Change max_value_in_flight based on channel being public

[TheBlueMatt]

If a channel isn't public, our "reduce max_value_in_flight to provide routed payments more privacy" thing doesn't make sense...cause the channel isn't routing payments. Thus, our default config should depend on if the channel is public here, IMO.

[simonadameit]

Hello @TheBlueMatt, I'm looking into this but as I'm just getting started with the code base I lack a bit of information.

My best guess is you are talking about the anti_probing_penalty_msat:

rust-lightning/lightning/src/routing/scoring.rs

Line 604 in bf3bc42

pub anti_probing_penalty_msat: u64,

If so, as far as I can see, that already get's only applied on public channels as channel_penalty_msat returns 0 for non-public hops:

rust-lightning/lightning/src/routing/scoring.rs

Line 1330 in bf3bc42

_ => return 0,

Given that you're aware of how this works much better than I am, I suppose you are talking about something different?

Cheers,
Simon

[tnull]

Hello @TheBlueMatt, I'm looking into this but as I'm just getting started with the code base I lack a bit of information.

My best guess is you are talking about the anti_probing_penalty_msat:

rust-lightning/lightning/src/routing/scoring.rs

Line 604 in bf3bc42

pub anti_probing_penalty_msat: u64,

Close, I think this issue is around the actual htlc_maximum_msat we set, not the anti_probing_penalty_msat we score peers with who set the former lower.

For context: generally, peers provide more privacy if they limit htlc_maximum_msat as this reduces the capability of probing peers to gain information about the actual liquidity, at least if it is above htlc_maximum_msat. E.g., if a peer sets htlc_maximum_msat to 10% of the channel capacity, a probing peer could only test the actual liquidity when it drops below these 10%. So for forwarding ('public') nodes, limiting htlc_maximum_msat is a privacy feature, but for non-forwarding nodes it just unnecessarily restricts our maximum HTLC size.

So, we should only apply the limit if we have any announced ('public') channels, i.e., can be considered a forwarding node.

[jbesraa]

hey @simonadameit
are you still interested in doing this?

[simonadameit]

@jbesraa Unfortunately I haven't had the time recently and if I find some time to dedicate to the project, I could just pick another issue if this is already done. So if you or someone else wants to work on it, please go ahead!

[Sharmalm]

Hii, @jbesraa I am interested in this issue, I can try this issue if you are not taking it :)

[jbesraa]

sure @Sharmalm, feel free to take this

[Sharmalm]

Thanks @jbesraa

[TheBlueMatt]

Don't think we should hold 112 on this.

[Sharmalm]

Hello everyone,
My approach to solve this issue is update the changes in configuration in lightning/src/util/config/ChannelConfig so that inbound_htlc_maximum_msat will only be included in if channel is public.