Merge pull request #2156 from alecchendev/2023-04-mpp-keysend
[rust-lightning] / lightning / src / ln / channel.rs
index 829ce3a997663ea5886144f878b0b027eaff2c0b..8cb73241562e7187deebd75dd3e3ef8858a9abc6 100644 (file)
@@ -73,6 +73,8 @@ pub struct AvailableBalances {
        pub outbound_capacity_msat: u64,
        /// The maximum value we can assign to the next outbound HTLC
        pub next_outbound_htlc_limit_msat: u64,
+       /// The minimum value we can assign to the next outbound HTLC
+       pub next_outbound_htlc_minimum_msat: u64,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq)]
@@ -432,6 +434,12 @@ pub(super) struct ReestablishResponses {
        pub shutdown_msg: Option<msgs::Shutdown>,
 }
 
+/// The return type of `force_shutdown`
+pub(crate) type ShutdownResult = (
+       Option<(PublicKey, OutPoint, ChannelMonitorUpdate)>,
+       Vec<(HTLCSource, PaymentHash, PublicKey, [u8; 32])>
+);
+
 /// If the majority of the channels funds are to the fundee and the initiator holds only just
 /// enough funds to cover their reserve value, channels are at risk of getting "stuck". Because the
 /// initiator controls the feerate, if they then go to increase the channel fee, they may have no
@@ -479,6 +487,13 @@ pub(crate) const MIN_AFFORDABLE_HTLC_COUNT: usize = 4;
 ///   * `EXPIRE_PREV_CONFIG_TICKS` = convergence_delay / tick_interval
 pub(crate) const EXPIRE_PREV_CONFIG_TICKS: usize = 5;
 
+/// The number of ticks that may elapse while we're waiting for a response to a
+/// [`msgs::RevokeAndACK`] or [`msgs::ChannelReestablish`] message before we attempt to disconnect
+/// them.
+///
+/// See [`Channel::sent_message_awaiting_response`] for more information.
+pub(crate) const DISCONNECT_PEER_AWAITING_RESPONSE_TICKS: usize = 2;
+
 struct PendingChannelMonitorUpdate {
        update: ChannelMonitorUpdate,
        /// In some cases we need to delay letting the [`ChannelMonitorUpdate`] go until after an
@@ -715,6 +730,19 @@ pub(super) struct Channel<Signer: ChannelSigner> {
        /// See-also <https://github.com/lightningnetwork/lnd/issues/4006>
        pub workaround_lnd_bug_4006: Option<msgs::ChannelReady>,
 
+       /// An option set when we wish to track how many ticks have elapsed while waiting for a response
+       /// from our counterparty after sending a message. If the peer has yet to respond after reaching
+       /// `DISCONNECT_PEER_AWAITING_RESPONSE_TICKS`, a reconnection should be attempted to try to
+       /// unblock the state machine.
+       ///
+       /// This behavior is mostly motivated by a lnd bug in which we don't receive a message we expect
+       /// to in a timely manner, which may lead to channels becoming unusable and/or force-closed. An
+       /// example of such can be found at <https://github.com/lightningnetwork/lnd/issues/7682>.
+       ///
+       /// This is currently only used when waiting for a [`msgs::ChannelReestablish`] or
+       /// [`msgs::RevokeAndACK`] message from the counterparty.
+       sent_message_awaiting_response: Option<usize>,
+
        #[cfg(any(test, fuzzing))]
        // When we receive an HTLC fulfill on an outbound path, we may immediately fulfill the
        // corresponding HTLC on the inbound path. If, then, the outbound path channel is
@@ -1130,6 +1158,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                        next_remote_commitment_tx_fee_info_cached: Mutex::new(None),
 
                        workaround_lnd_bug_4006: None,
+                       sent_message_awaiting_response: None,
 
                        latest_inbound_scid_alias: None,
                        outbound_scid_alias,
@@ -1489,6 +1518,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                        next_remote_commitment_tx_fee_info_cached: Mutex::new(None),
 
