builder: force full RGS sync on legacy mismatch

When deserializing `NodeMetrics`, keep reading the legacy RGS timestamp
field long enough to compare it with `NetworkGraph` during build. If the
values diverge, start the next rapid gossip sync from timestamp `0`
instead of trusting either partial state.

Generated with the assistance of AI.
Co-Authored-By: HAL 9000

Author: tnull

src/builder.rs

@@ -1161,11 +1161,13 @@ fn build_with_store_internal(
 		});
 
 	// Initialize the status fields.
-	let node_metrics = match node_metris_res {
-		Ok(metrics) => Arc::new(RwLock::new(metrics)),
+	let (node_metrics, legacy_latest_rgs_snapshot_timestamp) = match node_metris_res {
+		Ok((metrics, legacy_latest_rgs_snapshot_timestamp)) => {
+			(Arc::new(RwLock::new(metrics)), legacy_latest_rgs_snapshot_timestamp)
+		},
 		Err(e) => {
 			if e.kind() == std::io::ErrorKind::NotFound {
-				Arc::new(RwLock::new(NodeMetrics::default()))
+				(Arc::new(RwLock::new(NodeMetrics::default())), None)
 			} else {
 				log_error!(logger, "Failed to read node metrics from store: {}", e);
 				return Err(BuildError::ReadFailed);
@@ -1647,6 +1649,9 @@ fn build_with_store_internal(
 	// Initialize the GossipSource
 	// Use the configured gossip source, if the user set one, otherwise default to P2PNetwork.
 	let gossip_source_config = gossip_source_config.unwrap_or(&GossipSourceConfig::P2PNetwork);
+	let network_graph_rgs_timestamp = network_graph.get_last_rapid_gossip_sync_timestamp();
+	let force_full_rgs_sync = legacy_latest_rgs_snapshot_timestamp
+		.is_some_and(|legacy_timestamp| network_graph_rgs_timestamp != Some(legacy_timestamp));
 
 	let gossip_source = match gossip_source_config {
 		GossipSourceConfig::P2PNetwork => {
@@ -1660,7 +1665,7 @@ fn build_with_store_internal(
 		},
 		GossipSourceConfig::RapidGossipSync(rgs_server) => {
 			let latest_sync_timestamp =
-				network_graph.get_last_rapid_gossip_sync_timestamp().unwrap_or(0);
+				if force_full_rgs_sync { 0 } else { network_graph_rgs_timestamp.unwrap_or(0) };
 			Arc::new(GossipSource::new_rgs(
 				rgs_server.clone(),
 				latest_sync_timestamp,

src/io/utils.rs

@@ -20,6 +20,7 @@ use bdk_chain::tx_graph::ChangeSet as BdkTxGraphChangeSet;
 use bdk_chain::ConfirmationBlockTime;
 use bdk_wallet::ChangeSet as BdkWalletChangeSet;
 use bitcoin::Network;
+use lightning::_init_and_read_len_prefixed_tlv_fields;
 use lightning::ln::msgs::DecodeError;
 use lightning::routing::gossip::NetworkGraph;
 use lightning::routing::scoring::{
@@ -329,7 +330,7 @@ pub(crate) async fn read_output_sweeper(
 
 pub(crate) async fn read_node_metrics<L: Deref>(
 	kv_store: &DynStore, logger: L,
-) -> Result<NodeMetrics, std::io::Error>
+) -> Result<(NodeMetrics, Option<u32>), std::io::Error>
 where
 	L::Target: LdkLogger,
 {
@@ -340,10 +341,28 @@ where
 		NODE_METRICS_KEY,
 	)
 	.await?;
-	NodeMetrics::read(&mut &*reader).map_err(|e| {
+	let node_metrics = NodeMetrics::read(&mut &*reader).map_err(|e| {
 		log_error!(logger, "Failed to deserialize NodeMetrics: {}", e);
 		std::io::Error::new(std::io::ErrorKind::InvalidData, "Failed to deserialize NodeMetrics")
-	})
+	})?;
+
+	let legacy_latest_rgs_snapshot_timestamp = (|| {
+		let mut cursor = std::io::Cursor::new(reader.as_slice());
+		let legacy_reader = &mut cursor;
+		_init_and_read_len_prefixed_tlv_fields!(legacy_reader, {
+			(6, latest_rgs_snapshot_timestamp, option),
+		});
+		Ok(latest_rgs_snapshot_timestamp)
+	})()
+	.map_err(|e| {
+		log_error!(logger, "Failed to deserialize legacy NodeMetrics RGS state: {}", e);
+		std::io::Error::new(
+			std::io::ErrorKind::InvalidData,
+			"Failed to deserialize NodeMetrics legacy RGS state",
+		)
+	})?;
+
+	Ok((node_metrics, legacy_latest_rgs_snapshot_timestamp))
 }
 
 pub(crate) fn write_node_metrics<L: Deref>(