#!/bin/sh
# Copyright (c) 2007-2023 Roy Marples
# All rights reserved

# libc 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.

SYSCONFDIR=@SYSCONFDIR@
LIBEXECDIR=@LIBEXECDIR@
VARDIR=@VARDIR@
IFACEDIR="$VARDIR/interfaces"
NL="
"

# sed may not be available, and this is faster on small files
key_get_value()
{
	key="$1"
	shift

	if [ $# -eq 0 ]; then
		while read -r line; do
			case "$line" in
			"$key"*) echo "${line##$key}";;
			esac
		done
	else
		for x do
			while read -r line; do
				case "$line" in
				"$key"*) echo "${line##$key}";;
				esac
			done < "$x"
		done
	fi
}

keys_remove()
{
	while read -r line; do
		found=false
		for key do
			case "$line" in
			"$key"*|"#"*|" "*|"	"*|"") found=true;;
			esac
			$found && break
		done
		$found || echo "$line"
	done
}

local_nameservers="127.* 0.0.0.0 255.255.255.255 ::1"

# Support original resolvconf configuration layout
# as well as the openresolv config file
if [ -f "$SYSCONFDIR"/resolvconf.conf ]; then
	. "$SYSCONFDIR"/resolvconf.conf
elif [ -d "$SYSCONFDIR"/resolvconf ]; then
	SYSCONFDIR="$SYSCONFDIR/resolvconf"
	base="$SYSCONFDIR/resolv.conf.d/base"
	if [ -f "$base" ]; then
		prepend_nameservers="$(key_get_value "nameserver " "$base")"
		domain="$(key_get_value "domain " "$base")"
		prepend_search="$(key_get_value "search " "$base")"
		resolv_conf_options="$(key_get_value "options " "$base")"
		resolv_conf_sortlist="$(key_get_value "sortlist " "$base")"
	fi
	if [ -f "$SYSCONFDIR"/resolv.conf.d/head ]; then
		resolv_conf_head="$(cat "${SYSCONFDIR}"/resolv.conf.d/head)"
	fi
	if [ -f "$SYSCONFDIR"/resolv.conf.d/tail ]; then
		resolv_conf_tail="$(cat "$SYSCONFDIR"/resolv.conf.d/tail)"
	fi
fi
: ${resolv_conf:=/etc/resolv.conf}
: ${resolv_conf_tmp:="$resolv_conf.$$.openresolv"}
: ${libc_service:=nscd}
: ${list_resolv:=@SBINDIR@/resolvconf -l}
if [ "${resolv_conf_head-x}" = x ] && [ -f "$SYSCONFDIR"/resolv.conf.head ]
then
	resolv_conf_head="$(cat "${SYSCONFDIR}"/resolv.conf.head)"
fi
if [ "${resolv_conf_tail-x}" = x ] && [ -f "$SYSCONFDIR"/resolv.conf.tail ]
then
	resolv_conf_tail="$(cat "$SYSCONFDIR"/resolv.conf.tail)"
fi

backup=true
signature="# Generated by resolvconf"

uniqify()
{
	result=
	while [ -n "$1" ]; do
		case " $result " in
		*" $1 "*);;
		*) result="$result $1";;
		esac
		shift
	done
	echo "${result# *}"
}

case "${resolv_conf_passthrough:-NO}" in
[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1)
	backup=false
	newest=
	for conf in "$IFACEDIR"/*; do
		if [ -z "$newest" ] || [ "$conf" -nt "$newest" ]; then
			newest="$conf"
		fi
	done
	[ -z "$newest" ] && exit 0
	newconf="$(cat "$newest")$NL"
	;;
/dev/null|[Nn][Uu][Ll][Ll])
	: ${resolv_conf_local_only:=NO}
	if [ "$local_nameservers" = "127.* 0.0.0.0 255.255.255.255 ::1" ]; then
		local_nameservers=
	fi
	# Need to overwrite our variables.
	eval "$(@SBINDIR@/resolvconf -V)"
	;;

