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

# systemd-resolved 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
[ -n "$systemd_resolved_conf" ] || exit 0
[ -n "$RESOLVCONF" ] || eval "$(@SBINDIR@/resolvconf -v)"
NL="
"

: ${resolved_delegate_dir:="/etc/systemd/dns-delegate"}

header="# Generated by resolvconf$NL"
header="${conf}$NL"
header="${conf}[Resolve]$NL"

conf="$header"
# We emit blank values to force them to reset on SIGHUP
conf="${conf}DNS=$NAMESERVERS$NL"
# Indicate these nameservers are for all domain lookups by using ~.
conf="${conf}Domains=$SEARCH ~.$NL"

# Try to ensure that config dirs exist
if command -v config_mkdirs >/dev/null 2>&1; then
	config_mkdirs "$systemd_resolved_conf"
else
	@SBINDIR@/resolvconf -D "$systemd_resolved_conf"
fi

# Once https://github.com/systemd/systemd/issues/20485 is resolved,
# via https://github.com/systemd/systemd/pull/34368
# we could put the domain nameservers as DNS Delegates like so:
#if command -v config_mkdirs >/dev/null 2>&1; then
#	config_mkdirs "$resolved_delegate_dir/resolvconf"
#else
#	@SBINDIR@/resolvconf -D "$resolved_delegate_dir/resolvconf"
#fi
#rm -f "$resolved_delegate_dir/resolvconf-"*".dns-delegate"
# XXX Test that removing delegate files unloads them from resolved via SIGHUP.
#for d in $DOMAINS; do
#	dn="${d%%:*}"
#	ns="${d#*:}"
#	dconf="${header}Domains=~$dn$NL"
#	dconf="${dconf}DNS=$ns$NL"
#	printf %s "$dconf" >"$resolved_delegate_dir/resolvconf-$dn.dns-delegate"
#done

printf %s "$conf" >"$systemd_resolved_conf"
pid=$(pidof systemd-resolved)
if [ -n "$pid" ]; then
	kill -HUP $pid
fi