Use all valid routes during blinded path construction #9334

MPins · 2024-12-05T14:57:33Z

MaxNumPaths restriction moved from FindBlindedPaths to BuildBlindedPaymentPaths this way we can interact through all possibly routes.

If the reviewers agreed to this approach we will have to modify the TestFindBlindedPathsWithMC because it is considering that MaxNumPaths retriction is applied on FindBlindedPaths function.

coderabbitai · 2024-12-05T14:57:43Z

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ziggie1984 · 2024-12-07T00:34:31Z

This seems like the simpler solution to implement. Since we’re already querying all routes in FindBlindedPaths, it makes sense to just return them. However, it might be worthwhile to introduce a hard constant cap during the pathfinding process to prevent the array size from growing exponentially. Currently, the algorithm explores all possible paths within the given constraints. Instead, we could stop after finding, say, 100 routes in total, and then apply filtering to select the MaxNumPaths in BuildBlindedPaymentPaths, as proposed in this PR.

Probably the constraints of the Min/Max Hop number prevents these high numbers for routes but I think having a cap is kind of a sanity check.

MPins · 2024-12-09T11:52:30Z

This seems like the simpler solution to implement. Since we’re already querying all routes in FindBlindedPaths, it makes sense to just return them. However, it might be worthwhile to introduce a hard constant cap during the pathfinding process to prevent the array size from growing exponentially. Currently, the algorithm explores all possible paths within the given constraints. Instead, we could stop after finding, say, 100 routes in total, and then apply filtering to select the MaxNumPaths in BuildBlindedPaymentPaths, as proposed in this PR.

Probably the constraints of the Min/Max Hop number prevents these high numbers for routes but I think having a cap is kind of a sanity check.

Before the proposed changes we are querying all routes, sorting the routes based on probability and them capping them based on MaxNumPaths before returning from FindBlindedPaths. After the changes we are capping them just one step later after FindBlindedPaths return them to BuildBlindedPaymentPaths. The hard constant cap should be introduced after the sorting! I might be wrong, but it seems that we are getting too little introducing it!

ziggie1984 · 2024-12-09T12:46:26Z

The hard constant cap should be introduced after the sorting! I might be wrong, but it seems that we are getting too little introducing it!

I think we need to do way more when creating the path rather than creating the path and later checking the probability this does not seem efficient. I think we should build the path in the first place based on probability not just running a depth first search on all available paths. But I am not sure how difficult that might be because we went with the recusrive approach.

MPins · 2024-12-10T13:42:54Z

The hard constant cap should be introduced after the sorting! I might be wrong, but it seems that we are getting too little introducing it!

I think we need to do way more when creating the path rather than creating the path and later checking the probability this does not seem efficient. I think we should build the path in the first place based on probability not just running a depth first search on all available paths. But I am not sure how difficult that might be because we went with the recursive approach.

I think we might compute the total probability and sort the path list during the creation of it (into processNodeForBlindedPath), but I'm not sure it's worth it. What do you think?

ziggie1984 · 2024-12-12T10:09:14Z

yes let's keep it as is and focus only on the underlying issue.

routing/router.go

MPins · 2024-12-19T13:30:08Z

Hello @ziggie1984 gently reminder of review 😉

ziggie1984 · 2024-12-29T08:29:22Z

unit-test fail !

ziggie1984

Looking good I am missing 2 things here:

Can you add some logging stats how many routes are find in total, then how many are filtered out because of the probability as for example debug information. I am very curious whether routes will fail often at the level where the final route and relay information is accumulated.
I tend to introduce a max route variable for the blinded path finding in general, maybe a default of 50 routes, otherwise we look for everything which with a big number of blinded hops might be wasteful.

routing/blindedpath/blinded_path.go

routing/router_test.go

rpcserver.go

MPins · 2025-01-24T01:50:05Z

Looking good I am missing 2 things here:

Can you add some logging stats how many routes are find in total, then how many are filtered out because of the probability as for example debug information. I am very curious whether routes will fail often at the level where the final route and relay information is accumulated.

