Utilize ManualRoutingParameters to create new RouteParams

In addition to using PaymentParameters from the invoice, this commit
enables the creation of RouteParameters using the values optionally
set in ManualRoutingParameters.

lightning/src/ln/outbound_payment.rs

@@ -844,21 +844,19 @@ impl OutboundPayments {
 		SP: Fn(SendAlongPathArgs) -> Result<(), APIError>,
 	{
 		let payment_hash = invoice.payment_hash();
-		let max_total_routing_fee_msat;
+		let routing_params;
 		let retry_strategy;
 		match self.pending_outbound_payments.lock().unwrap().entry(payment_id) {
 			hash_map::Entry::Occupied(entry) => match entry.get() {
 				PendingOutboundPayment::AwaitingInvoice {
 					retry_strategy: retry, manual_routing_params, ..
 				} => {
 					retry_strategy = *retry;
-					max_total_routing_fee_msat = manual_routing_params.map(
-						|params| params.max_total_routing_fee_msat
-					).flatten();
+					routing_params = manual_routing_params.unwrap_or_else(|| ManualRoutingParameters::new());
 					*entry.into_mut() = PendingOutboundPayment::InvoiceReceived {
 						payment_hash,
 						retry_strategy: *retry,
-						max_total_routing_fee_msat,
+						max_total_routing_fee_msat: routing_params.max_total_routing_fee_msat,
 					};
 				},
 				_ => return Err(Bolt12PaymentError::DuplicateInvoice),
@@ -873,12 +871,10 @@ impl OutboundPayments {
 			return Err(Bolt12PaymentError::UnknownRequiredFeatures);
 		}
 
-		let mut route_params = RouteParameters::from_payment_params_and_value(
-			PaymentParameters::from_bolt12_invoice(&invoice), invoice.amount_msats()
+		let route_params = RouteParameters::from_payment_and_manual_params(
+			PaymentParameters::from_bolt12_invoice(&invoice), invoice.amount_msats(), routing_params
 		);
-		if let Some(max_fee_msat) = max_total_routing_fee_msat {
-			route_params.max_total_routing_fee_msat = Some(max_fee_msat);
-		}
+
 		self.send_payment_for_bolt12_invoice_internal(
 			payment_id, payment_hash, None, route_params, retry_strategy, router, first_hops,
 			inflight_htlcs, entropy_source, node_signer, node_id_lookup, secp_ctx, best_block_height,

lightning/src/routing/router.rs

@@ -607,6 +607,24 @@ impl RouteParameters {
 		Self { payment_params, final_value_msat, max_total_routing_fee_msat: Some(final_value_msat / 100 + 50_000) }
 	}
 
+	/// Constructs [`RouteParameters`] from the given [`PaymentParameters`], a payment amount,
+	/// and from the provided [`ManualRoutingParameters`].
+	/// 
+	/// [`Self::max_total_routing_fee_msat`] defaults to 1% of the payment amount + 50 sats
+	pub fn from_payment_and_manual_params(mut payment_params: PaymentParameters, final_value_msat: u64, manual_routing_params: ManualRoutingParameters) -> Self {
+		manual_routing_params.max_total_cltv_expiry_delta.map(|v| payment_params.max_total_cltv_expiry_delta = v);
+		manual_routing_params.max_path_count.map(|v| payment_params.max_path_count = v);
+		manual_routing_params.max_channel_saturation_power_of_half.map(|v| payment_params.max_channel_saturation_power_of_half = v);
+
+		let mut route_params = RouteParameters::from_payment_params_and_value(payment_params, final_value_msat);
+
+		manual_routing_params.max_total_routing_fee_msat.map(
+			|fee_msat| route_params.max_total_routing_fee_msat = Some(fee_msat)
+		);
+
+		route_params
+	}
+
 	/// Sets the maximum number of hops that can be included in a payment path, based on the provided
 	/// [`RecipientOnionFields`] and blinded paths.
 	pub fn set_max_path_length(