Update create_refund_builder to use create_blinded_paths

Aligned the `create_refund_builder` logic with
`create_offer_builder` by updating it to use `create_blinded_paths`.

Now that custom routers can be passed via
`create_refund_builder_using_router`, the default builder can
consistently generate full-length blinded paths without branching
logic.
This simplifies the default behavior while keeping flexibility
available for custom use cases.

Author: shaavan

lightning/src/ln/channelmanager.rs

@@ -8095,7 +8095,7 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 
 		let per_peer_state = self.per_peer_state.read().unwrap();
 		let peer_state_mutex = per_peer_state.get(counterparty_node_id)
-		    .ok_or_else(|| {
+			.ok_or_else(|| {
 				debug_assert!(false);
 				MsgHandleErrInternal::send_err_msg_no_close(
 					format!("Can't find a peer matching the passed counterparty node_id {}", counterparty_node_id),
@@ -10172,6 +10172,28 @@ impl Default for Bolt11InvoiceParameters {
 }
 
 macro_rules! create_offer_builder { ($self: ident, $builder: ty) => {
+	fn create_offer_builder_intern<PF>(&$self, make_path: PF) -> Result<$builder, Bolt12SemanticError>
+	where
+		PF: FnOnce(PublicKey, MessageContext, &secp256k1::Secp256k1<secp256k1::All>) -> Result<Option<BlindedMessagePath>, Bolt12SemanticError>,
+	{
+		let node_id = $self.get_our_node_id();
+		let expanded_key = &$self.inbound_payment_key;
+		let entropy = &*$self.entropy_source;
+		let secp_ctx = &$self.secp_ctx;
+
+		let nonce = Nonce::from_entropy_source(entropy);
+		let context = MessageContext::Offers(OffersContext::InvoiceRequest { nonce });
+
+		let mut builder = OfferBuilder::deriving_signing_pubkey(node_id, expanded_key, nonce, secp_ctx)
+			.chain_hash($self.chain_hash);
+
+		if let Some(path) = make_path(node_id, context, secp_ctx)? {
+			builder = builder.path(path)
+		}
+
+		Ok(builder.into())
+	}
+
 	/// Creates an [`OfferBuilder`] such that the [`Offer`] it builds is recognized by the
 	/// [`ChannelManager`] when handling [`InvoiceRequest`] messages for the offer. The offer's
 	/// expiration will be `absolute_expiry` if `Some`, otherwise it will not expire.
@@ -10196,21 +10218,12 @@ macro_rules! create_offer_builder { ($self: ident, $builder: ty) => {
 	/// [`Offer`]: crate::offers::offer::Offer
 	/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
 	pub fn create_offer_builder(&$self) -> Result<$builder, Bolt12SemanticError> {
-		let node_id = $self.get_our_node_id();
-		let expanded_key = &$self.inbound_payment_key;
-		let entropy = &*$self.entropy_source;
-		let secp_ctx = &$self.secp_ctx;
-
-		let nonce = Nonce::from_entropy_source(entropy);
-		let context = MessageContext::Offers(OffersContext::InvoiceRequest { nonce });
-		let path = $self.create_blinded_paths(context)
-			.and_then(|paths| paths.into_iter().next().ok_or(()))
-			.map_err(|_| Bolt12SemanticError::MissingPaths)?;
-		let builder = OfferBuilder::deriving_signing_pubkey(node_id, expanded_key, nonce, secp_ctx)
-			.chain_hash($self.chain_hash)
-			.path(path);
-
-		Ok(builder.into())
+		$self.create_offer_builder_intern(|_, context, _| {
+			$self.create_blinded_paths(context)
+				.and_then(|paths| paths.into_iter().next().ok_or(()))
+				.map(Some)
+				.map_err(|_| Bolt12SemanticError::MissingPaths)
+		})
 	}
 
