#! /bin/sh
#
# resolv.conf merge hook for rdnssd

# *************************************************************************
# *  Copyright © 2007-2009 Pierre Ynard.                                  *
# *  This program is free software: you can redistribute and/or modify    *
# *  it under the terms of the GNU General Public License as published by *
# *  the Free Software Foundation, versions 2 or 3 of the license.        *
# *                                                                       *
# *  This program 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.                         *
# *                                                                       *
# *  You should have received a copy of the GNU General Public License    *
# *  along with this program. If not, see <http://www.gnu.org/licenses/>. *
# *************************************************************************

PATH=/sbin:/bin
RESOLVCONF_TOOL=/sbin/resolvconf
RDNSSD_RESOLV_CONF=/var/run/rdnssd/resolv.conf

merge_resolv_conf()
{
	set -e

	# Max number of nameserver options taken into account. Should be as
	# defined in <resolv.h>
	MAXNS=3

	# This script tries to share available nameserver slots with IPv4
	# entries, for example to allow fallback to IPv4 if IPv6 fails. If
	# there is not enough room for all IPv6 and IPv4 entries, this script
	# will limit the IPv6 entries it adds to $RDNSS_LIMIT only.
	RDNSS_LIMIT=$(($MAXNS - 1))

	sysconfdir='/etc'
	resolvconf="$sysconfdir/resolv.conf"

	# These should be POSIX-compliant BREs
	RE_NSV4='^nameserver  *\([0-9]\{1,3\}\.\)\{3,3\}[0-9]\{1,3\} *$'
	RE_NSV4OR6='^nameserver  *[a-fA-F0-9:\.]\{1,46\}\(%[a-zA-Z0-9]\{1,\}\)\{,1\} *$'

	# Count how many IPv6 nameservers we can fit

	limit=$RDNSS_LIMIT

	nnsv4=`grep -c "$RE_NSV4" $resolvconf || [ $? -le 1 ]`
	room=$(($MAXNS - $nnsv4))

	if [ $limit -lt $room ]; then
		limit=$room
	fi

	# Merge and write the result

	{
		sed -e "/$RE_NSV4OR6/d" < $resolvconf
			[ $limit -gt 0 ] && sed -e "${limit}q" < $RDNSSD_RESOLV_CONF
		sed -ne "/$RE_NSV4/p" < $resolvconf
	} >| $resolvconf.tmp

	mv -f $resolvconf.tmp $resolvconf
}

[ -f "$RDNSSD_RESOLV_CONF" ] || exit 0

if [ -x "$RESOLVCONF_TOOL" ]; then
	$RESOLVCONF_TOOL -a 000.rdnssd < "$RDNSSD_RESOLV_CONF"
else
	merge_resolv_conf
fi

