Use real on-chain value where possible in get_claimable_balance

This uses the new `onchain_value_satoshis` fields in
`OnchainEvent::HTLCSpendConfirmation` and
`OnchainEvent::HTLCUpdate` to report the post-HTLC-transaction
value of HTLC claims, instead of the original HTLC's value.

Author: TheBlueMatt

lightning/src/chain/channelmonitor.rs

@@ -1441,16 +1441,20 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 						let mut delayed_output_pending = None;
 						for event in us.onchain_events_awaiting_threshold_conf.iter() {
 							match event.event {
-								OnchainEvent::HTLCUpdate { commitment_tx_output_idx, htlc_value_satoshis, .. }
+								OnchainEvent::HTLCUpdate {
+									commitment_tx_output_idx, onchain_value_satoshis, htlc_value_satoshis, .. }
 								if commitment_tx_output_idx == Some(htlc_commitment_tx_output_idx) => {
 									debug_assert!(htlc_update_pending.is_none());
-									htlc_update_pending =
-										Some((htlc_value_satoshis.unwrap(), event.confirmation_threshold()));
+									htlc_update_pending = Some((
+										onchain_value_satoshis.unwrap_or(htlc_value_satoshis.unwrap()),
+										event.confirmation_threshold()));
 								},
-								OnchainEvent::HTLCSpendConfirmation { commitment_tx_output_idx, preimage, .. }
+								OnchainEvent::HTLCSpendConfirmation {
+									commitment_tx_output_idx, preimage, onchain_value_satoshis, .. }
 								if commitment_tx_output_idx == htlc_commitment_tx_output_idx => {
 									debug_assert!(htlc_spend_pending.is_none());
-									htlc_spend_pending = Some((event.confirmation_threshold(), preimage.is_some()));
+									htlc_spend_pending = Some((event.confirmation_threshold(),
+										preimage.is_some(), onchain_value_satoshis));
 								},
 								OnchainEvent::MaturingOutput {
 									descriptor: SpendableOutputDescriptor::DelayedPaymentOutput(ref descriptor) }
@@ -1501,9 +1505,9 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 								// preimage, we lost funds to our counterparty! We will then continue
 								// to show it as ContentiousClaimable until ANTI_REORG_DELAY.
 								debug_assert!(htlc_update_pending.is_none());
-								if let Some((conf_thresh, true)) = htlc_spend_pending {
+								if let Some((conf_thresh, true, value)) = htlc_spend_pending {
 									res.push(Balance::ClaimableAwaitingConfirmations {
-										claimable_amount_satoshis: htlc.amount_msat / 1000,
+										claimable_amount_satoshis: value.unwrap_or(htlc.amount_msat / 1000),
 										confirmation_height: conf_thresh,
 									});
 								} else {

lightning/src/ln/monitor_tests.rs

@@ -228,6 +228,17 @@ fn sorted_vec<T: Ord>(mut v: Vec<T>) -> Vec<T> {
 	v
 }
 
+/// Asserts that `a` and `b` are close, but maybe off by up to 5.
+/// This is useful when checking fees and weights on transactions as things may vary by a few based
+/// on signature size and signature size estimation being non-exact.
+fn fuzzy_assert_eq<V: core::convert::TryInto<u64>>(a: V, b: V) {
+	let a_u64 = a.try_into().map_err(|_| ()).unwrap();
+	let b_u64 = b.try_into().map_err(|_| ()).unwrap();
+	eprintln!("Checking {} and {} for fuzzy equality", a_u64, b_u64);
+	assert!(a_u64 >= b_u64 - 5);
+	assert!(b_u64 >= a_u64 - 5);
+}
+
 fn do_test_claim_value_force_close(prev_commitment_tx: bool) {
 	// Tests `get_claimable_balances` with an HTLC across a force-close.
 	// We build a channel with an HTLC pending, then force close the channel and check that the
@@ -501,11 +512,14 @@ fn do_test_claim_value_force_close(prev_commitment_tx: bool) {
 	let node_b_htlc_claimable = nodes[1].best_block_info().1 + BREAKDOWN_TIMEOUT as u32;
 	mine_transaction(&nodes[1], &b_broadcast_txn[0]);
 
+	fuzzy_assert_eq(b_broadcast_txn[0].output[0].value,
+		3_000 - chan_feerate * b_broadcast_txn[0].weight() as u64 / 1_000);
+
 	assert_eq!(sorted_vec(vec![Balance::ClaimableAwaitingConfirmations {
 			claimable_amount_satoshis: 1_000,
 			confirmation_height: node_b_commitment_claimable,
 		}, Balance::ClaimableAwaitingConfirmations {
-			claimable_amount_satoshis: 3_000,
+			claimable_amount_satoshis: b_broadcast_txn[0].output[0].value,
 			confirmation_height: node_b_htlc_claimable,
 		}, Balance::ContentiousClaimable {
 			claimable_amount_satoshis: 4_000,
@@ -519,7 +533,7 @@ fn do_test_claim_value_force_close(prev_commitment_tx: bool) {
 	test_spendable_output(&nodes[1], &remote_txn[0]);
 
 	assert_eq!(sorted_vec(vec![Balance::ClaimableAwaitingConfirmations {
-			claimable_amount_satoshis: 3_000,
+			claimable_amount_satoshis: b_broadcast_txn[0].output[0].value,
 			confirmation_height: node_b_htlc_claimable,
 		}, Balance::ContentiousClaimable {
 			claimable_amount_satoshis: 4_000,