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 core::convert::TryInto;
17 use crate::chain::chaininterface::BroadcasterInterface;
18 use crate::chain::ClaimId;
19 use crate::io_extras::sink;
20 use crate::ln::chan_utils;
21 use crate::ln::chan_utils::{
22 ANCHOR_INPUT_WITNESS_WEIGHT, HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT,
23 HTLC_TIMEOUT_INPUT_ANCHOR_WITNESS_WEIGHT, ChannelTransactionParameters, HTLCOutputInCommitment
25 use crate::ln::features::ChannelTypeFeatures;
26 use crate::ln::PaymentPreimage;
27 use crate::prelude::*;
28 use crate::sign::{ChannelSigner, EcdsaChannelSigner, SignerProvider};
29 use crate::sync::Mutex;
30 use crate::util::logger::Logger;
32 use bitcoin::{OutPoint, PackedLockTime, PubkeyHash, Sequence, Script, Transaction, Txid, TxIn, TxOut, Witness, WPubkeyHash};
33 use bitcoin::blockdata::constants::WITNESS_SCALE_FACTOR;
34 use bitcoin::consensus::Encodable;
35 use bitcoin::secp256k1;
36 use bitcoin::secp256k1::{PublicKey, Secp256k1};
37 use bitcoin::secp256k1::ecdsa::Signature;
39 const EMPTY_SCRIPT_SIG_WEIGHT: u64 = 1 /* empty script_sig */ * WITNESS_SCALE_FACTOR as u64;
41 const BASE_INPUT_SIZE: u64 = 32 /* txid */ + 4 /* vout */ + 4 /* sequence */;
43 const BASE_INPUT_WEIGHT: u64 = BASE_INPUT_SIZE * WITNESS_SCALE_FACTOR as u64;
45 // TODO: Define typed abstraction over feerates to handle their conversions.
46 fn compute_feerate_sat_per_1000_weight(fee_sat: u64, weight: u64) -> u32 {
47 (fee_sat * 1000 / weight).try_into().unwrap_or(u32::max_value())
49 const fn fee_for_weight(feerate_sat_per_1000_weight: u32, weight: u64) -> u64 {
50 ((feerate_sat_per_1000_weight as u64 * weight) + 1000 - 1) / 1000
53 /// A descriptor used to sign for a commitment transaction's anchor output.
54 #[derive(Clone, Debug, PartialEq, Eq)]
55 pub struct AnchorDescriptor {
56 /// A unique identifier used along with `channel_value_satoshis` to re-derive the
57 /// [`InMemorySigner`] required to sign `input`.
59 /// [`InMemorySigner`]: crate::sign::InMemorySigner
60 pub channel_keys_id: [u8; 32],
61 /// The value in satoshis of the channel we're attempting to spend the anchor output of. This is
62 /// used along with `channel_keys_id` to re-derive the [`InMemorySigner`] required to sign
65 /// [`InMemorySigner`]: crate::sign::InMemorySigner
66 pub channel_value_satoshis: u64,
67 /// The transaction input's outpoint corresponding to the commitment transaction's anchor
69 pub outpoint: OutPoint,
72 /// A descriptor used to sign for a commitment transaction's HTLC output.
73 #[derive(Clone, Debug, PartialEq, Eq)]
74 pub struct HTLCDescriptor {
75 /// A unique identifier used along with `channel_value_satoshis` to re-derive the
76 /// [`InMemorySigner`] required to sign `input`.
78 /// [`InMemorySigner`]: crate::sign::InMemorySigner
79 pub channel_keys_id: [u8; 32],
80 /// The value in satoshis of the channel we're attempting to spend the anchor output of. This is
81 /// used along with `channel_keys_id` to re-derive the [`InMemorySigner`] required to sign
84 /// [`InMemorySigner`]: crate::sign::InMemorySigner
85 pub channel_value_satoshis: u64,
86 /// The necessary channel parameters that need to be provided to the re-derived
87 /// [`InMemorySigner`] through [`ChannelSigner::provide_channel_parameters`].
89 /// [`InMemorySigner`]: crate::sign::InMemorySigner
90 /// [`ChannelSigner::provide_channel_parameters`]: crate::sign::ChannelSigner::provide_channel_parameters
91 pub channel_parameters: ChannelTransactionParameters,
92 /// The txid of the commitment transaction in which the HTLC output lives.
93 pub commitment_txid: Txid,
94 /// The number of the commitment transaction in which the HTLC output lives.
95 pub per_commitment_number: u64,
96 /// The key tweak corresponding to the number of the commitment transaction in which the HTLC
97 /// output lives. This tweak is applied to all the basepoints for both parties in the channel to
98 /// arrive at unique keys per commitment.
100 /// See <https://github.com/lightning/bolts/blob/master/03-transactions.md#keys> for more info.