                        workaround_lnd_bug_4006: None,
+                       sent_message_awaiting_response: None,
 
                        latest_inbound_scid_alias: None,
                        outbound_scid_alias,
@@ -2676,6 +2706,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
        /// corner case properly.
        pub fn get_available_balances(&self) -> AvailableBalances {
                // Note that we have to handle overflow due to the above case.
+               let inbound_stats = self.get_inbound_pending_htlc_stats(None);
                let outbound_stats = self.get_outbound_pending_htlc_stats(None);
 
                let mut balance_msat = self.value_to_self_msat;
@@ -2686,10 +2717,112 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                }
                balance_msat -= outbound_stats.pending_htlcs_value_msat;
 
-               let outbound_capacity_msat = cmp::max(self.value_to_self_msat as i64
-                               - outbound_stats.pending_htlcs_value_msat as i64
-                               - self.counterparty_selected_channel_reserve_satoshis.unwrap_or(0) as i64 * 1000,
-                       0) as u64;
+               let outbound_capacity_msat = self.value_to_self_msat
+                               .saturating_sub(outbound_stats.pending_htlcs_value_msat)
+                               .saturating_sub(
+                                       self.counterparty_selected_channel_reserve_satoshis.unwrap_or(0) * 1000);
+
+               let mut available_capacity_msat = outbound_capacity_msat;
+
+               if self.is_outbound() {
+                       // We should mind channel commit tx fee when computing how much of the available capacity
+                       // can be used in the next htlc. Mirrors the logic in send_htlc.
+                       //
+                       // The fee depends on whether the amount we will be sending is above dust or not,
+                       // and the answer will in turn change the amount itself — making it a circular
+                       // dependency.
+                       // This complicates the computation around dust-values, up to the one-htlc-value.
+                       let mut real_dust_limit_timeout_sat = self.holder_dust_limit_satoshis;
+                       if !self.opt_anchors() {
+                               real_dust_limit_timeout_sat += self.feerate_per_kw as u64 * htlc_timeout_tx_weight(false) / 1000;
+                       }
+
+                       let htlc_above_dust = HTLCCandidate::new(real_dust_limit_timeout_sat * 1000, HTLCInitiator::LocalOffered);
+                       let max_reserved_commit_tx_fee_msat = FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE * self.next_local_commit_tx_fee_msat(htlc_above_dust, Some(()));
+                       let htlc_dust = HTLCCandidate::new(real_dust_limit_timeout_sat * 1000 - 1, HTLCInitiator::LocalOffered);
+                       let min_reserved_commit_tx_fee_msat = FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE * self.next_local_commit_tx_fee_msat(htlc_dust, Some(()));
+
+                       // We will first subtract the fee as if we were above-dust. Then, if the resulting
+                       // value ends up being below dust, we have this fee available again. In that case,
+                       // match the value to right-below-dust.
+                       let mut capacity_minus_commitment_fee_msat: i64 = (available_capacity_msat as i64) - (max_reserved_commit_tx_fee_msat as i64);
+                       if capacity_minus_commitment_fee_msat < (real_dust_limit_timeout_sat as i64) * 1000 {
