Trampoline Payload Construction Method #3386

arik-so · 2024-10-28T02:35:51Z

Introduce a method for constructing Trampoline payloads.

This will allow the non-Trampoline method to be modified to generate a Trampoline onion and finish its own regular payload construction.

Builds on top of #3333.

lightning/src/routing/router.rs

TheBlueMatt · 2024-10-29T14:40:29Z

lightning/src/routing/router.rs

@@ -454,6 +454,9 @@ impl_writeable_tlv_based!(BlindedTail, {
 pub struct Path {
 	/// The list of unblinded hops in this [`Path`]. Must be at least length one.
 	pub hops: Vec<RouteHop>,
+	/// The list of unblinded Trampoline hops. If present, must be at least one.
+	/// The public key of the first Trampoline hop must match the public key of the last regular hop.


I don't see why this needs to be true. Can we just have each trampoline hop be next hops starting after the last unblinded node.

TheBlueMatt · 2024-10-29T14:41:16Z

lightning/src/routing/router.rs

@@ -454,6 +454,9 @@ impl_writeable_tlv_based!(BlindedTail, {
 pub struct Path {
 	/// The list of unblinded hops in this [`Path`]. Must be at least length one.
 	pub hops: Vec<RouteHop>,
+	/// The list of unblinded Trampoline hops. If present, must be at least one.
+	/// The public key of the first Trampoline hop must match the public key of the last regular hop.
+	pub trampoline_hops: Vec<TrampolineHop>,


Seems weird to add this to the public API in a PR that doesn't use it. Can you go ahead and wire up build_trampoline_onion_payloads to build the valid onion in the same PR?

codecov · 2024-11-21T17:27:45Z

Codecov Report

Attention: Patch coverage is 27.39130% with 167 lines in your changes missing coverage. Please review.

Project coverage is 89.98%. Comparing base (726dd5c) to head (35a3693).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/onion_utils.rs	9.94%	161 Missing and 2 partials ⚠️
lightning/src/events/mod.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3386      +/-   ##
==========================================
+ Coverage   89.69%   89.98%   +0.29%     
==========================================
  Files         130      130              
  Lines      107335   109705    +2370     
  Branches   107335   109705    +2370     
==========================================
+ Hits        96273    98721    +2448     
+ Misses       8660     8657       -3     
+ Partials     2402     2327      -75

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TheBlueMatt

Ah I guess my previous comments still need to be addressed.

TheBlueMatt · 2024-11-25T15:39:39Z

lightning/src/routing/router.rs

@@ -404,13 +404,16 @@ pub struct BlindedTail {
 	pub excess_final_cltv_expiry_delta: u32,
 	/// The total amount paid on this [`Path`], excluding the fees.
 	pub final_value_msat: u64,
+	/// Used for determining the type of Trampoline path to construct
+	pub final_hop_supports_trampoline: bool


Should we instead consider storing a *Features of some form?

lightning/src/routing/router.rs

valentinewallace · 2024-12-10T21:31:39Z

lightning/src/ln/onion_utils.rs

+	Ok((res, value_msat, cltv))
+}
+
+fn build_trampoline_onion_payloads_callback<'a, H, B, F>(


Is there a way to DRY this with build_onion_payloads_callback, via implementing a trait on OutboundTrampolinePayload and OutboundOnionPayload that the common method is parameterized by? Kinda like what we do for decode_next_hop and how it works for both onion message and onion payment packets.

I'm not sure the payloads_callback is super DRYable, because all the response types that are being pushed vary strongly between RouteHop and TrampolineHop, but I think I was able to at least DRY up the onion_keys callback.

valentinewallace · 2024-12-12T19:07:21Z

lightning/src/events/mod.rs

@@ -1940,7 +1940,7 @@ impl MaybeReadable for Event {
 						payment_hash,
 						payment_failed_permanently,
 						failure,
-						path: Path { hops: path.unwrap(), blinded_tail },
+						path: Path { hops: path.unwrap(), trampoline_hops: vec![], blinded_tail },


I think we'll want to serialize these hops in the event(s) eventually so may be easy to just do it in this PR.

true, will add serialization

valentinewallace · 2024-12-12T20:20:05Z

lightning/src/ln/onion_utils.rs

+				onion_payloads.push(OutboundOnionPayload::TrampolineEntrypoint {
+					amt_to_forward: outer_total_msat,
+					outgoing_cltv_value: outer_starting_htlc_offset,
+					multipath_trampoline_data: None,


Shouldn't this be set to something?

oh yes, good catch, thank you

valentinewallace · 2024-12-12T20:26:44Z

lightning/src/ln/onion_utils.rs

+						cur_value_msat += final_value_msat;
+						callback(
+							PayloadCallbackAction::PushBack,
+							msgs::OutboundTrampolinePayload::BlindedReceive {


It looks like in https://github.com/lightning/bolts/blob/fa0594ac2af3531d734f1d707a146d6e13679451/bolt04/trampoline-payment-onion-test.json there can be final trampoline hops that are unblinded, but that doesn't look supported in the code atm. Are we explicitly only supporting trampoline to blinded paths?

yup, we deliberately are. We originally supported non-blinded destinations but decided not to.

