Add tests for currency-denominated Offer flows

Adds tests covering Offers whose amounts are denominated in fiat
currencies. These tests verify that:

* currency-denominated Offer amounts can be created
* InvoiceRequests correctly resolve amounts using CurrencyConversion
* Invoice construction validates and enforces the payable amount

This ensures the full Offer → InvoiceRequest → Invoice flow works
correctly when the original Offer amount is specified in currency.

Author: shaavan

lightning/src/ln/offers_tests.rs

@@ -52,6 +52,7 @@ use crate::blinded_path::message::OffersContext;
 use crate::events::{ClosureReason, Event, HTLCHandlingFailureType, PaidBolt12Invoice, PaymentFailureReason, PaymentPurpose};
 use crate::ln::channelmanager::{PaymentId, RecentPaymentDetails, self};
 use crate::ln::outbound_payment::{Bolt12PaymentError, RecipientOnionFields, Retry};
+use crate::offers::offer::{Amount, CurrencyCode};
 use crate::types::features::Bolt12InvoiceFeatures;
 use crate::ln::functional_test_utils::*;
 use crate::ln::msgs::{BaseMessageHandler, ChannelMessageHandler, Init, NodeAnnouncement, OnionMessage, OnionMessageHandler, RoutingMessageHandler, SocketAddress, UnsignedGossipMessage, UnsignedNodeAnnouncement};
@@ -916,6 +917,78 @@ fn creates_and_pays_for_offer_using_one_hop_blinded_path() {
 	expect_recent_payment!(bob, RecentPaymentDetails::Fulfilled, payment_id);
 }
 
+/// Checks that an offer can be paid through a one-hop blinded path and that ephemeral pubkeys are
+/// used rather than exposing a node's pubkey. However, the node's pubkey is still used as the
+/// introduction node of the blinded path.
+#[test]
+fn creates_and_pays_for_offer_with_fiat_amount_using_one_hop_blinded_path() {
+	let chanmon_cfgs = create_chanmon_cfgs(2);
+	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
+	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 10_000_000, 1_000_000_000);
+
+	let alice = &nodes[0];
+	let alice_id = alice.node.get_our_node_id();
+	let bob = &nodes[1];
+	let bob_id = bob.node.get_our_node_id();
+
+	let amount = Amount::Currency {
+		iso4217_code: CurrencyCode::new(*b"USD").unwrap(),
+		amount: 1000,
+	};
+
+	let offer = alice.node
+		.create_offer_builder().unwrap()
+		.amount(amount, &alice.node.flow.currency_conversion).unwrap()
+		.build();
+	assert_ne!(offer.issuer_signing_pubkey(), Some(alice_id));
+	assert!(!offer.paths().is_empty());
+	for path in offer.paths() {
+		assert!(check_compact_path_introduction_node(&path, bob, alice_id));
+	}
+
+	let payment_id = PaymentId([1; 32]);
+	bob.node.pay_for_offer(&offer, None, payment_id, Default::default()).unwrap();
+	expect_recent_payment!(bob, RecentPaymentDetails::AwaitingInvoice, payment_id);
+
+	let onion_message = bob.onion_messenger.next_onion_message_for_peer(alice_id).unwrap();
+	alice.onion_messenger.handle_onion_message(bob_id, &onion_message);
+
+	let (invoice_request, reply_path) = extract_invoice_request(alice, &onion_message);
+	let payment_context = PaymentContext::Bolt12Offer(Bolt12OfferContext {
+		offer_id: offer.id(),
+		invoice_request: InvoiceRequestFields {
+			payer_signing_pubkey: invoice_request.payer_signing_pubkey(),
+			quantity: None,
+			payer_note_truncated: None,
+			human_readable_name: None,
+		},
+	});
+	assert_eq!(invoice_request.amount_msats(&alice.node.flow.currency_conversion), Ok(1_000_000));
+	assert_ne!(invoice_request.payer_signing_pubkey(), bob_id);
+	assert!(check_dummy_hopped_path_length(&reply_path, alice, bob_id, DUMMY_HOPS_PATH_LENGTH));
+
+	let onion_message = alice.onion_messenger.next_onion_message_for_peer(bob_id).unwrap();
+	bob.onion_messenger.handle_onion_message(alice_id, &onion_message);
+
+	let (invoice, reply_path) = extract_invoice(bob, &onion_message);
+	assert_eq!(invoice.amount_msats(), 1_000_000);
+	assert_ne!(invoice.signing_pubkey(), alice_id);
+	assert!(!invoice.payment_paths().is_empty());
+	for path in invoice.payment_paths() {
+		assert_eq!(path.introduction_node(), &IntroductionNode::NodeId(alice_id));
+	}
+	assert!(check_dummy_hopped_path_length(&reply_path, bob, alice_id, DUMMY_HOPS_PATH_LENGTH));
+
+	route_bolt12_payment(bob, &[alice], &invoice);
+	expect_recent_payment!(bob, RecentPaymentDetails::Pending, payment_id);
+
+	claim_bolt12_payment(bob, &[alice], payment_context, &invoice);
+	expect_recent_payment!(bob, RecentPaymentDetails::Fulfilled, payment_id);
+}
+
 /// Checks that a refund can be paid through a one-hop blinded path and that ephemeral pubkeys are
 /// used rather than exposing a node's pubkey. However, the node's pubkey is still used as the
 /// introduction node of the blinded path.