101 pub per_commitment_point: PublicKey,
102 /// The details of the HTLC as it appears in the commitment transaction.
103 pub htlc: HTLCOutputInCommitment,
104 /// The preimage, if `Some`, to claim the HTLC output with. If `None`, the timeout path must be
106 pub preimage: Option<PaymentPreimage>,
107 /// The counterparty's signature required to spend the HTLC output.
108 pub counterparty_sig: Signature
111 impl HTLCDescriptor {
112 /// Returns the unsigned transaction input spending the HTLC output in the commitment
114 pub fn unsigned_tx_input(&self) -> TxIn {
115 chan_utils::build_htlc_input(&self.commitment_txid, &self.htlc, &ChannelTypeFeatures::anchors_zero_htlc_fee_and_dependencies())
118 /// Returns the delayed output created as a result of spending the HTLC output in the commitment
120 pub fn tx_output<C: secp256k1::Signing + secp256k1::Verification>(&self, secp: &Secp256k1<C>) -> TxOut {
121 let channel_params = self.channel_parameters.as_holder_broadcastable();
122 let broadcaster_keys = channel_params.broadcaster_pubkeys();
123 let counterparty_keys = channel_params.countersignatory_pubkeys();
124 let broadcaster_delayed_key = chan_utils::derive_public_key(
125 secp, &self.per_commitment_point, &broadcaster_keys.delayed_payment_basepoint
127 let counterparty_revocation_key = chan_utils::derive_public_revocation_key(
128 secp, &self.per_commitment_point, &counterparty_keys.revocation_basepoint
130 chan_utils::build_htlc_output(
131 0 /* feerate_per_kw */, channel_params.contest_delay(), &self.htlc,
132 &ChannelTypeFeatures::anchors_zero_htlc_fee_and_dependencies(), &broadcaster_delayed_key, &counterparty_revocation_key
136 /// Returns the witness script of the HTLC output in the commitment transaction.
137 pub fn witness_script<C: secp256k1::Signing + secp256k1::Verification>(&self, secp: &Secp256k1<C>) -> Script {
138 let channel_params = self.channel_parameters.as_holder_broadcastable();
139 let broadcaster_keys = channel_params.broadcaster_pubkeys();
140 let counterparty_keys = channel_params.countersignatory_pubkeys();
141 let broadcaster_htlc_key = chan_utils::derive_public_key(
142 secp, &self.per_commitment_point, &broadcaster_keys.htlc_basepoint
144 let counterparty_htlc_key = chan_utils::derive_public_key(
145 secp, &self.per_commitment_point, &counterparty_keys.htlc_basepoint
147 let counterparty_revocation_key = chan_utils::derive_public_revocation_key(
148 secp, &self.per_commitment_point, &counterparty_keys.revocation_basepoint
150 chan_utils::get_htlc_redeemscript_with_explicit_keys(
151 &self.htlc, &ChannelTypeFeatures::anchors_zero_htlc_fee_and_dependencies(), &broadcaster_htlc_key, &counterparty_htlc_key,
152 &counterparty_revocation_key,
156 /// Returns the fully signed witness required to spend the HTLC output in the commitment
158 pub fn tx_input_witness(&self, signature: &Signature, witness_script: &Script) -> Witness {
159 chan_utils::build_htlc_input_witness(
160 signature, &self.counterparty_sig, &self.preimage, witness_script, &ChannelTypeFeatures::anchors_zero_htlc_fee_and_dependencies() /* opt_anchors */
165 /// Represents the different types of transactions, originating from LDK, to be bumped.
166 #[derive(Clone, Debug, PartialEq, Eq)]
167 pub enum BumpTransactionEvent {
168 /// Indicates that a channel featuring anchor outputs is to be closed by broadcasting the local
169 /// commitment transaction. Since commitment transactions have a static feerate pre-agreed upon,
170 /// they may need additional fees to be attached through a child transaction using the popular
171 /// [Child-Pays-For-Parent](https://bitcoinops.org/en/topics/cpfp) fee bumping technique. This
172 /// child transaction must include the anchor input described within `anchor_descriptor` along
173 /// with additional inputs to meet the target feerate. Failure to meet the target feerate
174 /// decreases the confirmation odds of the transaction package (which includes the commitment
175 /// and child anchor transactions), possibly resulting in a loss of funds. Once the transaction
176 /// is constructed, it must be fully signed for and broadcast by the consumer of the event
177 /// along with the `commitment_tx` enclosed. Note that the `commitment_tx` must always be
178 /// broadcast first, as the child anchor transaction depends on it.
180 /// The consumer should be able to sign for any of the additional inputs included within the
181 /// child anchor transaction. To sign its anchor input, an [`InMemorySigner`] should be
182 /// re-derived through [`KeysManager::derive_channel_keys`] with the help of
183 /// [`AnchorDescriptor::channel_keys_id`] and [`AnchorDescriptor::channel_value_satoshis`]. The
184 /// anchor input signature can be computed with [`EcdsaChannelSigner::sign_holder_anchor_input`],
185 /// which can then be provided to [`build_anchor_input_witness`] along with the `funding_pubkey`
186 /// to obtain the full witness required to spend.
