Factor invoice requests into payment path length limiting

Async payments include the original invoice request in the payment onion.
Since invreqs may include blinded paths, it's important to factor them into our
max path length calculations since they may take up a significant portion of
the 1300-byte onion.

lightning/src/ln/onion_utils.rs

@@ -320,7 +320,8 @@ pub(crate) const MIN_FINAL_VALUE_ESTIMATE_WITH_OVERPAY: u64 = 100_000_000;
 
 pub(crate) fn set_max_path_length(
 	route_params: &mut RouteParameters, recipient_onion: &RecipientOnionFields,
-	keysend_preimage: Option<PaymentPreimage>, best_block_height: u32,
+	keysend_preimage: Option<PaymentPreimage>, invoice_request: Option<&InvoiceRequest>,
+	best_block_height: u32,
 ) -> Result<(), ()> {
 	const PAYLOAD_HMAC_LEN: usize = 32;
 	let unblinded_intermed_payload_len = msgs::OutboundOnionPayload::Forward {
@@ -367,7 +368,7 @@ pub(crate) fn set_max_path_length(
 		&recipient_onion,
 		best_block_height,
 		&keysend_preimage,
-		None,
+		invoice_request,
 		|_, payload| {
 			num_reserved_bytes = num_reserved_bytes
 				.saturating_add(payload.serialized_length())

lightning/src/ln/outbound_payment.rs

@@ -932,8 +932,9 @@ impl OutboundPayments {
 			custom_tlvs: vec![],
 		};
 		let route = match self.find_initial_route(
-			payment_id, payment_hash, &recipient_onion, None, &mut route_params, router,
-			&first_hops, &inflight_htlcs, node_signer, best_block_height, logger,
+			payment_id, payment_hash, &recipient_onion, keysend_preimage, invoice_request,
+			&mut route_params, router, &first_hops, &inflight_htlcs, node_signer, best_block_height,
+			logger,
 		) {
 			Ok(route) => route,
 			Err(e) => {
@@ -1055,7 +1056,7 @@ impl OutboundPayments {
 
 					if let Err(()) = onion_utils::set_max_path_length(
 						&mut route_params, &RecipientOnionFields::spontaneous_empty(), Some(keysend_preimage),
-						best_block_height
+						Some(invreq), best_block_height
 					) {
 						abandon_with_entry!(entry, PaymentFailureReason::RouteNotFound);
 						return Err(Bolt12PaymentError::SendingFailed(RetryableSendFailure::OnionPacketSizeExceeded))
@@ -1185,8 +1186,8 @@ impl OutboundPayments {
 	}
 
 	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>,
+		&self, payment_id: PaymentId, payment_hash: PaymentHash, recipient_onion: &RecipientOnionFields,
+		keysend_preimage: Option<PaymentPreimage>, invoice_request: Option<&InvoiceRequest>,
 		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>
@@ -1205,7 +1206,7 @@ impl OutboundPayments {
 		}
 
 		onion_utils::set_max_path_length(
-			route_params, recipient_onion, keysend_preimage, best_block_height
+			route_params, recipient_onion, keysend_preimage, invoice_request, best_block_height
 		)
 			.map_err(|()| {
 				log_error!(logger, "Can't construct an onion packet without exceeding 1300-byte onion \
@@ -1253,7 +1254,7 @@ impl OutboundPayments {
 		SP: Fn(SendAlongPathArgs) -> Result<(), APIError>,
 	{
 		let route = self.find_initial_route(
-			payment_id, payment_hash, &recipient_onion, keysend_preimage, &mut route_params, router,
+			payment_id, payment_hash, &recipient_onion, keysend_preimage, None, &mut route_params, router,
 			&first_hops, &inflight_htlcs, node_signer, best_block_height, logger,
 		)?;
 

lightning/src/routing/router.rs

@@ -613,8 +613,9 @@ impl RouteParameters {
 		&mut self, recipient_onion: &RecipientOnionFields, is_keysend: bool, best_block_height: u32
 	) -> Result<(), ()> {
 		let keysend_preimage_opt = is_keysend.then(|| PaymentPreimage([42; 32]));
+		// TODO: no way to account for the invoice request here yet
 		onion_utils::set_max_path_length(
-			self, recipient_onion, keysend_preimage_opt, best_block_height
+			self, recipient_onion, keysend_preimage_opt, None, best_block_height
 		)
 	}
 }