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

lightning/src/onion_message.rs

@@ -365,6 +365,11 @@ impl Destination {
 pub enum SendError {
 	/// Errored computing onion message packet keys.
 	Secp256k1(secp256k1::Error),
+	/// The provided [destination] was an invalid [blinded route], due to having 0 blinded hops.
+	///
+	/// [destination]: Destination
+	/// [blinded route]: BlindedRoute
+	MissingBlindedHops,
 	/// 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,
@@ -457,6 +462,11 @@ 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 {
@@ -806,6 +816,7 @@ mod tests {
 	use bitcoin::network::constants::Network;
 	use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
 
+	use core::mem;
 	use sync::Arc;
 
 	struct MessengerNode {
@@ -911,4 +922,19 @@ mod tests {
 		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);
+	}
 }