# very simple request, using lots of default values:
   { rd => 1, qd => [ [ "host.domain", "a"] ] }
  
   # more complex example, showing how flags etc. are named:
  
   {
      id => 10000,
      op => "query",
      rc => "nxdomain",
  
      # flags
      qr => 1,
      aa => 0,
      tc => 0,
      rd => 0,
      ra => 0,
      ad => 0,
      cd => 0,
  
      qd => [@rr], # query section
      an => [@rr], # answer section
      ns => [@rr], # authority section
      ar => [@rr], # additional records section
   }

=cut

sub dns_pack($) {
   my ($req) = @_;

   pack "nn nnnn a* a* a* a* a*",
      $req->{id},

      ! !$req->{qr}   * 0x8000
      + $opcode_id{$req->{op}} * 0x0800
      + ! !$req->{aa} * 0x0400
      + ! !$req->{tc} * 0x0200
      + ! !$req->{rd} * 0x0100
      + ! !$req->{ra} * 0x0080
      + ! !$req->{ad} * 0x0020
      + ! !$req->{cd} * 0x0010
      + $rcode_id{$req->{rc}} * 0x0001,

      scalar @{ $req->{qd} || [] },
      scalar @{ $req->{an} || [] },
      scalar @{ $req->{ns} || [] },
      $EDNS0 + scalar @{ $req->{ar} || [] }, # EDNS0 option included here

      (join "", map _enc_qd, @{ $req->{qd} || [] }),
      (join "", map _enc_rr, @{ $req->{an} || [] }),
      (join "", map _enc_rr, @{ $req->{ns} || [] }),
      (join "", map _enc_rr, @{ $req->{ar} || [] }),

      ($EDNS0 ? pack "C nnNn", 0, 41, MAX_PKT, 0, 0 : "") # EDNS0 option
}

our $ofs;
our $pkt;

# bitches
sub _dec_name {
   my @res;
   my $redir;
   my $ptr = $ofs;
   my $cnt;

   while () {
      return undef if ++$cnt >= 256; # to avoid DoS attacks

      my $len = ord substr $pkt, $ptr++, 1;

      if ($len >= 0xc0) {
         $ptr++;
         $ofs = $ptr if $ptr > $ofs;
         $ptr = (unpack "n", substr $pkt, $ptr - 2, 2) & 0x3fff;
      } elsif ($len) {
         push @res, substr $pkt, $ptr, $len;
         $ptr += $len;
      } else {
         $ofs = $ptr if $ptr > $ofs;
         return join ".", @res;
      }
   }
}

sub _dec_qd {
   my $qname = _dec_name;
   my ($qt, $qc) = unpack "nn", substr $pkt, $ofs; $ofs += 4;
   [$qname, $type_str{$qt} || $qt, $class_str{$qc} || $qc]
}

our %dec_rr = (
     1 => sub { join ".", unpack "C4", $_ }, # a
     2 => sub { local $ofs = $ofs - length; _dec_name }, # ns
     5 => sub { local $ofs = $ofs - length; _dec_name }, # cname
     6 => sub { 
             local $ofs = $ofs - length;
             my $mname = _dec_name;
             my $rname = _dec_name;