#!/bin/bash
set -e

listen_iface=${1}
listen_port=${2}
target_host=${3}
target_port=${4}

# Check non-empty
[[ -n "${listen_iface}" ]]
[[ -n "${listen_port}" ]]
[[ -n "${target_host}" ]]
[[ -n "${target_port}" ]]
# Check that ports is actually numbers
[[ ${listen_port} -eq ${listen_port} ]]
[[ ${target_port} -eq ${target_port} ]]

listen_address=$(ip -f inet addr show dev ${listen_iface} | grep -Po 'inet \K[\d.]+')
[[ -n "${listen_address}" ]]

echo " == Forwarding ${listen_address}:${listen_port} -> ${target_host}:${target_port}  == "

# Socat
socat -d -d TCP4-LISTEN:${listen_port},bind=${listen_address},su=nobody,fork,reuseaddr  TCP4:${target_host}:${target_port}