Implement Content Store fallback into content item loader

For HTTP Error responses and timeouts on Graphql requests, fall back
to content store and attach error information to prometheus labels.

Author: callumknights

lib/govuk_content_item_loader/govuk_conditional_content_item_loader.rb

@@ -9,7 +9,9 @@ def initialize(request:, content_store_client: GdsApi.content_store, publishing_
   end
 
   def load
-    can_load_from_graphql? ? content_item_from_graphql : content_item_from_content_store
+    return content_item_from_content_store unless can_load_from_graphql?
+
+    content_item_from_graphql || content_item_from_content_store
   end
 
   def can_load_from_graphql?
@@ -32,10 +34,10 @@ def content_item_from_graphql
     publishing_api_client.graphql_live_content_item(base_path)
   rescue GdsApi::HTTPErrorResponse => e
     set_prometheus_labels(graphql_status_code: e.code)
-    raise e
-  rescue GdsApi::TimedOutException => e
+    false
+  rescue GdsApi::TimedOutException
     set_prometheus_labels(graphql_api_timeout: true)
-    raise e
+    false
   end
 
   def content_item_from_content_store

spec/lib/govuk_conditional_content_item_loader_spec.rb

@@ -37,6 +37,7 @@ def initialize(code)
     context "when can load from GraphQL" do
       before do
         allow(loader).to receive(:can_load_from_graphql?).and_return(true)
+        allow(content_store_client).to receive(:content_item).with(base_path).and_return("item_from_cs")
         allow(publishing_api_client).to receive(:graphql_live_content_item).with(base_path).and_return("graphql_item")
       end
 
@@ -50,19 +51,19 @@ def initialize(code)
         expect(request.env["govuk.prometheus_labels"]["graphql_status_code"]).to eq(200)
       end
 
-      it "sets Prometheus labels and raises error for GdsApi::HTTPErrorResponse" do
+      it "sets Prometheus labels with error code information and falls back to content store" do
         error = GdsApi::HTTPErrorResponse.new(503)
         allow(publishing_api_client).to receive(:graphql_live_content_item).and_raise(error)
 
-        expect { loader.load }.to raise_error(GdsApi::HTTPErrorResponse)
+        expect(loader.load).to eq("item_from_cs")
         expect(request.env["govuk.prometheus_labels"]["graphql_status_code"]).to eq(503)
       end
 
-      it "sets Prometheus labels and raises error for GdsApi::TimedOutException" do
+      it "sets Prometheus labels with timeout information and falls back to content store" do
         error = GdsApi::TimedOutException.new
         allow(publishing_api_client).to receive(:graphql_live_content_item).and_raise(error)
 
-        expect { loader.load }.to raise_error(GdsApi::TimedOutException)
+        expect(loader.load).to eq("item_from_cs")
         expect(request.env["govuk.prometheus_labels"]["graphql_api_timeout"]).to be(true)
       end
     end