Use a tuple, not a struct, for PendingOnionMessage in bindings

Bindings aren't currently able to handle a struct with a generic
which is actually exposed - we map all structs concretely to a
single type, whereas having fluctuating types on a struct requires
mapping the inner field to a trait first.

Since this isn't super practical, we make `PendingOnionMessage` a
tuple in bindings, rather than a struct.

lightning/src/ln/channelmanager.rs

@@ -63,7 +63,7 @@ use crate::offers::merkle::SignError;
 use crate::offers::offer::{DerivedMetadata, Offer, OfferBuilder};
 use crate::offers::parse::Bolt12SemanticError;
 use crate::offers::refund::{Refund, RefundBuilder};
-use crate::onion_message::{Destination, OffersMessage, OffersMessageHandler, PendingOnionMessage};
+use crate::onion_message::{Destination, OffersMessage, OffersMessageHandler, PendingOnionMessage, new_pending_onion_message};
 use crate::sign::{EntropySource, KeysManager, NodeSigner, Recipient, SignerProvider, WriteableEcdsaChannelSigner};
 use crate::util::config::{UserConfig, ChannelConfig, ChannelConfigUpdate};
 use crate::util::wakers::{Future, Notifier};
@@ -7505,11 +7505,11 @@ where
 
 		let mut pending_offers_messages = self.pending_offers_messages.lock().unwrap();
 		if offer.paths().is_empty() {
-			let message = PendingOnionMessage {
+			let message = new_pending_onion_message(
-				contents: OffersMessage::InvoiceRequest(invoice_request),
+				OffersMessage::InvoiceRequest(invoice_request),
-				destination: Destination::Node(offer.signing_pubkey()),
+				Destination::Node(offer.signing_pubkey()),
-				reply_path: Some(reply_path),
+				Some(reply_path),
-			};
+			);
 			pending_offers_messages.push(message);
 		} else {
 			// Send as many invoice requests as there are paths in the offer (with an upper bound).
@@ -7517,11 +7517,11 @@ where
 			// one invoice for a given payment id will be paid, even if more than one is received.
 			const REQUEST_LIMIT: usize = 10;
 			for path in offer.paths().into_iter().take(REQUEST_LIMIT) {
-				let message = PendingOnionMessage {
+				let message = new_pending_onion_message(
-					contents: OffersMessage::InvoiceRequest(invoice_request.clone()),
+					OffersMessage::InvoiceRequest(invoice_request.clone()),
-					destination: Destination::BlindedPath(path.clone()),
+					Destination::BlindedPath(path.clone()),
-					reply_path: Some(reply_path.clone()),
+					Some(reply_path.clone()),
-				};
+				);
 				pending_offers_messages.push(message);
 			}
 		}
@@ -7574,19 +7574,19 @@ where
 
 				let mut pending_offers_messages = self.pending_offers_messages.lock().unwrap();
 				if refund.paths().is_empty() {
-					let message = PendingOnionMessage {
+					let message = new_pending_onion_message(
-						contents: OffersMessage::Invoice(invoice),
+						OffersMessage::Invoice(invoice),
-						destination: Destination::Node(refund.payer_id()),
+						Destination::Node(refund.payer_id()),
-						reply_path: Some(reply_path),
+						Some(reply_path),
-					};
+					);
 					pending_offers_messages.push(message);
 				} else {
 					for path in refund.paths() {
-						let message = PendingOnionMessage {
+						let message = new_pending_onion_message(
-							contents: OffersMessage::Invoice(invoice.clone()),
+							OffersMessage::Invoice(invoice.clone()),
-							destination: Destination::BlindedPath(path.clone()),
+							Destination::BlindedPath(path.clone()),
-							reply_path: Some(reply_path.clone()),
+							Some(reply_path.clone()),
-						};
+						);
 						pending_offers_messages.push(message);
 					}
 				}

lightning/src/onion_message/messenger.rs

@@ -159,6 +159,7 @@ where
 ///
 /// These are obtained when released from [`OnionMessenger`]'s handlers after which they are
 /// enqueued for sending.
+#[cfg(not(c_bindings))]
 pub struct PendingOnionMessage<T: OnionMessageContents> {
 	/// The message contents to send in an [`OnionMessage`].
 	pub contents: T,
@@ -170,6 +171,22 @@ pub struct PendingOnionMessage<T: OnionMessageContents> {
 	pub reply_path: Option<BlindedPath>,
 }
 
