Zero-fee commitments support by tankyleo · Pull Request #660 · lightningdevkit/ldk-node

tankyleo · 2025-10-13T13:14:22Z

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ldk-reviews-bot · 2025-10-13T13:14:24Z

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tnull · 2025-10-13T13:25:43Z

+	/// `option_anchor_zero_fee_commitments`. All the caveats and warnings in
+	/// [`AnchorChannelsConfig`] still apply.
+	/// [`AnchorChannelsConfig`]: Config::anchor_channels_config
+	pub enable_zero_fee_commitments: bool,


I don't think we'll wan to add a new flag here that's probably hard to understand for the user? Rather, shouldn't we enable this for the user based on our current 'trust model settings' here?

Also, from these docs it's very unclear what this setting even does, when the user would want to enable it, what drawbacks it has, etc

FWIW, thinking about it again it seems that we should never set negotiate_anchor_zero_fee_commitments until we're positive our chain sources support submitpackage/TRUC, no? And once we are positive, we would always set it?

Rather, shouldn't we enable this for the user based on our current 'trust model settings' here?

Don't quite follow here could you expand ? I think 0FC channels merit an explicit setting somewhere rather than derived from trust model settings.

Also, from these docs it's very unclear what this setting even does, when the user would want to enable it, what drawbacks it has, etc

Yes will expand

Don't quite follow here could you expand ? I think 0FC channels merit an explicit setting somewhere rather than derived from trust model settings.

Why, what do they fundamentally change for the user compared to our three current modes (fully trusted/keep 0-reserve, still try to claim/keep X reserve, try to claim)? Keep in mind that communicating these three modes to the user is already very hard, they always have a very hard time understanding what this means. Now, how would we communicate any changed assumptions for 0FC here? If we already trust our counterparty already, wouldn't we always want to enable 0FC for the UX improvements?

Why, what do they fundamentally change for the user compared to our three current modes (fully trusted/keep 0-reserve, still try to claim/keep X reserve, try to claim)?

Let me see I don't think they change anything ? Whether to enable or disable 0FC channels is orthogonal to these modes ie trusted_peers_no_reserve and per_channel_reserve_sats should have no influence on whether we enable 0FC channels (only that per_channel_reserve_sats should be set to some value). I suspect you don't agree :)

If we already trust our counterparty already, wouldn't we always want to enable 0FC for the UX improvements?

It seems to me trusting our counterparty -> keeping 0 reserve is orthogonal to whether the user wants to enable 0FC channels ? for example a user trusts their counterparty, but wants to wait for greater adoption of Core v29+ before using 0FC channels.

tankyleo · 2025-10-24T06:06:59Z

Marked as draft: I think we should wait for electrum and esplora submit package support before merging this PR.

tankyleo · 2025-10-27T05:28:19Z

Successfully opened some 0FC channels, made payments, and force closed them with the esplora diff in this branch.

https://mutinynet.com/tx/508a954d85f5b7daf224a2fdc54ea6de9a26c0f62f7d58284bf61c3cdfd346e6

tankyleo · 2026-06-24T06:54:41Z

Let me know if I can rebase

tankyleo · 2026-06-24T06:58:16Z

+	}
+
+	async fn get_node_version_inner(rpc_client: Arc<RpcClient>) -> Result<u64, RpcClientError> {
+		rpc_client.call_method::<serde_json::Value>("getnetworkinfo", &[]).await.and_then(|value| {


Can also look into properly parsing the return value here like how we did for submitpackage let me know

tnull

Feel free to squash/rebase

tnull · 2026-06-24T09:54:21Z


 const BCAST_PACKAGE_QUEUE_SIZE: usize = 50;

+pub(crate) enum TransactionsToBroadcast {


See comment above, I think I'd prefer a simple struct TransactionBroadcast that wraps a Vec, enforcing the rules in constructors that could even be called via From implementations?

Done below, let me know if this matches what you had in mind

tnull · 2026-06-24T09:56:22Z

 	}
 }

+pub struct SubmitPackageResponse(String);


Should we even return the full response string here rather than ()?

See the esplora and electrum chain sources, I prefer to log the full response at trace even in the success case for debugging purposes. We get information on replaced transactions, transactions already in the mempool, and transactions freshly accepted into the mempool.

`BroadcasterInterface::broadcast_transactions` requires that any passed vector containing multiple transactions must be a single child together with its parents. We will lean on this contract in upcoming commits, so here we fix a case where we broke this contract.

Implementations of `BroadcasterInterface` cannot assume any topological ordering on the transactions received, so here we order the received transactions before adding them to the broadcast queue. Any consumers of the queue can now assume all transactions received to be topologically sorted. Codex wrote the tests.

