Merge pull request #1444 from ViktorTigerstrom/2022-04-use-counterparty-htlc-max-for-chan-updates

Set `ChannelUpdate` `htlc_maximum_msat` using the peer's value

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -39,7 +39,7 @@ use util::events::ClosureReason;
 use util::ser::{Readable, ReadableArgs, Writeable, Writer, VecWriter};
 use util::logger::Logger;
 use util::errors::APIError;
-use util::config::{UserConfig, ChannelConfig, ChannelHandshakeLimits};
+use util::config::{UserConfig, ChannelConfig, ChannelHandshakeConfig, ChannelHandshakeLimits};
 use util::scid_utils::scid_from_parts;
 
 use io;
@@ -745,6 +745,12 @@ pub const COMMITMENT_TX_WEIGHT_PER_HTLC: u64 = 172;
 
 pub const ANCHOR_OUTPUT_VALUE_SATOSHI: u64 = 330;
 
+/// The percentage of the channel value `holder_max_htlc_value_in_flight_msat` used to be set to,
+/// before this was made configurable. The percentage was made configurable in LDK 0.0.107,
+/// although LDK 0.0.104+ enabled serialization of channels with a different value set for
+/// `holder_max_htlc_value_in_flight_msat`.
+pub const MAX_IN_FLIGHT_PERCENT_LEGACY: u8 = 10;
+
 /// Maximum `funding_satoshis` value according to the BOLT #2 specification, if
 /// `option_support_large_channel` (aka wumbo channels) is not supported.
 /// It's 2^24 - 1.
@@ -803,9 +809,22 @@ macro_rules! secp_check {
 }
 
 impl<Signer: Sign> Channel<Signer> {
-	// Convert constants + channel value to limits:
-	fn get_holder_max_htlc_value_in_flight_msat(channel_value_satoshis: u64) -> u64 {
-		channel_value_satoshis * 1000 / 10 //TODO
+	/// Returns the value to use for `holder_max_htlc_value_in_flight_msat` as a percentage of the
+	/// `channel_value_satoshis` in msat, set through
+	/// [`ChannelHandshakeConfig::max_inbound_htlc_value_in_flight_percent_of_channel`]
+	///
+	/// The effective percentage is lower bounded by 1% and upper bounded by 100%.
+	///
+	/// [`ChannelHandshakeConfig::max_inbound_htlc_value_in_flight_percent_of_channel`]: crate::util::config::ChannelHandshakeConfig::max_inbound_htlc_value_in_flight_percent_of_channel
+	fn get_holder_max_htlc_value_in_flight_msat(channel_value_satoshis: u64, config: &ChannelHandshakeConfig) -> u64 {
+		let configured_percent = if config.max_inbound_htlc_value_in_flight_percent_of_channel < 1 {
+			1
+		} else if config.max_inbound_htlc_value_in_flight_percent_of_channel > 100 {
+			100
+		} else {
+			config.max_inbound_htlc_value_in_flight_percent_of_channel as u64
+		};
+		channel_value_satoshis * 10 * configured_percent
 	}
 
 	/// Returns a minimum channel reserve value the remote needs to maintain,
@@ -964,7 +983,7 @@ impl<Signer: Sign> Channel<Signer> {
 			counterparty_dust_limit_satoshis: 0,
 			holder_dust_limit_satoshis: MIN_CHAN_DUST_LIMIT_SATOSHIS,
 			counterparty_max_htlc_value_in_flight_msat: 0,
-			holder_max_htlc_value_in_flight_msat: Self::get_holder_max_htlc_value_in_flight_msat(channel_value_satoshis),
+			holder_max_htlc_value_in_flight_msat: Self::get_holder_max_htlc_value_in_flight_msat(channel_value_satoshis, &config.own_channel_config),
 			counterparty_selected_channel_reserve_satoshis: None, // Filled in in accept_channel
 			holder_selected_channel_reserve_satoshis,
 			counterparty_htlc_minimum_msat: 0,
@@ -1282,7 +1301,7 @@ impl<Signer: Sign> Channel<Signer> {
 			counterparty_dust_limit_satoshis: msg.dust_limit_satoshis,
 			holder_dust_limit_satoshis: MIN_CHAN_DUST_LIMIT_SATOSHIS,
 			counterparty_max_htlc_value_in_flight_msat: cmp::min(msg.max_htlc_value_in_flight_msat, msg.funding_satoshis * 1000),
-			holder_max_htlc_value_in_flight_msat: Self::get_holder_max_htlc_value_in_flight_msat(msg.funding_satoshis),
+			holder_max_htlc_value_in_flight_msat: Self::get_holder_max_htlc_value_in_flight_msat(msg.funding_satoshis, &config.own_channel_config),
 			counterparty_selected_channel_reserve_satoshis: Some(msg.channel_reserve_satoshis),
 			holder_selected_channel_reserve_satoshis,
 			counterparty_htlc_minimum_msat: msg.htlc_minimum_msat,
@@ -4360,7 +4379,7 @@ impl<Signer: Sign> Channel<Signer> {
 			// channel might have been used to route very small values (either by honest users or as DoS).
 			self.channel_value_satoshis * 1000 * 9 / 10,
 
