Include Offer context in blinded payment paths

When constructing blinded payment paths for a Bolt12Invoice response,
include the OfferId so that the eventual payment can be correlated with
the Offer.

Author: jkczyz

lightning/src/blinded_path/payment.rs

@@ -12,6 +12,7 @@ use crate::ln::channelmanager::CounterpartyForwardingInfo;
 use crate::ln::features::BlindedHopFeatures;
 use crate::ln::msgs::DecodeError;
 use crate::offers::invoice::BlindedPayInfo;
+use crate::offers::offer::OfferId;
 use crate::util::ser::{HighZeroBytesDroppedBigSize, Readable, Writeable, Writer};
 
 #[allow(unused_imports)]
@@ -108,12 +109,28 @@ pub struct PaymentConstraints {
 pub enum PaymentContext {
 	/// The payment context was unknown.
 	Unknown(UnknownPaymentContext),
+
+	/// The payment was made for an invoice requested from a BOLT 12 [`Offer`].
+	///
+	/// [`Offer`]: crate::offers::offer::Offer
+	Bolt12Offer(Bolt12OfferContext),
 }
 
 /// An unknown payment context.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct UnknownPaymentContext(());
 
+/// The context of a payment made for an invoice requested from a BOLT 12 [`Offer`].
+///
+/// [`Offer`]: crate::offers::offer::Offer
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Bolt12OfferContext {
+	/// The identifier of the [`Offer`].
+	///
+	/// [`Offer`]: crate::offers::offer::Offer
+	pub offer_id: OfferId,
+}
+
 impl PaymentContext {
 	pub(crate) fn unknown() -> Self {
 		PaymentContext::Unknown(UnknownPaymentContext(()))
@@ -340,6 +357,7 @@ impl Readable for PaymentConstraints {
 impl_writeable_tlv_based_enum!(PaymentContext,
 	;
 	(0, Unknown),
+	(1, Bolt12Offer),
 );
 
 impl Writeable for UnknownPaymentContext {
@@ -354,6 +372,10 @@ impl Readable for UnknownPaymentContext {
 	}
 }
 
+impl_writeable_tlv_based!(Bolt12OfferContext, {
+	(0, offer_id, required),
+});
+
 #[cfg(test)]
 mod tests {
 	use bitcoin::secp256k1::PublicKey;

lightning/src/ln/channelmanager.rs

@@ -32,7 +32,7 @@ use bitcoin::secp256k1::Secp256k1;
 use bitcoin::{secp256k1, Sequence};
 
 use crate::blinded_path::{BlindedPath, NodeIdLookUp};
-use crate::blinded_path::payment::{PaymentConstraints, PaymentContext, ReceiveTlvs};
+use crate::blinded_path::payment::{Bolt12OfferContext, PaymentConstraints, PaymentContext, ReceiveTlvs};
 use crate::chain;
 use crate::chain::{Confirm, ChannelMonitorUpdateStatus, Watch, BestBlock};
 use crate::chain::chaininterface::{BroadcasterInterface, ConfirmationTarget, FeeEstimator, LowerBoundedFeeEstimator};
@@ -8826,7 +8826,10 @@ where
 
 		match self.create_inbound_payment(Some(amount_msats), relative_expiry, None) {
 			Ok((payment_hash, payment_secret)) => {
-				let payment_paths = self.create_blinded_payment_paths(amount_msats, payment_secret)
+				let payment_context = PaymentContext::unknown();
+				let payment_paths = self.create_blinded_payment_paths(
+					amount_msats, payment_secret, payment_context
+				)
 					.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
 				#[cfg(feature = "std")]
@@ -8992,7 +8995,7 @@ where
 	/// Creates multi-hop blinded payment paths for the given `amount_msats` by delegating to
 	/// [`Router::create_blinded_payment_paths`].
 	fn create_blinded_payment_paths(
-		&self, amount_msats: u64, payment_secret: PaymentSecret
+		&self, amount_msats: u64, payment_secret: PaymentSecret, payment_context: PaymentContext
 	) -> Result<Vec<(BlindedPayInfo, BlindedPath)>, ()> {
 		let secp_ctx = &self.secp_ctx;
 
@@ -9006,7 +9009,7 @@ where
 				max_cltv_expiry,
 				htlc_minimum_msat: 1,
 			},
-			payment_context: PaymentContext::unknown(),
+			payment_context,
 		};
 		self.router.create_blinded_payment_paths(
 			payee_node_id, first_hops, payee_tlvs, amount_msats, secp_ctx
@@ -10360,8 +10363,11 @@ where
 					},
 				};
 
+				let payment_context = PaymentContext::Bolt12Offer(Bolt12OfferContext {
+					offer_id: invoice_request.offer_id,
+				});
 				let payment_paths = match self.create_blinded_payment_paths(
-					amount_msats, payment_secret
+					amount_msats, payment_secret, payment_context
 				) {
 					Ok(payment_paths) => payment_paths,
 					Err(()) => {

lightning/src/offers/offer.rs

@@ -115,7 +115,7 @@ use std::time::SystemTime;
 pub(super) const IV_BYTES: &[u8; IV_LEN] = b"LDK Offer ~~~~~~";
 
 /// An identifier for an [`Offer`] built using [`DerivedMetadata`].
-#[derive(Clone, Copy, Debug, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct OfferId(pub [u8; 32]);
 
 impl OfferId {