Static invoice server: treat forwarded invoice requests as onion message forwards

fuzz/src/onion_message.rs

@@ -102,7 +102,7 @@ impl MessageRouter for TestMessageRouter {
 	fn find_path(
 		&self, _sender: PublicKey, _peers: Vec<PublicKey>, destination: Destination,
 	) -> Result<OnionMessagePath, ()> {
-		Ok(OnionMessagePath { intermediate_nodes: vec![], destination, first_node_addresses: None })
+		Ok(OnionMessagePath { intermediate_nodes: vec![], destination, first_node_addresses: vec![] })
 	}
 
 	fn create_blinded_paths<T: secp256k1::Signing + secp256k1::Verification>(
@@ -430,7 +430,7 @@ mod tests {
 		super::do_test(&<Vec<u8>>::from_hex(two_unblinded_hops_om).unwrap(), &logger);
 		{
 			let log_entries = logger.lines.lock().unwrap();
-			assert_eq!(log_entries.get(&("lightning::onion_message::messenger".to_string(), "Forwarding an onion message to peer 020202020202020202020202020202020202020202020202020202020202020202".to_string())), Some(&1));
+			assert_eq!(log_entries.get(&("lightning::onion_message::messenger".to_string(), "Forwarding an onion message to peer 020202020202020202020202020202020202020202020202020202020202020202 when forwarding peeled onion message from 020000000000000000000000000000000000000000000000000000000000000002".to_string())), Some(&1));
 		}
 
 		let two_unblinded_two_blinded_om = "\
@@ -471,7 +471,7 @@ mod tests {
 		super::do_test(&<Vec<u8>>::from_hex(two_unblinded_two_blinded_om).unwrap(), &logger);
 		{
 			let log_entries = logger.lines.lock().unwrap();
-			assert_eq!(log_entries.get(&("lightning::onion_message::messenger".to_string(), "Forwarding an onion message to peer 020202020202020202020202020202020202020202020202020202020202020202".to_string())), Some(&1));
+			assert_eq!(log_entries.get(&("lightning::onion_message::messenger".to_string(), "Forwarding an onion message to peer 020202020202020202020202020202020202020202020202020202020202020202 when forwarding peeled onion message from 020000000000000000000000000000000000000000000000000000000000000002".to_string())), Some(&1));
 		}
 
 		let three_blinded_om = "\
@@ -512,7 +512,7 @@ mod tests {
 		super::do_test(&<Vec<u8>>::from_hex(three_blinded_om).unwrap(), &logger);
 		{
 			let log_entries = logger.lines.lock().unwrap();
-			assert_eq!(log_entries.get(&("lightning::onion_message::messenger".to_string(), "Forwarding an onion message to peer 020202020202020202020202020202020202020202020202020202020202020202".to_string())), Some(&1));
+			assert_eq!(log_entries.get(&("lightning::onion_message::messenger".to_string(), "Forwarding an onion message to peer 020202020202020202020202020202020202020202020202020202020202020202 when forwarding peeled onion message from 020000000000000000000000000000000000000000000000000000000000000002".to_string())), Some(&1));
 		}
 	}
 }

lightning-dns-resolver/src/lib.rs

@@ -222,7 +222,7 @@ mod test {
 		) -> Result<OnionMessagePath, ()> {
 			Ok(OnionMessagePath {
 				destination,
-				first_node_addresses: None,
+				first_node_addresses: Vec::new(),
 				intermediate_nodes: Vec::new(),
 			})
 		}