 	/// Creates an [`OfferBuilder`] such that the [`Offer`] it builds is recognized by the
@@ -10239,32 +10252,63 @@ macro_rules! create_offer_builder { ($self: ident, $builder: ty) => {
 		&$self,
 		router: ME,
 	) -> Result<$builder, Bolt12SemanticError> {
+		$self.create_offer_builder_intern(|node_id, context, secp_ctx| {
+			let peers = $self.get_peers_for_blinded_path();
+			router.create_blinded_paths(node_id, context, peers, secp_ctx)
+				.map(|paths| paths.into_iter().next())
+				.map_err(|_| Bolt12SemanticError::MissingPaths)
+		})
+	}
+} }
+
+macro_rules! create_refund_builder { ($self: ident, $builder: ty) => {
+	fn create_refund_builder_intern<PF>(
+		&$self,
+		make_path: PF,
+		amount_msats: u64,
+		absolute_expiry: Duration,
+		payment_id: PaymentId,
+		retry_strategy: Retry,
+		route_params_config: RouteParametersConfig
+	) -> Result<$builder, Bolt12SemanticError>
+	where
+		PF: FnOnce(PublicKey, MessageContext, &secp256k1::Secp256k1<secp256k1::All>) -> Result<Option<BlindedMessagePath>, Bolt12SemanticError>,
+	{
 		let node_id = $self.get_our_node_id();
 		let expanded_key = &$self.inbound_payment_key;
 		let entropy = &*$self.entropy_source;
 		let secp_ctx = &$self.secp_ctx;
 
 		let nonce = Nonce::from_entropy_source(entropy);
-		let context = MessageContext::Offers(OffersContext::InvoiceRequest { nonce });
+		let context = MessageContext::Offers(
+			OffersContext::OutboundPayment { payment_id, nonce, hmac: None }
+		);
 
-		let peers = $self.get_peers_for_blinded_path();
+		// Create the base builder with common properties
+		let mut builder = RefundBuilder::deriving_signing_pubkey(
+			node_id, expanded_key, nonce, secp_ctx, amount_msats, payment_id
+		)?
+			.chain_hash($self.chain_hash)
+			.absolute_expiry(absolute_expiry);
 
-		let path = router.create_blinded_paths(node_id, context, peers, secp_ctx)
-			.map_err(|_| Bolt12SemanticError::MissingPaths)?
-			.into_iter().next();
+		// Add path if one is provided by the path creator
+		if let Some(path) = make_path(node_id, context, secp_ctx)? {
+			builder = builder.path(path);
+		}
 
-		let mut builder = OfferBuilder::deriving_signing_pubkey(node_id, expanded_key, nonce, secp_ctx)
-			.chain_hash($self.chain_hash);
+		// Handle persistence and payment tracking
+		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop($self);
 
-		if let Some(path) = path {
-			builder = builder.path(path)
-		}
+		let expiration = StaleExpiration::AbsoluteTimeout(absolute_expiry);
+		$self.pending_outbound_payments
+			.add_new_awaiting_invoice(
+				payment_id, expiration, retry_strategy, route_params_config, None,
+			)
+			.map_err(|_| Bolt12SemanticError::DuplicatePaymentId)?;
 
 		Ok(builder.into())
 	}
-} }
 
-macro_rules! create_refund_builder { ($self: ident, $builder: ty) => {
 	/// Creates a [`RefundBuilder`] such that the [`Refund`] it builds is recognized by the
 	/// [`ChannelManager`] when handling [`Bolt12Invoice`] messages for the refund.
 	///
@@ -10287,8 +10331,7 @@ macro_rules! create_refund_builder { ($self: ident, $builder: ty) => {
 	///
 	/// # Privacy
 	///
-	/// Uses [`MessageRouter`] to construct a [`BlindedMessagePath`] for the refund based on the given
-	/// `absolute_expiry` according to [`MAX_SHORT_LIVED_RELATIVE_EXPIRY`]. See those docs for
+	/// Uses [`MessageRouter`] to construct a [`BlindedMessagePath`] for the refund. See those docs for
 	/// privacy implications as well as those of the parameterized [`Router`], which implements
 	/// [`MessageRouter`].
 	///
@@ -10314,34 +10357,19 @@ macro_rules! create_refund_builder { ($self: ident, $builder: ty) => {
 		&$self, amount_msats: u64, absolute_expiry: Duration, payment_id: PaymentId,
 		retry_strategy: Retry, route_params_config: RouteParametersConfig
 	) -> Result<$builder, Bolt12SemanticError> {
-		let node_id = $self.get_our_node_id();
-		let expanded_key = &$self.inbound_payment_key;
-		let entropy = &*$self.entropy_source;
-		let secp_ctx = &$self.secp_ctx;
-
-		let nonce = Nonce::from_entropy_source(entropy);
-		let context = OffersContext::OutboundPayment { payment_id, nonce, hmac: None };
-		let path = $self.create_blinded_paths_using_absolute_expiry(context, Some(absolute_expiry))
-			.and_then(|paths| paths.into_iter().next().ok_or(()))
-			.map_err(|_| Bolt12SemanticError::MissingPaths)?;
-
-		let builder = RefundBuilder::deriving_signing_pubkey(
-			node_id, expanded_key, nonce, secp_ctx, amount_msats, payment_id
-		)?
-			.chain_hash($self.chain_hash)
-			.absolute_expiry(absolute_expiry)
-			.path(path);
-
-		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop($self);
-
-		let expiration = StaleExpiration::AbsoluteTimeout(absolute_expiry);
-		$self.pending_outbound_payments
-			.add_new_awaiting_invoice(
-				payment_id, expiration, retry_strategy, route_params_config, None,
-			)
-			.map_err(|_| Bolt12SemanticError::DuplicatePaymentId)?;
-
-		Ok(builder.into())
+		$self.create_refund_builder_intern(
+			|_, context, _| {
+				$self.create_blinded_paths(context)
+					.and_then(|paths| paths.into_iter().next().ok_or(()))
+					.map(Some)
+					.map_err(|_| Bolt12SemanticError::MissingPaths)
+			},
+			amount_msats,
+			absolute_expiry,
+			payment_id,
+			retry_strategy,
+			route_params_config
+		)
 	}
 
