Agents with Zero (Empty) arcs cannot get_links

[neonphog]

Agents with Zero (Empty) arcs cannot get_links

[neonphog]

@maackle

have you thought about this problem before and have any ideas

only so far as to think that we should solve it : )

should I just go for it?

go for it. Let me know if I can help with anything.

[maackle]

I found the source of this problem:

holochain/crates/kitsune_p2p/kitsune_p2p/src/spawn/actor/space.rs

Lines 941 to 942 in e3fb507

	.map_or(false, |arc| arc.contains(location))
	})

When finding local agents to route to, we're filtering by whether they hold the basis. Obviously this will be a problem for zero arcs, but also for non-full arcs, as you mention.

Ideally we can know if the basis of what we're asking for is something we authored, and then include the authoring agent in the list of local agents even if their arc doesn't cover it. @neonphog have you thought about this problem before and have any ideas, or should I just go for it?

[Connoropolous]

@maackle this is sounding like quite a big thing to solve, do you think that’s true?

[maackle]

I've got a solution mostly worked out for this, but hit a slight snag.

I added a new Kitsune->Host call, get_local_authors, for any KitsuneBasis, so the rpc_multi call can find out if any local agents are holding that basis and they can be mixed in with the other agents whose arc is covering the basis. The snag is that in Holochain, a "basis" is a AnyDhtHash which can have a number of multihash prefixes, but in Kitsune, a KitsuneBasis erases the hash type, so there's no way to go from KitsuneBasis back to AnyDhtHash to query the database.

One solution is to just query for every possible type of basis, which is only 2 now but may be 3 when we add AgentPubKey as a legit basis of its own (rather than via EntryHash), but this needlessly slows down the query a bit.

Another would be to just store the main 32 bytes of the basis in the DB, but that requires a database migration. @neonphog thoughts?

[neonphog]

@maackle - I'm not sure I understand why the basis is involved. I'm pretty sure it calls into all local agents always here - triggering, eventually a handler call here.

What I don't understand is why that database call is not returning results that were authored by this node...

[maackle]

@neonphog it's because of the line I mentioned, but here it is in context:

holochain/crates/kitsune_p2p/kitsune_p2p/src/spawn/actor/space.rs

Lines 930 to 951 in e3fb507

	fn handle_rpc_multi(
	&mut self,
	input: actor::RpcMulti,
	) -> KitsuneP2pHandlerResult<Vec<actor::RpcMultiResponse>> {
	let location = input.basis.get_loc();
	let local_agents_holding_basis = self
	.local_joined_agents
	.keys()
	.filter(|agent_key| {
	self.agent_arcs
	.get(*agent_key)
	.map_or(false, |arc| arc.contains(location))
	})
	.cloned()
	.collect();
	let fut = rpc_multi_logic::handle_rpc_multi(
	input,
	self.ro_inner.clone(),
	local_agents_holding_basis,
	);
	Ok(async move { fut.await }.boxed().into())
	}

The local_joined_agents in handle_rpc_multi_as_single is not actually all local joined agents, but only the local agents covering the basis. That generally excludes actual authors sometimes. So my idea was to mix back in the authors of that basis if they've been filtered out.

[neonphog]

@maackle - ah, gottcha. Or, perhaps it would be fine to just not filter the local agents. It should be relatively inexpensive to make a local call like that compared to a remote network call.