Zero-fee commitments support

.github/workflows/0fc-integration.yml

@@ -0,0 +1,49 @@
+name: CI Checks - 0FC Integration Tests
+
+on: [push, pull_request]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build-and-test:
+    timeout-minutes: 60
+    runs-on: self-hosted
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@v4
+      - name: Install Rust stable toolchain
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --profile=minimal --default-toolchain stable
+      - name: Enable caching for bitcoind
+        id: cache-bitcoind
+        uses: actions/cache@v4
+        with:
+          path: bin/bitcoind-${{ runner.os }}-${{ runner.arch }}
+          key: bitcoind-29.0-${{ runner.os }}-${{ runner.arch }}
+      - name: Enable caching for electrs
+        id: cache-electrs
+        uses: actions/cache@v4
+        with:
+          path: bin/electrs-${{ runner.os }}-${{ runner.arch }}
+          key: electrs-submit-package-${{ runner.os }}-${{ runner.arch }}
+      - name: Download bitcoind
+        if: "steps.cache-bitcoind.outputs.cache-hit != 'true'"
+        run: |
+          source ./scripts/download_bitcoind_electrs.sh
+          mkdir -p bin
+          mv "$BITCOIND_EXE" bin/bitcoind-${{ runner.os }}-${{ runner.arch }}
+      - name: Download electrs
+        if: "steps.cache-electrs.outputs.cache-hit != 'true'"
+        run: |
+          source ./scripts/build_electrs.sh
+          mkdir -p bin
+          mv "$ELECTRS_EXE" bin/electrs-${{ runner.os }}-${{ runner.arch }}
+      - name: Set bitcoind/electrs environment variables
+        run: |
+          echo "BITCOIND_EXE=$( pwd )/bin/bitcoind-${{ runner.os }}-${{ runner.arch }}" >> "$GITHUB_ENV"
+          echo "ELECTRS_EXE=$( pwd )/bin/electrs-${{ runner.os }}-${{ runner.arch }}" >> "$GITHUB_ENV"
+      - name: Test with 0FC enabled
+        run: |
+          RUSTFLAGS="--cfg no_download --cfg cycle_tests --cfg tokio_unstable --cfg zero_fee_commitment_tests" cargo test -- --test-threads=1

CHANGELOG.md

@@ -18,6 +18,8 @@
 - `EsploraSyncConfig` and `ElectrumSyncConfig` now support `force_wallet_full_scan`. When set,
   the on-chain wallet keeps using BDK `full_scan` instead of incremental sync until a full scan
   succeeds, allowing restored wallets to rediscover funds sent to previously-unknown addresses.
+- `Config::anchor_channels_config` is no longer optional, hence anchor channels can no longer be
+  disabled. We still negotiate legacy channels if the peer does not support anchor channels.
 
 ## Bug Fixes and Improvements
 - Building a fresh node against a Bitcoin Core RPC or REST chain source that fails to return the

Cargo.toml

@@ -135,6 +135,7 @@ check-cfg = [
 	"cfg(eclair_test)",
 	"cfg(cycle_tests)",
 	"cfg(hrn_tests)",
+	"cfg(zero_fee_commitment_tests)",
 ]
 
 [[bench]]

benches/payments.rs

@@ -121,13 +121,8 @@ fn payment_benchmark(c: &mut Criterion) {
 	let (bitcoind, electrsd) = setup_bitcoind_and_electrsd();
 	let chain_source = random_chain_source(&bitcoind, &electrsd);
 
