[test] Cover currency-denominated invoice verification paths

Add end-to-end and payer-side tests for currency-denominated
offers and invoices.

This consolidates coverage for the standard payment flow,
excessive invoice rejection, unverifiable fiat invoices when
conversion support is unavailable, and quantity-scaled invoice
requests.

The combined coverage exercises the main invoice amount
verification paths introduced by currency-denominated offer
support.

AI-assisted: Planning and writing the tests

Co-Authored-By: OpenAI Codex <codex@openai.com>

Author: shaavan

lightning/src/ln/offers_tests.rs

@@ -63,7 +63,7 @@ use crate::offers::invoice::Bolt12Invoice;
 use crate::offers::invoice_error::InvoiceError;
 use crate::offers::invoice_request::{InvoiceRequest, InvoiceRequestFields, InvoiceRequestVerifiedFromOffer};
 use crate::offers::nonce::Nonce;
-use crate::offers::offer::OfferBuilder;
+use crate::offers::offer::{Amount, CurrencyCode, OfferBuilder};
 use crate::offers::parse::Bolt12SemanticError;
 use crate::onion_message::messenger::{DefaultMessageRouter, Destination, MessageRouter, MessageSendInstructions, NodeIdMessageRouter, NullMessageRouter, PeeledOnion, DUMMY_HOPS_PATH_LENGTH, QR_CODED_DUMMY_HOPS_PATH_LENGTH};
 use crate::onion_message::offers::OffersMessage;
@@ -1554,6 +1554,64 @@ fn pays_bolt12_invoice_asynchronously() {
 	);
 }
 
+#[test]
+fn creates_and_pays_bolt12_invoice_for_currency_denominated_offer() {
+	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 offer = alice.node
+		.create_offer_builder()
+		.unwrap()
+		.amount(Amount::Currency {
+			iso4217_code: CurrencyCode::new(*b"USD").unwrap(),
+			amount: 10,
+		})
+		.build()
+		.unwrap();
+
+	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();
+	let (invoice_request, _) = extract_invoice_request(alice, &onion_message);
+	assert_eq!(invoice_request.amount_msats(), None);
+
+	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,
+		},
+		payment_metadata: None,
+	});
+
+	alice.onion_messenger.handle_onion_message(bob_id, &onion_message);
+
+	let invoice_onion_message = alice.onion_messenger.next_onion_message_for_peer(bob_id).unwrap();
+	let (invoice, _) = extract_invoice(bob, &invoice_onion_message);
+	assert_eq!(invoice.amount_msats(), 10_000);
+
+	bob.onion_messenger.handle_onion_message(alice_id, &invoice_onion_message);
+
+	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 an offer can be created using an unannounced node as a blinded path's introduction
 /// node. This is only preferred if there are no other options which may indicated either the offer
 /// is intended for the unannounced node or that the node is actually announced (e.g., an LSP) but

lightning/src/offers/invoice.rs

@@ -1917,6 +1917,7 @@ mod tests {
 	use crate::types::features::{Bolt12InvoiceFeatures, InvoiceRequestFeatures, OfferFeatures};
 	use crate::types::string::PrintableString;
 	use crate::util::ser::{BigSize, Iterable, Writeable};
+	use crate::util::test_utils::TestCurrencyConversion;
 	#[cfg(not(c_bindings))]
 	use {crate::offers::offer::OfferBuilder, crate::offers::refund::RefundBuilder};
 	#[cfg(c_bindings)]
@@ -2557,6 +2558,121 @@ mod tests {
 		}
 	}
 
+	#[test]
+	fn rejects_excessive_amount_for_currency_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 converter = TestCurrencyConversion {};
+
+		let invoice = OfferBuilder::new(recipient_pubkey(), &converter)
+			.amount(Amount::Currency {
+				iso4217_code: crate::offers::offer::CurrencyCode::new(*b"USD").unwrap(),
+				amount: 10,
+			})
+			.build()
+			.unwrap()
+			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id)
+			.unwrap()
+			.build_and_sign()
+			.unwrap()
+			.respond_with_no_std(&converter, payment_paths(), payment_hash(), now())
+			.unwrap()
+			.amount_msats_unchecked(10_001)
+			.build()
+			.unwrap()
+			.sign(recipient_sign)
+			.unwrap();
+
+		assert_eq!(
+			invoice.verify_amount_acceptable_for_payment(&converter),
+			Err(Bolt12SemanticError::ExcessiveAmount),
+		);
+	}
+
+	#[test]
+	fn fails_verifying_currency_offer_invoice_without_conversion_support() {
+		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 converter = TestCurrencyConversion {};
+
+		let invoice = OfferBuilder::new(recipient_pubkey(), &converter)
+			.amount(Amount::Currency {
+				iso4217_code: crate::offers::offer::CurrencyCode::new(*b"USD").unwrap(),
+				amount: 10,
+			})
+			.build()
+			.unwrap()
+			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id)
+			.unwrap()
+			.build_and_sign()
+			.unwrap()
+			.respond_with_no_std(&converter, payment_paths(), payment_hash(), now())
+			.unwrap()
+			.build()
+			.unwrap()
+			.sign(recipient_sign)
+			.unwrap();
+
+		assert_eq!(
+			invoice.verify_amount_acceptable_for_payment(&NullCurrencyConversion),
+			Err(Bolt12SemanticError::UnsupportedCurrency),
+		);
+	}
+
+	#[test]
+	fn verifies_currency_offer_invoice_amount_with_quantity() {
+		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 converter = TestCurrencyConversion {};
+
+		let invoice_request = OfferBuilder::new(recipient_pubkey(), &converter)
+			.amount(Amount::Currency {
+				iso4217_code: crate::offers::offer::CurrencyCode::new(*b"USD").unwrap(),
+				amount: 10,
+			})
+			.supported_quantity(Quantity::Unbounded)
+			.build()
+			.unwrap()
+			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id)
+			.unwrap()
+			.quantity(2)
+			.unwrap()
+			.build_and_sign()
+			.unwrap();
+
+		let invoice = invoice_request
+			.respond_with_no_std(&converter, payment_paths(), payment_hash(), now())
+			.unwrap()
+			.build()
+			.unwrap()
+			.sign(recipient_sign)
+			.unwrap();
+		assert_eq!(invoice.amount_msats(), 20_000);
+		assert_eq!(invoice.verify_amount_acceptable_for_payment(&converter), Ok(()));
+
+		let invoice = invoice_request
+			.respond_with_no_std(&converter, payment_paths(), payment_hash(), now())
+			.unwrap()
+			.amount_msats_unchecked(20_001)
+			.build()
+			.unwrap()
+			.sign(recipient_sign)
+			.unwrap();
+		assert_eq!(
+			invoice.verify_amount_acceptable_for_payment(&converter),
+			Err(Bolt12SemanticError::ExcessiveAmount),
+		);
+	}
+
 	#[test]
 	fn builds_invoice_with_fallback_address() {
 		let expanded_key = ExpandedKey::new([42; 32]);