// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.
//! Utilities for bumping transactions originating from [`Event`]s.
//!
//! [`Event`]: crate::events::Event
use alloc::collections::BTreeMap;
use core::ops::Deref;
use crate::chain::chaininterface::{BroadcasterInterface, fee_for_weight};
use crate::chain::ClaimId;
use crate::io_extras::sink;
use crate::ln::channel::ANCHOR_OUTPUT_VALUE_SATOSHI;
use crate::ln::types::ChannelId;
use crate::ln::chan_utils;
use crate::ln::chan_utils::{
ANCHOR_INPUT_WITNESS_WEIGHT, HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT,
HTLC_TIMEOUT_INPUT_ANCHOR_WITNESS_WEIGHT, HTLCOutputInCommitment
};
use crate::prelude::*;
use crate::sign::{
ChannelDerivationParameters, HTLCDescriptor, SignerProvider, P2WPKH_WITNESS_WEIGHT
};
use crate::sign::ecdsa::EcdsaChannelSigner;
use crate::sync::Mutex;
use crate::util::logger::Logger;
use bitcoin::{OutPoint, Psbt, PubkeyHash, Sequence, ScriptBuf, Transaction, TxIn, TxOut, Witness, WPubkeyHash};
use bitcoin::amount::Amount;
use bitcoin::constants::WITNESS_SCALE_FACTOR;
use bitcoin::locktime::absolute::LockTime;
use bitcoin::consensus::Encodable;
use bitcoin::secp256k1;
use bitcoin::secp256k1::{PublicKey, Secp256k1};
use bitcoin::secp256k1::ecdsa::Signature;
use bitcoin::transaction::Version;
pub(crate) const EMPTY_SCRIPT_SIG_WEIGHT: u64 = 1 /* empty script_sig */ * WITNESS_SCALE_FACTOR as u64;
const BASE_INPUT_SIZE: u64 = 32 /* txid */ + 4 /* vout */ + 4 /* sequence */;
pub(crate) const BASE_INPUT_WEIGHT: u64 = BASE_INPUT_SIZE * WITNESS_SCALE_FACTOR as u64;
/// A descriptor used to sign for a commitment transaction's anchor output.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct AnchorDescriptor {
/// The parameters required to derive the signer for the anchor input.
pub channel_derivation_parameters: ChannelDerivationParameters,
/// The transaction input's outpoint corresponding to the commitment transaction's anchor
/// output.
pub outpoint: OutPoint,
}
impl AnchorDescriptor {
/// Returns the UTXO to be spent by the anchor input, which can be obtained via
/// [`Self::unsigned_tx_input`].
pub fn previous_utxo(&self) -> TxOut {
TxOut {
script_pubkey: self.witness_script().to_p2wsh(),
value: Amount::from_sat(ANCHOR_OUTPUT_VALUE_SATOSHI),
}
}
/// Returns the unsigned transaction input spending the anchor output in the commitment
/// transaction.
pub fn unsigned_tx_input(&self) -> TxIn {
TxIn {
previous_output: self.outpoint.clone(),
script_sig: ScriptBuf::new(),
sequence: Sequence::ENABLE_RBF_NO_LOCKTIME,
witness: Witness::new(),
}
}
/// Returns the witness script of the anchor output in the commitment transaction.
pub fn witness_script(&self) -> ScriptBuf {
let channel_params = self.channel_derivation_parameters.transaction_parameters.as_holder_broadcastable();
chan_utils::get_anchor_redeemscript(&channel_params.broadcaster_pubkeys().funding_pubkey)
}
/// Returns the fully signed witness required to spend the anchor output in the commitment
/// transaction.
pub fn tx_input_witness(&self, signature: &Signature) -> Witness {
let channel_params = self.channel_derivation_parameters.transaction_parameters.as_holder_broadcastable();
chan_utils::build_anchor_input_witness(&channel_params.broadcaster_pubkeys().funding_pubkey, signature)
}
/// Derives the channel signer required to sign the anchor input.
pub fn derive_channel_signer<S: EcdsaChannelSigner, SP: Deref>(&self, signer_provider: &SP) -> S
where
SP::Target: SignerProvider<EcdsaSigner= S>
{
let mut signer = signer_provider.derive_channel_signer(
self.channel_derivation_parameters.value_satoshis,
self.channel_derivation_parameters.keys_id,
);
signer.provide_channel_parameters(&self.channel_derivation_parameters.transaction_parameters);
signer
}
}
/// Represents the different types of transactions, originating from LDK, to be bumped.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum BumpTransactionEvent {
/// Indicates that a channel featuring anchor outputs is to be closed by broadcasting the local
/// commitment transaction. Since commitment transactions have a static feerate pre-agreed upon,
/// they may need additional fees to be attached through a child transaction using the popular
/// [Child-Pays-For-Parent](https://bitcoinops.org/en/topics/cpfp) fee bumping technique. This
/// child transaction must include the anchor input described within `anchor_descriptor` along
/// with additional inputs to meet the target feerate. Failure to meet the target feerate
/// decreases the confirmation odds of the transaction package (which includes the commitment
/// and child anchor transactions), possibly resulting in a loss of funds. Once the transaction
/// is constructed, it must be fully signed for and broadcast by the consumer of the event
/// along with the `commitment_tx` enclosed. Note that the `commitment_tx` must always be
/// broadcast first, as the child anchor transaction depends on it.
///
/// The consumer should be able to sign for any of the additional inputs included within the
/// child anchor transaction. To sign its anchor input, an [`EcdsaChannelSigner`] should be
/// re-derived through [`AnchorDescriptor::derive_channel_signer`]. The anchor input signature
/// can be computed with [`EcdsaChannelSigner::sign_holder_anchor_input`], which can then be
/// provided to [`build_anchor_input_witness`] along with the `funding_pubkey` to obtain the
/// full witness required to spend.
