Routing to blinded payment paths #2120

valentinewallace · 2023-03-22T00:44:08Z

Support finding a route to a recipient who is behind blinded payment paths, which are provided in BOLT12 invoices.

finish tests

Based on ~~#2258~~, ~~#2305~~.

codecov-commenter · 2023-03-22T22:09:42Z

Codecov Report

Patch coverage: 94.61% and project coverage change: +0.81 🎉

Comparison is base (d78dd48) 90.48% compared to head (6c3ca55) 91.30%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2120      +/-   ##
==========================================
+ Coverage   90.48%   91.30%   +0.81%     
==========================================
  Files         104      106       +2     
  Lines       53920    63000    +9080     
  Branches    53920    63000    +9080     
==========================================
+ Hits        48792    57525    +8733     
- Misses       5128     5475     +347

Impacted Files	Coverage Δ
lightning/src/offers/invoice_request.rs	`93.38% <ø> (ø)`
lightning/src/offers/refund.rs	`94.39% <ø> (ø)`
lightning/src/offers/invoice.rs	`90.18% <94.11%> (ø)`
lightning/src/routing/router.rs	`93.55% <94.61%> (+0.34%)`	⬆️
lightning/src/offers/test_utils.rs	`96.72% <100.00%> (ø)`

... and 17 files with indirect coverage changes

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TheBlueMatt

We should definitely land at least the new serialization backwards-incompatible hints tlvs for the next release.

lightning/src/routing/router.rs

lightning/src/ln/features.rs

lightning/src/routing/router.rs

TheBlueMatt · 2023-05-09T22:30:04Z

lightning/src/routing/router.rs

+				if blinded_path.blinded_hops.len() == 0 {
+					return Err(LightningError{err: "0-hop blinded path provided".to_owned(), action: ErrorAction::IgnoreError});
+				} else if &blinded_path.introduction_node_id == our_node_pubkey {
+					log_info!(logger, "Got blinded path with ourselves as the introduction node, ignoring");


Should this get some kind of TODO? Or should we just always use this path directly?

We can't use these paths atm because get_route doesn't have the ability to "advance" the blinded path to the next hop (and we can't pathfind to ourselves, ofc). Previously discussed here: #2146 (comment)

Ah, I misunderstood that comment, so I think there's another way to handle this - let get_route return early with a 0-hop unblinded path portion and the blinded tail as-is. Then the paying code would handle it by detecting this case and doing the advancing itself.

Hmm, I don't see how that would work if the max_htlc of the 1 blinded hint isn't sufficient for the entire payment?

Mmm right, I suppose we could pre-select it as a path and then run the router to select more paths if needed? That seems like it would work pretty easy.

Yeah that sounds good! We might want to have another prefactor, though, because there's still assumptions that path.hops.len() > 0 scattered around. Will look into that.

FYI, two more notes on this approach:

We may end up double-booking our own channel liquidity, since we don't know which of our channels is being used inside the blinded path (double-booking liquidity is a general problem for blinded pathfinding anyway, though)

ISTM we'll always want to go through the process of selecting additional paths, because the blinded path where we are the intro node may be the most expensive option

For (1), we could decrement each of our available channel balances by the amount used on the path. Not sure it's if worth the additional complexity.

I'm gonna address this in a follow-up since this PR is growing. IMO our offers code should still advance blinded paths before pathfinding to them, though adding the behavior you describe is good for keeping find_route general-purpose

lightning/src/routing/router.rs

valentinewallace · 2023-05-16T21:35:52Z

Rebased to fix CI, also squashed.

lightning/src/routing/router.rs

alecchendev · 2023-06-13T23:48:38Z

lightning/src/routing/router.rs

+			fees: RoutingFees {
+				base_msat: blinded_payinfo.fee_base_msat,
+				proportional_millionths: blinded_payinfo.fee_proportional_millionths,


More of a comprehension question - if a recipient includes a dummy hop, we'll send extra sats for this dummy hop's fees that will go to the recipient right? Is there anything stopping a recipient from always making a sender slightly overpay as long as there's a route with enough liquidity?

