impossible to observe holepunch using Connectedness event when using an unlimited relay

[marten-seemann]

I'm trying to observe the establishment of a connection from relayed to direct (using DCuTR).

Initially I thought that I could use the Connectedness' Limited state for that. This works find when using a limited relay, but it fails for an unlimited relay:

go-libp2p/p2p/protocol/circuitv2/client/dial.go

Lines 181 to 182 in 4e85c96

	if limit := msg.GetLimit(); limit != nil {
	stat.Limited = true

A connection via an unlimited relay is considered Connected right away, and the establishment of a direct (hole-punched) connection doesn't trigger another event, since we're already "connected".

The best resolution I could come up with is the following: Split the Limited state into two: Relayed and RelayedUnlimited. This is a breaking change obviously, but at it's made explicit by the removal of Limited, forcing users of the library to rethink their logic.

[vyzo]

I think it would male more sense to have a Relayed flag, in conjunction with Limited.

[marten-seemann]

@vyzo A flag would be nice, but the problem is that EvtPeerConnectednessChanged.Connectedness is a single enum: it's either NotConnected, Limited or Connected. Now you probably could add another flag to EvtPeerConnectednessChanged, but that would likely break many existing use cases, in a way that invites DoS attacks.

I don't think many consumers of EvtPeerConnectednessChanged currently care about Limited, hence my suggestion to add more values to that enum.