From 6200c113694be7df65299cf468dad93073c4dd07 Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Wed, 26 May 2021 00:11:44 +0000
Subject: [PATCH] Persist network graph

---
 src/disk.rs | 28 ++++++++++++++++++++++++++--
 src/main.rs | 26 +++++++++++++++++++++++---
 2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/src/disk.rs b/src/disk.rs
index 827cb7e..2c1834a 100644
--- a/src/disk.rs
+++ b/src/disk.rs
@@ -1,11 +1,13 @@
 use crate::cli;
 use bitcoin::secp256k1::key::PublicKey;
+use bitcoin::BlockHash;
+use lightning::routing::network_graph::NetworkGraph;
 use lightning::util::logger::{Logger, Record};
-use lightning::util::ser::Writer;
+use lightning::util::ser::{Readable, Writeable, Writer};
 use std::collections::HashMap;
 use std::fs;
 use std::fs::File;
-use std::io::{BufRead, BufReader};
+use std::io::{BufRead, BufReader, BufWriter};
 use std::net::SocketAddr;
 use std::path::Path;
 use time::OffsetDateTime;
@@ -65,3 +67,25 @@ pub(crate) fn read_channel_peer_data(
 	}
 	Ok(peer_data)
 }
+
+pub(crate) fn persist_network(path: &Path, network_graph: &NetworkGraph) -> std::io::Result<()> {
+	let mut tmp_path = path.to_path_buf().into_os_string();
+	tmp_path.push(".tmp");
+	let file = fs::OpenOptions::new().write(true).create(true).open(&tmp_path)?;
+	let write_res = network_graph.write(&mut BufWriter::new(file));
+	if let Err(e) = write_res.and_then(|_| fs::rename(&tmp_path, path)) {
+		let _ = fs::remove_file(&tmp_path);
+		Err(e)
+	} else {
+		Ok(())
+	}
+}
+
+pub(crate) fn read_network(path: &Path, genesis_hash: BlockHash) -> NetworkGraph {
+	if let Ok(file) = File::open(path) {
+		if let Ok(graph) = NetworkGraph::read(&mut BufReader::new(file)) {
+			return graph;
+		}
+	}
+	NetworkGraph::new(genesis_hash)
+}
diff --git a/src/main.rs b/src/main.rs
index 892fd0e..cba93f6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -426,13 +426,33 @@ async fn start_ldk() {
 	}
 
 	// Step 11: Optional: Initialize the NetGraphMsgHandler
-	// XXX persist routing data
 	let genesis = genesis_block(args.network).header.block_hash();
-	let router = Arc::new(NetGraphMsgHandler::new(
-		genesis,
+	let network_graph_path = format!("{}/network_graph", ldk_data_dir.clone());
+	let network_graph = disk::read_network(Path::new(&network_graph_path), genesis);
+	let router = Arc::new(NetGraphMsgHandler::from_net_graph(
 		None::<Arc<dyn chain::Access + Send + Sync>>,
 		logger.clone(),
+		network_graph,
 	));
+	let router_persist = Arc::clone(&router);
+	tokio::spawn(async move {
+		let mut interval = tokio::time::interval(Duration::from_secs(600));
+		loop {
+			interval.tick().await;
+			if disk::persist_network(
+				Path::new(&network_graph_path),
+				&*router_persist.network_graph.read().unwrap(),
+			)
+			.is_err()
+			{
+				// Persistence errors here are non-fatal as we can just fetch the routing graph
+				// again later, but they may indicate a disk error which could be fatal elsewhere.
+				eprintln!(
+					"Warning: Failed to persist network graph, check your disk and permissions"
+				);
+			}
+		}
+	});
 
 	// Step 12: Initialize the PeerManager
 	let channel_manager: Arc<ChannelManager> = Arc::new(channel_manager);
-- 
2.39.5