#!/usr/bin/env bash

# This script determines the IPv6 address of a given domain. The so found
# address is then used to create an IPv4-to-IPv6 tunnel from this device to the
# IPv6 address.
# [6tunnel](https://packages.debian.org/de/sid/6tunnel) is used to create the
# proxy.
#
# Usage: ./ipv6-mapper.sh <DOMAIN> <HOST_PORT=443> <TARGET_PORT=443>

set -e

DOMAIN=${1}  # e.g. mysub.mydomain.com, must have a valid AAAA record

HOST_PORT=${2:-443}
TARGET_PORT=${3:-443}

if ! [ -x "$(command -v 6tunnel)" ]; then
        >&2 echo "Fatal error: 6tunnel is not installed. Abort."
        exit 1
fi

# Request current ipv6 address
IPv6=`dig +short "${DOMAIN}" AAAA`

if [ -z "$IPv6" ]; then
        >&2 echo "Fatal error: IPv6 DNS entry not available. Abort."
        exit 1
fi

echo "---------- [ start ipv4-to-ipv6-bridge ] ----------"
echo `date`
echo "Found IPv6 address: ${IPv6}"

proc_count=`ps -aux | grep "6tunnel ${HOST_PORT} ${IPv6}" | wc -l`
if [ proc_count = "0" ]; then
        # Kill all existing tunnel processes
        echo "Removing already established tunnel connections on this port"
        kill -9 `ps -aux | grep "6tunnel ${HOST_PORT}" | awk '{ print $2 }'`

        # Establish connection to new ip
        echo "Establish new tunnel connection"
        6tunnel ${HOST_PORT} ${IPv6} ${TARGET_PORT}

        echo "6tunnel connection has been updated. Finish."
else
        echo "6tunnel connection up to date. No need to update connection. Finish."
fi

echo "---------- [ end ipv4-to-ipv6-bridge   ] ----------"