188 /// It is possible to receive more than one instance of this event if a valid child anchor
189 /// transaction is never broadcast or is but not with a sufficient fee to be mined. Care should
190 /// be taken by the consumer of the event to ensure any future iterations of the child anchor
191 /// transaction adhere to the [Replace-By-Fee
192 /// rules](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md)
193 /// for fee bumps to be accepted into the mempool, and eventually the chain. As the frequency of
194 /// these events is not user-controlled, users may ignore/drop the event if they are no longer
195 /// able to commit external confirmed funds to the child anchor transaction.
197 /// The set of `pending_htlcs` on the commitment transaction to be broadcast can be inspected to
198 /// determine whether a significant portion of the channel's funds are allocated to HTLCs,
199 /// enabling users to make their own decisions regarding the importance of the commitment
200 /// transaction's confirmation. Note that this is not required, but simply exists as an option
201 /// for users to override LDK's behavior. On commitments with no HTLCs (indicated by those with
202 /// an empty `pending_htlcs`), confirmation of the commitment transaction can be considered to
205 /// [`InMemorySigner`]: crate::sign::InMemorySigner
206 /// [`KeysManager::derive_channel_keys`]: crate::sign::KeysManager::derive_channel_keys
207 /// [`EcdsaChannelSigner::sign_holder_anchor_input`]: crate::sign::EcdsaChannelSigner::sign_holder_anchor_input
208 /// [`build_anchor_input_witness`]: crate::ln::chan_utils::build_anchor_input_witness
210 /// The unique identifier for the claim of the anchor output in the commitment transaction.
212 /// The identifier must map to the set of external UTXOs assigned to the claim, such that
213 /// they can be reused when a new claim with the same identifier needs to be made, resulting
214 /// in a fee-bumping attempt.
216 /// The target feerate that the transaction package, which consists of the commitment
217 /// transaction and the to-be-crafted child anchor transaction, must meet.
218 package_target_feerate_sat_per_1000_weight: u32,
219 /// The channel's commitment transaction to bump the fee of. This transaction should be
220 /// broadcast along with the anchor transaction constructed as a result of consuming this
222 commitment_tx: Transaction,
223 /// The absolute fee in satoshis of the commitment transaction. This can be used along the
224 /// with weight of the commitment transaction to determine its feerate.
225 commitment_tx_fee_satoshis: u64,
226 /// The descriptor to sign the anchor input of the anchor transaction constructed as a
227 /// result of consuming this event.
228 anchor_descriptor: AnchorDescriptor,
229 /// The set of pending HTLCs on the commitment transaction that need to be resolved once the
230 /// commitment transaction confirms.
231 pending_htlcs: Vec<HTLCOutputInCommitment>,
233 /// Indicates that a channel featuring anchor outputs has unilaterally closed on-chain by a
234 /// holder commitment transaction and its HTLC(s) need to be resolved on-chain. With the
235 /// zero-HTLC-transaction-fee variant of anchor outputs, the pre-signed HTLC
236 /// transactions have a zero fee, thus requiring additional inputs and/or outputs to be attached
237 /// for a timely confirmation within the chain. These additional inputs and/or outputs must be
238 /// appended to the resulting HTLC transaction to meet the target feerate. Failure to meet the
239 /// target feerate decreases the confirmation odds of the transaction, possibly resulting in a
240 /// loss of funds. Once the transaction meets the target feerate, it must be signed for and
241 /// broadcast by the consumer of the event.
243 /// The consumer should be able to sign for any of the non-HTLC inputs added to the resulting
244 /// HTLC transaction. To sign HTLC inputs, an [`InMemorySigner`] should be re-derived through
245 /// [`KeysManager::derive_channel_keys`] with the help of `channel_keys_id` and
246 /// `channel_value_satoshis`. Each HTLC input's signature can be computed with
247 /// [`EcdsaChannelSigner::sign_holder_htlc_transaction`], which can then be provided to
248 /// [`HTLCDescriptor::tx_input_witness`] to obtain the fully signed witness required to spend.
250 /// It is possible to receive more than one instance of this event if a valid HTLC transaction
251 /// is never broadcast or is but not with a sufficient fee to be mined. Care should be taken by
252 /// the consumer of the event to ensure any future iterations of the HTLC transaction adhere to
253 /// the [Replace-By-Fee
254 /// rules](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md)
255 /// for fee bumps to be accepted into the mempool, and eventually the chain. As the frequency of
256 /// these events is not user-controlled, users may ignore/drop the event if either they are no
257 /// longer able to commit external confirmed funds to the HTLC transaction or the fee committed
258 /// to the HTLC transaction is greater in value than the HTLCs being claimed.
