Introduce RouteParametersV2 implementations

Also introduces a new set_max_path_length_v2 function that is thei
same as the original function but is for RouteParametersV2

Author: shaavan

lightning/src/ln/onion_utils.rs

@@ -16,7 +16,7 @@ use crate::ln::features::{ChannelFeatures, NodeFeatures};
 use crate::ln::msgs;
 use crate::ln::types::{PaymentHash, PaymentPreimage};
 use crate::routing::gossip::NetworkUpdate;
-use crate::routing::router::{Path, RouteHop, RouteParameters};
+use crate::routing::router::{Path, RouteHop, RouteParameters, RouteParametersV2};
 use crate::sign::NodeSigner;
 use crate::util::errors::{self, APIError};
 use crate::util::logger::Logger;
@@ -381,6 +381,74 @@ pub(crate) fn set_max_path_length(
 	Ok(())
 }
 
+pub(crate) fn set_max_path_length_v2(
+	route_params: &mut RouteParametersV2, recipient_onion: &RecipientOnionFields,
+	keysend_preimage: Option<PaymentPreimage>, best_block_height: u32,
+) -> Result<(), ()> {
+	const PAYLOAD_HMAC_LEN: usize = 32;
+	let unblinded_intermed_payload_len = msgs::OutboundOnionPayload::Forward {
+		short_channel_id: 42,
+		amt_to_forward: TOTAL_BITCOIN_SUPPLY_SATOSHIS,
+		outgoing_cltv_value: route_params.user_params.max_total_cltv_expiry_delta,
+	}
+	.serialized_length()
+	.saturating_add(PAYLOAD_HMAC_LEN);
+
+	const OVERPAY_ESTIMATE_MULTIPLER: u64 = 3;
+	let final_value_msat_with_overpay_buffer = core::cmp::max(
+		route_params.final_value_msat.saturating_mul(OVERPAY_ESTIMATE_MULTIPLER),
+		MIN_FINAL_VALUE_ESTIMATE_WITH_OVERPAY,
+	);
+
+	let blinded_tail_opt = route_params
+		.invoice_params
+		.payee
+		.blinded_route_hints()
+		.iter()
+		.max_by_key(|path| path.inner_blinded_path().serialized_length())
+		.map(|largest_path| BlindedTailHopIter {
+			hops: largest_path.blinded_hops().iter(),
+			blinding_point: largest_path.blinding_point(),
+			final_value_msat: final_value_msat_with_overpay_buffer,
+			excess_final_cltv_expiry_delta: 0,
+		});
+
+	let unblinded_route_hop = RouteHop {
+		pubkey: PublicKey::from_slice(&[2; 33]).unwrap(),
+		node_features: NodeFeatures::empty(),
+		short_channel_id: 42,
+		channel_features: ChannelFeatures::empty(),
+		fee_msat: final_value_msat_with_overpay_buffer,
+		cltv_expiry_delta: route_params.user_params.max_total_cltv_expiry_delta,
+		maybe_announced_channel: false,
+	};
+	let mut num_reserved_bytes: usize = 0;
+	let build_payloads_res = build_onion_payloads_callback(
+		core::iter::once(&unblinded_route_hop),
+		blinded_tail_opt,
+		final_value_msat_with_overpay_buffer,
+		&recipient_onion,
+		best_block_height,
+		&keysend_preimage,
+		|_, payload| {
+			num_reserved_bytes = num_reserved_bytes
+				.saturating_add(payload.serialized_length())
+				.saturating_add(PAYLOAD_HMAC_LEN);
+		},
+	);
+	debug_assert!(build_payloads_res.is_ok());
+
+	let max_path_length = 1300usize
+		.checked_sub(num_reserved_bytes)
+		.map(|p| p / unblinded_intermed_payload_len)
+		.and_then(|l| u8::try_from(l.saturating_add(1)).ok())
+		.ok_or(())?;
+
+	route_params.user_params.max_path_length =
+		core::cmp::min(max_path_length, route_params.user_params.max_path_length);
+	Ok(())
+}
+
 /// Length of the onion data packet. Before TLV-based onions this was 20 65-byte hops, though now
 /// the hops can be of variable length.
 pub(crate) const ONION_DATA_LEN: usize = 20 * 65;

lightning/src/routing/router.rs

@@ -998,9 +998,25 @@ impl Readable for RouteParametersV2 {
 }
 
 impl RouteParametersV2 {
-	// TODO: Introduce a function parallel to fn from_payment_params_and_value.
+	/// Constructs [`RouteParameters`] from the given [`PaymentParameters`] and a payment amount.
+	///
+	/// [`Self::max_total_routing_fee_msat`] defaults to 1% of the payment amount + 50 sats
+	pub fn from_params_and_value(mut user_params: UserParameters, invoice_params: InvoiceParameters, final_value_msat: u64) -> Self {
+		user_params.max_total_routing_fee_msat.get_or_insert_with(|| final_value_msat / 100 + 50_000);
 
-	// TODO: Introduce fn set_max_path_length(). First create onion_utils::set_max_path_length_v2
+		Self { user_params, invoice_params, final_value_msat }
+	}
+
+	/// 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(
+		&mut self, recipient_onion: &RecipientOnionFields, is_keysend: bool, best_block_height: u32
+	) -> Result<(), ()> {
+		let keysend_preimage_opt = is_keysend.then(|| PaymentPreimage([42; 32]));
+		onion_utils::set_max_path_length_v2(
+			self, recipient_onion, keysend_preimage_opt, best_block_height
+		)
+	}
 }
 
 #[derive(Clone, Copy)]