add http headers for services that respond to caching info

lib/travis/api/app/responders/service.rb

@@ -5,20 +5,37 @@ module Travis::Api::App::Responders
     end
 
     def apply
-      # TODO add caching headers depending on the resource
-      data = result
-      flash.concat(data.messages) if data && data.respond_to?(:messages)
-      data
+      cache_control
+      result = normalize(resource.run)
+      flash.concat(resource.messages) if result && resource.respond_to?(:messages)
+      result
     end
 
     private
 
+      def cache_control
+        if final?
+          endpoint.expires 31536000, :public # 1 year
+        elsif updated_at?
+          endpoint.cache_control :public, :must_revalidate
+          endpoint.last_modified resource.updated_at
+        end
+      end
+
+      def final?
+        resource.respond_to?(:final?) && resource.final?
+      end
+
+      def updated_at?
+        resource.respond_to?(:updated_at) && resource.updated_at
+      end
+
       # Services potentially return all sorts of things
       # If it's a string, true or false we'll wrap it into a hash.
       # If it's an active record or scope we just pass so it can be processed by the json responder.
       # If it's nil we also pass it but yield not_found.
-      def result
-        case result = resource.run
+      def normalize(result)
+        case result
         when String, true, false
           { result: result }
         else
@@ -27,4 +44,3 @@ module Travis::Api::App::Responders
       end
   end
 end
-