Update filter channels to limit to 3 hints per invoice

Author: freddiekrugerrand

lightning-invoice/src/utils.rs

@@ -509,6 +509,7 @@ fn _create_invoice_from_channelmanager_and_duration_since_epoch_with_payment_has
 ///
 /// The filtering is based on the following criteria:
 /// * Only one channel per counterparty node
+/// * Limited to three channels in total
 /// * Always select the channel with the highest inbound capacity per counterparty node
 /// * Prefer channels with capacity at least `min_inbound_capacity_msat` and where the channel
 ///   `is_usable` (i.e. the peer is connected).
@@ -629,6 +630,7 @@ fn filter_channels<L: Deref>(
 
 			include_channel
 		})
+		.take(3)
 		.map(route_hint_from_channel)
 		.collect::<Vec<RouteHint>>()
 }
@@ -852,6 +854,28 @@ mod test {
 		match_invoice_routes(Some(1_000_000_000), &nodes[0], scid_aliases);
 	}
 
+	#[test]
+	fn test_hints_limited_to_3() {
+		let chanmon_cfgs = create_chanmon_cfgs(5);
+		let node_cfgs = create_node_cfgs(5, &chanmon_cfgs);
+		let node_chanmgrs = create_node_chanmgrs(5, &node_cfgs, &[None,None,None, None, None]);
+		let nodes = create_network(5, &node_cfgs, &node_chanmgrs);
+
+		let _chan_1_0 = create_unannounced_chan_between_nodes_with_value(&nodes, 1, 0, 100_004, 0);
+		let _chan_2_0 = create_unannounced_chan_between_nodes_with_value(&nodes, 2, 0, 100_003, 0);
+		let _chan_3_0 = create_unannounced_chan_between_nodes_with_value(&nodes, 3, 0, 100_002, 0);
+		let _chan_4_0 = create_unannounced_chan_between_nodes_with_value(&nodes, 4, 0, 100_001, 0);
+
+		// Hints are randomly selected, so we can only assert that we limit our number of hints, not the
+		// actual hints that are included.
+		let invoice = create_invoice_from_channelmanager_and_duration_since_epoch(
+			&nodes[0].node, nodes[0].keys_manager, nodes[0].logger,
+			Currency::BitcoinTestnet, Some(500_000), "test".to_string(), Duration::from_secs(1234567),
+			3600, None).unwrap();
+
+		assert_eq!(invoice.private_routes().len(), 3, "expected 3 route hints");
+	}
+
 	#[test]
 	fn test_forwarding_info_not_assigned_channel_excluded_from_hints() {
 		let chanmon_cfgs = create_chanmon_cfgs(3);