Generate a PaymentForwarded event when a forwarded HTLC is claimed
[rust-lightning] / lightning / src / ln / channel.rs
index 06308b01cee0a3c1141ea426b7fcbd07343a2a99..b9a63f1c3215b80dc4883f45e8b9763d457ed867 100644 (file)
@@ -26,9 +26,10 @@ use ln::{PaymentPreimage, PaymentHash};
 use ln::features::{ChannelFeatures, InitFeatures};
 use ln::msgs;
 use ln::msgs::{DecodeError, OptionalField, DataLossProtect};
-use ln::channelmanager::{BestBlock, PendingHTLCStatus, HTLCSource, HTLCFailReason, HTLCFailureMsg, PendingHTLCInfo, RAACommitmentOrder, BREAKDOWN_TIMEOUT, MIN_CLTV_EXPIRY_DELTA, MAX_LOCAL_BREAKDOWN_TIMEOUT};
+use ln::channelmanager::{PendingHTLCStatus, HTLCSource, HTLCFailReason, HTLCFailureMsg, PendingHTLCInfo, RAACommitmentOrder, BREAKDOWN_TIMEOUT, MIN_CLTV_EXPIRY_DELTA, MAX_LOCAL_BREAKDOWN_TIMEOUT};
 use ln::chan_utils::{CounterpartyCommitmentSecrets, TxCreationKeys, HTLCOutputInCommitment, HTLC_SUCCESS_TX_WEIGHT, HTLC_TIMEOUT_TX_WEIGHT, make_funding_redeemscript, ChannelPublicKeys, CommitmentTransaction, HolderCommitmentTransaction, ChannelTransactionParameters, CounterpartyChannelTransactionParameters, MAX_HTLCS, get_commitment_transaction_number_obscure_factor};
 use ln::chan_utils;
+use chain::BestBlock;
 use chain::chaininterface::{FeeEstimator,ConfirmationTarget};
 use chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitorUpdateStep, HTLC_FAIL_BACK_BUFFER};
 use chain::transaction::{OutPoint, TransactionData};
@@ -43,8 +44,8 @@ use util::scid_utils::scid_from_parts;
 use prelude::*;
 use core::{cmp,mem,fmt};
 use core::ops::Deref;
-#[cfg(any(test, feature = "fuzztarget"))]
-use std::sync::Mutex;
+#[cfg(any(test, feature = "fuzztarget", debug_assertions))]
+use sync::Mutex;
 use bitcoin::hashes::hex::ToHex;
 use bitcoin::blockdata::opcodes::all::OP_PUSHBYTES_0;
 
@@ -114,8 +115,8 @@ enum InboundHTLCState {
        /// commitment transaction without it as otherwise we'll have to force-close the channel to
        /// claim it before the timeout (obviously doesn't apply to revoked HTLCs that we can't claim
        /// anyway). That said, ChannelMonitor does this for us (see
-       /// ChannelMonitor::would_broadcast_at_height) so we actually remove the HTLC from our own
-       /// local state before then, once we're sure that the next commitment_signed and
+       /// ChannelMonitor::should_broadcast_holder_commitment_txn) so we actually remove the HTLC from
+       /// our own local state before then, once we're sure that the next commitment_signed and
        /// ChannelMonitor::provide_latest_local_commitment_tx will not include this HTLC.
        LocalRemoved(InboundHTLCRemovalReason),
 }
@@ -288,7 +289,7 @@ impl HTLCCandidate {
 }
 
 /// Information needed for constructing an invoice route hint for this channel.
-#[derive(Clone)]
+#[derive(Clone, Debug, PartialEq)]
 pub struct CounterpartyForwardingInfo {
        /// Base routing fee in millisatoshis.
        pub fee_base_msat: u32,
@@ -300,6 +301,36 @@ pub struct CounterpartyForwardingInfo {
        pub cltv_expiry_delta: u16,
 }
 
+/// A return value enum for get_update_fulfill_htlc. See UpdateFulfillCommitFetch variants for
+/// description
+enum UpdateFulfillFetch {
+       NewClaim {
+               monitor_update: ChannelMonitorUpdate,
+               htlc_value_msat: u64,
+               msg: Option<msgs::UpdateFulfillHTLC>,
+       },
+       DuplicateClaim {},
+}
+
+/// The return type of get_update_fulfill_htlc_and_commit.
+pub enum UpdateFulfillCommitFetch {
+       /// Indicates the HTLC fulfill is new, and either generated an update_fulfill message, placed
+       /// it in the holding cell, or re-generated the update_fulfill message after the same claim was
+       /// previously placed in the holding cell (and has since been removed).
+       NewClaim {
+               /// The ChannelMonitorUpdate which places the new payment preimage in the channel monitor
+               monitor_update: ChannelMonitorUpdate,
+               /// The value of the HTLC which was claimed, in msat.
+               htlc_value_msat: u64,
+               /// The update_fulfill message and commitment_signed message (if the claim was not placed
+               /// in the holding cell).
+               msgs: Option<(msgs::UpdateFulfillHTLC, msgs::CommitmentSigned)>,
+       },
+       /// Indicates the HTLC fulfill is duplicative and already existed either in the holding cell
+       /// or has been forgotten (presumably previously claimed).
+       DuplicateClaim {},
+}
+
 // TODO: We should refactor this to be an Inbound/OutboundChannel until initial setup handshaking
 // has been completed, and then turn into a Channel to get compiler-time enforcement of things like
 // calling channel_id() before we're set up or things like get_outbound_funding_signed on an
@@ -308,6 +339,9 @@ pub struct CounterpartyForwardingInfo {
 // Holder designates channel data owned for the benefice of the user client.
 // Counterparty designates channel data owned by the another channel participant entity.
 pub(super) struct Channel<Signer: Sign> {
+       #[cfg(any(test, feature = "_test_utils"))]
+       pub(crate) config: ChannelConfig,
+       #[cfg(not(any(test, feature = "_test_utils")))]
        config: ChannelConfig,
 
        user_id: u64,
@@ -373,10 +407,10 @@ pub(super) struct Channel<Signer: Sign> {
 
        #[cfg(debug_assertions)]
        /// Max to_local and to_remote outputs in a locally-generated commitment transaction
-       holder_max_commitment_tx_output: ::std::sync::Mutex<(u64, u64)>,
+       holder_max_commitment_tx_output: Mutex<(u64, u64)>,
        #[cfg(debug_assertions)]
        /// Max to_local and to_remote outputs in a remote-generated commitment transaction
-       counterparty_max_commitment_tx_output: ::std::sync::Mutex<(u64, u64)>,
+       counterparty_max_commitment_tx_output: Mutex<(u64, u64)>,
 
        last_sent_closing_fee: Option<(u32, u64, Signature)>, // (feerate, fee, holder_sig)
 
@@ -396,7 +430,7 @@ pub(super) struct Channel<Signer: Sign> {
        counterparty_max_htlc_value_in_flight_msat: u64,
        //get_holder_max_htlc_value_in_flight_msat(): u64,
        /// minimum channel reserve for self to maintain - set by them.
-       counterparty_selected_channel_reserve_satoshis: u64,
+       counterparty_selected_channel_reserve_satoshis: Option<u64>,
        // get_holder_selected_channel_reserve_satoshis(channel_value_sats: u64): u64
        counterparty_htlc_minimum_msat: u64,
        holder_htlc_minimum_msat: u64,
@@ -405,7 +439,7 @@ pub(super) struct Channel<Signer: Sign> {
        #[cfg(not(test))]
        counterparty_max_accepted_htlcs: u16,
        //implied by OUR_MAX_HTLCS: max_accepted_htlcs: u16,
-       minimum_depth: u32,
+       minimum_depth: Option<u32>,
 
        counterparty_forwarding_info: Option<CounterpartyForwardingInfo>,
 
@@ -434,6 +468,24 @@ pub(super) struct Channel<Signer: Sign> {
        next_local_commitment_tx_fee_info_cached: Mutex<Option<CommitmentTxInfoCached>>,
        #[cfg(any(test, feature = "fuzztarget"))]
        next_remote_commitment_tx_fee_info_cached: Mutex<Option<CommitmentTxInfoCached>>,
+
+       /// lnd has a long-standing bug where, upon reconnection, if the channel is not yet confirmed
+       /// they will not send a channel_reestablish until the channel locks in. Then, they will send a
+       /// funding_locked *before* sending the channel_reestablish (which is clearly a violation of
+       /// the BOLT specs). We copy c-lightning's workaround here and simply store the funding_locked
+       /// message until we receive a channel_reestablish.
+       ///
+       /// See-also <https://github.com/lightningnetwork/lnd/issues/4006>
+       pub workaround_lnd_bug_4006: Option<msgs::FundingLocked>,
+
+       #[cfg(any(test, feature = "fuzztarget"))]
+       // 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
+       // disconnected and reconnected (before we've exchange commitment_signed and revoke_and_ack
+       // messages), they may re-broadcast their update_fulfill_htlc, causing a duplicate claim. This
+       // is fine, but as a sanity check in our failure to generate the second claim, we check here
+       // that the original was a claim, and that we aren't now trying to fulfill a failed HTLC.
+       historical_inbound_htlc_fulfills: HashSet<u64>,
 }
 
