Tunnel TCP traffic via socat. #socat

socat-forward-tcp.sh

#!/bin/bash

PUBLIC_IP4_IFACE=eth2
LISTEN_IFACE=${PUBLIC_IP4_IFACE}

listen_address=$(ip -f inet addr show dev ${LISTEN_IFACE} | grep -Po 'inet \K[\d.]+')
listen_port=${1}
target_host=${2}
target_port=${3}

if [ -z "${listen_port}" ]; then
    echo "${0} <listen-port> <target-host> <target-port>" && exit 1;
fi
if [ -z "${target_host}" ]; then
    echo "${0} <listen-port> <target-host> <target-port>" && exit 1;
fi
if [ -z "${target_port}" ]; then
    echo "${0} <listen-port> <target-host> <target-port>" && exit 1;
fi

# Test that ports is actually numbers
[[ ${listen_port} -eq ${listen_port} ]]
[[ ${target_port} -eq ${target_port} ]]

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}