lightning/src/offers/invoice.rs

@@ -1894,7 +1894,7 @@ mod tests {
 	use crate::offers::merkle::{self, SignError, SignatureTlvStreamRef, TaggedHash, TlvStream};
 	use crate::offers::nonce::Nonce;
 	use crate::offers::offer::{
-		Amount, ExperimentalOfferTlvStreamRef, OfferTlvStreamRef, Quantity,
+		Amount, CurrencyCode, ExperimentalOfferTlvStreamRef, OfferTlvStreamRef, Quantity,
 	};
 	use crate::offers::parse::{Bolt12ParseError, Bolt12SemanticError};
 	use crate::offers::payer::PayerTlvStreamRef;
@@ -2096,6 +2096,54 @@ mod tests {
 		}
 	}
 
+	#[test]
+	fn builds_invoice_for_fiat_offer() {
+		let expanded_key = ExpandedKey::new([42; 32]);
+		let entropy = FixedEntropy {};
+		let nonce = Nonce::from_entropy_source(&entropy);
+		let secp_ctx = Secp256k1::new();
+		let payment_id = PaymentId([1; 32]);
+		let conversion = TestCurrencyConversion;
+		let currency_amount =
+			Amount::Currency { iso4217_code: CurrencyCode::new(*b"USD").unwrap(), amount: 10 };
+		let expected_amount_msats = 10_000;
+
+		let payment_paths = payment_paths();
+		let payment_hash = payment_hash();
+		let now = now();
+		let unsigned_invoice = OfferBuilder::new(recipient_pubkey())
+			.amount(currency_amount, &conversion)
+			.unwrap()
+			.build()
+			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id, &conversion)
+			.unwrap()
+			.build_and_sign()
+			.unwrap()
+			.respond_with_no_std(&conversion, payment_paths.clone(), payment_hash, now)
+			.unwrap()
+			.build()
+			.unwrap();
+
+		let (_, offer_tlv_stream, _, invoice_tlv_stream, _, _, _) =
+			unsigned_invoice.contents.as_tlv_stream();
+		assert_eq!(unsigned_invoice.amount(), Some(currency_amount));
+		assert_eq!(offer_tlv_stream.currency, Some(b"USD"));
+		assert_eq!(offer_tlv_stream.amount, Some(10));
+		assert_eq!(invoice_tlv_stream.amount, Some(expected_amount_msats));
+		assert_eq!(unsigned_invoice.amount_msats(), expected_amount_msats);
+		assert_eq!(unsigned_invoice.payment_paths(), payment_paths.as_slice());
+
+		#[cfg(c_bindings)]
+		let mut unsigned_invoice = unsigned_invoice;
+		let invoice = unsigned_invoice.sign(recipient_sign).unwrap();
+		let (_, offer_tlv_stream, _, invoice_tlv_stream, _, _, _, _) = invoice.as_tlv_stream();
+		assert_eq!(invoice.amount(), Some(currency_amount));
+		assert_eq!(offer_tlv_stream.currency, Some(b"USD"));
+		assert_eq!(offer_tlv_stream.amount, Some(10));
+		assert_eq!(invoice_tlv_stream.amount, Some(expected_amount_msats));
+		assert_eq!(invoice.amount_msats(), expected_amount_msats);
+	}
+
 	#[test]
 	fn builds_invoice_for_refund_with_defaults() {
 		let payment_paths = payment_paths();