Add a RecipientOnionFields argument to spontaneous payment sends

While most lightning nodes don't (currently) support providing a
payment secret or payment metadata for spontaneous payments,
there's no specific technical reason why we shouldn't support
sending those fields to a recipient.

Further, when we eventually move to allowing custom TLV entries in
the recipient's onion TLV stream, we'll want to support it for
spontaneous payments as well.

Here we simply add the new `RecipientOnionFields` struct as an
argument to the spontaneous payment send methods. We don't yet
plumb it through the payment sending logic, which will come when we
plumb the new struct through the sending logic to replace the
existing payment secret arguments.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -230,6 +230,10 @@ pub struct RecipientOnionFields {
 	///
 	/// If you do not have one, the [`Route`] you pay over must not contain multiple paths as
 	/// multi-path payments require a recipient-provided secret.
+	///
+	/// Note that for spontaneous payments most lightning nodes do not currently support MPP
+	/// receives, thus you should generally never be providing a secret here for spontaneous
+	/// payments.
 	pub payment_secret: Option<PaymentSecret>,
 }
 
@@ -2727,7 +2731,7 @@ where
 	/// Note that `route` must have exactly one path.
 	///
 	/// [`send_payment`]: Self::send_payment
-	pub fn send_spontaneous_payment(&self, route: &Route, payment_preimage: Option<PaymentPreimage>, payment_id: PaymentId) -> Result<PaymentHash, PaymentSendFailure> {
+	pub fn send_spontaneous_payment(&self, route: &Route, payment_preimage: Option<PaymentPreimage>, recipient_onion: RecipientOnionFields, payment_id: PaymentId) -> Result<PaymentHash, PaymentSendFailure> {
 		let best_block_height = self.best_block.read().unwrap().height();
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(&self.total_consistency_lock, &self.persistence_notifier);
 		self.pending_outbound_payments.send_spontaneous_payment_with_route(
@@ -2744,7 +2748,7 @@ where
 	/// payments.
 	///
 	/// [`PaymentParameters::for_keysend`]: crate::routing::router::PaymentParameters::for_keysend
-	pub fn send_spontaneous_payment_with_retry(&self, payment_preimage: Option<PaymentPreimage>, payment_id: PaymentId, route_params: RouteParameters, retry_strategy: Retry) -> Result<PaymentHash, RetryableSendFailure> {
+	pub fn send_spontaneous_payment_with_retry(&self, payment_preimage: Option<PaymentPreimage>, recipient_onion: RecipientOnionFields, payment_id: PaymentId, route_params: RouteParameters, retry_strategy: Retry) -> Result<PaymentHash, RetryableSendFailure> {
 		let best_block_height = self.best_block.read().unwrap().height();
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(&self.total_consistency_lock, &self.persistence_notifier);
 		self.pending_outbound_payments.send_spontaneous_payment(payment_preimage, payment_id,
@@ -8007,7 +8011,8 @@ mod tests {
 		pass_along_path(&nodes[0], &[&nodes[1]], 200_000, our_payment_hash, Some(payment_secret), events.drain(..).next().unwrap(), false, None);
 
 		// Next, send a keysend payment with the same payment_hash and make sure it fails.
-		nodes[0].node.send_spontaneous_payment(&route, Some(payment_preimage), PaymentId(payment_preimage.0)).unwrap();
+		nodes[0].node.send_spontaneous_payment(&route, Some(payment_preimage),
+			RecipientOnionFields::spontaneous_empty(), PaymentId(payment_preimage.0)).unwrap();
 		check_added_monitors!(nodes[0], 1);
 		let mut events = nodes[0].node.get_and_clear_pending_msg_events();
 		assert_eq!(events.len(), 1);
@@ -8127,7 +8132,8 @@ mod tests {
 			&nodes[0].node.get_our_node_id(), &route_params, &nodes[0].network_graph,
 			None, nodes[0].logger, &scorer, &random_seed_bytes
 		).unwrap();
-		nodes[0].node.send_spontaneous_payment(&route, Some(payment_preimage), PaymentId(payment_preimage.0)).unwrap();
+		nodes[0].node.send_spontaneous_payment(&route, Some(payment_preimage),
+			RecipientOnionFields::spontaneous_empty(), PaymentId(payment_preimage.0)).unwrap();
 		check_added_monitors!(nodes[0], 1);
 		let mut events = nodes[0].node.get_and_clear_pending_msg_events();
 		assert_eq!(events.len(), 1);
@@ -8160,7 +8166,8 @@ mod tests {
 			&nodes[0].node.get_our_node_id(), &route_params, &nodes[0].network_graph,
 			None, nodes[0].logger, &scorer, &random_seed_bytes
 		).unwrap();
-		let payment_hash = nodes[0].node.send_spontaneous_payment(&route, Some(payment_preimage), PaymentId(payment_preimage.0)).unwrap();
+		let payment_hash = nodes[0].node.send_spontaneous_payment(&route, Some(payment_preimage),
+			RecipientOnionFields::spontaneous_empty(), PaymentId(payment_preimage.0)).unwrap();
 		check_added_monitors!(nodes[0], 1);
 		let mut events = nodes[0].node.get_and_clear_pending_msg_events();
 		assert_eq!(events.len(), 1);

