1 // This file is Copyright its original authors, visible in version control
4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
7 // You may not use this file except in accordance with one or both of these
10 //! Utilities for bumping transactions originating from [`Event`]s.
12 //! [`Event`]: crate::events::Event
14 use alloc::collections::BTreeMap;
17 use crate::chain::chaininterface::{BroadcasterInterface, fee_for_weight};
18 use crate::chain::ClaimId;
19 use crate::io_extras::sink;
20 use crate::ln::channel::ANCHOR_OUTPUT_VALUE_SATOSHI;
21 use crate::ln::chan_utils;
22 use crate::ln::chan_utils::{
23 ANCHOR_INPUT_WITNESS_WEIGHT, HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT,
24 HTLC_TIMEOUT_INPUT_ANCHOR_WITNESS_WEIGHT, HTLCOutputInCommitment
26 use crate::prelude::*;
28 ChannelDerivationParameters, HTLCDescriptor, SignerProvider, P2WPKH_WITNESS_WEIGHT
30 use crate::sign::ecdsa::{EcdsaChannelSigner, WriteableEcdsaChannelSigner};
31 use crate::sync::Mutex;
32 use crate::util::logger::Logger;
34 use bitcoin::{OutPoint, PubkeyHash, Sequence, ScriptBuf, Transaction, TxIn, TxOut, Witness, WPubkeyHash};
35 use bitcoin::blockdata::constants::WITNESS_SCALE_FACTOR;
36 use bitcoin::blockdata::locktime::absolute::LockTime;
37 use bitcoin::consensus::Encodable;
38 use bitcoin::psbt::PartiallySignedTransaction;
39 use bitcoin::secp256k1;
40 use bitcoin::secp256k1::Secp256k1;
41 use bitcoin::secp256k1::ecdsa::Signature;
43 const EMPTY_SCRIPT_SIG_WEIGHT: u64 = 1 /* empty script_sig */ * WITNESS_SCALE_FACTOR as u64;
45 const BASE_INPUT_SIZE: u64 = 32 /* txid */ + 4 /* vout */ + 4 /* sequence */;
47 const BASE_INPUT_WEIGHT: u64 = BASE_INPUT_SIZE * WITNESS_SCALE_FACTOR as u64;
49 /// A descriptor used to sign for a commitment transaction's anchor output.
50 #[derive(Clone, Debug, PartialEq, Eq)]
51 pub struct AnchorDescriptor {
52 /// The parameters required to derive the signer for the anchor input.
53 pub channel_derivation_parameters: ChannelDerivationParameters,
54 /// The transaction input's outpoint corresponding to the commitment transaction's anchor
56 pub outpoint: OutPoint,
59 impl AnchorDescriptor {
60 /// Returns the UTXO to be spent by the anchor input, which can be obtained via
61 /// [`Self::unsigned_tx_input`].
62 pub fn previous_utxo(&self) -> TxOut {
64 script_pubkey: self.witness_script().to_v0_p2wsh(),
65 value: ANCHOR_OUTPUT_VALUE_SATOSHI,
69 /// Returns the unsigned transaction input spending the anchor output in the commitment
71 pub fn unsigned_tx_input(&self) -> TxIn {
73 previous_output: self.outpoint.clone(),
74 script_sig: ScriptBuf::new(),
75 sequence: Sequence::ENABLE_RBF_NO_LOCKTIME,
76 witness: Witness::new(),
80 /// Returns the witness script of the anchor output in the commitment transaction.
81 pub fn witness_script(&self) -> ScriptBuf {
82 let channel_params = self.channel_derivation_parameters.transaction_parameters.as_holder_broadcastable();
83 chan_utils::get_anchor_redeemscript(&channel_params.broadcaster_pubkeys().funding_pubkey)
86 /// Returns the fully signed witness required to spend the anchor output in the commitment
88 pub fn tx_input_witness(&self, signature: &Signature) -> Witness {
89 let channel_params = self.channel_derivation_parameters.transaction_parameters.as_holder_broadcastable();
90 chan_utils::build_anchor_input_witness(&channel_params.broadcaster_pubkeys().funding_pubkey, signature)
93 /// Derives the channel signer required to sign the anchor input.
94 pub fn derive_channel_signer<S: WriteableEcdsaChannelSigner, SP: Deref>(&self, signer_provider: &SP) -> S
96 SP::Target: SignerProvider<EcdsaSigner= S>
98 let mut signer = signer_provider.derive_channel_signer(
99 self.channel_derivation_parameters.value_satoshis,
100 self.channel_derivation_parameters.keys_id,
102 signer.provide_channel_parameters(&self.channel_derivation_parameters.transaction_parameters);
107 /// Represents the different types of transactions, originating from LDK, to be bumped.
108 #[derive(Clone, Debug, PartialEq, Eq)]
109 pub enum BumpTransactionEvent {
110 /// Indicates that a channel featuring anchor outputs is to be closed by broadcasting the local
111 /// commitment transaction. Since commitment transactions have a static feerate pre-agreed upon,
112 /// they may need additional fees to be attached through a child transaction using the popular
113 /// [Child-Pays-For-Parent](https://bitcoinops.org/en/topics/cpfp) fee bumping technique. This
114 /// child transaction must include the anchor input described within `anchor_descriptor` along
115 /// with additional inputs to meet the target feerate. Failure to meet the target feerate
116 /// decreases the confirmation odds of the transaction package (which includes the commitment
117 /// and child anchor transactions), possibly resulting in a loss of funds. Once the transaction
118 /// is constructed, it must be fully signed for and broadcast by the consumer of the event
119 /// along with the `commitment_tx` enclosed. Note that the `commitment_tx` must always be
120 /// broadcast first, as the child anchor transaction depends on it.