-			self.holder_max_htlc_value_in_flight_msat
+			self.counterparty_max_htlc_value_in_flight_msat
 		);
 	}
 
@@ -5877,13 +5896,18 @@ impl<Signer: Sign> Writeable for Channel<Signer> {
 		let chan_type = if self.channel_type != ChannelTypeFeatures::only_static_remote_key() {
 			Some(&self.channel_type) } else { None };
 
-		// The same logic applies for `holder_selected_channel_reserve_satoshis` and
-		// `holder_max_htlc_value_in_flight_msat` values other than the defaults.
+		// The same logic applies for `holder_selected_channel_reserve_satoshis` values other than
+		// the default, and when `holder_max_htlc_value_in_flight_msat` is configured to be set to
+		// a different percentage of the channel value then 10%, which older versions of LDK used
+		// to set it to before the percentage was made configurable.
 		let serialized_holder_selected_reserve =
 			if self.holder_selected_channel_reserve_satoshis != Self::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis)
 			{ Some(self.holder_selected_channel_reserve_satoshis) } else { None };
+
+		let mut old_max_in_flight_percent_config = UserConfig::default().own_channel_config;
+		old_max_in_flight_percent_config.max_inbound_htlc_value_in_flight_percent_of_channel = MAX_IN_FLIGHT_PERCENT_LEGACY;
 		let serialized_holder_htlc_max_in_flight =
-			if self.holder_max_htlc_value_in_flight_msat != Self::get_holder_max_htlc_value_in_flight_msat(self.channel_value_satoshis)
+			if self.holder_max_htlc_value_in_flight_msat != Self::get_holder_max_htlc_value_in_flight_msat(self.channel_value_satoshis, &old_max_in_flight_percent_config)
 			{ Some(self.holder_max_htlc_value_in_flight_msat) } else { None };
 
 		write_tlv_fields!(writer, {
@@ -6153,7 +6177,7 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<(&'a K, u32)> for Channel<Signer>
 		let mut target_closing_feerate_sats_per_kw = None;
 		let mut monitor_pending_finalized_fulfills = Some(Vec::new());
 		let mut holder_selected_channel_reserve_satoshis = Some(Self::get_holder_selected_channel_reserve_satoshis(channel_value_satoshis));
-		let mut holder_max_htlc_value_in_flight_msat = Some(Self::get_holder_max_htlc_value_in_flight_msat(channel_value_satoshis));
+		let mut holder_max_htlc_value_in_flight_msat = Some(Self::get_holder_max_htlc_value_in_flight_msat(channel_value_satoshis, &UserConfig::default().own_channel_config));
 		// Prior to supporting channel type negotiation, all of our channels were static_remotekey
 		// only, so we default to that if none was written.
 		let mut channel_type = Some(ChannelTypeFeatures::only_static_remote_key());
@@ -6656,6 +6680,79 @@ mod tests {
 		}
 	}
 
