00README.md

usage: arp-to-mqtt [-t <prefix>] [-h host] [-i <interface>]

A utility script to dump an ARP table to a set of MQTT topics.

For each MAC with an IP publish a message to

<prefix>/<mac of interface>/<mac of device>/ip

and

<prefix>/<mac of interface>/<mac of device>/hostname

if the IP was resolved to a hostname

arp-to-mqtt

#!/bin/bash

set -e

PATH=/bin:/sbin:/usr/bin:/usr/sbin:

mqtt_broker=localhost
mqtt_id=arp_to_mqtt_$(hostname --fqdn)

if=eth0
topic_prefix=/arp
arp_args=()

while getopts ":h:t:i:n" opt; do
  case $opt in
    h)
      mqtt_broker="$OPTARG"
      OPTIND=1
      shift 2
      ;;
    t)
      topic_prefix="$OPTARG"
      OPTIND=1
      shift 2
      ;;
    i)
      if="$OPTARG"
      OPTIND=1
      shift 2
      ;;
    n)
      arp_args+=(-n)
      OPTIND=1
      shift
      ;;
    *)
      echo "Invalid option: -$OPTARG" >&2
      exit 1
      break
      ;;
  esac
done

if [ $# -gt 0 ]
then
  echo "Bad argument: $@"
  exit 1
fi

if_mac=$(/sbin/ifconfig "$if"|sed -n -e 's,.*ether \([^ ]*\) .*,\1,p')

pub() {
  path=$1; shift;
  msg=$1; shift;

#  echo -e "$path" "\t=\t" "$msg"

  opts=()

  if [[ $msg == "" ]]
  then
    opts+=(-n)
#    return
  else
    opts+=(-m)
    opts+=("$msg")
  fi

  opts+=(-q 0)
  opts+=(-r)

  mosquitto_pub -i "$mqtt_id" -h "$mqtt_broker" -t "$topic_prefix/$path" "${opts[@]}"
}

timestamp=$(date +%s)

/usr/sbin/arp -i "$if" "${arp_args[@]}" -a | \
    sed -n -e '/<incomplete>/d' \
        -e 's,\([^ ]\) (\([^)]*\)) at \([^ ]*\) .*,\1;\2;\3,p' | while IFS=';' read hostname ip mac rest
do
#  pub "$if_mac/$mac" ""

  pub "$if_mac/$mac/ip" "$ip"

  if [[ $hostname == '?' ]]
  then
    hostname=""
  fi

  pub "$if_mac/$mac/hostname" "$hostname"
done