lightning/src/ln/functional_tests.rs

@@ -9318,7 +9318,8 @@ fn test_keysend_payments_to_public_node() {
 	let route = find_route(&payer_pubkey, &route_params, &network_graph, None, nodes[0].logger, &scorer, &random_seed_bytes).unwrap();
 
 	let test_preimage = PaymentPreimage([42; 32]);
-	let payment_hash = nodes[0].node.send_spontaneous_payment(&route, Some(test_preimage), PaymentId(test_preimage.0)).unwrap();
+	let payment_hash = nodes[0].node.send_spontaneous_payment(&route, Some(test_preimage),
+		RecipientOnionFields::spontaneous_empty(), PaymentId(test_preimage.0)).unwrap();
 	check_added_monitors!(nodes[0], 1);
 	let mut events = nodes[0].node.get_and_clear_pending_msg_events();
 	assert_eq!(events.len(), 1);
@@ -9353,7 +9354,8 @@ fn test_keysend_payments_to_private_node() {
 	).unwrap();
 
 	let test_preimage = PaymentPreimage([42; 32]);
-	let payment_hash = nodes[0].node.send_spontaneous_payment(&route, Some(test_preimage), PaymentId(test_preimage.0)).unwrap();
+	let payment_hash = nodes[0].node.send_spontaneous_payment(&route, Some(test_preimage),
+		RecipientOnionFields::spontaneous_empty(), PaymentId(test_preimage.0)).unwrap();
 	check_added_monitors!(nodes[0], 1);
 	let mut events = nodes[0].node.get_and_clear_pending_msg_events();
 	assert_eq!(events.len(), 1);

lightning/src/ln/payment_tests.rs

@@ -1079,7 +1079,8 @@ fn claimed_send_payment_idempotent() {
 
 			// Further, if we try to send a spontaneous payment with the same payment_id it should
 			// also be rejected.
-			let send_result = nodes[0].node.send_spontaneous_payment(&route, None, payment_id);
+			let send_result = nodes[0].node.send_spontaneous_payment(
+				&route, None, RecipientOnionFields::spontaneous_empty(), payment_id);
 			match send_result {
 				Err(PaymentSendFailure::DuplicatePayment) => {},
 				_ => panic!("Unexpected send result: {:?}", send_result),
@@ -1153,7 +1154,8 @@ fn abandoned_send_payment_idempotent() {
 
 			// Further, if we try to send a spontaneous payment with the same payment_id it should
 			// also be rejected.
-			let send_result = nodes[0].node.send_spontaneous_payment(&route, None, payment_id);
+			let send_result = nodes[0].node.send_spontaneous_payment(
+				&route, None, RecipientOnionFields::spontaneous_empty(), payment_id);
 			match send_result {
 				Err(PaymentSendFailure::DuplicatePayment) => {},
 				_ => panic!("Unexpected send result: {:?}", send_result),
@@ -1663,7 +1665,9 @@ fn do_automatic_retries(test: AutoRetry) {
 		pass_along_path(&nodes[0], &[&nodes[1], &nodes[2]], amt_msat, payment_hash, Some(payment_secret), msg_events.pop().unwrap(), true, None);
 		claim_payment_along_route(&nodes[0], &[&[&nodes[1], &nodes[2]]], false, payment_preimage);
 	} else if test == AutoRetry::Spontaneous {
-		nodes[0].node.send_spontaneous_payment_with_retry(Some(payment_preimage), PaymentId(payment_hash.0), route_params, Retry::Attempts(1)).unwrap();
+		nodes[0].node.send_spontaneous_payment_with_retry(Some(payment_preimage),
+			RecipientOnionFields::spontaneous_empty(), PaymentId(payment_hash.0), route_params,
+			Retry::Attempts(1)).unwrap();
 		pass_failed_attempt_with_retry_along_path!(channel_id_2, true);
 
 		// Open a new channel with liquidity on the second hop so we can find a route for the retry