+#[cfg(c_bindings)]
+/// An [`OnionMessage`] for [`OnionMessenger`] to send.
+///
+/// These are obtained when released from [`OnionMessenger`]'s handlers after which they are
+/// enqueued for sending.
+pub type PendingOnionMessage<T: OnionMessageContents> = (T, Destination, Option<BlindedPath>);
+
+pub(crate) fn new_pending_onion_message<T: OnionMessageContents>(
+	contents: T, destination: Destination, reply_path: Option<BlindedPath>
+) -> PendingOnionMessage<T> {
+	#[cfg(not(c_bindings))]
+	return PendingOnionMessage { contents, destination, reply_path };
+	#[cfg(c_bindings)]
+	return (contents, destination, reply_path);
+}
+
 /// A trait defining behavior for routing an [`OnionMessage`].
 pub trait MessageRouter {
 	/// Returns a route for sending an [`OnionMessage`] to the given [`Destination`].
@@ -286,7 +303,15 @@ pub trait CustomOnionMessageHandler {
 	///
 	/// Typically, this is used for messages initiating a message flow rather than in response to
 	/// another message. The latter should use the return value of [`Self::handle_custom_message`].
+	#[cfg(not(c_bindings))]
 	fn release_pending_custom_messages(&self) -> Vec<PendingOnionMessage<Self::CustomMessage>>;
+
+	/// Releases any [`Self::CustomMessage`]s that need to be sent.
+	///
+	/// Typically, this is used for messages initiating a message flow rather than in response to
+	/// another message. The latter should use the return value of [`Self::handle_custom_message`].
+	#[cfg(c_bindings)]
+	fn release_pending_custom_messages(&self) -> Vec<(Self::CustomMessage, Destination, Option<BlindedPath>)>;
 }
 
 /// A processed incoming onion message, containing either a Forward (another onion message)
@@ -686,7 +711,10 @@ where
 	fn next_onion_message_for_peer(&self, peer_node_id: PublicKey) -> Option<OnionMessage> {
 		// Enqueue any initiating `OffersMessage`s to send.
 		for message in self.offers_handler.release_pending_messages() {
+			#[cfg(not(c_bindings))]
 			let PendingOnionMessage { contents, destination, reply_path } = message;
+			#[cfg(c_bindings)]
+			let (contents, destination, reply_path) = message;
 			self.find_path_and_enqueue_onion_message(
 				contents, destination, reply_path, format_args!("when sending OffersMessage")
 			);
@@ -694,7 +722,10 @@ where
 
 		// Enqueue any initiating `CustomMessage`s to send.
 		for message in self.custom_handler.release_pending_custom_messages() {
+			#[cfg(not(c_bindings))]
 			let PendingOnionMessage { contents, destination, reply_path } = message;
+			#[cfg(c_bindings)]
+			let (contents, destination, reply_path) = message;
 			self.find_path_and_enqueue_onion_message(
 				contents, destination, reply_path, format_args!("when sending CustomMessage")
 			);

lightning/src/onion_message/mod.rs

@@ -33,3 +33,4 @@ pub use self::messenger::{SimpleArcOnionMessenger, SimpleRefOnionMessenger};
 pub use self::offers::{OffersMessage, OffersMessageHandler};
 pub use self::packet::{Packet, ParsedOnionMessageContents};
 pub(crate) use self::packet::ControlTlvs;
+pub(crate) use self::messenger::new_pending_onion_message;

lightning/src/onion_message/offers.rs

@@ -44,7 +44,15 @@ pub trait OffersMessageHandler {
 	///
 	/// Typically, this is used for messages initiating a payment flow rather than in response to
 	/// another message. The latter should use the return value of [`Self::handle_message`].
+	#[cfg(not(c_bindings))]
 	fn release_pending_messages(&self) -> Vec<PendingOnionMessage<OffersMessage>> { vec![] }
+
+	/// Releases any [`OffersMessage`]s that need to be sent.
+	///
+	/// Typically, this is used for messages initiating a payment flow rather than in response to
+	/// another message. The latter should use the return value of [`Self::handle_message`].
+	#[cfg(c_bindings)]
+	fn release_pending_messages(&self) -> Vec<(OffersMessage, crate::onion_message::Destination, Option<crate::blinded_path::BlindedPath>)> { vec![] }
 }
 
 /// Possible BOLT 12 Offers messages sent and received via an [`OnionMessage`].