To establish a TCP-connection and be keeping it alive

sockping.sh

#!/bin/bash

function log {
    echo $(date) ' >> ' $* >&2
}

function die {
    echo $* >&2
    exit 1
}

while getopts ":m:h:p:" OPT; do
    case "${OPT}" in
        m)
            MODE="${OPTARG}"
            ;;
        h)
            HOST="${OPTARG}"
            ;;
        p)
            PORT="${OPTARG}"
            ;;
        \?)
            die "Invalid option: -${OPTARG}"
            ;;
        :)
            die "Option -${OPTARG} requires an argument."
            ;;
    esac
done

case "${MODE}" in

    client)
        [[ -z "${HOST}" ]] && die "Host isn't defined"
        [[ -z "${PORT}" ]] && die "Port isn't defined"
        socat TCP:${HOST}:${PORT} EXEC:"${0} -m client-ping",su-d=nobody
        ;;

    client-ping)
        PING=1
        while :; do
            # Sending ping
            echo -e "$(date +%s)\t${PING}"
            # Receiving pong
            read STRING
            # Checking latency
            TIME_NEW="$(date +%s)"
            if [[ ! -z "${TIME_OLD}" ]]; then
                LATENCY=$(( ${TIME_NEW} - ${TIME_OLD} ))
                if [[ "${LATENCY}" -gt 2 ]]; then
                    log "The latency is too high (${TIME_NEW} - ${TIME_OLD} = ${LATENCY})"
                fi
            fi
            TIME_OLD="${TIME_NEW}"
            # Checking sequence delta
            PONG="$(echo "${STRING}" | cut -f 2)"
            [[ -z ${PONG} ]] && die "Invalid reply: ${STRING}"
            STEP=$(( ${PONG} - ${PING} ))
            [[ "${STEP}" -ne 1 ]] && log "Unexpected sequence step (${PING} - ${PONG} = ${STEP})"
            PING=$(( ${PONG} + 1 ))
            # Sleeping
            sleep 1
        done
        ;;

    server)
        [[ -z "${PORT}" ]] && die "Port isn't defined"
        while : ; do
                socat TCP-LISTEN:${PORT},fork,su=nobody EXEC:"${0} -m server-ping"
                sleep 1
                log "Restarting"
        done
        ;;

    server-ping)
        log "${SOCAT_PEERADDR} connected"
        while :; do
            read STRING
            PING="$(echo "${STRING}" | cut -f 2)"
            [[ -z ${PING} ]] && die "Invalid request: ${STRING}"
            PONG=$(( ${PING} + 1 ))
            echo -e "$(date +%s)\t${PONG}"
            #
            [[ $(( ${PONG} % 10000 )) -eq 0 ]] && log "Sent the ${PONG}'th pong!"
        done
        ;;

    *)
        die "Invalid mode: ${MODE}"
        ;;

esac