API: Detect concurrent modifications when updating transaction

[Sobuno]

I am using the API to update transactions through this flow:

1. Firefly Data Importer adds transactions
2. Firefly sends webhook to my service
3. My service does some data cleanup (e.g. removing EndToEndID: NOTPROVIDED from the description) locally
4. My service PUTS the data using the REST API

My worry is that I'll at some point be acting on stale data, i.e. some rule or something else has changed the data meanwhile and I'll be updating the transaction, potentially wiping out their changes. I am already only PUT'ing the fields I update to avoid collisions

Would it be possible to utilize the 412 Precondition Failed status code for doing "Optimistic locking"? See https://developer.mozilla.org/en-US/docs/Web/HTTP/Conditional_requests#avoiding_the_lost_update_problem_with_optimistic_locking for details. I see that the updated_at timestamp is already present on the transaction when I fetch it, so it should "just" be a matter of comparing a header value with that value and rejecting with 412 if it's violated.

[JC5]

Hey, thanks for starting a discussion.

This is indeed on my list somewhere to implement :)