///
/// It is possible to receive more than one instance of this event if a valid child anchor
/// transaction is never broadcast or is but not with a sufficient fee to be mined. Care should
/// be taken by the consumer of the event to ensure any future iterations of the child anchor
/// transaction adhere to the [Replace-By-Fee
/// rules](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md)
/// for fee bumps to be accepted into the mempool, and eventually the chain. As the frequency of
/// these events is not user-controlled, users may ignore/drop the event if they are no longer
/// able to commit external confirmed funds to the child anchor transaction.
///
/// The set of `pending_htlcs` on the commitment transaction to be broadcast can be inspected to
/// determine whether a significant portion of the channel's funds are allocated to HTLCs,
/// enabling users to make their own decisions regarding the importance of the commitment
/// transaction's confirmation. Note that this is not required, but simply exists as an option
/// for users to override LDK's behavior. On commitments with no HTLCs (indicated by those with
/// an empty `pending_htlcs`), confirmation of the commitment transaction can be considered to
/// be not urgent.
///
/// [`EcdsaChannelSigner`]: crate::sign::ecdsa::EcdsaChannelSigner
/// [`EcdsaChannelSigner::sign_holder_anchor_input`]: crate::sign::ecdsa::EcdsaChannelSigner::sign_holder_anchor_input
/// [`build_anchor_input_witness`]: crate::ln::chan_utils::build_anchor_input_witness
ChannelClose {
/// The `channel_id` of the channel which has been closed.
channel_id: ChannelId,
/// Counterparty in the closed channel.
counterparty_node_id: PublicKey,
/// The unique identifier for the claim of the anchor output in the commitment transaction.
///
/// The identifier must map to the set of external UTXOs assigned to the claim, such that
/// they can be reused when a new claim with the same identifier needs to be made, resulting
/// in a fee-bumping attempt.
claim_id: ClaimId,
/// The target feerate that the transaction package, which consists of the commitment
/// transaction and the to-be-crafted child anchor transaction, must meet.
package_target_feerate_sat_per_1000_weight: u32,
/// The channel's commitment transaction to bump the fee of. This transaction should be
/// broadcast along with the anchor transaction constructed as a result of consuming this
/// event.
commitment_tx: Transaction,
/// The absolute fee in satoshis of the commitment transaction. This can be used along the
/// with weight of the commitment transaction to determine its feerate.
commitment_tx_fee_satoshis: u64,
/// The descriptor to sign the anchor input of the anchor transaction constructed as a
/// result of consuming this event.
anchor_descriptor: AnchorDescriptor,
/// The set of pending HTLCs on the commitment transaction that need to be resolved once the
/// commitment transaction confirms.
pending_htlcs: Vec<HTLCOutputInCommitment>,
},
/// Indicates that a channel featuring anchor outputs has unilaterally closed on-chain by a
/// holder commitment transaction and its HTLC(s) need to be resolved on-chain. With the
/// zero-HTLC-transaction-fee variant of anchor outputs, the pre-signed HTLC
/// transactions have a zero fee, thus requiring additional inputs and/or outputs to be attached
/// for a timely confirmation within the chain. These additional inputs and/or outputs must be
/// appended to the resulting HTLC transaction to meet the target feerate. Failure to meet the
/// target feerate decreases the confirmation odds of the transaction, possibly resulting in a
/// loss of funds. Once the transaction meets the target feerate, it must be signed for and
/// broadcast by the consumer of the event.
///
/// The consumer should be able to sign for any of the non-HTLC inputs added to the resulting
/// HTLC transaction. To sign HTLC inputs, an [`EcdsaChannelSigner`] should be re-derived
/// through [`HTLCDescriptor::derive_channel_signer`]. Each HTLC input's signature can be
/// computed with [`EcdsaChannelSigner::sign_holder_htlc_transaction`], which can then be
/// provided to [`HTLCDescriptor::tx_input_witness`] to obtain the fully signed witness required
/// to spend.
///
/// It is possible to receive more than one instance of this event if a valid HTLC transaction
/// is never broadcast or is but not with a sufficient fee to be mined. Care should be taken by
/// the consumer of the event to ensure any future iterations of the HTLC transaction adhere to
/// the [Replace-By-Fee
/// rules](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md)
/// for fee bumps to be accepted into the mempool, and eventually the chain. As the frequency of
/// these events is not user-controlled, users may ignore/drop the event if either they are no
/// longer able to commit external confirmed funds to the HTLC transaction or the fee committed
/// to the HTLC transaction is greater in value than the HTLCs being claimed.
///
/// [`EcdsaChannelSigner`]: crate::sign::ecdsa::EcdsaChannelSigner
/// [`EcdsaChannelSigner::sign_holder_htlc_transaction`]: crate::sign::ecdsa::EcdsaChannelSigner::sign_holder_htlc_transaction
HTLCResolution {
/// The `channel_id` of the channel which has been closed.
channel_id: ChannelId,
/// Counterparty in the closed channel.
counterparty_node_id: PublicKey,
/// The unique identifier for the claim of the HTLCs in the confirmed commitment
/// transaction.
///
/// The identifier must map to the set of external UTXOs assigned to the claim, such that
/// they can be reused when a new claim with the same identifier needs to be made, resulting
/// in a fee-bumping attempt.
claim_id: ClaimId,
/// The target feerate that the resulting HTLC transaction must meet.
target_feerate_sat_per_1000_weight: u32,
/// The set of pending HTLCs on the confirmed commitment that need to be claimed, preferably
/// by the same transaction.
htlc_descriptors: Vec<HTLCDescriptor>,
/// The locktime required for the resulting HTLC transaction.
tx_lock_time: LockTime,
},
}
/// An input that must be included in a transaction when performing coin selection through
/// [`CoinSelectionSource::select_confirmed_utxos`]. It is guaranteed to be a SegWit input, so it
/// must have an empty [`TxIn::script_sig`] when spent.
