Introduce handle_message_received test

- Add a test to verify the functionality of the handle_message_received
  function.
- Ensure the test covers scenarios where InvoiceRequest messages are retried
  for PendingOutboundPayments after a simulated connection loss.

Author: shaavan

lightning/src/ln/offers_tests.rs

@@ -1056,6 +1056,78 @@ fn send_invoice_for_refund_with_distinct_reply_path() {
 	assert_eq!(reply_path.unwrap().introduction_node(), &IntroductionNode::NodeId(nodes[6].node.get_our_node_id()));
 }
 
+/// Verifies that the invoice request message can be retried if it fails to reach the
+/// payee on the first attempt.
+#[test]
+fn creates_and_pays_for_offer_with_retry() {
+	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(None).unwrap()
+		.amount_msats(10_000_000)
+		.build().unwrap();
+	assert_ne!(offer.signing_pubkey(), Some(alice_id));
+	assert!(!offer.paths().is_empty());
+	for path in offer.paths() {
+		assert_eq!(path.introduction_node(), &IntroductionNode::NodeId(alice_id));
+	}
+	let payment_id = PaymentId([1; 32]);
+	bob.node.pay_for_offer(&offer, None, None, None, payment_id, Retry::Attempts(0), None).unwrap();
+	expect_recent_payment!(bob, RecentPaymentDetails::AwaitingInvoice, payment_id);
+
+	let _lost_onion_message = bob.onion_messenger.next_onion_message_for_peer(alice_id).unwrap();
+
+	// Simulate a scenario where the original onion_message is lost before reaching Alice.
+	// Use handle_message_received to regenerate the message.
+	bob.node.message_received();
+	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_id: invoice_request.payer_id(),
+			quantity: None,
+			payer_note_truncated: None,
+		},
+	});
+	assert_eq!(invoice_request.amount_msats(), None);
+	assert_ne!(invoice_request.payer_id(), bob_id);
+	assert_eq!(reply_path.introduction_node(), &IntroductionNode::NodeId(bob_id));
+	let onion_message = alice.onion_messenger.next_onion_message_for_peer(bob_id).unwrap();
+	bob.onion_messenger.handle_onion_message(&alice_id, &onion_message);
+
+	// Expect no more OffersMessage to be enqueued by this point, even after calling
+	// handle_message_received.
+	bob.node.message_received();
+
+	assert!(bob.onion_messenger.next_onion_message_for_peer(alice_id).is_none());
+
+	let (invoice, _) = extract_invoice(bob, &onion_message);
+	assert_eq!(invoice.amount_msats(), 10_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));
+	}
+	route_bolt12_payment(bob, &[alice], &invoice);
+	expect_recent_payment!(bob, RecentPaymentDetails::Pending, payment_id);
+	claim_bolt12_payment(bob, &[alice], payment_context);
+	expect_recent_payment!(bob, RecentPaymentDetails::Fulfilled, payment_id);
+}
+
 /// Checks that a deferred invoice can be paid asynchronously from an Event::InvoiceReceived.
 #[test]
 fn pays_bolt12_invoice_asynchronously() {