 #[cfg(any(test, feature = "fuzztarget"))]
@@ -446,7 +498,6 @@ struct CommitmentTxInfoCached {
 }
 
 pub const OUR_MAX_HTLCS: u16 = 50; //TODO
-const SPENDING_INPUT_FOR_A_OUTPUT_WEIGHT: u64 = 79; // prevout: 36, nSequence: 4, script len: 1, witness lengths: (3+1)/4, sig: 73/4, if-selector: 1, redeemScript: (6 ops + 2*33 pubkeys + 1*2 delay)/4
 
 #[cfg(not(test))]
 const COMMITMENT_TX_BASE_WEIGHT: u64 = 724;
@@ -586,9 +637,9 @@ impl<Signer: Sign> Channel<Signer> {
                        monitor_pending_failures: Vec::new(),
 
                        #[cfg(debug_assertions)]
-                       holder_max_commitment_tx_output: ::std::sync::Mutex::new((channel_value_satoshis * 1000 - push_msat, push_msat)),
+                       holder_max_commitment_tx_output: Mutex::new((channel_value_satoshis * 1000 - push_msat, push_msat)),
                        #[cfg(debug_assertions)]
-                       counterparty_max_commitment_tx_output: ::std::sync::Mutex::new((channel_value_satoshis * 1000 - push_msat, push_msat)),
+                       counterparty_max_commitment_tx_output: Mutex::new((channel_value_satoshis * 1000 - push_msat, push_msat)),
 
                        last_sent_closing_fee: None,
 
@@ -600,11 +651,11 @@ impl<Signer: Sign> Channel<Signer> {
                        counterparty_dust_limit_satoshis: 0,
                        holder_dust_limit_satoshis: MIN_DUST_LIMIT_SATOSHIS,
                        counterparty_max_htlc_value_in_flight_msat: 0,
-                       counterparty_selected_channel_reserve_satoshis: 0,
+                       counterparty_selected_channel_reserve_satoshis: None, // Filled in in accept_channel
                        counterparty_htlc_minimum_msat: 0,
                        holder_htlc_minimum_msat: if config.own_channel_config.our_htlc_minimum_msat == 0 { 1 } else { config.own_channel_config.our_htlc_minimum_msat },
                        counterparty_max_accepted_htlcs: 0,
-                       minimum_depth: 0, // Filled in in accept_channel
+                       minimum_depth: None, // Filled in in accept_channel
 
                        counterparty_forwarding_info: None,
 
@@ -633,6 +684,11 @@ impl<Signer: Sign> Channel<Signer> {
                        next_local_commitment_tx_fee_info_cached: Mutex::new(None),
                        #[cfg(any(test, feature = "fuzztarget"))]
                        next_remote_commitment_tx_fee_info_cached: Mutex::new(None),
+
+                       workaround_lnd_bug_4006: None,
+
+                       #[cfg(any(test, feature = "fuzztarget"))]
+                       historical_inbound_htlc_fulfills: HashSet::new(),
                })
        }
 
@@ -825,9 +881,9 @@ impl<Signer: Sign> Channel<Signer> {
                        monitor_pending_failures: Vec::new(),
 
                        #[cfg(debug_assertions)]
-                       holder_max_commitment_tx_output: ::std::sync::Mutex::new((msg.push_msat, msg.funding_satoshis * 1000 - msg.push_msat)),
+                       holder_max_commitment_tx_output: Mutex::new((msg.push_msat, msg.funding_satoshis * 1000 - msg.push_msat)),
                        #[cfg(debug_assertions)]
-                       counterparty_max_commitment_tx_output: ::std::sync::Mutex::new((msg.push_msat, msg.funding_satoshis * 1000 - msg.push_msat)),
+                       counterparty_max_commitment_tx_output: Mutex::new((msg.push_msat, msg.funding_satoshis * 1000 - msg.push_msat)),
 
                        last_sent_closing_fee: None,
 
@@ -840,11 +896,11 @@ impl<Signer: Sign> Channel<Signer> {
                        counterparty_dust_limit_satoshis: msg.dust_limit_satoshis,
                        holder_dust_limit_satoshis: MIN_DUST_LIMIT_SATOSHIS,
                        counterparty_max_htlc_value_in_flight_msat: cmp::min(msg.max_htlc_value_in_flight_msat, msg.funding_satoshis * 1000),
-                       counterparty_selected_channel_reserve_satoshis: msg.channel_reserve_satoshis,
+                       counterparty_selected_channel_reserve_satoshis: Some(msg.channel_reserve_satoshis),
                        counterparty_htlc_minimum_msat: msg.htlc_minimum_msat,
                        holder_htlc_minimum_msat: if config.own_channel_config.our_htlc_minimum_msat == 0 { 1 } else { config.own_channel_config.our_htlc_minimum_msat },
                        counterparty_max_accepted_htlcs: msg.max_accepted_htlcs,
-                       minimum_depth: config.own_channel_config.minimum_depth,
+                       minimum_depth: Some(config.own_channel_config.minimum_depth),
 
                        counterparty_forwarding_info: None,
 
@@ -876,6 +932,11 @@ impl<Signer: Sign> Channel<Signer> {
                        next_local_commitment_tx_fee_info_cached: Mutex::new(None),
                        #[cfg(any(test, feature = "fuzztarget"))]
                        next_remote_commitment_tx_fee_info_cached: Mutex::new(None),
+
+                       workaround_lnd_bug_4006: None,
+
+                       #[cfg(any(test, feature = "fuzztarget"))]
+                       historical_inbound_htlc_fulfills: HashSet::new(),
                };
 
                Ok(chan)
@@ -1023,7 +1084,7 @@ impl<Signer: Sign> Channel<Signer> {
                        } else {
                                self.counterparty_max_commitment_tx_output.lock().unwrap()
                        };
-                       debug_assert!(broadcaster_max_commitment_tx_output.0 <= value_to_self_msat as u64 || value_to_self_msat / 1000 >= self.counterparty_selected_channel_reserve_satoshis as i64);
+                       debug_assert!(broadcaster_max_commitment_tx_output.0 <= value_to_self_msat as u64 || value_to_self_msat / 1000 >= self.counterparty_selected_channel_reserve_satoshis.unwrap() as i64);
                        broadcaster_max_commitment_tx_output.0 = cmp::max(broadcaster_max_commitment_tx_output.0, value_to_self_msat as u64);
                        debug_assert!(broadcaster_max_commitment_tx_output.1 <= value_to_remote_msat as u64 || value_to_remote_msat / 1000 >= Channel::<Signer>::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis) as i64);
                        broadcaster_max_commitment_tx_output.1 = cmp::max(broadcaster_max_commitment_tx_output.1, value_to_remote_msat as u64);
@@ -1203,20 +1264,7 @@ impl<Signer: Sign> Channel<Signer> {
                make_funding_redeemscript(&self.get_holder_pubkeys().funding_pubkey, self.counterparty_funding_pubkey())
        }
 