#[derive(Clone, Debug, Hash, PartialOrd, Ord, PartialEq, Eq)]
pub struct Input {
/// The unique identifier of the input.
pub outpoint: OutPoint,
/// The UTXO being spent by the input.
pub previous_utxo: TxOut,
/// The upper-bound weight consumed by the input's full [`TxIn::script_sig`] and
/// [`TxIn::witness`], each with their lengths included, required to satisfy the output's
/// script.
pub satisfaction_weight: u64,
}
/// An unspent transaction output that is available to spend resulting from a successful
/// [`CoinSelection`] attempt.
#[derive(Clone, Debug, Hash, PartialOrd, Ord, PartialEq, Eq)]
pub struct Utxo {
/// The unique identifier of the output.
pub outpoint: OutPoint,
/// The output to spend.
pub output: TxOut,
/// The upper-bound weight consumed by the input's full [`TxIn::script_sig`] and [`TxIn::witness`], each
/// with their lengths included, required to satisfy the output's script. The weight consumed by
/// the input's `script_sig` must account for [`WITNESS_SCALE_FACTOR`].
pub satisfaction_weight: u64,
}
impl Utxo {
/// Returns a `Utxo` with the `satisfaction_weight` estimate for a legacy P2PKH output.
pub fn new_p2pkh(outpoint: OutPoint, value: Amount, pubkey_hash: &PubkeyHash) -> Self {
let script_sig_size = 1 /* script_sig length */ +
1 /* OP_PUSH73 */ +
73 /* sig including sighash flag */ +
1 /* OP_PUSH33 */ +
33 /* pubkey */;
Self {
outpoint,
output: TxOut {
value,
script_pubkey: ScriptBuf::new_p2pkh(pubkey_hash),
},
satisfaction_weight: script_sig_size * WITNESS_SCALE_FACTOR as u64 + 1 /* empty witness */,
}
}
/// Returns a `Utxo` with the `satisfaction_weight` estimate for a P2WPKH nested in P2SH output.
pub fn new_nested_p2wpkh(outpoint: OutPoint, value: Amount, pubkey_hash: &WPubkeyHash) -> Self {
let script_sig_size = 1 /* script_sig length */ +
1 /* OP_0 */ +
1 /* OP_PUSH20 */ +
20 /* pubkey_hash */;
Self {
outpoint,
output: TxOut {
value,
script_pubkey: ScriptBuf::new_p2sh(&ScriptBuf::new_p2wpkh(pubkey_hash).script_hash()),
},
satisfaction_weight: script_sig_size * WITNESS_SCALE_FACTOR as u64 + P2WPKH_WITNESS_WEIGHT,
}
}
/// Returns a `Utxo` with the `satisfaction_weight` estimate for a SegWit v0 P2WPKH output.
pub fn new_v0_p2wpkh(outpoint: OutPoint, value: Amount, pubkey_hash: &WPubkeyHash) -> Self {
Self {
outpoint,
output: TxOut {
value,
script_pubkey: ScriptBuf::new_p2wpkh(pubkey_hash),
},
satisfaction_weight: EMPTY_SCRIPT_SIG_WEIGHT + P2WPKH_WITNESS_WEIGHT,
}
}
}
/// The result of a successful coin selection attempt for a transaction requiring additional UTXOs
/// to cover its fees.
#[derive(Clone, Debug)]
pub struct CoinSelection {
/// The set of UTXOs (with at least 1 confirmation) to spend and use within a transaction
/// requiring additional fees.
pub confirmed_utxos: Vec<Utxo>,
/// An additional output tracking whether any change remained after coin selection. This output
/// should always have a value above dust for its given `script_pubkey`. It should not be
/// spent until the transaction it belongs to confirms to ensure mempool descendant limits are
/// not met. This implies no other party should be able to spend it except us.
pub change_output: Option<TxOut>,
}
/// An abstraction over a bitcoin wallet that can perform coin selection over a set of UTXOs and can
/// sign for them. The coin selection method aims to mimic Bitcoin Core's `fundrawtransaction` RPC,
/// which most wallets should be able to satisfy. Otherwise, consider implementing [`WalletSource`],
/// which can provide a default implementation of this trait when used with [`Wallet`].
pub trait CoinSelectionSource {
/// Performs coin selection of a set of UTXOs, with at least 1 confirmation each, that are
/// available to spend. Implementations are free to pick their coin selection algorithm of
/// choice, as long as the following requirements are met:
///
/// 1. `must_spend` contains a set of [`Input`]s that must be included in the transaction
/// throughout coin selection, but must not be returned as part of the result.
/// 2. `must_pay_to` contains a set of [`TxOut`]s that must be included in the transaction
/// throughout coin selection. In some cases, like when funding an anchor transaction, this
/// set is empty. Implementations should ensure they handle this correctly on their end,
/// e.g., Bitcoin Core's `fundrawtransaction` RPC requires at least one output to be
/// provided, in which case a zero-value empty OP_RETURN output can be used instead.
/// 3. Enough inputs must be selected/contributed for the resulting transaction (including the
/// inputs and outputs noted above) to meet `target_feerate_sat_per_1000_weight`.
///
/// Implementations must take note that [`Input::satisfaction_weight`] only tracks the weight of
/// the input's `script_sig` and `witness`. Some wallets, like Bitcoin Core's, may require
/// providing the full input weight. Failing to do so may lead to underestimating fee bumps and
/// delaying block inclusion.
///
/// The `claim_id` must map to the set of external UTXOs assigned to the claim, such that they
/// can be re-used within new fee-bumped iterations of the original claiming transaction,
/// ensuring that claims don't double spend each other. If a specific `claim_id` has never had a
/// transaction associated with it, and all of the available UTXOs have already been assigned to
/// other claims, implementations must be willing to double spend their UTXOs. The choice of
/// which UTXOs to double spend is left to the implementation, but it must strive to keep the
/// set of other claims being double spent to a minimum.
fn select_confirmed_utxos(
&self, claim_id: ClaimId, must_spend: Vec<Input>, must_pay_to: &[TxOut],
target_feerate_sat_per_1000_weight: u32,
) -> Result<CoinSelection, ()>;
/// Signs and provides the full witness for all inputs within the transaction known to the
/// trait (i.e., any provided via [`CoinSelectionSource::select_confirmed_utxos`]).
