Changed: Only apply Rails #initialize hooks once per app.

Author: delner

lib/ddtrace/contrib/rails/patcher.rb

@@ -32,10 +32,12 @@ def patch_before_intialize
         end
 
         def before_intialize(app)
-          # Middleware must be added before the application is initialized.
-          # Otherwise the middleware stack will be frozen.
-          # Sometimes we don't want to activate middleware e.g. OpenTracing, etc.
-          add_middleware(app) if Datadog.configuration[:rails][:middleware]
+          do_once(:rails_before_initialize, for: app) do
+            # Middleware must be added before the application is initialized.
+            # Otherwise the middleware stack will be frozen.
+            # Sometimes we don't want to activate middleware e.g. OpenTracing, etc.
+            add_middleware(app) if Datadog.configuration[:rails][:middleware]
+          end
         end
 
         def add_middleware(app)
@@ -59,10 +61,12 @@ def patch_after_intialize
         end
 
         def after_intialize(app)
-          # Finish configuring the tracer after the application is initialized.
-          # We need to wait for some things, like application name, middleware stack, etc.
-          setup_tracer
-          instrument_rails
+          do_once(:rails_after_initialize, for: app) do
+            # Finish configuring the tracer after the application is initialized.
+            # We need to wait for some things, like application name, middleware stack, etc.
+            setup_tracer
+            instrument_rails
+          end
         end
 
         # Configure Rails tracing with settings

spec/ddtrace/contrib/rails/railtie_spec.rb

@@ -22,12 +22,19 @@ def index
 
   RSpec::Matchers.define :have_kind_of_middleware do |expected|
     match do |actual|
+      found = 0
       while actual
-        return true if actual.class <= expected
+        found += 1 if actual.class <= expected
         without_warnings { actual = actual.instance_variable_get(:@app) }
       end
-      false
+      found == (count || 1)
     end
+
+    chain :once do
+      @count = 1
+    end
+
+    chain :copies, :count
   end
 
   before(:each) do
@@ -44,8 +51,8 @@ def index
     context 'set to true' do
       let(:rails_options) { super().merge(middleware: true) }
 
-      it { expect(app).to have_kind_of_middleware(Datadog::Contrib::Rack::TraceMiddleware) }
-      it { expect(app).to have_kind_of_middleware(Datadog::Contrib::Rails::ExceptionMiddleware) }
+      it { expect(app).to have_kind_of_middleware(Datadog::Contrib::Rack::TraceMiddleware).once }
+      it { expect(app).to have_kind_of_middleware(Datadog::Contrib::Rails::ExceptionMiddleware).once }
     end
 
     context 'set to false' do
@@ -56,4 +63,28 @@ def index
       it { expect(app).to_not have_kind_of_middleware(Datadog::Contrib::Rails::ExceptionMiddleware) }
     end
   end
+
+  describe 'when load hooks run twice' do
+    before(:each) do
+      # Set expectations
+      expect(Datadog::Contrib::Rails::Patcher).to receive(:add_middleware)
+        .with(a_kind_of(Rails::Application))
+        .once
+        .and_call_original
+
+      without_warnings do
+        # Then load the app, which run load hooks
+        app
+
+        # Then manually re-run load hooks
+        ActiveSupport.run_load_hooks(:before_initialize, app)
+        ActiveSupport.run_load_hooks(:after_initialize, app)
+      end
+    end
+
+    it 'only includes the middleware once' do
+      expect(app).to have_kind_of_middleware(Datadog::Contrib::Rack::TraceMiddleware).once
+      expect(app).to have_kind_of_middleware(Datadog::Contrib::Rails::ExceptionMiddleware).once
+    end
+  end
 end