-f enforce affordability at holding free

Author: Antoine Riard

lightning/src/ln/channel.rs

@@ -292,6 +292,7 @@ struct HTLCStats {
 	pending_htlcs_value_msat: u64,
 	on_counterparty_tx_dust_exposure_msat: u64,
 	on_holder_tx_dust_exposure_msat: u64,
+	holding_cell_msat: u64,
 }
 
 /// Used when calculating whether we or the remote can afford an additional HTLC.
@@ -1931,6 +1932,7 @@ impl<Signer: Sign> Channel<Signer> {
 			pending_htlcs_value_msat: 0,
 			on_counterparty_tx_dust_exposure_msat: 0,
 			on_holder_tx_dust_exposure_msat: 0,
+			holding_cell_msat: 0,
 		};
 
 		let counterparty_dust_limit_timeout_sat = (self.get_dust_buffer_feerate(outbound_feerate_update) as u64 * HTLC_TIMEOUT_TX_WEIGHT / 1000) + self.counterparty_dust_limit_satoshis;
@@ -1954,6 +1956,7 @@ impl<Signer: Sign> Channel<Signer> {
 			pending_htlcs_value_msat: 0,
 			on_counterparty_tx_dust_exposure_msat: 0,
 			on_holder_tx_dust_exposure_msat: 0,
+			holding_cell_msat: 0,
 		};
 
 		let counterparty_dust_limit_success_sat = (self.get_dust_buffer_feerate(outbound_feerate_update) as u64 * HTLC_SUCCESS_TX_WEIGHT / 1000) + self.counterparty_dust_limit_satoshis;
@@ -1972,6 +1975,7 @@ impl<Signer: Sign> Channel<Signer> {
 			if let &HTLCUpdateAwaitingACK::AddHTLC { ref amount_msat, .. } = update {
 				stats.pending_htlcs += 1;
 				stats.pending_htlcs_value_msat += amount_msat;
+				stats.holding_cell_msat += amount_msat;
 				if *amount_msat / 1000 < counterparty_dust_limit_success_sat {
 					stats.on_counterparty_tx_dust_exposure_msat += amount_msat;
 				}
@@ -2448,7 +2452,7 @@ impl<Signer: Sign> Channel<Signer> {
 		let total_fee_sat = Channel::<Signer>::commit_tx_fee_sat(feerate_per_kw, num_htlcs);
 		if update_fee {
 			let counterparty_reserve_we_require = Channel::<Signer>::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis);
-			if counterparty_balance_msat * 1000 < total_fee_sat + counterparty_reserve_we_require {
+			if counterparty_balance_msat < total_fee_sat * 1000 + counterparty_reserve_we_require * 1000 {
 				return Err((None, ChannelError::Close("Funding remote cannot afford proposed new fee".to_owned())));
 			}
 		}
@@ -2692,12 +2696,7 @@ impl<Signer: Sign> Channel<Signer> {
 				return Ok((None, htlcs_to_fail));
 			}
 			let update_fee = if let Some(feerate) = self.holding_cell_update_fee.take() {
-				assert!(self.is_outbound());
-				self.pending_update_fee = Some((feerate, FeeUpdateState::Outbound));
-				Some(msgs::UpdateFee {
-					channel_id: self.channel_id,
-					feerate_per_kw: feerate as u32,
-				})
+				self.send_update_fee(feerate, logger)
 			} else {
 				None
 			};
@@ -2986,10 +2985,10 @@ impl<Signer: Sign> Channel<Signer> {
 		// Before proposing a feerate update, check that we can actually afford the new fee.
 		let inbound_stats = self.get_inbound_pending_htlc_stats(Some(feerate_per_kw));
 		let outbound_stats = self.get_outbound_pending_htlc_stats(Some(feerate_per_kw));
-		let total_fee_sat = Channel::<Signer>::commit_tx_fee_sat(feerate_per_kw, (inbound_stats.pending_htlcs + CONCURRENT_INBOUND_HTLC_FEE_BUFFER + outbound_stats.pending_htlcs) as usize);
 		let keys = if let Ok(keys) = self.build_holder_transaction_keys(self.cur_holder_commitment_transaction_number) { keys } else { return None; };
-		let holder_balance_msat = self.build_commitment_transaction(self.cur_holder_commitment_transaction_number, &keys, true, true, logger).4;
-		if holder_balance_msat * 1000 < total_fee_sat + self.counterparty_selected_channel_reserve_satoshis.unwrap() {
+		let (_, _, num_htlcs, _, holder_balance_msat, _) = self.build_commitment_transaction(self.cur_holder_commitment_transaction_number, &keys, true, true, logger);
+		let total_fee_sat = Channel::<Signer>::commit_tx_fee_sat(feerate_per_kw, num_htlcs + CONCURRENT_INBOUND_HTLC_FEE_BUFFER as usize);
+		if holder_balance_msat < total_fee_sat * 1000 + self.counterparty_selected_channel_reserve_satoshis.unwrap() * 1000 {
 			//TODO: auto-close after a number of failures?
 			log_debug!(logger, "Cannot afford to send new feerate at {}", feerate_per_kw);
 			return None;
@@ -4575,8 +4574,8 @@ impl<Signer: Sign> Channel<Signer> {
 			let counterparty_balance_msat = self.build_commitment_transaction(self.cur_holder_commitment_transaction_number, &keys, true, true, logger).5;
 			let htlc_candidate = HTLCCandidate::new(amount_msat, HTLCInitiator::LocalOffered);
 			let counterparty_commit_tx_fee_msat = self.next_remote_commit_tx_fee_msat(htlc_candidate, None);
-			let holder_selected_chan_reserve = Channel::<Signer>::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis);
-			if counterparty_balance_msat < counterparty_commit_tx_fee_msat + holder_selected_chan_reserve {
+			let holder_selected_chan_reserve_msat = Channel::<Signer>::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis) * 1000;
+			if counterparty_balance_msat < counterparty_commit_tx_fee_msat + holder_selected_chan_reserve_msat {
 				return Err(ChannelError::Ignore("Cannot send value that would put counterparty balance under holder-announced channel reserve value".to_owned()));
 			}
 		}
@@ -4599,7 +4598,7 @@ impl<Signer: Sign> Channel<Signer> {
 			}
 		}
 
-		let holder_balance_msat = self.build_commitment_transaction(self.cur_holder_commitment_transaction_number, &keys, true, true, logger).4 as u64;
+		let holder_balance_msat = self.build_commitment_transaction(self.cur_holder_commitment_transaction_number, &keys, true, true, logger).4 as u64 - outbound_stats.holding_cell_msat;
 		if holder_balance_msat < amount_msat {
 			return Err(ChannelError::Ignore(format!("Cannot send value that would overdraw remaining funds. Amount: {}, pending value to self {}", amount_msat, holder_balance_msat)));
 		}