*)
	[ -z "$RESOLVCONF" ] && eval "$(@SBINDIR@/resolvconf -v)"
	;;
esac
case "${resolv_conf_passthrough:-NO}" in
[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1) ;;
*)
	: ${domain:=$DOMAIN}
	newsearch="$(uniqify $prepend_search $SEARCH $append_search)"
	NS="$LOCALNAMESERVERS $NAMESERVERS"
	newns=
	gotlocal=false
	for n in $(uniqify $prepend_nameservers $NS $append_nameservers); do
		add=true
		islocal=false
		for l in $local_nameservers; do
			case "$n" in
			$l) islocal=true; gotlocal=true; break;;
			esac
		done
		if ! $islocal; then
			case "${resolv_conf_local_only:-YES}" in
			[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1)
				$gotlocal && add=false;;
			esac
		fi
		$add && newns="$newns $n"
	done

	# Hold our new resolv.conf in a variable to save on temporary files
	newconf="$signature$NL"
	if [ -n "$resolv_conf_head" ]; then
		newconf="$newconf$resolv_conf_head$NL"
	fi

	[ -n "$domain" ] && newconf="${newconf}domain $domain$NL"
	if [ -n "$newsearch" ] && [ "$newsearch" != "$domain" ]; then
		newconf="${newconf}search $newsearch$NL"
	fi
	for n in $newns; do
		newconf="${newconf}nameserver $n$NL"
	done

	# Now add anything we don't care about such as sortlist and options
	stuff="$($list_resolv | keys_remove nameserver domain search)"
	if [ -n "$stuff" ]; then
		newconf="$newconf$stuff$NL"
	fi

	# Append any user defined ones
	if [ -n "$resolv_conf_options" ]; then
		newconf="${newconf}options $resolv_conf_options$NL"
	fi
	if [ -n "$resolv_conf_sortlist" ]; then
		newconf="${newconf}sortlist $resolv_conf_sortlist$NL"
	fi

	if [ -n "$resolv_conf_tail" ]; then
		newconf="$newconf$resolv_conf_tail$NL"
	fi
	;;
esac

# Check if the file has actually changed or not
if [ -e "$resolv_conf" ]; then
	[ "$(cat "$resolv_conf")" = "$(printf %s "$newconf")" ] && exit 0
fi

# Change is good.
# If the old file does not have our signature, back it up.
# If the new file just has our signature, restore the backup.
if $backup; then
	if [ "$newconf" = "$signature$NL" ]; then
		if [ -e "$resolv_conf.bak" ]; then
			newconf="$(cat "$resolv_conf.bak")$NL"
		fi
	elif [ -e "$resolv_conf" ]; then
		read line <"$resolv_conf"
		if [ "$line" != "$signature" ]; then
			cp "$resolv_conf" "$resolv_conf.bak"
		fi
	fi
fi

# There are pros and cons for writing directly to resolv.conf
# instead of a temporary file and then moving it over.
# The default is to write to resolv.conf as it has the least
# issues and has been the long standing default behaviour.
case "${resolv_conf_mv:-NO}" in
[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|[Oo][Nn]|1)
	# Protect against symlink attack, ensure new file does not exist
	rm -f "$resolv_conf_tmp"
	# Keep original file owner, group and mode
	[ -r "$resolv_conf" ] && cp -p "$resolv_conf" "$resolv_conf_tmp"
	# Create our resolv.conf now
	if (umask 022; printf %s "$newconf" >"$resolv_conf_tmp"); then
		mv "$resolv_conf_tmp" "$resolv_conf"
	fi
	;;
*)
	(umask 022; printf %s "$newconf" >"$resolv_conf")
	;;
esac

if [ -n "$libc_restart" ]; then
	eval $libc_restart
elif [ -n "$RESTARTCMD" ]; then
	set -- ${libc_service}
	eval "$RESTARTCMD"
else
	@SBINDIR@/resolvconf -r ${libc_service}
fi

retval=0
# Notify users of the resolver
for script in "$LIBEXECDIR"/libc.d/*; do
	if [ -f "$script" ]; then
		if [ -x "$script" ]; then
			"$script" "$@"
		else
			(. "$script")
		fi
		retval=$(($retval + $?))
	fi
done
exit $retval