Redirect to home page on invalid urls

Every now and again we get invalid urls which causes the check for
unknown formats to blow up. In these circumstances we should catch
the invalid URI error and redirect to the home page.

app/controllers/application_controller.rb

@@ -29,6 +29,8 @@ def url_without_format
     URI.parse(request.original_url).tap do |uri|
       uri.path = File.join(File.dirname(request.path), File.basename(request.path, '.*'))
     end.to_s
+  rescue URI::InvalidURIError => e
+    home_url
   end
 
   def redirect_to_url_without_format

spec/controllers/application_controller_spec.rb

@@ -100,4 +100,18 @@ def index
       expect(controller.class.helpers).to respond_to :public_petition_facets
     end
   end
+
+  context "when the url has an invalid format" do
+    let(:exception) { URI::InvalidURIError.new }
+
+    before do
+      allow(request).to receive(:format).and_return(nil)
+      allow(request).to receive(:original_url).and_return("https://petition.parliament.uk/petitions.json]")
+    end
+
+    it "redirects to the home page" do
+      get :index
+      expect(response).to redirect_to("https://petition.parliament.uk/")
+    end
+  end
 end