Using netcat to proxy a host.

Host Proxy

#!/bin/env bash

PORT="${1}"
TARGET="${2}"
[ -z "${3}" ] && TPORT="${1}" || TPORT="${3}" 

if [ -z "$1" ] || [ -z "$2" ]; then
    echo "Usage: $0 <port> <target> [target port]"
    exit 1
fi

## Create TMP Directory to hold pid files and fifos
TMP="$(mktemp -d)"

FIN="${TMP}/in"
FOUT="${TMP}/out"

## Create FIFOs
mkfifo "$FIN"
mkfifo "$FOUT"

echo Created Temp Directory: ${TMP}
echo Logging Directory: ${LOGD}
echo ----------------------------------------
echo Proxing Host: ${TARGET}:${TPORT} 
echo Listening on: ${PORT}
echo ----------------------------------------

## Signal handler for a clean exit.
function stop_proxy {

    ## Kill all processes in the PID files
    for i in `ls ${TMP}/*.pid 2> /dev/null`; do
        stop_pid "$(cat $i)"
    done

    ## Dump the fifos and the tmp dir
    rm -f "${FIN}" "${FOUT}"
    rmdir ${TMP}

    exit 0
}

function stop_pid {
    rm -f "${TMP}/${1}.pid" && kill $1 2> /dev/null
}

function store_pid {
    ## only create this if we have a valid PID
    [ ! -z "${1}" ] && echo $1 > "${TMP}/${1}.pid"
}


## grab signal hander    
trap 'stop_proxy' INT

while true; do
    ## start proxy intake and grap pid (fork)
    nc -l -p $PORT < $FOUT | tee -a "${FIN}" | sed "s|^|CLIENT\||g" &
    sleep 1
    CLIENT="$(jobs -p | tail -n1)"
    store_pid $CLIENT

    ## start proxy forward and grab pid (fork)
    nc "$TARGET" "$TPORT" < $FIN | tee -a "${FOUT}" | sed "s|^|SERVER\||g" &
    SERV="$(jobs -p | tail -n1)"
    store_pid $SERV

    ## Wait for -l to end
    wait $CLIENT

    ## Clean up PID file
    rm "${TMP}/${CLIENT}.pid"

    ## Stop other server connection
    stop_pid $SERV
done