122 /// The consumer should be able to sign for any of the additional inputs included within the
123 /// child anchor transaction. To sign its anchor input, an [`EcdsaChannelSigner`] should be
124 /// re-derived through [`AnchorDescriptor::derive_channel_signer`]. The anchor input signature
125 /// can be computed with [`EcdsaChannelSigner::sign_holder_anchor_input`], which can then be
126 /// provided to [`build_anchor_input_witness`] along with the `funding_pubkey` to obtain the
127 /// full witness required to spend.
129 /// It is possible to receive more than one instance of this event if a valid child anchor
130 /// transaction is never broadcast or is but not with a sufficient fee to be mined. Care should
131 /// be taken by the consumer of the event to ensure any future iterations of the child anchor
132 /// transaction adhere to the [Replace-By-Fee
133 /// rules](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md)
134 /// for fee bumps to be accepted into the mempool, and eventually the chain. As the frequency of
135 /// these events is not user-controlled, users may ignore/drop the event if they are no longer
136 /// able to commit external confirmed funds to the child anchor transaction.
138 /// The set of `pending_htlcs` on the commitment transaction to be broadcast can be inspected to
139 /// determine whether a significant portion of the channel's funds are allocated to HTLCs,
140 /// enabling users to make their own decisions regarding the importance of the commitment
141 /// transaction's confirmation. Note that this is not required, but simply exists as an option
142 /// for users to override LDK's behavior. On commitments with no HTLCs (indicated by those with
143 /// an empty `pending_htlcs`), confirmation of the commitment transaction can be considered to
146 /// [`EcdsaChannelSigner`]: crate::sign::ecdsa::EcdsaChannelSigner
147 /// [`EcdsaChannelSigner::sign_holder_anchor_input`]: crate::sign::ecdsa::EcdsaChannelSigner::sign_holder_anchor_input
148 /// [`build_anchor_input_witness`]: crate::ln::chan_utils::build_anchor_input_witness
150 /// The unique identifier for the claim of the anchor output in the commitment transaction.
152 /// The identifier must map to the set of external UTXOs assigned to the claim, such that
153 /// they can be reused when a new claim with the same identifier needs to be made, resulting
154 /// in a fee-bumping attempt.
156 /// The target feerate that the transaction package, which consists of the commitment
157 /// transaction and the to-be-crafted child anchor transaction, must meet.
158 package_target_feerate_sat_per_1000_weight: u32,
159 /// The channel's commitment transaction to bump the fee of. This transaction should be
160 /// broadcast along with the anchor transaction constructed as a result of consuming this
162 commitment_tx: Transaction,
163 /// The absolute fee in satoshis of the commitment transaction. This can be used along the
164 /// with weight of the commitment transaction to determine its feerate.
165 commitment_tx_fee_satoshis: u64,
166 /// The descriptor to sign the anchor input of the anchor transaction constructed as a
167 /// result of consuming this event.
168 anchor_descriptor: AnchorDescriptor,
169 /// The set of pending HTLCs on the commitment transaction that need to be resolved once the
170 /// commitment transaction confirms.
171 pending_htlcs: Vec<HTLCOutputInCommitment>,
173 /// Indicates that a channel featuring anchor outputs has unilaterally closed on-chain by a
174 /// holder commitment transaction and its HTLC(s) need to be resolved on-chain. With the
175 /// zero-HTLC-transaction-fee variant of anchor outputs, the pre-signed HTLC
176 /// transactions have a zero fee, thus requiring additional inputs and/or outputs to be attached
177 /// for a timely confirmation within the chain. These additional inputs and/or outputs must be
178 /// appended to the resulting HTLC transaction to meet the target feerate. Failure to meet the
179 /// target feerate decreases the confirmation odds of the transaction, possibly resulting in a
180 /// loss of funds. Once the transaction meets the target feerate, it must be signed for and
181 /// broadcast by the consumer of the event.
183 /// The consumer should be able to sign for any of the non-HTLC inputs added to the resulting
184 /// HTLC transaction. To sign HTLC inputs, an [`EcdsaChannelSigner`] should be re-derived
185 /// through [`HTLCDescriptor::derive_channel_signer`]. Each HTLC input's signature can be
186 /// computed with [`EcdsaChannelSigner::sign_holder_htlc_transaction`], which can then be
187 /// provided to [`HTLCDescriptor::tx_input_witness`] to obtain the fully signed witness required
190 /// It is possible to receive more than one instance of this event if a valid HTLC transaction
191 /// is never broadcast or is but not with a sufficient fee to be mined. Care should be taken by
192 /// the consumer of the event to ensure any future iterations of the HTLC transaction adhere to
193 /// the [Replace-By-Fee
194 /// rules](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md)
195 /// for fee bumps to be accepted into the mempool, and eventually the chain. As the frequency of
196 /// these events is not user-controlled, users may ignore/drop the event if either they are no
197 /// longer able to commit external confirmed funds to the HTLC transaction or the fee committed
198 /// to the HTLC transaction is greater in value than the HTLCs being claimed.
