Expose @service from Gruf::Controllers::Request to interceptors

[pedelman]

I would like to instrument Gruf endpoints with New Relic. For this I plan to create an interceptor which will utilize the ControllerInstrumentation#perform_action_with_newrelic_trace. http://www.rubydoc.info/github/newrelic/rpm/NewRelic%2FAgent%2FInstrumentation%2FControllerInstrumentation:perform_action_with_newrelic_trace

In order for the requests to show up correctly, I need to pass in the class_name of the controller / service. It seems like the @service is a natural fit for this use case.

https://github.com/bigcommerce/gruf/blob/master/lib/gruf/controllers/request.rb#L54

Herre is an example of the code I wrote which can instrument Gruf endpoints using newrelic, (maybe this is something which can also be brought into Gruf).

require 'new_relic/agent'

module Interceptors
  module Gruf
    ##
    # New Relic transaction tracing for Gruf endpoints
    #
    class NewRelicTracer < ::Gruf::Interceptors::ServerInterceptor
      include ::NewRelic::Agent::Instrumentation::ControllerInstrumentation

      def call
        opts = {
          category: :controller,
          class_name: request.instance_variable_get('@service'),
          name: request.method_key
        }

        perform_action_with_newrelic_trace(opts) do
          yield
        end
      end
    end
  end
end

I would also gladly open a pr to add an attr_reader for the service but figure we may want to have a different approach to expose these values.

[pedelman]

Ping @splittingred @mattolson @ncancelliere @billthompson

Also @Parad0X this is pretty similar to the exposing of the rpc_desc, perhaps the approach can be similar, I know @splittingred has some ideas on how we want to expose these attributes to interceptors.