///
/// If your wallet does not support signing PSBTs you can call `psbt.extract_tx()` to get the
/// unsigned transaction and then sign it with your wallet.
fn sign_psbt(&self, psbt: Psbt) -> Result<Transaction, ()>;
}
/// An alternative to [`CoinSelectionSource`] that can be implemented and used along [`Wallet`] to
/// provide a default implementation to [`CoinSelectionSource`].
pub trait WalletSource {
/// Returns all UTXOs, with at least 1 confirmation each, that are available to spend.
fn list_confirmed_utxos(&self) -> Result<Vec<Utxo>, ()>;
/// Returns a script to use for change above dust resulting from a successful coin selection
/// attempt.
fn get_change_script(&self) -> Result<ScriptBuf, ()>;
/// Signs and provides the full [`TxIn::script_sig`] and [`TxIn::witness`] for all inputs within
/// the transaction known to the wallet (i.e., any provided via
/// [`WalletSource::list_confirmed_utxos`]).
///
/// If your wallet does not support signing PSBTs you can call `psbt.extract_tx()` to get the
/// unsigned transaction and then sign it with your wallet.
fn sign_psbt(&self, psbt: Psbt) -> Result<Transaction, ()>;
}
/// A wrapper over [`WalletSource`] that implements [`CoinSelection`] by preferring UTXOs that would
/// avoid conflicting double spends. If not enough UTXOs are available to do so, conflicting double
/// spends may happen.
pub struct Wallet<W: Deref, L: Deref>
where
W::Target: WalletSource,
L::Target: Logger
{
source: W,
logger: L,
// TODO: Do we care about cleaning this up once the UTXOs have a confirmed spend? We can do so
// by checking whether any UTXOs that exist in the map are no longer returned in
// `list_confirmed_utxos`.
locked_utxos: Mutex<HashMap<OutPoint, ClaimId>>,
}
impl<W: Deref, L: Deref> Wallet<W, L>
where
W::Target: WalletSource,
L::Target: Logger
{
/// Returns a new instance backed by the given [`WalletSource`] that serves as an implementation
/// of [`CoinSelectionSource`].
pub fn new(source: W, logger: L) -> Self {
Self { source, logger, locked_utxos: Mutex::new(new_hash_map()) }
}
/// Performs coin selection on the set of UTXOs obtained from
/// [`WalletSource::list_confirmed_utxos`]. Its algorithm can be described as "smallest
/// above-dust-after-spend first", with a slight twist: we may skip UTXOs that are above dust at
/// the target feerate after having spent them in a separate claim transaction if
/// `force_conflicting_utxo_spend` is unset to avoid producing conflicting transactions. If
/// `tolerate_high_network_feerates` is set, we'll attempt to spend UTXOs that contribute at
/// least 1 satoshi at the current feerate, otherwise, we'll only attempt to spend those which
/// contribute at least twice their fee.
fn select_confirmed_utxos_internal(
&self, utxos: &[Utxo], claim_id: ClaimId, force_conflicting_utxo_spend: bool,
tolerate_high_network_feerates: bool, target_feerate_sat_per_1000_weight: u32,
preexisting_tx_weight: u64, input_amount_sat: Amount, target_amount_sat: Amount,
) -> Result<CoinSelection, ()> {
let mut locked_utxos = self.locked_utxos.lock().unwrap();
let mut eligible_utxos = utxos.iter().filter_map(|utxo| {
if let Some(utxo_claim_id) = locked_utxos.get(&utxo.outpoint) {
if *utxo_claim_id != claim_id && !force_conflicting_utxo_spend {
log_trace!(self.logger, "Skipping UTXO {} to prevent conflicting spend", utxo.outpoint);
return None;
}
}
let fee_to_spend_utxo = Amount::from_sat(fee_for_weight(
target_feerate_sat_per_1000_weight, BASE_INPUT_WEIGHT + utxo.satisfaction_weight,
));
let should_spend = if tolerate_high_network_feerates {
utxo.output.value > fee_to_spend_utxo
} else {
utxo.output.value >= fee_to_spend_utxo * 2
};
if should_spend {
Some((utxo, fee_to_spend_utxo))
} else {
log_trace!(self.logger, "Skipping UTXO {} due to dust proximity after spend", utxo.outpoint);
None
}
}).collect::<Vec<_>>();
eligible_utxos.sort_unstable_by_key(|(utxo, _)| utxo.output.value);
let mut selected_amount = input_amount_sat;
let mut total_fees = Amount::from_sat(fee_for_weight(target_feerate_sat_per_1000_weight, preexisting_tx_weight));
let mut selected_utxos = Vec::new();
for (utxo, fee_to_spend_utxo) in eligible_utxos {
if selected_amount >= target_amount_sat + total_fees {
break;
}
selected_amount += utxo.output.value;
total_fees += fee_to_spend_utxo;
selected_utxos.push(utxo.clone());
}
if selected_amount < target_amount_sat + total_fees {
log_debug!(self.logger, "Insufficient funds to meet target feerate {} sat/kW",
target_feerate_sat_per_1000_weight);
return Err(());
}
for utxo in &selected_utxos {
locked_utxos.insert(utxo.outpoint, claim_id);
}
core::mem::drop(locked_utxos);
let remaining_amount = selected_amount - target_amount_sat - total_fees;
let change_script = self.source.get_change_script()?;
let change_output_fee = fee_for_weight(
target_feerate_sat_per_1000_weight,
(8 /* value */ + change_script.consensus_encode(&mut sink()).unwrap() as u64) *
WITNESS_SCALE_FACTOR as u64,
);
let change_output_amount = Amount::from_sat(remaining_amount.to_sat().saturating_sub(change_output_fee));
let change_output = if change_output_amount < change_script.minimal_non_dust() {
log_debug!(self.logger, "Coin selection attempt did not yield change output");
None
} else {
Some(TxOut { script_pubkey: change_script, value: change_output_amount })
};
Ok(CoinSelection {
confirmed_utxos: selected_utxos,
change_output,
})
}
}
impl<W: Deref, L: Deref> CoinSelectionSource for Wallet<W, L>
where
W::Target: WalletSource,
L::Target: Logger
{
fn select_confirmed_utxos(
&self, claim_id: ClaimId, must_spend: Vec<Input>, must_pay_to: &[TxOut],
target_feerate_sat_per_1000_weight: u32,
) -> Result<CoinSelection, ()> {
let utxos = self.source.list_confirmed_utxos()?;
// TODO: Use fee estimation utils when we upgrade to bitcoin v0.30.0.