-       /// Builds the htlc-success or htlc-timeout transaction which spends a given HTLC output
-       /// @local is used only to convert relevant internal structures which refer to remote vs local
-       /// to decide value of outputs and direction of HTLCs.
-       fn build_htlc_transaction(&self, prev_hash: &Txid, htlc: &HTLCOutputInCommitment, local: bool, keys: &TxCreationKeys, feerate_per_kw: u32) -> Transaction {
-               chan_utils::build_htlc_transaction(prev_hash, feerate_per_kw, if local { self.get_counterparty_selected_contest_delay() } else { self.get_holder_selected_contest_delay() }, htlc, &keys.broadcaster_delayed_payment_key, &keys.revocation_key)
-       }
-
-       /// Per HTLC, only one get_update_fail_htlc or get_update_fulfill_htlc call may be made.
-       /// In such cases we debug_assert!(false) and return a ChannelError::Ignore. Thus, will always
-       /// return Ok(_) if debug assertions are turned on or preconditions are met.
-       ///
-       /// Note that it is still possible to hit these assertions in case we find a preimage on-chain
-       /// but then have a reorg which settles on an HTLC-failure on chain.
-       fn get_update_fulfill_htlc<L: Deref>(&mut self, htlc_id_arg: u64, payment_preimage_arg: PaymentPreimage, logger: &L) -> Result<(Option<msgs::UpdateFulfillHTLC>, Option<ChannelMonitorUpdate>), ChannelError> where L::Target: Logger {
+       fn get_update_fulfill_htlc<L: Deref>(&mut self, htlc_id_arg: u64, payment_preimage_arg: PaymentPreimage, logger: &L) -> UpdateFulfillFetch where L::Target: Logger {
                // Either ChannelFunded got set (which means it won't be unset) or there is no way any
                // caller thought we could have something claimed (cause we wouldn't have accepted in an
                // incoming HTLC anyway). If we got to ShutdownComplete, callers aren't allowed to call us,
@@ -1233,6 +1281,7 @@ impl<Signer: Sign> Channel<Signer> {
                // these, but for now we just have to treat them as normal.
 
                let mut pending_idx = core::usize::MAX;
+               let mut htlc_value_msat = 0;
                for (idx, htlc) in self.pending_inbound_htlcs.iter().enumerate() {
                        if htlc.htlc_id == htlc_id_arg {
                                assert_eq!(htlc.payment_hash, payment_hash_calc);
@@ -1242,9 +1291,9 @@ impl<Signer: Sign> Channel<Signer> {
                                                if let &InboundHTLCRemovalReason::Fulfill(_) = reason {
                                                } else {
                                                        log_warn!(logger, "Have preimage and want to fulfill HTLC with payment hash {} we already failed against channel {}", log_bytes!(htlc.payment_hash.0), log_bytes!(self.channel_id()));
+                                                       debug_assert!(false, "Tried to fulfill an HTLC that was already failed");
                                                }
-                                               debug_assert!(false, "Tried to fulfill an HTLC that was already fail/fulfilled");
-                                               return Ok((None, None));
+                                               return UpdateFulfillFetch::DuplicateClaim {};
                                        },
                                        _ => {
                                                debug_assert!(false, "Have an inbound HTLC we tried to claim before it was fully committed to");
@@ -1252,11 +1301,16 @@ impl<Signer: Sign> Channel<Signer> {
                                        }
                                }
                                pending_idx = idx;
+                               htlc_value_msat = htlc.amount_msat;
                                break;
                        }
                }
                if pending_idx == core::usize::MAX {
-                       return Err(ChannelError::Ignore("Unable to find a pending HTLC which matched the given HTLC ID".to_owned()));
+                       #[cfg(any(test, feature = "fuzztarget"))]
+                       // If we failed to find an HTLC to fulfill, make sure it was previously fulfilled and
+                       // this is simply a duplicate claim, not previously failed and we lost funds.
+                       debug_assert!(self.historical_inbound_htlc_fulfills.contains(&htlc_id_arg));
+                       return UpdateFulfillFetch::DuplicateClaim {};
                }
 
                // Now update local state:
@@ -1278,8 +1332,9 @@ impl<Signer: Sign> Channel<Signer> {
                                                if htlc_id_arg == htlc_id {
                                                        // Make sure we don't leave latest_monitor_update_id incremented here:
                                                        self.latest_monitor_update_id -= 1;
-                                                       debug_assert!(false, "Tried to fulfill an HTLC that was already fulfilled");
-                                                       return Ok((None, None));
+                                                       #[cfg(any(test, feature = "fuzztarget"))]
+                                                       debug_assert!(self.historical_inbound_htlc_fulfills.contains(&htlc_id_arg));
+                                                       return UpdateFulfillFetch::DuplicateClaim {};
                                                }
                                        },
                                        &HTLCUpdateAwaitingACK::FailHTLC { htlc_id, .. } => {
@@ -1288,7 +1343,7 @@ impl<Signer: Sign> Channel<Signer> {
                                                        // TODO: We may actually be able to switch to a fulfill here, though its
                                                        // rare enough it may not be worth the complexity burden.
                                                        debug_assert!(false, "Tried to fulfill an HTLC that was already failed");
-                                                       return Ok((None, Some(monitor_update)));
+                                                       return UpdateFulfillFetch::NewClaim { monitor_update, htlc_value_msat, msg: None };
                                                }
                                        },
                                        _ => {}
@@ -1298,52 +1353,60 @@ impl<Signer: Sign> Channel<Signer> {
                        self.holding_cell_htlc_updates.push(HTLCUpdateAwaitingACK::ClaimHTLC {
                                payment_preimage: payment_preimage_arg, htlc_id: htlc_id_arg,
                        });
-                       return Ok((None, Some(monitor_update)));
+                       #[cfg(any(test, feature = "fuzztarget"))]
+                       self.historical_inbound_htlc_fulfills.insert(htlc_id_arg);
+                       return UpdateFulfillFetch::NewClaim { monitor_update, htlc_value_msat, msg: None };
                }
+               #[cfg(any(test, feature = "fuzztarget"))]
+               self.historical_inbound_htlc_fulfills.insert(htlc_id_arg);
 
                {
                        let htlc = &mut self.pending_inbound_htlcs[pending_idx];
                        if let InboundHTLCState::Committed = htlc.state {
                        } else {
                                debug_assert!(false, "Have an inbound HTLC we tried to claim before it was fully committed to");
-                               return Ok((None, Some(monitor_update)));
+                               return UpdateFulfillFetch::NewClaim { monitor_update, htlc_value_msat, msg: None };
                        }
                        log_trace!(logger, "Upgrading HTLC {} to LocalRemoved with a Fulfill in channel {}!", log_bytes!(htlc.payment_hash.0), log_bytes!(self.channel_id));
                        htlc.state = InboundHTLCState::LocalRemoved(InboundHTLCRemovalReason::Fulfill(payment_preimage_arg.clone()));
                }
 
-               Ok((Some(msgs::UpdateFulfillHTLC {
-                       channel_id: self.channel_id(),
-                       htlc_id: htlc_id_arg,
-                       payment_preimage: payment_preimage_arg,
-               }), Some(monitor_update)))
+               UpdateFulfillFetch::NewClaim {
+                       monitor_update,
+                       htlc_value_msat,
+                       msg: Some(msgs::UpdateFulfillHTLC {
+                               channel_id: self.channel_id(),
+                               htlc_id: htlc_id_arg,
+                               payment_preimage: payment_preimage_arg,
+                       }),
+               }
        }
 
