#!/bin/sh
#
# Script to update resolv.conf, the libc resolver configuration file,
# and to notify users of the libc resolver of changes
#
# Assumption: On entry, PWD contains the resolv.conf-type files.
#
# This script is part of the resolvconf package.
#
# Set REPORT_ABSENT_SYMLINK=no to inhibit warning message that
# /etc/resolv.conf is not a symbolic link
#
# Set TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS=no
# to allow additional nameserver addresses to be listed in
# resolv.conf after an initial loopback address 127.* or ::1.
#

set -e
PATH=/sbin:/bin

[ -x /lib/resolvconf/list-records ] || exit 1

# Default override
[ -r /etc/default/resolvconf ] && . /etc/default/resolvconf

ETC=/etc
ETCRESOLVCONF="${ETC}/resolvconf"
RESOLVCONFDIR="${ETCRESOLVCONF}/resolv.conf.d"
BASEFILE="${RESOLVCONFDIR}/base"
HEADFILE="${RESOLVCONFDIR}/head"
TAILFILE="${RESOLVCONFDIR}/tail"
DYNAMICRSLVCNFFILE="/run/resolvconf/resolv.conf"
TMPFILE="${DYNAMICRSLVCNFFILE}_new.$$"

# Set unset variables to their defaults
if [ -z "$REPORT_ABSENT_SYMLINK" ] ; then
# '..._ALTERED_...' is the old deprecated name for this variable
if [ "$REPORT_ALTERED_SYMLINK" ] ; then
REPORT_ABSENT_SYMLINK="$REPORT_ALTERED_SYMLINK"
else
# Set to default value
REPORT_ABSENT_SYMLINK=y
fi
fi

if [ -z "$TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS" ] ; then
# '..._127' is the old deprecated name for this variable
if [ "$TRUNCATE_NAMESERVER_LIST_AFTER_127" ] ; then
TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS="$TRUNCATE_NAMESERVER_LIST_AFTER_127"
else
# Set to default value
TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS=y
fi
fi


report_warning() { echo "$0: Warning: $*" >&2 ; }

resolv_conf_is_symlinked_to_dynamic_file() {
[ -L ${ETC}/resolv.conf ] && [ "$(readlink -m ${ETC}/resolv.conf)" = "$DYNAMICRSLVCNFFILE" ]
}

if ! resolv_conf_is_symlinked_to_dynamic_file ; then
case "$REPORT_ABSENT_SYMLINK" in
y|Y|yes|YES|Yes)
report_warning "${ETC}/resolv.conf is not a symbolic link to $DYNAMICRSLVCNFFILE"
;;
esac
fi

# Args are candidate items not containing spaces
# Returns RSLT -- space-separated list of items without duplicates
#
# Stores arguments (minus duplicates) in RSLT, separated by spaces
uniquify()
{
RSLT=""
local D
while [ "$1" ] ; do
# Remove the root domain suffix
D="${1%.}"
for E in $RSLT ; do
[ "$D" = "$E" ] && { shift ; continue 2 ; }
done
RSLT="${RSLT:+$RSLT }$D"
shift
done
}

# Args are candidate items not containing spaces
# Returns NSMSRVS -- space-separate list of no more than 3 items,
# without duplicates,
# truncated after loopback address if TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS set affirmatively
uniquify_nameserver_list()
{
NMSRVRS=""
N=0
while [ "$1" ] ; do
for E in $NMSRVRS ; do
[ "$1" = "$E" ] && { shift ; continue 2 ; }
done
NMSRVRS="${NMSRVRS:+$NMSRVRS }$1"
case "$TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS" in (y|Y|yes|YES|Yes) case "$1" in (127.*|::1) return 0 ;; esac ;; esac
N=$(($N + 1))
[ "$N" = 3 ] && return 0
shift
done
}

RSLVCNFFILES="$(/lib/resolvconf/list-records)"

[ -f "$BASEFILE" ] && RSLVCNFFILES="$RSLVCNFFILES
$BASEFILE"

### Compile list of nameservers ###
NMSRVRS=""
if [ "$RSLVCNFFILES" ] ; then
uniquify_nameserver_list $(sed -n 's/^[[:space:]]*nameserver[[:space:]]\+//p' $RSLVCNFFILES)
fi

### Compile search list ###
SRCHS=""
if [ "$RSLVCNFFILES" ] ; then
uniquify $(sed -n 's/^[[:space:]]*\(\(search\)\|\(domain\)\)[[:space:]]\+//p' $RSLVCNFFILES)
SRCHS="$RSLT"
fi

clean_up() { rm -f "$TMPFILE" ; }
trap clean_up EXIT
clean_up

### Make the file ###
: > "$TMPFILE"
[ -f "$HEADFILE" ] && cat "$HEADFILE" >> "$TMPFILE"
for N in $NMSRVRS ; do echo "nameserver $N" >> "$TMPFILE" ; done
[ "$SRCHS" ] && echo "search $SRCHS" >> "$TMPFILE"
[ "$RSLVCNFFILES" ] && sed -e '/^[[:space:]]*$/d' -e '/^[[:space:]]*#/d' -e '/^[[:space:]]*\(\(nameserver\)\|\(search\)\|\(domain\)\)[[:space:]]/d' $RSLVCNFFILES >> "$TMPFILE" 2>/dev/null
[ -f "$TAILFILE" ] && cat "$TAILFILE" >> "$TMPFILE"

### Put the file in place ###

if [ -f "$DYNAMICRSLVCNFFILE" ] && [ "$(cat $TMPFILE)" = "$(cat $DYNAMICRSLVCNFFILE)" ] ; then
# The file has not changed
rm -f "$TMPFILE"
exit 0
fi

# The file has changed
mv -f "$TMPFILE" "$DYNAMICRSLVCNFFILE"

# Only notify users of /etc/resolv.conf if /etc/resolv.conf is actually
# symlinked to the file we have just updated.
resolv_conf_is_symlinked_to_dynamic_file || exit 0

# Restart nscd
NSCD_RESTARTED=""
NSCD_PIDFILE=""
[ -s /var/run/nscd.pid ] && NSCD_PIDFILE="/var/run/nscd.pid"
[ -s /var/run/nscd/nscd.pid ] && NSCD_PIDFILE="/var/run/nscd/nscd.pid"
if \
[ "$NSCD_PIDFILE" ] \
&& [ -x /usr/sbin/nscd ] \
&& [ -x /etc/init.d/nscd ] \
&& [ -s /etc/nscd.conf ] \
&& grep -q '[[:space:]]*enable-cache[[:space:]]\+hosts[[:space:]]\+yes' /etc/nscd.conf \
&& start-stop-daemon --stop --quiet --pidfile="$NSCD_PIDFILE" --exec /usr/sbin/nscd --retry=TERM/3/HUP/5 \
&& start-stop-daemon --stop --quiet --oknodo --exec /usr/sbin/nscd --retry=0/5
then
echo "Stopped Name Service Cache Daemon: nscd."
/etc/init.d/nscd start && { sleep 0.1 ; NSCD_RESTARTED=yes ; }
fi

# Notify users of the resolver
if [ -d "${ETCRESOLVCONF}/update-libc.d" ] ; then
exec run-parts ${NSCD_RESTARTED:+--arg="--nscd"} "${ETCRESOLVCONF}/update-libc.d"
fi

exit 0