Make our in-flight limit percentage configurable

Author: ViktorTigerstrom

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;
@@ -803,9 +803,23 @@ 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, based on how many of the percent its been configured to
+	/// be set to by the user.
+	///
+	/// As we only allow the user to set the percentage to a value between `1-100`, if the user
+	/// sets a value less than `1`, the function will result in `1` percent of the
+	/// `channel_value_satoshis`, as well as `100` percent if the user has set a value larger
+	/// than `100`.
+	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 +978,7 @@ 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 +1296,7 @@ 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,
@@ -5877,13 +5891,15 @@ 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 the default value of
+		// `ChannelHandshakeConfig::max_inbound_htlc_value_in_flight_percent_of_channel`.
 		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 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, &UserConfig::default().own_channel_config)
 			{ Some(self.holder_max_htlc_value_in_flight_msat) } else { None };
 
 		write_tlv_fields!(writer, {
@@ -6153,7 +6169,7 @@ 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());

lightning/src/util/config.rs

@@ -48,6 +48,28 @@ 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 how many the percent 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 won't be backwards compatible with LDK versions prior
+	/// to 0.0.100.
+	///
+	/// Note that this caps the total value for inbound HTLCs in-flight only, and there's currently
+	/// no availability to configure the cap for the total value of outbound HTLCs in-flight.
+	/// This effects the in-flight HTLC balance, which [`ChannelConfig::cltv_expiry_delta`] is
+	/// applied to.
+	///
+	/// This does not cap the total value of the non-HTLC-encumbered balance which
+	/// [`ChannelHandshakeConfig::our_to_self_delay`] is applied to.
+	///
+	/// 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 +100,7 @@ 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,
 		}
 	}