Use channel's real funding amounts when processing RGS data

Neither `channel_announcement`s nor `channel_update`s contain a
channel's actual funding amount, complicating scoring as nodes may
set an `htlc_maximum_msat` to something less than the funding
amount. When scoring, we use `htlc_maximum_msat` anyway if we don't
know the funding amount, but its not a perfect proxy.

In
lightningdevkit/rapid-gossip-sync-server#102
we started including a channel's real funding amount in RGS data,
and here we start parsing it and including it in our network graph.

Fixes #1559

Author: TheBlueMatt

lightning-background-processor/src/lib.rs

@@ -2521,6 +2521,7 @@ mod tests {
 				.network_graph
 				.add_channel_from_partial_announcement(
 					42,
+					None,
 					53,
 					features,
 					$nodes[0].node.get_our_node_id().into(),

lightning-rapid-gossip-sync/src/processing.rs

@@ -267,8 +267,26 @@ where
 				latest_seen_timestamp
 			);
 
+			let mut funding_sats: Option<u64> = None;
+
+			if version >= 2 && has_additional_data {
+				// forwards compatibility
+				let additional_data: Vec<u8> = Readable::read(read_cursor)?;
+				let mut cursor = &additional_data[..];
+				let funding_sats_read: BigSize = Readable::read(&mut cursor)?;
+				funding_sats = Some(funding_sats_read.0);
+				if !cursor.is_empty() {
+					log_gossip!(
+						self.logger,
+						"Ignoring {} bytes of additional data in channel announcement",
+						cursor.len()
+					);
+				}
+			}
+
 			let announcement_result = network_graph.add_channel_from_partial_announcement(
 				short_channel_id,
+				funding_sats,
 				backdated_timestamp as u64,
 				features,
 				node_id_1,
@@ -286,16 +304,6 @@ where
 					return Err(lightning_error.into());
 				}
 			}
-
-			if version >= 2 && has_additional_data {
-				// forwards compatibility
-				let additional_data: Vec<u8> = Readable::read(read_cursor)?;
-				log_gossip!(
-					self.logger,
-					"Ignoring {} bytes of additional data in channel announcement",
-					additional_data.len()
-				);
-			}
 		}
 
 		for modification in node_modifications {
@@ -664,7 +672,7 @@ mod tests {
 			0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 			0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 			0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-			0, 0, 0, 1, 0, 0, 1, 0, 255, 128, 0, 0, 0, 0, 0, 0, 1, 0, 147, 23, 23, 23, 23, 23, 23,
+			0, 0, 0, 1, 0, 0, 1, 0, 255, 128, 0, 0, 0, 0, 0, 0, 1, 0, 147, 42, 23, 23, 23, 23, 23,
 			23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
 			23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
 			23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
@@ -685,9 +693,11 @@ mod tests {
 			"Ignoring 255 bytes of additional data in node announcement",
 			3,
 		);
+		// Note that our extra data is 147 bytes long, but the first byte (42) is read as the
+		// channel's funding amount (as a BigSize).
 		logger.assert_log_contains(
 			"lightning_rapid_gossip_sync::processing",
-			"Ignoring 147 bytes of additional data in channel announcement",
+			"Ignoring 146 bytes of additional data in channel announcement",
 			1,
 		);
 		logger.assert_log_contains(

lightning/src/routing/gossip.rs

@@ -2006,8 +2006,8 @@ where
 	///
 	/// All other parameters as used in [`msgs::UnsignedChannelAnnouncement`] fields.
 	pub fn add_channel_from_partial_announcement(
-		&self, short_channel_id: u64, timestamp: u64, features: ChannelFeatures, node_id_1: NodeId,
-		node_id_2: NodeId,
+		&self, short_channel_id: u64, capacity_sats: Option<u64>, timestamp: u64,
+		features: ChannelFeatures, node_id_1: NodeId, node_id_2: NodeId,
 	) -> Result<(), LightningError> {
 		if node_id_1 == node_id_2 {
 			return Err(LightningError {
@@ -2022,7 +2022,7 @@ where
 			one_to_two: None,
 			node_two: node_id_2,
 			two_to_one: None,
-			capacity_sats: None,
+			capacity_sats,
 			announcement_message: None,
 			announcement_received_time: timestamp,
 			node_one_counter: u32::max_value(),