DuckDNS updater for (open)BSD

duckdns.sh

#!/bin/sh
#
# duckdns.sh -d <domain[,...,domain]> -t <token> [clear|noverify] [force]
# noverify - Don't fail if public inet address can't be bound to the router
# 	because of modem+gateway combos forced on you by shitty ISPs.
#	CAUTION: It's best if your NAT is 1:1 or you at least have some control
#		over port forwarding, or DDNS isn't going to be as useful...
# force - Always update, even if the logs indicate no change is necessary
# clear - Not allowed with or "noverify"
#

_bsdl='
Copyright (c) 2021, masato9000@users.noreply.github.com
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
'

_DUCKDIR="/var/db/duckdns"
_DUCKLOG="duckdns.log"
_CFDNS4=1.1.1.1
_CFDNS6=2606:4700:4700::1111

unset _DOCLEAR _NOVERIFY _DOFORCE _DOV4 _DOV6 _INETPUB _INETPUB6

####	Process args
while [ $# -gt 0 ]; do
	case $1 in
		-d)
			_DOMAINS=$2
			shift 2
			;;
		-t)
			_TOKEN=$2
			shift 2
			;;
		clear)
			_DOCLEAR=1
			shift
			;;
		noverify)
			_NOVERIFY=1
			shift
			;;
		force)
			_DOFORCE="FORCED "
			_DOV4=1
			_DOV6=1
			shift
			;;
		*)
			echo Invalid arguments. PLEASE READ ME.
			exit 1
			;;
	esac

	if [ -n "$_DOCLEAR" ] && [ -n "$_NOVERIFY" ]; then
		echo Invalid argument combination. PLEASE READ ME.
		exit 1
	fi
done

	if [ -z "$_DOMAINS" ] || [ -z "$_TOKEN" ]; then
		echo both domain list and API token must be specified
		exit 1
	fi

_DUCKURL="https://www.duckdns.org/update?domains=${_DOMAINS}&token=${_TOKEN}&verbose=true"

do_clear() {
	echo clearing records for $_DOMAINS | sed 's/,/, /g'
	_response=$(curl --connect-timeout 15 "${_DUCKURL}&clear=true")
	case "${_response}X" in
		X)
			echo No Response Received
			exit 1
			;;
		KO*)
			echo Server Responded with
			echo "$_response"
			exit 1
			;;
		OK*)
			echo "$_response"
			;;
		*)
			echo Unknown Error
			exit 1
			;;
	esac
}

do_update() {
	echo updating records for $_DOMAINS | sed 's/,/, /g'
	unset _upd4 _upd6
	[ -n "$_DOV4" ] || [ -n "$_DOCLEAR" ] && _upd4="&ip=$_INETPUB"
	[ -n "$_DOV6" ] && [ -n "$_INETPUB6" ] && _upd6="&ipv6=$_INETPUB6"
	_response=$(curl --connect-timeout 15 \
		"${_DUCKURL}${_upd4}${_upd6}")

	case "${_response}X" in
		X)
			echo No Response Received
			exit 1
			;;
		KO*)
			echo Server Responded with
			echo "$_response"
			exit 1
			;;
		OK*)
			echo "$_response"
			;;
		*)
			echo Unknown Error
			exit 1
			;;
	esac
	
}

do_log() {
	echo [${_DOFORCE}UPDATE: $_TODAY] >> "${_DUCKDIR}/${_DUCKLOG}"
	[ -n "$_DOV4" ] && echo "inet:	$_INETPUB" >> "${_DUCKDIR}/${_DUCKLOG}"
	[ -n "$_DOV6" ] && echo "inet6:	$_INETPUB6" >> "${_DUCKDIR}/${_DUCKLOG}"
}

_TODAY="$(date +%Y.%m.%d\ %H:%M:%S)"

####	Verify or set up history
[ -d "$_DUCKDIR" ] && [ -w "$_DUCKDIR" ] || mkdir -p "$_DUCKDIR" || exit 1
[ -f "${_DUCKDIR}/${_DUCKLOG}" ] &&  [ -w "${_DUCKDIR}/${_DUCKLOG}" ] || touch "${_DUCKDIR}/${_DUCKLOG}" || exit 1

####	Import addresses from history
_LASTV4=$(grep '^inet:' "${_DUCKDIR}/${_DUCKLOG}" | tail -n 1)
_LASTV4=${_LASTV4##*[[:space:]]}
_LASTV6=$(grep '^inet6:' "${_DUCKDIR}/${_DUCKLOG}" | tail -n 1)
_LASTV6=${_LASTV6##*[[:space:]]}

####	Clear can be attempted at this point
if [ -n "$_DOCLEAR" ]; then
	if [ -n "$_LASTV4" ] || [ -n "$_LASTV6" ] || [ -n "$_DOFORCE" ]; then
		do_clear
		[ -n "$_LASTV4" ] && _DOV4=1
		[ -n "$_LASTV6" ] && _DOV6=1
		do_log
	fi
	exit
fi

####	Detect interface with default ip route
_EXTIF=$(netstat -f inet -rn | awk '/^default/ {print $NF}')
if [ -z "$_EXTIF" ]; then
	echo No IP default route. Updates only work over IP. Aborting.
	exit 1
fi

####	Detect our real IP addresses (thanks CloudFlare!)
_INETPUB=$(dig +short txt ch whoami.cloudflare @$_CFDNS4 | tr -d '"')

if [ ${_INETPUB} != ${_INETPUB#;;} ] ; then
	echo Cannot determine public IP. Either we\'re down or CF is down.
	exit 1
fi

_INETPUB6=$(dig +short txt ch whoami.cloudflare @$_CFDNS6 | tr -d '"')

####	Determine which updates should be made
[ "${_INETPUB}X" = "${_LASTV4}X" ] || _DOV4=1
[ "${_INETPUB6}X" = "${_LASTV6}X" ] || _DOV6=1

####	Verify addresses are bound to external NIC
if ! ifconfig $_EXTIF | grep $_INETPUB; then
	echo Public IP is not bound to THIS system's outbound interface
	echo Looks like we\'re NATed. 
	if [ -n "$_NOVERIFY" ]; then
		echo noverify OK. Will update DNS with real public IP.
	else
		echo If you\'re aware and this is OK, use the noverify flag
		exit 1
	fi
fi

if [ -n "$_INETPUB6" ] && ! ifconfig $_EXTIF | grep $_INETPUB6; then
	echo Public IPv6 is not bound to THIS system\'s outbound interface
	echo Something nonstandard is happening. Not touching ipv6.
	unset _DOV6
fi

# If we lose our inet6 and have to clear, must clear both and then update
if [ -n "$_DOV6" ] && [ -z "$_INETPUB6" ]; then
	_DOCLEAR=1
	do_clear
fi

if [ -n "$_DOV4" ] || [ -n "$_DOV6" ] || [ -n "$_DOCLEAR" ]; then
	do_update
	do_log
fi

While this could be done by the simple example on the duckdns spec page, I felt like doing a bit more...

• Keeps a history of updates
• Using the history, does not update if there's been no change
• Can be manually run to force an update or clear domain records. (not that anything's stopping you from using those flags in cron)

I have it running every 3 minutes in my router's crontab