f - add OnionMessageContentsType trait

Author: jkczyz

lightning/src/onion_message/messenger.rs

@@ -23,7 +23,7 @@ use crate::ln::features::{InitFeatures, NodeFeatures};
 use crate::ln::msgs::{self, OnionMessageHandler};
 use crate::ln::onion_utils;
 use crate::ln::peer_handler::IgnoringMessageHandler;
-pub use super::packet::{CustomOnionMessageContents, OnionMessageContents};
+pub use super::packet::{CustomOnionMessageContents, OnionMessageContents, OnionMessageContentsType};
 use super::offers::OffersMessageHandler;
 use super::packet::{BIG_PACKET_HOP_DATA_LEN, ForwardControlTlvs, Packet, Payload, ReceiveControlTlvs, SMALL_PACKET_HOP_DATA_LEN};
 use crate::util::logger::Logger;
@@ -161,7 +161,7 @@ where
 /// enqueued for sending.
 ///
 /// [`OnionMessage`]: crate::ln::msgs::OnionMessage
-pub struct PendingOnionMessage<T> {
+pub struct PendingOnionMessage<T: OnionMessageContentsType> {
 	/// The message contents to send in an [`OnionMessage`].
 	///
 	/// [`OnionMessage`]: crate::ln::msgs::OnionMessage

lightning/src/onion_message/packet.rs

@@ -118,6 +118,13 @@ pub enum OnionMessageContents<T: CustomOnionMessageContents> {
 	Custom(T),
 }
 
+/// A type used within a variant of [`OnionMessageContents`].
+pub trait OnionMessageContentsType {}
+
+impl OnionMessageContentsType for OffersMessage {}
+
+impl<T: CustomOnionMessageContents> OnionMessageContentsType for T {}
+
 impl<T: CustomOnionMessageContents> OnionMessageContents<T> {
 	/// Returns the type that was used to decode the message payload.
 	///