 	/// Creates a [`RefundBuilder`] such that the [`Refund`] it builds is recognized by the
@@ -10392,41 +10420,19 @@ macro_rules! create_refund_builder { ($self: ident, $builder: ty) => {
 		&$self, router: ME, amount_msats: u64, absolute_expiry: Duration, payment_id: PaymentId,
 		retry_strategy: Retry, route_params_config: RouteParametersConfig
 	) -> Result<$builder, Bolt12SemanticError> {
-		let node_id = $self.get_our_node_id();
-		let expanded_key = &$self.inbound_payment_key;
-		let entropy = &*$self.entropy_source;
-		let secp_ctx = &$self.secp_ctx;
-
-		let nonce = Nonce::from_entropy_source(entropy);
-		let context = MessageContext::Offers(
-			OffersContext::OutboundPayment { payment_id, nonce, hmac: None }
-		);
-
-		let peers = $self.get_peers_for_blinded_path();
-		let path = router.create_blinded_paths(node_id, context, peers, secp_ctx)
-			.map_err(|_| Bolt12SemanticError::MissingPaths)?
-			.into_iter().next();
-
-		let mut builder = RefundBuilder::deriving_signing_pubkey(
-			node_id, expanded_key, nonce, secp_ctx, amount_msats, payment_id
-		)?
-			.chain_hash($self.chain_hash)
-			.absolute_expiry(absolute_expiry);
-
-		if let Some(path) = path {
-			builder = builder.path(path)
-		}
-
-		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop($self);
-
-		let expiration = StaleExpiration::AbsoluteTimeout(absolute_expiry);
-		$self.pending_outbound_payments
-			.add_new_awaiting_invoice(
-				payment_id, expiration, retry_strategy, route_params_config, None,
-			)
-			.map_err(|_| Bolt12SemanticError::DuplicatePaymentId)?;
-
-		Ok(builder.into())
+		$self.create_refund_builder_intern(
+			|node_id, context, secp_ctx| {
+				let peers = $self.get_peers_for_blinded_path();
+				router.create_blinded_paths(node_id, context, peers, secp_ctx)
+					.map(|paths| paths.into_iter().next())
+					.map_err(|_| Bolt12SemanticError::MissingPaths)
+			},
+			amount_msats,
+			absolute_expiry,
+			payment_id,
+			retry_strategy,
+			route_params_config
+		)
 	}
 } }
 

lightning/src/ln/offers_tests.rs

@@ -454,10 +454,11 @@ fn creates_short_lived_refund() {
 	let bob = &nodes[1];
 	let bob_id = bob.node.get_our_node_id();
 
+	let router = CompactMessageRouter::new(alice.network_graph, alice.node.entropy_source);
 	let absolute_expiry = bob.node.duration_since_epoch() + MAX_SHORT_LIVED_RELATIVE_EXPIRY;
 	let payment_id = PaymentId([1; 32]);
 	let refund = bob.node
-		.create_refund_builder(10_000_000, absolute_expiry, payment_id, Retry::Attempts(0), RouteParametersConfig::default())
+		.create_refund_builder_using_router(router, 10_000_000, absolute_expiry, payment_id, Retry::Attempts(0), RouteParametersConfig::default())
 		.unwrap()
 		.build().unwrap();
 	assert_eq!(refund.absolute_expiry(), Some(absolute_expiry));