client.rb

require_relative "./shared"

seen_ids = []

$q.subscribe(:block => true, :manual_ack => true) do |delivery_info, metadata, payload|
  data = JSON.parse(payload)
  p "Got #{data["id"]} (#{data["nack"]})"

  if seen_ids.include?(data["id"])
    raise "Dup! Already seen this message"
  end

  seen_ids << data["id"]

  if data["nack"]
    $channel.nack(delivery_info.delivery_tag, false, true)
  else
    $channel.ack(delivery_info.delivery_tag)
  end
end

producer.rb

require_relative "./shared"

1.upto(Float::INFINITY) do |i|
  payload = {
    :id => i,
    :nack => (i == 2)
  }

  $x.publish(payload.to_json, :routing_key => $q.name)
end

$conn.close

shared.rb

require "bunny"
require "json"

$conn = Bunny.new
$conn.start

$channel = $conn.create_channel
$q = $channel.queue("foo", :auto_delete => false)
$x = $channel.fanout("one")