Using RabbitMQ as Message Broker for RPC (Server)

rabbitmq_server.rb

#!/usr/bin/env ruby
require 'bunny'
require 'json'
require './calculator'

calculator = Calculator.new

# connect to RabbitMQ
conn = Bunny.new
conn.start

# create a channel and exchange that both client and server know about
ch = conn.create_channel
q  = ch.queue('calc')
x  = ch.default_exchange

q.subscribe(block: true) do |delivery_info, properties, payload|
  req_message = JSON.parse payload

  # calculate a result
  result = calculator.send *(req_message['params'].unshift(req_message['method']))

  reply = {
    'id' => req_message['id'],
    'result' => result,
    'jsonrpc' => '2.0'
  }

  # enqueue our reply in the return queue
  x.publish(JSON.generate(reply), {
    routing_key: properties.reply_to, 
    correlation_id: properties.correlation_id
  })
end