-	let (node_a, node_b) = setup_two_nodes_with_store(
-		&chain_source,
-		false,
-		true,
-		false,
-		common::TestStoreType::Sqlite,
-	);
+	let (node_a, node_b) =
+		setup_two_nodes_with_store(&chain_source, false, false, common::TestStoreType::Sqlite);
 
 	let runtime =
 		tokio::runtime::Builder::new_multi_thread().worker_threads(4).enable_all().build().unwrap();

bindings/ldk_node.udl

@@ -246,6 +246,7 @@ enum NodeError {
 	"LnurlAuthFailed",
 	"LnurlAuthTimeout",
 	"InvalidLnurl",
+	"ChainSourceNotSupported",
 };
 
 typedef dictionary NodeStatus;

scripts/build_electrs.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+set -eox pipefail
+
+# Our Esplora-based tests require `electrs` binaries. Here, we
+# download the code, build the binaries, and export their location
+# via `ELECTRS_EXE` which will be used by the `electrsd` crates in
+# our tests.
+
+HOST_PLATFORM="$(rustc --version --verbose | grep "host:" | awk '{ print $2 }')"
+ELECTRS_GIT_REPO="https://github.com/tankyleo/blockstream-electrs.git"
+ELECTRS_TAG="2026-05-26-electrum-submit-package"
+ELECTRS_REV="8c06d8010e43f793b1a65f83695ea846e5cd83ed"
+if [[ "$HOST_PLATFORM" != *linux* && "$HOST_PLATFORM" != *darwin* ]]; then
+	printf "\n\n"
+	echo "Unsupported platform: $HOST_PLATFORM Exiting.."
+	exit 1
+fi
+
+DL_TMP_DIR=$(mktemp -d)
+trap 'rm -rf -- "$DL_TMP_DIR"' EXIT
+
+pushd "$DL_TMP_DIR"
+git clone --branch "$ELECTRS_TAG" --depth 1 "$ELECTRS_GIT_REPO" blockstream-electrs
+cd blockstream-electrs
+CURRENT_HEAD=$(git rev-parse HEAD)
+if [ "$CURRENT_HEAD" != "$ELECTRS_REV" ]; then
+  echo "ERROR: HEAD does not match expected commit"
+  echo "expected: $ELECTRS_REV"
+  echo "actual:   $CURRENT_HEAD"
+  exit 1
+fi
+RUSTFLAGS="" cargo build
+export ELECTRS_EXE="$DL_TMP_DIR"/blockstream-electrs/target/debug/electrs
+chmod +x "$ELECTRS_EXE"
+popd

src/chain/bitcoind.rs

@@ -14,6 +14,7 @@ use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
 
 use base64::prelude::BASE64_STANDARD;
 use base64::Engine;
+use bitcoin::transaction::Version;
 use bitcoin::{BlockHash, FeeRate, Network, OutPoint, Transaction, Txid};
 use lightning::chain::chaininterface::ConfirmationTarget as LdkConfirmationTarget;
 use lightning::chain::{BlockLocator, Listen};
@@ -41,6 +42,7 @@ use crate::fee_estimator::{
 };
 use crate::io::utils::update_and_persist_node_metrics;
 use crate::logger::{log_bytes, log_debug, log_error, log_info, log_trace, LdkLogger, Logger};
+use crate::tx_broadcaster::SortedTransactions;
 use crate::types::{ChainMonitor, ChannelManager, DynStore, Sweeper, Wallet};
 use crate::{Error, PersistedNodeMetrics};
 
@@ -119,6 +121,30 @@ impl BitcoindChainSource {
 		self.api_client.utxo_source()
 	}
 
+	pub(super) async fn validate_zero_fee_commitments_support(&self) -> Result<(), Error> {
+		let node_version_result = tokio::time::timeout(
+			Duration::from_secs(CHAIN_POLLING_TIMEOUT_SECS),
+			self.api_client.get_node_version(),
+		)
+		.await
+		.map_err(|e| {
+			log_error!(self.logger, "Failed to get node version: {:?}", e);
+			Error::ConnectionFailed
+		})?;
+
+		let node_version = node_version_result.map_err(|e| {
+			log_error!(self.logger, "Failed to get node version: {:?}", e);
+			Error::ConnectionFailed
+		})?;
+
+		// v26 first shipped the `submitpackage` RPC, but we need v29 to relay ephemeral dust
+		if node_version < 290000 {
+			log_error!(self.logger, "Bitcoin backend MUST be greater than or equal to v29");
+			return Err(Error::ChainSourceNotSupported);
+		}
+		Ok(())
+	}
+
 	pub(super) async fn continuously_sync_wallets(
 		&self, mut stop_sync_receiver: tokio::sync::watch::Receiver<()>,
 		onchain_wallet: Arc<Wallet>, channel_manager: Arc<ChannelManager>,
@@ -571,46 +597,59 @@ impl BitcoindChainSource {
 		Ok(())
 	}
 
