Refactor initial route finding to separate method

This will be used later in send_payment_for_bolt12_invoice instead of
find_route_and_send_payment as it will allow for returning
RetryableSendFailure when path finding fails.

Author: jkczyz

lightning/src/ln/outbound_payment.rs

@@ -925,25 +925,17 @@ impl OutboundPayments {
 			!pmt.is_awaiting_invoice())
 	}
 
-	/// Errors immediately on [`RetryableSendFailure`] error conditions. Otherwise, further errors may
-	/// be surfaced asynchronously via [`Event::PaymentPathFailed`] and [`Event::PaymentFailed`].
-	///
-	/// [`Event::PaymentPathFailed`]: crate::events::Event::PaymentPathFailed
-	/// [`Event::PaymentFailed`]: crate::events::Event::PaymentFailed
-	fn send_payment_internal<R: Deref, NS: Deref, ES: Deref, IH, SP, L: Deref>(
-		&self, payment_id: PaymentId, payment_hash: PaymentHash, recipient_onion: RecipientOnionFields,
-		keysend_preimage: Option<PaymentPreimage>, retry_strategy: Retry, mut route_params: RouteParameters,
-		router: &R, first_hops: Vec<ChannelDetails>, inflight_htlcs: IH, entropy_source: &ES,
-		node_signer: &NS, best_block_height: u32, logger: &L,
-		pending_events: &Mutex<VecDeque<(events::Event, Option<EventCompletionAction>)>>, send_payment_along_path: SP,
-	) -> Result<(), RetryableSendFailure>
+	fn find_initial_route<R: Deref, NS: Deref, IH, L: Deref>(
+		&self, payment_id: PaymentId, payment_hash: PaymentHash,
+		recipient_onion: &RecipientOnionFields, keysend_preimage: Option<PaymentPreimage>,
+		route_params: &mut RouteParameters, router: &R, first_hops: &Vec<ChannelDetails>,
+		inflight_htlcs: &IH, node_signer: &NS, best_block_height: u32, logger: &L,
+	) -> Result<Route, RetryableSendFailure>
 	where
 		R::Target: Router,
-		ES::Target: EntropySource,
 		NS::Target: NodeSigner,
 		L::Target: Logger,
 		IH: Fn() -> InFlightHtlcs,
-		SP: Fn(SendAlongPathArgs) -> Result<(), APIError>,
 	{
 		#[cfg(feature = "std")] {
 			if has_expired(&route_params) {
@@ -954,7 +946,7 @@ impl OutboundPayments {
 		}
 
 		onion_utils::set_max_path_length(
-			&mut route_params, &recipient_onion, keysend_preimage, best_block_height
+			route_params, recipient_onion, keysend_preimage, best_block_height
 		)
 			.map_err(|()| {
 				log_error!(logger, "Can't construct an onion packet without exceeding 1300-byte onion \
@@ -963,7 +955,7 @@ impl OutboundPayments {
 			})?;
 
 		let mut route = router.find_route_with_id(
-			&node_signer.get_node_id(Recipient::Node).unwrap(), &route_params,
+			&node_signer.get_node_id(Recipient::Node).unwrap(), route_params,
 			Some(&first_hops.iter().collect::<Vec<_>>()), inflight_htlcs(),
 			payment_hash, payment_id,
 		).map_err(|_| {
@@ -972,12 +964,40 @@ impl OutboundPayments {
 			RetryableSendFailure::RouteNotFound
 		})?;
 
-		if route.route_params.as_ref() != Some(&route_params) {
+		if route.route_params.as_ref() != Some(route_params) {
 			debug_assert!(false,
 				"Routers are expected to return a Route which includes the requested RouteParameters");
 			route.route_params = Some(route_params.clone());
 		}
 
+		Ok(route)
+	}
+
+	/// Errors immediately on [`RetryableSendFailure`] error conditions. Otherwise, further errors may
+	/// be surfaced asynchronously via [`Event::PaymentPathFailed`] and [`Event::PaymentFailed`].
+	///
+	/// [`Event::PaymentPathFailed`]: crate::events::Event::PaymentPathFailed
+	/// [`Event::PaymentFailed`]: crate::events::Event::PaymentFailed
+	fn send_payment_internal<R: Deref, NS: Deref, ES: Deref, IH, SP, L: Deref>(
+		&self, payment_id: PaymentId, payment_hash: PaymentHash, recipient_onion: RecipientOnionFields,
+		keysend_preimage: Option<PaymentPreimage>, retry_strategy: Retry, mut route_params: RouteParameters,
+		router: &R, first_hops: Vec<ChannelDetails>, inflight_htlcs: IH, entropy_source: &ES,
+		node_signer: &NS, best_block_height: u32, logger: &L,
+		pending_events: &Mutex<VecDeque<(events::Event, Option<EventCompletionAction>)>>, send_payment_along_path: SP,
+	) -> Result<(), RetryableSendFailure>
+	where
+		R::Target: Router,
+		ES::Target: EntropySource,
+		NS::Target: NodeSigner,
+		L::Target: Logger,
+		IH: Fn() -> InFlightHtlcs,
+		SP: Fn(SendAlongPathArgs) -> Result<(), APIError>,
+	{
+		let route = self.find_initial_route(
+			payment_id, payment_hash, &recipient_onion, keysend_preimage, &mut route_params, router,
+			&first_hops, &inflight_htlcs, node_signer, best_block_height, logger,
+		)?;
+
 		let onion_session_privs = self.add_new_pending_payment(payment_hash,
 			recipient_onion.clone(), payment_id, keysend_preimage, &route, Some(retry_strategy),
 			Some(route_params.payment_params.clone()), entropy_source, best_block_height)