Not filling mesh peers if there are less than D of them when joining a topic

[NIC619]

What is wrong?

In GossipSubRouter.Join() if there are fanout peers but not enough of them, it won't selects the remaining number of peers (D-x) from peers.gossipsub[topic] as suggested in the spec.

go-libp2p-pubsub/gossipsub.go

Lines 269 to 274 in 4221a39

	gmap, ok = gs.fanout[topic]
	if ok {
	gs.mesh[topic] = gmap
	delete(gs.fanout, topic)
	delete(gs.lastpub, topic)
	} else {

[raulk]

Hey @vyzo, is there a misalignment between implementation and spec?

[vyzo]

it's a minor bug I would say.

[raulk]

@vyzo

it's a minor bug I would say.

Please elaborate. OP probably wants to understand impact and where the bug is: in the spec or the implementation.

[vyzo]

The bug is in the implementation.
The mesh should be filled at D peers if the fanout peers are less, which is what the spec says.
The impact is minimal, the next heartbeat will fill the mesh.

[raulk]

@vyzo — let’s fix the implementation promptly. Several teams are using this as the reference implementation, and it creates confusion, despite the impact being minimal, in theory.

[vyzo]

Added some code to handle this in #196.