Only allow creating 1-hop blinded paths.

Useful until forwarding and receiving to multi-hop blinded paths is supported.

Author: valentinewallace

lightning/src/blinded_path/mod.rs

@@ -76,6 +76,19 @@ impl BlindedPath {
 		})
 	}
 
+	/// Create a one-hop blinded path for a payment.
+	pub fn one_hop_for_payment<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>(
+		payee_node_id: PublicKey, payee_tlvs: payment::ReceiveTlvs, entropy_source: &ES,
+		secp_ctx: &Secp256k1<T>
+	) -> Result<(BlindedPayInfo, Self), ()> {
+		// This value is not considered in pathfinding for 1-hop blinded paths, because it's intended to
+		// be in relation to a specific channel.
+		let htlc_maximum_msat = u64::max_value();
+		Self::new_for_payment(
+			&[], payee_node_id, payee_tlvs, htlc_maximum_msat, entropy_source, secp_ctx
+		)
+	}
+
 	/// Create a blinded path for a payment, to be forwarded along `intermediate_nodes`.
 	///
 	/// Errors if:
@@ -85,7 +98,7 @@ impl BlindedPath {
 	///
 	/// [`ForwardTlvs`]: crate::blinded_path::payment::ForwardTlvs
 	//  TODO: make all payloads the same size with padding + add dummy hops
-	pub fn new_for_payment<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>(
+	pub(crate) fn new_for_payment<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>(
 		intermediate_nodes: &[payment::ForwardNode], payee_node_id: PublicKey,
 		payee_tlvs: payment::ReceiveTlvs, htlc_maximum_msat: u64, entropy_source: &ES,
 		secp_ctx: &Secp256k1<T>

lightning/src/ln/blinded_payment_tests.rs

@@ -43,9 +43,8 @@ fn do_one_hop_blinded_path(success: bool) {
 		},
 	};
 	let mut secp_ctx = Secp256k1::new();
-	let blinded_path = BlindedPath::new_for_payment(
-		&[], nodes[1].node.get_our_node_id(), payee_tlvs, chan_upd.htlc_maximum_msat,
-		&chanmon_cfgs[1].keys_manager, &secp_ctx
+	let blinded_path = BlindedPath::one_hop_for_payment(
+		nodes[1].node.get_our_node_id(), payee_tlvs, &chanmon_cfgs[1].keys_manager, &secp_ctx
 	).unwrap();
 
 	let route_params = RouteParameters {
@@ -85,9 +84,8 @@ fn mpp_to_one_hop_blinded_path() {
 			htlc_minimum_msat: chan_upd_1_3.htlc_minimum_msat,
 		},
 	};
-	let blinded_path = BlindedPath::new_for_payment(
-		&[], nodes[3].node.get_our_node_id(), payee_tlvs, u64::max_value(),
-		&chanmon_cfgs[3].keys_manager, &secp_ctx
+	let blinded_path = BlindedPath::one_hop_for_payment(
+		nodes[3].node.get_our_node_id(), payee_tlvs, &chanmon_cfgs[3].keys_manager, &secp_ctx
 	).unwrap();
 
 	let bolt12_features: Bolt12InvoiceFeatures =