+impl SpendableOutputDescriptor {
+ /// Turns this into a [`bitcoin::psbt::Input`] which can be used to create a
+ /// [`PartiallySignedTransaction`] which spends the given descriptor.
+ ///
+ /// Note that this does not include any signatures, just the information required to
+ /// construct the transaction and sign it.
+ ///
+ /// This is not exported to bindings users as there is no standard serialization for an input.
+ /// See [`Self::create_spendable_outputs_psbt`] instead.
+ pub fn to_psbt_input(&self) -> bitcoin::psbt::Input {
+ match self {
+ SpendableOutputDescriptor::StaticOutput { output, .. } => {
+ // Is a standard P2WPKH, no need for witness script
+ bitcoin::psbt::Input {
+ witness_utxo: Some(output.clone()),
+ ..Default::default()
+ }
+ },
+ SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
+ // TODO we could add the witness script as well
+ bitcoin::psbt::Input {
+ witness_utxo: Some(descriptor.output.clone()),
+ ..Default::default()
+ }
+ },
+ SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
+ // TODO we could add the witness script as well
+ bitcoin::psbt::Input {
+ witness_utxo: Some(descriptor.output.clone()),
+ ..Default::default()
+ }
+ },
+ }
+ }
+
+ /// Creates an unsigned [`PartiallySignedTransaction`] which spends the given descriptors to
+ /// the given outputs, plus an output to the given change destination (if sufficient
+ /// change value remains). The PSBT will have a feerate, at least, of the given value.
+ ///
+ /// The `locktime` argument is used to set the transaction's locktime. If `None`, the
+ /// transaction will have a locktime of 0. It it recommended to set this to the current block
+ /// height to avoid fee sniping, unless you have some specific reason to use a different
+ /// locktime.
+ ///
+ /// Returns the PSBT and expected max transaction weight.
+ ///
+ /// Returns `Err(())` if the output value is greater than the input value minus required fee,
+ /// if a descriptor was duplicated, or if an output descriptor `script_pubkey`
+ /// does not match the one we can spend.
+ ///
+ /// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
+ pub fn create_spendable_outputs_psbt(descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32, locktime: Option<LockTime>) -> Result<(PartiallySignedTransaction, u64), ()> {
+ let mut input = Vec::with_capacity(descriptors.len());
+ let mut input_value = 0;
+ let mut witness_weight = 0;
+ let mut output_set = HashSet::with_capacity(descriptors.len());
+ for outp in descriptors {
+ match outp {
+ SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
+ if !output_set.insert(descriptor.outpoint) { return Err(()); }
+ let sequence =
+ if descriptor.channel_transaction_parameters.as_ref()
+ .map(|channel_params| channel_params.channel_type_features.supports_anchors_zero_fee_htlc_tx())
+ .unwrap_or(false)
+ {
+ Sequence::from_consensus(1)
+ } else {
+ Sequence::ZERO
+ };
+ input.push(TxIn {
+ previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
+ script_sig: ScriptBuf::new(),
+ sequence,
+ witness: Witness::new(),
+ });
+ witness_weight += descriptor.max_witness_length();
+ #[cfg(feature = "grind_signatures")]
+ { witness_weight -= 1; } // Guarantees a low R signature
+ input_value += descriptor.output.value;
+ },
+ SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
+ if !output_set.insert(descriptor.outpoint) { return Err(()); }
+ input.push(TxIn {
+ previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
+ script_sig: ScriptBuf::new(),
+ sequence: Sequence(descriptor.to_self_delay as u32),
+ witness: Witness::new(),
+ });
+ witness_weight += DelayedPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
+ #[cfg(feature = "grind_signatures")]
+ { witness_weight -= 1; } // Guarantees a low R signature
+ input_value += descriptor.output.value;
+ },
+ SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output, .. } => {
+ if !output_set.insert(*outpoint) { return Err(()); }
