//! Utitilies for bumping transactions originating from [`super::Event`]s.
+use core::convert::TryInto;
+use core::ops::Deref;
+
+use crate::chain::chaininterface::BroadcasterInterface;
use crate::chain::ClaimId;
+use crate::sign::{ChannelSigner, EcdsaChannelSigner, SignerProvider};
+use crate::io_extras::sink;
use crate::ln::PaymentPreimage;
use crate::ln::chan_utils;
-use crate::ln::chan_utils::{ChannelTransactionParameters, HTLCOutputInCommitment};
+use crate::ln::chan_utils::{
+ ANCHOR_INPUT_WITNESS_WEIGHT, HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT,
+ HTLC_TIMEOUT_INPUT_ANCHOR_WITNESS_WEIGHT, ChannelTransactionParameters, HTLCOutputInCommitment
+};
+use crate::events::Event;
+use crate::prelude::HashMap;
+use crate::util::logger::Logger;
-use bitcoin::{OutPoint, PackedLockTime, Script, Transaction, Txid, TxIn, TxOut, Witness};
+use bitcoin::{OutPoint, PackedLockTime, PubkeyHash, Sequence, Script, Transaction, Txid, TxIn, TxOut, Witness, WPubkeyHash};
+use bitcoin::blockdata::constants::WITNESS_SCALE_FACTOR;
+use bitcoin::consensus::Encodable;
use bitcoin::secp256k1;
use bitcoin::secp256k1::{PublicKey, Secp256k1};
use bitcoin::secp256k1::ecdsa::Signature;
+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 */;
+
+const BASE_INPUT_WEIGHT: u64 = BASE_INPUT_SIZE * WITNESS_SCALE_FACTOR as u64;
+
+// TODO: Define typed abstraction over feerates to handle their conversions.
+fn compute_feerate_sat_per_1000_weight(fee_sat: u64, weight: u64) -> u32 {
+ (fee_sat * 1000 / weight).try_into().unwrap_or(u32::max_value())
+}
+const fn fee_for_weight(feerate_sat_per_1000_weight: u32, weight: u64) -> u64 {
+ ((feerate_sat_per_1000_weight as u64 * weight) + 1000 - 1) / 1000
+}
+
/// A descriptor used to sign for a commitment transaction's anchor output.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct AnchorDescriptor {
tx_lock_time: PackedLockTime,
},
}
+
+/// 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.
+pub struct Input {
+ /// The unique identifier of the input.
+ pub outpoint: OutPoint,
+ /// 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)]
+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 {
+ const P2WPKH_WITNESS_WEIGHT: u64 = 1 /* num stack items */ +
+ 1 /* sig length */ +
+ 73 /* sig including sighash flag */ +
+ 1 /* pubkey length */ +
+ 33 /* pubkey */;
+
+ /// Returns a `Utxo` with the `satisfaction_weight` estimate for a legacy P2PKH output.
+ pub fn new_p2pkh(outpoint: OutPoint, value: u64, 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: Script::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: u64, 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: Script::new_p2sh(&Script::new_v0_p2wpkh(pubkey_hash).script_hash()),
+ },
+ satisfaction_weight: script_sig_size * WITNESS_SCALE_FACTOR as u64 + Self::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: u64, pubkey_hash: &WPubkeyHash) -> Self {
+ Self {
+ outpoint,
+ output: TxOut {
+ value,
+ script_pubkey: Script::new_v0_p2wpkh(pubkey_hash),
+ },
+ satisfaction_weight: EMPTY_SCRIPT_SIG_WEIGHT + Self::P2WPKH_WITNESS_WEIGHT,
+ }
+ }
+}
+
+/// The result of a successful coin selection attempt for a transaction requiring additional UTXOs
+/// to cover its fees.
+pub struct CoinSelection {
+ /// The set of UTXOs (with at least 1 confirmation) to spend and use within a transaction
+ /// requiring additional fees.
+ 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.
+ 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.
+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: &[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`]).
+ fn sign_tx(&self, tx: &mut Transaction) -> Result<(), ()>;
+}
+
+/// 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).
+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.
+ 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, mut coin_selection: CoinSelection) {
+ for utxo in coin_selection.confirmed_utxos.drain(..) {
+ tx.input.push(TxIn {
+ previous_output: utxo.outpoint,
+ script_sig: Script::new(),
+ sequence: Sequence::ZERO,
+ witness: Witness::new(),
+ });
+ }
+ if let Some(change_output) = coin_selection.change_output.take() {
+ 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.
+ tx.output.push(TxOut {
+ value: 0,
+ script_pubkey: Script::new_op_return(&[]),
+ });
+ }
+ }
+
+ /// Returns an unsigned transaction spending an anchor output of the commitment transaction, and
+ /// any additional UTXOs sourced, to bump the commitment transaction's fee.
+ fn build_anchor_tx(
+ &self, claim_id: ClaimId, target_feerate_sat_per_1000_weight: u32,
+ commitment_tx: &Transaction, anchor_descriptor: &AnchorDescriptor,
+ ) -> Result<Transaction, ()> {
+ let must_spend = vec![Input {
+ outpoint: anchor_descriptor.outpoint,
+ satisfaction_weight: commitment_tx.weight() as u64 + ANCHOR_INPUT_WITNESS_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT,
+ }];
+ let coin_selection = self.utxo_source.select_confirmed_utxos(
+ claim_id, &must_spend, &[], target_feerate_sat_per_1000_weight,
+ )?;
+
+ let mut tx = Transaction {
+ version: 2,
+ lock_time: PackedLockTime::ZERO, // TODO: Use next best height.
