#!/bin/bash
#
# /usr/local/sbin/nsupdate-ddns.sh
#
# Update DDNS server with current public IP.
#
# Copyright 2012 - Jean-Sebastien Morisset - http://surniaulula.com/
#
# This script is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation; either version 3 of the License, or (at your option) any later
# version.
#
# This script is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
# details at http://www.gnu.org/licenses/.

ddns_domain="ddns.MY_DOMAIN_NAME.com"
my_fqdn="`hostname -s`.$ddns_domain"
key_file="`echo /etc/named.d/K$my_fqdn.+157+*.private`"
if_active="`/sbin/ifconfig -a|egrep '(status: active|inet addr:.*Bcast:.*Mask:)'`"
ip_check_url="http://checkip.dyndns.org/"	# website that displays our IP (see regex bellow)

# read command line opts (works better than getopt)
while :
do
	for arg in "$@"
	do
		case $arg in
			-f|--force)
				force="1"
				shift 1
				;;
			-h|--help)
				echo "purpose: update $my_fqdn ddns entry with current public ip."
				echo " syntax: $0 [--help|--force|--visual|--keygen]"
				exit 0
				;;
			-k|--keygen)
				if [ -f "$key_file" ]
				then
					echo "  error: $key_file already exists!"
					exit 1
				fi
				mkdir -p /etc/named.d	# just in case
				cd /etc/named.d && dnssec-keygen -a HMAC-MD5 -b 512 -n USER $my_fqdn.
				key_file="`echo /etc/named.d/K$my_fqdn.+157+*.private`"
				if [ ! -f "$key_file" ]
				then
					echo "  error: $key_file file not found!"
					exit 1
				fi
				chmod 600 $key_file	# just to make sure
				secret="`sed -n 's/^Key: //p' $key_file`"
				if [ -z "$secret" ]
				then
					echo "  error: secret key not found in $Key_file!"
					exit 1
				fi
				cat <<EOF

The following instructions are provided as an example. The file names, their
location, and content may vary depending on the DNS server configuration. The
/etc/named.d/keys.conf file shown in this example is included by
/etc/named.conf and owned by root:named with permissions 640 (only root and the
named group members can view the secret keys).

1) Add the following to /etc/named.d/keys.conf:

	key $my_fqdn. {
		algorithm "HMAC-MD5";
		secret "$secret";
	};

2) Add the following to the $ddns_domain zone definition 
update-policy section:

	grant "$my_fqdn." name $my_fqdn. A TXT;

Here's an example of a complete zone definition for $ddns_domain:

	zone "$ddns_domain" in { 
		type master;
		file "master/db.$ddns_domain";
		allow-transfer { acl_lan_slaves; acl_isp_slaves; };
		update-policy { 
			grant "$my_fqdn." name $my_fqdn. A TXT;
		};
	};

EOF
				exit 0
				;;
			-v|--visual)
				visual="1"
				shift 1
				;;
			*)	args[$(( i++ ))]="$1"
				shift 1
				;;
		esac
		continue 2
	done
	break
done

# reset $1, $2, etc. with left-over paramters
set -- "${args[@]}"

if [ -z "$if_active" ]
then
	echo "warning: no active network interface found."
	exit 0
elif [ ! -f "/etc/resolv.conf" ]
then
	echo "  error: /etc/resolv.conf file missing!"
	exit 1
elif [ ! -f "$key_file" ]
then
	echo "  error: $key_file file not found!"
	echo "   info: use --keygen to generate the private/public key pair."
	exit 1
fi

[ -z "$ip_old" ] && ip_old="`/usr/bin/host $my_fqdn.|sed -n 's/^.*has address \([0-9][0-9\.]*\)$/\1/p'`"
[ -z "$ip_new" ] && ip_new="`/usr/bin/curl --silent --max-time 15 $ip_check_url | \
	sed -n 's/^.*IP Address: *\([0-9][0-9\.]*\)<.*$/\1/p'`"

[ -n "$visual" ] && echo "old ip: $ip_old"
[ -n "$visual" ] && echo "new ip: $ip_new"

if [ -z "$ip_old" ]
then
	echo "  error: cannot determine current ddns ip address!"
	exit 1
elif [ -z "$ip_new" ]
then
	echo "  error: cannot determine public ip address!"
	exit 1
elif [ "$ip_new" = "$ip_old" ]
then
	[ -n "$visual" ] && echo "  info: current ddns ip and public ip are identical."
	[ -n "$visual" -a -n "$force" ] && echo ""
elif [ "$ip_new" != "$ip_old" ]
then
	[ -n "$visual" ] && echo "  info: current ddns ip and public ip are different."
	[ -n "$visual" ] && echo ""
fi

if [ -n "$force" -o "$ip_new" != "$ip_old" ]
then
	{ 
		echo "server $ddns_domain"
		echo "zone $ddns_domain"
		echo "update delete $my_fqdn. A"
		echo "update add $my_fqdn. 10 A $ip_new"
		[ -n "$visual" ] && echo "show"
		echo "send"
	} | /usr/bin/nsupdate -k $key_file || exit $?
fi

exit 0