[spec]: start to set the dont_forward bit in ChannelUpdate

[Crypt-iQ]

We need to start setting the bit at index 1 in the ChannelUpdate message flags per lightning/bolts@6fee63f. It is only set for updates that we don't want forwarded. See the spec change for more details.

[saubyk]

prioed for 17

[oldmonad]

Hi, a new contributor here. Can I take a stab at this?

[saubyk]

Hi @oldmonad if you're interested, please go through the problem statement and the linked spec.
Once your analysis is complete, please provide a concise plan of action on this issue, before attempting a pr. Thanks.

[oldmonad]

Got it

[oldmonad]

Hi @saubyk, I provided a brief overview of the issue and action plan in this document. I would greatly appreciate any feedback.

[ellemouton]

thanks for the outline @oldmonad!

I think we just need to start setting the bit so that other impls dont start rejecting our channel_updates but I dont think we necessarily need to make this one required on our side. Keep to hear what @Crypt-iQ thinks though.

[Crypt-iQ]

We don't need to make the htlc_maximum_msat bit required because that may cause newer LND nodes to disconnect from older nodes. We'll need to set the dont_forward bit in funding/manager.go when sending out a channel update:

lnd/funding/manager.go

Line 3076 in 1052b13

func (f *Manager) addToRouterGraph(completeChan *channeldb.OpenChannel,

and also in discovery/gossiper.go when sending the update to the remote peer:

lnd/discovery/gossiper.go

Line 1731 in 1052b13

if edgeInfo.Info.AuthProof == nil {

Also, this bit should be set even if aliases aren't used. It would be nice if all newer channels persisted the bit from the start and older channels performed an on-the-fly migration similar to what was done for the htlc-maximum bit here:

lnd/routing/localchans/manager.go

Lines 199 to 201 in 1052b13

	// This is an on-the-fly migration.
	case !edge.MessageFlags.HasMaxHtlc():
	edge.MaxHTLC = amtMax

I'll have to check if there are any other callsites that I'm forgetting

[ziggie1984]

@oldmonad are you still working on this ?

[ziggie1984]

Also, this bit should be set even if aliases aren't used. It would be nice if all newer channels persisted the bit from the start and older channels performed an on-the-fly migration similar to what was done for the htlc-maximum bit here:

Did I understand it correctly by "even channel which are not using aliases" but they have to be private tho, that's at least what I implemented. Basically you did all the work have not fund another place where we should set this bit ;)

[Crypt-iQ]

Yup they need to be private for the flag to be set