+	#[test]
+	fn test_configured_holder_max_htlc_value_in_flight() {
+		let feeest = TestFeeEstimator{fee_est: 15000};
+		let logger = test_utils::TestLogger::new();
+		let secp_ctx = Secp256k1::new();
+		let seed = [42; 32];
+		let network = Network::Testnet;
+		let keys_provider = test_utils::TestKeysInterface::new(&seed, network);
+		let outbound_node_id = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32]).unwrap());
+		let inbound_node_id = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[7; 32]).unwrap());
+
+		let mut config_2_percent = UserConfig::default();
+		config_2_percent.own_channel_config.max_inbound_htlc_value_in_flight_percent_of_channel = 2;
+		let mut config_99_percent = UserConfig::default();
+		config_99_percent.own_channel_config.max_inbound_htlc_value_in_flight_percent_of_channel = 99;
+		let mut config_0_percent = UserConfig::default();
+		config_0_percent.own_channel_config.max_inbound_htlc_value_in_flight_percent_of_channel = 0;
+		let mut config_101_percent = UserConfig::default();
+		config_101_percent.own_channel_config.max_inbound_htlc_value_in_flight_percent_of_channel = 101;
+
+		// Test that `new_outbound` creates a channel with the correct value for
+		// `holder_max_htlc_value_in_flight_msat`, when configured with a valid percentage value,
+		// which is set to the lower bound + 1 (2%) of the `channel_value`.
+		let chan_1 = Channel::<EnforcingSigner>::new_outbound(&&feeest, &&keys_provider, outbound_node_id, &InitFeatures::known(), 10000000, 100000, 42, &config_2_percent, 0, 42).unwrap();
+		let chan_1_value_msat = chan_1.channel_value_satoshis * 1000;
+		assert_eq!(chan_1.holder_max_htlc_value_in_flight_msat, (chan_1_value_msat as f64 * 0.02) as u64);
+
+		// Test with the upper bound - 1 of valid values (99%).
+		let chan_2 = Channel::<EnforcingSigner>::new_outbound(&&feeest, &&keys_provider, outbound_node_id, &InitFeatures::known(), 10000000, 100000, 42, &config_99_percent, 0, 42).unwrap();
+		let chan_2_value_msat = chan_2.channel_value_satoshis * 1000;
+		assert_eq!(chan_2.holder_max_htlc_value_in_flight_msat, (chan_2_value_msat as f64 * 0.99) as u64);
+
+		let chan_1_open_channel_msg = chan_1.get_open_channel(genesis_block(network).header.block_hash());
+
+		// Test that `new_from_req` creates a channel with the correct value for
+		// `holder_max_htlc_value_in_flight_msat`, when configured with a valid percentage value,
+		// which is set to the lower bound - 1 (2%) of the `channel_value`.
+		let chan_3 = Channel::<EnforcingSigner>::new_from_req(&&feeest, &&keys_provider, inbound_node_id, &InitFeatures::known(), &chan_1_open_channel_msg, 7, &config_2_percent, 0, &&logger, 42).unwrap();
+		let chan_3_value_msat = chan_3.channel_value_satoshis * 1000;
+		assert_eq!(chan_3.holder_max_htlc_value_in_flight_msat, (chan_3_value_msat as f64 * 0.02) as u64);
+
+		// Test with the upper bound - 1 of valid values (99%).
+		let chan_4 = Channel::<EnforcingSigner>::new_from_req(&&feeest, &&keys_provider, inbound_node_id, &InitFeatures::known(), &chan_1_open_channel_msg, 7, &config_99_percent, 0, &&logger, 42).unwrap();
+		let chan_4_value_msat = chan_4.channel_value_satoshis * 1000;
+		assert_eq!(chan_4.holder_max_htlc_value_in_flight_msat, (chan_4_value_msat as f64 * 0.99) as u64);
+
+		// Test that `new_outbound` uses the lower bound of the configurable percentage values (1%)
+		// if `max_inbound_htlc_value_in_flight_percent_of_channel` is set to a value less than 1.
+		let chan_5 = Channel::<EnforcingSigner>::new_outbound(&&feeest, &&keys_provider, outbound_node_id, &InitFeatures::known(), 10000000, 100000, 42, &config_0_percent, 0, 42).unwrap();
+		let chan_5_value_msat = chan_5.channel_value_satoshis * 1000;
+		assert_eq!(chan_5.holder_max_htlc_value_in_flight_msat, (chan_5_value_msat as f64 * 0.01) as u64);
+
+		// Test that `new_outbound` uses the upper bound of the configurable percentage values
+		// (100%) if `max_inbound_htlc_value_in_flight_percent_of_channel` is set to a larger value
+		// than 100.
+		let chan_6 = Channel::<EnforcingSigner>::new_outbound(&&feeest, &&keys_provider, outbound_node_id, &InitFeatures::known(), 10000000, 100000, 42, &config_101_percent, 0, 42).unwrap();
+		let chan_6_value_msat = chan_6.channel_value_satoshis * 1000;
+		assert_eq!(chan_6.holder_max_htlc_value_in_flight_msat, chan_6_value_msat);
+
+		// Test that `new_from_req` uses the lower bound of the configurable percentage values (1%)
+		// if `max_inbound_htlc_value_in_flight_percent_of_channel` is set to a value less than 1.
+		let chan_7 = Channel::<EnforcingSigner>::new_from_req(&&feeest, &&keys_provider, inbound_node_id, &InitFeatures::known(), &chan_1_open_channel_msg, 7, &config_0_percent, 0, &&logger, 42).unwrap();
+		let chan_7_value_msat = chan_7.channel_value_satoshis * 1000;
+		assert_eq!(chan_7.holder_max_htlc_value_in_flight_msat, (chan_7_value_msat as f64 * 0.01) as u64);
+
+		// Test that `new_from_req` uses the upper bound of the configurable percentage values
+		// (100%) if `max_inbound_htlc_value_in_flight_percent_of_channel` is set to a larger value
+		// than 100.
+		let chan_8 = Channel::<EnforcingSigner>::new_from_req(&&feeest, &&keys_provider, inbound_node_id, &InitFeatures::known(), &chan_1_open_channel_msg, 7, &config_101_percent, 0, &&logger, 42).unwrap();
+		let chan_8_value_msat = chan_8.channel_value_satoshis * 1000;
+		assert_eq!(chan_8.holder_max_htlc_value_in_flight_msat, chan_8_value_msat);
+	}
+
 	#[test]
 	fn channel_update() {
 		let feeest = TestFeeEstimator{fee_est: 15000};

