Add a send_spontaneous_payment_probe method

We add the capability to send a payment probe given an amount and a
payee node id.

Author: tnull

bindings/ldk_node.udl

@@ -74,6 +74,8 @@ interface LDKNode {
 	[Throws=NodeError]
 	void send_payment_probe([ByRef]Invoice invoice);
 	[Throws=NodeError]
+	void send_spontaneous_payment_probe(u64 amount_msat, PublicKey node_id);
+	[Throws=NodeError]
 	Invoice receive_payment(u64 amount_msat, [ByRef]string description, u32 expiry_secs);
 	[Throws=NodeError]
 	Invoice receive_variable_amount_payment([ByRef]string description, u32 expiry_secs);

src/lib.rs

@@ -1322,6 +1322,29 @@ impl<K: KVStore + Sync + Send + 'static> Node<K> {
 		self.send_payment_probe_internal(route_params)
 	}
 
+	/// Sends payment probes over all paths of a route that would be used to pay the given
+	/// amount to the given `node_id`.
+	///
+	/// This may be used to send "pre-flight" probes, i.e., to train our scorer before conducting
+	/// the actual payment. Note this is only useful if there likely is sufficient time for the
+	/// probe to settle before sending out the actual payment, e.g., when waiting for user
+	/// confirmation in a wallet UI.
+	pub fn send_spontaneous_payment_probe(
+		&self, amount_msat: u64, node_id: PublicKey,
+	) -> Result<(), Error> {
+		let rt_lock = self.runtime.read().unwrap();
+		if rt_lock.is_none() {
+			return Err(Error::NotRunning);
+		}
+
+		let payment_params =
+			PaymentParameters::from_node_id(node_id, self.config.default_cltv_expiry_delta);
+
+		let route_params = RouteParameters { payment_params, final_value_msat: amount_msat };
+
+		self.send_payment_probe_internal(route_params)
+	}
+
 	fn send_payment_probe_internal(&self, route_params: RouteParameters) -> Result<(), Error> {
 		let payer = self.channel_manager.get_our_node_id();
 		let first_hops = self.channel_manager.list_usable_channels();