Include a one-hop blinded path in Offer and Refund

While this doesn't add much privacy over not including any blinded
paths, it allows us to exercise code for receiving on blinded paths.

Author: jkczyz

lightning/src/blinded_path/mod.rs

@@ -57,7 +57,7 @@ pub struct BlindedHop {
 
 impl BlindedPath {
 	/// Create a one-hop blinded path for a message.
-	pub fn one_hop_for_message<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>(
+	pub fn one_hop_for_message<ES: EntropySource + ?Sized, T: secp256k1::Signing + secp256k1::Verification>(
 		recipient_node_id: PublicKey, entropy_source: &ES, secp_ctx: &Secp256k1<T>
 	) -> Result<Self, ()> {
 		Self::new_for_message(&[recipient_node_id], entropy_source, secp_ctx)
@@ -68,7 +68,7 @@ impl BlindedPath {
 	///
 	/// Errors if less than one hop is provided or if `node_pk`(s) are invalid.
 	//  TODO: make all payloads the same size with padding + add dummy hops
-	pub fn new_for_message<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>(
+	pub fn new_for_message<ES: EntropySource + ?Sized, T: secp256k1::Signing + secp256k1::Verification>(
 		node_pks: &[PublicKey], entropy_source: &ES, secp_ctx: &Secp256k1<T>
 	) -> Result<Self, ()> {
 		if node_pks.is_empty() { return Err(()) }

lightning/src/ln/channelmanager.rs

@@ -30,6 +30,7 @@ use bitcoin::secp256k1::{SecretKey,PublicKey};
 use bitcoin::secp256k1::Secp256k1;
 use bitcoin::{LockTime, secp256k1, Sequence};
 
+use crate::blinded_path::BlindedPath;
 use crate::chain;
 use crate::chain::{Confirm, ChannelMonitorUpdateStatus, Watch, BestBlock};
 use crate::chain::chaininterface::{BroadcasterInterface, ConfirmationTarget, FeeEstimator, LowerBoundedFeeEstimator};
@@ -6824,6 +6825,9 @@ where
 	/// Creates an [`OfferBuilder`] such that the [`Offer`] it builds is recognized by the
 	/// [`ChannelManager`] when handling [`InvoiceRequest`] messages for the offer.
 	///
+	/// Uses a one-hop [`BlindedPath`] for the offer with [`ChannelManager::get_our_node_id`] as the
+	/// introduction node and a derived signing pubkey for recipient privacy.
+	///
 	/// [`Offer`]: crate::offers::offer::Offer
 	/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
 	pub fn create_offer_builder(
@@ -6833,16 +6837,20 @@ where
 		let expanded_key = &self.inbound_payment_key;
 		let entropy = &*self.entropy_source;
 		let secp_ctx = &self.secp_ctx;
+		let path = self.create_one_hop_blinded_path();
 
-		// TODO: Set blinded paths
 		OfferBuilder::deriving_signing_pubkey(description, node_id, expanded_key, entropy, secp_ctx)
+			.path(path)
 	}
 
 	/// Creates a [`RefundBuilder`] such that the [`Refund`] it builds is recognized by the
 	/// [`ChannelManager`] when handling [`Bolt12Invoice`] messages for the refund.
 	///
 	/// The provided `payment_id` is used to ensure that only one invoice is paid for the refund.
 	///
+	/// Uses a one-hop [`BlindedPath`] for the refund with [`ChannelManager::get_our_node_id`] as
+	/// the introduction node and a derived payer id for sender privacy.
+	///
 	/// [`Refund`]: crate::offers::refund::Refund
 	/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
 	pub fn create_refund_builder(
@@ -6852,11 +6860,12 @@ where
 		let expanded_key = &self.inbound_payment_key;
 		let entropy = &*self.entropy_source;
 		let secp_ctx = &self.secp_ctx;
+		let path = self.create_one_hop_blinded_path();
 
-		// TODO: Set blinded paths
 		let builder = RefundBuilder::deriving_payer_id(
 			description, node_id, expanded_key, entropy, secp_ctx, amount_msats, payment_id
-		)?;
+		)?.path(path);
+
 		self.pending_outbound_payments
 			.add_new_awaiting_invoice(payment_id, retry_strategy)
 			.map_err(|_| Bolt12SemanticError::DuplicatePaymentId)?;
@@ -6964,6 +6973,15 @@ where
 		inbound_payment::get_payment_preimage(payment_hash, payment_secret, &self.inbound_payment_key)
 	}
 
+	/// Creates a one-hop blinded path with [`ChannelManager::get_our_node_id`] as the introduction
+	/// node.
+	fn create_one_hop_blinded_path(&self) -> BlindedPath {
+		let entropy_source = self.entropy_source.deref();
+		let secp_ctx = &self.secp_ctx;
+		BlindedPath::one_hop_for_message(self.get_our_node_id(), entropy_source, secp_ctx).unwrap()
+
+	}
+
 	/// Gets a fake short channel id for use in receiving [phantom node payments]. These fake scids
 	/// are used when constructing the phantom invoice's route hints.
 	///

lightning/src/routing/router.rs

@@ -90,6 +90,7 @@ pub trait Router {
 		&self, payer: &PublicKey, route_params: &RouteParameters,
 		first_hops: Option<&[&ChannelDetails]>, inflight_htlcs: InFlightHtlcs
 	) -> Result<Route, LightningError>;
+
 	/// Finds a [`Route`] for a payment between the given `payer` and a payee.
 	///
 	/// The `payee` and the payment's value are given in [`RouteParameters::payment_params`]