grpc: ReadResp.caught_up never sent for subscription on nonexistent stream

[FeepingCreature]

Describe the bug
When subscribing to a nonexistent stream, ReadResp.caught_up is never sent.

To Reproduce
Steps to reproduce the behavior:

1. GRPC connect to a stream that does not exist.
2. Receive the subscription confirmation.

Expected behavior
A perfunctory ReadResp.caught_up should be sent.

Actual behavior
No notifications are received.

EventStore details

• EventStore server version: 23.10.0-jammy

Additional context
This is necessary because there is otherwise no way to differentiate "we have reached the end of the stream" and "we have not received any events yet".

With a normal read we'd get 'stream_not_found', but for a subscription we get 'confirmation' instead.

[FeepingCreature]

As a workaround, I just went ahead and read the first event of the stream on subscription start.

[ylorph]

To add to the plot:

scenarios :

• subcribing to a stream that was never appended to => should have ReadResp.caught_up
• subscribing to a stream that was appended and completely truncated or soft-delete => should have ReadResp.caught_up

[timothycoleman]

Hi @FeepingCreature, thanks for the bug report. Coincidentally we found and fixed this last week #4108 it'll be released in v24.2. In v24.2 subscriptions will also transition back to catchup rather than drop if there are too many live events arriving at once