260 /// [`InMemorySigner`]: crate::sign::InMemorySigner
261 /// [`KeysManager::derive_channel_keys`]: crate::sign::KeysManager::derive_channel_keys
262 /// [`EcdsaChannelSigner::sign_holder_htlc_transaction`]: crate::sign::EcdsaChannelSigner::sign_holder_htlc_transaction
263 /// [`HTLCDescriptor::tx_input_witness`]: HTLCDescriptor::tx_input_witness
265 /// The unique identifier for the claim of the HTLCs in the confirmed commitment
268 /// The identifier must map to the set of external UTXOs assigned to the claim, such that
269 /// they can be reused when a new claim with the same identifier needs to be made, resulting
270 /// in a fee-bumping attempt.
272 /// The target feerate that the resulting HTLC transaction must meet.
273 target_feerate_sat_per_1000_weight: u32,
274 /// The set of pending HTLCs on the confirmed commitment that need to be claimed, preferably
275 /// by the same transaction.
276 htlc_descriptors: Vec<HTLCDescriptor>,
277 /// The locktime required for the resulting HTLC transaction.
278 tx_lock_time: PackedLockTime,
282 /// An input that must be included in a transaction when performing coin selection through
283 /// [`CoinSelectionSource::select_confirmed_utxos`]. It is guaranteed to be a SegWit input, so it
284 /// must have an empty [`TxIn::script_sig`] when spent.
286 /// The unique identifier of the input.
287 pub outpoint: OutPoint,
288 /// The upper-bound weight consumed by the input's full [`TxIn::script_sig`] and
289 /// [`TxIn::witness`], each with their lengths included, required to satisfy the output's
291 pub satisfaction_weight: u64,
294 /// An unspent transaction output that is available to spend resulting from a successful
295 /// [`CoinSelection`] attempt.
296 #[derive(Clone, Debug)]
298 /// The unique identifier of the output.
299 pub outpoint: OutPoint,
300 /// The output to spend.
302 /// The upper-bound weight consumed by the input's full [`TxIn::script_sig`] and [`TxIn::witness`], each
303 /// with their lengths included, required to satisfy the output's script. The weight consumed by
304 /// the input's `script_sig` must account for [`WITNESS_SCALE_FACTOR`].
305 pub satisfaction_weight: u64,
309 const P2WPKH_WITNESS_WEIGHT: u64 = 1 /* num stack items */ +
311 73 /* sig including sighash flag */ +
312 1 /* pubkey length */ +
315 /// Returns a `Utxo` with the `satisfaction_weight` estimate for a legacy P2PKH output.
316 pub fn new_p2pkh(outpoint: OutPoint, value: u64, pubkey_hash: &PubkeyHash) -> Self {
317 let script_sig_size = 1 /* script_sig length */ +
319 73 /* sig including sighash flag */ +
326 script_pubkey: Script::new_p2pkh(pubkey_hash),
328 satisfaction_weight: script_sig_size * WITNESS_SCALE_FACTOR as u64 + 1 /* empty witness */,
332 /// Returns a `Utxo` with the `satisfaction_weight` estimate for a P2WPKH nested in P2SH output.
333 pub fn new_nested_p2wpkh(outpoint: OutPoint, value: u64, pubkey_hash: &WPubkeyHash) -> Self {
334 let script_sig_size = 1 /* script_sig length */ +
337 20 /* pubkey_hash */;
342 script_pubkey: Script::new_p2sh(&Script::new_v0_p2wpkh(pubkey_hash).script_hash()),
344 satisfaction_weight: script_sig_size * WITNESS_SCALE_FACTOR as u64 + Self::P2WPKH_WITNESS_WEIGHT,
348 /// Returns a `Utxo` with the `satisfaction_weight` estimate for a SegWit v0 P2WPKH output.
349 pub fn new_v0_p2wpkh(outpoint: OutPoint, value: u64, pubkey_hash: &WPubkeyHash) -> Self {
354 script_pubkey: Script::new_v0_p2wpkh(pubkey_hash),
356 satisfaction_weight: EMPTY_SCRIPT_SIG_WEIGHT + Self::P2WPKH_WITNESS_WEIGHT,
361 /// The result of a successful coin selection attempt for a transaction requiring additional UTXOs
362 /// to cover its fees.
363 pub struct CoinSelection {
364 /// The set of UTXOs (with at least 1 confirmation) to spend and use within a transaction
365 /// requiring additional fees.
366 pub confirmed_utxos: Vec<Utxo>,
367 /// An additional output tracking whether any change remained after coin selection. This output
368 /// should always have a value above dust for its given `script_pubkey`. It should not be
369 /// spent until the transaction it belongs to confirms to ensure mempool descendant limits are
370 /// not met. This implies no other party should be able to spend it except us.
