Merge pull request #4484 from tankyleo/2026-03-accept-high-dust-limits

Set max channel dust limit to 10,000 sats for all zero-fee-htlc-tx chans

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -982,8 +982,11 @@ pub const TOTAL_BITCOIN_SUPPLY_SATOSHIS: u64 = 21_000_000 * 1_0000_0000;
 /// implementations use this value for their dust limit today.
 pub const MAX_STD_OUTPUT_DUST_LIMIT_SATOSHIS: u64 = 546;
 
+/// The maximum channel dust limit we will accept from our counterparty for non-anchor channels.
+pub const MAX_LEGACY_CHAN_DUST_LIMIT_SATOSHIS: u64 = MAX_STD_OUTPUT_DUST_LIMIT_SATOSHIS;
+
 /// The maximum channel dust limit we will accept from our counterparty.
-pub const MAX_CHAN_DUST_LIMIT_SATOSHIS: u64 = MAX_STD_OUTPUT_DUST_LIMIT_SATOSHIS;
+pub const MAX_CHAN_DUST_LIMIT_SATOSHIS: u64 = 10_000;
 
 /// The dust limit is used for both the commitment transaction outputs as well as the closing
 /// transactions. For cooperative closing transactions, we require segwit outputs, though accept
@@ -3644,8 +3647,14 @@ impl<SP: SignerProvider> ChannelContext<SP> {
 		if open_channel_fields.dust_limit_satoshis < MIN_CHAN_DUST_LIMIT_SATOSHIS {
 			return Err(ChannelError::close(format!("dust_limit_satoshis ({}) is less than the implementation limit ({})", open_channel_fields.dust_limit_satoshis, MIN_CHAN_DUST_LIMIT_SATOSHIS)));
 		}
-		if open_channel_fields.dust_limit_satoshis >  MAX_CHAN_DUST_LIMIT_SATOSHIS {
-			return Err(ChannelError::close(format!("dust_limit_satoshis ({}) is greater than the implementation limit ({})", open_channel_fields.dust_limit_satoshis, MAX_CHAN_DUST_LIMIT_SATOSHIS)));
+
+		let max_chan_dust_limit_satoshis = if channel_type.supports_anchors_zero_fee_htlc_tx() || channel_type.supports_anchor_zero_fee_commitments() {
+			MAX_CHAN_DUST_LIMIT_SATOSHIS
+		} else {
+			MAX_LEGACY_CHAN_DUST_LIMIT_SATOSHIS
+		};
+		if open_channel_fields.dust_limit_satoshis > max_chan_dust_limit_satoshis {
+			return Err(ChannelError::close(format!("dust_limit_satoshis ({}) is greater than the implementation limit ({})", open_channel_fields.dust_limit_satoshis, max_chan_dust_limit_satoshis)));
 		}
 
 		// Convert things into internal flags and prep our state:
@@ -4426,8 +4435,14 @@ impl<SP: SignerProvider> ChannelContext<SP> {
 		if common_fields.dust_limit_satoshis < MIN_CHAN_DUST_LIMIT_SATOSHIS {
 			return Err(ChannelError::close(format!("dust_limit_satoshis ({}) is less than the implementation limit ({})", common_fields.dust_limit_satoshis, MIN_CHAN_DUST_LIMIT_SATOSHIS)));
 		}
-		if common_fields.dust_limit_satoshis > MAX_CHAN_DUST_LIMIT_SATOSHIS {
-			return Err(ChannelError::close(format!("dust_limit_satoshis ({}) is greater than the implementation limit ({})", common_fields.dust_limit_satoshis, MAX_CHAN_DUST_LIMIT_SATOSHIS)));
+
+		let max_chan_dust_limit_satoshis = if channel_type.supports_anchors_zero_fee_htlc_tx() || channel_type.supports_anchor_zero_fee_commitments() {
+			MAX_CHAN_DUST_LIMIT_SATOSHIS
+		} else {
+			MAX_LEGACY_CHAN_DUST_LIMIT_SATOSHIS
+		};
+		if common_fields.dust_limit_satoshis > max_chan_dust_limit_satoshis {
+			return Err(ChannelError::close(format!("dust_limit_satoshis ({}) is greater than the implementation limit ({})", common_fields.dust_limit_satoshis, max_chan_dust_limit_satoshis)));
 		}
 		if common_fields.minimum_depth > peer_limits.max_minimum_depth {
 			return Err(ChannelError::close(format!("We consider the minimum depth to be unreasonably large. Expected minimum: ({}). Actual: ({})", peer_limits.max_minimum_depth, common_fields.minimum_depth)));
@@ -6280,15 +6295,18 @@ fn get_holder_max_htlc_value_in_flight_msat(
 /// Guaranteed to return a value no larger than channel_value_satoshis
 ///
 /// This is used both for outbound and inbound channels and has lower bound
-/// of `MIN_THEIR_CHAN_RESERVE_SATOSHIS`.
+/// of `MIN_THEIR_CHAN_RESERVE_SATOSHIS`, and the `dust_limit_satoshis` of
+/// the counterparty.
 pub(crate) fn get_holder_selected_channel_reserve_satoshis(
-	channel_value_satoshis: u64, config: &UserConfig,
+	channel_value_satoshis: u64, their_dust_limit_satoshis: u64, config: &UserConfig,
 ) -> u64 {
 	let counterparty_chan_reserve_prop_mil =
 		config.channel_handshake_config.their_channel_reserve_proportional_millionths as u64;
 	let calculated_reserve =
 		channel_value_satoshis.saturating_mul(counterparty_chan_reserve_prop_mil) / 1_000_000;
-	cmp::min(channel_value_satoshis, cmp::max(calculated_reserve, MIN_THEIR_CHAN_RESERVE_SATOSHIS))
+	let channel_reserve_satoshis = cmp::max(calculated_reserve, MIN_THEIR_CHAN_RESERVE_SATOSHIS);
+	let channel_reserve_satoshis = cmp::max(channel_reserve_satoshis, their_dust_limit_satoshis);
+	cmp::min(channel_value_satoshis, channel_reserve_satoshis)
 }
 