lightning/src/events/mod.rs

@@ -972,7 +972,9 @@ pub enum Event {
 	ConnectionNeeded {
 		/// The node id for the node needing a connection.
 		node_id: PublicKey,
-		/// Sockets for connecting to the node.
+		/// Sockets for connecting to the node, if available. We don't require these addresses to be
+		/// present in case the node id corresponds to a known peer that is offline and can be awoken,
+		/// such as via the LSPS5 protocol.
 		addresses: Vec<msgs::SocketAddress>,
 	},
 	/// Indicates a [`Bolt12Invoice`] in response to an [`InvoiceRequest`] or a [`Refund`] was
@@ -1617,6 +1619,9 @@ pub enum Event {
 	/// `OnionMessenger` was initialized with
 	/// [`OnionMessenger::new_with_offline_peer_interception`], see its docs.
 	///
+	/// The offline peer should be awoken if possible on receipt of this event, such as via the LSPS5
+	/// protocol.
+	///
 	/// # Failure Behavior and Persistence
 	/// This event will eventually be replayed after failures-to-handle (i.e., the event handler
 	/// returning `Err(ReplayEvent ())`), but won't be persisted across restarts.
@@ -1661,6 +1666,14 @@ pub enum Event {
 		/// recipient is online to provide a new invoice. This path should be persisted and
 		/// later provided to [`ChannelManager::respond_to_static_invoice_request`].
 		///
+		/// This path's [`BlindedMessagePath::introduction_node`] MUST be set to our node or one of our
+		/// peers. This is because, for DoS protection, invoice requests forwarded over this path are
+		/// treated by our node like any other onion message forward and will not generate
+		/// [`Event::ConnectionNeeded`] if the first hop in the path is not our peer.
+		///
+		/// If the next-hop peer in the path is offline, if configured to do so we will generate an
+		/// [`Event::OnionMessageIntercepted`] for the invoice request.
+		///
 		/// [`ChannelManager::respond_to_static_invoice_request`]: crate::ln::channelmanager::ChannelManager::respond_to_static_invoice_request
 		invoice_request_path: BlindedMessagePath,
 		/// Useful for the recipient to replace a specific invoice stored by us as the static invoice

lightning/src/ln/async_payments_tests.rs

@@ -2887,6 +2887,21 @@ fn async_payment_e2e() {
 		.into_iter()
 		.find_map(|ev| {
 			if let Event::OnionMessageIntercepted { message, .. } = ev {
+				// At least one of the intercepted onion messages will be an invoice request that the
+				// invoice server is attempting to forward to the recipient, ignore that as we're testing
+				// the static invoice flow
+				let peeled_onion = recipient.onion_messenger.peel_onion_message(&message).unwrap();
+				if matches!(
+					peeled_onion,
+					PeeledOnion::Offers(OffersMessage::InvoiceRequest { .. }, _, _)
+				) {
+					return None;
+				}
+
+				assert!(matches!(
+					peeled_onion,
+					PeeledOnion::AsyncPayments(AsyncPaymentsMessage::HeldHtlcAvailable(_), _, _)
+				));
 				Some(message)
 			} else {
 				None

lightning/src/offers/flow.rs

@@ -1169,9 +1169,9 @@ where
 	) {
 		let mut pending_offers_messages = self.pending_offers_messages.lock().unwrap();
 		let message = OffersMessage::InvoiceRequest(invoice_request);
-		let instructions = MessageSendInstructions::WithSpecifiedReplyPath {
+		let instructions = MessageSendInstructions::ForwardedMessage {
 			destination: Destination::BlindedPath(destination),
-			reply_path: reply_path.into_blinded_path(),
+			reply_path: Some(reply_path.into_blinded_path()),
 		};
 		pending_offers_messages.push((message, instructions));
 	}

lightning/src/onion_message/async_payments.rs

@@ -169,6 +169,11 @@ pub struct ServeStaticInvoice {
 	/// [`Bolt12Invoice`] if the recipient is online at the time. Use this path to forward the
 	/// [`InvoiceRequest`] to the async recipient.
 	///
+	/// This path's [`BlindedMessagePath::introduction_node`] MUST be set to the static invoice server
+	/// node or one of its peers. This is because, for DoS protection, invoice requests forwarded over
+	/// this path are treated by the server node like any other onion message forward and the server
+	/// will not directly connect to the introduction node if they are not already peers.
+	///
 	/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
 	/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
 	pub forward_invoice_request_path: BlindedMessagePath,