371 pub change_output: Option<TxOut>,
374 /// An abstraction over a bitcoin wallet that can perform coin selection over a set of UTXOs and can
375 /// sign for them. The coin selection method aims to mimic Bitcoin Core's `fundrawtransaction` RPC,
376 /// which most wallets should be able to satisfy. Otherwise, consider implementing [`WalletSource`],
377 /// which can provide a default implementation of this trait when used with [`Wallet`].
378 pub trait CoinSelectionSource {
379 /// Performs coin selection of a set of UTXOs, with at least 1 confirmation each, that are
380 /// available to spend. Implementations are free to pick their coin selection algorithm of
381 /// choice, as long as the following requirements are met:
383 /// 1. `must_spend` contains a set of [`Input`]s that must be included in the transaction
384 /// throughout coin selection, but must not be returned as part of the result.
385 /// 2. `must_pay_to` contains a set of [`TxOut`]s that must be included in the transaction
386 /// throughout coin selection. In some cases, like when funding an anchor transaction, this
387 /// set is empty. Implementations should ensure they handle this correctly on their end,
388 /// e.g., Bitcoin Core's `fundrawtransaction` RPC requires at least one output to be
389 /// provided, in which case a zero-value empty OP_RETURN output can be used instead.
390 /// 3. Enough inputs must be selected/contributed for the resulting transaction (including the
391 /// inputs and outputs noted above) to meet `target_feerate_sat_per_1000_weight`.
393 /// Implementations must take note that [`Input::satisfaction_weight`] only tracks the weight of
394 /// the input's `script_sig` and `witness`. Some wallets, like Bitcoin Core's, may require
395 /// providing the full input weight. Failing to do so may lead to underestimating fee bumps and
396 /// delaying block inclusion.
398 /// The `claim_id` must map to the set of external UTXOs assigned to the claim, such that they
399 /// can be re-used within new fee-bumped iterations of the original claiming transaction,
400 /// ensuring that claims don't double spend each other. If a specific `claim_id` has never had a
401 /// transaction associated with it, and all of the available UTXOs have already been assigned to
402 /// other claims, implementations must be willing to double spend their UTXOs. The choice of
403 /// which UTXOs to double spend is left to the implementation, but it must strive to keep the
404 /// set of other claims being double spent to a minimum.
405 fn select_confirmed_utxos(
406 &self, claim_id: ClaimId, must_spend: &[Input], must_pay_to: &[TxOut],
407 target_feerate_sat_per_1000_weight: u32,
408 ) -> Result<CoinSelection, ()>;
409 /// Signs and provides the full witness for all inputs within the transaction known to the
410 /// trait (i.e., any provided via [`CoinSelectionSource::select_confirmed_utxos`]).
411 fn sign_tx(&self, tx: &mut Transaction) -> Result<(), ()>;
414 /// An alternative to [`CoinSelectionSource`] that can be implemented and used along [`Wallet`] to
415 /// provide a default implementation to [`CoinSelectionSource`].
416 pub trait WalletSource {
417 /// Returns all UTXOs, with at least 1 confirmation each, that are available to spend.
418 fn list_confirmed_utxos(&self) -> Result<Vec<Utxo>, ()>;
419 /// Returns a script to use for change above dust resulting from a successful coin selection
421 fn get_change_script(&self) -> Result<Script, ()>;
422 /// Signs and provides the full [`TxIn::script_sig`] and [`TxIn::witness`] for all inputs within
423 /// the transaction known to the wallet (i.e., any provided via
424 /// [`WalletSource::list_confirmed_utxos`]).
425 fn sign_tx(&self, tx: &mut Transaction) -> Result<(), ()>;
428 /// A wrapper over [`WalletSource`] that implements [`CoinSelection`] by preferring UTXOs that would
429 /// avoid conflicting double spends. If not enough UTXOs are available to do so, conflicting double
430 /// spends may happen.
431 pub struct Wallet<W: Deref> where W::Target: WalletSource {
433 // TODO: Do we care about cleaning this up once the UTXOs have a confirmed spend? We can do so
434 // by checking whether any UTXOs that exist in the map are no longer returned in
435 // `list_confirmed_utxos`.
436 locked_utxos: Mutex<HashMap<OutPoint, ClaimId>>,
439 impl<W: Deref> Wallet<W> where W::Target: WalletSource {
440 /// Returns a new instance backed by the given [`WalletSource`] that serves as an implementation
441 /// of [`CoinSelectionSource`].
442 pub fn new(source: W) -> Self {
443 Self { source, locked_utxos: Mutex::new(HashMap::new()) }
446 /// Performs coin selection on the set of UTXOs obtained from
447 /// [`WalletSource::list_confirmed_utxos`]. Its algorithm can be described as "smallest
448 /// above-dust-after-spend first", with a slight twist: we may skip UTXOs that are above dust at
449 /// the target feerate after having spent them in a separate claim transaction if
450 /// `force_conflicting_utxo_spend` is unset to avoid producing conflicting transactions. If
451 /// `tolerate_high_network_feerates` is set, we'll attempt to spend UTXOs that contribute at
452 /// least 1 satoshi at the current feerate, otherwise, we'll only attempt to spend those which
453 /// contribute at least twice their fee.