200 /// [`EcdsaChannelSigner`]: crate::sign::ecdsa::EcdsaChannelSigner
201 /// [`EcdsaChannelSigner::sign_holder_htlc_transaction`]: crate::sign::ecdsa::EcdsaChannelSigner::sign_holder_htlc_transaction
203 /// The unique identifier for the claim of the HTLCs in the confirmed commitment
206 /// The identifier must map to the set of external UTXOs assigned to the claim, such that
207 /// they can be reused when a new claim with the same identifier needs to be made, resulting
208 /// in a fee-bumping attempt.
210 /// The target feerate that the resulting HTLC transaction must meet.
211 target_feerate_sat_per_1000_weight: u32,
212 /// The set of pending HTLCs on the confirmed commitment that need to be claimed, preferably
213 /// by the same transaction.
214 htlc_descriptors: Vec<HTLCDescriptor>,
215 /// The locktime required for the resulting HTLC transaction.
216 tx_lock_time: LockTime,
220 /// An input that must be included in a transaction when performing coin selection through
221 /// [`CoinSelectionSource::select_confirmed_utxos`]. It is guaranteed to be a SegWit input, so it
222 /// must have an empty [`TxIn::script_sig`] when spent.
223 #[derive(Clone, Debug, Hash, PartialOrd, Ord, PartialEq, Eq)]
225 /// The unique identifier of the input.
226 pub outpoint: OutPoint,
227 /// The UTXO being spent by the input.
228 pub previous_utxo: TxOut,
229 /// The upper-bound weight consumed by the input's full [`TxIn::script_sig`] and
230 /// [`TxIn::witness`], each with their lengths included, required to satisfy the output's
232 pub satisfaction_weight: u64,
235 /// An unspent transaction output that is available to spend resulting from a successful
236 /// [`CoinSelection`] attempt.
237 #[derive(Clone, Debug, Hash, PartialOrd, Ord, PartialEq, Eq)]
239 /// The unique identifier of the output.
240 pub outpoint: OutPoint,
241 /// The output to spend.
243 /// The upper-bound weight consumed by the input's full [`TxIn::script_sig`] and [`TxIn::witness`], each
244 /// with their lengths included, required to satisfy the output's script. The weight consumed by
245 /// the input's `script_sig` must account for [`WITNESS_SCALE_FACTOR`].
246 pub satisfaction_weight: u64,
250 /// Returns a `Utxo` with the `satisfaction_weight` estimate for a legacy P2PKH output.
251 pub fn new_p2pkh(outpoint: OutPoint, value: u64, pubkey_hash: &PubkeyHash) -> Self {
252 let script_sig_size = 1 /* script_sig length */ +
254 73 /* sig including sighash flag */ +
261 script_pubkey: ScriptBuf::new_p2pkh(pubkey_hash),
263 satisfaction_weight: script_sig_size * WITNESS_SCALE_FACTOR as u64 + 1 /* empty witness */,
267 /// Returns a `Utxo` with the `satisfaction_weight` estimate for a P2WPKH nested in P2SH output.
269 /// This is not exported to bindings users as WPubkeyHash is not yet exported
270 pub fn new_nested_p2wpkh(outpoint: OutPoint, value: u64, pubkey_hash: &WPubkeyHash) -> Self {
271 let script_sig_size = 1 /* script_sig length */ +
274 20 /* pubkey_hash */;
279 script_pubkey: ScriptBuf::new_p2sh(&ScriptBuf::new_v0_p2wpkh(pubkey_hash).script_hash()),
281 satisfaction_weight: script_sig_size * WITNESS_SCALE_FACTOR as u64 + P2WPKH_WITNESS_WEIGHT,
285 /// Returns a `Utxo` with the `satisfaction_weight` estimate for a SegWit v0 P2WPKH output.
287 /// This is not exported to bindings users as WPubkeyHash is not yet exported
288 pub fn new_v0_p2wpkh(outpoint: OutPoint, value: u64, pubkey_hash: &WPubkeyHash) -> Self {
293 script_pubkey: ScriptBuf::new_v0_p2wpkh(pubkey_hash),
295 satisfaction_weight: EMPTY_SCRIPT_SIG_WEIGHT + P2WPKH_WITNESS_WEIGHT,
300 /// The result of a successful coin selection attempt for a transaction requiring additional UTXOs
301 /// to cover its fees.
302 #[derive(Clone, Debug)]
303 pub struct CoinSelection {
304 /// The set of UTXOs (with at least 1 confirmation) to spend and use within a transaction
305 /// requiring additional fees.
306 pub confirmed_utxos: Vec<Utxo>,
307 /// An additional output tracking whether any change remained after coin selection. This output
308 /// should always have a value above dust for its given `script_pubkey`. It should not be
309 /// spent until the transaction it belongs to confirms to ensure mempool descendant limits are
310 /// not met. This implies no other party should be able to spend it except us.
