simln-lib/feat: Surface send_to_route for SimGraph #268

chuksys · 2025-05-16T17:25:17Z

Description

This PR makes it possible for a user of simln-lib (in sim-node mode) to send payments to a predetermined route. This addresses the need for end-users to send custom payments, crucial for scenarios like channel jamming attacks or pathfinding experiments, which the current activity paradigm doesn't support.

Changes

A send_to_route method was added to SimGraph.
A track_payment_to_route method was added to SimGraph.
A build_payment_route helper function was added.
3 test cases were added to test successful route payment and tracking, route building errors and payment tracking errors.

This PR closes #257

simln-lib/src/sim_node.rs

carlaKC

Worried about the layering of adding this functionality to SimGraph, would like to take another look at the high level design here.

Also needs a rebase!

carlaKC · 2025-05-22T16:44:52Z

simln-lib/src/sim_node.rs

+/// Uses the provided `hops` and `amount_msat` to build an LDK route.
+/// This is a helper function to build a route easily.
+/// The route built using this function can be passed into `SimGraph::send_to_route`.
+pub fn build_payment_route(


Hm, not sure that we need this helper for an advanced user?

Perhaps we an just point to build_route_from_hops on the docs for send_to_route?

carlaKC · 2025-05-22T16:45:01Z

simln-lib/src/sim_node.rs

        })
    }
+
+    pub async fn send_to_route(


I'm not sure about adding this in SimGraph - feels like a layering violation. I can see how the discussion on the issue was a bit ambiguous - should have pointed out that it should still go on the node even though we don't need to implement it on the other types.

I think that this should live on SimNode so that we can re-use the infrastructure that's already there (eg, we wouldn't need another track payment function, we already have it).

I think it's reasonable to expect the end user to look up the dispatching node that they want and then call SimNode.send_to_route.

chuksys · 2025-05-26T17:35:01Z

I didn't add any test cases this time around since test_simulated_node in tests already does most of the testing we require by testing the dispatch_payment fn (this is most of the functionality for the send_to_route fn except the newly derived route).

carlaKC

Looking good, just one API q from me + a test ask.

carlaKC · 2025-05-27T15:59:25Z

simln-lib/src/sim_node.rs

+        let preimage = PaymentPreimage(rand::random());
+        let payment_hash = preimage.into();


Hm I wonder whether there's any use for people to pass in their own payment hash?

WDYT, I'm on the fence...

I think this could be helpful if the user wants to simulate payments in an application that relies on a custom payment flow - for example the user could have a payment flow that requires generating the preimage and hash much earlier in their process, perhaps for coordination with other parts of their application, well before the send_to_route method is called.

I think allowing users to pass in their own payment hash would give them the flexibility to accurately model such scenarios.

simln-lib/src/sim_node.rs

carlaKC · 2025-06-02T14:07:39Z

simln-lib/src/sim_node.rs

@@ -526,6 +526,37 @@ impl<'a, T: SimNetwork> SimNode<'a, T> {
            scorer,
        }
    }
+
+    /// send_to_route dispatches a payment to a specified route.


Nit: don't need to include send_to_route in doc, just start with "Dispatches"

afaik this is rust convention, since the doc will always be displayed along with its function (unlike golang, where the convention is to alway start with the name).

Ignore all the places where we do this wrong in the codebase :')

Ignore all the places where we do this wrong in the codebase :')

: )

carlaKC · 2025-06-02T14:09:26Z

simln-lib/src/sim_node.rs

    /// provided is triggered. This call will fail if the hash provided was not obtained by calling send_payment first.
+    /// Payment hashes passed into send_to_route can also be tracked using track_payment.


nit: "This call will fail if the hash provided was not obtained by calling send_payment or track_payment* first?

Update: *track_payment -> send_to_route, my bad!

simln-lib/src/sim_node.rs

carlaKC · 2025-06-02T14:10:24Z

simln-lib/src/sim_node.rs

+        .map_err(|e| {
+            SimulationError::SimulatedNetworkError(format!(
+                "An Error occurred while building route - {}",
+                e.err
+            ))
+        });


Don't need to map the error in a test - just unwrap?

simln-lib/src/sim_node.rs

carlaKC

LGTM! go ahead with squash and I'll hit the button

carlaKC self-requested a review May 16, 2025 17:37

chuksys commented May 16, 2025

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carlaKC requested a review from f3r10 May 20, 2025 15:23

carlaKC reviewed May 22, 2025

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chuksys force-pushed the surface-send-to-route branch from bd09d2b to b1db235 Compare May 26, 2025 16:57

chuksys requested a review from carlaKC May 26, 2025 17:35

chuksys force-pushed the surface-send-to-route branch from e7684ad to f7f511a Compare May 27, 2025 14:52

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chuksys force-pushed the surface-send-to-route branch from f7f511a to 3f14a70 Compare May 29, 2025 15:43

chuksys requested a review from carlaKC May 29, 2025 15:56

carlaKC reviewed Jun 2, 2025

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chuksys requested a review from carlaKC June 3, 2025 12:41

carlaKC approved these changes Jun 3, 2025

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simln-lib/feat: Surface send_to_route for SimGraph

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chuksys force-pushed the surface-send-to-route branch from c3b6cfc to dce1f3f Compare June 3, 2025 13:55

carlaKC merged commit fefbfc7 into bitcoin-dev-project:main Jun 3, 2025
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simln-lib/feat: Surface send_to_route for SimGraph #268

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		let preimage = PaymentPreimage(rand::random());
		let payment_hash = preimage.into();

		/// provided is triggered. This call will fail if the hash provided was not obtained by calling send_payment first.
		/// Payment hashes passed into send_to_route can also be tracked using track_payment.

simln-lib/feat: Surface send_to_route for SimGraph #268

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chuksys commented May 16, 2025

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