454 fn select_confirmed_utxos_internal(
455 &self, utxos: &[Utxo], claim_id: ClaimId, force_conflicting_utxo_spend: bool,
456 tolerate_high_network_feerates: bool, target_feerate_sat_per_1000_weight: u32,
457 preexisting_tx_weight: u64, target_amount_sat: u64,
458 ) -> Result<CoinSelection, ()> {
459 let mut locked_utxos = self.locked_utxos.lock().unwrap();
460 let mut eligible_utxos = utxos.iter().filter_map(|utxo| {
461 if let Some(utxo_claim_id) = locked_utxos.get(&utxo.outpoint) {
462 if *utxo_claim_id != claim_id && !force_conflicting_utxo_spend {
466 let fee_to_spend_utxo = fee_for_weight(
467 target_feerate_sat_per_1000_weight, BASE_INPUT_WEIGHT as u64 + utxo.satisfaction_weight,
469 let should_spend = if tolerate_high_network_feerates {
470 utxo.output.value > fee_to_spend_utxo
472 utxo.output.value >= fee_to_spend_utxo * 2
475 Some((utxo, fee_to_spend_utxo))
479 }).collect::<Vec<_>>();
480 eligible_utxos.sort_unstable_by_key(|(utxo, _)| utxo.output.value);
482 let mut selected_amount = 0;
483 let mut total_fees = fee_for_weight(target_feerate_sat_per_1000_weight, preexisting_tx_weight);
484 let mut selected_utxos = Vec::new();
485 for (utxo, fee_to_spend_utxo) in eligible_utxos {
486 if selected_amount >= target_amount_sat + total_fees {
489 selected_amount += utxo.output.value;
490 total_fees += fee_to_spend_utxo;
491 selected_utxos.push(utxo.clone());
493 if selected_amount < target_amount_sat + total_fees {
496 for utxo in &selected_utxos {
497 locked_utxos.insert(utxo.outpoint, claim_id);
499 core::mem::drop(locked_utxos);
501 let remaining_amount = selected_amount - target_amount_sat - total_fees;
502 let change_script = self.source.get_change_script()?;
503 let change_output_fee = fee_for_weight(
504 target_feerate_sat_per_1000_weight,
505 (8 /* value */ + change_script.consensus_encode(&mut sink()).unwrap() as u64) *
506 WITNESS_SCALE_FACTOR as u64,
508 let change_output_amount = remaining_amount.saturating_sub(change_output_fee);
509 let change_output = if change_output_amount < change_script.dust_value().to_sat() {
512 Some(TxOut { script_pubkey: change_script, value: change_output_amount })
516 confirmed_utxos: selected_utxos,
522 impl<W: Deref> CoinSelectionSource for Wallet<W> where W::Target: WalletSource {
523 fn select_confirmed_utxos(
524 &self, claim_id: ClaimId, must_spend: &[Input], must_pay_to: &[TxOut],
525 target_feerate_sat_per_1000_weight: u32,
526 ) -> Result<CoinSelection, ()> {
527 let utxos = self.source.list_confirmed_utxos()?;
528 // TODO: Use fee estimation utils when we upgrade to bitcoin v0.30.0.
529 const BASE_TX_SIZE: u64 = 4 /* version */ + 1 /* input count */ + 1 /* output count */ + 4 /* locktime */;
530 let total_output_size: u64 = must_pay_to.iter().map(|output|
531 8 /* value */ + 1 /* script len */ + output.script_pubkey.len() as u64
533 let total_satisfaction_weight: u64 = must_spend.iter().map(|input| input.satisfaction_weight).sum();
534 let total_input_weight = (BASE_INPUT_WEIGHT * must_spend.len() as u64) + total_satisfaction_weight;
536 let preexisting_tx_weight = 2 /* segwit marker & flag */ + total_input_weight +
537 ((BASE_TX_SIZE + total_output_size) * WITNESS_SCALE_FACTOR as u64);
538 let target_amount_sat = must_pay_to.iter().map(|output| output.value).sum();
539 let do_coin_selection = |force_conflicting_utxo_spend: bool, tolerate_high_network_feerates: bool| {
540 self.select_confirmed_utxos_internal(
541 &utxos, claim_id, force_conflicting_utxo_spend, tolerate_high_network_feerates,
542 target_feerate_sat_per_1000_weight, preexisting_tx_weight, target_amount_sat,
545 do_coin_selection(false, false)
546 .or_else(|_| do_coin_selection(false, true))
547 .or_else(|_| do_coin_selection(true, false))
548 .or_else(|_| do_coin_selection(true, true))
551 fn sign_tx(&self, tx: &mut Transaction) -> Result<(), ()> {
552 self.source.sign_tx(tx)
556 /// A handler for [`Event::BumpTransaction`] events that sources confirmed UTXOs from a
557 /// [`CoinSelectionSource`] to fee bump transactions via Child-Pays-For-Parent (CPFP) or
558 /// Replace-By-Fee (RBF).