 /// This is for legacy reasons, present for forward-compatibility.
@@ -13267,7 +13285,15 @@ impl<SP: SignerProvider> OutboundV1Channel<SP> {
 		channel_value_satoshis: u64, push_msat: u64, user_id: u128, config: &UserConfig, current_chain_height: u32,
 		outbound_scid_alias: u64, temporary_channel_id: Option<ChannelId>, logger: L
 	) -> Result<OutboundV1Channel<SP>, APIError> {
-		let holder_selected_channel_reserve_satoshis = get_holder_selected_channel_reserve_satoshis(channel_value_satoshis, config);
+		// At this point, we do not know what `dust_limit_satoshis` the counterparty will want for themselves,
+		// so we set the channel reserve with no regard for their dust limit, and fail the channel if they want
+		// a dust limit higher than our selected reserve.
+		let their_dust_limit_satoshis = 0;
+		let holder_selected_channel_reserve_satoshis = get_holder_selected_channel_reserve_satoshis(
+			channel_value_satoshis,
+			their_dust_limit_satoshis,
+			config
+		);
 		if holder_selected_channel_reserve_satoshis < MIN_CHAN_DUST_LIMIT_SATOSHIS {
 			// Protocol level safety check in place, although it should never happen because
 			// of `MIN_THEIR_CHAN_RESERVE_SATOSHIS`
@@ -13649,7 +13675,11 @@ impl<SP: SignerProvider> InboundV1Channel<SP> {
 		// support this channel type.
 		let channel_type = channel_type_from_open_channel(&msg.common_fields, our_supported_features)?;
 
-		let holder_selected_channel_reserve_satoshis = get_holder_selected_channel_reserve_satoshis(msg.common_fields.funding_satoshis, config);
+		let holder_selected_channel_reserve_satoshis = get_holder_selected_channel_reserve_satoshis(
+			msg.common_fields.funding_satoshis,
+			msg.common_fields.dust_limit_satoshis,
+			config
+		);
 		let counterparty_pubkeys = ChannelPublicKeys {
 			funding_pubkey: msg.common_fields.funding_pubkey,
 			revocation_basepoint: RevocationBasepoint::from(msg.common_fields.revocation_basepoint),

lightning/src/ln/channel_open_tests.rs

@@ -470,7 +470,7 @@ pub fn test_insane_channel_opens() {
 	// funding satoshis
 	let channel_value_sat = 31337; // same as funding satoshis
 	let channel_reserve_satoshis =
-		get_holder_selected_channel_reserve_satoshis(channel_value_sat, &legacy_cfg);
+		get_holder_selected_channel_reserve_satoshis(channel_value_sat, 0, &legacy_cfg);
 	let push_msat = (channel_value_sat - channel_reserve_satoshis) * 1000;
 
 	// Have node0 initiate a channel to node1 with aforementioned parameters
@@ -880,8 +880,7 @@ pub fn bolt2_open_channel_sane_dust_limit() {
 	nodes[0].node.create_channel(node_b_id, value_sats, push_msat, 42, None, None).unwrap();
 	let mut node0_to_1_send_open_channel =
 		get_event_msg!(nodes[0], MessageSendEvent::SendOpenChannel, node_b_id);
-	node0_to_1_send_open_channel.common_fields.dust_limit_satoshis = 547;
-	node0_to_1_send_open_channel.channel_reserve_satoshis = 100001;
+	node0_to_1_send_open_channel.common_fields.dust_limit_satoshis = 10_001;
 
 	nodes[1].node.handle_open_channel(node_a_id, &node0_to_1_send_open_channel);
 	let events = nodes[1].node.get_and_clear_pending_events();
@@ -893,7 +892,7 @@ pub fn bolt2_open_channel_sane_dust_limit() {
 		{
 			Err(APIError::ChannelUnavailable { err }) => assert_eq!(
 				err,
-				"dust_limit_satoshis (547) is greater than the implementation limit (546)"
+				"dust_limit_satoshis (10001) is greater than the implementation limit (10000)"
 			),
 			_ => panic!(),
 		},

lightning/src/ln/functional_tests.rs

@@ -413,7 +413,7 @@ pub fn test_inbound_outbound_capacity_is_not_zero() {
 	assert_eq!(channels0.len(), 1);
 	assert_eq!(channels1.len(), 1);
 
