netcrap

#!/bin/bash

# SPDX-License-Identifier: GPL-3.0-only
# Copyright 2024, Mattias Bengtsson <mattias.jc.bengtsson@gmail.com>

set -e
set -o pipefail


################################################################################

function add-impairment {
    sudo tc qdisc add dev "${ARG_DEV}" root netem "${@}"
}

# shellcheck disable=SC2317
function show-impairments {
    sudo tc qdisc show dev "${ARG_DEV}"
}

function turn-on {
    echo Turning on network impairments...

    add-impairment delay 100000ms
}

function turn-off {
    echo Turning off network impairments...

    sudo tc qdisc delete dev "${ARG_DEV}" root netem
}

function is-netdev {
    test -L "/sys/class/net/${1}"
}

################################################################################


function error {
    echo "ERROR: ${*}" >/dev/stderr
}

function usage {
    cat <<EOM

Usage: $(basename "${0}") [-h | --help] <on|off>

  -h, --help    Show this help message.

EOM
}

function parse-args {
    local opts flags script

    script="$(basename "${0}")"
    flags="help,on,off"
    opts="$(getopt -o h --long "${flags}" -n "${script}" -- "${@}")"
    eval set -- "$opts"

    OPT_STATE=on
    ARG_DEV=

    while true; do
        case "${1}" in
            -h | --help)
                usage
                exit
                ;;
            --on)
                OPT_STATE=on
                shift
                ;;
            --off)
                OPT_STATE=off
                shift
                ;;
            --) shift; break ;;
            *)  break ;;
        esac
    done

    if [ "${#}" -lt 1 ]; then
        usage
        echo
        error "No device!"
        return 2
    fi

    ARG_DEV="${1}"
    shift

    if ! is-netdev "${ARG_DEV}"; then
        error "Not a network device: ${ARG_DEV}!"
        return 3
    fi

    export OPT_STATE
    export ARG_DEV
}

function main {
    parse-args "${@}"
    case "${OPT_STATE}" in
        on)   turn-on           ;;
        off)  turn-off          ;;
    esac
}

main "${@}"; exit