560 /// [`Event::BumpTransaction`]: crate::events::Event::BumpTransaction
561 pub struct BumpTransactionEventHandler<B: Deref, C: Deref, SP: Deref, L: Deref>
563 B::Target: BroadcasterInterface,
564 C::Target: CoinSelectionSource,
565 SP::Target: SignerProvider,
572 secp: Secp256k1<secp256k1::All>,
575 impl<B: Deref, C: Deref, SP: Deref, L: Deref> BumpTransactionEventHandler<B, C, SP, L>
577 B::Target: BroadcasterInterface,
578 C::Target: CoinSelectionSource,
579 SP::Target: SignerProvider,
582 /// Returns a new instance capable of handling [`Event::BumpTransaction`] events.
584 /// [`Event::BumpTransaction`]: crate::events::Event::BumpTransaction
585 pub fn new(broadcaster: B, utxo_source: C, signer_provider: SP, logger: L) -> Self {
591 secp: Secp256k1::new(),
595 /// Updates a transaction with the result of a successful coin selection attempt.
596 fn process_coin_selection(&self, tx: &mut Transaction, mut coin_selection: CoinSelection) {
597 for utxo in coin_selection.confirmed_utxos.drain(..) {
599 previous_output: utxo.outpoint,
600 script_sig: Script::new(),
601 sequence: Sequence::ZERO,
602 witness: Witness::new(),
605 if let Some(change_output) = coin_selection.change_output.take() {
606 tx.output.push(change_output);
607 } else if tx.output.is_empty() {
608 // We weren't provided a change output, likely because the input set was a perfect
609 // match, but we still need to have at least one output in the transaction for it to be
610 // considered standard. We choose to go with an empty OP_RETURN as it is the cheapest
611 // way to include a dummy output.
612 tx.output.push(TxOut {
614 script_pubkey: Script::new_op_return(&[]),
619 /// Returns an unsigned transaction spending an anchor output of the commitment transaction, and
620 /// any additional UTXOs sourced, to bump the commitment transaction's fee.
622 &self, claim_id: ClaimId, target_feerate_sat_per_1000_weight: u32,
623 commitment_tx: &Transaction, anchor_descriptor: &AnchorDescriptor,
624 ) -> Result<Transaction, ()> {
625 let must_spend = vec![Input {
626 outpoint: anchor_descriptor.outpoint,
627 satisfaction_weight: commitment_tx.weight() as u64 + ANCHOR_INPUT_WITNESS_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT,
629 let coin_selection = self.utxo_source.select_confirmed_utxos(
630 claim_id, &must_spend, &[], target_feerate_sat_per_1000_weight,
633 let mut tx = Transaction {
635 lock_time: PackedLockTime::ZERO, // TODO: Use next best height.
637 previous_output: anchor_descriptor.outpoint,
638 script_sig: Script::new(),
639 sequence: Sequence::ZERO,
640 witness: Witness::new(),
644 self.process_coin_selection(&mut tx, coin_selection);
648 /// Handles a [`BumpTransactionEvent::ChannelClose`] event variant by producing a fully-signed
649 /// transaction spending an anchor output of the commitment transaction to bump its fee and
650 /// broadcasts them to the network as a package.
651 fn handle_channel_close(
652 &self, claim_id: ClaimId, package_target_feerate_sat_per_1000_weight: u32,
653 commitment_tx: &Transaction, commitment_tx_fee_sat: u64, anchor_descriptor: &AnchorDescriptor,
654 ) -> Result<(), ()> {
655 // Compute the feerate the anchor transaction must meet to meet the overall feerate for the
656 // package (commitment + anchor transactions).
657 let commitment_tx_sat_per_1000_weight: u32 = compute_feerate_sat_per_1000_weight(
658 commitment_tx_fee_sat, commitment_tx.weight() as u64,
660 if commitment_tx_sat_per_1000_weight >= package_target_feerate_sat_per_1000_weight {
661 // If the commitment transaction already has a feerate high enough on its own, broadcast
662 // it as is without a child.
