Disable MPP routing when the payee does not support it

Author: TheBlueMatt

lightning/src/ln/features.rs

@@ -574,7 +574,6 @@ impl<T: sealed::BasicMPP> Features<T> {
 		<T as sealed::BasicMPP>::requires_feature(&self.flags)
 	}
 	// We currently never test for this since we don't actually *generate* multipath routes.
-	#[allow(dead_code)]
 	pub(crate) fn supports_basic_mpp(&self) -> bool {
 		<T as sealed::BasicMPP>::supports_feature(&self.flags)
 	}

lightning/src/routing/router.rs

@@ -15,7 +15,7 @@
 use bitcoin::secp256k1::key::PublicKey;
 
 use ln::channelmanager::ChannelDetails;
-use ln::features::{ChannelFeatures, NodeFeatures, InvoiceFeatures};
+use ln::features::{ChannelFeatures, InvoiceFeatures, NodeFeatures};
 use ln::msgs::{DecodeError, ErrorAction, LightningError, MAX_VALUE_MSAT};
 use routing::network_graph::{NetworkGraph, RoutingFees};
 use util::ser::{Writeable, Readable};
@@ -314,6 +314,10 @@ fn compute_fees(amount_msat: u64, channel_fees: RoutingFees) -> Option<u64> {
 
 /// Gets a route from us (payer) to the given target node (payee).
 ///
+/// If the payee provided features in their invoice, they should be provided via payee_features.
+/// Without this, any knowledge we have of the payee's features may be used if they are available
+/// in the network graph, however MPP routing will be disabled and routing is more likely to fail.
+///
 /// Extra routing hops between known nodes and the target will be used if they are included in
 /// last_hops.
 ///
@@ -396,6 +400,17 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, paye
 	const ROUTE_CAPACITY_PROVISION_FACTOR: u64 = 3;
 	let recommended_value_msat = final_value_msat * ROUTE_CAPACITY_PROVISION_FACTOR as u64;
 
+	// Allow MPP only if we have a features set from somewhere that indicates the payee supports
+	// it. If the payee supports it they're supposed to include it in the invoice, so that should
+	// work reliably.
+	let allow_mpp = if let Some(features) = &payee_features {
+		features.supports_basic_mpp()
+	} else if let Some(node) = network.get_nodes().get(&payee) {
+		if let Some(node_info) = node.announcement_info.as_ref() {
+			node_info.features.supports_basic_mpp()
+		} else { false }
+	} else { false };
+
 	// Step (1).
 	// Prepare the data we'll use for payee-to-payer search by
 	// inserting first hops suggested by the caller as targets.
@@ -484,8 +499,13 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, paye
 					// the absolute liquidity contribution is lowered,
 					// thus increasing the number of potential channels to be selected.
 
-					// Derive the minimal liquidity contribution with a ratio of 20 (5%, rounded up).
-					let minimal_value_contribution_msat: u64 = (recommended_value_msat - already_collected_value_msat + 19) / 20;
+					// Derive the minimal liquidity contribution with a ratio of 20 (5%, rounded up)
+					// or 100% if we're not allowed to do multipath payments.
+					let minimal_value_contribution_msat: u64 = if allow_mpp {
+						(recommended_value_msat - already_collected_value_msat + 19) / 20
+					} else {
+						final_value_msat
+					};
 					// Verify the liquidity offered by this channel complies to the minimal contribution.
 					let contributes_sufficient_value = available_value_contribution_msat >= minimal_value_contribution_msat;
 
@@ -866,6 +886,11 @@ pub fn get_route<L: Deref>(our_node_id: &PublicKey, network: &NetworkGraph, paye
 			}
 		}
 
+		if !allow_mpp {
+			// If we don't support MPP, no use trying to gather more value ever.
+			break 'paths_collection;
+		}
+
 		// Step (3).
 		// Stop either when recommended value is reached,
 		// or if during last iteration no new path was found.