add error handling for .txt + .json formats

app/controllers/error_controller.rb

@@ -5,7 +5,11 @@ class ErrorController < ApplicationController
   respond_to :html
 
   def show
-    render @status.to_s, status: @status.to_i
+    respond_to do |format|
+      format.html { render @status.to_s, status: @status.to_i }
+      format.json { render json: json_response, status: @status.to_i }
+      format.text { render plain: plain_text_response, status: @status.to_i }
+    end
   rescue
     send_honeybadger_notification!
 
@@ -15,6 +19,18 @@ def show
 
   private
 
+    def json_response
+      %({"error": true, "status": #{@status.to_i}, "message": "#{status_message}"})
+    end
+
+    def plain_text_response
+      "#{@status} #{status_message}"
+    end
+
+    def status_message
+      Rack::Utils::HTTP_STATUS_CODES.fetch(@status, '')
+    end
+
     def send_honeybadger_notification!
       Honeybadger.notify(
         'An error occurred causing a 500 page to render',

spec/features/error_page_spec.rb

@@ -11,6 +11,32 @@
       expect(response).to have_http_status(:not_found)
       expect(response.body).to include 'The page you requested could not be found.'
     end
+
+    context '.txt' do
+      it 'renders the error in plain text' do
+        without_detailed_exceptions do
+          get '/this/does/not/exist.txt'
+        end
+
+        expect(response).to have_http_status(:not_found)
+        expect(response.body).to eq '404 Not Found'
+      end
+    end
+
+    context '.json' do
+      let(:json_response) do
+        %({"error": true, "status": 404, "message": "Not Found"})
+      end
+
+      it 'renders the error as json' do
+        without_detailed_exceptions do
+          get '/this/does/not/exist.json'
+        end
+
+        expect(response).to have_http_status(:not_found)
+        expect(response.body).to eq json_response
+      end
+    end
   end
 
   describe '500 (catch-all)' do