311 pub change_output: Option<TxOut>,
314 /// An abstraction over a bitcoin wallet that can perform coin selection over a set of UTXOs and can
315 /// sign for them. The coin selection method aims to mimic Bitcoin Core's `fundrawtransaction` RPC,
316 /// which most wallets should be able to satisfy. Otherwise, consider implementing [`WalletSource`],
317 /// which can provide a default implementation of this trait when used with [`Wallet`].
318 pub trait CoinSelectionSource {
319 /// Performs coin selection of a set of UTXOs, with at least 1 confirmation each, that are
320 /// available to spend. Implementations are free to pick their coin selection algorithm of
321 /// choice, as long as the following requirements are met:
323 /// 1. `must_spend` contains a set of [`Input`]s that must be included in the transaction
324 /// throughout coin selection, but must not be returned as part of the result.
325 /// 2. `must_pay_to` contains a set of [`TxOut`]s that must be included in the transaction
326 /// throughout coin selection. In some cases, like when funding an anchor transaction, this
327 /// set is empty. Implementations should ensure they handle this correctly on their end,
328 /// e.g., Bitcoin Core's `fundrawtransaction` RPC requires at least one output to be
329 /// provided, in which case a zero-value empty OP_RETURN output can be used instead.
330 /// 3. Enough inputs must be selected/contributed for the resulting transaction (including the
331 /// inputs and outputs noted above) to meet `target_feerate_sat_per_1000_weight`.
333 /// Implementations must take note that [`Input::satisfaction_weight`] only tracks the weight of
334 /// the input's `script_sig` and `witness`. Some wallets, like Bitcoin Core's, may require
335 /// providing the full input weight. Failing to do so may lead to underestimating fee bumps and
336 /// delaying block inclusion.
338 /// The `claim_id` must map to the set of external UTXOs assigned to the claim, such that they
339 /// can be re-used within new fee-bumped iterations of the original claiming transaction,
340 /// ensuring that claims don't double spend each other. If a specific `claim_id` has never had a
341 /// transaction associated with it, and all of the available UTXOs have already been assigned to
342 /// other claims, implementations must be willing to double spend their UTXOs. The choice of
343 /// which UTXOs to double spend is left to the implementation, but it must strive to keep the
344 /// set of other claims being double spent to a minimum.
345 fn select_confirmed_utxos(
346 &self, claim_id: ClaimId, must_spend: Vec<Input>, must_pay_to: &[TxOut],
347 target_feerate_sat_per_1000_weight: u32,
348 ) -> Result<CoinSelection, ()>;
349 /// Signs and provides the full witness for all inputs within the transaction known to the
350 /// trait (i.e., any provided via [`CoinSelectionSource::select_confirmed_utxos`]).
352 /// If your wallet does not support signing PSBTs you can call `psbt.extract_tx()` to get the
353 /// unsigned transaction and then sign it with your wallet.
354 fn sign_psbt(&self, psbt: PartiallySignedTransaction) -> Result<Transaction, ()>;
357 /// An alternative to [`CoinSelectionSource`] that can be implemented and used along [`Wallet`] to
358 /// provide a default implementation to [`CoinSelectionSource`].
359 pub trait WalletSource {
360 /// Returns all UTXOs, with at least 1 confirmation each, that are available to spend.
361 fn list_confirmed_utxos(&self) -> Result<Vec<Utxo>, ()>;
362 /// Returns a script to use for change above dust resulting from a successful coin selection
364 fn get_change_script(&self) -> Result<ScriptBuf, ()>;
365 /// Signs and provides the full [`TxIn::script_sig`] and [`TxIn::witness`] for all inputs within
366 /// the transaction known to the wallet (i.e., any provided via
367 /// [`WalletSource::list_confirmed_utxos`]).
369 /// If your wallet does not support signing PSBTs you can call `psbt.extract_tx()` to get the
370 /// unsigned transaction and then sign it with your wallet.
371 fn sign_psbt(&self, psbt: PartiallySignedTransaction) -> Result<Transaction, ()>;
374 /// A wrapper over [`WalletSource`] that implements [`CoinSelection`] by preferring UTXOs that would
375 /// avoid conflicting double spends. If not enough UTXOs are available to do so, conflicting double
376 /// spends may happen.
377 pub struct Wallet<W: Deref, L: Deref>
379 W::Target: WalletSource,
384 // TODO: Do we care about cleaning this up once the UTXOs have a confirmed spend? We can do so
385 // by checking whether any UTXOs that exist in the map are no longer returned in
386 // `list_confirmed_utxos`.
387 locked_utxos: Mutex<HashMap<OutPoint, ClaimId>>,
390 impl<W: Deref, L: Deref> Wallet<W, L>
392 W::Target: WalletSource,
395 /// Returns a new instance backed by the given [`WalletSource`] that serves as an implementation
396 /// of [`CoinSelectionSource`].
397 pub fn new(source: W, logger: L) -> Self {
398 Self { source, logger, locked_utxos: Mutex::new(HashMap::new()) }
401 /// Performs coin selection on the set of UTXOs obtained from
402 /// [`WalletSource::list_confirmed_utxos`]. Its algorithm can be described as "smallest
403 /// above-dust-after-spend first", with a slight twist: we may skip UTXOs that are above dust at
404 /// the target feerate after having spent them in a separate claim transaction if
405 /// `force_conflicting_utxo_spend` is unset to avoid producing conflicting transactions. If
406 /// `tolerate_high_network_feerates` is set, we'll attempt to spend UTXOs that contribute at
407 /// least 1 satoshi at the current feerate, otherwise, we'll only attempt to spend those which
408 /// contribute at least twice their fee.
