Prefer one-hop blinded path to Tor intro nodes

If a node is announced, prefer using a one-hop blinded path with it as
the introduction node to using a two-hop blinded path with a Tor-only
introduction node. The one-hop blinded path is more reliable, thus only
use Tor-only nodes if the recipient is unannounced. And then, prefer
non-Tor-only nodes.

Author: jkczyz

lightning/src/ln/offers_tests.rs

@@ -250,7 +250,7 @@ fn prefers_non_tor_nodes_in_blinded_paths() {
 	disconnect_peers(david, &[bob, &nodes[4], &nodes[5]]);
 
 	let tor = SocketAddress::OnionV2([255, 254, 253, 252, 251, 250, 249, 248, 247, 246, 38, 7]);
-	announce_node_address(charlie, &[alice, bob, david, &nodes[4], &nodes[5]], tor);
+	announce_node_address(charlie, &[alice, bob, david, &nodes[4], &nodes[5]], tor.clone());
 
 	let offer = bob.node
 		.create_offer_builder("coffee".to_string()).unwrap()
@@ -259,8 +259,23 @@ fn prefers_non_tor_nodes_in_blinded_paths() {
 	assert_ne!(offer.signing_pubkey(), bob_id);
 	assert!(!offer.paths().is_empty());
 	for path in offer.paths() {
+		assert_ne!(path.introduction_node_id, bob_id);
 		assert_ne!(path.introduction_node_id, charlie_id);
 	}
+
+	// Use a one-hop blinded path when Bob is announced and all his peers are Tor-only.
+	announce_node_address(&nodes[4], &[alice, bob, charlie, david, &nodes[5]], tor.clone());
+	announce_node_address(&nodes[5], &[alice, bob, charlie, david, &nodes[4]], tor.clone());
+
+	let offer = bob.node
+		.create_offer_builder("coffee".to_string()).unwrap()
+		.amount_msats(10_000_000)
+		.build().unwrap();
+	assert_ne!(offer.signing_pubkey(), bob_id);
+	assert!(!offer.paths().is_empty());
+	for path in offer.paths() {
+		assert_eq!(path.introduction_node_id, bob_id);
+	}
 }
 
 /// Checks that blinded paths prefer an introduction node that is the most connected.

lightning/src/onion_message/messenger.rs

@@ -358,6 +358,9 @@ where
 		const MIN_PEER_CHANNELS: usize = 3;
 
 		let network_graph = self.network_graph.deref().read_only();
+		let is_recipient_announced =
+			network_graph.nodes().contains_key(&NodeId::from_pubkey(&recipient));
+
 		let mut peer_info = peers.iter()
 			// Limit to peers with announced channels
 			.filter_map(|pubkey|
@@ -366,6 +369,8 @@ where
 					.filter(|info| info.channels.len() >= MIN_PEER_CHANNELS)
 					.map(|info| (*pubkey, info.is_tor_only(), info.channels.len()))
 			)
+			// Exclude Tor-only nodes when the recipient is announced.
+			.filter(|(_, is_tor_only, _)| !(*is_tor_only && is_recipient_announced))
 			.collect::<Vec<_>>();
 
 		// Prefer using non-Tor nodes with the most channels as the introduction node.
@@ -382,7 +387,7 @@ where
 		match paths {
 			Ok(paths) if !paths.is_empty() => Ok(paths),
 			_ => {
-				if network_graph.nodes().contains_key(&NodeId::from_pubkey(&recipient)) {
+				if is_recipient_announced {
 					BlindedPath::one_hop_for_message(recipient, &*self.entropy_source, secp_ctx)
 						.map(|path| vec![path])
 				} else {