lightning/src/ln/functional_tests.rs

@@ -26,7 +26,7 @@ use ln::chan_utils::{htlc_success_tx_weight, htlc_timeout_tx_weight, HTLCOutputI
 use routing::router::{PaymentParameters, Route, RouteHop, RouteParameters, find_route, get_route};
 use ln::features::{ChannelFeatures, InitFeatures, InvoiceFeatures, NodeFeatures};
 use ln::msgs;
-use ln::msgs::{ChannelMessageHandler, RoutingMessageHandler, ErrorAction};
+use ln::msgs::{ChannelMessageHandler, RoutingMessageHandler, OptionalField, ErrorAction};
 use util::enforcing_trait_impls::EnforcingSigner;
 use util::{byte_utils, test_utils};
 use util::events::{Event, MessageSendEvent, MessageSendEventsProvider, PaymentPurpose, ClosureReason};
@@ -8143,6 +8143,58 @@ fn test_override_0msat_htlc_minimum() {
 	assert_eq!(res.htlc_minimum_msat, 1);
 }
 
+#[test]
+fn test_channel_update_has_correct_htlc_maximum_msat() {
+	// Tests that the `ChannelUpdate` message has the correct values for `htlc_maximum_msat` set.
+	// Bolt 7 specifies that if present `htlc_maximum_msat`:
+	// 1. MUST be set to less than or equal to the channel capacity. In LDK, this is capped to
+	// 90% of the `channel_value`.
+	// 2. MUST be set to less than or equal to the `max_htlc_value_in_flight_msat` received from the peer.
+
+	let mut config_30_percent = UserConfig::default();
+	config_30_percent.channel_options.announced_channel = true;
+	config_30_percent.own_channel_config.max_inbound_htlc_value_in_flight_percent_of_channel = 30;
+	let mut config_50_percent = UserConfig::default();
+	config_50_percent.channel_options.announced_channel = true;
+	config_50_percent.own_channel_config.max_inbound_htlc_value_in_flight_percent_of_channel = 50;
+	let mut config_95_percent = UserConfig::default();
+	config_95_percent.channel_options.announced_channel = true;
+	config_95_percent.own_channel_config.max_inbound_htlc_value_in_flight_percent_of_channel = 95;
+	let mut config_100_percent = UserConfig::default();
+	config_100_percent.channel_options.announced_channel = true;
+	config_100_percent.own_channel_config.max_inbound_htlc_value_in_flight_percent_of_channel = 100;
+
+	let chanmon_cfgs = create_chanmon_cfgs(4);
+	let node_cfgs = create_node_cfgs(4, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(4, &node_cfgs, &[Some(config_30_percent), Some(config_50_percent), Some(config_95_percent), Some(config_100_percent)]);
+	let nodes = create_network(4, &node_cfgs, &node_chanmgrs);
+
+	let channel_value_satoshis = 100000;
+	let channel_value_msat = channel_value_satoshis * 1000;
+	let channel_value_30_percent_msat = (channel_value_msat as f64 * 0.3) as u64;
+	let channel_value_50_percent_msat = (channel_value_msat as f64 * 0.5) as u64;
+	let channel_value_90_percent_msat = (channel_value_msat as f64 * 0.9) as u64;
+
+	let (node_0_chan_update, node_1_chan_update, _, _)  = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, channel_value_satoshis, 10001, InitFeatures::known(), InitFeatures::known());
+	let (node_2_chan_update, node_3_chan_update, _, _)  = create_announced_chan_between_nodes_with_value(&nodes, 2, 3, channel_value_satoshis, 10001, InitFeatures::known(), InitFeatures::known());
+
+	// Assert that `node[0]`'s `ChannelUpdate` is capped at 50 percent of the `channel_value`, as
+	// that's the value of `node[1]`'s `holder_max_htlc_value_in_flight_msat`.