const BASE_TX_SIZE: u64 = 4 /* version */ + 1 /* input count */ + 1 /* output count */ + 4 /* locktime */;
let total_output_size: u64 = must_pay_to.iter().map(|output|
8 /* value */ + 1 /* script len */ + output.script_pubkey.len() as u64
).sum();
let total_satisfaction_weight: u64 = must_spend.iter().map(|input| input.satisfaction_weight).sum();
let total_input_weight = (BASE_INPUT_WEIGHT * must_spend.len() as u64) + total_satisfaction_weight;
let preexisting_tx_weight = 2 /* segwit marker & flag */ + total_input_weight +
((BASE_TX_SIZE + total_output_size) * WITNESS_SCALE_FACTOR as u64);
let input_amount_sat = must_spend.iter().map(|input| input.previous_utxo.value).sum();
let target_amount_sat = must_pay_to.iter().map(|output| output.value).sum();
let do_coin_selection = |force_conflicting_utxo_spend: bool, tolerate_high_network_feerates: bool| {
log_debug!(self.logger, "Attempting coin selection targeting {} sat/kW (force_conflicting_utxo_spend = {}, tolerate_high_network_feerates = {})",
target_feerate_sat_per_1000_weight, force_conflicting_utxo_spend, tolerate_high_network_feerates);
self.select_confirmed_utxos_internal(
&utxos, claim_id, force_conflicting_utxo_spend, tolerate_high_network_feerates,
target_feerate_sat_per_1000_weight, preexisting_tx_weight, input_amount_sat, target_amount_sat,
)
};
do_coin_selection(false, false)
.or_else(|_| do_coin_selection(false, true))
.or_else(|_| do_coin_selection(true, false))
.or_else(|_| do_coin_selection(true, true))
}
fn sign_psbt(&self, psbt: Psbt) -> Result<Transaction, ()> {
self.source.sign_psbt(psbt)
}
}
/// A handler for [`Event::BumpTransaction`] events that sources confirmed UTXOs from a
/// [`CoinSelectionSource`] to fee bump transactions via Child-Pays-For-Parent (CPFP) or
/// Replace-By-Fee (RBF).
///
/// [`Event::BumpTransaction`]: crate::events::Event::BumpTransaction
pub struct BumpTransactionEventHandler<B: Deref, C: Deref, SP: Deref, L: Deref>
where
B::Target: BroadcasterInterface,
C::Target: CoinSelectionSource,
SP::Target: SignerProvider,
L::Target: Logger,
{
broadcaster: B,
utxo_source: C,
signer_provider: SP,
logger: L,
secp: Secp256k1<secp256k1::All>,
}
impl<B: Deref, C: Deref, SP: Deref, L: Deref> BumpTransactionEventHandler<B, C, SP, L>
where
B::Target: BroadcasterInterface,
C::Target: CoinSelectionSource,
SP::Target: SignerProvider,
L::Target: Logger,
{
/// Returns a new instance capable of handling [`Event::BumpTransaction`] events.
///
/// [`Event::BumpTransaction`]: crate::events::Event::BumpTransaction
pub fn new(broadcaster: B, utxo_source: C, signer_provider: SP, logger: L) -> Self {
Self {
broadcaster,
utxo_source,
signer_provider,
logger,
secp: Secp256k1::new(),
}
}
/// Updates a transaction with the result of a successful coin selection attempt.
fn process_coin_selection(&self, tx: &mut Transaction, coin_selection: &CoinSelection) {
for utxo in coin_selection.confirmed_utxos.iter() {
tx.input.push(TxIn {
previous_output: utxo.outpoint,
script_sig: ScriptBuf::new(),
sequence: Sequence::ZERO,
witness: Witness::new(),
});
}
if let Some(change_output) = coin_selection.change_output.clone() {
tx.output.push(change_output);
} else if tx.output.is_empty() {
// We weren't provided a change output, likely because the input set was a perfect
// match, but we still need to have at least one output in the transaction for it to be
// considered standard. We choose to go with an empty OP_RETURN as it is the cheapest
// way to include a dummy output.
if tx.input.len() <= 1 {
// Transactions have to be at least 65 bytes in non-witness data, which we can run
// under if we have too few witness inputs.
log_debug!(self.logger, "Including large OP_RETURN output since an output is needed and a change output was not provided and the transaction is small");
debug_assert!(!tx.input.is_empty());
tx.output.push(TxOut {
value: Amount::ZERO,
// Minimum transaction size is 60 bytes, so we need a 5-byte script to get a
// 65 byte transaction. We do that as OP_RETURN <3 0 bytes, plus 1 byte len>.
script_pubkey: ScriptBuf::new_op_return(&[0, 0, 0]),
});
debug_assert_eq!(tx.base_size(), 65);
} else {
log_debug!(self.logger, "Including dummy OP_RETURN output since an output is needed and a change output was not provided");
tx.output.push(TxOut {
value: Amount::ZERO,
script_pubkey: ScriptBuf::new_op_return(&[]),
});
}
}
}
/// Handles a [`BumpTransactionEvent::ChannelClose`] event variant by producing a fully-signed
/// transaction spending an anchor output of the commitment transaction to bump its fee and
/// broadcasts them to the network as a package.
