Clean up test_duplicate_payment_hash_one_failure_one_success

`test_duplicate_payment_hash_one_failure_one_success` makes a
number of assumptions which rely on our specific CLTV constants,
which we intend to change. Specifically, it relies on forwarding
two HTLCs, one which goes one hop longer, and that it can close
the channel with both HTLCs sitting on chain with enough time to
claim that it doesn't give up on them but also that they get
claimed in separate transactions.

Here we clean up, simplify, and better document the test such that
it is more resilient to future CLTV constant changes.

Author: TheBlueMatt

lightning/src/ln/functional_tests.rs

@@ -5362,115 +5362,119 @@ pub fn test_onchain_to_onchain_claim() {
 #[xtest(feature = "_externalize_tests")]
 pub fn test_duplicate_payment_hash_one_failure_one_success() {
 	// Topology : A --> B --> C --> D
-	// We route 2 payments with same hash between B and C, one will be timeout, the other successfully claim
-	// Note that because C will refuse to generate two payment secrets for the same payment hash,
-	// we forward one of the payments onwards to D.
-	let chanmon_cfgs = create_chanmon_cfgs(4);
-	let node_cfgs = create_node_cfgs(4, &chanmon_cfgs);
+	//                          \-> E
+	// We route 2 payments with same hash between B and C, one we will time out on chain, the other
+	// successfully claim.
+	let chanmon_cfgs = create_chanmon_cfgs(5);
+	let node_cfgs = create_node_cfgs(5, &chanmon_cfgs);
 	// When this test was written, the default base fee floated based on the HTLC count.
 	// It is now fixed, so we simply set the fee to the expected value here.
 	let mut config = test_default_channel_config();
 	config.channel_config.forwarding_fee_base_msat = 196;
-	let node_chanmgrs = create_node_chanmgrs(4, &node_cfgs,
-		&[Some(config.clone()), Some(config.clone()), Some(config.clone()), Some(config.clone())]);
-	let mut nodes = create_network(4, &node_cfgs, &node_chanmgrs);
+	let node_chanmgrs = create_node_chanmgrs(5, &node_cfgs,
+		&[Some(config.clone()), Some(config.clone()), Some(config.clone()), Some(config.clone()), Some(config.clone())]);
+	let mut nodes = create_network(5, &node_cfgs, &node_chanmgrs);
 
+	// Create the required channels and route one HTLC from A to D and another from A to E.
 	create_announced_chan_between_nodes(&nodes, 0, 1);
 	let chan_2 = create_announced_chan_between_nodes(&nodes, 1, 2);
 	create_announced_chan_between_nodes(&nodes, 2, 3);
+	create_announced_chan_between_nodes(&nodes, 2, 4);
 