-	pub(crate) async fn process_broadcast_package(&self, package: Vec<Transaction>) {
-		// While it's a bit unclear when we'd be able to lean on Bitcoin Core >v28
-		// features, we should eventually switch to use `submitpackage` via the
-		// `rust-bitcoind-json-rpc` crate rather than just broadcasting individual
-		// transactions.
-		for tx in &package {
-			let txid = tx.compute_txid();
-			let timeout_fut = tokio::time::timeout(
-				Duration::from_secs(DEFAULT_TX_BROADCAST_TIMEOUT_SECS),
-				self.api_client.broadcast_transaction(tx),
-			);
-			match timeout_fut.await {
-				Ok(res) => match res {
-					Ok(id) => {
-						debug_assert_eq!(id, txid);
-						log_trace!(self.logger, "Successfully broadcast transaction {}", txid);
-					},
-					Err(e) => {
-						log_error!(self.logger, "Failed to broadcast transaction {}: {}", txid, e);
-						log_trace!(
-							self.logger,
-							"Failed broadcast transaction bytes: {}",
-							log_bytes!(tx.encode())
-						);
+	fn log_broadcast_error(
+		&self, e: impl core::fmt::Display, txids: &[Txid], txs: &SortedTransactions,
+	) {
+		log_error!(self.logger, "Failed to broadcast transaction(s) {:?}: {}", txids, e);
+		log_trace!(self.logger, "Failed broadcast transaction bytes:");
+		for tx in txs.iter() {
+			log_trace!(self.logger, "{}", log_bytes!(tx.encode()));
+		}
+	}
+
+	pub(crate) async fn process_transaction_broadcast(&self, txs: SortedTransactions) {
+		let all_txs_are_v3 = txs.iter().all(|tx| tx.version == Version::non_standard(3));
+		match txs.len() {
+			2.. if all_txs_are_v3 => {
+				let txids: Vec<_> = txs.iter().map(|tx| tx.compute_txid()).collect();
+				let timeout_fut = tokio::time::timeout(
+					Duration::from_secs(DEFAULT_TX_BROADCAST_TIMEOUT_SECS),
+					self.api_client.submit_package(&txs),
+				);
+				match timeout_fut.await {
+					Ok(res) => match res {
+						Ok(result) => {
+							log_trace!(self.logger, "Successfully broadcast package {:?}", txids);
+							log_trace!(self.logger, "Successfully broadcast package {}", result);
+						},
+						Err(e) => self.log_broadcast_error(e, &txids, &txs),
 					},
-				},
-				Err(e) => {
-					log_error!(
-						self.logger,
-						"Failed to broadcast transaction due to timeout {}: {}",
-						txid,
-						e
-					);
-					log_trace!(
-						self.logger,
-						"Failed broadcast transaction bytes: {}",
-						log_bytes!(tx.encode())
+					Err(e) => self.log_broadcast_error(e, &txids, &txs),
+				}
+			},
+			_ => {
+				for tx in txs.iter() {
+					let txid = tx.compute_txid();
+					let timeout_fut = tokio::time::timeout(
+						Duration::from_secs(DEFAULT_TX_BROADCAST_TIMEOUT_SECS),
+						self.api_client.broadcast_transaction(tx),
 					);
-				},
-			}
+					match timeout_fut.await {
+						Ok(res) => match res {
+							Ok(id) => {
+								debug_assert_eq!(id, txid);
+								log_trace!(
+									self.logger,
+									"Successfully broadcast transaction {}",
+									txid
+								);
+							},
+							Err(e) => self.log_broadcast_error(e, &[txid], &txs),
+						},
+						Err(e) => self.log_broadcast_error(e, &[txid], &txs),
+					}
+				}
+			},
 		}
 	}
 }
@@ -748,6 +787,31 @@ impl BitcoindClient {
 		}
 	}
 