409 fn select_confirmed_utxos_internal(
410 &self, utxos: &[Utxo], claim_id: ClaimId, force_conflicting_utxo_spend: bool,
411 tolerate_high_network_feerates: bool, target_feerate_sat_per_1000_weight: u32,
412 preexisting_tx_weight: u64, input_amount_sat: u64, target_amount_sat: u64,
413 ) -> Result<CoinSelection, ()> {
414 let mut locked_utxos = self.locked_utxos.lock().unwrap();
415 let mut eligible_utxos = utxos.iter().filter_map(|utxo| {
416 if let Some(utxo_claim_id) = locked_utxos.get(&utxo.outpoint) {
417 if *utxo_claim_id != claim_id && !force_conflicting_utxo_spend {
418 log_trace!(self.logger, "Skipping UTXO {} to prevent conflicting spend", utxo.outpoint);
422 let fee_to_spend_utxo = fee_for_weight(
423 target_feerate_sat_per_1000_weight, BASE_INPUT_WEIGHT + utxo.satisfaction_weight,
425 let should_spend = if tolerate_high_network_feerates {
426 utxo.output.value > fee_to_spend_utxo
428 utxo.output.value >= fee_to_spend_utxo * 2
431 Some((utxo, fee_to_spend_utxo))
433 log_trace!(self.logger, "Skipping UTXO {} due to dust proximity after spend", utxo.outpoint);
436 }).collect::<Vec<_>>();
437 eligible_utxos.sort_unstable_by_key(|(utxo, _)| utxo.output.value);
439 let mut selected_amount = input_amount_sat;
440 let mut total_fees = fee_for_weight(target_feerate_sat_per_1000_weight, preexisting_tx_weight);
441 let mut selected_utxos = Vec::new();
442 for (utxo, fee_to_spend_utxo) in eligible_utxos {
443 if selected_amount >= target_amount_sat + total_fees {
446 selected_amount += utxo.output.value;
447 total_fees += fee_to_spend_utxo;
448 selected_utxos.push(utxo.clone());
450 if selected_amount < target_amount_sat + total_fees {
451 log_debug!(self.logger, "Insufficient funds to meet target feerate {} sat/kW",
452 target_feerate_sat_per_1000_weight);
455 for utxo in &selected_utxos {
456 locked_utxos.insert(utxo.outpoint, claim_id);
458 core::mem::drop(locked_utxos);
460 let remaining_amount = selected_amount - target_amount_sat - total_fees;
461 let change_script = self.source.get_change_script()?;
462 let change_output_fee = fee_for_weight(
463 target_feerate_sat_per_1000_weight,
464 (8 /* value */ + change_script.consensus_encode(&mut sink()).unwrap() as u64) *
465 WITNESS_SCALE_FACTOR as u64,
467 let change_output_amount = remaining_amount.saturating_sub(change_output_fee);
468 let change_output = if change_output_amount < change_script.dust_value().to_sat() {
469 log_debug!(self.logger, "Coin selection attempt did not yield change output");
472 Some(TxOut { script_pubkey: change_script, value: change_output_amount })
476 confirmed_utxos: selected_utxos,
482 impl<W: Deref, L: Deref> CoinSelectionSource for Wallet<W, L>
484 W::Target: WalletSource,
487 fn select_confirmed_utxos(
488 &self, claim_id: ClaimId, must_spend: Vec<Input>, must_pay_to: &[TxOut],
489 target_feerate_sat_per_1000_weight: u32,
490 ) -> Result<CoinSelection, ()> {
491 let utxos = self.source.list_confirmed_utxos()?;
492 // TODO: Use fee estimation utils when we upgrade to bitcoin v0.30.0.
493 const BASE_TX_SIZE: u64 = 4 /* version */ + 1 /* input count */ + 1 /* output count */ + 4 /* locktime */;
494 let total_output_size: u64 = must_pay_to.iter().map(|output|
495 8 /* value */ + 1 /* script len */ + output.script_pubkey.len() as u64
497 let total_satisfaction_weight: u64 = must_spend.iter().map(|input| input.satisfaction_weight).sum();
498 let total_input_weight = (BASE_INPUT_WEIGHT * must_spend.len() as u64) + total_satisfaction_weight;
500 let preexisting_tx_weight = 2 /* segwit marker & flag */ + total_input_weight +
501 ((BASE_TX_SIZE + total_output_size) * WITNESS_SCALE_FACTOR as u64);
502 let input_amount_sat: u64 = must_spend.iter().map(|input| input.previous_utxo.value).sum();
503 let target_amount_sat = must_pay_to.iter().map(|output| output.value).sum();
504 let do_coin_selection = |force_conflicting_utxo_spend: bool, tolerate_high_network_feerates: bool| {
505 log_debug!(self.logger, "Attempting coin selection targeting {} sat/kW (force_conflicting_utxo_spend = {}, tolerate_high_network_feerates = {})",
506 target_feerate_sat_per_1000_weight, force_conflicting_utxo_spend, tolerate_high_network_feerates);
507 self.select_confirmed_utxos_internal(
508 &utxos, claim_id, force_conflicting_utxo_spend, tolerate_high_network_feerates,
509 target_feerate_sat_per_1000_weight, preexisting_tx_weight, input_amount_sat, target_amount_sat,
512 do_coin_selection(false, false)
513 .or_else(|_| do_coin_selection(false, true))
514 .or_else(|_| do_coin_selection(true, false))
515 .or_else(|_| do_coin_selection(true, true))
518 fn sign_psbt(&self, psbt: PartiallySignedTransaction) -> Result<Transaction, ()> {
519 self.source.sign_psbt(psbt)
523 /// A handler for [`Event::BumpTransaction`] events that sources confirmed UTXOs from a
524 /// [`CoinSelectionSource`] to fee bump transactions via Child-Pays-For-Parent (CPFP) or
525 /// Replace-By-Fee (RBF).