I tend to introduce a max route variable for the blinded path finding in general, maybe a default of 50 routes, otherwise we look for everything which with a big number of blinded hops might be wasteful.

Hello Ziggie, I had addressed your comments, thank you! Ready for your next review!

Abdulkbk

Thanks for the PR. I looked through the changes and left some comments/questions.

routing/router.go

routing/blindedpath/blinded_path_test.go

MPins

Thank you @Abdulkbk for your review!

routing/router.go

MPins · 2025-01-31T21:04:54Z

@ziggie1984 and @Abdulkbk , it is ready for your review. 🤝

ziggie1984

Looking good, I want to get @ellemouton opinion on the recursive abort criteria in case we have a maximum number of paths.

Missing release notes for LND 20.

routing/blindedpath/blinded_path.go

ziggie1984 · 2025-02-01T17:32:27Z

routing/router.go

 	for _, route := range routes {
-		if len(bestRoutes) >= int(restrictions.MaxNumPaths) {
+		if len(allRoutes) >= maxRoutes {


that is not what I meant, my idea was to exit the recursion early when enough paths are found,

I was more thinking of restricting the recursion in processNodeForBlindedPath but I would like to get @ellemouton opinion on this and also this can probably done in another PR.

Currently our DFS exhausts all Paths which exist in the graph, so I was thinking we could abort the DFS after we already have a hopSet of let's say 100 ?

Imagine we have a minRouteLen of 2 and a maxRouteLen of 6, each node has more than 100 channels, when reaching the depth of 6, we could easily accumulate > 1000 routes which seems unreasonable.

But the above restrictions we do not need, because really makes not difference we already have all the paths in memory.

You right, thanks for the explanation.

The point is that, in the current implementation, we first retrieve all the routes and then sort them to prioritize those with the highest success probability.

Instead, we should modify the process to evaluate the probability of each route during the iteration, keeping only the best ones.

seems like this is removed but not in this commit, can you make sure this is removed also in this commit

routing/router_test.go

routing/blindedpath/blinded_path_test.go

yyforyongyu · 2025-02-10T02:59:02Z

There is no release notes for LND 20 yet. Should I create it?

Yeah feel free to open a PR!

ziggie1984 · 2025-02-14T09:02:40Z

please make sure the check commits passes, you can run this script locally as well:

scripts/check-each-commit.sh upstream/master

ziggie1984

It's close let's bring it over the finish line 💪

ziggie1984 · 2025-02-14T09:58:29Z

routing/blindedpath/blinded_path.go

@@ -100,6 +100,9 @@ type BuildBlindedPathCfg struct {
 	// route.
 	MinNumHops uint8

+	// MaxNumPaths is the maximum number of blinded paths to select.


The MaxNumPath can now be removed from BlindedPathRestrictions we are not using it anymore there. Super confusing to have all this MaxPaths variables.

You right, thanks!

ziggie1984 · 2025-02-14T10:07:07Z

routing/router.go

 	for _, route := range routes {
-		if len(bestRoutes) >= int(restrictions.MaxNumPaths) {
+		if len(allRoutes) >= maxRoutes {


seems like this is removed but not in this commit, can you make sure this is removed also in this commit

ziggie1984 · 2025-02-14T10:09:28Z

routing/router.go

@@ -640,6 +640,8 @@ func (r *ChannelRouter) FindBlindedPaths(destination route.Vertex,
 		probability float64
 	}

+	totalRoutesFound := 0


We don't need this counters, we just get the information by comparing the different lengths of the arrays.

routes and paths

ziggie1984 · 2025-02-14T10:12:09Z

routing/router.go

@@ -640,6 +640,8 @@ func (r *ChannelRouter) FindBlindedPaths(destination route.Vertex,
 		probability float64
 	}


can you be more verbose in the commit msg: Something like:

We now return all possible paths found by the pathfinder and only remove those which do have a low probability.