+	pub(crate) async fn get_node_version(&self) -> Result<u64, BitcoindClientError> {
+		match self {
+			BitcoindClient::Rpc { rpc_client, .. } => {
+				Self::get_node_version_inner(Arc::clone(rpc_client))
+					.await
+					.map_err(BitcoindClientError::Rpc)
+			},
+			BitcoindClient::Rest { rpc_client, .. } => {
+				// Bitcoin Core's REST interface does not support `getnetworkinfo`
+				// so we use the RPC client.
+				Self::get_node_version_inner(Arc::clone(rpc_client))
+					.await
+					.map_err(BitcoindClientError::Rpc)
+			},
+		}
+	}
+
+	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| {
+			value["version"].as_u64().ok_or(RpcClientError::InvalidData(String::from(
+				"The version field in the `getnetworkinfo` response should be a u64",
+			)))
+		})
+	}
+
 	/// Broadcasts the provided transaction.
 	pub(crate) async fn broadcast_transaction(
 		&self, tx: &Transaction,
@@ -776,6 +840,38 @@ impl BitcoindClient {
 		rpc_client.call_method::<Txid>("sendrawtransaction", &[tx_json]).await
 	}
 
+	/// Submits the provided package
+	pub(crate) async fn submit_package(
+		&self, package: &SortedTransactions,
+	) -> Result<String, BitcoindClientError> {
+		match self {
+			BitcoindClient::Rpc { rpc_client, .. } => {
+				Self::submit_package_inner(Arc::clone(rpc_client), package)
+					.await
+					.map_err(BitcoindClientError::Rpc)
+			},
+			BitcoindClient::Rest { rpc_client, .. } => {
+				// Bitcoin Core's REST interface does not support submitting packages
+				// so we use the RPC client.
+				Self::submit_package_inner(Arc::clone(rpc_client), package)
+					.await
+					.map_err(BitcoindClientError::Rpc)
+			},
+		}
+	}
+
+	async fn submit_package_inner(
+		rpc_client: Arc<RpcClient>, package: &SortedTransactions,
+	) -> Result<String, RpcClientError> {
+		let package_serialized: Vec<_> =
+			package.iter().map(|tx| bitcoin::consensus::encode::serialize_hex(tx)).collect();
+		let package_json = serde_json::json!(package_serialized);
+		rpc_client
+			.call_method::<SubmitPackageResponse>("submitpackage", &[package_json])
+			.await
+			.map(|response| response.0)
+	}
+
 	/// Retrieve the fee estimate needed for a transaction to begin
 	/// confirmation within the provided `num_blocks`.
 	pub(crate) async fn get_fee_estimate_for_target(
@@ -1327,6 +1423,23 @@ impl TryInto<GetMempoolEntryResponse> for JsonResponse {
 	}
 }
 
+pub struct SubmitPackageResponse(String);
+
+impl TryInto<SubmitPackageResponse> for JsonResponse {
+	type Error = String;
+	fn try_into(self) -> Result<SubmitPackageResponse, String> {
+		let response = self.0.to_string();
+		let res = self.0.as_object().ok_or("Failed to parse submitpackage response".to_string())?;
+
+		match res["package_msg"].as_str() {
+			Some("success") => Ok(SubmitPackageResponse(response)),
+			Some(_) | None => {
+				return Err(response);
+			},
+		}
+	}
+}
+
 #[derive(Debug, Clone)]
 pub(crate) struct MempoolEntry {
 	/// The transaction id