#!/bin/sh

# dnssec-trigger script handling possible backup and restore of resolv.conf

SCRIPT_NAME="dnssec-trigger-resolvconf-handle.sh"

STATE_DIR="/var/run/dnssec-trigger"

RESOLV_CONF="/etc/resolv.conf"

RESOLV_CONF_BAK="$STATE_DIR/resolv.conf.bak"

NM_CONFIG="/etc/NetworkManager/NetworkManager.conf"

usage()

{

    echo

    echo "This script backs up or restores /etc/resolv.conf content"

    echo "Usage: $SCRIPT_NAME [backup|restore]"

}

# check number of arguments

if ! [ "$#" -eq 1 ]; then

    echo "ERROR: Wrong number of arguments!"

    usage

    exit 1

fi

does_nm_handle_resolv_conf()

{

    grep -x "^dns=none" $NM_CONFIG &> /dev/null

    echo "$?"

}

backup_resolv_conf()

{

    # find out if NM handles the resolv.conf

    if [ "`does_nm_handle_resolv_conf`" -eq 0 ]; then

        cp -fp $RESOLV_CONF $RESOLV_CONF_BAK

    fi

}

restore_resolv_conf()

{

    # if we have a backup and NM does not handle resolv.conf -> restore it

    if [ "`does_nm_handle_resolv_conf`" -eq 0 ] && [ -s $RESOLV_CONF_BAK ]; then

        cp -fp $RESOLV_CONF_BAK $RESOLV_CONF

    else

        # let NM rewrite the resolv.conf

        systemctl restart NetworkManager.service

    fi

}

case "$1" in

    backup)

        backup_resolv_conf

        ;;

    restore)

        restore_resolv_conf

        ;;

    *)

        echo "ERROR: Wrong argument!"

        usage

        exit 1

esac

exit 0