#!/bin/sh
# Copyright (c) 2025 Roy Marples
# All rights reserved

# resolvectl subscriber for resolvconf

# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#     * Redistributions of source code must retain the above copyright
#       notice, this list of conditions and the following disclaimer.
#     * 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.

[ -f "@SYSCONFDIR@"/resolvconf.conf ] || exit 0
. "@SYSCONFDIR@/resolvconf.conf" || exit 1

case "${resolvectl:-NO}" in
[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1) ;;
*) exit 0;;
esac

# If we don't have resolvectl or systemd-resolved isn't running then
# we can't do much.
# We can't persist our data in /run/systemd/resolve/netif/$ifindex
# because systemd-resolved keeps it somehow, ie we can't change it
# once we have inserted it
if ! [ -d /sys/class/net ] || \
   ! type resolvectl >/dev/null 2>&1 || \
   ! pidof systemd-resolved >/dev/null
then
	exit 1
fi

# resolvectl only accepts resolv.conf setup per physical interface
# although resolvconf has always hinted that the named configuration
# should be $interface.$protocol, this has never been a fixed requirement.
# Because resolvectl only accepts one configuration per interface we need
# to try and merge the resolv.conf's together.
# Luckily resolvconf makes this easy for us.

# Returns a list of resolvconf entries for a real interface
get_resolvconf_interfaces() {
	IFACE="$1"
	[ -d /sys/class/net/"$IFACE" ] || return 1

	IFACES=
	for IFACE_PROTO in $(@SBINDIR@/resolvconf -Li "$IFACE" "$IFACE.*" 2>/dev/null); do
		# ens5 will work with ens5.dhcp and ens5.ra,
		# but not ens5.5 or ens5.5.dhcp
		if [ "$IFACE_PROTO" != "$IFACE" ]; then
			# Ensure that ens5.5.dhcp doesn't work for ens5
			if [ "${IFACE_PROTO%.*}" != "$IFACE" ]; then
				continue
			fi
			# Ensure that ens5.dhcp isn't a real interface
			# as ens5.5 likely is and the .5 matches the .dhcp
			if [ -d /sys/class/net/"$IFACE_PROTO" ]; then
				continue
			fi
		fi
		IFACES="$IFACES${IFACES:+ }$IFACE_PROTO"
	done
	echo "$IFACES"
}

# For the given interface, apply a list of resolvconf entries
apply_resolvconf() {
	IFACE="$1"
	shift

	if [ -z "$1" ]; then
		resolvectl revert "$IFACE"
		return
	fi

	# Set the default-route property first to avoid leakage.
	# If any entry is private, the whole interface has to be private.
	# If a more granular approach is needed, consider using the
	# systemd-resolved subscriber instead which supports DNS delegates.
	if [ -n "$(@SBINDIR@/resolvconf -p $@)" ]; then
		resolvectl default-route "$IFACE" false
	else
		resolvectl default-route "$IFACE" true
	fi

	# Now set domain and dns
	DOMAIN=$(@SBINDIR@/resolvconf -L $@ 2>/dev/null | sed -n -e "s/domain //p" -e "s/search //p")
	NS=$(@SBINDIR@/resolvconf -L $@ 2>/dev/null | sed -n -e "s/nameserver //p")
	if [ -n "$DOMAIN" ]; then
		# If any entry is marked as not searchable, we mark all the
		# domains as non searchable.
		# If a more granular approach is needed, consider using the
		# systemd-resolved subscriber instead which supports DNS delegates.
		if [ -n "$(@SBINDIR@/resolvconf -pp $@)" ]; then
			ND=
			for d in $DOMAIN; do
				ND="$ND${ND:+ }~$d"
			done
			DOMAIN="$ND"
		fi
		resolvectl domain "$IFACE" $DOMAIN
	else
		resolvectl domain "$IFACE" ""
	fi
	if [ -n "$NS" ]; then
		resolvectl dns "$IFACE" $NS
	else
		resolvectl dns "$IFACE" ""
	fi
}

# To get the full features of resolvconf, we need to work out each interface
# for every resolvconf addition and deletion
# This is because resolvconf.conf might have changed OR an exclusive
# interface deleted which makes other interfaces visible.
cd /sys/class/net
for IFACE in *; do
	if [ "$IFACE" = lo ]; then
		# systemd-resolved doesn't work with lo
		continue
	fi

	IFACES=$(get_resolvconf_interfaces "$IFACE")
	apply_resolvconf "$IFACE" $IFACES
done

# warn about resolv.conf with no matching interface
FAILED=
for IFACE_PROTO in $(@SBINDIR@/resolvconf -Li); do
	IFACE="${IFACE_PROTO%.*}"
	if [ "$IFACE" = lo ]; then
		# Don't warn about loopback interface as that is typically
		# used to configure libc for a nameserver on it and the libc
		# subscriber will process that just fine.
		continue
	fi

	if ! [ -d "/sys/class/net/$IFACE" ]; then
		FAILED="$FAILED${FAILED:+ }$IFACE_PROTO"
	fi
done
if [ -n "$FAILED" ]; then
	echo "Could not apply resolv.conf to resolvectl: $FAILED" >&2
fi