sh/relay_overlord_discovery_packet.sh

#!/bin/sh
#
# Copyright 2015 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
#
# This script relays Overlord LAN discovery packets to a interface
#

. "$(dirname "$(readlink -f "$0")")/common.sh" || exit 1

QUIT=false

clean_up() {
  QUIT=true
  pkill -9 -P $$
}

get_broadcast_ip() {
  local iface="$1"
  # There are two version of ifconfig producing different output
  # 1st:
  #   192.168.0.1  netmask 255.255.255.0  broadcast 192.168.0.255
  # 2nd:
  #   inet addr:192.168.0.1  Bcast:192.168.0.255  Mask:255.255.255.0
  echo "$(ifconfig $iface | awk \
    '/broadcast/ { print $6 } /Bcast/ { split($3, p, ":"); print p[2] }')"
}

main() {
  if [ "$#" -ne "1" ]; then
    alert "ERROR: Usage: $0 interface"
    exit 1
  fi

  local bcast_ip="$(get_broadcast_ip "$1")"
  if [ -z "${bcast_ip}" ]; then
    die "Can not find interface $1"
  fi

  while true; do
    socat -u UDP-RECVFROM:4456 UDP-DATAGRAM:${bcast_ip}:4456,broadcast
    if ${QUIT}; then
      break
    fi
    sleep 1
  done
}

trap clean_up EXIT INT

main "$@"