+                               let one_htlc_difference_msat = max_reserved_commit_tx_fee_msat - min_reserved_commit_tx_fee_msat;
+                               debug_assert!(one_htlc_difference_msat != 0);
+                               capacity_minus_commitment_fee_msat += one_htlc_difference_msat as i64;
+                               capacity_minus_commitment_fee_msat = cmp::min(real_dust_limit_timeout_sat as i64 * 1000 - 1, capacity_minus_commitment_fee_msat);
+                               available_capacity_msat = cmp::max(0, cmp::min(capacity_minus_commitment_fee_msat, available_capacity_msat as i64)) as u64;
+                       } else {
+                               available_capacity_msat = capacity_minus_commitment_fee_msat as u64;
+                       }
+               } else {
+                       // If the channel is inbound (i.e. counterparty pays the fee), we need to make sure
+                       // sending a new HTLC won't reduce their balance below our reserve threshold.
+                       let mut real_dust_limit_success_sat = self.counterparty_dust_limit_satoshis;
+                       if !self.opt_anchors() {
+                               real_dust_limit_success_sat += self.feerate_per_kw as u64 * htlc_success_tx_weight(false) / 1000;
+                       }
+
+                       let htlc_above_dust = HTLCCandidate::new(real_dust_limit_success_sat * 1000, HTLCInitiator::LocalOffered);
+                       let max_reserved_commit_tx_fee_msat = self.next_remote_commit_tx_fee_msat(htlc_above_dust, None);
+
+                       let holder_selected_chan_reserve_msat = self.holder_selected_channel_reserve_satoshis * 1000;
+                       let remote_balance_msat = (self.channel_value_satoshis * 1000 - self.value_to_self_msat)
+                               .saturating_sub(inbound_stats.pending_htlcs_value_msat);
+
+                       if remote_balance_msat < max_reserved_commit_tx_fee_msat + holder_selected_chan_reserve_msat {
+                               // If another HTLC's fee would reduce the remote's balance below the reserve limit
+                               // we've selected for them, we can only send dust HTLCs.
+                               available_capacity_msat = cmp::min(available_capacity_msat, real_dust_limit_success_sat * 1000 - 1);
+                       }
+               }
+
+               let mut next_outbound_htlc_minimum_msat = self.counterparty_htlc_minimum_msat;
+
+               // If we get close to our maximum dust exposure, we end up in a situation where we can send
+               // between zero and the remaining dust exposure limit remaining OR above the dust limit.
+               // Because we cannot express this as a simple min/max, we prefer to tell the user they can
+               // send above the dust limit (as the router can always overpay to meet the dust limit).
+               let mut remaining_msat_below_dust_exposure_limit = None;
+               let mut dust_exposure_dust_limit_msat = 0;
+
+               let (htlc_success_dust_limit, htlc_timeout_dust_limit) = if self.opt_anchors() {
+                       (self.counterparty_dust_limit_satoshis, self.holder_dust_limit_satoshis)
+               } else {
+                       let dust_buffer_feerate = self.get_dust_buffer_feerate(None) as u64;
+                       (self.counterparty_dust_limit_satoshis + dust_buffer_feerate * htlc_success_tx_weight(false) / 1000,
+                        self.holder_dust_limit_satoshis       + dust_buffer_feerate * htlc_timeout_tx_weight(false) / 1000)
