#!/bin/sh -
#
# KISS Dynamic DNS service (no locking (hint lockf wrapper), no advanced checking)
# 'ping' is based on ssh call or CGI call
#
# = INSTALL - SSH =
# 1) Make sure to allow rndc reload in your sudoers file
#    sudo_user  ALL=(ALL) NOPASSWD: /usr/sbin/rndc reload
# 2) prefix your ssh authorized key to allow only this script
#    command="/home/rvdzwet/dyndns.sh" 
# 3) Call for the remote host like this
#    ssh -a -p 1022 -i id_rsa zweot.vanderzwet.net `hostname`
#
# = INSTALL - CGI =
# XXX:TODO
#
# = USAGE =
# Make sure your DNS entries has zones like this to allow remote updating
#   example 60 IN A 192.0.32.10
#   example 60 IN TXT "dyndns"
#
# Rick van der Zwet <info@rickvanderzwet.nl>
#
ZONE='vanderzwet.net'
ZONEFILE="/etc/namedb/master/$ZONE"


### NO USER EDITABLE PARTS BELOW HERE ###
# SSH specific details
HOSTNAME=`echo $SSH_ORIGINAL_COMMAND | tr -c -d '[a-zA-Z0-9\-_\.]' | cut -d ' ' -f 1 | cut -d '.' -f 1`
REMOTEIP=`echo $SSH_CLIENT | cut -d ' ' -f 1`

# Tmpfile creation for editing 'in between'
TMPFILE=`mktemp -t $(basename $0 .sh).XXX`
trap "rm -f $TMPFILE; exit 1" 0 1 2 15
cp $ZONEFILE $TMPFILE || exit 1


# See whether there exists a dynamic entry for it, like this
# example 60 IN A 192.0.32.10
# example 60 IN TXT "dyndns"
LINENR=`awk -v host=$HOSTNAME '{if ($1 == host) { if ($4 == "A") { line=NR } else if($5 ~ /dyndns/) {print line; exit} }}' $TMPFILE`
if [ -z "$LINENR" ]; then
  echo "$HOSTNAME does not exists or is not marked as dynamic"
  exit 1
fi

# Do we need to update the entry
OLDIP=`awk -v linenr=$LINENR 'NR==linenr {print $5}' $TMPFILE`
if [ "$OLDIP" = "$REMOTEIP" ]; then
  echo "No changes"
  exit 0
fi

# Update the entry
sed -i '' "${LINENR}s/$OLDIP/$REMOTEIP/" $TMPFILE || exit 1

# Update serial of zone name
# YYYYMMDDNN where NN is from 00 till 99
TODAY=`date "+%Y%m%d"`
OLDSERIAL=`sed -n '1,10s/.*\([0-9]\{10\}\).*/\1/p' $TMPFILE`
if [ -z "$OLDSERIAL" ]; then
  echo "Error Unable to find SERIAL of zone"
  exit 1
fi
if `echo $OLDSERIAL | grep -q "^$TODAY"`; then
  if `echo $OLDSERIAL | grep -q '99$'`; then
    echo "Sorry domain update limit reached no more updates for today"
    exit 1
  fi
  NEWSERIAL=`expr $OLDSERIAL + 1`
else
  NEWSERIAL="${TODAY}00"
fi
sed -i '' "1,10s/$OLDSERIAL/$NEWSERIAL/g" $TMPFILE || exit 1

# Install and activate
if \! `/usr/sbin/named-checkzone -q $TMPFILE $ZONE`; then
  echo "New zone failed to validate"
  exit 1
fi
cp $TMPFILE $ZONEFILE
sudo /usr/sbin/rndc reload
echo "Entry updated"