Support currency-denominated Offers in InvoiceBuilder

Adds currency conversion support when responding to an `InvoiceRequest`
and constructing the `InvoiceBuilder`.

When the underlying Offer specifies its amount in a currency denomination,
the `CurrencyConversion` implementation is used to resolve the payable
amount into millisatoshis and ensure the invoice amount satisfies the
Offer's requirements.

This reintroduces the currency validation intentionally skipped during
`InvoiceRequest` parsing, keeping parsing focused on structural
validation while enforcing amount correctness at the time the Invoice
is constructed.

Author: shaavan

lightning/src/ln/channelmanager.rs

@@ -5715,6 +5715,7 @@ impl<
 			let features = self.bolt12_invoice_features();
 			let outbound_pmts_res = self.pending_outbound_payments.static_invoice_received(
 				invoice,
+				&self.flow.currency_conversion,
 				payment_id,
 				features,
 				best_block_height,

lightning/src/ln/offers_tests.rs

@@ -2367,6 +2367,7 @@ fn fails_paying_invoice_with_unknown_required_features() {
 		.build().unwrap();
 
 	let payment_id = PaymentId([1; 32]);
+	let conversion = TestCurrencyConversion;
 	david.node.pay_for_offer(&offer, None, payment_id, Default::default()).unwrap();
 
 	connect_peers(david, bob);
@@ -2401,7 +2402,7 @@ fn fails_paying_invoice_with_unknown_required_features() {
 
 	let invoice = match verified_invoice_request {
 		InvoiceRequestVerifiedFromOffer::DerivedKeys(request) => {
-			request.respond_using_derived_keys_no_std(payment_paths, payment_hash, created_at).unwrap()
+			request.respond_using_derived_keys_no_std(&conversion, payment_paths, payment_hash, created_at).unwrap()
 				.features_unchecked(Bolt12InvoiceFeatures::unknown())
 				.build_and_sign(&secp_ctx).unwrap()
 		},

lightning/src/ln/outbound_payment.rs

@@ -24,6 +24,7 @@ use crate::ln::channelmanager::{
 use crate::ln::msgs::DecodeError;
 use crate::ln::onion_utils;
 use crate::ln::onion_utils::{DecodedOnionFailure, HTLCFailReason};
+use crate::offers::currency::CurrencyConversion;
 use crate::offers::invoice::{Bolt12Invoice, DerivedSigningPubkey, InvoiceBuilder};
 use crate::offers::invoice_request::InvoiceRequest;
 use crate::offers::nonce::Nonce;
@@ -1230,9 +1231,10 @@ impl OutboundPayments {
 		Ok(())
 	}
 
-	pub(super) fn static_invoice_received<ES: EntropySource>(
-		&self, invoice: &StaticInvoice, payment_id: PaymentId, features: Bolt12InvoiceFeatures,
-		best_block_height: u32, duration_since_epoch: Duration, entropy_source: ES,
+	pub(super) fn static_invoice_received<'a, ES: EntropySource, CC: CurrencyConversion>(
+		&'a self, invoice: &StaticInvoice, currency_conversion: &'a CC, payment_id: PaymentId,
+		features: Bolt12InvoiceFeatures, best_block_height: u32, duration_since_epoch: Duration,
+		entropy_source: ES,
 		pending_events: &Mutex<VecDeque<(events::Event, Option<EventCompletionAction>)>>,
 	) -> Result<(), Bolt12PaymentError> {
 		macro_rules! abandon_with_entry {
@@ -1280,6 +1282,7 @@ impl OutboundPayments {
 
 					let amount_msat = match InvoiceBuilder::<DerivedSigningPubkey>::amount_msats(
 						invreq,
+						currency_conversion,
 					) {
 						Ok(amt) => amt,
 						Err(_) => {
@@ -3311,7 +3314,7 @@ mod tests {
 			.build().unwrap()
 			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id, &conversion).unwrap()
 			.build_and_sign().unwrap()
-			.respond_with_no_std(payment_paths(), payment_hash(), created_at).unwrap()
+			.respond_with_no_std(&conversion, payment_paths(), payment_hash(), created_at).unwrap()
 			.build().unwrap()
 			.sign(recipient_sign).unwrap();
 
@@ -3361,7 +3364,7 @@ mod tests {
 			.build().unwrap()
 			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id, &conversion).unwrap()
 			.build_and_sign().unwrap()
-			.respond_with_no_std(payment_paths(), payment_hash(), now()).unwrap()
+			.respond_with_no_std(&conversion, payment_paths(), payment_hash(), now()).unwrap()
 			.build().unwrap()
 			.sign(recipient_sign).unwrap();
 