lightning/src/onion_message/functional_tests.rs

@@ -419,7 +419,7 @@ fn two_unblinded_hops() {
 	let path = OnionMessagePath {
 		intermediate_nodes: vec![nodes[1].node_id],
 		destination: Destination::Node(nodes[2].node_id),
-		first_node_addresses: None,
+		first_node_addresses: Vec::new(),
 	};
 
 	nodes[0].messenger.send_onion_message_using_path(path, test_msg, None).unwrap();
@@ -494,7 +494,7 @@ fn two_unblinded_two_blinded() {
 	let path = OnionMessagePath {
 		intermediate_nodes: vec![nodes[1].node_id, nodes[2].node_id],
 		destination: Destination::BlindedPath(blinded_path),
-		first_node_addresses: None,
+		first_node_addresses: Vec::new(),
 	};
 
 	nodes[0].messenger.send_onion_message_using_path(path, test_msg, None).unwrap();
@@ -660,7 +660,7 @@ fn too_big_packet_error() {
 	let path = OnionMessagePath {
 		intermediate_nodes: hops,
 		destination: Destination::Node(hop_node_id),
-		first_node_addresses: None,
+		first_node_addresses: Vec::new(),
 	};
 	let err = nodes[0].messenger.send_onion_message_using_path(path, test_msg, None).unwrap_err();
 	assert_eq!(err, SendError::TooBigPacket);
@@ -822,7 +822,7 @@ fn reply_path() {
 	let path = OnionMessagePath {
 		intermediate_nodes: vec![nodes[1].node_id, nodes[2].node_id],
 		destination: Destination::Node(nodes[3].node_id),
-		first_node_addresses: None,
+		first_node_addresses: Vec::new(),
 	};
 	let intermediate_nodes = [
 		MessageForwardNode { node_id: nodes[2].node_id, short_channel_id: None },
@@ -959,7 +959,7 @@ fn many_hops() {
 	let path = OnionMessagePath {
 		intermediate_nodes,
 		destination: Destination::Node(nodes[num_nodes - 1].node_id),
-		first_node_addresses: None,
+		first_node_addresses: Vec::new(),
 	};
 	nodes[0].messenger.send_onion_message_using_path(path, test_msg, None).unwrap();
 	nodes[num_nodes - 1].custom_message_handler.expect_message(TestCustomMessage::Pong);
@@ -1012,6 +1012,29 @@ fn requests_peer_connection_for_buffered_messages() {
 	connect_peers(&nodes[0], &nodes[1]);
 	assert!(nodes[0].messenger.next_onion_message_for_peer(nodes[1].node_id).is_some());
 	assert!(nodes[0].messenger.next_onion_message_for_peer(nodes[1].node_id).is_none());
+
+	// Buffer an onion message for a disconnected node who is not in the network graph.
+	disconnect_peers(&nodes[0], &nodes[2]);
+
+	let message = TestCustomMessage::Ping;
+	let destination = Destination::Node(nodes[2].node_id);
+	let instructions = MessageSendInstructions::WithoutReplyPath { destination };
+	nodes[0].messenger.send_onion_message(message.clone(), instructions.clone()).unwrap();
+
+	// Check that a ConnectionNeeded event for the peer is provided
+	let events = release_events(&nodes[0]);
+	assert_eq!(events.len(), 1);
+	match &events[0] {
+		Event::ConnectionNeeded { node_id, addresses } => {
+			assert_eq!(*node_id, nodes[2].node_id);
+			assert!(addresses.is_empty());
+		},
+		e => panic!("Unexpected event: {:?}", e),
+	}
+
+	// Release the buffered onion message when reconnected
+	connect_peers(&nodes[0], &nodes[2]);
+	assert!(nodes[0].messenger.next_onion_message_for_peer(nodes[2].node_id).is_some());
 }
 
 #[test]