Acking a by-category stream, doesn' seem to work

[askasp]

Hey again, I will try to contribute by finding the error myself, but I can post it here in the mean time.

It seems that acking on a persistent subscription on a by-category stream is not working.
:ok = Spear.ack(JaaApiLive.EventStoreDbClient, sub, msg)
evaluates fine, but the event is sent over and over.

My guess is that it is somehow related to the event being a link as it is a projection stream.

[the-mikedavis]

ah another nice find! Thanks for trying out spear and finding all my embarrassing bugs 😁

I suspect that this is just like the other problem: the link data that we would need to acknowledge events is probably currently discarded. In this case instead of the .metadata.stream_revision field on a link, I think we need the .id. The event_store.client.persistent_subscriptions.ReadReq.Ack message looks like this: it's pretty thin, just a list of event IDs to acknowledge as a batch. I suspect it needs these event IDs to line up with the ID of the link instead of the resolved event when acknowledging persistent subscriptions.

I'm sure that there's a way that isn't too messy to fix this in the current code-base but I think it's probably wiser for me to bite the bullet of the refactor in #36 (and ideally some real testing in #35) before/during tackling this problem. Right now links are a bit of an after-thought and I'd like to change that.

The day is just getting started here in the CDT timezone, I'll have this fixed in a jiffy!

[the-mikedavis]

Ok so it looks like the .id hypothesis was correct. #38 added a new :link field to t:Spear.Event.t/0 which Spear.ack/3 and Spear.nack/4 now respect and use to source each event's ID. I didn't add any test cases yet for projected streams but I set up a persistent subscription locally in my IEx and ack-ed my way through a category stream and it appears to be working like expected 👍

v0.9.0 is a bit of a breaking change if you're depending on Spear.Event.metadata.link explicitly. Upgrading should be as easy as matching on the :link top-level field instead of that metadata field

# before
def revision(%Spear.Event{metadata: %{link: %{stream_revision: revision}}}), do: revision
def revision(%Spear.Event{metadata: %{stream_revision: revision}}), do: revision

# after
def revision(%Spear.Event{link: %Spear.Event{} = link}), do: revision(link)
def revision(%Spear.Event{metadata: %{stream_revision: revision}}), do: revision

Also if you're looking into using persistent subscriptions, be sure to check out Broadway. It's has a really nice Acknowledger behaviour that fits well with the persistent subscription ack/nack/park system. We recently built a producer for regular and persistent subscriptions. Our producers are a bit experimental and surely has some bugs to iron out but they makes writing event-handling topologies really slick (here's an example handler).

Thanks again for reporting, glad to have you trying out the library! 🙂

[askasp]

It is my pleasure! And thanks for being so responsive (and insanely productive).

I really liked the thorough explanation. I figured it had to be something regarding resolved id's but I became lost trying to figure out how to fix it 🙈