663 self.broadcaster.broadcast_transactions(&[&commitment_tx]);
667 let mut anchor_tx = self.build_anchor_tx(
668 claim_id, package_target_feerate_sat_per_1000_weight, commitment_tx, anchor_descriptor,
670 debug_assert_eq!(anchor_tx.output.len(), 1);
672 self.utxo_source.sign_tx(&mut anchor_tx)?;
673 let signer = self.signer_provider.derive_channel_signer(
674 anchor_descriptor.channel_value_satoshis, anchor_descriptor.channel_keys_id,
676 let anchor_sig = signer.sign_holder_anchor_input(&anchor_tx, 0, &self.secp)?;
677 anchor_tx.input[0].witness =
678 chan_utils::build_anchor_input_witness(&signer.pubkeys().funding_pubkey, &anchor_sig);
680 self.broadcaster.broadcast_transactions(&[&commitment_tx, &anchor_tx]);
684 /// Returns an unsigned, fee-bumped HTLC transaction, along with the set of signers required to
685 /// fulfill the witness for each HTLC input within it.
687 &self, claim_id: ClaimId, target_feerate_sat_per_1000_weight: u32,
688 htlc_descriptors: &[HTLCDescriptor], tx_lock_time: PackedLockTime,
689 ) -> Result<(Transaction, HashMap<[u8; 32], <SP::Target as SignerProvider>::Signer>), ()> {
690 let mut tx = Transaction {
692 lock_time: tx_lock_time,
696 // Unfortunately, we need to derive the signer for each HTLC ahead of time to obtain its
698 let mut signers = HashMap::new();
699 let mut must_spend = Vec::with_capacity(htlc_descriptors.len());
700 for htlc_descriptor in htlc_descriptors {
701 signers.entry(htlc_descriptor.channel_keys_id)
703 self.signer_provider.derive_channel_signer(
704 htlc_descriptor.channel_value_satoshis, htlc_descriptor.channel_keys_id,
708 let htlc_input = htlc_descriptor.unsigned_tx_input();
709 must_spend.push(Input {
710 outpoint: htlc_input.previous_output.clone(),
711 satisfaction_weight: EMPTY_SCRIPT_SIG_WEIGHT + if htlc_descriptor.preimage.is_some() {
712 HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT
714 HTLC_TIMEOUT_INPUT_ANCHOR_WITNESS_WEIGHT
717 tx.input.push(htlc_input);
718 let htlc_output = htlc_descriptor.tx_output(&self.secp);
719 tx.output.push(htlc_output);
722 let coin_selection = self.utxo_source.select_confirmed_utxos(
723 claim_id, &must_spend, &tx.output, target_feerate_sat_per_1000_weight,
725 self.process_coin_selection(&mut tx, coin_selection);
729 /// Handles a [`BumpTransactionEvent::HTLCResolution`] event variant by producing a
730 /// fully-signed, fee-bumped HTLC transaction that is broadcast to the network.
731 fn handle_htlc_resolution(
732 &self, claim_id: ClaimId, target_feerate_sat_per_1000_weight: u32,
733 htlc_descriptors: &[HTLCDescriptor], tx_lock_time: PackedLockTime,
734 ) -> Result<(), ()> {
735 let (mut htlc_tx, signers) = self.build_htlc_tx(
736 claim_id, target_feerate_sat_per_1000_weight, htlc_descriptors, tx_lock_time,
739 self.utxo_source.sign_tx(&mut htlc_tx)?;
740 for (idx, htlc_descriptor) in htlc_descriptors.iter().enumerate() {
741 let signer = signers.get(&htlc_descriptor.channel_keys_id).unwrap();
742 let htlc_sig = signer.sign_holder_htlc_transaction(
743 &htlc_tx, idx, htlc_descriptor, &self.secp
745 let witness_script = htlc_descriptor.witness_script(&self.secp);
746 htlc_tx.input[idx].witness = htlc_descriptor.tx_input_witness(&htlc_sig, &witness_script);
749 self.broadcaster.broadcast_transactions(&[&htlc_tx]);
753 /// Handles all variants of [`BumpTransactionEvent`].
754 pub fn handle_event(&self, event: &BumpTransactionEvent) {
756 BumpTransactionEvent::ChannelClose {
757 claim_id, package_target_feerate_sat_per_1000_weight, commitment_tx,
758 anchor_descriptor, commitment_tx_fee_satoshis, ..
760 if let Err(_) = self.handle_channel_close(
761 *claim_id, *package_target_feerate_sat_per_1000_weight, commitment_tx,
762 *commitment_tx_fee_satoshis, anchor_descriptor,
764 log_error!(self.logger, "Failed bumping commitment transaction fee for {}",
765 commitment_tx.txid());
768 BumpTransactionEvent::HTLCResolution {
769 claim_id, target_feerate_sat_per_1000_weight, htlc_descriptors, tx_lock_time,
771 if let Err(_) = self.handle_htlc_resolution(
772 *claim_id, *target_feerate_sat_per_1000_weight, htlc_descriptors, *tx_lock_time,
774 log_error!(self.logger, "Failed bumping HTLC transaction fee for commitment {}",
775 htlc_descriptors[0].commitment_txid);