Introduce RecipientData in ReceiveTlvs

1. This struct will be used by the node to add data along with the
   reply_path sent to the counterparty. The node expects to
   receive this data back and use it for doing further processing.
2. In its first iteration, RecipientData contains the payment_id of
   the corresponding Outbound BOLT12 Payment.
3. This will be used in a later commit to abandon outbound payments
   that have failed to complete for some reason.

Author: shaavan

lightning/src/blinded_path/message.rs

@@ -13,6 +13,7 @@
 
 use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey};
 
+use crate::ln::channelmanager::PaymentId;
 #[allow(unused_imports)]
 use crate::prelude::*;
 
@@ -56,6 +57,28 @@ pub(crate) struct ReceiveTlvs {
 	/// sending to. This is useful for receivers to check that said blinded path is being used in
 	/// the right context.
 	pub(crate) path_id: Option<[u8; 32]>,
+	pub recipient_data: RecipientData,
+}
+
+/// Represents additional data appended along with the sent reply path.
+///
+/// This data can be utilized by the final recipient for further processing
+/// upon receiving it back.
+#[derive(Clone, Debug)]
+pub struct RecipientData {
+	/// Payment ID of the outbound BOLT12 payment.
+	pub payment_id: Option<PaymentId>
+	// TODO: Introduce a more general form of RecipientData
+	// that can be used by Custom Messages
+}
+
+impl RecipientData {
+	/// Creates a new, empty RecipientData instance.
+	pub fn new() -> Self {
+		RecipientData {
+			payment_id: None,
+		}
+	}
 }
 
 impl Writeable for ForwardTlvs {
@@ -77,8 +100,10 @@ impl Writeable for ForwardTlvs {
 impl Writeable for ReceiveTlvs {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
 		// TODO: write padding
+		let RecipientData { payment_id } = self.recipient_data;
 		encode_tlv_stream!(writer, {
 			(6, self.path_id, option),
+			(65537, payment_id, option),
 		});
 		Ok(())
 	}
@@ -99,7 +124,7 @@ pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 			None => NextMessageHop::NodeId(*pubkey),
 		})
 		.map(|next_hop| ControlTlvs::Forward(ForwardTlvs { next_hop, next_blinding_override: None }))
-		.chain(core::iter::once(ControlTlvs::Receive(ReceiveTlvs { path_id: None })));
+		.chain(core::iter::once(ControlTlvs::Receive(ReceiveTlvs { path_id: None, recipient_data: RecipientData::new() })));
 
 	utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
 }

lightning/src/ln/offers_tests.rs

@@ -187,7 +187,7 @@ fn extract_invoice_request<'a, 'b, 'c>(
 	node: &Node<'a, 'b, 'c>, message: &OnionMessage
 ) -> (InvoiceRequest, BlindedPath) {
 	match node.onion_messenger.peel_onion_message(message) {
-		Ok(PeeledOnion::Receive(message, _, reply_path)) => match message {
+		Ok(PeeledOnion::Receive(message, _, _, reply_path)) => match message {
 			ParsedOnionMessageContents::Offers(offers_message) => match offers_message {
 				OffersMessage::InvoiceRequest(invoice_request) => (invoice_request, reply_path.unwrap()),
 				OffersMessage::Invoice(invoice) => panic!("Unexpected invoice: {:?}", invoice),
@@ -202,7 +202,7 @@ fn extract_invoice_request<'a, 'b, 'c>(
 
 fn extract_invoice<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>, message: &OnionMessage) -> Bolt12Invoice {
 	match node.onion_messenger.peel_onion_message(message) {
-		Ok(PeeledOnion::Receive(message, _, _)) => match message {
+		Ok(PeeledOnion::Receive(message, _, _, _)) => match message {
 			ParsedOnionMessageContents::Offers(offers_message) => match offers_message {
 				OffersMessage::InvoiceRequest(invoice_request) => panic!("Unexpected invoice_request: {:?}", invoice_request),
 				OffersMessage::Invoice(invoice) => invoice,
@@ -219,7 +219,7 @@ fn extract_invoice_error<'a, 'b, 'c>(
 	node: &Node<'a, 'b, 'c>, message: &OnionMessage
 ) -> InvoiceError {
 	match node.onion_messenger.peel_onion_message(message) {
-		Ok(PeeledOnion::Receive(message, _, _)) => match message {
+		Ok(PeeledOnion::Receive(message, _, _, _)) => match message {
 			ParsedOnionMessageContents::Offers(offers_message) => match offers_message {
 				OffersMessage::InvoiceRequest(invoice_request) => panic!("Unexpected invoice_request: {:?}", invoice_request),
 				OffersMessage::Invoice(invoice) => panic!("Unexpected invoice: {:?}", invoice),