+               };
+               let on_counterparty_dust_htlc_exposure_msat = inbound_stats.on_counterparty_tx_dust_exposure_msat + outbound_stats.on_counterparty_tx_dust_exposure_msat;
+               if on_counterparty_dust_htlc_exposure_msat as i64 + htlc_success_dust_limit as i64 * 1000 - 1 > self.get_max_dust_htlc_exposure_msat() as i64 {
+                       remaining_msat_below_dust_exposure_limit =
+                               Some(self.get_max_dust_htlc_exposure_msat().saturating_sub(on_counterparty_dust_htlc_exposure_msat));
+                       dust_exposure_dust_limit_msat = cmp::max(dust_exposure_dust_limit_msat, htlc_success_dust_limit * 1000);
+               }
+
+               let on_holder_dust_htlc_exposure_msat = inbound_stats.on_holder_tx_dust_exposure_msat + outbound_stats.on_holder_tx_dust_exposure_msat;
+               if on_holder_dust_htlc_exposure_msat as i64 + htlc_timeout_dust_limit as i64 * 1000 - 1 > self.get_max_dust_htlc_exposure_msat() as i64 {
+                       remaining_msat_below_dust_exposure_limit = Some(cmp::min(
+                               remaining_msat_below_dust_exposure_limit.unwrap_or(u64::max_value()),
+                               self.get_max_dust_htlc_exposure_msat().saturating_sub(on_holder_dust_htlc_exposure_msat)));
+                       dust_exposure_dust_limit_msat = cmp::max(dust_exposure_dust_limit_msat, htlc_timeout_dust_limit * 1000);
+               }
+
+               if let Some(remaining_limit_msat) = remaining_msat_below_dust_exposure_limit {
+                       if available_capacity_msat < dust_exposure_dust_limit_msat {
+                               available_capacity_msat = cmp::min(available_capacity_msat, remaining_limit_msat);
+                       } else {
+                               next_outbound_htlc_minimum_msat = cmp::max(next_outbound_htlc_minimum_msat, dust_exposure_dust_limit_msat);
+                       }
+               }
+
+               available_capacity_msat = cmp::min(available_capacity_msat,
+                       self.counterparty_max_htlc_value_in_flight_msat - outbound_stats.pending_htlcs_value_msat);
+
+               if outbound_stats.pending_htlcs + 1 > self.counterparty_max_accepted_htlcs as u32 {
+                       available_capacity_msat = 0;
+               }
+
                AvailableBalances {
                        inbound_capacity_msat: cmp::max(self.channel_value_satoshis as i64 * 1000
                                        - self.value_to_self_msat as i64
@@ -2697,10 +2830,8 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                                        - self.holder_selected_channel_reserve_satoshis as i64 * 1000,
                                0) as u64,
                        outbound_capacity_msat,
-                       next_outbound_htlc_limit_msat: cmp::max(cmp::min(outbound_capacity_msat as i64,
-                                       self.counterparty_max_htlc_value_in_flight_msat as i64
-                                               - outbound_stats.pending_htlcs_value_msat as i64),
-                               0) as u64,
+                       next_outbound_htlc_limit_msat: available_capacity_msat,
+                       next_outbound_htlc_minimum_msat,
                        balance_msat,
                }
        }
@@ -2724,10 +2855,16 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                feerate_per_kw as u64 * (commitment_tx_base_weight(opt_anchors) + num_htlcs as u64 * COMMITMENT_TX_WEIGHT_PER_HTLC) / 1000
        }
 