ziggie1984 · 2025-02-14T10:13:27Z

routing/router.go

@@ -708,9 +708,6 @@ func (r *ChannelRouter) FindBlindedPaths(destination route.Vertex,
 	// Return all routes, capped by the maxNumberOfRoutes.
 	allRoutes := make([]*route.Route, 0, len(routes))
 	for _, route := range routes {
-		if len(allRoutes) >= maxRoutes {


this change should be in the previous commit

ziggie1984 · 2025-02-14T10:36:22Z

routing/router_test.go

@@ -3249,27 +3245,12 @@ func TestFindBlindedPathsWithMC(t *testing.T) {
 		"alice,charlie,dave",
 	})

-	// Change the MaxNumPaths to 1 to assert that only the best route is


in this file there is a typo: fluke => flake

It is not a typo ... "fluke" and "flake" have different meanings, though they sound similar. Fluke is a lucky or random event that happens by chance.

ziggie1984 · 2025-02-14T10:44:42Z

rpcserver.go

@@ -6168,6 +6168,7 @@ func (r *rpcServer) AddInvoice(ctx context.Context,
 				MaxHTLCMsat: 0,
 			},
 			MinNumPathHops: blindingRestrictions.NumHops,
+			MaxNumPaths:    blindingRestrictions.MaxNumPaths,


Given my understanding we can use the config values here directly without adding a middle step assigning it to the restrictions struct.

ziggie1984 · 2025-02-14T10:45:33Z

routing/blindedpath/blinded_path_test.go

@@ -547,35 +547,58 @@ func genBlindedRouteData(rand *rand.Rand) *record.BlindedRouteData {
 // an example mentioned in this spec document:
 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md


Try keeping the commit msg below 50 chars, so its not overflowing like you see here.

ziggie1984 · 2025-02-14T10:56:26Z

routing/blindedpath/blinded_path_test.go

@@ -547,35 +547,58 @@ func genBlindedRouteData(rand *rand.Rand) *record.BlindedRouteData {
 // an example mentioned in this spec document:
 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md
 // This example does not use any dummy hops.
+// Added Dave to test MaxNumPaths restriction.


can we add a isolated test which does nothing more than testing the maxPaths. Now the test feels a bit confusing, we can just add a new test, make sure the paths are returned but not check all the values which we expect.

I think we can make it clear with better comments.

ziggie1984 · 2025-02-14T11:05:26Z

docs/release-notes/release-notes-0.20.0.md

+* [Fixed a bug](https://github.com/lightningnetwork/lnd/pull/9334) when 
+constructing blinded payment paths for an invoice, we select up to MaxNumPaths 
+candidate routes and pass them forward. This process may result in running out 
+of paths if some of them are discarded for any reason later. This PR return all 
+possible routes and then do the MaxPath cap later on.


Suggested change

* [Fixed a bug](https://github.com/lightningnetwork/lnd/pull/9334) when

constructing blinded payment paths for an invoice, we select up to MaxNumPaths

candidate routes and pass them forward. This process may result in running out

of paths if some of them are discarded for any reason later. This PR return all

possible routes and then do the MaxPath cap later on.

[Fixed a bug](https://github.com/lightningnetwork/lnd/pull/9334) in constructing blinded payment paths for invoices. The restriction on the maximum number of paths is now applied later during pathfinding, ensuring that all potential paths are considered before filtering out ineligible ones. This allows for better utilization of the available paths for payments.

Much better thanks 👍

MPins · 2025-02-14T11:08:54Z

please make sure the check commits passes, you can run this script locally as well:

scripts/check-each-commit.sh upstream/master

Thanks ... now it is fixed.

MPins

Thanks, everything addressed!

MPins · 2025-02-14T11:54:20Z

docs/release-notes/release-notes-0.20.0.md

+* [Fixed a bug](https://github.com/lightningnetwork/lnd/pull/9334) when 
+constructing blinded payment paths for an invoice, we select up to MaxNumPaths 
+candidate routes and pass them forward. This process may result in running out 
+of paths if some of them are discarded for any reason later. This PR return all 
+possible routes and then do the MaxPath cap later on.


Much better thanks 👍

MPins · 2025-02-14T12:31:37Z

routing/blindedpath/blinded_path.go

@@ -100,6 +100,9 @@ type BuildBlindedPathCfg struct {
 	// route.
 	MinNumHops uint8

+	// MaxNumPaths is the maximum number of blinded paths to select.