+ input.push(TxIn {
+ previous_output: outpoint.into_bitcoin_outpoint(),
+ script_sig: ScriptBuf::new(),
+ sequence: Sequence::ZERO,
+ witness: Witness::new(),
+ });
+ witness_weight += 1 + 73 + 34;
+ #[cfg(feature = "grind_signatures")]
+ { witness_weight -= 1; } // Guarantees a low R signature
+ input_value += output.value;
+ }
+ }
+ if input_value > MAX_VALUE_MSAT / 1000 { return Err(()); }
+ }
+ let mut tx = Transaction {
+ version: 2,
+ lock_time: locktime.unwrap_or(LockTime::ZERO),
+ input,
+ output: outputs,
+ };
+ let expected_max_weight =
+ transaction_utils::maybe_add_change_output(&mut tx, input_value, witness_weight, feerate_sat_per_1000_weight, change_destination_script)?;
+
+ let psbt_inputs = descriptors.iter().map(|d| d.to_psbt_input()).collect::<Vec<_>>();
+ let psbt = PartiallySignedTransaction {
+ inputs: psbt_inputs,
+ outputs: vec![Default::default(); tx.output.len()],
+ unsigned_tx: tx,
+ xpub: Default::default(),
+ version: 0,
+ proprietary: Default::default(),
+ unknown: Default::default(),
+ };
+ Ok((psbt, expected_max_weight))
+ }
+}
+
+/// The parameters required to derive a channel signer via [`SignerProvider`].
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct ChannelDerivationParameters {
+ /// The value in satoshis of the channel we're attempting to spend the anchor output of.
+ pub value_satoshis: u64,
+ /// The unique identifier to re-derive the signer for the associated channel.
+ pub keys_id: [u8; 32],
+ /// The necessary channel parameters that need to be provided to the re-derived signer through
+ /// [`ChannelSigner::provide_channel_parameters`].
+ pub transaction_parameters: ChannelTransactionParameters,
+}
+
+impl_writeable_tlv_based!(ChannelDerivationParameters, {
+ (0, value_satoshis, required),
+ (2, keys_id, required),
+ (4, transaction_parameters, required),
+});
+
+/// A descriptor used to sign for a commitment transaction's HTLC output.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct HTLCDescriptor {
+ /// The parameters required to derive the signer for the HTLC input.
+ pub channel_derivation_parameters: ChannelDerivationParameters,
+ /// The txid of the commitment transaction in which the HTLC output lives.
+ pub commitment_txid: Txid,
+ /// The number of the commitment transaction in which the HTLC output lives.
+ pub per_commitment_number: u64,
+ /// The key tweak corresponding to the number of the commitment transaction in which the HTLC
+ /// output lives. This tweak is applied to all the basepoints for both parties in the channel to
+ /// arrive at unique keys per commitment.
+ ///
+ /// See <https://github.com/lightning/bolts/blob/master/03-transactions.md#keys> for more info.
+ pub per_commitment_point: PublicKey,
+ /// The feerate to use on the HTLC claiming transaction. This is always `0` for HTLCs
+ /// originating from a channel supporting anchor outputs, otherwise it is the channel's
+ /// negotiated feerate at the time the commitment transaction was built.
+ pub feerate_per_kw: u32,
+ /// The details of the HTLC as it appears in the commitment transaction.
+ pub htlc: HTLCOutputInCommitment,
+ /// The preimage, if `Some`, to claim the HTLC output with. If `None`, the timeout path must be
+ /// taken.
+ pub preimage: Option<PaymentPreimage>,
+ /// The counterparty's signature required to spend the HTLC output.
+ pub counterparty_sig: Signature
+}
+
+impl_writeable_tlv_based!(HTLCDescriptor, {
+ (0, channel_derivation_parameters, required),
+ (1, feerate_per_kw, (default_value, 0)),
+ (2, commitment_txid, required),
+ (4, per_commitment_number, required),
+ (6, per_commitment_point, required),
+ (8, htlc, required),
+ (10, preimage, option),
+ (12, counterparty_sig, required),
+});
+
+impl HTLCDescriptor {
+ /// Returns the outpoint of the HTLC output in the commitment transaction. This is the outpoint
+ /// being spent by the HTLC input in the HTLC transaction.