 	let node_max_height = nodes.iter().map(|node| node.blocks.lock().unwrap().len()).max().unwrap() as u32;
-	connect_blocks(&nodes[0], node_max_height - nodes[0].best_block_info().1);
-	connect_blocks(&nodes[1], node_max_height - nodes[1].best_block_info().1);
-	connect_blocks(&nodes[2], node_max_height - nodes[2].best_block_info().1);
-	connect_blocks(&nodes[3], node_max_height - nodes[3].best_block_info().1);
-
-	let (our_payment_preimage, duplicate_payment_hash, ..) = route_payment(&nodes[0], &[&nodes[1], &nodes[2]], 900_000);
-
-	let payment_secret = nodes[3].node.create_inbound_payment_for_hash(duplicate_payment_hash, None, 7200, None).unwrap();
-	// We reduce the final CLTV here by a somewhat arbitrary constant to keep it under the one-byte
-	// script push size limit so that the below script length checks match
-	// ACCEPTED_HTLC_SCRIPT_WEIGHT.
-	let payment_params = PaymentParameters::from_node_id(nodes[3].node.get_our_node_id(), TEST_FINAL_CLTV - 40)
-		.with_bolt11_features(nodes[3].node.bolt11_invoice_features()).unwrap();
-	let (route, _, _, _) = get_route_and_payment_hash!(nodes[0], nodes[3], payment_params, 800_000);
-	send_along_route_with_secret(&nodes[0], route, &[&[&nodes[1], &nodes[2], &nodes[3]]], 800_000, duplicate_payment_hash, payment_secret);
-
+	connect_blocks(&nodes[0], node_max_height * 2 - nodes[0].best_block_info().1);
+	connect_blocks(&nodes[1], node_max_height * 2 - nodes[1].best_block_info().1);
+	connect_blocks(&nodes[2], node_max_height * 2 - nodes[2].best_block_info().1);
+	connect_blocks(&nodes[3], node_max_height * 2 - nodes[3].best_block_info().1);
+	connect_blocks(&nodes[4], node_max_height * 2 - nodes[4].best_block_info().1);
+
+	let (our_payment_preimage, duplicate_payment_hash, ..) = route_payment(&nodes[0], &[&nodes[1], &nodes[2], &nodes[3]], 900_000);
+
+	let payment_secret = nodes[4].node.create_inbound_payment_for_hash(duplicate_payment_hash, None, 7200, None).unwrap();
+	let payment_params = PaymentParameters::from_node_id(nodes[4].node.get_our_node_id(), TEST_FINAL_CLTV)
+		.with_bolt11_features(nodes[4].node.bolt11_invoice_features()).unwrap();
+	let (route, _, _, _) = get_route_and_payment_hash!(nodes[0], nodes[4], payment_params, 800_000);
+	send_along_route_with_secret(&nodes[0], route, &[&[&nodes[1], &nodes[2], &nodes[4]]], 800_000, duplicate_payment_hash, payment_secret);
+
+	// Now mine C's commitment transaction on node B and mine enough blocks to get the HTLC timeout
+	// transaction (which we'll split in two so that we can resolve the HTLCs differently).
 	let commitment_txn = get_local_commitment_txn!(nodes[2], chan_2.2);
 	assert_eq!(commitment_txn[0].input.len(), 1);
+	assert_eq!(commitment_txn[0].output.len(), 3);
 	check_spends!(commitment_txn[0], chan_2.3);
 
 	mine_transaction(&nodes[1], &commitment_txn[0]);
 	check_closed_broadcast!(nodes[1], true);
 	check_added_monitors!(nodes[1], 1);
 	check_closed_event!(nodes[1], 1, ClosureReason::CommitmentTxConfirmed, [nodes[2].node.get_our_node_id()], 100000);
-	connect_blocks(&nodes[1], TEST_FINAL_CLTV - 40 + MIN_CLTV_EXPIRY_DELTA as u32); // Confirm blocks until the HTLC expires
 
-	let htlc_timeout_tx;
-	{ // Extract one of the two HTLC-Timeout transaction
-		let node_txn = nodes[1].tx_broadcaster.txn_broadcasted.lock().unwrap();
-		// ChannelMonitor: timeout tx * 2-or-3
-		assert!(node_txn.len() == 2 || node_txn.len() == 3);
+	// Confirm blocks until both HTLCs expire and get a transaction which times out one HTLC.
+	connect_blocks(&nodes[1], TEST_FINAL_CLTV + config.channel_config.cltv_expiry_delta as u32);
 
-		check_spends!(node_txn[0], commitment_txn[0]);
-		assert_eq!(node_txn[0].input.len(), 1);
-		assert_eq!(node_txn[0].output.len(), 1);
-
-		if node_txn.len() > 2 {
-			check_spends!(node_txn[1], commitment_txn[0]);
-			assert_eq!(node_txn[1].input.len(), 1);
-			assert_eq!(node_txn[1].output.len(), 1);
-			assert_eq!(node_txn[0].input[0].previous_output, node_txn[1].input[0].previous_output);
-
-			check_spends!(node_txn[2], commitment_txn[0]);
-			assert_eq!(node_txn[2].input.len(), 1);
-			assert_eq!(node_txn[2].output.len(), 1);
-			assert_ne!(node_txn[0].input[0].previous_output, node_txn[2].input[0].previous_output);
-		} else {
-			check_spends!(node_txn[1], commitment_txn[0]);
-			assert_eq!(node_txn[1].input.len(), 1);
-			assert_eq!(node_txn[1].output.len(), 1);
-			assert_ne!(node_txn[0].input[0].previous_output, node_txn[1].input[0].previous_output);
-		}
+	let htlc_timeout_tx = {
+		let mut node_txn = nodes[1].tx_broadcaster.txn_broadcasted.lock().unwrap();
+		assert_eq!(node_txn.len(), 1);
 
