ZeroConf is a multicast DNS client and server written in pure Ruby. Use it to find multicast services, or advertise your own!

I've got some Elgato Key lights that can be controlled via the network. In this example, we're going to use ZeroConf to find them on the network, then we'll connect with net/http and control them.

Lets start by getting a list of Multicast DNS services on the network:

all_services = ZeroConf.find_services
service = all_services.grep(/_elg/).first # => "_elg._tcp.local"

We've found the Elgato service name on the network, next lets get the host names and connection information:

addr_infos = ZeroConf.find_addrinfos(service)

I have two lights on my network, and both of them have an IPv4 and IPv6 addresses, so we get back an array with 4 tuples:

[["elgato-key-light-2d93.local", #<Addrinfo: 10.0.1.249:9123 (elgato-key-light-2d93.local)>],
 ["elgato-key-light-2d93.local", #<Addrinfo: [fe80::3e6a:9dff:fe19:b313]:9123 (elgato-key-light-2d93.local)>],
 ["elgato-key-light-48c6.local", #<Addrinfo: 10.0.1.151:9123 (elgato-key-light-48c6.local)>],
 ["elgato-key-light-48c6.local", #<Addrinfo: [fe80::3e6a:9dff:fe19:3a99]:9123 (elgato-key-light-48c6.local)>]]

We can connect either via IP address or host name. In this example, I'm just going to get the unique host names and ports, connect to those, and shut off the lights.

require "uri"
require "net/http"
require "json"

# Get unique host / port
connection_info = addr_infos.uniq(&:first).map { |host, addr| [host, addr.ip_port] }

# Turn the lights off
connection_info.each { |host, port|
  req = Net::HTTP::Put.new("/elgato/lights")
  req.body = { "numberOfLights": 1, "lights": [ { "on": 0 } ] }.to_json
  Net::HTTP.start(host, port) { |http| http.request(req) }
}

Here is the whole script:

require "zeroconf"
require "uri"
require "net/http"
require "json"

# Find all services
all_services = ZeroConf.find_services

# Look for Elgato
service = all_services.grep(/_elg/).