-       // Get the commitment tx fee for the local's (i.e. our) next commitment transaction based on the
-       // number of pending HTLCs that are on track to be in our next commitment tx, plus an additional
-       // HTLC if `fee_spike_buffer_htlc` is Some, plus a new HTLC given by `new_htlc_amount`. Dust HTLCs
-       // are excluded.
+       /// Get the commitment tx fee for the local's (i.e. our) next commitment transaction based on the
+       /// number of pending HTLCs that are on track to be in our next commitment tx.
+       ///
+       /// Optionally includes the `HTLCCandidate` given by `htlc` and an additional non-dust HTLC if
+       /// `fee_spike_buffer_htlc` is `Some`.
+       ///
+       /// The first extra HTLC is useful for determining whether we can accept a further HTLC, the
+       /// second allows for creating a buffer to ensure a further HTLC can always be accepted/added.
+       ///
+       /// Dust HTLCs are excluded.
        fn next_local_commit_tx_fee_msat(&self, htlc: HTLCCandidate, fee_spike_buffer_htlc: Option<()>) -> u64 {
                assert!(self.is_outbound());
 
@@ -2821,10 +2958,16 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                res
        }
 
-       // Get the commitment tx fee for the remote's next commitment transaction based on the number of
-       // pending HTLCs that are on track to be in their next commitment tx, plus an additional HTLC if
-       // `fee_spike_buffer_htlc` is Some, plus a new HTLC given by `new_htlc_amount`. Dust HTLCs are
-       // excluded.
+       /// Get the commitment tx fee for the remote's next commitment transaction based on the number of
+       /// pending HTLCs that are on track to be in their next commitment tx
+       ///
+       /// Optionally includes the `HTLCCandidate` given by `htlc` and an additional non-dust HTLC if
+       /// `fee_spike_buffer_htlc` is `Some`.
+       ///
+       /// The first extra HTLC is useful for determining whether we can accept a further HTLC, the
+       /// second allows for creating a buffer to ensure a further HTLC can always be accepted/added.
+       ///
+       /// Dust HTLCs are excluded.
        fn next_remote_commit_tx_fee_msat(&self, htlc: HTLCCandidate, fee_spike_buffer_htlc: Option<()>) -> u64 {
                assert!(!self.is_outbound());
 
@@ -3526,6 +3669,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                // OK, we step the channel here and *then* if the new generation fails we can fail the
                // channel based on that, but stepping stuff here should be safe either way.
                self.channel_state &= !(ChannelState::AwaitingRemoteRevoke as u32);
+               self.sent_message_awaiting_response = None;
                self.counterparty_prev_commitment_point = self.counterparty_cur_commitment_point;
                self.counterparty_cur_commitment_point = Some(msg.next_per_commitment_point);
                self.cur_counterparty_commitment_transaction_number -= 1;
@@ -3841,6 +3985,8 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                        }
                }
 
+               self.sent_message_awaiting_response = None;
+
                self.channel_state |= ChannelState::PeerDisconnected as u32;
                log_trace!(logger, "Peer disconnection resulted in {} remote-announced HTLC drops on channel {}", inbound_drop_count, log_bytes!(self.channel_id()));
        }
@@ -3943,6 +4089,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                        Some(self.get_last_revoke_and_ack())
                } else { None };
                let commitment_update = if self.monitor_pending_commitment_signed {
+                       self.mark_awaiting_response();
                        Some(self.get_last_commitment_update(logger))
                } else { None };
 
@@ -4132,6 +4279,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                // Go ahead and unmark PeerDisconnected as various calls we may make check for it (and all
                // remaining cases either succeed or ErrorMessage-fail).
                self.channel_state &= !(ChannelState::PeerDisconnected as u32);
+               self.sent_message_awaiting_response = None;
 
                let shutdown_msg = if self.channel_state & (ChannelState::LocalShutdownSent as u32) != 0 {
                        assert!(self.shutdown_scriptpubkey.is_some());
@@ -4192,7 +4340,11 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                // revoke_and_ack, not on sending commitment_signed, so we add one if have
                // AwaitingRemoteRevoke set, which indicates we sent a commitment_signed but haven't gotten
                // the corresponding revoke_and_ack back yet.
-               let next_counterparty_commitment_number = INITIAL_COMMITMENT_NUMBER - self.cur_counterparty_commitment_transaction_number + if (self.channel_state & ChannelState::AwaitingRemoteRevoke as u32) != 0 { 1 } else { 0 };
+               let is_awaiting_remote_revoke = self.channel_state & ChannelState::AwaitingRemoteRevoke as u32 != 0;
+               if is_awaiting_remote_revoke && !self.is_awaiting_monitor_update() {
+                       self.mark_awaiting_response();
+               }
+               let next_counterparty_commitment_number = INITIAL_COMMITMENT_NUMBER - self.cur_counterparty_commitment_transaction_number + if is_awaiting_remote_revoke { 1 } else { 0 };
 
                let channel_ready = if msg.next_local_commitment_number == 1 && INITIAL_COMMITMENT_NUMBER - self.cur_holder_commitment_transaction_number == 1 {
                        // We should never have to worry about MonitorUpdateInProgress resending ChannelReady
@@ -4361,6 +4513,28 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                }), None))
        }
 
