Handle uncaught exceptions

app/controllers/waste_carriers_engine/application_controller.rb

@@ -2,6 +2,8 @@
 
 module WasteCarriersEngine
   class ApplicationController < ActionController::Base
+    include WasteCarriersEngine::CanAddDebugLogging
+
     # Prevent CSRF attacks by raising an exception.
     # For APIs, you may want to use :null_session instead.
     protect_from_forgery with: :exception
@@ -10,5 +12,13 @@ class ApplicationController < ActionController::Base
     layout "application"
 
     default_form_builder GOVUKDesignSystemFormBuilder::FormBuilder
+
+    rescue_from StandardError do |e|
+      Airbrake.notify e
+      Rails.logger.error "Unhandled exception: #{e}"
+      log_transient_registration_details("Uncaught system error", @transient_registration)
+      redirect_to "/bo/pages/system_error"
+    end
+
   end
 end

app/services/concerns/waste_carriers_engine/can_add_debug_logging.rb

@@ -4,39 +4,37 @@ module WasteCarriersEngine
   module CanAddDebugLogging
     extend ActiveSupport::Concern
 
-    # rubocop:disable Metrics/MethodLength, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
+    # rubocop:disable Metrics/MethodLength, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity, Metrics/AbcSize
     def log_transient_registration_details(description, transient_registration)
       return unless FeatureToggle.active?(:additional_debug_logging)
 
-      error = if transient_registration.nil?
-                StandardError.new("#{description}: transient_registration is nil")
-              else
-                StandardError.new(
-                  "#{description}: " \
-                  "type: #{transient_registration.class}, " \
-                  "reg_identifier #{transient_registration.reg_identifier}, " \
-                  "from_magic_link: #{from_magic_link(transient_registration)}, " \
-                  "workflow_state: #{transient_registration.workflow_state}, " \
-                  "workflow_history: #{transient_registration.workflow_history}, " \
-                  "tier: #{transient_registration.tier}, " \
-                  "account_email: #{transient_registration.account_email}, " \
-                  "expires_on: #{transient_registration.expires_on}, " \
-                  "renew_token: #{renew_token(transient_registration)}, " \
-                  "metaData.route: #{transient_registration.metaData.route}, " \
-                  "created_at: #{transient_registration.created_at}, " \
-                  "orders: #{transient_registration.finance_details&.orders}, " \
-                  "payments: #{transient_registration.finance_details&.payments}"
-                )
-              end
-      Airbrake.notify(error, reg_identifier: transient_registration.reg_identifier) if defined?(Airbrake)
-      Rails.logger.warn error
+      details = if transient_registration.nil?
+                  { transient_registration: nil }
+                else
+                  { type: transient_registration.class.to_s,
+                    reg_identifier: transient_registration.reg_identifier,
+                    from_magic_link: from_magic_link(transient_registration),
+                    workflow_state: transient_registration.workflow_state,
+                    workflow_history: transient_registration.workflow_history.to_s,
+                    tier: transient_registration.tier,
+                    account_email: transient_registration.account_email,
+                    expires_on: transient_registration.expires_on,
+                    renew_token: renew_token(transient_registration),
+                    "metaData.route": transient_registration.metaData.route,
+                    created_at: transient_registration.created_at,
+                    orders: transient_registration.finance_details&.orders.to_s,
+                    payments: transient_registration.finance_details&.payments.to_s }
+                end
+      Airbrake.notify(StandardError.new(description), details) if defined?(Airbrake)
+      Rails.logger.warn "#{description}: #{details}"
 
     # Handle any exceptions which arise while logging
     rescue StandardError => e
-      Airbrake.notify(e, reg_identifier: transient_registration.reg_identifier) if defined?(Airbrake)
-      Rails.logger.warn "Error writing transient registration details to the log: #{e}"
+      Airbrake.notify(e, reg_identifier: transient_registration&.reg_identifier) if defined?(Airbrake)
+      Rails.logger.warn "Error writing debugging information for transient registration " \
+                        "#{transient_registration&.reg_identifier} to the log: #{e}"
     end
-    # rubocop:enable Metrics/MethodLength, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
+    # rubocop:enable Metrics/MethodLength, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity, Metrics/AbcSize
 
     private
 

app/views/pages/system_error.html.erb

@@ -0,0 +1,8 @@
+<% content_for :title, I18n.t(".system_error_title")  %>
+
+<div class="govuk-grid-row">
+  <div class="govuk-grid-column-two-thirds">
+    <h1 class="govuk-heading-m"><%= I18n.t(".system_error_heading") %></h1>
+    <p class="govuk-body"><%= I18n.t(".system_error_text") %></p>
+  </div>
+</div>

config/locales/en.yml

@@ -44,6 +44,10 @@ en:
           other: "%{count} addresses found"
 
   # Custom error pages
+  system_error_title: System error
+  system_error_heading: A system error has occurred
+  system_error_text: We are unable to complete this request at this time. Please try again later.
+
   invalid_reg_identifier_title: Cannot find page
   invalid_reg_identifier_heading: We cannot find that page
   invalid_reg_identifier_text: If you have recently completed a registration then check your email.

spec/services/waste_carriers_engine/registration_completion_service_spec.rb

@@ -341,6 +341,16 @@ module WasteCarriersEngine
               expect(Airbrake).to have_received(:notify).at_least(:once)
             end
           end
+
+          context "when the additional logging raises an exception" do
+            before { allow(transient_registration).to receive(:metaData).and_raise(StandardError) }
+
+            it "catches the exception and notifies Airbrake anyway" do
+              described_class.new.log_transient_registration_details("foo", transient_registration)
+
+              expect(Airbrake).to have_received(:notify)
+            end
+          end
         end
       end
     end