Expose counterparty forwarding info in ChannelDetails.

Useful for constructing route hints for private channels in invoices.

Co-authored-by: Valentine Wallace <vwallace@protonmail.com>
Co-authored-by: Antoine Riard <ariard@student.42.fr>

fuzz/src/router.rs

@@ -212,6 +212,7 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 								inbound_capacity_msat: 0,
 								is_live: true,
 								outbound_capacity_msat: 0,
+								counterparty_forwarding_info: None,
 							});
 						}
 						Some(&first_hops_vec[..])

lightning/src/ln/channel.rs

@@ -282,6 +282,7 @@ impl HTLCCandidate {
 }
 
 /// Information needed for constructing an invoice route hint for this channel.
+#[derive(Clone)]
 pub struct CounterpartyForwardingInfo {
 	/// Base routing fee in millisatoshis.
 	pub fee_base_msat: u32,
@@ -4132,6 +4133,11 @@ impl<Signer: Sign> Channel<Signer> {
 		}
 	}
 
+	/// Get forwarding information for the counterparty.
+	pub fn counterparty_forwarding_info(&self) -> Option<CounterpartyForwardingInfo> {
+		self.counterparty_forwarding_info.clone()
+	}
+
 	pub fn channel_update(&mut self, msg: &msgs::ChannelUpdate) -> Result<(), ChannelError> {
 		let usable_channel_value_msat = (self.channel_value_satoshis - self.counterparty_selected_channel_reserve_satoshis) * 1000;
 		if msg.contents.htlc_minimum_msat >= usable_channel_value_msat {
@@ -4756,7 +4762,7 @@ mod tests {
 	use ln::channel::{Channel,Sign,InboundHTLCOutput,OutboundHTLCOutput,InboundHTLCState,OutboundHTLCState,HTLCOutputInCommitment,HTLCCandidate,HTLCInitiator,TxCreationKeys};
 	use ln::channel::MAX_FUNDING_SATOSHIS;
 	use ln::features::InitFeatures;
-	use ln::msgs::{OptionalField, DataLossProtect, DecodeError};
+	use ln::msgs::{ChannelUpdate, DataLossProtect, DecodeError, OptionalField, UnsignedChannelUpdate};
 	use ln::chan_utils;
 	use ln::chan_utils::{ChannelPublicKeys, HolderCommitmentTransaction, CounterpartyChannelTransactionParameters, HTLC_SUCCESS_TX_WEIGHT, HTLC_TIMEOUT_TX_WEIGHT};
 	use chain::chaininterface::{FeeEstimator,ConfirmationTarget};
@@ -4767,6 +4773,7 @@ mod tests {
 	use util::test_utils;
 	use util::logger::Logger;
 	use bitcoin::secp256k1::{Secp256k1, Message, Signature, All};
+	use bitcoin::secp256k1::ffi::Signature as FFISignature;
 	use bitcoin::secp256k1::key::{SecretKey,PublicKey};
 	use bitcoin::hashes::sha256::Hash as Sha256;
 	use bitcoin::hashes::Hash;
@@ -5023,6 +5030,54 @@ mod tests {
 		}
 	}
 
+	#[test]
+	fn channel_update() {
+		let feeest = TestFeeEstimator{fee_est: 15000};
+		let secp_ctx = Secp256k1::new();
+		let seed = [42; 32];
+		let network = Network::Testnet;
+		let chain_hash = genesis_block(network).header.block_hash();
+		let keys_provider = test_utils::TestKeysInterface::new(&seed, network);
+
+		// Create a channel.
+		let node_b_node_id = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32]).unwrap());
+		let config = UserConfig::default();
+		let mut node_a_chan = Channel::<EnforcingSigner>::new_outbound(&&feeest, &&keys_provider, node_b_node_id, 10000000, 100000, 42, &config).unwrap();
+		assert!(node_a_chan.counterparty_forwarding_info.is_none());
+		assert_eq!(node_a_chan.holder_htlc_minimum_msat, 1); // the default
+		assert!(node_a_chan.counterparty_forwarding_info().is_none());
+
+		// Make sure that receiving a channel update will update the Channel as expected.
+		let update = ChannelUpdate {
+			contents: UnsignedChannelUpdate {
+				chain_hash,
+				short_channel_id: 0,
+				timestamp: 0,
+				flags: 0,
+				cltv_expiry_delta: 100,
+				htlc_minimum_msat: 5,
+				htlc_maximum_msat: OptionalField::Absent,
+				fee_base_msat: 110,
+				fee_proportional_millionths: 11,
+				excess_data: Vec::new(),
+			},
+			signature: Signature::from(unsafe { FFISignature::new() })
+		};
+		node_a_chan.channel_update(&update).unwrap();
+
+		// The counterparty can send an update with a higher minimum HTLC, but that shouldn't
+		// change our official htlc_minimum_msat.
+		assert_eq!(node_a_chan.holder_htlc_minimum_msat, 1);
+		match node_a_chan.counterparty_forwarding_info() {
+			Some(info) => {
+				assert_eq!(info.cltv_expiry_delta, 100);
+				assert_eq!(info.fee_base_msat, 110);
+				assert_eq!(info.fee_proportional_millionths, 11);
+			},
+			None => panic!("expected counterparty forwarding info to be Some")
+		}
+	}
+
 	#[test]
 	fn outbound_commitment_test() {
 		// Test vectors from BOLT 3 Appendix C:

