Pay::Stripe::PaymentMethod.sync attaching to wrong customer in rare (?) conditions

[fschwahn]

This is issue is a bit weird, but what happened in our app is this:

• customer.updated-webhook is triggered (because the default payment method changed)
• Pay::Stripe::PaymentMethod.sync is invoked (here: https://github.com/pay-rails/pay/blob/master/lib/pay/stripe/webhooks/customer_updated.rb#L16)
• object returned by ::Stripe::PaymentMethod.retrieve has object.customer == nil
• Pay::Customer.find_by(processor: :stripe, processor_id: object.customer) just returns any Pay::Customer without a processor_id set.

--> Payment method is attached to the wrong Pay::Customer

---

I'm not sure why object.customer was nil for the returned payment method object, this may well have been a temporary Stripe bug, but it still seems dangerous.

Maybe Pay::Stripe::PaymentMethod.sync should return (or raise?) in case object.customer is nil?

[cjilbert504]

Hey @fschwahn - The code already does return if the find_by call does not find a Pay::Customer:

pay_customer = Pay::Customer.find_by(processor: :stripe, processor_id: object.customer)
return unless pay_customer

That said, we may need to add an additional check like you mentioned.

Also, I am wondering if it is possible that you actually had a Pay::Customer record in your database that had a processor_id of nil. If so that would be why a seemingly random Pay::Customer record was given a different customers new default payment method.

For example:

irb(main):006:0> pay_customer = Pay::Customer.find_by(processor: :stripe, processor_id: nil)
=> 
#<Pay::Customer:0x000000055555555b8
...
irb(main):007:0> _
=> 
#<Pay::Customer:0x000000055555555b8
 id: 716567020,              
 owner_type: "User",         
 owner_id: 555555555,        
 processor: "stripe",        
 processor_id: nil,          
 default: true,              
 data: nil,                  
 deleted_at: nil,
 created_at: Thu, 17 Aug 2023 00:48:02.303326000 UTC +00:00,
 updated_at: Thu, 17 Aug 2023 00:48:02.303326000 UTC +00:00,
 payment_method_token: nil>
irb(main):008:0> 

[fschwahn]

Also, I am wondering if it is possible that you actually had a Pay::Customer record in your database that had a processor_id of nil

Yes, I forgot to mention that. We have a few of those in our database, because creating the customer in Stripe failed (in our case due to an invalid email address).

I see now that this is quite an edge case, but probably still worth to add the guard?

[excid3]

Yeah, this should definitely return if object.customer is nil. Same for other places we do this.