f: Append all available paths to offer and refund.

- Instead of appending just a single blinded path to offers and refunds,
  update the code to append all paths returned by create_blinded_paths.
- This change allows MessageRouter to control the number of blinded paths
  appended to offers and refunds, providing flexibility for them to contain
  more than one path.

Author: shaavan

lightning/src/ln/channelmanager.rs

@@ -9126,14 +9126,16 @@ macro_rules! create_offer_builder { ($self: ident, $builder: ty) => {
 		);
 		let builder = match blinded_path {
 			Some(blinded_path) => {
-				let path = $self
+				let paths = $self
 					.create_blinded_paths(context, blinded_path)
-					.and_then(|paths| paths.into_iter().next().ok_or(()))
 					.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
-				OfferBuilder::deriving_signing_pubkey(node_id, expanded_key, nonce, secp_ctx)
-					.chain_hash($self.chain_hash)
-					.path(path)
+				let offer_builder = OfferBuilder::deriving_signing_pubkey(node_id, expanded_key, nonce, secp_ctx)
+					.chain_hash($self.chain_hash);
+
+				paths.into_iter().fold(offer_builder, |builder, path| {
+					builder.path(path)
+				})
 			}
 
 			None => OfferBuilder::deriving_signing_pubkey(node_id, expanded_key, nonce, secp_ctx)
@@ -9206,18 +9208,20 @@ macro_rules! create_refund_builder { ($self: ident, $builder: ty) => {
 
 		let builder = match blinded_path {
 			Some(blinded_path) => {
-				let path = $self
+				let paths = $self
 					.create_blinded_paths(context, blinded_path)
-					.and_then(|paths| paths.into_iter().next().ok_or(()))
 					.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
-				RefundBuilder::deriving_signing_pubkey(
+				let refund_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)
+				.absolute_expiry(absolute_expiry);
+
+				paths.into_iter().fold(refund_builder, |builder, path| {
+					builder.path(path)
+				})
 			}
 
 			None => RefundBuilder::deriving_signing_pubkey(
@@ -9226,7 +9230,6 @@ macro_rules! create_refund_builder { ($self: ident, $builder: ty) => {
 			)?
 			.chain_hash($self.chain_hash)
 			.absolute_expiry(absolute_expiry)
-			.absolute_expiry(absolute_expiry),
 		};
 
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop($self);

lightning/src/ln/offers_tests.rs

@@ -369,8 +369,8 @@ fn prefers_more_connected_nodes_in_blinded_paths() {
 		.build().unwrap();
 	assert_ne!(offer.issuer_signing_pubkey(), Some(bob_id));
 	assert!(!offer.paths().is_empty());
-	for path in offer.paths() {
-		let introduction_node_id = resolve_introduction_node(david, &path);
+	if let Some(first_path) = offer.paths().iter().next() {
+		let introduction_node_id = resolve_introduction_node(david, &first_path);
 		assert_eq!(introduction_node_id, nodes[4].node.get_our_node_id());
 	}
 }