-       pub fn get_update_fulfill_htlc_and_commit<L: Deref>(&mut self, htlc_id: u64, payment_preimage: PaymentPreimage, logger: &L) -> Result<(Option<(msgs::UpdateFulfillHTLC, msgs::CommitmentSigned)>, Option<ChannelMonitorUpdate>), ChannelError> where L::Target: Logger {
-               match self.get_update_fulfill_htlc(htlc_id, payment_preimage, logger)? {
-                       (Some(update_fulfill_htlc), Some(mut monitor_update)) => {
-                               let (commitment, mut additional_update) = self.send_commitment_no_status_check(logger)?;
+       pub fn get_update_fulfill_htlc_and_commit<L: Deref>(&mut self, htlc_id: u64, payment_preimage: PaymentPreimage, logger: &L) -> Result<UpdateFulfillCommitFetch, (ChannelError, ChannelMonitorUpdate)> where L::Target: Logger {
+               match self.get_update_fulfill_htlc(htlc_id, payment_preimage, logger) {
+                       UpdateFulfillFetch::NewClaim { mut monitor_update, htlc_value_msat, msg: Some(update_fulfill_htlc) } => {
+                               let (commitment, mut additional_update) = match self.send_commitment_no_status_check(logger) {
+                                       Err(e) => return Err((e, monitor_update)),
+                                       Ok(res) => res
+                               };
                                // send_commitment_no_status_check may bump latest_monitor_id but we want them to be
                                // strictly increasing by one, so decrement it here.
                                self.latest_monitor_update_id = monitor_update.update_id;
                                monitor_update.updates.append(&mut additional_update.updates);
-                               Ok((Some((update_fulfill_htlc, commitment)), Some(monitor_update)))
-                       },
-                       (Some(update_fulfill_htlc), None) => {
-                               let (commitment, monitor_update) = self.send_commitment_no_status_check(logger)?;
-                               Ok((Some((update_fulfill_htlc, commitment)), Some(monitor_update)))
+                               Ok(UpdateFulfillCommitFetch::NewClaim { monitor_update, htlc_value_msat, msgs: Some((update_fulfill_htlc, commitment)) })
                        },
-                       (None, Some(monitor_update)) => Ok((None, Some(monitor_update))),
-                       (None, None) => Ok((None, None))
+                       UpdateFulfillFetch::NewClaim { monitor_update, htlc_value_msat, msg: None } =>
+                               Ok(UpdateFulfillCommitFetch::NewClaim { monitor_update, htlc_value_msat, msgs: None }),
+                       UpdateFulfillFetch::DuplicateClaim {} => Ok(UpdateFulfillCommitFetch::DuplicateClaim {}),
                }
        }
 
-       /// Per HTLC, only one get_update_fail_htlc or get_update_fulfill_htlc call may be made.
-       /// In such cases we debug_assert!(false) and return a ChannelError::Ignore. Thus, will always
-       /// return Ok(_) if debug assertions are turned on or preconditions are met.
-       ///
-       /// Note that it is still possible to hit these assertions in case we find a preimage on-chain
-       /// but then have a reorg which settles on an HTLC-failure on chain.
+       /// We can only have one resolution per HTLC. In some cases around reconnect, we may fulfill
+       /// an HTLC more than once or fulfill once and then attempt to fail after reconnect. We cannot,
+       /// however, fail more than once as we wait for an upstream failure to be irrevocably committed
+       /// before we fail backwards.
+       /// If we do fail twice, we debug_assert!(false) and return Ok(None). Thus, will always return
+       /// Ok(_) if debug assertions are turned on or preconditions are met.
        pub fn get_update_fail_htlc<L: Deref>(&mut self, htlc_id_arg: u64, err_packet: msgs::OnionErrorPacket, logger: &L) -> Result<Option<msgs::UpdateFailHTLC>, ChannelError> where L::Target: Logger {
                if (self.channel_state & (ChannelState::ChannelFunded as u32)) != (ChannelState::ChannelFunded as u32) {
                        panic!("Was asked to fail an HTLC when channel was not in an operational state");
@@ -1359,8 +1422,11 @@ impl<Signer: Sign> Channel<Signer> {
                        if htlc.htlc_id == htlc_id_arg {
                                match htlc.state {
                                        InboundHTLCState::Committed => {},
-                                       InboundHTLCState::LocalRemoved(_) => {
-                                               debug_assert!(false, "Tried to fail an HTLC that was already fail/fulfilled");
+                                       InboundHTLCState::LocalRemoved(ref reason) => {
+                                               if let &InboundHTLCRemovalReason::Fulfill(_) = reason {
+                                               } else {
+                                                       debug_assert!(false, "Tried to fail an HTLC that was already failed");
+                                               }
                                                return Ok(None);
                                        },
                                        _ => {
@@ -1372,7 +1438,11 @@ impl<Signer: Sign> Channel<Signer> {
                        }
                }
                if pending_idx == core::usize::MAX {
-                       return Err(ChannelError::Ignore("Unable to find a pending HTLC which matched the given HTLC ID".to_owned()));
+                       #[cfg(any(test, feature = "fuzztarget"))]
+                       // If we failed to find an HTLC to fail, make sure it was previously fulfilled and this
+                       // is simply a duplicate fail, not previously failed and we failed-back too early.
+                       debug_assert!(self.historical_inbound_htlc_fulfills.contains(&htlc_id_arg));
+                       return Ok(None);
                }
 
                // Now update local state:
@@ -1381,8 +1451,9 @@ impl<Signer: Sign> Channel<Signer> {
                                match pending_update {
                                        &HTLCUpdateAwaitingACK::ClaimHTLC { htlc_id, .. } => {
                                                if htlc_id_arg == htlc_id {
-                                                       debug_assert!(false, "Tried to fail an HTLC that was already fulfilled");
-                                                       return Err(ChannelError::Ignore("Unable to find a pending HTLC which matched the given HTLC ID".to_owned()));
+                                                       #[cfg(any(test, feature = "fuzztarget"))]
+                                                       debug_assert!(self.historical_inbound_htlc_fulfills.contains(&htlc_id_arg));
+                                                       return Ok(None);
                                                }
                                        },
                                        &HTLCUpdateAwaitingACK::FailHTLC { htlc_id, .. } => {
@@ -1475,6 +1546,12 @@ impl<Signer: Sign> Channel<Signer> {
                if msg.minimum_depth > config.peer_channel_config_limits.max_minimum_depth {
                        return Err(ChannelError::Close(format!("We consider the minimum depth to be unreasonably large. Expected minimum: ({}). Actual: ({})", config.peer_channel_config_limits.max_minimum_depth, msg.minimum_depth)));
                }
+               if msg.minimum_depth == 0 {
+                       // Note that if this changes we should update the serialization minimum version to
+                       // indicate to older clients that they don't understand some features of the current
+                       // channel.
+                       return Err(ChannelError::Close("Minimum confirmation depth must be at least 1".to_owned()));
+               }
 
                let counterparty_shutdown_scriptpubkey = if their_features.supports_upfront_shutdown_script() {
                        match &msg.shutdown_scriptpubkey {
@@ -1498,10 +1575,10 @@ impl<Signer: Sign> Channel<Signer> {
 
                self.counterparty_dust_limit_satoshis = msg.dust_limit_satoshis;
                self.counterparty_max_htlc_value_in_flight_msat = cmp::min(msg.max_htlc_value_in_flight_msat, self.channel_value_satoshis * 1000);
-               self.counterparty_selected_channel_reserve_satoshis = msg.channel_reserve_satoshis;
+               self.counterparty_selected_channel_reserve_satoshis = Some(msg.channel_reserve_satoshis);
                self.counterparty_htlc_minimum_msat = msg.htlc_minimum_msat;
                self.counterparty_max_accepted_htlcs = msg.max_accepted_htlcs;
-               self.minimum_depth = msg.minimum_depth;
+               self.minimum_depth = Some(msg.minimum_depth);
 
                let counterparty_pubkeys = ChannelPublicKeys {
                        funding_pubkey: msg.funding_pubkey,
@@ -1703,7 +1780,8 @@ impl<Signer: Sign> Channel<Signer> {
 
        pub fn funding_locked<L: Deref>(&mut self, msg: &msgs::FundingLocked, logger: &L) -> Result<(), ChannelError> where L::Target: Logger {
                if self.channel_state & (ChannelState::PeerDisconnected as u32) == ChannelState::PeerDisconnected as u32 {
-                       return Err(ChannelError::Close("Peer sent funding_locked when we needed a channel_reestablish".to_owned()));
+                       self.workaround_lnd_bug_4006 = Some(msg.clone());
+                       return Err(ChannelError::Ignore("Peer sent funding_locked when we needed a channel_reestablish. The peer is likely lnd, see https://github.com/lightningnetwork/lnd/issues/4006".to_owned()));
                }
 