@@ -3427,7 +3430,7 @@ mod tests {
 			.build().unwrap()
 			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id, &conversion).unwrap()
 			.build_and_sign().unwrap()
-			.respond_with_no_std(payment_paths(), payment_hash(), now()).unwrap()
+			.respond_with_no_std(&conversion, payment_paths(), payment_hash(), now()).unwrap()
 			.build().unwrap()
 			.sign(recipient_sign).unwrap();
 

lightning/src/offers/flow.rs

@@ -43,7 +43,7 @@ use crate::offers::invoice_request::{
 	InvoiceRequest, InvoiceRequestBuilder, InvoiceRequestVerifiedFromOffer, VerifiedInvoiceRequest,
 };
 use crate::offers::nonce::Nonce;
-use crate::offers::offer::{Amount, DerivedMetadata, Offer, OfferBuilder};
+use crate::offers::offer::{DerivedMetadata, Offer, OfferBuilder};
 use crate::offers::parse::Bolt12SemanticError;
 use crate::offers::refund::{Refund, RefundBuilder};
 use crate::offers::static_invoice::{StaticInvoice, StaticInvoiceBuilder};
@@ -866,10 +866,7 @@ impl<MR: MessageRouter, CC: CurrencyConversion, L: Logger> OffersMessageFlow<MR,
 		let payment_context =
 			PaymentContext::AsyncBolt12Offer(AsyncBolt12OfferContext { offer_nonce });
 
-		let amount_msat = offer.amount().and_then(|amount| match amount {
-			Amount::Bitcoin { amount_msats } => Some(amount_msats),
-			Amount::Currency { .. } => None,
-		});
+		let amount_msat = offer.resolve_offer_amount(&self.currency_conversion)?;
 
 		let created_at = self.duration_since_epoch();
 
@@ -998,9 +995,12 @@ impl<MR: MessageRouter, CC: CurrencyConversion, L: Logger> OffersMessageFlow<MR,
 		F: Fn(u64, u32) -> Result<(PaymentHash, PaymentSecret), Bolt12SemanticError>,
 	{
 		let relative_expiry = DEFAULT_RELATIVE_EXPIRY.as_secs() as u32;
+		let conversion = &self.currency_conversion;
 
-		let amount_msats =
-			InvoiceBuilder::<DerivedSigningPubkey>::amount_msats(&invoice_request.inner)?;
+		let amount_msats = InvoiceBuilder::<DerivedSigningPubkey>::amount_msats(
+			&invoice_request.inner,
+			conversion,
+		)?;
 
 		let (payment_hash, payment_secret) = get_payment_info(amount_msats, relative_expiry)?;
 
@@ -1021,9 +1021,10 @@ impl<MR: MessageRouter, CC: CurrencyConversion, L: Logger> OffersMessageFlow<MR,
 			.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
 		#[cfg(feature = "std")]
-		let builder = invoice_request.respond_using_derived_keys(payment_paths, payment_hash);
+		let builder = invoice_request.respond_using_derived_keys(conversion, payment_paths, payment_hash);
 		#[cfg(not(feature = "std"))]
 		let builder = invoice_request.respond_using_derived_keys_no_std(
+			conversion,
 			payment_paths,
 			payment_hash,
 			Duration::from_secs(self.highest_seen_timestamp.load(Ordering::Acquire) as u64),
@@ -1057,9 +1058,12 @@ impl<MR: MessageRouter, CC: CurrencyConversion, L: Logger> OffersMessageFlow<MR,
 		F: Fn(u64, u32) -> Result<(PaymentHash, PaymentSecret), Bolt12SemanticError>,
 	{
 		let relative_expiry = DEFAULT_RELATIVE_EXPIRY.as_secs() as u32;
+		let conversion = &self.currency_conversion;
 
-		let amount_msats =
-			InvoiceBuilder::<DerivedSigningPubkey>::amount_msats(&invoice_request.inner)?;
+		let amount_msats = InvoiceBuilder::<DerivedSigningPubkey>::amount_msats(
+			&invoice_request.inner,
+			conversion,
+		)?;
 
 		let (payment_hash, payment_secret) = get_payment_info(amount_msats, relative_expiry)?;
 
@@ -1080,9 +1084,10 @@ impl<MR: MessageRouter, CC: CurrencyConversion, L: Logger> OffersMessageFlow<MR,
 			.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
 		#[cfg(feature = "std")]
-		let builder = invoice_request.respond_with(payment_paths, payment_hash);
+		let builder = invoice_request.respond_with(conversion, payment_paths, payment_hash);
 		#[cfg(not(feature = "std"))]
 		let builder = invoice_request.respond_with_no_std(
+			conversion,
 			payment_paths,
 			payment_hash,
 			Duration::from_secs(self.highest_seen_timestamp.load(Ordering::Acquire) as u64),