[LSPS5 FollowUp] Simplify LSPS5/client peer state #3969

martinsaposnic · 2025-07-28T18:32:02Z

Addressing some LSPS5 follow ups, specifically comments #3662 (comment) and #3662 (comment)

This PR introduces changes so the LSPS5/client drops the TimeProvider, and now instead of just expiring pending requests after a certain time, it just keeps the 5 most recent requests of each type (the 5 here can be changed, not married to the value, I put it just to put something. Thoughts @tnull @TheBlueMatt ?)

My preference for implementing this was:

Keep the ergonomics of the hashmap's O(1) get function
Have something like VecDeque with_capacity to be able to truncate / evict the last value when a new value comes in
LSPS5/client was recently reviewed so I wanted to minimize changes for the reviewers happiness

Some alternatives for making this change were

Add a new dependency like linked-hash-map (just saying it out loud makes me nervous lol)
Have a Vec or VecDeque with capacity to keep track of the requests, truncate when limit is reached, and then do vec.iter().position(|v, _, _| v == r_id) for retrieval (which is kind of ugly and not O(1) like in hashmaps)
Define a new type BoundedMap, which is a fixed size map with a defined capacity and FIFO eviction

I went with the last option, but I'm open to alternatives

Also, the last commit introduces a change where the peerstate is cleaned if there are no pending requests with that peer

ldk-reviews-bot · 2025-07-28T18:32:05Z

👋 Thanks for assigning @tnull as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

codecov · 2025-07-28T18:46:09Z

Codecov Report

❌ Patch coverage is 96.29630% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.99%. Comparing base (61e5819) to head (cf23e91).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning-liquidity/src/lsps5/client.rs	96.25%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3969      +/-   ##
==========================================
+ Coverage   88.94%   88.99%   +0.04%     
==========================================
  Files         174      174              
  Lines      124201   124199       -2     
  Branches   124201   124199       -2     
==========================================
+ Hits       110472   110525      +53     
+ Misses      11251    11200      -51     
+ Partials     2478     2474       -4

Flag	Coverage Δ
fuzzing	`22.64% <0.00%> (+<0.01%)`	⬆️
tests	`88.81% <96.29%> (+0.04%)`	⬆️

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tnull

Did a first pass, mostly looks good.

tnull · 2025-07-29T12:29:37Z

lightning-liquidity/src/utils/bounded_map.rs

+		}
+
+		self.map.insert(key.clone(), value);
+		self.order.push_back(key.clone());


I think this clone is unnecessary?

tnull · 2025-07-29T12:31:55Z

lightning-liquidity/src/utils/bounded_map.rs

+			if let Some(oldest) = self.order.pop_front() {
+				self.map.remove(&oldest);
+			}
+		}


Can we sprinkle in some debug_asserts ensuring that neither map nor order ever exceed cap at the end of the methods taking &mut?

tnull · 2025-07-29T12:35:45Z

lightning-liquidity/src/utils/bounded_map.rs

+		assert!(m.get(&"key").is_none());
+	}
+
+	#[test]


These tests would be a prime example were proptests would be easily applicable and would extend test coverage.

tnull · 2025-07-29T12:36:49Z

lightning-liquidity/src/utils/mod.rs

@@ -57,4 +57,5 @@ mod tests {
 	}
 }

+pub(crate) mod bounded_map;


Huh, why are these mod definitions at the bottom by now? Let's move them to the top please, and let's keep pub and pub(crate) definitions in separate groups.

tnull · 2025-07-29T12:38:35Z

lightning-liquidity/src/lsps5/client.rs

@@ -345,6 +351,19 @@ where
 			}
 		};
 		self.with_peer_state(*counterparty_node_id, handle_response);
+
+		let mut outer_state_lock = self.per_peer_state.write().unwrap();


Mind moving this out to a dedicated method?

ldk-reviews-bot · 2025-07-29T12:40:52Z

👋 The first review has been submitted!

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martinsaposnic · 2025-07-30T18:57:28Z

thanks for the review @tnull ! all comments are addressed in fixup commits

lightning-liquidity/src/lsps5/client.rs

tnull

Feel free to squash fixups!

martinsaposnic · 2025-07-31T12:24:55Z

done! @tnull

tnull

LGTM

ldk-reviews-bot · 2025-08-01T13:28:44Z

✅ Added second reviewer: @valentinewallace

TheBlueMatt

Have a Vec or VecDeque with capacity to keep track of the requests, truncate when limit is reached, and then do vec.iter().position(|v, _, _| v == r_id) for retrieval (which is kind of ugly and not O(1) like in hashmaps)

Sure, but for N=5 its probably faster than doing the SipHash-1-3 required to do that HashMap O(1), not to mention it avoids a second allocated datastructure. Let's definitely not overengineer this - walking a Vec is totally fine for N=5.