527 /// [`Event::BumpTransaction`]: crate::events::Event::BumpTransaction
528 pub struct BumpTransactionEventHandler<B: Deref, C: Deref, SP: Deref, L: Deref>
530 B::Target: BroadcasterInterface,
531 C::Target: CoinSelectionSource,
532 SP::Target: SignerProvider,
539 secp: Secp256k1<secp256k1::All>,
542 impl<B: Deref, C: Deref, SP: Deref, L: Deref> BumpTransactionEventHandler<B, C, SP, L>
544 B::Target: BroadcasterInterface,
545 C::Target: CoinSelectionSource,
546 SP::Target: SignerProvider,
549 /// Returns a new instance capable of handling [`Event::BumpTransaction`] events.
551 /// [`Event::BumpTransaction`]: crate::events::Event::BumpTransaction
552 pub fn new(broadcaster: B, utxo_source: C, signer_provider: SP, logger: L) -> Self {
558 secp: Secp256k1::new(),
562 /// Updates a transaction with the result of a successful coin selection attempt.
563 fn process_coin_selection(&self, tx: &mut Transaction, coin_selection: &CoinSelection) {
564 for utxo in coin_selection.confirmed_utxos.iter() {
566 previous_output: utxo.outpoint,
567 script_sig: ScriptBuf::new(),
568 sequence: Sequence::ZERO,
569 witness: Witness::new(),
572 if let Some(change_output) = coin_selection.change_output.clone() {
573 tx.output.push(change_output);
574 } else if tx.output.is_empty() {
575 // We weren't provided a change output, likely because the input set was a perfect
576 // match, but we still need to have at least one output in the transaction for it to be
577 // considered standard. We choose to go with an empty OP_RETURN as it is the cheapest
578 // way to include a dummy output.
579 log_debug!(self.logger, "Including dummy OP_RETURN output since an output is needed and a change output was not provided");
580 tx.output.push(TxOut {
582 script_pubkey: ScriptBuf::new_op_return(&[]),
587 /// Handles a [`BumpTransactionEvent::ChannelClose`] event variant by producing a fully-signed
588 /// transaction spending an anchor output of the commitment transaction to bump its fee and
589 /// broadcasts them to the network as a package.
590 fn handle_channel_close(
591 &self, claim_id: ClaimId, package_target_feerate_sat_per_1000_weight: u32,
592 commitment_tx: &Transaction, commitment_tx_fee_sat: u64, anchor_descriptor: &AnchorDescriptor,
593 ) -> Result<(), ()> {
594 // Our commitment transaction already has fees allocated to it, so we should take them into
595 // account. We do so by pretending the commitment tranasction's fee and weight are part of
597 let mut anchor_utxo = anchor_descriptor.previous_utxo();
598 anchor_utxo.value += commitment_tx_fee_sat;
599 let must_spend = vec![Input {
600 outpoint: anchor_descriptor.outpoint,
601 previous_utxo: anchor_utxo,
602 satisfaction_weight: commitment_tx.weight().to_wu() + ANCHOR_INPUT_WITNESS_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT,
604 #[cfg(debug_assertions)]
605 let must_spend_amount = must_spend.iter().map(|input| input.previous_utxo.value).sum::<u64>();
607 log_debug!(self.logger, "Peforming coin selection for commitment package (commitment and anchor transaction) targeting {} sat/kW",
608 package_target_feerate_sat_per_1000_weight);
609 let coin_selection: CoinSelection = self.utxo_source.select_confirmed_utxos(
610 claim_id, must_spend, &[], package_target_feerate_sat_per_1000_weight,
613 let mut anchor_tx = Transaction {
615 lock_time: LockTime::ZERO, // TODO: Use next best height.