-	let reserve = get_holder_selected_channel_reserve_satoshis(100_000, &default_config);
+	let reserve = get_holder_selected_channel_reserve_satoshis(100_000, 0, &default_config);
 	assert_eq!(channels0[0].inbound_capacity_msat, 95000000 - reserve * 1000);
 	assert_eq!(channels1[0].outbound_capacity_msat, 95000000 - reserve * 1000);
 

lightning/src/ln/htlc_reserve_unit_tests.rs

@@ -50,7 +50,7 @@ fn do_test_counterparty_no_reserve(send_from_initiator: bool) {
 	push_amt -= feerate_per_kw as u64
 		* (commitment_tx_base_weight(&channel_type_features) + 4 * COMMITMENT_TX_WEIGHT_PER_HTLC)
 		/ 1000 * 1000;
-	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, &default_config) * 1000;
+	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, 0, &default_config) * 1000;
 
 	let push = if send_from_initiator { 0 } else { push_amt };
 	let temp_channel_id =
@@ -1008,7 +1008,7 @@ pub fn test_chan_reserve_violation_outbound_htlc_inbound_chan() {
 		&channel_type_features,
 	);
 
-	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, &default_config) * 1000;
+	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, 0, &default_config) * 1000;
 
 	let _ = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100_000, push_amt);
 
@@ -1052,7 +1052,7 @@ pub fn test_chan_reserve_violation_inbound_htlc_outbound_channel() {
 		MIN_AFFORDABLE_HTLC_COUNT as u64,
 		&channel_type_features,
 	);
-	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, &default_config) * 1000;
+	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, 0, &default_config) * 1000;
 	let chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100_000, push_amt);
 
 	// Send four HTLCs to cover the initial push_msat buffer we're required to include
@@ -1130,7 +1130,7 @@ pub fn test_chan_reserve_dust_inbound_htlcs_outbound_chan() {
 		MIN_AFFORDABLE_HTLC_COUNT as u64,
 		&channel_type_features,
 	);
-	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, &default_config) * 1000;
+	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, 0, &default_config) * 1000;
 	create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100000, push_amt);
 
 	let (htlc_success_tx_fee_sat, _) =

lightning/src/ln/payment_tests.rs

@@ -4985,7 +4985,7 @@ fn test_htlc_forward_considers_anchor_outputs_value() {
 		create_announced_chan_between_nodes_with_value(&nodes, 1, 2, CHAN_AMT, PUSH_MSAT);
 
 	let channel_reserve_msat =
-		get_holder_selected_channel_reserve_satoshis(CHAN_AMT, &config) * 1000;
+		get_holder_selected_channel_reserve_satoshis(CHAN_AMT, 0, &config) * 1000;
 	let commitment_fee_msat = chan_utils::commit_tx_fee_sat(
 		*nodes[1].fee_estimator.sat_per_kw.lock().unwrap(),
 		2,

lightning/src/ln/update_fee_tests.rs

@@ -408,7 +408,8 @@ pub fn do_test_update_fee_that_funder_cannot_afford(channel_type_features: Chann
 	);
 	let channel_id = chan.2;
 	let secp_ctx = Secp256k1::new();
-	let bs_channel_reserve_sats = get_holder_selected_channel_reserve_satoshis(channel_value, &cfg);
+	let bs_channel_reserve_sats =
+		get_holder_selected_channel_reserve_satoshis(channel_value, 0, &cfg);
 	let (anchor_outputs_value_sats, outputs_num_no_htlcs) =
 		if channel_type_features.supports_anchors_zero_fee_htlc_tx() {
 			(ANCHOR_OUTPUT_VALUE_SATOSHI * 2, 4)
@@ -892,7 +893,7 @@ pub fn test_chan_init_feerate_unaffordability() {
 
 	// During open, we don't have a "counterparty channel reserve" to check against, so that
 	// requirement only comes into play on the open_channel handling side.
-	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, &default_config) * 1000;
+	push_amt -= get_holder_selected_channel_reserve_satoshis(100_000, 0, &default_config) * 1000;
 	nodes[0].node.create_channel(node_b_id, 100_000, push_amt, 42, None, None).unwrap();
 	let mut open_channel_msg =
 		get_event_msg!(nodes[0], MessageSendEvent::SendOpenChannel, node_b_id);