+       // Marks a channel as waiting for a response from the counterparty. If it's not received
+       // [`DISCONNECT_PEER_AWAITING_RESPONSE_TICKS`] after sending our own to them, then we'll attempt
+       // a reconnection.
+       fn mark_awaiting_response(&mut self) {
+               self.sent_message_awaiting_response = Some(0);
+       }
+
+       /// Determines whether we should disconnect the counterparty due to not receiving a response
+       /// within our expected timeframe.
+       ///
+       /// This should be called on every [`super::channelmanager::ChannelManager::timer_tick_occurred`].
+       pub fn should_disconnect_peer_awaiting_response(&mut self) -> bool {
+               let ticks_elapsed = if let Some(ticks_elapsed) = self.sent_message_awaiting_response.as_mut() {
+                       ticks_elapsed
+               } else {
+                       // Don't disconnect when we're not waiting on a response.
+                       return false;
+               };
+               *ticks_elapsed += 1;
+               *ticks_elapsed >= DISCONNECT_PEER_AWAITING_RESPONSE_TICKS
+       }
+
        pub fn shutdown<SP: Deref>(
                &mut self, signer_provider: &SP, their_features: &InitFeatures, msg: &msgs::Shutdown
        ) -> Result<(Option<msgs::Shutdown>, Option<&ChannelMonitorUpdate>, Vec<(HTLCSource, PaymentHash)>), ChannelError>
@@ -5044,10 +5218,25 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                self.pending_monitor_updates.is_empty()
        }
 
+       pub fn complete_all_mon_updates_through(&mut self, update_id: u64) {
+               self.pending_monitor_updates.retain(|upd| {
+                       if upd.update.update_id <= update_id {
+                               assert!(!upd.blocked, "Completed update must have flown");
+                               false
+                       } else { true }
+               });
+       }
+
        pub fn complete_one_mon_update(&mut self, update_id: u64) {
                self.pending_monitor_updates.retain(|upd| upd.update.update_id != update_id);
        }
 
+       /// Returns an iterator over all unblocked monitor updates which have not yet completed.
+       pub fn uncompleted_unblocked_mon_updates(&self) -> impl Iterator<Item=&ChannelMonitorUpdate> {
+               self.pending_monitor_updates.iter()
+                       .filter_map(|upd| if upd.blocked { None } else { Some(&upd.update) })
+       }
+
        /// Returns true if funding_created was sent/received.
        pub fn is_funding_initiated(&self) -> bool {
                self.channel_state >= ChannelState::FundingSent as u32
@@ -5733,7 +5922,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 
        /// May panic if called on a channel that wasn't immediately-previously
        /// self.remove_uncommitted_htlcs_and_mark_paused()'d
-       pub fn get_channel_reestablish<L: Deref>(&self, logger: &L) -> msgs::ChannelReestablish where L::Target: Logger {
+       pub fn get_channel_reestablish<L: Deref>(&mut self, logger: &L) -> msgs::ChannelReestablish where L::Target: Logger {
                assert_eq!(self.channel_state & ChannelState::PeerDisconnected as u32, ChannelState::PeerDisconnected as u32);
                assert_ne!(self.cur_counterparty_commitment_transaction_number, INITIAL_COMMITMENT_NUMBER);
                // Prior to static_remotekey, my_current_per_commitment_point was critical to claiming
@@ -5752,6 +5941,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                        log_info!(logger, "Sending a data_loss_protect with no previous remote per_commitment_secret for channel {}", log_bytes!(self.channel_id()));
                        [0;32]
                };
+               self.mark_awaiting_response();
                msgs::ChannelReestablish {
                        channel_id: self.channel_id(),
                        // The protocol has two different commitment number concepts - the "commitment
@@ -5833,8 +6023,15 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                        return Err(ChannelError::Ignore("Cannot send 0-msat HTLC".to_owned()));
                }
 
