When encountering StaleObjectError when checking out, retry

app/controllers/checkout_controller.rb

@@ -23,7 +23,7 @@ class CheckoutController < Spree::CheckoutController
           return if redirect_to_paypal_express_form_if_needed
         end
 
-        if @order.next
+        if advance_order_state(@order)
           state_callback(:after)
         else
           if @order.errors.present?
@@ -83,6 +83,19 @@ class CheckoutController < Spree::CheckoutController
     params[:order]
   end
 
+  def advance_order_state(order)
+    result = false
+    tries = 3
+
+    begin
+      result = order.next
+    rescue ActiveRecord::StaleObjectError
+      retry unless (tries -= 1).zero?
+    end
+
+    result
+  end
+
 
   def update_failed
     clear_ship_address

spec/controllers/checkout_controller_spec.rb

@@ -55,7 +55,7 @@ describe CheckoutController do
   it "doesn't copy the previous shipping address from a pickup order" do
     old_order = create(:order, bill_address: create(:address), ship_address: create(:address))
     Spree::Order.stub_chain(:order, :where, :where, :limit, :detect).and_return(old_order)
-    controller.send(:find_last_used_addresses, "email").last.should == nil 
+    controller.send(:find_last_used_addresses, "email").last.should == nil
   end
 
   describe "building the order" do
@@ -69,7 +69,7 @@ describe CheckoutController do
       get :edit
       assigns[:order].ship_address.address1.should be_nil
     end
-    
+
     it "clears the ship address when re-rendering edit" do
       controller.should_receive(:clear_ship_address).and_return true
       order.stub(:update_attributes).and_return false
@@ -119,6 +119,32 @@ describe CheckoutController do
       response.status.should == 200
       response.body.should == {path: spree.order_path(order)}.to_json
     end
+
+    describe "stale object handling" do
+      it "retries when a stale object error is encountered" do
+        order.stub(:update_attributes).and_return true
+        controller.stub(:state_callback)
+
+        # The first time, raise a StaleObjectError. The second time, succeed.
+        order.stub(:next).once.
+          and_raise(ActiveRecord::StaleObjectError.new(Spree::Variant.new, 'update'))
+        order.stub(:next).once do
+          order.update_column :state, 'complete'
+          true
+        end
+
+        xhr :post, :update, order: {}, use_route: :spree
+        response.status.should == 200
+      end
+
+      it "tries a maximum of 3 times before giving up and returning an error" do
+        order.stub(:update_attributes).and_return true
+        order.stub(:next) { raise ActiveRecord::StaleObjectError.new(Spree::Variant.new, 'update') }
+
+        xhr :post, :update, order: {}, use_route: :spree
+        response.status.should == 400
+      end
+    end
   end
 
   describe "Paypal routing" do