lightning/src/ln/channelmanager.rs

@@ -39,6 +39,9 @@ use chain::Watch;
 use chain::chaininterface::{BroadcasterInterface, FeeEstimator};
 use chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitorUpdateStep, ChannelMonitorUpdateErr, HTLC_FAIL_BACK_BUFFER, CLTV_CLAIM_BUFFER, LATENCY_GRACE_PERIOD_BLOCKS, ANTI_REORG_DELAY, MonitorEvent, CLOSED_CHANNEL_UPDATE_ID};
 use chain::transaction::{OutPoint, TransactionData};
+// Since this struct is returned in `list_channels` methods, expose it here in case users want to
+// construct one themselves.
+pub use ln::channel::CounterpartyForwardingInfo;
 use ln::channel::{Channel, ChannelError};
 use ln::features::{InitFeatures, NodeFeatures};
 use routing::router::{Route, RouteHop};
@@ -574,6 +577,10 @@ pub struct ChannelDetails {
 	/// True if the channel is (a) confirmed and funding_locked messages have been exchanged, (b)
 	/// the peer is connected, and (c) no monitor update failure is pending resolution.
 	pub is_live: bool,
+
+	/// Information on the fees and requirements that the counterparty requires when forwarding
+	/// payments to us through this channel.
+	pub counterparty_forwarding_info: Option<CounterpartyForwardingInfo>,
 }
 
 /// If a payment fails to send, it can be in one of several states. This enum is returned as the
@@ -892,6 +899,7 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 					outbound_capacity_msat,
 					user_id: channel.get_user_id(),
 					is_live: channel.is_live(),
+					counterparty_forwarding_info: channel.counterparty_forwarding_info(),
 				});
 			}
 		}

lightning/src/routing/router.rs

@@ -1473,6 +1473,7 @@ mod tests {
 			outbound_capacity_msat: 100000,
 			inbound_capacity_msat: 100000,
 			is_live: true,
+			counterparty_forwarding_info: None,
 		}];
 
 		if let Err(LightningError{err, action: ErrorAction::IgnoreError}) = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, Some(&our_chans.iter().collect::<Vec<_>>()), &Vec::new(), 100, 42, Arc::clone(&logger)) {
@@ -1790,6 +1791,7 @@ mod tests {
 			outbound_capacity_msat: 250_000_000,
 			inbound_capacity_msat: 0,
 			is_live: true,
+			counterparty_forwarding_info: None,
 		}];
 		let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, Some(&our_chans.iter().collect::<Vec<_>>()),  &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
 		assert_eq!(route.paths[0].len(), 2);
@@ -1837,6 +1839,7 @@ mod tests {
 			outbound_capacity_msat: 250_000_000,
 			inbound_capacity_msat: 0,
 			is_live: true,
+			counterparty_forwarding_info: None,
 		}];
 		let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, Some(&our_chans.iter().collect::<Vec<_>>()), &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
 		assert_eq!(route.paths[0].len(), 2);
@@ -1901,6 +1904,7 @@ mod tests {
 			outbound_capacity_msat: 250_000_000,
 			inbound_capacity_msat: 0,
 			is_live: true,
+			counterparty_forwarding_info: None,
 		}];
 		let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[2], None, Some(&our_chans.iter().collect::<Vec<_>>()), &Vec::new(), 100, 42, Arc::clone(&logger)).unwrap();
 		assert_eq!(route.paths[0].len(), 2);
@@ -2037,6 +2041,7 @@ mod tests {
 			outbound_capacity_msat: 250_000_000,
 			inbound_capacity_msat: 0,
 			is_live: true,
+			counterparty_forwarding_info: None,
 		}];
 		let mut last_hops = last_hops(&nodes);
 		let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[6], None, Some(&our_chans.iter().collect::<Vec<_>>()), &last_hops.iter().collect::<Vec<_>>(), 100, 42, Arc::clone(&logger)).unwrap();
@@ -2165,6 +2170,7 @@ mod tests {
 			outbound_capacity_msat: 100000,
 			inbound_capacity_msat: 100000,
 			is_live: true,
+			counterparty_forwarding_info: None,
 		}];
 		let route = get_route(&source_node_id, &NetworkGraph::new(genesis_block(Network::Testnet).header.block_hash()), &target_node_id, None, Some(&our_chans.iter().collect::<Vec<_>>()), &last_hops.iter().collect::<Vec<_>>(), 100, 42, Arc::new(test_utils::TestLogger::new())).unwrap();
 
@@ -2296,6 +2302,7 @@ mod tests {
 			outbound_capacity_msat: 200_000_000,
 			inbound_capacity_msat: 0,
 			is_live: true,
+			counterparty_forwarding_info: None,
 		}];
 
 		{