fn handle_channel_close(
&self, claim_id: ClaimId, package_target_feerate_sat_per_1000_weight: u32,
commitment_tx: &Transaction, commitment_tx_fee_sat: u64, anchor_descriptor: &AnchorDescriptor,
) -> Result<(), ()> {
// Our commitment transaction already has fees allocated to it, so we should take them into
// account. We do so by pretending the commitment transaction's fee and weight are part of
// the anchor input.
let mut anchor_utxo = anchor_descriptor.previous_utxo();
let commitment_tx_fee_sat = Amount::from_sat(commitment_tx_fee_sat);
anchor_utxo.value += commitment_tx_fee_sat;
let starting_package_and_fixed_input_satisfaction_weight =
commitment_tx.weight().to_wu() + ANCHOR_INPUT_WITNESS_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT;
let mut package_and_fixed_input_satisfaction_weight =
starting_package_and_fixed_input_satisfaction_weight;
loop {
let must_spend = vec![Input {
outpoint: anchor_descriptor.outpoint,
previous_utxo: anchor_utxo.clone(),
satisfaction_weight: package_and_fixed_input_satisfaction_weight,
}];
let must_spend_amount = must_spend.iter().map(|input| input.previous_utxo.value).sum::<Amount>();
log_debug!(self.logger, "Performing coin selection for commitment package (commitment and anchor transaction) targeting {} sat/kW",
package_target_feerate_sat_per_1000_weight);
let coin_selection: CoinSelection = self.utxo_source.select_confirmed_utxos(
claim_id, must_spend, &[], package_target_feerate_sat_per_1000_weight,
)?;
let mut anchor_tx = Transaction {
version: Version::TWO,
lock_time: LockTime::ZERO, // TODO: Use next best height.
input: vec![anchor_descriptor.unsigned_tx_input()],
output: vec![],
};
let total_satisfaction_weight = ANCHOR_INPUT_WITNESS_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT +
coin_selection.confirmed_utxos.iter().map(|utxo| utxo.satisfaction_weight).sum::<u64>();
let total_input_amount = must_spend_amount +
coin_selection.confirmed_utxos.iter().map(|utxo| utxo.output.value).sum();
self.process_coin_selection(&mut anchor_tx, &coin_selection);
let anchor_txid = anchor_tx.compute_txid();
// construct psbt
let mut anchor_psbt = Psbt::from_unsigned_tx(anchor_tx).unwrap();
// add witness_utxo to anchor input
anchor_psbt.inputs[0].witness_utxo = Some(anchor_descriptor.previous_utxo());
// add witness_utxo to remaining inputs
for (idx, utxo) in coin_selection.confirmed_utxos.into_iter().enumerate() {
// add 1 to skip the anchor input
let index = idx + 1;
debug_assert_eq!(anchor_psbt.unsigned_tx.input[index].previous_output, utxo.outpoint);
if utxo.output.script_pubkey.is_witness_program() {
anchor_psbt.inputs[index].witness_utxo = Some(utxo.output);
}
}
debug_assert_eq!(anchor_psbt.unsigned_tx.output.len(), 1);
let unsigned_tx_weight = anchor_psbt.unsigned_tx.weight().to_wu() - (anchor_psbt.unsigned_tx.input.len() as u64 * EMPTY_SCRIPT_SIG_WEIGHT);
let package_fee = total_input_amount -
anchor_psbt.unsigned_tx.output.iter().map(|output| output.value).sum();
let package_weight = unsigned_tx_weight + 2 /* wit marker */ + total_satisfaction_weight + commitment_tx.weight().to_wu();
if package_fee.to_sat() * 1000 / package_weight < package_target_feerate_sat_per_1000_weight.into() {
// On the first iteration of the loop, we may undershoot the target feerate because
// we had to add an OP_RETURN output in `process_coin_selection` which we didn't
// select sufficient coins for. Here we detect that case and go around again
// seeking additional weight.
if package_and_fixed_input_satisfaction_weight == starting_package_and_fixed_input_satisfaction_weight {
debug_assert!(anchor_psbt.unsigned_tx.output[0].script_pubkey.is_op_return(),
"Coin selection failed to select sufficient coins for its change output");
package_and_fixed_input_satisfaction_weight += anchor_psbt.unsigned_tx.output[0].weight().to_wu();
continue;
} else {
debug_assert!(false, "Coin selection failed to select sufficient coins");
}
}
log_debug!(self.logger, "Signing anchor transaction {}", anchor_txid);
anchor_tx = self.utxo_source.sign_psbt(anchor_psbt)?;
let signer = anchor_descriptor.derive_channel_signer(&self.signer_provider);
let anchor_sig = signer.sign_holder_anchor_input(&anchor_tx, 0, &self.secp)?;
anchor_tx.input[0].witness = anchor_descriptor.tx_input_witness(&anchor_sig);
#[cfg(debug_assertions)] {
let signed_tx_weight = anchor_tx.weight().to_wu();
let expected_signed_tx_weight = unsigned_tx_weight + 2 /* wit marker */ + total_satisfaction_weight;
// Our estimate should be within a 1% error margin of the actual weight and we should
// never underestimate.
assert!(expected_signed_tx_weight >= signed_tx_weight &&
expected_signed_tx_weight - (expected_signed_tx_weight / 100) <= signed_tx_weight);
let expected_package_fee = Amount::from_sat(fee_for_weight(package_target_feerate_sat_per_1000_weight,
signed_tx_weight + commitment_tx.weight().to_wu()));
// Our feerate should always be at least what we were seeking. It may overshoot if
// the coin selector burned funds to an OP_RETURN without a change output.
assert!(package_fee >= expected_package_fee);
}
log_info!(self.logger, "Broadcasting anchor transaction {} to bump channel close with txid {}",
anchor_txid, commitment_tx.compute_txid());
self.broadcaster.broadcast_transactions(&[&commitment_tx, &anchor_tx]);
return Ok(());
}
}
/// Handles a [`BumpTransactionEvent::HTLCResolution`] event variant by producing a
/// fully-signed, fee-bumped HTLC transaction that is broadcast to the network.
