Error when attempting to send an OM to a blinded route with 0 hops

Author: valentinewallace

lightning/src/onion_message/functional_tests.rs

@@ -119,3 +119,17 @@ fn too_big_packet_error() {
 	let err = nodes[0].messenger.send_onion_message(&hops, Destination::Node(hop_node_id)).unwrap_err();
 	assert_eq!(err, SendError::TooBigPacket);
 }
+
+#[test]
+fn invalid_blinded_route_error() {
+	// Make sure we error as expected if a provided blinded route has 0 hops.
+	let mut nodes = create_nodes(3);
+	let (node1, node2, node3) = (nodes.remove(0), nodes.remove(0), nodes.remove(0));
+
+	let secp_ctx = Secp256k1::new();
+	let mut blinded_route = BlindedRoute::new::<EnforcingSigner, _, _>(&[node2.get_node_pk(), node3.get_node_pk()], &*node3.keys_manager, &secp_ctx).unwrap();
+	blinded_route.blinded_hops.clear();
+
+	let err = node1.messenger.send_onion_message(&[], Destination::BlindedRoute(blinded_route)).unwrap_err();
+	assert_eq!(err, SendError::MissingBlindedHops);
+}

lightning/src/onion_message/messenger.rs

@@ -118,6 +118,8 @@ pub enum SendError {
 	/// Because implementations such as Eclair will drop onion messages where the message packet
 	/// exceeds 32834 bytes, we refuse to send messages where the packet exceeds this size.
 	TooBigPacket,
+	/// The provided [Destination] was an invalid [super::BlindedRoute], due to having 0 blinded hops.
+	MissingBlindedHops,
 }
 
 impl<Signer: Sign, K: Deref, L: Deref> OnionMessenger<Signer, K, L>
@@ -140,6 +142,11 @@ impl<Signer: Sign, K: Deref, L: Deref> OnionMessenger<Signer, K, L>
 	/// Send an empty onion message to `destination`, routing it through `intermediate_nodes`.
 	/// See [`OnionMessenger`] for example usage.
 	pub fn send_onion_message(&self, intermediate_nodes: &[PublicKey], destination: Destination) -> Result<(), SendError> {
+		if let Destination::BlindedRoute(BlindedRoute { ref blinded_hops, .. }) = destination {
+			if blinded_hops.is_empty() {
+				return Err(SendError::MissingBlindedHops);
+			}
+		}
 		let blinding_secret_bytes = self.keys_manager.get_secure_random_bytes();
 		let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
 		let (introduction_node_id, blinding_point) = if intermediate_nodes.len() != 0 {