616 input: vec![anchor_descriptor.unsigned_tx_input()],
620 #[cfg(debug_assertions)]
621 let total_satisfaction_weight = ANCHOR_INPUT_WITNESS_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT +
622 coin_selection.confirmed_utxos.iter().map(|utxo| utxo.satisfaction_weight).sum::<u64>();
623 #[cfg(debug_assertions)]
624 let total_input_amount = must_spend_amount +
625 coin_selection.confirmed_utxos.iter().map(|utxo| utxo.output.value).sum::<u64>();
627 self.process_coin_selection(&mut anchor_tx, &coin_selection);
628 let anchor_txid = anchor_tx.txid();
631 let mut anchor_psbt = PartiallySignedTransaction::from_unsigned_tx(anchor_tx).unwrap();
632 // add witness_utxo to anchor input
633 anchor_psbt.inputs[0].witness_utxo = Some(anchor_descriptor.previous_utxo());
634 // add witness_utxo to remaining inputs
635 for (idx, utxo) in coin_selection.confirmed_utxos.into_iter().enumerate() {
636 // add 1 to skip the anchor input
638 debug_assert_eq!(anchor_psbt.unsigned_tx.input[index].previous_output, utxo.outpoint);
639 if utxo.output.script_pubkey.is_witness_program() {
640 anchor_psbt.inputs[index].witness_utxo = Some(utxo.output);
644 debug_assert_eq!(anchor_psbt.unsigned_tx.output.len(), 1);
645 #[cfg(debug_assertions)]
646 let unsigned_tx_weight = anchor_psbt.unsigned_tx.weight().to_wu() - (anchor_psbt.unsigned_tx.input.len() as u64 * EMPTY_SCRIPT_SIG_WEIGHT);
648 log_debug!(self.logger, "Signing anchor transaction {}", anchor_txid);
649 anchor_tx = self.utxo_source.sign_psbt(anchor_psbt)?;
651 let signer = anchor_descriptor.derive_channel_signer(&self.signer_provider);
652 let anchor_sig = signer.sign_holder_anchor_input(&anchor_tx, 0, &self.secp)?;
653 anchor_tx.input[0].witness = anchor_descriptor.tx_input_witness(&anchor_sig);
655 #[cfg(debug_assertions)] {
656 let signed_tx_weight = anchor_tx.weight().to_wu();
657 let expected_signed_tx_weight = unsigned_tx_weight + total_satisfaction_weight;
658 // Our estimate should be within a 1% error margin of the actual weight and we should
659 // never underestimate.
660 assert!(expected_signed_tx_weight >= signed_tx_weight &&
661 expected_signed_tx_weight - (expected_signed_tx_weight / 100) <= signed_tx_weight);
663 let expected_package_fee = fee_for_weight(package_target_feerate_sat_per_1000_weight,
664 signed_tx_weight + commitment_tx.weight().to_wu());
665 let package_fee = total_input_amount -
666 anchor_tx.output.iter().map(|output| output.value).sum::<u64>();
667 // Our fee should be within a 5% error margin of the expected fee based on the
668 // feerate and transaction weight and we should never pay less than required.
669 let fee_error_margin = expected_package_fee * 5 / 100;
670 assert!(package_fee >= expected_package_fee &&
671 package_fee - fee_error_margin <= expected_package_fee);
674 log_info!(self.logger, "Broadcasting anchor transaction {} to bump channel close with txid {}",
675 anchor_txid, commitment_tx.txid());
676 self.broadcaster.broadcast_transactions(&[&commitment_tx, &anchor_tx]);
680 /// Handles a [`BumpTransactionEvent::HTLCResolution`] event variant by producing a
681 /// fully-signed, fee-bumped HTLC transaction that is broadcast to the network.
682 fn handle_htlc_resolution(
683 &self, claim_id: ClaimId, target_feerate_sat_per_1000_weight: u32,
684 htlc_descriptors: &[HTLCDescriptor], tx_lock_time: LockTime,
685 ) -> Result<(), ()> {
686 let mut htlc_tx = Transaction {
688 lock_time: tx_lock_time,
692 let mut must_spend = Vec::with_capacity(htlc_descriptors.len());
693 for htlc_descriptor in htlc_descriptors {
694 let htlc_input = htlc_descriptor.unsigned_tx_input();
695 must_spend.push(Input {
696 outpoint: htlc_input.previous_output.clone(),
697 previous_utxo: htlc_descriptor.previous_utxo(&self.secp),
698 satisfaction_weight: EMPTY_SCRIPT_SIG_WEIGHT + if htlc_descriptor.preimage.is_some() {
699 HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT
701 HTLC_TIMEOUT_INPUT_ANCHOR_WITNESS_WEIGHT
704 htlc_tx.input.push(htlc_input);
705 let htlc_output = htlc_descriptor.tx_output(&self.secp);
706 htlc_tx.output.push(htlc_output);
709 log_debug!(self.logger, "Peforming coin selection for HTLC transaction targeting {} sat/kW",
710 target_feerate_sat_per_1000_weight);
712 #[cfg(debug_assertions)]
713 let must_spend_satisfaction_weight =
714 must_spend.iter().map(|input| input.satisfaction_weight).sum::<u64>();
715 #[cfg(debug_assertions)]
716 let must_spend_amount = must_spend.iter().map(|input| input.previous_utxo.value).sum::<u64>();
718 let coin_selection: CoinSelection = self.utxo_source.select_confirmed_utxos(