-		assert_eq!(node_txn[0].input[0].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT);
-		assert_eq!(node_txn[1].input[0].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT);
-		// Assign htlc_timeout_tx to the forwarded HTLC (with value ~800 sats). The received HTLC
-		// (with value 900 sats) will be claimed in the below `claim_funds` call.
-		if node_txn.len() > 2 {
-			assert_eq!(node_txn[2].input[0].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT);
-			htlc_timeout_tx = if node_txn[2].output[0].value.to_sat() < 900 { node_txn[2].clone() } else { node_txn[0].clone() };
-		} else {
-			htlc_timeout_tx = if node_txn[0].output[0].value.to_sat() < 900 { node_txn[1].clone() } else { node_txn[0].clone() };
+		let mut tx = node_txn.pop().unwrap();
+		check_spends!(tx, commitment_txn[0]);
+		assert_eq!(tx.input.len(), 2);
+		assert_eq!(tx.output.len(), 1);
+		// Note that the witness script lengths are one longer than our constant as the CLTV value
+		// went to two bytes rather than one.
+		assert_eq!(tx.input[0].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT + 1);
+		assert_eq!(tx.input[1].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT + 1);
+
+		// Split the HTLC claim transaction into two, one for each HTLC.
+		if commitment_txn[0].output[tx.input[1].previous_output.vout as usize].value.to_sat() < 850 {
+			tx.input.remove(1);
 		}
-	}
+		if commitment_txn[0].output[tx.input[0].previous_output.vout as usize].value.to_sat() < 850 {
+			tx.input.remove(0);
+		}
+		assert_eq!(tx.input.len(), 1);
+		tx
+	};
 
-	nodes[2].node.claim_funds(our_payment_preimage);
-	expect_payment_claimed!(nodes[2], duplicate_payment_hash, 900_000);
+	// Now give node E the payment preimage and pass it back to C.
+	nodes[4].node.claim_funds(our_payment_preimage);
+	expect_payment_claimed!(nodes[4], duplicate_payment_hash, 800_000);
+	check_added_monitors!(nodes[4], 1);
+	let updates = get_htlc_update_msgs!(nodes[4], nodes[2].node.get_our_node_id());
+	nodes[2].node.handle_update_fulfill_htlc(nodes[4].node.get_our_node_id(), &updates.update_fulfill_htlcs[0]);
+	let _cs_updates = get_htlc_update_msgs!(nodes[2], nodes[1].node.get_our_node_id());
+	expect_payment_forwarded!(nodes[2], nodes[1], nodes[4], Some(196), false, false);
+	check_added_monitors!(nodes[2], 1);
+	commitment_signed_dance!(nodes[2], nodes[4], &updates.commitment_signed, false);
 
