Fix Vary header (#138)

lib/inertia_rails/renderer.rb

@@ -25,7 +25,11 @@ def initialize(component, controller, request, response, render_method, props: n
     end
 
     def render
-      @response.set_header('Vary', [@request.headers['Vary'], 'X-Inertia'].compact.join(', '))
+      if @response.headers["Vary"].blank?
+        @response.headers["Vary"] = 'X-Inertia'
+      else
+        @response.headers["Vary"] = "#{@response.headers["Vary"]}, X-Inertia"
+      end
       if @request.headers['X-Inertia']
         @response.set_header('X-Inertia', 'true')
         @render_method.call json: page, status: @response.status, content_type: Mime[:json]

spec/dummy/app/controllers/inertia_render_test_controller.rb

@@ -18,6 +18,12 @@ def component
     render inertia: 'TestComponent'
   end
 
+  def vary_header
+    response.headers["Vary"] = 'Accept-Language'
+
+    render inertia: 'TestComponent'
+  end
+
   def lazy_props
     render inertia: 'TestComponent', props: {
       name: 'Brian',

spec/dummy/config/routes.rb

@@ -5,6 +5,7 @@
   get 'props' => 'inertia_render_test#props'
   get 'view_data' => 'inertia_render_test#view_data'
   get 'component' => 'inertia_render_test#component'
+  get 'vary_header' => 'inertia_render_test#vary_header'
   get 'share' => 'inertia_share_test#share'
   get 'share_with_inherited' => 'inertia_child_share_test#share_with_inherited'
   get 'empty_test' => 'inertia_test#empty_test'

spec/inertia/rendering_spec.rb

@@ -44,10 +44,10 @@
 
       context 'when another Vary header is present' do
         it 'has the proper headers' do
-          get component_path, headers: {'Vary' => 'Accept'}
+          get vary_header_path
 
           expect(response.headers['X-Inertia']).to be_nil
-          expect(response.headers['Vary']).to eq 'Accept, X-Inertia'
+          expect(response.headers['Vary']).to eq 'Accept-Language, X-Inertia'
           expect(response.headers['Content-Type']).to eq 'text/html; charset=utf-8'
         end
       end