CP-990: add stale-while-revalidate headers to the supplier table

Author: cnorthwood

app/controllers/concerns/.keep

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module Cacheable
+  extend ActiveSupport::Concern
+
+  included do
+    after_action :cache_control_header
+
+    protected
+
+    def cache_control_header
+      # Allow clients to cache as we do not have log-in in this app, and cache at the CDN level
+      # via s-maxage, allowing stale content to be served if there are upstream errors
+      expires_in(
+        5.minutes,
+        public: true,
+        "s-maxage": 5.minutes,
+        stale_while_revalidate: 1.minute,
+        stale_if_error: 1.day
+      )
+    end
+  end
+end

app/controllers/concerns/cacheable.rb

@@ -5,6 +5,7 @@ class SuppliersController < ApplicationController
     class SupplierNotFoundError < StandardError; end
 
     include SwiftypeMeta
+    include Cacheable
 
     rescue_from SupplierNotFoundError, with: :not_found
     rescue_from Contentful::GraphqlAdapter::QueryError, with: :internal_server_error
@@ -13,7 +14,6 @@ class SupplierNotFoundError < StandardError; end
     before_action :set_suppliers, :set_unranked_supplier, :set_next_quarter_release, only: :index
     before_action :set_quarter_date, only: %i[index show]
     before_action :set_page_meta_tags, :set_swiftype_meta_tags
-    after_action :cache_control_header
 
     attr_accessor :supplier, :unranked_supplier, :quarter_date, :next_quarter_release
 
@@ -126,14 +126,5 @@ def custom_data_layer_properties
         }
       end
     end
-
-    def cache_control_header
-      expires_in(
-        5.minutes,
-        public: true,
-        "s-maxage": 5.minutes,
-        must_revalidate: true
-      )
-    end
   end
 end

app/controllers/csr_table/suppliers_controller.rb

@@ -36,6 +36,12 @@
         it "contains the correct canonical url" do
           expect(response.body).to include("<link href='https://www.citizensadvice.org.uk#{CSR_APP_PATH}' rel='canonical'>")
         end
+
+        it "returns headers to allow the CDN to cache it" do
+          expect(response.headers["Cache-Control"]).to eq(
+            "max-age=300, public, stale-while-revalidate=60, stale-if-error=86400, s-maxage=300"
+          )
+        end
       end
 
       context "when visiting the supplier index" do