Find who's online in the local network

arp-server.rb

#!/usr/bin/env ruby

require "redis"
require "sinatra"
require "sinatra/json"

redis = Redis.new

get "/" do
  macs_online  = redis.smembers("mac-online")

  names_online = if macs_online.empty?
    []
  else
    redis.hmget("mapping", macs_online).compact.uniq
  end

  names_all = redis.hvals("mapping")
  result = names_all.reduce({}) {|acc, name| acc[name] = names_online.include?(name) ? "online" : "offline"; acc}
  json result
end

post "/devices-online" do
  data =  request.body.read
  mac_addresses = data.split("\n")

  redis.del("mac-online")
  redis.sadd("mac-online", mac_addresses)

  status 200
end

post "/devices-mapping" do
  data =  request.body.read
  mac_mapping = data.split("\n").map{|e| e.split(",")}.flatten

  redis.del("mapping")
  redis.hmset("mapping", *mac_mapping)

  redis.del("mac-all")
  redis.sadd("mac-all", Hash[*mac_mapping].keys)

  status 200
end

arp.sh

#!/usr/bin/env bash

echo "Scanning..."

MACS_ONLINE=`sudo nmap -sn 192.168.1.0/24 | grep -Eio "([0-9A-F]{2}:){5}[0-9A-F]{2}"`
MACS_MAPPING=$(<arp-mapping.csv)

echo "Done."
echo "Uploading data..."

curl http://localhost:4567/devices-mapping -d "$MACS_MAPPING" -XPOST --header 'Content-Type: text/csv'
curl http://localhost:4567/devices-online -d "$MACS_ONLINE" -XPOST --header 'Content-Type: text/csv'

echo "Done."

Gemfile

source "https://rubygems.org"

ruby "2.1.0"

gem "sinatra"
gem "sinatra-contrib"
gem "redis"

mapping.csv