Invalidate cache for builds badge

Closes #13982

app/controllers/projects/badges_controller.rb

 class Projects::BadgesController < Projects::ApplicationController
+  before_action :set_no_cache
+
   def build
     respond_to do |format|
       format.html { render_404 }
@@ -8,4 +10,15 @@ class Projects::BadgesController < Projects::ApplicationController
       end
     end
   end
+
+  private
+
+  def set_no_cache
+    expires_now
+
+    # Add some deprecated headers for older agents
+    #
+    response.headers['Pragma'] = 'no-cache'
+    response.headers['Expires'] = 'Fri, 01 Jan 1990 00:00:00 GMT'
+  end
 end

features/project/badges/build.feature

@@ -20,3 +20,8 @@ Feature: Project Badges Build
     And project has another build that is running
     When I display builds badge for a master branch
     Then I should see a build running badge
+
+  Scenario: I want to see a fresh badge on each request
+    Given recent build is successful
+    When I display builds badge for a master branch
+    Then I should see a badge that has not been cached

features/steps/project/badges/build.rb

@@ -20,6 +20,10 @@ class Spinach::Features::ProjectBadgesBuild < Spinach::FeatureSteps
     expect_badge('running')
   end
 
+  step 'I should see a badge that has not been cached' do
+    expect(page.response_headers).to include('Cache-Control' => 'no-cache')
+  end
+
   def expect_badge(status)
     svg = Nokogiri::XML.parse(page.body)
     expect(page.response_headers).to include('Content-Type' => 'image/svg+xml')