#!/bin/sh
#
# Script to update resolv.conf, the libc resolver configuration file,
# and to notify users of the libc resolver of changes
#
# Assumption: On entry, PWD contains the resolv.conf-type files
#
# This script is part of the resolvconf package
#
# Licensed under the GNU GPL.  See /usr/share/doc/resolvconf/copyright.
#
# Written by Thomas Hood <jdthood@yahoo.co.uk>

set -e
PATH=/sbin:/bin:/usr/bin

[ -x /lib/resolvconf/list-records ] || exit 1

# Set REPORT_ABSENT_SYMLINK=no to inhibit reports that
# /etc/resolv.conf is not a symbolic link

# Default value
REPORT_ABSENT_SYMLINK=no
TRUNCATE_NAMESERVER_LIST_AFTER_127=y

# Default override
[ -r /etc/default/resolvconf ] && . /etc/default/resolvconf

ETC=/etc
ETCRESOLVCONF="${ETC}/resolvconf"
RESOLVCONFDIR="${ETCRESOLVCONF}/resolv.conf.d"
BASEFILE="${RESOLVCONFDIR}/base"
HEADFILE="${RESOLVCONFDIR}/head"
TAILFILE="${RESOLVCONFDIR}/tail"
DYNAMICRSLVCNFFILE="${ETCRESOLVCONF}/run/resolv.conf"
TMPFILE="${DYNAMICRSLVCNFFILE}_new.$$"

report_warning() { echo "$0: Warning: $*" >&2 ; }

if [ ! -L ${ETC}/resolv.conf ] || [ ! "$(readlink ${ETC}/resolv.conf)" = "$DYNAMICRSLVCNFFILE" ] ; then
	case "$REPORT_ABSENT_SYMLINK" in
		y|Y|yes|YES|Yes)
			report_warning "${ETC}/resolv.conf is not a symbolic link to $DYNAMICRSLVCNFFILE"
			;;
	esac
	# Old name for the variable was '...ALTERED...' so accept that for now
	case "$REPORT_ALTERED_SYMLINK" in
		y|Y|yes|YES|Yes)
			report_warning "${ETC}/resolv.conf is not a symbolic link to $DYNAMICRSLVCNFFILE"
			;;
	esac
fi

# Args are candidate items not containing spaces
# Returns RSLT -- space-separated list of items without duplicates
#
# Stores arguments (minus duplicates) in RSLT, separated by spaces
uniquify()
{
	RSLT=""
	local D
	while [ "$1" ] ; do
		# Remove the root domain suffix
		D="${1%.}"
		for E in $RSLT ; do
			[ "$D" = "$E" ] && { shift ; continue 2 ; }
		done
		RSLT="${RSLT:+$RSLT }$D"
		shift
	done
}

# Args are candidate items not containing spaces
# Returns NSMSRVS -- space-separate list of no more than 3 items,
#                    without duplicates,
#                    truncated after 127.* if TRUNCATE_NAMESERVER_LIST_AFTER_127 set affirmatively
uniquify_nameserver_list()
{
	NMSRVRS=""
	N=0
	while [ "$1" ] ; do
		for E in $NMSRVRS ; do
			[ "$1" = "$E" ] && { shift ; continue 2 ; }
		done
		NMSRVRS="${NMSRVRS:+$NMSRVRS }$1"
		case "$TRUNCATE_NAMESERVER_LIST_AFTER_127" in (y|Y|yes|YES|Yes) case "$1" in (127.*) return 0 ;; esac ;; esac
		N=$(($N + 1))
		[ "$N" = 3 ] && return 0
		shift
	done
}

RSLVCNFFILES="$(/lib/resolvconf/list-records)"

[ -f "$BASEFILE" ] && RSLVCNFFILES="$BASEFILE
$RSLVCNFFILES"

### Compile list of nameservers ###
NMSRVRS=""
if [ "$RSLVCNFFILES" ] ; then
	uniquify_nameserver_list $(sed -n 's/^[[:space:]]*nameserver[[:space:]]\+//p' $RSLVCNFFILES)
fi

### Compile search list ###
SRCHS=""
if [ "$RSLVCNFFILES" ] ; then
	uniquify $(sed -n 's/^[[:space:]]*\(\(search\)\|\(domain\)\)[[:space:]]\+//p' $RSLVCNFFILES)
	SRCHS="$RSLT"
fi

clean_up() { rm -f "$TMPFILE" ; }
trap clean_up EXIT
clean_up

### Make the file ###
: > "$TMPFILE"
[ -f "$HEADFILE" ] && cat "$HEADFILE" >> "$TMPFILE"
for N in $NMSRVRS ; do echo "nameserver $N" >> "$TMPFILE" ; done
[ "$SRCHS" ] && echo "search $SRCHS" >> "$TMPFILE"
[ "$RSLVCNFFILES" ] && sed -e '/^[[:space:]]*$/d' -e '/^[[:space:]]*#/d' -e '/^[[:space:]]*\(\(nameserver\)\|\(search\)\|\(domain\)\)[[:space:]]/d' $RSLVCNFFILES >> "$TMPFILE" 2>/dev/null
[ -f "$TAILFILE" ] && cat "$TAILFILE" >> "$TMPFILE"

### Put the file in place ###

move_rslvcnf() {
	cat "$TMPFILE" > "$DYNAMICRSLVCNFFILE"
	rm -f "$TMPFILE"
}

# On init, just put it in place
if [ "$1" = "-i" ] ; then
	ln -sf "${ETC}/resolv.conf" "$DYNAMICRSLVCNFFILE"
	move_rslvcnf
	exit 0
fi

if [ -f "$DYNAMICRSLVCNFFILE" ] && [ "$(cat $TMPFILE)" = "$(cat $DYNAMICRSLVCNFFILE)" ] ; then
	# The file has not changed
	rm -f "$TMPFILE"
	exit 0
fi

# The file has changed
move_rslvcnf

# Restart nscd
NSCD_RESTARTED=""
NSCD_PIDFILE=""
[ -s /var/run/nscd.pid ] && NSCD_PIDFILE="/var/run/nscd.pid"
[ -s /var/run/nscd/nscd.pid ] && NSCD_PIDFILE="/var/run/nscd/nscd.pid"
if \
	[ "$NSCD_PIDFILE" ] \
	&& [ -x /usr/sbin/nscd ] \
	&& [ -x /etc/init.d/nscd ] \
	&& [ -s /etc/nscd.conf ] \
	&& grep -q '^[[:space:]]*enable-cache[[:space:]]\+hosts[[:space:]]\+yes' /etc/nscd.conf
then
	echo "Restarting Name Service Cache Daemon: nscd (if needed)"
	/etc/init.d/nscd condrestart && { sleep 0.1 ; NSCD_RESTARTED=yes ; }
fi

# Notify users of the resolver
exec run-parts ${NSCD_RESTARTED:+--arg="--nscd"} "${ETCRESOLVCONF}/update-libc.d"