The patch adds support for the `broadcast_package` method added in electrum protocol v1.6. Upcoming commits will require this patch to pass CI.

The mempool/electrs docker image used in those tests only supports submitpackage via the esplora interface, not the electrum interface.

We bump the Bitcoin Core version used in kotlin and python tests to support ephemeral dust. This is required for 0FC channels.

Do this roundtrip at the same time we make a roundtrip to retrieve the feerates to keep startup as fast as possible.

We rely on the `BroadcasterInterface` contract whereby any multi-transaction vector must be a single child and its parents, and must be broadcasted together as a package using `submitpackage`. In a prior commit, we added the guarantee that any packages received from the broadcast queue are already topologically sorted, and hence can be passed directly to the `submit_package` Bitcoin Core RPC.

tankyleo · 2026-06-25T03:52:02Z

Rebased, squashed the previous fixups, added a few more

tnull · 2026-06-25T08:58:39Z

 	}

+	pub(super) async fn validate_zero_fee_commitments_support(&self) -> Result<(), Error> {
+		self.esplora_client.submit_package(&super::dummy_package(), None, None).await.map_err(


Especially if we already submitted this package before, couldn't the backend return an different error that we'd misinterpret as 'doesn't support submitpackage'? E.g., typical transaction broadcast errors are 'already known' or 'missing-inputs'. Why can't we ever hit them here?

I've looked down the stack, and also had codex review the mempool-electrs and blockstream-electrs code.

already-known and missing-inputs errors get placed in the package_msg and error fields of the response, but still yield status 200.

Non 200 error codes are for transport-level errors, not for errors returned in the fields of the submitpackage response. As long as Bitcoin Core RPC returns some valid response for submitpackage, we get back 200.

Hmm, if we always get back a 200 if there's no connectivity error, then I'm still confused why we interpret any error here as Esplora server does not support submitpackage? Shouldn't we only match on 404 (assuming that's what's returned if the endpoint isn't known?)

Also want to note that this way of checking support for Electrum/Esplora is error prone as it will pass if the service runs bitcoind v26+ I believe, while we require v29+ in reality?

tnull · 2026-06-25T09:04:53Z

 			.init_features;
-		let anchor_channel = init_features.requires_anchors_zero_fee_htlc_tx();
+		let anchor_channel = init_features.requires_anchors_zero_fee_htlc_tx()
+			|| init_features.requires_anchor_zero_fee_commitments();


Hmm, pre-existing, but it seems for init features we should be using supports_?

Yes @febyeji had a similar question further above in this comment: #660 (comment)

Can we revisit these checks in a standalone PR ?

Can we revisit these checks in a standalone PR ?

Well, if we touch it here we should at least not add incorrect code if we think it's incorrect. If you prefer a separate PR, feel free to open an base this one on top, but could also make it a prefactor commit.

tankyleo · 2026-06-25T15:30:43Z

Let me know if I can squash

tnull

Please squash!

tnull · 2026-06-26T06:12:15Z

 	}

-	pub(crate) async fn process_broadcast_package(&self, txs: TransactionBroadcast) {
+	fn log_broadcast_error(&self, e: impl core::fmt::Display, txids: &[Txid], txs: &[Transaction]) {


Please make the DRYing up a freestanding prefactor commit and then use it in a fixup to your code (to not touch unrelated preexisting code in your commits)

tnull · 2026-06-26T06:15:58Z

-		let spawn_fut =
-			self.runtime.spawn_blocking(move || electrum_client.transaction_broadcast(&tx));
+		let spawn_fut = self.runtime.spawn_blocking({
+			let tx = tx.clone();


Why do we need this clone now?

tnull · 2026-06-26T06:19:40Z

+		let txids: Vec<_> = package.iter().map(|tx| tx.compute_txid()).collect();
+
+		let spawn_fut = self.runtime.spawn_blocking({
+			let package = package.clone();


Can we avoid cloning the whole package? It seems it's only required because we need the reference later for logging, but previously we intentionally avoided the allocations. Can we do the same still here and above?

tnull · 2026-06-26T06:32:50Z

 					total_anchor_channels_reserve_sats(&self.channel_manager, &self.config);
 				let spendable_amount_sats =
 					self.wallet.get_spendable_amount_sats(cur_anchor_reserve_sats).unwrap_or(0);
+				let anchor_channel = init_features.requires_anchors_zero_fee_htlc_tx()


Claude:

/home/tnull/workspace/ldk-node-pr-660/src/liquidity/service/lsps2.rs:455: git diff --check upstream/main...HEAD fails because added lines contain trailing \r whitespace at lines 455, 456, and 459.

