#!/bin/sh
#
# Script to update the resolver list for dnsmasq
#
# N.B. Resolvconf may run us even if dnsmasq is not (yet) running.
# If dnsmasq is installed then we go ahead and update the resolver list
# in case dnsmasq is started later.
#
# Assumption: On entry, PWD contains the resolv.conf-type files.
#
# This file is part of the dnsmasq package.
#

set -e

RUN_DIR="/run/dnsmasq"
RSLVRLIST_FILE="${RUN_DIR}/resolv.conf"
TMP_FILE="${RSLVRLIST_FILE}_new.$$"
MY_NAME_FOR_RESOLVCONF="dnsmasq"

[ -x /usr/sbin/dnsmasq ] || exit 0
[ -x /lib/resolvconf/list-records ] || exit 1

PATH=/bin:/sbin

report_err() { echo "$0: Error: $*" >&2 ; }

# Stores arguments (minus duplicates) in RSLT, separated by spaces
# Doesn't work properly if an argument itself contains whitespace
uniquify()
{
	RSLT=""
	while [ "$1" ] ; do
		for E in $RSLT ; do
			[ "$1" = "$E" ] && { shift ; continue 2 ; }
		done
		RSLT="${RSLT:+$RSLT }$1"
		shift
	done
}

if [ ! -d "$RUN_DIR" ] && ! mkdir --parents --mode=0755 "$RUN_DIR" ; then
	report_err "Failed trying to create directory $RUN_DIR"
	exit 1
fi

RSLVCNFFILES=""
for F in $(/lib/resolvconf/list-records --after "lo.$MY_NAME_FOR_RESOLVCONF") ; do
	case "$F" in
	    "lo.$MY_NAME_FOR_RESOLVCONF")
		# Omit own record
		;;
	    lo.*)
		# Include no more records after one for a local nameserver
		RSLVCNFFILES="${RSLVCNFFILES:+$RSLVCNFFILES }$F"
		break
		;;
	  *)
		RSLVCNFFILES="${RSLVCNFFILES:+$RSLVCNFFILES }$F"
		;;
	esac
done

NMSRVRS=""
if [ "$RSLVCNFFILES" ] ; then
	uniquify $(sed -n -e 's/^[[:space:]]*nameserver[[:space:]]\+//p' $RSLVCNFFILES)
	NMSRVRS="$RSLT"
fi

# Dnsmasq uses the mtime of $RSLVRLIST_FILE, with a resolution of one second,
# to detect changes in the file. This means that if a resolvconf update occurs
# within one second of the previous one then dnsmasq may fail to notice the
# more recent change. To work around this problem we sleep one second here
# if necessary in order to ensure that the new mtime is different.
if [ -f "$RSLVRLIST_FILE" ] && [ "$(ls -go --time-style='+%s' "$RSLVRLIST_FILE" | { read p h s t n ; echo "$t" ; })" = "$(date +%s)" ] ; then
	sleep 1
fi

clean_up() { rm -f "$TMP_FILE" ; }
trap clean_up EXIT
: >| "$TMP_FILE"
for N in $NMSRVRS ; do echo "nameserver $N" >> "$TMP_FILE" ; done
mv -f "$TMP_FILE" "$RSLVRLIST_FILE"