+	// Mine the commitment transaction on node C and get the HTLC success transactions it will
+	// generate (note that the ChannelMonitor doesn't differentiate between HTLCs once it has the
+	// preimage).
 	mine_transaction(&nodes[2], &commitment_txn[0]);
-	check_added_monitors!(nodes[2], 2);
+	check_added_monitors!(nodes[2], 1);
 	check_closed_event!(nodes[2], 1, ClosureReason::CommitmentTxConfirmed, [nodes[1].node.get_our_node_id()], 100000);
-	let events = nodes[2].node.get_and_clear_pending_msg_events();
-	match events[0] {
-		MessageSendEvent::UpdateHTLCs { .. } => {},
-		_ => panic!("Unexpected event"),
-	}
-	match events[2] {
-		MessageSendEvent::BroadcastChannelUpdate { .. } => {},
-		_ => panic!("Unexepected event"),
-	}
+	check_closed_broadcast(&nodes[2], 1, true);
+
 	let htlc_success_txn: Vec<_> = nodes[2].tx_broadcaster.txn_broadcasted.lock().unwrap().clone();
 	assert_eq!(htlc_success_txn.len(), 2); // ChannelMonitor: HTLC-Success txn (*2 due to 2-HTLC outputs)
 	check_spends!(htlc_success_txn[0], commitment_txn[0]);
 	check_spends!(htlc_success_txn[1], commitment_txn[0]);
 	assert_eq!(htlc_success_txn[0].input.len(), 1);
-	assert_eq!(htlc_success_txn[0].input[0].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT);
+	// Note that the witness script lengths are one longer than our constant as the CLTV value went
+	// to two bytes rather than one.
+	assert_eq!(htlc_success_txn[0].input[0].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT + 1);
 	assert_eq!(htlc_success_txn[1].input.len(), 1);
-	assert_eq!(htlc_success_txn[1].input[0].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT);
+	assert_eq!(htlc_success_txn[1].input[0].witness.last().unwrap().len(), ACCEPTED_HTLC_SCRIPT_WEIGHT + 1);
 	assert_ne!(htlc_success_txn[0].input[0].previous_output, htlc_success_txn[1].input[0].previous_output);
-	assert_ne!(htlc_success_txn[1].input[0].previous_output, htlc_timeout_tx.input[0].previous_output);
 
+	let htlc_success_tx_to_confirm =
+		if htlc_success_txn[0].input[0].previous_output == htlc_timeout_tx.input[0].previous_output {
+			&htlc_success_txn[1]
+		} else {
+			&htlc_success_txn[0]
+		};
+	assert_ne!(htlc_success_tx_to_confirm.input[0].previous_output, htlc_timeout_tx.input[0].previous_output);
+
+	// Mine the HTLC timeout transaction on node B.
 	mine_transaction(&nodes[1], &htlc_timeout_tx);
 	connect_blocks(&nodes[1], ANTI_REORG_DELAY - 1);
 	expect_pending_htlcs_forwardable_and_htlc_handling_failed!(nodes[1], vec![HTLCDestination::NextHopChannel { node_id: Some(nodes[2].node.get_our_node_id()), channel_id: chan_2.2 }]);
@@ -5484,14 +5488,13 @@ pub fn test_duplicate_payment_hash_one_failure_one_success() {
 
 	nodes[0].node.handle_update_fail_htlc(nodes[1].node.get_our_node_id(), &htlc_updates.update_fail_htlcs[0]);
 	assert!(nodes[0].node.get_and_clear_pending_msg_events().is_empty());
-	{
-		commitment_signed_dance!(nodes[0], nodes[1], &htlc_updates.commitment_signed, false, true);
-	}
+	commitment_signed_dance!(nodes[0], nodes[1], &htlc_updates.commitment_signed, false, true);
 	expect_payment_failed_with_update!(nodes[0], duplicate_payment_hash, false, chan_2.0.contents.short_channel_id, true);
 
-	// Solve 2nd HTLC by broadcasting on B's chain HTLC-Success Tx from C
-	mine_transaction(&nodes[1], &htlc_success_txn[1]);
-	expect_payment_forwarded!(nodes[1], nodes[0], nodes[2], Some(196), true, true);
+	// Finally, give node B the HTLC success transaction and ensure it extracts the preimage to
+	// provide to node A.
+	mine_transaction(&nodes[1], htlc_success_tx_to_confirm);
+	expect_payment_forwarded!(nodes[1], nodes[0], nodes[2], Some(392), true, true);
 	let updates = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
 	assert!(updates.update_add_htlcs.is_empty());
 	assert!(updates.update_fail_htlcs.is_empty());