=s'       => \$::MACADD,
    't=s'       => \$::TIMEOUT,
    'V|verbose' => \$::VERBOSE,
    'h|help' => \$::HELP,)) {
  print $::USAGE;
  exit 1;
}

if ($::HELP) { print $::USAGE; exit 0; }

my $nic;
if ($::IF) {
  $nic = $::IF;
} else {
   print $::USAGE;
   exit 1;
}

my $start = Time::HiRes::gettimeofday();
$start =~ s/(\d.*)\.(\d.*)/$1/;

if (!$nic) { print "specify a nic\n"; print $::USAGE;  exit 1;}
my $IP = `ifconfig $nic | grep "inet addr" | awk '{print \$2}' | awk -F: '{print \$2}'`;
my $MAC;
if ($::MACADD) {
  $MAC = $::MACADD;
} else {
  $MAC = `ifconfig $nic | grep "HWaddr" | /usr/bin/awk '{print \$5}'`;
}

chomp($IP);
chomp($MAC);

if ($::VERBOSE) {
  print "Send out dhcp discover from: NIC = $nic, IP = $IP, MAC = $MAC\n";
}
if (!$IP || !$MAC) { print "Cannot find IP/MAC\n"; exit 1;}


# check the distro
my $os;
if (-f "/etc/redhat-release") {
  $os = "rh";
} elsif (-f "/etc/SuSE-release") {
  $os = "sles";
} else {
  print "Only support the redhat and sles OS.\n";
  exit 1;
}
# fork a process to capture the packet by tcpdump
my $pid = fork;
if (!defined $pid) { print "Fork failed.\n"; exit 1;}
my $dumpfile = "/tmp/dhcpdumpfile.log";
if ($pid == 0) {
  # Child process 
  my $cmd = "tcpdump -i $IF port 68 -n -vvvvvv > $dumpfile 2>/dev/null";
  `$cmd`;
  exit 0;
}

# generate the discover package
my $package = packdhcppkg($MAC);

# send out the package
my $sock = IO::Socket::INET->new(Proto => 'udp',
  Broadcast => 1,
  #ReusePort => 1,
  PeerPort => '67',
  #LocalAddr => 0,
  LocalAddr => $IP,
  LocalPort => '68',
  PeerAddr => inet_ntoa(INADDR_BROADCAST));

unless ($sock) {
  print "Create socket error: $@\n";
  kill_child();
  exit 1;
}

my $timeout = 10;
if ($::TIMEOUT) {
  $timeout = $::TIMEOUT;
}

my $end  = Time::HiRes::gettimeofday();
$end =~ s/(\d.*)\.(\d.*)/$1/;
while ($end - $start <= $timeout) {
  $sock->send($package) or die "Send discover error: $@\n";
  sleep 2;
  $end  = Time::HiRes::gettimeofday();
  $end =~ s/(\d.*)\.(\d.*)/$1/;
}


kill_child();
#kill the child process
kill 15, $pid;
my @pidoftcpdump = `ps -ef | grep -E "[0-9]+:[0-9]+:[0-9]+ tcpdump -i $IF" | awk -F' ' '{print \$2}'`;
foreach my $cpid (@pidoftcpdump) {
  kill 15, $cpid;
#  print "try to kill $cpid\n";
}

sleep 2;
open (FILE, "<$dumpfile") or die "Cannot open $dumpfile\n";
my %output;
my @snack = ();
my @siaddr = ();
my $newsection = 0;
my $offer = 0;
$chaddr = ();
$ciaddr = ();
$siaddr = ();
while (<FILE>) {
  $line = $_;

  if ($line =~ /^\d\d:\d\d:\d\d/) {
    # A new packet was captured. Parse the last one.
    if ($::VERBOSE) {
      print "The server I found: mac = $chaddr, clientip = $ciaddr, serverip = $siaddr, offer = $offer.\n";
    }
    if ($os == "sles") { $offer = 1;}
    if ($chaddr =~ /$MAC/i && $offer && $ciaddr && $siaddr && $rsiaddr) {
      $output{$rsiaddr}{'client'} = $ciaddr;
      $output{$rsiaddr}{'nextsv'} = $siaddr;
    } elsif ($nack && $siaddr && !grep(/^$siaddr$/, @snack)) {
      push @snack, $siaddr;
    } elsif ($siaddr && ! grep(/^$siaddr$/,@server)) {
      push @server, $siaddr;
    }
    $offer = 0;
    $nack = 0;
    $chaddr = ();
    $ciaddr = ();
    $siaddr = ();
    $rsiaddr = (); # the server which responsing the dhcp request
  } 
  if ($line =~ /(\d+\.\d+\.\d+\.\d+)\.[\d\w]+ > \d+\./) {
    $rsiaddr = $1;
  }
  if ($line =~ /\s*DHCP-Message.*: Offer/) {
    $offer = 1;
  } elsif ($line =~ /\s*DHCP-Message.*: NACK/) {
    $nack = 1;
  } 
  if ($line =~ /\s*Client-Ethernet-Address (..:..:..:..:..:..)/) {
    $chaddr = $1;
  }
  if ($line =~/\s*Your-IP (\d+\.\d+\.\d+.\d+)/) {
    $ciaddr = $1;
  }
  if ($line =~/\s*Server-IP (\d+\.\d+\.\d+.\d+)/) {
    $siaddr = $1;
  }
}