Dummy hops don't cost extra fees, since agregated fees for use of the entire blinded path are calculated by the recipient per https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments, based on the non-dummy hops' feerates. I think the recipient could make the sender overpay, though, if they just added extra fees on top of the aggregated fees?

Dummy hops don't cost extra fees, since agregated fees for use of the entire blinded path are calculated by the recipient per https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments

Oh I see, thanks

I think the recipient could make the sender overpay, though, if they just added extra fees on top of the aggregated fees?

I realize reading more of the proposal that recipients are even encouraged to in order to avoid probing, although I also saw this section where the recipient pays the blinded fees which was interesting. But yea, seems like nothing's really stopping a recipient from getting the sender to overpay as long as its not outrageous...🤷

lightning/src/routing/router.rs

valentinewallace · 2023-06-15T21:16:15Z

Squashed.

jkczyz

Largely looks good though I need to do a more detailed pass at the last commit still.

lightning/src/routing/router.rs

To make it uniform with PaymentParameters' Payee::Blinded::route_hints.

TheBlueMatt

LGTM, I think, feel free to squash fixups.

lightning/src/routing/router.rs

TheBlueMatt

One small thing worth fixing in a followup, though I'm not even sure the code is actually reachable.

lightning/src/routing/router.rs

It's unclear what values 1-hop blinded paths should set their BlindedPayInfos to, because those values are meant to refer to the fees/cltv delta on the path *between* the intro node and the destination. We zero out these values in the new variant's methods so they don't mess with path finding/construction.

We don't need to collect a vec of Results anymore.

Sending to them is still disallowed, for now.

valentinewallace force-pushed the 2023-03-blinded-pathfinding branch 2 times, most recently from 6841e43 to 6e6f76e Compare March 22, 2023 00:48

jkczyz self-requested a review March 22, 2023 19:18

valentinewallace force-pushed the 2023-03-blinded-pathfinding branch 3 times, most recently from c0c4a84 to d5c978c Compare March 22, 2023 21:43

valentinewallace marked this pull request as ready for review March 23, 2023 17:10

TheBlueMatt added this to the 0.0.115 milestone Mar 25, 2023

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valentinewallace mentioned this pull request Apr 3, 2023

Blinded pathfinding groundwork #2146

Merged

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valentinewallace force-pushed the 2023-03-blinded-pathfinding branch from fb85bbd to 79e3442 Compare May 2, 2023 22:15

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jkczyz mentioned this pull request May 10, 2023

BOLT12 Offers Tracking Issue #1970

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60 tasks

valentinewallace added this to the 0.0.116 milestone May 15, 2023

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valentinewallace added 4 commits June 16, 2023 11:14

Reverse (BlindedPath, BlindedPayInfo) tuple order in offers invoice.

3184393

To make it uniform with PaymentParameters' Payee::Blinded::route_hints.

Add utils for creating blinded PaymentParameters

6a54098

Replace max_channel_saturation_power_of_half hardcode with const

a291881

Routing: accommodate for blinded paths in used liquidity tracking

be59d01

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valentinewallace added 4 commits June 19, 2023 09:54

Update CandidateRouteHop::short_channel_id to be optional

b3a27ac

Router: clean up Path construction

25a7073

We don't need to collect a vec of Results anymore.

Implement routing to blinded payment paths

6c3ca55

Sending to them is still disallowed, for now.

valentinewallace dismissed TheBlueMatt’s stale review via 6c3ca55 June 19, 2023 13:55

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TheBlueMatt merged commit ba342de into lightningdevkit:main Jun 20, 2023

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Routing to blinded payment paths #2120

Routing to blinded payment paths #2120

valentinewallace commented Mar 22, 2023 •

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Routing to blinded payment paths #2120

Routing to blinded payment paths #2120

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