tnull · 2026-06-26T06:34:07Z

 	}

+	pub(super) async fn validate_zero_fee_commitments_support(&self) -> Result<(), Error> {
+		self.esplora_client.submit_package(&super::dummy_package(), None, None).await.map_err(


Also want to note that this way of checking support for Electrum/Esplora is error prone as it will pass if the service runs bitcoind v26+ I believe, while we require v29+ in reality?

tnull · 2026-06-26T06:54:40Z


 const BCAST_PACKAGE_QUEUE_SIZE: usize = 50;

+pub(crate) struct TransactionBroadcast(Vec<Transaction>);


Btw, this is now redudant/overlapping with the BroadcastPackage in #888. Not sure if you want to coordinate to use exactly the same type in both PRs ahead of time, or just have one rebase depending what ends up landing first? @tankyleo @jkczyz

tankyleo requested a review from tnull October 13, 2025 13:14

tnull reviewed Oct 13, 2025

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tankyleo force-pushed the 25-10-0fc-channel-config branch from cb1cdf9 to c874049 Compare October 24, 2025 06:05

tankyleo requested a review from tnull October 24, 2025 06:06

tankyleo marked this pull request as draft October 24, 2025 06:06

tankyleo force-pushed the 25-10-0fc-channel-config branch from c874049 to ef3ba7a Compare October 27, 2025 05:15

tankyleo force-pushed the 25-10-0fc-channel-config branch from ef3ba7a to 3ebd017 Compare October 29, 2025 08:56

tankyleo changed the title ~~Add AnchorChannelsConfig::enable_zero_fee_commitments~~ Zero-fee commitments support Oct 30, 2025

tankyleo self-assigned this Oct 30, 2025

tankyleo added this to Weekly Goals Oct 30, 2025

tankyleo force-pushed the 25-10-0fc-channel-config branch from 3ebd017 to eda13d4 Compare November 11, 2025 04:16

tankyleo removed this from Weekly Goals Nov 12, 2025

tankyleo force-pushed the 25-10-0fc-channel-config branch 4 times, most recently from e136f33 to d4a2a04 Compare November 19, 2025 19:11

tankyleo force-pushed the 25-10-0fc-channel-config branch 9 times, most recently from 771f45b to a7c7911 Compare May 29, 2026 00:36

tankyleo marked this pull request as ready for review May 29, 2026 01:08

tankyleo requested a review from benthecarman May 29, 2026 01:08

tankyleo requested a review from tnull June 24, 2026 06:54

tankyleo commented Jun 24, 2026

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tnull reviewed Jun 24, 2026

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tankyleo added 7 commits June 25, 2026 00:46

Use a patched blockstream-electrs in CI

7d43482

The patch adds support for the `broadcast_package` method added in electrum protocol v1.6. Upcoming commits will require this patch to pass CI.

f: Assert HEAD matches the expected rev

ce4abd0

Switch cln lnd and eclair interop tests to esplora

6f7e34a

The mempool/electrs docker image used in those tests only supports submitpackage via the esplora interface, not the electrum interface.

Bump Bitcoin Core version used in kotlin and python tests

f5a260a

We bump the Bitcoin Core version used in kotlin and python tests to support ephemeral dust. This is required for 0FC channels.

Check that the chain source supports 0FC channels

68acdd9

Do this roundtrip at the same time we make a roundtrip to retrieve the feerates to keep startup as fast as possible.

tankyleo force-pushed the 25-10-0fc-channel-config branch from 34eeb06 to a8779ef Compare June 25, 2026 02:00

tankyleo added 9 commits June 25, 2026 02:07

f: cover ChainSourceNotSupported variant

92ca474

f: Use submitpackage to point to the specific RPC call

1031204

f: Add todo to switch electrum to protocol_version API

a667888

f: rework TransactionBroadcast type

91872b2

f: DRY the broadcast logic and errors across all chain sources

11b8b42

Include 0FC channels in anchor channel checks

3bc0b46

f: Include 0fc channels in ReserveType checks

ebfb6cf

Negotiate 0FC channels if the anchor config is set

fcf54fd

tankyleo force-pushed the 25-10-0fc-channel-config branch from a8779ef to fcf54fd Compare June 25, 2026 02:07

tankyleo requested a review from tnull June 25, 2026 03:46

tnull reviewed Jun 25, 2026

View reviewed changes

tankyleo requested a review from tnull June 25, 2026 15:30

tnull reviewed Jun 26, 2026

View reviewed changes


		const BCAST_PACKAGE_QUEUE_SIZE: usize = 50;

		pub(crate) enum TransactionsToBroadcast {


		const BCAST_PACKAGE_QUEUE_SIZE: usize = 50;

		pub(crate) struct TransactionBroadcast(Vec<Transaction>);

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