-               if amount_msat < self.counterparty_htlc_minimum_msat {
-                       return Err(ChannelError::Ignore(format!("Cannot send less than their minimum HTLC value ({})", self.counterparty_htlc_minimum_msat)));
+               let available_balances = self.get_available_balances();
+               if amount_msat < available_balances.next_outbound_htlc_minimum_msat {
+                       return Err(ChannelError::Ignore(format!("Cannot send less than our next-HTLC minimum - {} msat",
+                               available_balances.next_outbound_htlc_minimum_msat)));
+               }
+
+               if amount_msat > available_balances.next_outbound_htlc_limit_msat {
+                       return Err(ChannelError::Ignore(format!("Cannot send more than our next-HTLC maximum - {} msat",
+                               available_balances.next_outbound_htlc_limit_msat)));
                }
 
                if (self.channel_state & (ChannelState::PeerDisconnected as u32)) != 0 {
@@ -5847,74 +6044,6 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                        return Err(ChannelError::Ignore("Cannot send an HTLC while disconnected from channel counterparty".to_owned()));
                }
 
-               let inbound_stats = self.get_inbound_pending_htlc_stats(None);
-               let outbound_stats = self.get_outbound_pending_htlc_stats(None);
-               if outbound_stats.pending_htlcs + 1 > self.counterparty_max_accepted_htlcs as u32 {
-                       return Err(ChannelError::Ignore(format!("Cannot push more than their max accepted HTLCs ({})", self.counterparty_max_accepted_htlcs)));
-               }
-               // Check their_max_htlc_value_in_flight_msat
-               if outbound_stats.pending_htlcs_value_msat + amount_msat > self.counterparty_max_htlc_value_in_flight_msat {
-                       return Err(ChannelError::Ignore(format!("Cannot send value that would put us over the max HTLC value in flight our peer will accept ({})", self.counterparty_max_htlc_value_in_flight_msat)));
-               }
-
-               if !self.is_outbound() {
-                       // Check that we won't violate the remote channel reserve by adding this HTLC.
-                       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_msat = self.holder_selected_channel_reserve_satoshis * 1000;
-                       let remote_balance_msat = (self.channel_value_satoshis * 1000 - self.value_to_self_msat).saturating_sub(inbound_stats.pending_htlcs_value_msat);
-                       if remote_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()));
-                       }
-               }
-
-               let (htlc_success_dust_limit, htlc_timeout_dust_limit) = if self.opt_anchors() {
-                       (0, 0)
-               } else {
-                       let dust_buffer_feerate = self.get_dust_buffer_feerate(None) as u64;
-                       (dust_buffer_feerate * htlc_success_tx_weight(false) / 1000,
-                               dust_buffer_feerate * htlc_timeout_tx_weight(false) / 1000)
-               };
-               let exposure_dust_limit_success_sats = htlc_success_dust_limit + self.counterparty_dust_limit_satoshis;
-               if amount_msat / 1000 < exposure_dust_limit_success_sats {
-                       let on_counterparty_dust_htlc_exposure_msat = inbound_stats.on_counterparty_tx_dust_exposure_msat + outbound_stats.on_counterparty_tx_dust_exposure_msat + amount_msat;
-                       if on_counterparty_dust_htlc_exposure_msat > self.get_max_dust_htlc_exposure_msat() {
-                               return Err(ChannelError::Ignore(format!("Cannot send value that would put our exposure to dust HTLCs at {} over the limit {} on counterparty commitment tx",
-                                       on_counterparty_dust_htlc_exposure_msat, self.get_max_dust_htlc_exposure_msat())));
-                       }
-               }
-
-               let exposure_dust_limit_timeout_sats = htlc_timeout_dust_limit + self.holder_dust_limit_satoshis;
-               if amount_msat / 1000 <  exposure_dust_limit_timeout_sats {
-                       let on_holder_dust_htlc_exposure_msat = inbound_stats.on_holder_tx_dust_exposure_msat + outbound_stats.on_holder_tx_dust_exposure_msat + amount_msat;
-                       if on_holder_dust_htlc_exposure_msat > self.get_max_dust_htlc_exposure_msat() {