                let non_shutdown_state = self.channel_state & (!MULTI_STATE_FLAGS);
@@ -1771,8 +1849,22 @@ impl<Signer: Sign> Channel<Signer> {
        /// corner case properly.
        pub fn get_inbound_outbound_available_balance_msat(&self) -> (u64, u64) {
                // Note that we have to handle overflow due to the above case.
-               (cmp::max(self.channel_value_satoshis as i64 * 1000 - self.value_to_self_msat as i64 - self.get_inbound_pending_htlc_stats().1 as i64, 0) as u64,
-               cmp::max(self.value_to_self_msat as i64 - self.get_outbound_pending_htlc_stats().1 as i64, 0) as u64)
+               (
+                       cmp::max(self.channel_value_satoshis as i64 * 1000
+                               - self.value_to_self_msat as i64
+                               - self.get_inbound_pending_htlc_stats().1 as i64
+                               - Self::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis) as i64 * 1000,
+                       0) as u64,
+                       cmp::max(self.value_to_self_msat as i64
+                               - self.get_outbound_pending_htlc_stats().1 as i64
+                               - self.counterparty_selected_channel_reserve_satoshis.unwrap_or(0) as i64 * 1000,
+                       0) as u64
+               )
+       }
+
+       pub fn get_holder_counterparty_selected_channel_reserve_satoshis(&self) -> (u64, Option<u64>) {
+               (Self::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis),
+               self.counterparty_selected_channel_reserve_satoshis)
        }
 
        // Get the fee cost of a commitment tx with a given number of HTLC outputs.
@@ -2050,7 +2142,7 @@ impl<Signer: Sign> Channel<Signer> {
                        // Check that they won't violate our local required channel reserve by adding this HTLC.
                        let htlc_candidate = HTLCCandidate::new(msg.amount_msat, HTLCInitiator::RemoteOffered);
                        let local_commit_tx_fee_msat = self.next_local_commit_tx_fee_msat(htlc_candidate, None);
-                       if self.value_to_self_msat < self.counterparty_selected_channel_reserve_satoshis * 1000 + local_commit_tx_fee_msat {
+                       if self.value_to_self_msat < self.counterparty_selected_channel_reserve_satoshis.unwrap() * 1000 + local_commit_tx_fee_msat {
                                return Err(ChannelError::Close("Cannot accept HTLC that would put our balance under counterparty-announced channel reserve value".to_owned()));
                        }
                }
@@ -2081,7 +2173,7 @@ impl<Signer: Sign> Channel<Signer> {
 
        /// Marks an outbound HTLC which we have received update_fail/fulfill/malformed
        #[inline]
-       fn mark_outbound_htlc_removed(&mut self, htlc_id: u64, check_preimage: Option<PaymentHash>, fail_reason: Option<HTLCFailReason>) -> Result<&HTLCSource, ChannelError> {
+       fn mark_outbound_htlc_removed(&mut self, htlc_id: u64, check_preimage: Option<PaymentHash>, fail_reason: Option<HTLCFailReason>) -> Result<&OutboundHTLCOutput, ChannelError> {
                for htlc in self.pending_outbound_htlcs.iter_mut() {
                        if htlc.htlc_id == htlc_id {
                                match check_preimage {
@@ -2100,13 +2192,13 @@ impl<Signer: Sign> Channel<Signer> {
                                        OutboundHTLCState::AwaitingRemoteRevokeToRemove(_) | OutboundHTLCState::AwaitingRemovedRemoteRevoke(_) | OutboundHTLCState::RemoteRemoved(_) =>
                                                return Err(ChannelError::Close(format!("Remote tried to fulfill/fail HTLC ({}) that they'd already fulfilled/failed", htlc_id))),
                                }
-                               return Ok(&htlc.source);
+                               return Ok(htlc);
                        }
                }
                Err(ChannelError::Close("Remote tried to fulfill/fail an HTLC we couldn't find".to_owned()))
        }
 
-       pub fn update_fulfill_htlc(&mut self, msg: &msgs::UpdateFulfillHTLC) -> Result<HTLCSource, ChannelError> {
+       pub fn update_fulfill_htlc(&mut self, msg: &msgs::UpdateFulfillHTLC) -> Result<(HTLCSource, u64), ChannelError> {
                if (self.channel_state & (ChannelState::ChannelFunded as u32)) != (ChannelState::ChannelFunded as u32) {
                        return Err(ChannelError::Close("Got fulfill HTLC message when channel was not in an operational state".to_owned()));
                }
@@ -2115,7 +2207,7 @@ impl<Signer: Sign> Channel<Signer> {
                }
 
                let payment_hash = PaymentHash(Sha256::hash(&msg.payment_preimage.0[..]).into_inner());
-               self.mark_outbound_htlc_removed(msg.htlc_id, Some(payment_hash), None).map(|source| source.clone())
+               self.mark_outbound_htlc_removed(msg.htlc_id, Some(payment_hash), None).map(|htlc| (htlc.source.clone(), htlc.amount_msat))
        }
 
        pub fn update_fail_htlc(&mut self, msg: &msgs::UpdateFailHTLC, fail_reason: HTLCFailReason) -> Result<(), ChannelError> {
@@ -2222,7 +2314,10 @@ impl<Signer: Sign> Channel<Signer> {
                let mut htlcs_and_sigs = Vec::with_capacity(htlcs_cloned.len());
                for (idx, (htlc, source)) in htlcs_cloned.drain(..).enumerate() {
                        if let Some(_) = htlc.transaction_output_index {
-                               let htlc_tx = self.build_htlc_transaction(&commitment_txid, &htlc, true, &keys, feerate_per_kw);
+                               let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, feerate_per_kw,
+                                       self.get_counterparty_selected_contest_delay().unwrap(), &htlc,
+                                       &keys.broadcaster_delayed_payment_key, &keys.revocation_key);
+
                                let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, &keys);
                                let htlc_sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, SigHashType::All)[..]);
                                log_trace!(logger, "Checking HTLC tx signature {} by key {} against tx {} (sighash {}) with redeemscript {} in channel {}.",
@@ -2405,24 +2500,28 @@ impl<Signer: Sign> Channel<Signer> {
                                                }
                                        },
                                        &HTLCUpdateAwaitingACK::ClaimHTLC { ref payment_preimage, htlc_id, .. } => {
-                                               match self.get_update_fulfill_htlc(htlc_id, *payment_preimage, logger) {
-                                                       Ok((update_fulfill_msg_option, additional_monitor_update_opt)) => {
-                                                               update_fulfill_htlcs.push(update_fulfill_msg_option.unwrap());
-                                                               if let Some(mut additional_monitor_update) = additional_monitor_update_opt {
-                                                                       monitor_update.updates.append(&mut additional_monitor_update.updates);
-                                                               }
-                                                       },
-                                                       Err(e) => {
-                                                               if let ChannelError::Ignore(_) = e {}
-                                                               else {
-                                                                       panic!("Got a non-IgnoreError action trying to fulfill holding cell HTLC");
-                                                               }
-                                                       }
-                                               }
+                                               // If an HTLC claim was previously added to the holding cell (via
+                                               // `get_update_fulfill_htlc`, then generating the claim message itself must
+                                               // not fail - any in between attempts to claim the HTLC will have resulted
+                                               // in it hitting the holding cell again and we cannot change the state of a
+                                               // holding cell HTLC from fulfill to anything else.
+                                               let (update_fulfill_msg_option, mut additional_monitor_update) =
+                                                       if let UpdateFulfillFetch::NewClaim { msg, monitor_update, .. } = self.get_update_fulfill_htlc(htlc_id, *payment_preimage, logger) {
+                                                               (msg, monitor_update)
+                                                       } else { unreachable!() };
+                                               update_fulfill_htlcs.push(update_fulfill_msg_option.unwrap());
+                                               monitor_update.updates.append(&mut additional_monitor_update.updates);
                                        },
                                        &HTLCUpdateAwaitingACK::FailHTLC { htlc_id, ref err_packet } => {
                                                match self.get_update_fail_htlc(htlc_id, err_packet.clone(), logger) {
-                                                       Ok(update_fail_msg_option) => update_fail_htlcs.push(update_fail_msg_option.unwrap()),
+                                                       Ok(update_fail_msg_option) => {
+                                                               // If an HTLC failure was previously added to the holding cell (via
+                                                               // `get_update_fail_htlc`) then generating the fail message itself
+                                                               // must not fail - we should never end up in a state where we
+                                                               // double-fail an HTLC or fail-then-claim an HTLC as it indicates
+                                                               // we didn't wait for a full revocation before failing.
+                                                               update_fail_htlcs.push(update_fail_msg_option.unwrap())
+                                                       },
                                                        Err(e) => {
                                                                if let ChannelError::Ignore(_) = e {}
                                                                else {
@@ -3322,6 +3421,10 @@ impl<Signer: Sign> Channel<Signer> {
                self.channel_id
        }
 
