Filter route hints for phantom invoices

Filter the route hints in `create_phantom_invoice` based on the
following criteria:

* Only one channel per real participating node in the phantom invoice
* Always select the channel with the highest inbound capacity
* Filter out channels with a lower inbound capacity than the invoice amt

Author: ViktorTigerstrom

lightning-invoice/src/utils.rs

@@ -64,42 +64,43 @@ pub fn create_phantom_invoice<Signer: Sign, K: Deref>(
 	}
 
 	for hint in phantom_route_hints {
-		for channel in &hint.channels {
-			let short_channel_id = match channel.short_channel_id {
-				Some(id) => id,
-				None => continue,
-			};
-			let forwarding_info = match &channel.counterparty.forwarding_info {
-				Some(info) => info.clone(),
-				None => continue,
-			};
-			invoice = invoice.private_route(RouteHint(vec![
-					RouteHintHop {
-						src_node_id: channel.counterparty.node_id,
-						short_channel_id,
-						fees: RoutingFees {
-							base_msat: forwarding_info.fee_base_msat,
-							proportional_millionths: forwarding_info.fee_proportional_millionths,
-						},
-						cltv_expiry_delta: forwarding_info.cltv_expiry_delta,
-						htlc_minimum_msat: None,
-						htlc_maximum_msat: None,
+		// Filter one route hint per "real" node.
+		let channel_pubkey_selector = |_channel: ChannelDetails| hint.real_node_pubkey.clone();
+		let route_hint_from_channel = |channel: ChannelDetails, short_channel_id: u64, forwarding_info: CounterpartyForwardingInfo| {
+			RouteHint(vec![
+				RouteHintHop {
+					src_node_id: channel.counterparty.node_id,
+					short_channel_id,
+					fees: RoutingFees {
+						base_msat: forwarding_info.fee_base_msat,
+						proportional_millionths: forwarding_info.fee_proportional_millionths,
+					},
+					cltv_expiry_delta: forwarding_info.cltv_expiry_delta,
+					htlc_minimum_msat: None,
+					htlc_maximum_msat: None,
+				},
+				RouteHintHop {
+					src_node_id: hint.real_node_pubkey,
+					short_channel_id: hint.phantom_scid,
+					fees: RoutingFees {
+						base_msat: 0,
+						proportional_millionths: 0,
 					},
-					RouteHintHop {
-						src_node_id: hint.real_node_pubkey,
-						short_channel_id: hint.phantom_scid,
-						fees: RoutingFees {
-							base_msat: 0,
-							proportional_millionths: 0,
-						},
-						cltv_expiry_delta: MIN_CLTV_EXPIRY_DELTA,
-						htlc_minimum_msat: None,
-						htlc_maximum_msat: None,
-					}])
-			);
+					cltv_expiry_delta: MIN_CLTV_EXPIRY_DELTA,
+					htlc_minimum_msat: None,
+					htlc_maximum_msat: None,}])
+		};
+		let route_hints = filter_channels(
+			hint.channels.clone(),
+			amt_msat,
+			false,
+			channel_pubkey_selector,
+			route_hint_from_channel
+		);
+		for hint in route_hints {
+			invoice = invoice.private_route(hint);
 		}
 	}
-
 	let raw_invoice = match invoice.build_raw() {
 		Ok(inv) => inv,
 		Err(e) => return Err(SignOrCreationError::CreationError(e))