valentinewallace · 2024-12-12T20:31:49Z

lightning/src/ln/onion_route_tests.rs

+	let trampoline_onion_keys = construct_trampoline_onion_keys(&Secp256k1::new(), &trampoline_hops, &trampoline_session_key).unwrap();
+	let trampoline_onion_packet = construct_trampoline_onion_packet(trampoline_payloads, trampoline_onion_keys, [0u8; 32], &associated_data, None).unwrap();
+	let trampoline_onion_packet_hex = trampoline_onion_packet.encode().to_lower_hex_string();
+	assert_eq!(trampoline_onion_packet_hex, "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");


Would it be possible to generate and check the overall payment onion from the test vector as well as the inner trampoline onion?

sure, I can extend that

valentinewallace · 2024-12-13T20:41:38Z

lightning/src/ln/onion_route_tests.rs

+	let outer_session_key = SecretKey::from_slice(&<Vec<u8>>::from_hex("4f777e8dac16e6dfe333066d9efb014f7a51d11762ff76eca4d3a95ada99ba3e").unwrap()).unwrap();
+	let outer_onion_keys = onion_utils::construct_onion_keys(&Secp256k1::new(), &outer_hops, &outer_session_key).unwrap();
+	let outer_onion_prng_seed = onion_utils::gen_pad_from_shared_secret(&outer_session_key.secret_bytes());
+	let outer_onion_packet = onion_utils::construct_onion_packet(outer_payloads, outer_onion_keys, outer_onion_prng_seed, &associated_data).unwrap();


Can we use create_payment_onion instead? I think we don't currently have coverage of that method when trampoline hops are present and generally better to use the public API when testing

ok, I think I have some ideas for how to do it precisely enough for it to match the test vectors. Not entirely sure yet if it will work, but I'll see what I can do

I pushed changes addressing the other comments, but this one will take a little while

valentinewallace · 2024-12-13T20:42:10Z

lightning/src/events/mod.rs

@@ -1584,6 +1584,7 @@ impl Writeable for Event {
 					(9, None::<RouteParameters>, option), // retry in LDK versions prior to 0.0.115
 					(11, payment_id, option),
 					(13, failure, required),
+					(15, path.trampoline_hops, required_vec),


nit: use optional_vec so we don't write it when it's empty

valentinewallace · 2024-12-13T20:42:56Z

lightning/src/events/mod.rs

@@ -2085,7 +2088,7 @@ impl MaybeReadable for Event {
 					Ok(Some(Event::PaymentPathSuccessful {
 						payment_id: payment_id.0.unwrap(),
 						payment_hash,
-						path: Path { hops: path, blinded_tail },
+						path: Path { hops: path, trampoline_hops: vec![], blinded_tail },


Needs ser for this event too

TheBlueMatt reviewed Oct 29, 2024

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arik-so force-pushed the arik/trampoline/payload-construction branch 2 times, most recently from 7cad33e to 856ce97 Compare November 19, 2024 23:04

arik-so force-pushed the arik/trampoline/payload-construction branch from 856ce97 to 5ea3ada Compare November 21, 2024 17:15

TheBlueMatt reviewed Nov 25, 2024

View reviewed changes

arik-so force-pushed the arik/trampoline/payload-construction branch from 5ea3ada to af1818b Compare December 5, 2024 01:19

arik-so mentioned this pull request Dec 5, 2024

Trampoline #2299

Open

29 tasks

arik-so force-pushed the arik/trampoline/payload-construction branch 4 times, most recently from ee68783 to 4dd0fea Compare December 9, 2024 05:31

valentinewallace reviewed Dec 10, 2024

View reviewed changes

arik-so force-pushed the arik/trampoline/payload-construction branch 3 times, most recently from 67100ce to dc679c0 Compare December 11, 2024 07:23

arik-so added 4 commits December 12, 2024 09:13

Calculate Trampoline onion size dynamically

4077d64

Keep track of Trampoline support in blinded tails

2d1f582

Create TrampolineHop struct

6fb690e

Add trampoline_hops field to Path

3c83538

arik-so force-pushed the arik/trampoline/payload-construction branch from dc679c0 to 7477b1a Compare December 12, 2024 17:14

valentinewallace reviewed Dec 12, 2024

View reviewed changes

f: serialize trampoline hops in event

eec1685

arik-so force-pushed the arik/trampoline/payload-construction branch from 7477b1a to ba71d6e Compare December 13, 2024 10:34

valentinewallace reviewed Dec 13, 2024

View reviewed changes

f: write trampoline hops as optional vec

0aa469f

arik-so force-pushed the arik/trampoline/payload-construction branch from ba71d6e to b934379 Compare December 13, 2024 22:03

arik-so added 3 commits December 13, 2024 14:54

f: ser/de PaymentPathSuccessful

94d8f2e

Trampoline payload construction method

f044acb

Introduce construct_trampoline_onion_keys method

0700bb2

arik-so added 5 commits December 13, 2024 14:54

f: DRY up onion_utils

7054de6

add Trampoline blinded path serialization unit tests

a5eeee3

f: check outer onion test vector

3e95247

Construct Trampoline component in create_payment_onion

a308936

f: set multipath_trampoline_data

6569246

arik-so force-pushed the arik/trampoline/payload-construction branch from b934379 to 6569246 Compare December 13, 2024 22:54

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Trampoline Payload Construction Method #3386

Trampoline Payload Construction Method #3386

arik-so commented Oct 28, 2024 •

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Trampoline Payload Construction Method #3386

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Trampoline Payload Construction Method #3386

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arik-so commented Oct 28, 2024 •

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