#!/bin/sh

# Utility to regenerate an nsd database from parts

# Copyright (c) 2013 Taylor R. Campbell
# 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 ``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 HOLDERS 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.

# Example:
#
# You are the administrator of the multi-user host eland.example.com.
# Your users, don, jon, and ron, have own the zones don.example.com,
# jon.example.com, and ron.example.com.  nsd is configured to use zones
# in the files
#
#    /etc/nsd/zones/don.zone
#    /etc/nsd/zones/jon.zone
#    /etc/nsd/zones/ron.zone
#
# but the users want to update their own zones without privileges.  So
# they own
#
#    /home/don/myzone
#    /home/ron/dns/zone
#    /home/jon/public_html/jon.example.com
#
# and store their zone files there.  You create symlinks
#
#    /etc/nsd/zones/don.zone.link -> /home/don/myzone
#    /etc/nsd/zones/jon.zone.link -> /home/ron/dns/zone
#    /etc/nsd/zones/ron.zone.link -> /home/jon/public_html/jon.example.com
#
# and every time you want nsd to publish whatever don, jon, or ron have
# put in their files, you run `nsd-update'.  You might create a fifo
#
#    mkfifo -m 0622 /var/run/nsd-update.fifo
#
# and use
#
#    fifowatchd -p /var/run/nsd-updated.pid -d 3 /var/run/nsd-update.fifo \
#       /bin/sh -c \
#         '/usr/local/sbin/nsd-update 2>&1 \
#          | logger -t nsd-update -p daemon.notice'
#
# to watch it, so that anyone can run
#
#    echo >> /var/run/nsd-update.fifo
#
# to request that nsd's zones be updated.  Any zone files with errors
# will be ignored.

set -Ceu

# Set some parameters.
: ${NSD_BINDIR:='@NSD_BINDIR@'}
: ${NSD_CONF:='@NSD_CONF@'}

# Make NSD_CONF an absolute pathname.
case $NSD_CONF in
/*)     ;;
*/*)    NSD_CONF="$(cd -- "${NSD_CONF%/*}" && pwd)/${NSD_CONF##*/}";;
*)      NSD_CONF="$(pwd)/${NSD_CONF}";;
esac

NSD_CHECKCONF="${NSD_BINDIR}/nsd-checkconf"
NSD_CHECKZONE="${NSD_BINDIR}/nsd-checkzone"

NSD_DB="$("$NSD_CHECKCONF" -o database -- "$NSD_CONF")"
NSD_PIDFILE="$("$NSD_CHECKCONF" -o pidfile -- "$NSD_CONF")"
NSD_ZONESDIR="$("$NSD_CHECKCONF" -o zonesdir -- "$NSD_CONF")"

# XXX Gronk.  Seems to be no nice way to get this in the config file.
case $NSD_PIDFILE in
*/*)    NSD_PIDDIR="${NSD_PIDFILE%/*}";;
*)      NSD_PIDDIR="";;
esac
: ${NSD_LOCKFILE:="${NSD_PIDDIR:+${NSD_PIDDIR}/}nsd.lock"}

# Utilities.
progname="${0##*/}"

note ()
{
    printf >&2 '%s: ' "$progname"
    printf >&2 "$@"
    printf >&2 '\n'
}

warn ()
{
    note "warning: $@"
}

fail ()
{
    note "error: $@"
    exit 1
}

rm_variables=

rm_on_exit ()
{
    rm_variables="${rm_variables+${rm_variables} }$@"
}

clean ()
{
    for var in $rm_variables; do
        eval "pathname=\$${var}"
        if [ -n "$pathname" ]; then
            rm -f -- "$pathname"
        fi
    done
}

reset_clean ()
{
    rm_variables=
    trap clean EXIT HUP INT TERM
}

reset_clean

# Parse arguments.
if [ $# -ne 0 ]; then
    fail 'usage: %s' "$progname"
fi

# Enter the zones directory in case any pathnames are relative.
if [ -n "$NSD_ZONESDIR" ]; then
    cd -- "$NSD_ZONESDIR"
fi

# Lock the zone database.  Wait at most three seconds before failing.
lockfd=3
exec 3>> "$NSD_LOCKFILE"
flock --wait 3 "$lockfd"

"$NSD_CHECKCONF" -o zones -- "$NSD_CONF" \
| (
    reset_clean                 # subshell

    zonefile_tmp=
    rm_on_exit zonefile_tmp

    while read zone; do
        # Read the configuration file.
        zonefile="$("$NSD_CHECKCONF" -z "$zone" -o zonefile -- "$NSD_CONF")"

        # Sanity-check the link.
        zonefile_link="${zonefile}.link"
        if [ ! -h "$zonefile_link" ]; then
            # If there's no link, assume it is maintained some other
            # way, and don't complain.
            continue
        fi
        if [ ! -f "$zonefile_link" ]; then
            warn 'zone %s link is broken: %s -> %s' "$zone" "$zonefile_link" \
                "$(readlink -- "$zonefile_link")"
            continue
        fi

        # Grab a snapshot of the new zone file.
        zonefile_tmp="${zonefile}.tmp"
        rm -f -- "$zonefile_tmp"
        cat < "$zonefile_link" > "$zonefile_tmp"
        if cmp -s -- "$zonefile" "$zonefile_tmp"; then
            # No changes; skip this.
            continue
        fi

        # All set.  Check the zone.
        if "$NSD_CHECKZONE" "$zone" "$zonefile_tmp"; then
            # Zone file seems OK -- commit it.
            mv -f -- "$zonefile_tmp" "$zonefile"
            zonefile_tmp=
        else
            warn 'zone not changed because file is broken: %s' "$zone"
            # Leave the zone file snapshot around for post-mortem analysis.
            zonefile_tmp=
        fi
    done

    # Notify nsd.
    if ! pid="$(head -c 16 < "$NSD_PIDFILE")"; then
        warn 'can'\''t read pidfile; is nsd running?'
    elif ! kill -HUP "$pid"; then
        warn 'can'\''t send SIGHUP; is nsd running?'
    fi
)