+	assert_eq!(node_0_chan_update.contents.htlc_maximum_msat, OptionalField::Present(channel_value_50_percent_msat));
+	// Assert that `node[1]`'s `ChannelUpdate` is capped at 30 percent of the `channel_value`, as
+	// that's the value of `node[0]`'s `holder_max_htlc_value_in_flight_msat`.
+	assert_eq!(node_1_chan_update.contents.htlc_maximum_msat, OptionalField::Present(channel_value_30_percent_msat));
+
+	// Assert that `node[2]`'s `ChannelUpdate` is capped at 90 percent of the `channel_value`, as
+	// the value of `node[3]`'s `holder_max_htlc_value_in_flight_msat` (100%), exceeds 90% of the
+	// `channel_value`.
+	assert_eq!(node_2_chan_update.contents.htlc_maximum_msat, OptionalField::Present(channel_value_90_percent_msat));
+	// Assert that `node[3]`'s `ChannelUpdate` is capped at 90 percent of the `channel_value`, as
+	// the value of `node[2]`'s `holder_max_htlc_value_in_flight_msat` (95%), exceeds 90% of the
+	// `channel_value`.
+	assert_eq!(node_3_chan_update.contents.htlc_maximum_msat, OptionalField::Present(channel_value_90_percent_msat));
+}
+
 #[test]
 fn test_manually_accept_inbound_channel_request() {
 	let mut manually_accept_conf = UserConfig::default();

lightning/src/util/config.rs

@@ -48,6 +48,30 @@ pub struct ChannelHandshakeConfig {
 	/// Default value: 1. If the value is less than 1, it is ignored and set to 1, as is required
 	/// by the protocol.
 	pub our_htlc_minimum_msat: u64,
+	/// Sets the percentage of the channel value we will cap the total value of outstanding inbound
+	/// HTLCs to.
+	///
+	/// This can be set to a value between 1-100, where the value corresponds to the percent of the
+	/// channel value in whole percentages.
+	///
+	/// Note that:
+	/// * If configured to another value than the default value 10, any new channels created with
+	/// the non default value will cause versions of LDK prior to 0.0.104 to refuse to read the
+	/// `ChannelManager`.
+	///
+	/// * This caps the total value for inbound HTLCs in-flight only, and there's currently
+	/// no way to configure the cap for the total value of outbound HTLCs in-flight.
+	///
+	/// * The requirements for your node being online to ensure the safety of HTLC-encumbered funds
+	/// are different from the non-HTLC-encumbered funds. This makes this an important knob to
+	/// restrict exposure to loss due to being offline for too long.
+	/// See [`ChannelHandshakeConfig::our_to_self_delay`] and [`ChannelConfig::cltv_expiry_delta`]
+	/// for more information.
+	///
+	/// Default value: 10.
+	/// Minimum value: 1, any values less than 1 will be treated as 1 instead.
+	/// Maximum value: 100, any values larger than 100 will be treated as 100 instead.
+	pub max_inbound_htlc_value_in_flight_percent_of_channel: u8,
 	/// If set, we attempt to negotiate the `scid_privacy` (referred to as `scid_alias` in the
 	/// BOLTs) option for outbound private channels. This provides better privacy by not including
 	/// our real on-chain channel UTXO in each invoice and requiring that our counterparty only
@@ -78,6 +102,7 @@ impl Default for ChannelHandshakeConfig {
 			minimum_depth: 6,
 			our_to_self_delay: BREAKDOWN_TIMEOUT,
 			our_htlc_minimum_msat: 1,
+			max_inbound_htlc_value_in_flight_percent_of_channel: 10,
 			negotiate_scid_privacy: false,
 		}
 	}