lightning/src/onion_message/messenger.rs

@@ -16,7 +16,7 @@ use bitcoin::hashes::sha256::Hash as Sha256;
 use bitcoin::secp256k1::{self, PublicKey, Scalar, Secp256k1, SecretKey};
 
 use crate::blinded_path::{BlindedPath, IntroductionNode, NextMessageHop, NodeIdLookUp};
-use crate::blinded_path::message::{advance_path_by_one, ForwardNode, ForwardTlvs, ReceiveTlvs};
+use crate::blinded_path::message::{advance_path_by_one, ForwardNode, ForwardTlvs, ReceiveTlvs, RecipientData};
 use crate::blinded_path::utils;
 use crate::events::{Event, EventHandler, EventsProvider};
 use crate::sign::{EntropySource, NodeSigner, Recipient};
@@ -651,7 +651,7 @@ pub enum PeeledOnion<T: OnionMessageContents> {
 	/// Forwarded onion, with the next node id and a new onion
 	Forward(NextMessageHop, OnionMessage),
 	/// Received onion message, with decrypted contents, path_id, and reply path
-	Receive(ParsedOnionMessageContents<T>, Option<[u8; 32]>, Option<BlindedPath>)
+	Receive(ParsedOnionMessageContents<T>, Option<[u8; 32]>, RecipientData, Option<BlindedPath>)
 }
 
 
@@ -801,9 +801,9 @@ where
 		(control_tlvs_ss, custom_handler.deref(), logger.deref())
 	) {
 		Ok((Payload::Receive::<ParsedOnionMessageContents<<<CMH as Deref>::Target as CustomOnionMessageHandler>::CustomMessage>> {
-			message, control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id }), reply_path,
+			message, control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id , recipient_data }), reply_path,
 		}, None)) => {
-			Ok(PeeledOnion::Receive(message, path_id, reply_path))
+			Ok(PeeledOnion::Receive(message, path_id, recipient_data, reply_path))
 		},
 		Ok((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
 			next_hop, next_blinding_override
@@ -1236,7 +1236,7 @@ where
 	fn handle_onion_message(&self, peer_node_id: &PublicKey, msg: &OnionMessage) {
 		let logger = WithContext::from(&self.logger, Some(*peer_node_id), None, None);
 		match self.peel_onion_message(msg) {
-			Ok(PeeledOnion::Receive(message, path_id, reply_path)) => {
+			Ok(PeeledOnion::Receive(message, path_id, _, reply_path)) => {
 				log_trace!(
 					logger,
 					"Received an onion message with path_id {:02x?} and {} reply_path: {:?}",
@@ -1523,7 +1523,7 @@ fn packet_payloads_and_keys<T: OnionMessageContents, S: secp256k1::Signing + sec
 		}, prev_control_tlvs_ss.unwrap()));
 	} else {
 		payloads.push((Payload::Receive {
-			control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id: None, }),
+			control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id: None, recipient_data: RecipientData::new() }),
 			reply_path: reply_path.take(),
 			message,
 		}, prev_control_tlvs_ss.unwrap()));

lightning/src/onion_message/packet.rs

@@ -13,7 +13,7 @@ use bitcoin::secp256k1::PublicKey;
 use bitcoin::secp256k1::ecdh::SharedSecret;
 
 use crate::blinded_path::{BlindedPath, NextMessageHop};
-use crate::blinded_path::message::{ForwardTlvs, ReceiveTlvs};
+use crate::blinded_path::message::{ForwardTlvs, ReceiveTlvs, RecipientData};
 use crate::blinded_path::utils::Padding;
 use crate::ln::msgs::DecodeError;
 use crate::ln::onion_utils;
@@ -304,6 +304,7 @@ impl Readable for ControlTlvs {
 			(4, next_node_id, option),
 			(6, path_id, option),
 			(8, next_blinding_override, option),
+			(65537, payment_id, option),
 		});
 		let _padding: Option<Padding> = _padding;
 
@@ -325,6 +326,7 @@ impl Readable for ControlTlvs {
 		} else if valid_recv_fmt {
 			ControlTlvs::Receive(ReceiveTlvs {
 				path_id,
+				recipient_data: RecipientData { payment_id },
 			})
 		} else {
 			return Err(DecodeError::InvalidValue)