Fix http.route tag for rack apps mounted in Rails

lib/datadog/tracing/contrib/rack/middlewares.rb

@@ -141,17 +141,6 @@ def set_request_tags!(trace, request_span, env, status, headers, response, origi
             if status != 404 && (last_route = trace.get_tag(Tracing::Metadata::Ext::HTTP::TAG_ROUTE))
               last_script_name = trace.get_tag(Tracing::Metadata::Ext::HTTP::TAG_ROUTE_PATH) || ''
 
-              # If the last_script_name is empty but the env['SCRIPT_NAME'] is NOT empty
-              # then the current rack request was not routed and must be accounted for
-              # which only happens in pure nested rack requests i.e /rack/rack/hello/world
-              #
-              # To account for the unaccounted nested rack requests of /rack/hello/world,
-              # we use 'PATH_INFO knowing that rack cannot have named parameters
-              if last_script_name == '' && env['SCRIPT_NAME'] && env['SCRIPT_NAME'] != ''
-                last_script_name = last_route
-                last_route = env['PATH_INFO']
-              end
-
               # Clear the route and route path tags from the request trace to avoid possibility of misplacement
               trace.clear_tag(Tracing::Metadata::Ext::HTTP::TAG_ROUTE)
               trace.clear_tag(Tracing::Metadata::Ext::HTTP::TAG_ROUTE_PATH)
@@ -218,10 +207,6 @@ def set_request_tags!(trace, request_span, env, status, headers, response, origi
               request_span.set_tag(Tracing::Metadata::Ext::HTTP::TAG_USER_AGENT, user_agent)
             end
 
-            if request_span.get_tag(Tracing::Metadata::Ext::HTTP::TAG_ROUTE).nil? && status != 404
-              request_span.set_tag(Tracing::Metadata::Ext::HTTP::TAG_ROUTE, env['PATH_INFO'])
-            end
-
             HeaderTagging.tag_request_headers(request_span, request_header_collection, configuration)
             HeaderTagging.tag_response_headers(request_span, headers, configuration) if headers
 

spec/datadog/tracing/contrib/action_pack/action_dispatch/journey/router_spec.rb

@@ -23,20 +23,43 @@
 
     describe '#find_routes' do
       before do
-        engine.routes.append do
+        stub_const('AuthEngine', Module.new)
+
+        stub_const(
+          'AuthEngine::TokensController',
+          Class.new(ActionController::Base) do
+            def create
+              head :ok
+            end
+          end
+        )
+
+        auth_engine = stub_const(
+          'AuthEngine::Engine',
+          Class.new(::Rails::Engine) do
+            isolate_namespace AuthEngine
+          end
+        )
+
+        auth_engine.routes.append do
           get '/sign-in' => 'tokens#create'
         end
 
-        auth_engine = engine
-        rack_status_app = rack_app.new
+        rack_status_app = stub_const(
+          'RackStatusApp',
+          Class.new do
+            def call(_env)
+              [200, {'Content-Type' => 'text/plain'}, ['OK']]
+            end
+          end
+        )
 
         rails_test_application.instance.routes.append do
           namespace :api, defaults: {format: :json} do
             resources :users, only: %i[show]
 
             mount auth_engine => '/auth'
-
-            match '/status', to: rack_status_app, via: :get
+            mount rack_status_app.new => '/status'
           end
 
           get '/items/:id', to: 'items#by_id', id: /\d+/
@@ -47,17 +70,6 @@
         end
       end
 
-      let(:rack_app) do
-        stub_const(
-          'RackStatusApp',
-          Class.new do
-            def call(_env)
-              [200, {'Content-Type' => 'text/plain'}, ['OK']]
-            end
-          end
-        )
-      end
-
       let(:controllers) { [users_controller, items_controller, books_controller] }
 
       let(:users_controller) do
@@ -101,37 +113,6 @@ def show
         )
       end
 
-      let(:status_controller) do
-        stub_const(
-          'StatusesController',
-          Class.new(ActionController::Base) do
-            def show
-              head :ok
-            end
-          end
-        )
-      end
-
-      let(:engine) do
-        stub_const('AuthEngine', Module.new)
-
-        stub_const(
-          'AuthEngine::TokensController',
-          Class.new(ActionController::Base) do
-            def create
-              head :ok
-            end
-          end
-        )
-
-        stub_const(
-          'AuthEngine::Engine',
-          Class.new(::Rails::Engine) do
-            isolate_namespace AuthEngine
-          end
-        )
-      end
-
       context 'with default configuration' do
         before do
           Datadog.configure do |c|
@@ -208,8 +189,8 @@ def create
           expect(request_span.tags).not_to have_key('http.route.path')
         end
 
-        it 'sets http.route for a route to a rack app' do
-          get '/api/status'
+        it 'sets http.route for a route to a mounted rack app' do
+          get '/api/status/some_path'
 
           request_span = spans.first