Add method to count total fees in a Route #999

Author: galderz

lightning/src/routing/router.rs

@@ -71,6 +71,17 @@ pub struct Route {
 	pub paths: Vec<Vec<RouteHop>>,
 }
 
+impl Route {
+	/// Returns the total amount of fees payed on this Route.
+	fn get_total_fees(&self) -> u64 {
+		// Do not count last hop of each path since that's the full value of the payment
+		return self.paths.iter()
+			.flat_map(|path| path.split_last().unwrap().1)
+			.map(|hop| &hop.fee_msat)
+			.sum();
+	}
+}
+
 const SERIALIZATION_VERSION: u8 = 1;
 const MIN_SERIALIZATION_VERSION: u8 = 1;
 
@@ -3425,6 +3436,7 @@ mod tests {
 				total_amount_paid_msat += path.last().unwrap().fee_msat;
 			}
 			assert_eq!(total_amount_paid_msat, 200_000);
+			assert_eq!(route.get_total_fees(), 150_000);
 		}
 
 	}
@@ -3831,6 +3843,121 @@ mod tests {
 		}
 	}
 
+	// Tweaked from available_liquidity_last_hop_test
+	#[test]
+	fn total_fees_single_path() {
+		// Check that total fees in single path payment are calculated properly
+		let (secp_ctx, net_graph_msg_handler, _, logger) = build_graph();
+		let (our_privkey, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+
+		// Path via {node7, node2, node4} is channels {12, 13, 6, 11}.
+		// {12, 13, 11} have the capacities of 100, {6} has a capacity of 50.
+		// Total capacity: 50 sats.
+		// Fee in first channel does not count since that's opened by the originating node.
+		// So, only the fees of the last 3 channels count towards total fees.
+
+		// Disable other potential paths.
+		update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+			chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+			short_channel_id: 2,
+			timestamp: 2,
+			flags: 2,
+			cltv_expiry_delta: 0,
+			htlc_minimum_msat: 0,
+			htlc_maximum_msat: OptionalField::Present(100_000),
+			fee_base_msat: 0,
+			fee_proportional_millionths: 0,
+			excess_data: Vec::new()
+		});
+		update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+			chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+			short_channel_id: 7,
+			timestamp: 2,
+			flags: 2,
+			cltv_expiry_delta: 0,
+			htlc_minimum_msat: 0,
+			htlc_maximum_msat: OptionalField::Present(100_000),
+			fee_base_msat: 0,
+			fee_proportional_millionths: 0,
+			excess_data: Vec::new()
+		});
+
+		// Limit capacities
+
+		update_channel(&net_graph_msg_handler, &secp_ctx, &our_privkey, UnsignedChannelUpdate {
+			chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+			short_channel_id: 12,
+			timestamp: 2,
+			flags: 0,
+			cltv_expiry_delta: 0,
+			htlc_minimum_msat: 0,
+			htlc_maximum_msat: OptionalField::Present(100_000),
+			fee_base_msat: 210,
+			fee_proportional_millionths: 0,
+			excess_data: Vec::new()
+		});
+		update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[7], UnsignedChannelUpdate {
+			chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+			short_channel_id: 13,
+			timestamp: 2,
+			flags: 0,
+			cltv_expiry_delta: 0,
+			htlc_minimum_msat: 0,
+			htlc_maximum_msat: OptionalField::Present(100_000),
+			fee_base_msat: 220,
+			fee_proportional_millionths: 0,
+			excess_data: Vec::new()
+		});
+
+		update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[2], UnsignedChannelUpdate {
+			chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+			short_channel_id: 6,
+			timestamp: 2,
+			flags: 0,
+			cltv_expiry_delta: 0,
+			htlc_minimum_msat: 0,
+			htlc_maximum_msat: OptionalField::Present(50_000),
+			fee_base_msat: 280,
+			fee_proportional_millionths: 0,
+			excess_data: Vec::new()
+		});
+		update_channel(&net_graph_msg_handler, &secp_ctx, &privkeys[4], UnsignedChannelUpdate {
+			chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+			short_channel_id: 11,
+			timestamp: 2,
+			flags: 0,
+			cltv_expiry_delta: 0,
+			htlc_minimum_msat: 0,
+			htlc_maximum_msat: OptionalField::Present(100_000),
+			fee_base_msat: 290,
+			fee_proportional_millionths: 0,
+			excess_data: Vec::new()
+		});
+
+		{
+			// Now, attempt to route 49 sats (just a bit below the capacity).
+			let route = get_route(&our_id, &net_graph_msg_handler.network_graph.read().unwrap(), &nodes[3],
+								  Some(InvoiceFeatures::known()), None, &Vec::new(), 49_000, 42, Arc::clone(&logger)).unwrap();
+			assert_eq!(route.paths.len(), 1);
+
+			let mut total_value_transferred_msat = 0;
+			let mut total_paid_msat = 0;
+			for path in &route.paths {
+				assert_eq!(path.len(), 4);
+				assert_eq!(path.last().unwrap().pubkey, nodes[3]);
+				total_value_transferred_msat += path.last().unwrap().fee_msat;
+				for hop in path {
+					total_paid_msat += hop.fee_msat;
+				}
+			}
+			// If we paid fee, this would be higher.
+			assert_eq!(total_value_transferred_msat, 49_000);
+			let total_fees_paid = total_paid_msat - total_value_transferred_msat;
+			assert_eq!(total_fees_paid, 790);
+			assert_eq!(route.get_total_fees(), 790);
+		}
+	}
+
 	#[cfg(not(feature = "no-std"))]
 	pub(super) fn random_init_seed() -> u64 {
 		// Because the default HashMap in std pulls OS randomness, we can use it as a (bad) RNG.