+ input: vec![TxIn {
+ previous_output: anchor_descriptor.outpoint,
+ script_sig: Script::new(),
+ sequence: Sequence::ZERO,
+ witness: Witness::new(),
+ }],
+ output: vec![],
+ };
+ self.process_coin_selection(&mut tx, coin_selection);
+ Ok(tx)
+ }
+
+ /// 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<(), ()> {
+ // Compute the feerate the anchor transaction must meet to meet the overall feerate for the
+ // package (commitment + anchor transactions).
+ let commitment_tx_sat_per_1000_weight: u32 = compute_feerate_sat_per_1000_weight(
+ commitment_tx_fee_sat, commitment_tx.weight() as u64,
+ );
+ if commitment_tx_sat_per_1000_weight >= package_target_feerate_sat_per_1000_weight {
+ // If the commitment transaction already has a feerate high enough on its own, broadcast
+ // it as is without a child.
+ self.broadcaster.broadcast_transactions(&[&commitment_tx]);
+ return Ok(());
+ }
+
+ let mut anchor_tx = self.build_anchor_tx(
+ claim_id, package_target_feerate_sat_per_1000_weight, commitment_tx, anchor_descriptor,
+ )?;
+ debug_assert_eq!(anchor_tx.output.len(), 1);
+
+ self.utxo_source.sign_tx(&mut anchor_tx)?;
+ let signer = self.signer_provider.derive_channel_signer(
+ anchor_descriptor.channel_value_satoshis, anchor_descriptor.channel_keys_id,
+ );
+ let anchor_sig = signer.sign_holder_anchor_input(&anchor_tx, 0, &self.secp)?;
+ anchor_tx.input[0].witness =
+ chan_utils::build_anchor_input_witness(&signer.pubkeys().funding_pubkey, &anchor_sig);
+
+ self.broadcaster.broadcast_transactions(&[&commitment_tx, &anchor_tx]);
+ Ok(())
+ }
+
+ /// Returns an unsigned, fee-bumped HTLC transaction, along with the set of signers required to
+ /// fulfill the witness for each HTLC input within it.
+ fn build_htlc_tx(
+ &self, claim_id: ClaimId, target_feerate_sat_per_1000_weight: u32,
+ htlc_descriptors: &[HTLCDescriptor], tx_lock_time: PackedLockTime,
+ ) -> Result<(Transaction, HashMap<[u8; 32], <SP::Target as SignerProvider>::Signer>), ()> {
+ let mut tx = Transaction {
+ version: 2,
+ lock_time: tx_lock_time,
+ input: vec![],
+ output: vec![],
+ };
+ // Unfortunately, we need to derive the signer for each HTLC ahead of time to obtain its
+ // input.
+ let mut signers = HashMap::new();
+ let mut must_spend = Vec::with_capacity(htlc_descriptors.len());
+ for htlc_descriptor in htlc_descriptors {
+ let signer = signers.entry(htlc_descriptor.channel_keys_id)
+ .or_insert_with(||
+ self.signer_provider.derive_channel_signer(
+ htlc_descriptor.channel_value_satoshis, htlc_descriptor.channel_keys_id,
+ )
+ );
+ let per_commitment_point = signer.get_per_commitment_point(
+ htlc_descriptor.per_commitment_number, &self.secp
+ );
+
+ let htlc_input = htlc_descriptor.unsigned_tx_input();
+ must_spend.push(Input {
+ outpoint: htlc_input.previous_output.clone(),
+ 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
+ },
+ });
+ tx.input.push(htlc_input);
+ let htlc_output = htlc_descriptor.tx_output(&per_commitment_point, &self.secp);
+ tx.output.push(htlc_output);
+ }
+
+ let coin_selection = self.utxo_source.select_confirmed_utxos(
+ claim_id, &must_spend, &tx.output, target_feerate_sat_per_1000_weight,
+ )?;
+ self.process_coin_selection(&mut tx, coin_selection);
+ Ok((tx, signers))
+ }
+
+ /// 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: PackedLockTime,
+ ) -> Result<(), ()> {
+ let (mut htlc_tx, signers) = self.build_htlc_tx(
+ claim_id, target_feerate_sat_per_1000_weight, htlc_descriptors, tx_lock_time,
+ )?;
+
+ self.utxo_source.sign_tx(&mut htlc_tx)?;
+ for (idx, htlc_descriptor) in htlc_descriptors.iter().enumerate() {
+ let signer = signers.get(&htlc_descriptor.channel_keys_id).unwrap();
+ let htlc_sig = signer.sign_holder_htlc_transaction(
+ &htlc_tx, idx, htlc_descriptor, &self.secp
+ )?;
+ let per_commitment_point = signer.get_per_commitment_point(
+ htlc_descriptor.per_commitment_number, &self.secp
+ );
+ let witness_script = htlc_descriptor.witness_script(&per_commitment_point, &self.secp);
+ htlc_tx.input[idx].witness = htlc_descriptor.tx_input_witness(&htlc_sig, &witness_script);
+ }
+
+ self.broadcaster.broadcast_transactions(&[&htlc_tx]);
+ Ok(())
+ }
+
+ /// Handles all variants of [`BumpTransactionEvent`], immediately returning otherwise.
+ pub fn handle_event(&self, event: &Event) {
+ let event = if let Event::BumpTransaction(event) = event {
+ event
+ } else {
+ return;
+ };
+ match event {
+ BumpTransactionEvent::ChannelClose {
+ claim_id, package_target_feerate_sat_per_1000_weight, commitment_tx,
+ anchor_descriptor, commitment_tx_fee_satoshis, ..
+ } => {
+ 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.txid());
+ }
+ }
+ BumpTransactionEvent::HTLCResolution {
+ claim_id, target_feerate_sat_per_1000_weight, htlc_descriptors, tx_lock_time,
+ } => {
+ 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);
+ }
+ }
+ }
+ }
+}
projects / rust-lightning / commitdiff