Client will no longer use a time provider to expire pending requests. Instead, it will just keep the X most recent requests (coming in next commit).

martinsaposnic · 2025-08-04T14:49:26Z

Have a Vec or VecDeque with capacity to keep track of the requests, truncate when limit is reached, and then do vec.iter().position(|v, _, _| v == r_id) for retrieval (which is kind of ugly and not O(1) like in hashmaps)

Sure, but for N=5 its probably faster than doing the SipHash-1-3 required to do that HashMap O(1), not to mention it avoids a second allocated datastructure. Let's definitely not overengineer this - walking a Vec is totally fine for N=5.

thanks for reviewing @TheBlueMatt

just pushed fixup commit ec6a9f0 where I drop the bounded_map and change everything so it uses vecs for keeping track of the client's pending requests. let me know what you think

TheBlueMatt

I think this LGTM, feel free to squash if @tnull is fine with dropping the fancy map.

tnull

Fixup LGTM, please squash so we can get this landed.

martinsaposnic · 2025-08-05T11:01:40Z

thanks for taking a look @tnull. fixup squashed!

offtopic question about process:

I'm not sure if there's an easy way to verify that the squash was actually just a squash and nothing more. for example, I just split the fixup into the last two commits and reworded the second one. I did not change anything else, but there's no easy way for you to quickly confirm that I didn't accidentally change something else

tnull · 2025-08-05T12:44:29Z

I'm not sure if there's an easy way to verify that the squash was actually just a squash and nothing more. for example, I just split the fixup into the last two commits and reworded the second one. I did not change anything else, but there's no easy way for you to quickly confirm that I didn't accidentally change something else

For one you can hit the 'Compare' button above to see the diff between pushes. I also always check out the working branch locally to review, so can simply do a diff to see if/what changed. As a bonus you can use range-diff to review the diff even after a rebase.

tnull

Going ahead landing this given that the current state had two 'LGTM' before

ldk-reviews-bot requested a review from valentinewallace July 28, 2025 18:42

martinsaposnic force-pushed the simplify-lsps5-client-peer-state branch from c8e9948 to fba3056 Compare July 28, 2025 19:36

tnull requested review from tnull and removed request for valentinewallace July 29, 2025 08:49

tnull reviewed Jul 29, 2025

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martinsaposnic mentioned this pull request Jul 30, 2025

LSPS5 Follow ups #3944

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martinsaposnic requested a review from tnull July 30, 2025 18:57

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martinsaposnic force-pushed the simplify-lsps5-client-peer-state branch from 1332159 to 91c7904 Compare July 30, 2025 19:35

tnull reviewed Jul 31, 2025

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martinsaposnic force-pushed the simplify-lsps5-client-peer-state branch from 91c7904 to 5d25ab1 Compare July 31, 2025 12:14

martinsaposnic requested a review from tnull July 31, 2025 12:24

martinsaposnic force-pushed the simplify-lsps5-client-peer-state branch from 5d25ab1 to 993c366 Compare July 31, 2025 16:01

tnull previously approved these changes Aug 1, 2025

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ldk-reviews-bot requested a review from valentinewallace August 1, 2025 13:28

tnull requested review from TheBlueMatt and removed request for valentinewallace August 1, 2025 13:28

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Get rid of TimeProvider on LSPS5/client.

d2c7c66

Client will no longer use a time provider to expire pending requests. Instead, it will just keep the X most recent requests (coming in next commit).

martinsaposnic dismissed tnull’s stale review via ec6a9f0 August 4, 2025 14:45

martinsaposnic force-pushed the simplify-lsps5-client-peer-state branch from 993c366 to ec6a9f0 Compare August 4, 2025 14:45

martinsaposnic requested a review from TheBlueMatt August 4, 2025 14:49

martinsaposnic mentioned this pull request Aug 4, 2025

LSPS5 -> More follow ups #3987

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martinsaposnic requested a review from tnull August 4, 2025 15:27

TheBlueMatt reviewed Aug 4, 2025

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tnull reviewed Aug 5, 2025

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martinsaposnic added 2 commits August 5, 2025 07:53

Use VecDeque on LSPS5/Client to limit amount of pending requests

9ab2d27

Remove peerState if there are no pending requests with that peer

cf23e91

martinsaposnic force-pushed the simplify-lsps5-client-peer-state branch from ec6a9f0 to cf23e91 Compare August 5, 2025 10:54

martinsaposnic requested a review from tnull August 5, 2025 11:34

tnull approved these changes Aug 5, 2025

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tnull merged commit d704eb8 into lightningdevkit:main Aug 5, 2025
23 of 24 checks passed

[LSPS5 FollowUp] Simplify LSPS5/client peer state #3969

[LSPS5 FollowUp] Simplify LSPS5/client peer state #3969

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