+       pub fn minimum_depth(&self) -> Option<u32> {
+               self.minimum_depth
+       }
+
        /// Gets the "user_id" value passed into the construction of this channel. It has no special
        /// meaning and exists only to allow users to have a persistent identifier of a channel.
        pub fn get_user_id(&self) -> u64 {
@@ -3349,8 +3452,9 @@ impl<Signer: Sign> Channel<Signer> {
                &self.channel_transaction_parameters.holder_pubkeys
        }
 
-       fn get_counterparty_selected_contest_delay(&self) -> u16 {
-               self.channel_transaction_parameters.counterparty_parameters.as_ref().unwrap().selected_contest_delay
+       pub fn get_counterparty_selected_contest_delay(&self) -> Option<u16> {
+               self.channel_transaction_parameters.counterparty_parameters
+                       .as_ref().map(|params| params.selected_contest_delay)
        }
 
        fn get_counterparty_pubkeys(&self) -> &ChannelPublicKeys {
@@ -3390,7 +3494,7 @@ impl<Signer: Sign> Channel<Signer> {
        }
 
        pub fn get_fee_proportional_millionths(&self) -> u32 {
-               self.config.fee_proportional_millionths
+               self.config.forwarding_fee_proportional_millionths
        }
 
        pub fn get_cltv_expiry_delta(&self) -> u16 {
@@ -3424,7 +3528,7 @@ impl<Signer: Sign> Channel<Signer> {
                ChannelValueStat {
                        value_to_self_msat: self.value_to_self_msat,
                        channel_value_msat: self.channel_value_satoshis * 1000,
-                       channel_reserve_msat: self.counterparty_selected_channel_reserve_satoshis * 1000,
+                       channel_reserve_msat: self.counterparty_selected_channel_reserve_satoshis.unwrap() * 1000,
                        pending_outbound_htlcs_amount_msat: self.pending_outbound_htlcs.iter().map(|ref h| h.amount_msat).sum::<u64>(),
                        pending_inbound_htlcs_amount_msat: self.pending_inbound_htlcs.iter().map(|ref h| h.amount_msat).sum::<u64>(),
                        holding_cell_outbound_amount_msat: {
@@ -3463,24 +3567,8 @@ impl<Signer: Sign> Channel<Signer> {
 
        /// Gets the fee we'd want to charge for adding an HTLC output to this Channel
        /// Allowed in any state (including after shutdown)
-       pub fn get_holder_fee_base_msat<F: Deref>(&self, fee_estimator: &F) -> u32
-               where F::Target: FeeEstimator
-       {
-               // For lack of a better metric, we calculate what it would cost to consolidate the new HTLC
-               // output value back into a transaction with the regular channel output:
-
-               // the fee cost of the HTLC-Success/HTLC-Timeout transaction:
-               let mut res = self.feerate_per_kw as u64 * cmp::max(HTLC_TIMEOUT_TX_WEIGHT, HTLC_SUCCESS_TX_WEIGHT) / 1000;
-
-               if self.is_outbound() {
-                       // + the marginal fee increase cost to us in the commitment transaction:
-                       res += self.feerate_per_kw as u64 * COMMITMENT_TX_WEIGHT_PER_HTLC / 1000;
-               }
-
-               // + the marginal cost of an input which spends the HTLC-Success/HTLC-Timeout output:
-               res += fee_estimator.get_est_sat_per_1000_weight(ConfirmationTarget::Normal) as u64 * SPENDING_INPUT_FOR_A_OUTPUT_WEIGHT / 1000;
-
-               res as u32
+       pub fn get_outbound_forwarding_fee_base_msat(&self) -> u32 {
+               self.config.forwarding_fee_base_msat
        }
 
        /// Returns true if we've ever received a message from the remote end for this Channel
@@ -3499,7 +3587,7 @@ impl<Signer: Sign> Channel<Signer> {
        /// is_usable() and considers things like the channel being temporarily disabled.
        /// Allowed in any state (including after shutdown)
        pub fn is_live(&self) -> bool {
-               self.is_usable() && (self.channel_state & (ChannelState::PeerDisconnected as u32 | ChannelState::MonitorUpdateFailed as u32) == 0)
+               self.is_usable() && (self.channel_state & (ChannelState::PeerDisconnected as u32) == 0)
        }
 
        /// Returns true if this channel has been marked as awaiting a monitor update to move forward.
@@ -3541,7 +3629,7 @@ impl<Signer: Sign> Channel<Signer> {
                        self.funding_tx_confirmation_height = 0;
                }
 
-               if funding_tx_confirmations < self.minimum_depth as i64 {
+               if funding_tx_confirmations < self.minimum_depth.unwrap_or(0) as i64 {
                        return None;
                }
 
@@ -3696,10 +3784,10 @@ impl<Signer: Sign> Channel<Signer> {
                        // the funding transaction's confirmation count has dipped below minimum_depth / 2,
                        // close the channel and hope we can get the latest state on chain (because presumably
                        // the funding transaction is at least still in the mempool of most nodes).
-                       if funding_tx_confirmations < self.minimum_depth as i64 / 2 {
+                       if funding_tx_confirmations < self.minimum_depth.unwrap() as i64 / 2 {
                                return Err(msgs::ErrorMessage {
                                        channel_id: self.channel_id(),
-                                       data: format!("Funding transaction was un-confirmed. Locked at {} confs, now have {} confs.", self.minimum_depth, funding_tx_confirmations),
+                                       data: format!("Funding transaction was un-confirmed. Locked at {} confs, now have {} confs.", self.minimum_depth.unwrap(), funding_tx_confirmations),
                                });
                        }
                }
@@ -3794,7 +3882,7 @@ impl<Signer: Sign> Channel<Signer> {
                        max_htlc_value_in_flight_msat: Channel::<Signer>::get_holder_max_htlc_value_in_flight_msat(self.channel_value_satoshis),
                        channel_reserve_satoshis: Channel::<Signer>::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis),
                        htlc_minimum_msat: self.holder_htlc_minimum_msat,
-                       minimum_depth: self.minimum_depth,
+                       minimum_depth: self.minimum_depth.unwrap(),
                        to_self_delay: self.get_holder_selected_contest_delay(),
                        max_accepted_htlcs: OUR_MAX_HTLCS,
                        funding_pubkey: keys.funding_pubkey,
@@ -4016,10 +4104,18 @@ impl<Signer: Sign> Channel<Signer> {
 
        /// Adds a pending outbound HTLC to this channel, note that you probably want
        /// send_htlc_and_commit instead cause you'll want both messages at once.
-       /// This returns an option instead of a pure UpdateAddHTLC as we may be in a state where we are
-       /// waiting on the remote peer to send us a revoke_and_ack during which time we cannot add new
-       /// HTLCs on the wire or we wouldn't be able to determine what they actually ACK'ed.
-       /// You MUST call send_commitment prior to any other calls on this Channel
+       ///
+       /// This returns an optional UpdateAddHTLC as we may be in a state where we cannot add HTLCs on
+       /// the wire:
+       /// * In cases where we're waiting on the remote peer to send us a revoke_and_ack, we
+       ///   wouldn't be able to determine what they actually ACK'ed if we have two sets of updates
+       ///   awaiting ACK.
+       /// * In cases where we're marked MonitorUpdateFailed, we cannot commit to a new state as we
+       ///   may not yet have sent the previous commitment update messages and will need to regenerate
+       ///   them.
+       ///
+       /// You MUST call send_commitment prior to calling any other methods on this Channel!
+       ///
        /// If an Err is returned, it's a ChannelError::Ignore!
        pub fn send_htlc(&mut self, amount_msat: u64, payment_hash: PaymentHash, cltv_expiry: u32, source: HTLCSource, onion_routing_packet: msgs::OnionPacket) -> Result<Option<msgs::UpdateAddHTLC>, ChannelError> {
                if (self.channel_state & (ChannelState::ChannelFunded as u32 | BOTH_SIDES_SHUTDOWN_MASK)) != (ChannelState::ChannelFunded as u32) {
@@ -4038,14 +4134,14 @@ impl<Signer: Sign> Channel<Signer> {
                        return Err(ChannelError::Ignore(format!("Cannot send less than their minimum HTLC value ({})", self.counterparty_htlc_minimum_msat)));
                }
 