close(FILE);

my $sn = scalar(keys %output);
print "\n++++++++++++++++++++++++++++++++++\n";
print "There are $sn servers reply the dhcp discover.\n";
foreach my $server (keys %output) {
  print "    Server:$server assign IP [$output{$server}{'client'}] to you. The next server is [$output{$server}{'nextsv'}]!\n"; 
}
print "++++++++++++++++++++++++++++++++++\n\n";

if (scalar(@snack)) {
  print "===================================\n";
  print "The dhcp servers which sending out NACK in present network:\n";
  foreach my $nack (@snack) {
    print "    $nack\n";
  }
}

if (scalar(@server)) {
  print "===================================\n";
  print "The dhcp servers in present network:\n";
  foreach my $s (@server) {
    print "    $s\n";
  }
}

#`rm -f $dumpfile`;
exit 0;


sub packdhcppkg{
  my $mymac = shift;
  my $package;

  # add the operation type. 1 - request
  $package .= pack("C*",1);

  # add the hardware type. 1 - ethernet
  $package .= pack("C*",1);

  # add the length of hardware add
  $package .= pack("C*",6);

  # add the hops
  $package .= pack("C*",0);

  # add the transaction id
  $package .= pack("C*",60,61,62,63);

  # add the elapsed time
  $package .= pack("C*",0,0);

  # add the flag 00 - broadcast
  $package .= pack("C*",128,0);

  # add the IP of client
  $package .= pack("C*",0,0,0,0);

  # add the your IP
  $package .= pack("C*",0,0,0,0);

  # add the next server IP
  $package .= pack("C*",0,0,0,0);

  # add the relay agent IP
  $package .= pack("C*",0,0,0,0);

  # add the mac address of the client
  my @macval;
  if ($mymac) {
    my @strmac = split(/:/, $mymac);
    foreach (@strmac) {
      push @macval, hex($_);
    }
    $package .= pack("C*",@macval);
  } else {
    @macval = ('0','0','50','51','52','53');
    $package .= pack("C*",@macval);
  }

  # add 10 padding for mac
  my @macpad;
  foreach (1..10) {
    push @macpad, "0";
  }
  $package .= pack("C*",@macpad);

  # add the hostname of server
  my @hs;
  foreach (1..64) {
    push @hs, "0";
  }
  $package .= pack("C*",@hs);

  # add the file name
  my @fn;
  foreach (1..128) {
    push @fn, "0";
  }
  $package .= pack("C*",@fn);

  # add the magic cookie
  $package .= pack("C*",99,130,83,99);

  # add the dhcp message type. The last num: 1 - dhcp discover
  $package .= pack("C*",53,1,1);

  # add the client identifier
  $package .= pack("C*",61,7,1); #type, length, hwtype
  $package .= pack("C*",@macval);

  # add the parameter request list
  $package .= pack("C*",55,10); #type, length
  $package .= pack("C*",1,3,6,12,15,28,40,41,42,119);

  # add the end option
  $package .= pack("C*",255);

  # pad the package to 300
  @strpack = unpack("W*",$package);
  my $curleng = length($strpack);

  my @padding;
  foreach (1..35){
    push @padding, '0';
  }

  $package .= pack("C*",@padding);

  return $package;
}

sub kill_child {
  kill 15, $pid;
  my @pidoftcpdump = `ps -ef | grep -E "[0-9]+:[0-9]+:[0-9]+ tcpdump -i $IF" | awk -F' ' '{print \$2}'`;
  foreach my $cpid (@pidoftcpdump) {
    kill 15, $cpid;
    #print "try to kill $cpid\n";
  }
}