attach_to.rb

#!/usr/bin/env ruby

require "excon"
require "active_support"
require "active_support/subscriber"

# Translates excon instrumentation events into rails style with
# namespace last. Yuck!
class ExconToRailsInstrumentor
  def self.instrument(name, datum, &block)
    namespace, *event = name.split(".")
    rails_name = [event, namespace].flatten.join(".")
    ActiveSupport::Notifications.instrument(rails_name, datum, &block)
  end
end

# Subscriber class that is compatible with `attach_to`.
module Excon
  class Subscriber < ActiveSupport::Subscriber
    def request(event)
      puts event.name
    end

    def response(event)
      puts event.name
    end
  end
end

# This effectively just sets up some callbacks that sort of look like this:
# * notifier.subscribe("request.excon", Proc { Excon::Subscriber.new.request(event) })
# * notifier.subscribe("response.excon", Proc { Excon::Subscriber.new.response(event) })
Excon::Subscriber.attach_to "excon"

Excon.get("https://google.com", :instrumentor => ExconToRailsInstrumentor)

# $ ./attach_to.rb
# request.excon
# response.excon

subscribe.rb

#!/usr/bin/env ruby

require "excon"
require "active_support"

# Subscribe to request notifications.
ActiveSupport::Notifications.subscribe(/excon.request/) do |name, started, finished, unique_id, data|
  puts name
end

# Subscribe to response notifications.
ActiveSupport::Notifications.subscribe(/excon.response/) do |name, started, finished, unique_id, data|
  puts name
end

# Register ActiveSupport::Notifications as the thing we call `instrument` on. The name passed as the 
# first paramater to insturment is opque. It simply needs to match what we expect in our subscribe calls above.

Excon.get('http://google.com', :instrumentor => ActiveSupport::Notifications)

# $ ./instrument.rb
# excon.request
# excon.response