-               if (self.channel_state & (ChannelState::PeerDisconnected as u32 | ChannelState::MonitorUpdateFailed as u32)) != 0 {
+               if (self.channel_state & (ChannelState::PeerDisconnected as u32)) != 0 {
                        // Note that this should never really happen, if we're !is_live() on receipt of an
                        // incoming HTLC for relay will result in us rejecting the HTLC and we won't allow
                        // the user to send directly into a !is_live() channel. However, if we
                        // disconnected during the time the previous hop was doing the commitment dance we may
                        // end up getting here after the forwarding delay. In any case, returning an
                        // IgnoreError will get ChannelManager to do the right thing and fail backwards now.
-                       return Err(ChannelError::Ignore("Cannot send an HTLC while disconnected/frozen for channel monitor update".to_owned()));
+                       return Err(ChannelError::Ignore("Cannot send an HTLC while disconnected from channel counterparty".to_owned()));
                }
 
                let (outbound_htlc_count, htlc_outbound_value_msat) = self.get_outbound_pending_htlc_stats();
@@ -4060,7 +4156,7 @@ impl<Signer: Sign> Channel<Signer> {
                if !self.is_outbound() {
                        // Check that we won't violate the remote channel reserve by adding this HTLC.
                        let counterparty_balance_msat = self.channel_value_satoshis * 1000 - self.value_to_self_msat;
-                       let holder_selected_chan_reserve_msat = Channel::<Signer>::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis);
+                       let holder_selected_chan_reserve_msat = Channel::<Signer>::get_holder_selected_channel_reserve_satoshis(self.channel_value_satoshis) * 1000;
                        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);
                        if counterparty_balance_msat < holder_selected_chan_reserve_msat + counterparty_commit_tx_fee_msat {
@@ -4084,13 +4180,13 @@ impl<Signer: Sign> Channel<Signer> {
 
                // 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 * 1000;
+               let chan_reserve_msat = self.counterparty_selected_channel_reserve_satoshis.unwrap() * 1000;
                if pending_value_to_self_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)));
                }
 
                // Now update local state:
-               if (self.channel_state & (ChannelState::AwaitingRemoteRevoke as u32)) == (ChannelState::AwaitingRemoteRevoke as u32) {
+               if (self.channel_state & (ChannelState::AwaitingRemoteRevoke as u32 | ChannelState::MonitorUpdateFailed as u32)) != 0 {
                        self.holding_cell_htlc_updates.push(HTLCUpdateAwaitingACK::AddHTLC {
                                amount_msat,
                                payment_hash,
@@ -4289,8 +4385,7 @@ impl<Signer: Sign> Channel<Signer> {
        }
 
        pub fn channel_update(&mut self, msg: &msgs::ChannelUpdate) -> Result<(), ChannelError> {
-               let usable_channel_value_msat = (self.channel_value_satoshis - self.counterparty_selected_channel_reserve_satoshis) * 1000;
-               if msg.contents.htlc_minimum_msat >= usable_channel_value_msat {
+               if msg.contents.htlc_minimum_msat >= self.channel_value_satoshis * 1000 {
                        return Err(ChannelError::Close("Minimum htlc value is greater than channel value".to_string()));
                }
                self.counterparty_forwarding_info = Some(CounterpartyForwardingInfo {
@@ -4417,7 +4512,7 @@ fn is_unsupported_shutdown_script(their_features: &InitFeatures, script: &Script
        return !script.is_p2pkh() && !script.is_p2sh() && !script.is_v0_p2wpkh() && !script.is_v0_p2wsh()
 }
 
-const SERIALIZATION_VERSION: u8 = 1;
+const SERIALIZATION_VERSION: u8 = 2;
 const MIN_SERIALIZATION_VERSION: u8 = 1;
 
 impl_writeable_tlv_based_enum!(InboundHTLCRemovalReason,;
@@ -4459,7 +4554,13 @@ impl<Signer: Sign> Writeable for Channel<Signer> {
                write_ver_prefix!(writer, SERIALIZATION_VERSION, MIN_SERIALIZATION_VERSION);
 
                self.user_id.write(writer)?;
-               self.config.write(writer)?;
+
+               // Write out the old serialization for the config object. This is read by version-1
+               // deserializers, but we will read the version in the TLV at the end instead.
+               self.config.forwarding_fee_proportional_millionths.write(writer)?;
+               self.config.cltv_expiry_delta.write(writer)?;
+               self.config.announced_channel.write(writer)?;
+               self.config.commit_upfront_shutdown_pubkey.write(writer)?;
 
                self.channel_id.write(writer)?;
                (self.channel_state | ChannelState::PeerDisconnected as u32).write(writer)?;
@@ -4618,11 +4719,16 @@ impl<Signer: Sign> Writeable for Channel<Signer> {
                self.counterparty_dust_limit_satoshis.write(writer)?;
                self.holder_dust_limit_satoshis.write(writer)?;
                self.counterparty_max_htlc_value_in_flight_msat.write(writer)?;
-               self.counterparty_selected_channel_reserve_satoshis.write(writer)?;
+
+               // Note that this field is ignored by 0.0.99+ as the TLV Optional variant is used instead.
+               self.counterparty_selected_channel_reserve_satoshis.unwrap_or(0).write(writer)?;
+
                self.counterparty_htlc_minimum_msat.write(writer)?;
                self.holder_htlc_minimum_msat.write(writer)?;
                self.counterparty_max_accepted_htlcs.write(writer)?;
-               self.minimum_depth.write(writer)?;
+
+               // Note that this field is ignored by 0.0.99+ as the TLV Optional variant is used instead.
+               self.minimum_depth.unwrap_or(0).write(writer)?;
 
                match &self.counterparty_forwarding_info {
                        Some(info) => {
@@ -4647,7 +4753,25 @@ impl<Signer: Sign> Writeable for Channel<Signer> {
 
                self.channel_update_status.write(writer)?;
 
-               write_tlv_fields!(writer, {}, {(0, self.announcement_sigs)});
+               #[cfg(any(test, feature = "fuzztarget"))]
+               (self.historical_inbound_htlc_fulfills.len() as u64).write(writer)?;
+               #[cfg(any(test, feature = "fuzztarget"))]
+               for htlc in self.historical_inbound_htlc_fulfills.iter() {
+                       htlc.write(writer)?;
+               }
+
+               write_tlv_fields!(writer, {
+                       (0, self.announcement_sigs, option),
+                       // minimum_depth and counterparty_selected_channel_reserve_satoshis used to have a
+                       // default value instead of being Option<>al. Thus, to maintain compatibility we write
+                       // them twice, once with their original default values above, and once as an option
+                       // here. On the read side, old versions will simply ignore the odd-type entries here,
+                       // and new versions map the default values to None and allow the TLV entries here to
+                       // override that.
+                       (1, self.minimum_depth, option),
+                       (3, self.counterparty_selected_channel_reserve_satoshis, option),
+                       (5, self.config, required),
+               });
 
