factorio headless server w+ instant updates

#!/bin/sh
### [ -- v config here v -- ]
INSTALL_ROOT='/home/factorio'
BRANCH='experimental'
URL_BASE='https://www.factorio.com'
### [ -- ^ config here ^ -- ]

###

URL_WATCH=${URL_BASE}'/download-headless/'${BRANCH}
REGEX_VERSION_URL='/get-download/([^/]+)/headless/linux64'
REGEX_URL_HTML='href="('${REGEX_VERSION_URL}')"'
PID_SRV=''

D=/dev/null
readonly D

log() { echo "# $@"; }


random() {
  local n x
  if [ $1 -lt 1 ]; then
    echo 0
    return
  fi
  if [ $1 -lt 255 ]; then
    n=1
  elif [ $1 -lt 65535 ]; then
    n=2
  else
    n=4
  fi
  x='0x'$(dd if=/dev/urandom bs=$n count=1 2>$D | xxd -ps)
  # x=$((x + 0))
  echo $((x % $1))
}

http_test() {
  curl -kLI "$1" 2>$D | grep -Eqe '^HTTP/\S+ 2.. '
}

http_get() {
  curl -kL "$1" 2>$D
}

get_relative_url_upstream() {
  http_get "${URL_WATCH}" | grep -Eoe "${REGEX_URL_HTML}" | \
  sed -re "s#${REGEX_URL_HTML}#\1#" | head -n 1
}

get_version_local() {
  "${INSTALL_ROOT}/bin/factorio" --version 2>&1 | \
  sed -nre '/^Version:\s+(\S+)\s.*$/{s##\1#;p;}'
}

get_version_upstream() {
  get_relative_url_upstream | sed -re "s#${REGEX_VERSION_URL}#\1#"
}

process_present() {
  [ -n "$1" ] || return 1
  /bin/ps -p "$1" 0<$D 1>$D 2>$D
}

process_sig() {
  /bin/kill -s "$2" "$1" 0<$D 1>$D 2>$D
}

stop_server() {
  [ -n "$1" ] || return

  if process_present "$1"; then
    process_sig "$1" TERM
    sleep 5
    process_sig "$1" KILL
  fi
}

start_server() {
  [ -n "${INSTALL_ROOT}" ] || return 1
  [ -d "${INSTALL_ROOT}" ] || return 1

  cd "${INSTALL_ROOT}/"
  "${INSTALL_ROOT}/bin/factorio" --verbose \
    --bind 127.0.0.1:34197 \
    --config ${INSTALL_ROOT}/cfg/server.ini \
    --mod-directory ${INSTALL_ROOT}/var/mods \
    --map-settings ${INSTALL_ROOT}/cfg/map-settings.json \
    --start-server ${INSTALL_ROOT}/var/saves/my-awesome-server.zip \
  1>&2 <$D &
  echo $!
}

###

while :; do
  log 'is upstream info is available?'
  if http_test "${URL_WATCH}"; then
    log 'OK, upstream info is available'

    VER_UPSTREAM=$(get_version_upstream)
    VER_LOCAL=$(get_version_local)

    log 'local version: ' "${VER_LOCAL}"
    log 'remote version:' "${VER_UPSTREAM}"

    if [ "${VER_LOCAL}" = "${VER_UPSTREAM}" ]; then
      log "versions are equal, update isn't required"
    else
      log "versions are different, begin update"

      log 'is upstream tarball is available?'

      URL_TARBALL=${URL_BASE}$(get_relative_url_upstream)
      if http_test "${URL_TARBALL}"; then
        log 'OK, upstream tarball is available'

        DTMP=$(mktemp -d)
        cd "${DTMP}/"

        log 'downloading tarball'

        http_get "${URL_TARBALL}" > "${VER_UPSTREAM}.t"
        tar --strip-components=1 -xf "${VER_UPSTREAM}.t"

        log 'processing tarball'

        strip \
          --remove-section=.comment \
          --remove-section=.note \
        bin/x64/factorio

        if [ -n "${PID_SRV}" ]; then
          log 'stopping server'

          stop_server ${PID_SRV}; PID_SRV=''
          sleep 5
        fi

        log 'updating installation'

        cp bin/x64/factorio "${INSTALL_ROOT}/bin/factorio"
        rm -rf "${INSTALL_ROOT}/data"
        tar cf - data | (cd "${INSTALL_ROOT}/"; tar xf -;)

        log 'update is complete'

        cd /; rm -rf "${DTMP}/"
      else
        log 'FAIL, upstream tarball is NOT available'
      fi
    fi
  else
    log 'FAIL, upstream info is NOT available'
  fi

  if [ -n "${PID_SRV}" ]; then
    if ! process_present ${PID_SRV}; then
      log 'server is gone away, try to restart'

      PID_SRV=''
    fi
  fi
  if [ -z "${PID_SRV}" ]; then
    log 'starting server'

    PID_SRV=$(start_server)
    sleep 5

    if ! process_present "${PID_SRV}"; then
      log 'server is gone away after startup, quit!'
      exit 1
    fi
  fi

  wait=$(($(random 1800) + 1800))
  log "sleep for a while (${wait} seconds)"
  sleep ${wait}
done