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

lightning/src/onion_message/functional_tests.rs

@@ -17,6 +17,7 @@ use util::test_utils;
 use bitcoin::network::constants::Network;
 use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
 
+use core::mem;
 use sync::Arc;
 
 struct MessengerNode {
@@ -123,3 +124,18 @@ 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(vec![node2.get_node_pk(), node3.get_node_pk()], &node3.keys_manager, &secp_ctx).unwrap();
+	let mut empty_hops = Vec::new();
+	mem::swap(&mut empty_hops, &mut blinded_route.blinded_hops);
+
+	let err = node1.messenger.send_onion_message(vec![], Destination::BlindedRoute(blinded_route)).unwrap_err();
+	assert_eq!(err, SendError::MissingBlindedHops);
+}

lightning/src/onion_message/messenger.rs

@@ -118,6 +118,11 @@ 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 [blinded route], due to having 0 blinded hops.
+	///
+	/// [destination]: Destination
+	/// [blinded route]: super::blinded_route::BlindedRoute
+	MissingBlindedHops,
 }
 
 impl<Signer: Sign, K: Deref, L: Deref> OnionMessenger<Signer, K, L>
@@ -139,6 +144,11 @@ impl<Signer: Sign, K: Deref, L: Deref> OnionMessenger<Signer, K, L>
 
 	/// Send an empty onion message to `destination`, routing it through `intermediate_nodes`.
 	pub fn send_onion_message(&self, intermediate_nodes: Vec<PublicKey>, destination: Destination) -> Result<(), SendError> {
+		if let Destination::BlindedRoute(BlindedRoute { ref blinded_hops, .. }) = destination {
+			if blinded_hops.len() == 0 {
+				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 {