                Ok(())
        }
@@ -4657,10 +4781,21 @@ const MAX_ALLOC_SIZE: usize = 64*1024;
 impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
                where K::Target: KeysInterface<Signer = Signer> {
        fn read<R : ::std::io::Read>(reader: &mut R, keys_source: &'a K) -> Result<Self, DecodeError> {
-               let _ver = read_ver_prefix!(reader, SERIALIZATION_VERSION);
+               let ver = read_ver_prefix!(reader, SERIALIZATION_VERSION);
 
                let user_id = Readable::read(reader)?;
-               let config: ChannelConfig = Readable::read(reader)?;
+
+               let mut config = Some(ChannelConfig::default());
+               if ver == 1 {
+                       // Read the old serialization of the ChannelConfig from version 0.0.98.
+                       config.as_mut().unwrap().forwarding_fee_proportional_millionths = Readable::read(reader)?;
+                       config.as_mut().unwrap().cltv_expiry_delta = Readable::read(reader)?;
+                       config.as_mut().unwrap().announced_channel = Readable::read(reader)?;
+                       config.as_mut().unwrap().commit_upfront_shutdown_pubkey = Readable::read(reader)?;
+               } else {
+                       // Read the 8 bytes of backwards-compatibility ChannelConfig data.
+                       let mut _val: u64 = Readable::read(reader)?;
+               }
 
                let channel_id = Readable::read(reader)?;
                let channel_state = Readable::read(reader)?;
@@ -4790,11 +4925,26 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
                let counterparty_dust_limit_satoshis = Readable::read(reader)?;
                let holder_dust_limit_satoshis = Readable::read(reader)?;
                let counterparty_max_htlc_value_in_flight_msat = Readable::read(reader)?;
-               let counterparty_selected_channel_reserve_satoshis = Readable::read(reader)?;
+               let mut counterparty_selected_channel_reserve_satoshis = None;
+               if ver == 1 {
+                       // Read the old serialization from version 0.0.98.
+                       counterparty_selected_channel_reserve_satoshis = Some(Readable::read(reader)?);
+               } else {
+                       // Read the 8 bytes of backwards-compatibility data.
+                       let _dummy: u64 = Readable::read(reader)?;
+               }
                let counterparty_htlc_minimum_msat = Readable::read(reader)?;
                let holder_htlc_minimum_msat = Readable::read(reader)?;
                let counterparty_max_accepted_htlcs = Readable::read(reader)?;
-               let minimum_depth = Readable::read(reader)?;
+
+               let mut minimum_depth = None;
+               if ver == 1 {
+                       // Read the old serialization from version 0.0.98.
+                       minimum_depth = Some(Readable::read(reader)?);
+               } else {
+                       // Read the 4 bytes of backwards-compatibility data.
+                       let _dummy: u32 = Readable::read(reader)?;
+               }
 
                let counterparty_forwarding_info = match <u8 as Readable>::read(reader)? {
                        0 => None,
@@ -4819,8 +4969,23 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
 
                let channel_update_status = Readable::read(reader)?;
 
+               #[cfg(any(test, feature = "fuzztarget"))]
+               let mut historical_inbound_htlc_fulfills = HashSet::new();
+               #[cfg(any(test, feature = "fuzztarget"))]
+               {
+                       let htlc_fulfills_len: u64 = Readable::read(reader)?;
+                       for _ in 0..htlc_fulfills_len {
+                               assert!(historical_inbound_htlc_fulfills.insert(Readable::read(reader)?));
+                       }
+               }
+
                let mut announcement_sigs = None;
-               read_tlv_fields!(reader, {}, {(0, announcement_sigs)});
+               read_tlv_fields!(reader, {
+                       (0, announcement_sigs, option),
+                       (1, minimum_depth, option),
+                       (3, counterparty_selected_channel_reserve_satoshis, option),
+                       (5, config, option), // Note that if none is provided we will *not* overwrite the existing one.
+               });
 
                let mut secp_ctx = Secp256k1::new();
                secp_ctx.seeded_randomize(&keys_source.get_secure_random_bytes());
@@ -4828,7 +4993,7 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
                Ok(Channel {
                        user_id,
 
-                       config,
+                       config: config.unwrap(),
                        channel_id,
                        channel_state,
                        secp_ctx,
@@ -4864,9 +5029,9 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
                        feerate_per_kw,
 
                        #[cfg(debug_assertions)]
-                       holder_max_commitment_tx_output: ::std::sync::Mutex::new((0, 0)),
+                       holder_max_commitment_tx_output: Mutex::new((0, 0)),
                        #[cfg(debug_assertions)]
-                       counterparty_max_commitment_tx_output: ::std::sync::Mutex::new((0, 0)),
+                       counterparty_max_commitment_tx_output: Mutex::new((0, 0)),
 
                        last_sent_closing_fee,
 
@@ -4904,6 +5069,11 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
                        next_local_commitment_tx_fee_info_cached: Mutex::new(None),
                        #[cfg(any(test, feature = "fuzztarget"))]
                        next_remote_commitment_tx_fee_info_cached: Mutex::new(None),
+
+                       workaround_lnd_bug_4006: None,
+
+                       #[cfg(any(test, feature = "fuzztarget"))]
+                       historical_inbound_htlc_fulfills,
                })
        }
 }
@@ -4920,13 +5090,14 @@ mod tests {
        use bitcoin::hashes::hex::FromHex;
        use hex;
        use ln::{PaymentPreimage, PaymentHash};
-       use ln::channelmanager::{BestBlock, HTLCSource};
+       use ln::channelmanager::HTLCSource;
        use ln::channel::{Channel,InboundHTLCOutput,OutboundHTLCOutput,InboundHTLCState,OutboundHTLCState,HTLCOutputInCommitment,HTLCCandidate,HTLCInitiator,TxCreationKeys};
        use ln::channel::MAX_FUNDING_SATOSHIS;
        use ln::features::InitFeatures;
        use ln::msgs::{ChannelUpdate, DataLossProtect, DecodeError, OptionalField, UnsignedChannelUpdate};
        use ln::chan_utils;
        use ln::chan_utils::{ChannelPublicKeys, HolderCommitmentTransaction, CounterpartyChannelTransactionParameters, HTLC_SUCCESS_TX_WEIGHT, HTLC_TIMEOUT_TX_WEIGHT};
+       use chain::BestBlock;
        use chain::chaininterface::{FeeEstimator,ConfirmationTarget};
        use chain::keysinterface::{InMemorySigner, KeysInterface, BaseSign};
        use chain::transaction::OutPoint;
@@ -4941,7 +5112,7 @@ mod tests {
        use bitcoin::hashes::sha256::Hash as Sha256;
        use bitcoin::hashes::Hash;
        use bitcoin::hash_types::{Txid, WPubkeyHash};
-       use std::sync::Arc;
+       use sync::Arc;
        use prelude::*;
 
        struct TestFeeEstimator {
@@ -5273,6 +5444,7 @@ mod tests {
                config.channel_options.announced_channel = false;
                let mut chan = Channel::<InMemorySigner>::new_outbound(&&feeest, &&keys_provider, counterparty_node_id, 10_000_000, 100000, 42, &config).unwrap(); // Nothing uses their network key in this test
                chan.holder_dust_limit_satoshis = 546;
+               chan.counterparty_selected_channel_reserve_satoshis = Some(0); // Filled in in accept_channel
 
                let funding_info = OutPoint{ txid: Txid::from_hex("8984484a580b825b9972d7adb15050b3ab624ccd731946b3eeddb92f4e7ef6be").unwrap(), index: 0 };
 
@@ -5360,7 +5532,9 @@ mod tests {
                                        let remote_signature = Signature::from_der(&hex::decode($counterparty_htlc_sig_hex).unwrap()[..]).unwrap();
 
                                        let ref htlc = htlcs[$htlc_idx];
-                                       let htlc_tx = chan.build_htlc_transaction(&unsigned_tx.txid, &htlc, true, &keys, chan.feerate_per_kw);
+                                       let htlc_tx = chan_utils::build_htlc_transaction(&unsigned_tx.txid, chan.feerate_per_kw,
+                                               chan.get_counterparty_selected_contest_delay().unwrap(),
+                                               &htlc, &keys.broadcaster_delayed_payment_key, &keys.revocation_key);
                                        let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, &keys);
                                        let htlc_sighash = Message::from_slice(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, SigHashType::All)[..]).unwrap();
                                        secp_ctx.verify(&htlc_sighash, &remote_signature, &keys.countersignatory_htlc_key).unwrap();