add test of rack middleware in Rails

lib/splunk/otel/instrumentation/action_pack/railtie.rb

@@ -6,8 +6,6 @@ module ActionPack
       # Install the Rack middleware for RUM responses
       class Railtie < ::Rails::Railtie
         config.before_initialize do |app|
-          OpenTelemetry::Instrumentation::Rack::Instrumentation.instance.install({})
-
           app.middleware.insert_before(
             0,
             Splunk::Otel::Rack::RumMiddleware

splunk-otel.gemspec

@@ -34,6 +34,7 @@ Gem::Specification.new do |spec|
   # development dependencies
   spec.add_development_dependency "rubocop-rake", "~> 0.6.0"
   spec.add_development_dependency "simplecov", "~> 0.21.2"
+  spec.add_development_dependency "rails", "~> 7.0.0"
 
   spec.metadata = {
     "rubygems_mfa_required" => "true"

test/splunk/instrumentation/rails_test.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require 'rails'
+
+require "test_helper"
+require "opentelemetry/sdk"
+require "opentelemetry/instrumentation/rack"
+require "splunk/otel"
+require "splunk/otel/instrumentation/rack"
+require "rack/test"
+require 'test_helpers/app_config.rb'
+
+module Splunk
+  class RumRailsTest < Test::Unit::TestCase
+    include Rack::Test::Methods
+
+    DEFAULT_RAILS_APP = AppConfig.initialize_app
+    ::Rails.application = DEFAULT_RAILS_APP
+
+    def setup
+      with_env("OTEL_SERVICE_NAME" => "test-service") do
+        Splunk::Otel.configure do |c|
+            c.use 'OpenTelemetry::Instrumentation::ActionPack'
+        end
+      end
+    end
+
+    def teardown
+      OpenTelemetry.tracer_provider.shutdown
+    end
+
+    def app
+      DEFAULT_RAILS_APP
+    end
+
+    test "RUM response from Rack middleware" do
+      get "/ok"
+
+      assert last_response.ok?
+      assert_equal "OK", last_response.body
+
+      response_headers = last_response.headers
+      assert_equal "Server-Timing", response_headers["Access-Control-Expose-Headers"]
+      assert_match(/traceparent;desc="00-\w{32}-\w{16}-01"/, response_headers["Server-Timing"])
+    end
+  end
+end

test/test_helpers/app_config.rb

@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+class Application < Rails::Application; end
+require 'action_controller/railtie'
+require_relative 'middlewares'
+require_relative 'controllers'
+require_relative 'routes'
+
+module AppConfig
+  extend self
+
+  def initialize_app(use_exceptions_app: false, remove_rack_tracer_middleware: false)
+    new_app = Application.new
+    new_app.config.secret_key_base = 'secret_key_base'
+
+    # Ensure we don't see this Rails warning when testing
+    new_app.config.eager_load = false
+
+    # Prevent tests from creating log/*.log
+    new_app.config.logger = Logger.new(File::NULL)
+
+    new_app.config.filter_parameters = [:param_to_be_filtered]
+
+    case Rails.version
+    when /^6\.0/
+      apply_rails_6_0_configs(new_app)
+    when /^6\.1/
+      apply_rails_6_1_configs(new_app)
+    when /^7\./
+      apply_rails_7_configs(new_app)
+    end
+
+    remove_rack_middleware(new_app) if remove_rack_tracer_middleware
+    add_exceptions_app(new_app) if use_exceptions_app
+    add_middlewares(new_app)
+
+    new_app.initialize!
+
+    draw_routes(new_app)
+
+    new_app
+  end
+
+  private
+
+  def remove_rack_middleware(application)
+    application.middleware.delete(
+      OpenTelemetry::Instrumentation::Rack::Middlewares::TracerMiddleware
+    )
+  end
+
+  def add_exceptions_app(application)
+    application.config.exceptions_app = lambda do |env|
+      ExceptionsController.action(:show).call(env)
+    end
+  end
+
+  def add_middlewares(application)
+    application.middleware.insert_after(
+      ActionDispatch::DebugExceptions,
+      ExceptionRaisingMiddleware
+    )
+
+    application.middleware.insert_after(
+      ActionDispatch::DebugExceptions,
+      RedirectMiddleware
+    )
+  end
+
+  def apply_rails_6_0_configs(application)
+    # Required in Rails 6
+    application.config.hosts << 'example.org'
+    # Creates a lot of deprecation warnings on subsequent app initializations if not explicitly set.
+    application.config.action_view.finalize_compiled_template_methods = ActionView::Railtie::NULL_OPTION
+  end
+
+  def apply_rails_6_1_configs(application)
+    # Required in Rails 6
+    application.config.hosts << 'example.org'
+  end
+
+  def apply_rails_7_configs(application)
+    # Required in Rails 7
+    application.config.hosts << 'example.org'
+
+    # Unfreeze values which may have been frozen on previous initializations.
+    ActiveSupport::Dependencies.autoload_paths =
+      ActiveSupport::Dependencies.autoload_paths.dup
+    ActiveSupport::Dependencies.autoload_once_paths =
+      ActiveSupport::Dependencies.autoload_once_paths.dup
+  end
+end

test/test_helpers/controllers.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require_relative 'controllers/example_controller'
+require_relative 'controllers/exceptions_controller'

test/test_helpers/controllers/example_controller.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+class ExampleController < ActionController::Base
+  include ::Rails.application.routes.url_helpers
+
+  def ok
+    render plain: "OK"
+  end
+
+  def internal_server_error
+    raise :internal_server_error
+  end
+end

test/test_helpers/controllers/exceptions_controller.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+class ExceptionsController < ActionController::Base
+  def show
+    render plain: 'oops', status: :internal_server_error
+  end
+end

test/test_helpers/middlewares.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require_relative 'middlewares/exception_raising_middleware'
+require_relative 'middlewares/redirect_middleware'

test/test_helpers/middlewares/exception_raising_middleware.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+class ExceptionRaisingMiddleware
+  def initialize(app, _options = {})
+    @app = app
+  end
+
+  def call(env)
+    raise 'a little hell' if should_raise?(env)
+
+    @app.call(env)
+  end
+
+  private
+
+  def should_raise?(env)
+    env['PATH_INFO'] == '/exception' || env['QUERY_STRING'].include?('raise_in_middleware')
+  end
+end

test/test_helpers/middlewares/redirect_middleware.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+class RedirectMiddleware
+  def initialize(app, _options = {})
+    @app = app
+  end
+
+  def call(env)
+    return [307, {}, 'Temporary Redirect'] if should_redirect?(env)
+
+    @app.call(env)
+  end
+
+  private
+
+  def should_redirect?(env)
+    env['PATH_INFO'] == '/redirection' || env['QUERY_STRING'].include?('redirect_in_middleware')
+  end
+end

test/test_helpers/routes.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+def draw_routes(rails_app)
+  rails_app.routes.draw do
+    get '/ok', to: 'example#ok'
+    get '/internal_server_error', to: 'example#internal_server_error'
+  end
+end