You right, thanks!

MPins · 2025-02-14T13:16:28Z

routing/blindedpath/blinded_path_test.go

@@ -547,35 +547,58 @@ func genBlindedRouteData(rand *rand.Rand) *record.BlindedRouteData {
 // an example mentioned in this spec document:
 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md
 // This example does not use any dummy hops.
+// Added Dave to test MaxNumPaths restriction.


I think we can make it clear with better comments.

MPins · 2025-02-14T14:35:01Z

routing/router_test.go

 	routes, err := ctx.router.FindBlindedPaths(
 		dave, 1000, probabilitySrc, &BlindedPathRestrictions{
 			MinDistanceFromIntroNode: 2,
 			NumHops:                  2,
-			MaxNumPaths:              3,


I didn't modify the test logic, but as I understand it, there's no probability difference affecting the expected order. So there is no reason to assert it.

MPins · 2025-02-14T14:38:21Z

routing/router_test.go

@@ -3249,27 +3245,12 @@ func TestFindBlindedPathsWithMC(t *testing.T) {
 		"alice,charlie,dave",
 	})

-	// Change the MaxNumPaths to 1 to assert that only the best route is


It is not a typo ... "fluke" and "flake" have different meanings, though they sound similar. Fluke is a lucky or random event that happens by chance.

MPins · 2025-02-14T15:24:20Z

@ziggie1984 notice that the last changes broke some tests ... I'll be fixing today! And let you know.

We now return all possible paths found by the pathfinder and only remove those which do have a low probability.

MaxNumPaths restriction moved from FindBlindedPaths to BuildBlindedPaymentPaths this way we can interact through all possibly routes when creating a new blinded path.

MaxNumPaths restriction moved from FindBlindedPaths to BuildBlindedPaymentPaths this way we have to fill the MaxNumPaths parameter when calling this function.

MPins changed the title ~~route blinding: use all valid routes during path construction iteration instead of the currently capped set by MaxNumPaths~~ Use all valid routes during path construction iteration instead of the currently capped set by MaxNumPaths Dec 5, 2024

MPins changed the title ~~Use all valid routes during path construction iteration instead of the currently capped set by MaxNumPaths~~ use all valid routes during blinded path construction Dec 5, 2024

MPins changed the title ~~use all valid routes during blinded path construction~~ Use all valid routes during blinded path construction Dec 5, 2024

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MPins added 7 commits February 15, 2025 00:03

blindedpath: add the MaxNumPaths restriction on BuildBlindedPaymentPaths

b216350

invoicesrpc: included MaxNumPaths to be used on BuildBlindedPaymentPaths

5f25e39

lnd: added MaxNumPaths on blindedPathCfg to be used on AddInvoice

e84ea05

routing: no MaxNumPaths restriction on FindBlindedPaths

2d45148

We now return all possible paths found by the pathfinder and only remove those which do have a low probability.

routing: modify the TestFindBlindedPathsWithMC to not use MaxNumPaths

7e21ebe

MaxNumPaths restriction moved from FindBlindedPaths to BuildBlindedPaymentPaths this way we can interact through all possibly routes when creating a new blinded path.

blindedpath: update tests to use MaxNumPaths in BuildBlindedPaymentPaths

ed223a6

MaxNumPaths restriction moved from FindBlindedPaths to BuildBlindedPaymentPaths this way we have to fill the MaxNumPaths parameter when calling this function.

doc: release-notes-0.20.0

4cb3e36

MPins force-pushed the issue-9076 branch from 1d6fc66 to 4cb3e36 Compare February 15, 2025 03:03

		@@ -640,6 +640,8 @@ func (r *ChannelRouter) FindBlindedPaths(destination route.Vertex,
		probability float64
		}

		@@ -547,35 +547,58 @@ func genBlindedRouteData(rand rand.Rand) record.BlindedRouteData {
		// an example mentioned in this spec document:
		// https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md

Use all valid routes during blinded path construction #9334

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