functions

#!/bin/sh

set -e

PATH=/usr/sbin:/sbin:$PATH

CONF_DIR=/etc/ddns-update
CONF=$CONF_DIR/ddns-update.conf

[ ! -f "$CONF" ] || source "$CONF"

set_defaults() {
	[ -n "$INTERVAL" ] || INTERVAL=300
	[ -n "$EXTERNAL" ] || EXTERNAL=true
	[ -n "$IF" ] && OUT_IF=$IF || IF=eth0

	# other implementation can be
	# HOST=$(expr `cat /proc/sys/kernel/hostname` : '\([^.][^.]*\)\..*')
	# HOST=$(sed  's/\..*//' < /proc/sys/kernel/hostname)
	# ZONE=$(expr `cat /proc/sys/kernel/hostname` : '[^.][^.]*\.\(.*\)')
	# ZONE=$(sed -n 's/[^.]*\.//p' < /proc/sys/kernel/hostname)
	[ -n "$HOST" ]   || HOST=`cut -d. -f1 < /proc/sys/kernel/hostname`
	[ -n "$ZONE" ]   || ZONE=`cut -d. -f2- < /proc/sys/kernel/hostname`
	FQDN="$HOST.$ZONE."

	[ -n "$TTL" ]    || TTL=600
	[ -n "$KEY" ]    || KEY="$CONF_DIR/K$ZONE.*.private"
	[ -n "$CMD" ]    || CMD=curl
	[ -n "$SERVER" ] || SERVER=`find_primary_dns $ZONE`
	[ ! $FORCE_TCP ] || TCP="-v"
	if [ $USE_IPV6 ]; then
		RRTYPE="AAAA"
		TYPE="inet6"
	else
		RRTYPE="A"
		TYPE="inet"
	fi
	[ -n "$USEPROXY" ]      || USEPROXY=true
	[ -n "$IP_LOOKUP_URL" ] || IP_LOOKUP_URL="http://myexternalip.com/raw"
	[ -n "$ALLOW_PRIVATE" ] || ALLOW_PRIVATE=false
	[ -n "$USE_LOGGER" ]	|| USE_LOGGER=true
	[ -z "$LOGFILE" ]	|| LOGGER_OPT="-f $LOGFILE"
}

log() {
	if $USE_LOGGER ; then
		logger -t ddns-update $LOGGER_OPT "$@"
	elif [ -f "$LOGFILE" ]; then
		echo "$@" >> $LOGFILE
	else
		echo "$@"
	fi
}

web_query() {
	case $CMD in
		curl)
			[ -z "$OUT_IF" ] || OUT_PARAM="--interface $IF"
			$USEPROXY || NOPROXY="--noproxy '*'"
			curl $NOPROXY $OUT_PARAM -s "$@"
			;;
		wget*)
			if [ $CMD == "wget_busybox" ]; then
				$USEPROXY || NOPROXY="--proxy off"
			else
				[ -z "$OUT_IF" ] || OUT_PARAM="--bind-address `get_interface_ip`"
				$USEPROXY || NOPROXY="--no-proxy"
			fi
			wget $NOPROXY $OUT_PARAM -q -O - "$@"
			;;
		links)
			$USEPROXY && links -source "$@" || no_proxy='*' links -source "$@"
			;;
		fetch)
			fetch -q -o - "$@"
			;;
		*)
			$CMD "$@"
			;;
	esac
}

# $1 = domain ie zone
find_primary_dns() {
	local result
	if `command -v dig >/dev/null 2>&1` ; then
		result=`dig +nocmd +nosearch +noall +answer +short soa $1 | cut -d' ' -f1`
	elif `command -v nslookup >/dev/null 2>&1` ; then
		result=`nslookup -type=soa -nosearch $1 2>/dev/null | grep origin | tr -d '[:space:]' | cut -d= -f2`
	fi
	if [ -z "$result" ]; then
		result=`web_query "http://api.hackertarget.com/dnslookup/?q=$1" | grep SOA | awk '{ print $5 }'`
	fi
	echo $result
}

# $1 = FQDN, $2 = DNS to query
find_dns_ip() {
	local server
	if `command -v dig >/dev/null 2>&1` ; then
		[ $# -lt 2 ] || server="@$2"
		result=`dig $server $1 +nocmd +nosearch +noall +answer +short | tail -1`
	elif `command -v nslookup >/dev/null 2>&1` ; then
		[ $# -lt 2 ] || server="$2"
		result=`nslookup -nosearch $1 $server 2>/dev/null | grep -i Address | sed "s/Address.*: //g" | tail -1`
	fi
	if [ -z "$result" ]; then
		result=`web_query "http://api.hackertarget.com/dnslookup/?q=$1" | awk '{ print $5 }' | tail -1`
	fi
	echo $result
}

get_interface_ip() {
	#command -v ip >/dev/null 2>&1 && IP=ip || IP=/sbin/ip
	ip -family $TYPE addr show $IF | grep $TYPE | sed "s/.*$TYPE \([0-9.]*\).*/\1/" | head -1
}

get_external_ip() {
	web_query "$IP_LOOKUP_URL"
}

discover_ip() {
	DNS_IP="`find_dns_ip $FQDN $SERVER`"
	if [ -z "$NEW_IP" ]; then
		$EXTERNAL && NEW_IP="`get_external_ip`" || NEW_IP="`get_interface_ip`"
	fi
}

send_update()
{
	if [ -f $KEY ]; then
		command -v chcon >/dev/null 2>&1 && chcon -t dnssec_t $KEY >/dev/null 2>&1 ||:
		log "Send update to $SERVER host: $FQDN from: $DNS_IP to: $NEW_IP ttl: $TTL"
		nsupdate $TCP -k $KEY <<-EOF
			server $SERVER
			zone $ZONE
			update delete $FQDN $RRTYPE
			update add $FQDN $TTL $RRTYPE $NEW_IP
			send
		EOF
	else
		log "Error: Key file ($KEY) missing for dns update!"
		exit 1
	fi
}

ddns_update() {
	if [ "$DNS_IP" != "$NEW_IP" ]; then
		if ! $ALLOW_PRIVATE ; then
			case "$NEW_IP" in
				10.* | 172.1[6-9].* | 172.2[0-9].* | 172.3[0-1].* | 192.168.*)
					log "Error: Private IP address update not allowed ($NEW_IP)."
					exit 1
					;;
				*)
        				;;
			esac
		fi

		send_update
		RC=$?
		if [ $RC != 0 ]; then
			log "Error: Updating $FQDN failed (RC=$RC)."
		else
			log "DNS Update was succesful."
		fi
	fi
	return $RC
}

discover_update() {
	discover_ip
	ddns_update
}

set_defaults