Semantic FIN and Filters / Forward

[vasilvv]

Currently, we use FIN to indicate that a subgroup stream has been completed; this FIN has a semantic meaning (relays have to forward it).

How does this interact with filters? If I have a filter that stops at (15, 10), but the subgroup goes on, the publisher is expected to send a FIN after (15, 10), which is not where the original publisher would put it.

How does this interact with forward? Assume I have a really long group. If I send Forward=0, does the publisher has to cleanly fin the subgroup stream, reset it or what? What happens if I set Forward=1, and that subgroup is still open? Or if it's been closed so long ago that the relay evicted all the information about it from the cache?

[afrind]

Presently you cannot set an end object in a filter, only an end group. I think this issue might have been one of the motivations?

If we land a proposal like #1164 and the last object in a subgroup is omitted, I think the answer is - you wait for an ack and reset, or send reset_stream_at.

[afrind]

I missed the second part of your issue

How does this interact with forward? Assume I have a really long group. If I send Forward=0, does the publisher has to cleanly fin the subgroup stream, reset it or what? What happens if I set Forward=1, and that subgroup is still open?

Relays/publishers don't have to immediately terminate open streams when Forward goes from 0->1. The only normative rules are you can't send a FIN if you didn't send the final object in the subgroup, and a relay MUST NOT forward an Object on an existing Subgroup stream unless it is the next Object in that Subgroup. But if Forward=0 causes an object to be missed - the logical thing to do is reset it. If Forward=0 and the end of subgroup is reached and the final object has been sent, I think it's fine to FIN the stream.

Or if it's been closed so long ago that the relay evicted all the information about it from the cache?

I think the same logic applies.

Are you asking for editorial clarification or a design change?

[vasilvv]

I am not sure if it's editorial or design, but we definitely should describe what happens to existing streams when Forward changes.

[afrind]

I think we can address this with an Editorial PR.