fn handle_htlc_resolution(
&self, claim_id: ClaimId, target_feerate_sat_per_1000_weight: u32,
htlc_descriptors: &[HTLCDescriptor], tx_lock_time: LockTime,
) -> Result<(), ()> {
let mut htlc_tx = Transaction {
version: Version::TWO,
lock_time: tx_lock_time,
input: vec![],
output: vec![],
};
let mut must_spend = Vec::with_capacity(htlc_descriptors.len());
for htlc_descriptor in htlc_descriptors {
let htlc_input = htlc_descriptor.unsigned_tx_input();
must_spend.push(Input {
outpoint: htlc_input.previous_output.clone(),
previous_utxo: htlc_descriptor.previous_utxo(&self.secp),
satisfaction_weight: EMPTY_SCRIPT_SIG_WEIGHT + if htlc_descriptor.preimage.is_some() {
HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT
} else {
HTLC_TIMEOUT_INPUT_ANCHOR_WITNESS_WEIGHT
},
});
htlc_tx.input.push(htlc_input);
let htlc_output = htlc_descriptor.tx_output(&self.secp);
htlc_tx.output.push(htlc_output);
}
log_debug!(self.logger, "Performing coin selection for HTLC transaction targeting {} sat/kW",
target_feerate_sat_per_1000_weight);
#[cfg(debug_assertions)]
let must_spend_satisfaction_weight =
must_spend.iter().map(|input| input.satisfaction_weight).sum::<u64>();
#[cfg(debug_assertions)]
let must_spend_amount = must_spend.iter().map(|input| input.previous_utxo.value.to_sat()).sum::<u64>();
let coin_selection: CoinSelection = self.utxo_source.select_confirmed_utxos(
claim_id, must_spend, &htlc_tx.output, target_feerate_sat_per_1000_weight,
)?;
#[cfg(debug_assertions)]
let total_satisfaction_weight = must_spend_satisfaction_weight +
coin_selection.confirmed_utxos.iter().map(|utxo| utxo.satisfaction_weight).sum::<u64>();
#[cfg(debug_assertions)]
let total_input_amount = must_spend_amount +
coin_selection.confirmed_utxos.iter().map(|utxo| utxo.output.value.to_sat()).sum::<u64>();
self.process_coin_selection(&mut htlc_tx, &coin_selection);
// construct psbt
let mut htlc_psbt = Psbt::from_unsigned_tx(htlc_tx).unwrap();
// add witness_utxo to htlc inputs
for (i, htlc_descriptor) in htlc_descriptors.iter().enumerate() {
debug_assert_eq!(htlc_psbt.unsigned_tx.input[i].previous_output, htlc_descriptor.outpoint());
htlc_psbt.inputs[i].witness_utxo = Some(htlc_descriptor.previous_utxo(&self.secp));
}
// add witness_utxo to remaining inputs
for (idx, utxo) in coin_selection.confirmed_utxos.into_iter().enumerate() {
// offset to skip the htlc inputs
let index = idx + htlc_descriptors.len();
debug_assert_eq!(htlc_psbt.unsigned_tx.input[index].previous_output, utxo.outpoint);
if utxo.output.script_pubkey.is_witness_program() {
htlc_psbt.inputs[index].witness_utxo = Some(utxo.output);
}
}
#[cfg(debug_assertions)]
let unsigned_tx_weight = htlc_psbt.unsigned_tx.weight().to_wu() - (htlc_psbt.unsigned_tx.input.len() as u64 * EMPTY_SCRIPT_SIG_WEIGHT);
log_debug!(self.logger, "Signing HTLC transaction {}", htlc_psbt.unsigned_tx.compute_txid());
htlc_tx = self.utxo_source.sign_psbt(htlc_psbt)?;
let mut signers = BTreeMap::new();
for (idx, htlc_descriptor) in htlc_descriptors.iter().enumerate() {
let signer = signers.entry(htlc_descriptor.channel_derivation_parameters.keys_id)
.or_insert_with(|| htlc_descriptor.derive_channel_signer(&self.signer_provider));
let htlc_sig = signer.sign_holder_htlc_transaction(&htlc_tx, idx, htlc_descriptor, &self.secp)?;
let witness_script = htlc_descriptor.witness_script(&self.secp);
htlc_tx.input[idx].witness = htlc_descriptor.tx_input_witness(&htlc_sig, &witness_script);
}
#[cfg(debug_assertions)] {
let signed_tx_weight = htlc_tx.weight().to_wu();
let expected_signed_tx_weight = unsigned_tx_weight + total_satisfaction_weight;
// Our estimate should be within a 1% error margin of the actual weight and we should
// never underestimate.
assert!(expected_signed_tx_weight >= signed_tx_weight &&
expected_signed_tx_weight - (expected_signed_tx_weight / 100) <= signed_tx_weight);
let expected_signed_tx_fee = fee_for_weight(target_feerate_sat_per_1000_weight, signed_tx_weight);
let signed_tx_fee = total_input_amount -
htlc_tx.output.iter().map(|output| output.value.to_sat()).sum::<u64>();
// Our feerate should always be at least what we were seeking. It may overshoot if
// the coin selector burned funds to an OP_RETURN without a change output.
assert!(signed_tx_fee >= expected_signed_tx_fee);
}
log_info!(self.logger, "Broadcasting {}", log_tx!(htlc_tx));
self.broadcaster.broadcast_transactions(&[&htlc_tx]);
Ok(())
}
/// Handles all variants of [`BumpTransactionEvent`].
pub fn handle_event(&self, event: &BumpTransactionEvent) {
match event {
BumpTransactionEvent::ChannelClose {
claim_id, package_target_feerate_sat_per_1000_weight, commitment_tx,
commitment_tx_fee_satoshis, anchor_descriptor, ..