-                               return Err(ChannelError::Ignore(format!("Cannot send value that would put our exposure to dust HTLCs at {} over the limit {} on holder commitment tx",
-                                       on_holder_dust_htlc_exposure_msat, self.get_max_dust_htlc_exposure_msat())));
-                       }
-               }
-
-               let holder_balance_msat = self.value_to_self_msat
-                       .saturating_sub(outbound_stats.pending_htlcs_value_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)));
-               }
-
-               // `2 *` and extra HTLC are for the fee spike buffer.
-               let commit_tx_fee_msat = if self.is_outbound() {
-                       let htlc_candidate = HTLCCandidate::new(amount_msat, HTLCInitiator::LocalOffered);
-                       FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE * self.next_local_commit_tx_fee_msat(htlc_candidate, Some(()))
-               } else { 0 };
-               if holder_balance_msat - amount_msat < commit_tx_fee_msat {
-                       return Err(ChannelError::Ignore(format!("Cannot send value that would not leave enough to pay for fees. Pending value to self: {}. local_commit_tx_fee {}", holder_balance_msat, commit_tx_fee_msat)));
-               }
-
-               // Check self.counterparty_selected_channel_reserve_satoshis (the amount we must keep as
-               // reserve for the remote to have something to claim if we misbehave)
-               let chan_reserve_msat = self.counterparty_selected_channel_reserve_satoshis.unwrap() * 1000;
-               if holder_balance_msat - amount_msat - commit_tx_fee_msat < chan_reserve_msat {
-                       return Err(ChannelError::Ignore(format!("Cannot send value that would put our balance under counterparty-announced channel reserve value ({})", chan_reserve_msat)));
-               }
-
                let need_holding_cell = (self.channel_state & (ChannelState::AwaitingRemoteRevoke as u32 | ChannelState::MonitorUpdateInProgress as u32)) != 0;
                log_debug!(logger, "Pushing new outbound HTLC for {} msat {}", amount_msat,
                        if force_holding_cell { "into holding cell" }
@@ -6234,7 +6363,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
        /// those explicitly stated to be allowed after shutdown completes, eg some simple getters).
        /// Also returns the list of payment_hashes for channels which we can safely fail backwards
        /// immediately (others we will have to allow to time out).
-       pub fn force_shutdown(&mut self, should_broadcast: bool) -> (Option<(OutPoint, ChannelMonitorUpdate)>, Vec<(HTLCSource, PaymentHash, PublicKey, [u8; 32])>) {
+       pub fn force_shutdown(&mut self, should_broadcast: bool) -> ShutdownResult {
                // Note that we MUST only generate a monitor update that indicates force-closure - we're
                // called during initialization prior to the chain_monitor in the encompassing ChannelManager
                // being fully configured in some cases. Thus, its likely any monitor events we generate will
@@ -6263,7 +6392,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
                        // See test_duplicate_chan_id and test_pre_lockin_no_chan_closed_update for more.
                        if self.channel_state & (ChannelState::FundingSent as u32 | ChannelState::ChannelReady as u32 | ChannelState::ShutdownComplete as u32) != 0 {
                                self.latest_monitor_update_id = CLOSED_CHANNEL_UPDATE_ID;
-                               Some((funding_txo, ChannelMonitorUpdate {
+                               Some((self.get_counterparty_node_id(), funding_txo, ChannelMonitorUpdate {
                                        update_id: self.latest_monitor_update_id,
                                        updates: vec![ChannelMonitorUpdateStep::ChannelForceClosed { should_broadcast }],
                                }))
@@ -7096,6 +7225,7 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
                        next_remote_commitment_tx_fee_info_cached: Mutex::new(None),
 
                        workaround_lnd_bug_4006: None,
+                       sent_message_awaiting_response: None,
 
                        latest_inbound_scid_alias,
                        // Later in the ChannelManager deserialization phase we scan for channels and assign scid aliases if its missing