#!/usr/bin/perl -w
#
# Copyright (C) 2016  Internet Systems Consortium, Inc. ("ISC")
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
# AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
# OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
# PERFORMANCE OF THIS SOFTWARE.

#
# Don't respond if the "norespond" file exists; otherwise respond to
# any A or AAAA query.
#

use IO::File;
use IO::Socket;
use Net::DNS;
use Net::DNS::Packet;

my $sock = IO::Socket::INET->new(LocalAddr => "10.53.0.5",
   LocalPort => 5300, Proto => "udp") or die "$!";

my $pidf = new IO::File "ans.pid", "w" or die "cannot open pid file: $!";
print $pidf "$$\n" or die "cannot write pid file: $!";
$pidf->close or die "cannot close pid file: $!";
sub rmpid { unlink "ans.pid"; exit 1; };

$SIG{INT} = \&rmpid;
$SIG{TERM} = \&rmpid;

my $octet = 0;

for (;;) {
	$sock->recv($buf, 512);

	print "**** request from " , $sock->peerhost, " port ", $sock->peerport, "\n";

	my $packet;

	if ($Net::DNS::VERSION > 0.68) {
		$packet = new Net::DNS::Packet(\$buf, 0);
		$@ and die $@;
	} else {
		my $err;
		($packet, $err) = new Net::DNS::Packet(\$buf, 0);
		$err and die $err;
	}

	print "REQUEST:\n";
	$packet->print;

	$packet->header->qr(1);

	my @questions = $packet->question;
	my $qname = $questions[0]->qname;
	my $qtype = $questions[0]->qtype;

	$packet->header->aa(1);
	if ($qtype eq "A") {
		$packet->push("answer",
			      new Net::DNS::RR($qname .
					       " 0 A 192.0.2." . $octet));
		$octet = $octet + 1;
	} elsif ($qtype eq "AAAA") {
		$packet->push("answer",
			      new Net::DNS::RR($qname .
						" 300 AAAA 2001:db8:beef::1"));
	}

	$sock->send($packet->data);
	print "RESPONSE:\n";
	$packet->print;
	print "\n";
}