} => {
log_info!(self.logger, "Handling channel close bump (claim_id = {}, commitment_txid = {})",
log_bytes!(claim_id.0), commitment_tx.compute_txid());
if let Err(_) = self.handle_channel_close(
*claim_id, *package_target_feerate_sat_per_1000_weight, commitment_tx,
*commitment_tx_fee_satoshis, anchor_descriptor,
) {
log_error!(self.logger, "Failed bumping commitment transaction fee for {}",
commitment_tx.compute_txid());
}
}
BumpTransactionEvent::HTLCResolution {
claim_id, target_feerate_sat_per_1000_weight, htlc_descriptors, tx_lock_time, ..
} => {
log_info!(self.logger, "Handling HTLC bump (claim_id = {}, htlcs_to_claim = {})",
log_bytes!(claim_id.0), log_iter!(htlc_descriptors.iter().map(|d| d.outpoint())));
if let Err(_) = self.handle_htlc_resolution(
*claim_id, *target_feerate_sat_per_1000_weight, htlc_descriptors, *tx_lock_time,
) {
log_error!(self.logger, "Failed bumping HTLC transaction fee for commitment {}",
htlc_descriptors[0].commitment_txid);
}
}
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::io::Cursor;
use crate::ln::chan_utils::ChannelTransactionParameters;
use crate::util::ser::Readable;
use crate::util::test_utils::{TestBroadcaster, TestLogger};
use crate::sign::KeysManager;
use bitcoin::hashes::Hash;
use bitcoin::hex::FromHex;
use bitcoin::{Network, ScriptBuf, Transaction, Txid};
struct TestCoinSelectionSource {
// (commitment + anchor value, commitment + input weight, target feerate, result)
expected_selects: Mutex<Vec<(u64, u64, u32, CoinSelection)>>,
}
impl CoinSelectionSource for TestCoinSelectionSource {
fn select_confirmed_utxos(
&self,
_claim_id: ClaimId,
must_spend: Vec<Input>,
_must_pay_to: &[TxOut],
target_feerate_sat_per_1000_weight: u32
) -> Result<CoinSelection, ()> {
let mut expected_selects = self.expected_selects.lock().unwrap();
let (weight, value, feerate, res) = expected_selects.remove(0);
assert_eq!(must_spend.len(), 1);
assert_eq!(must_spend[0].satisfaction_weight, weight);
assert_eq!(must_spend[0].previous_utxo.value.to_sat(), value);
assert_eq!(target_feerate_sat_per_1000_weight, feerate);
Ok(res)
}
fn sign_psbt(&self, psbt: Psbt) -> Result<Transaction, ()> {
let mut tx = psbt.unsigned_tx;
for input in tx.input.iter_mut() {
if input.previous_output.txid != Txid::from_byte_array([44; 32]) {
// Channel output, add a realistic size witness to make the assertions happy
input.witness = Witness::from_slice(&[vec![42; 162]]);
}
}
Ok(tx)
}
}
impl Drop for TestCoinSelectionSource {
fn drop(&mut self) {
assert!(self.expected_selects.lock().unwrap().is_empty());
}
}
#[test]
fn test_op_return_under_funds() {
// Test what happens if we have to select coins but the anchor output value itself suffices
// to pay the required fee.
//
// This tests a case that occurred on mainnet (with the below transaction) where the target
// feerate (of 868 sat/kW) was met by the anchor output's 330 sats alone. This caused the
// use of an OP_RETURN which created a transaction which, at the time, was less than 64
// bytes long (the current code generates a 65 byte transaction instead to meet
// standardness rule). It also tests the handling of selection failure where we selected
// coins which were insufficient once the OP_RETURN output was added, causing us to need to
// select coins again with additional weight.
// Tx 18032ad172a5f28fa6e16392d6cc57ea47895781434ce15d03766cc47a955fb9
let commitment_tx_bytes = Vec::<u8>::from_hex("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").unwrap();
let commitment_tx: Transaction = Readable::read(&mut Cursor::new(&commitment_tx_bytes)).unwrap();
let total_commitment_weight = commitment_tx.weight().to_wu() + ANCHOR_INPUT_WITNESS_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT;
let commitment_and_anchor_fee = 930 + 330;
let op_return_weight = TxOut {
value: Amount::ZERO,
script_pubkey: ScriptBuf::new_op_return(&[0; 3]),
}.weight().to_wu();
let broadcaster = TestBroadcaster::new(Network::Testnet);
let source = TestCoinSelectionSource {
expected_selects: Mutex::new(vec![
(total_commitment_weight, commitment_and_anchor_fee, 868, CoinSelection { confirmed_utxos: Vec::new(), change_output: None }),
(total_commitment_weight + op_return_weight, commitment_and_anchor_fee, 868, CoinSelection {
confirmed_utxos: vec![Utxo {
outpoint: OutPoint { txid: Txid::from_byte_array([44; 32]), vout: 0 },
output: TxOut { value: Amount::from_sat(200), script_pubkey: ScriptBuf::new() },
satisfaction_weight: 5, // Just the script_sig and witness lengths
}],
change_output: None,
})
]),
};
let signer = KeysManager::new(&[42; 32], 42, 42);
let logger = TestLogger::new();
let handler = BumpTransactionEventHandler::new(&broadcaster, &source, &signer, &logger);
handler.handle_event(&BumpTransactionEvent::ChannelClose {
channel_id: ChannelId([42; 32]),
counterparty_node_id: PublicKey::from_slice(&[2; 33]).unwrap(),
claim_id: ClaimId([42; 32]),
package_target_feerate_sat_per_1000_weight: 868,
commitment_tx_fee_satoshis: 930,
commitment_tx,
anchor_descriptor: AnchorDescriptor {
channel_derivation_parameters: ChannelDerivationParameters {
value_satoshis: 42_000_000,
keys_id: [42; 32],
transaction_parameters: ChannelTransactionParameters::test_dummy(),
},
outpoint: OutPoint { txid: Txid::from_byte_array([42; 32]), vout: 0 },
},
pending_htlcs: Vec::new(),
});
}
}