719 claim_id, must_spend, &htlc_tx.output, target_feerate_sat_per_1000_weight,
722 #[cfg(debug_assertions)]
723 let total_satisfaction_weight = must_spend_satisfaction_weight +
724 coin_selection.confirmed_utxos.iter().map(|utxo| utxo.satisfaction_weight).sum::<u64>();
725 #[cfg(debug_assertions)]
726 let total_input_amount = must_spend_amount +
727 coin_selection.confirmed_utxos.iter().map(|utxo| utxo.output.value).sum::<u64>();
729 self.process_coin_selection(&mut htlc_tx, &coin_selection);
732 let mut htlc_psbt = PartiallySignedTransaction::from_unsigned_tx(htlc_tx).unwrap();
733 // add witness_utxo to htlc inputs
734 for (i, htlc_descriptor) in htlc_descriptors.iter().enumerate() {
735 debug_assert_eq!(htlc_psbt.unsigned_tx.input[i].previous_output, htlc_descriptor.outpoint());
736 htlc_psbt.inputs[i].witness_utxo = Some(htlc_descriptor.previous_utxo(&self.secp));
738 // add witness_utxo to remaining inputs
739 for (idx, utxo) in coin_selection.confirmed_utxos.into_iter().enumerate() {
740 // offset to skip the htlc inputs
741 let index = idx + htlc_descriptors.len();
742 debug_assert_eq!(htlc_psbt.unsigned_tx.input[index].previous_output, utxo.outpoint);
743 if utxo.output.script_pubkey.is_witness_program() {
744 htlc_psbt.inputs[index].witness_utxo = Some(utxo.output);
748 #[cfg(debug_assertions)]
749 let unsigned_tx_weight = htlc_psbt.unsigned_tx.weight().to_wu() - (htlc_psbt.unsigned_tx.input.len() as u64 * EMPTY_SCRIPT_SIG_WEIGHT);
751 log_debug!(self.logger, "Signing HTLC transaction {}", htlc_psbt.unsigned_tx.txid());
752 htlc_tx = self.utxo_source.sign_psbt(htlc_psbt)?;
754 let mut signers = BTreeMap::new();
755 for (idx, htlc_descriptor) in htlc_descriptors.iter().enumerate() {
756 let signer = signers.entry(htlc_descriptor.channel_derivation_parameters.keys_id)
757 .or_insert_with(|| htlc_descriptor.derive_channel_signer(&self.signer_provider));
758 let htlc_sig = signer.sign_holder_htlc_transaction(&htlc_tx, idx, htlc_descriptor, &self.secp)?;
759 let witness_script = htlc_descriptor.witness_script(&self.secp);
760 htlc_tx.input[idx].witness = htlc_descriptor.tx_input_witness(&htlc_sig, &witness_script);
763 #[cfg(debug_assertions)] {
764 let signed_tx_weight = htlc_tx.weight().to_wu();
765 let expected_signed_tx_weight = unsigned_tx_weight + total_satisfaction_weight;
766 // Our estimate should be within a 1% error margin of the actual weight and we should
767 // never underestimate.
768 assert!(expected_signed_tx_weight >= signed_tx_weight &&
769 expected_signed_tx_weight - (expected_signed_tx_weight / 100) <= signed_tx_weight);
771 let expected_signed_tx_fee = fee_for_weight(target_feerate_sat_per_1000_weight, signed_tx_weight);
772 let signed_tx_fee = total_input_amount -
773 htlc_tx.output.iter().map(|output| output.value).sum::<u64>();
774 // Our fee should be within a 5% error margin of the expected fee based on the
775 // feerate and transaction weight and we should never pay less than required.
776 let fee_error_margin = expected_signed_tx_fee * 5 / 100;
777 assert!(signed_tx_fee >= expected_signed_tx_fee &&
778 signed_tx_fee - fee_error_margin <= expected_signed_tx_fee);
781 log_info!(self.logger, "Broadcasting {}", log_tx!(htlc_tx));
782 self.broadcaster.broadcast_transactions(&[&htlc_tx]);
786 /// Handles all variants of [`BumpTransactionEvent`].
787 pub fn handle_event(&self, event: &BumpTransactionEvent) {
789 BumpTransactionEvent::ChannelClose {
790 claim_id, package_target_feerate_sat_per_1000_weight, commitment_tx,
791 commitment_tx_fee_satoshis, anchor_descriptor, ..
793 log_info!(self.logger, "Handling channel close bump (claim_id = {}, commitment_txid = {})",
794 log_bytes!(claim_id.0), commitment_tx.txid());
795 if let Err(_) = self.handle_channel_close(
796 *claim_id, *package_target_feerate_sat_per_1000_weight, commitment_tx,
797 *commitment_tx_fee_satoshis, anchor_descriptor,
799 log_error!(self.logger, "Failed bumping commitment transaction fee for {}",
800 commitment_tx.txid());
803 BumpTransactionEvent::HTLCResolution {
804 claim_id, target_feerate_sat_per_1000_weight, htlc_descriptors, tx_lock_time,
806 log_info!(self.logger, "Handling HTLC bump (claim_id = {}, htlcs_to_claim = {})",
807 log_bytes!(claim_id.0), log_iter!(htlc_descriptors.iter().map(|d| d.outpoint())));
808 if let Err(_) = self.handle_htlc_resolution(
809 *claim_id, *target_feerate_sat_per_1000_weight, htlc_descriptors, *tx_lock_time,
811 log_error!(self.logger, "Failed bumping HTLC transaction fee for commitment {}",
812 htlc_descriptors[0].commitment_txid);