+ pub fn outpoint(&self) -> bitcoin::OutPoint {
+ bitcoin::OutPoint {
+ txid: self.commitment_txid,
+ vout: self.htlc.transaction_output_index.unwrap(),
+ }
+ }
+
+ /// Returns the UTXO to be spent by the HTLC input, which can be obtained via
+ /// [`Self::unsigned_tx_input`].
+ pub fn previous_utxo<C: secp256k1::Signing + secp256k1::Verification>(&self, secp: &Secp256k1<C>) -> TxOut {
+ TxOut {
+ script_pubkey: self.witness_script(secp).to_v0_p2wsh(),
+ value: self.htlc.amount_msat / 1000,
+ }
+ }
+
+ /// Returns the unsigned transaction input spending the HTLC output in the commitment
+ /// transaction.
+ pub fn unsigned_tx_input(&self) -> TxIn {
+ chan_utils::build_htlc_input(
+ &self.commitment_txid, &self.htlc, &self.channel_derivation_parameters.transaction_parameters.channel_type_features
+ )
+ }
+
+ /// Returns the delayed output created as a result of spending the HTLC output in the commitment
+ /// transaction.
+ pub fn tx_output<C: secp256k1::Signing + secp256k1::Verification>(&self, secp: &Secp256k1<C>) -> TxOut {
+ let channel_params = self.channel_derivation_parameters.transaction_parameters.as_holder_broadcastable();
+ let broadcaster_keys = channel_params.broadcaster_pubkeys();
+ let counterparty_keys = channel_params.countersignatory_pubkeys();
+ let broadcaster_delayed_key = DelayedPaymentKey::from_basepoint(
+ secp, &broadcaster_keys.delayed_payment_basepoint, &self.per_commitment_point
+ );
+ let counterparty_revocation_key = &RevocationKey::from_basepoint(&secp, &counterparty_keys.revocation_basepoint, &self.per_commitment_point);
+ chan_utils::build_htlc_output(
+ self.feerate_per_kw, channel_params.contest_delay(), &self.htlc,
+ channel_params.channel_type_features(), &broadcaster_delayed_key, &counterparty_revocation_key
+ )
+ }
+
+ /// Returns the witness script of the HTLC output in the commitment transaction.
+ pub fn witness_script<C: secp256k1::Signing + secp256k1::Verification>(&self, secp: &Secp256k1<C>) -> ScriptBuf {
+ let channel_params = self.channel_derivation_parameters.transaction_parameters.as_holder_broadcastable();
+ let broadcaster_keys = channel_params.broadcaster_pubkeys();
+ let counterparty_keys = channel_params.countersignatory_pubkeys();
+ let broadcaster_htlc_key = HtlcKey::from_basepoint(
+ secp, &broadcaster_keys.htlc_basepoint, &self.per_commitment_point
+ );
+ let counterparty_htlc_key = HtlcKey::from_basepoint(
+ secp, &counterparty_keys.htlc_basepoint, &self.per_commitment_point,
+ );
+ let counterparty_revocation_key = &RevocationKey::from_basepoint(&secp, &counterparty_keys.revocation_basepoint, &self.per_commitment_point);
+ chan_utils::get_htlc_redeemscript_with_explicit_keys(
+ &self.htlc, channel_params.channel_type_features(), &broadcaster_htlc_key, &counterparty_htlc_key,
+ &counterparty_revocation_key,
+ )
+ }
+
+ /// Returns the fully signed witness required to spend the HTLC output in the commitment
+ /// transaction.
+ pub fn tx_input_witness(&self, signature: &Signature, witness_script: &Script) -> Witness {
+ chan_utils::build_htlc_input_witness(
+ signature, &self.counterparty_sig, &self.preimage, witness_script,
+ &self.channel_derivation_parameters.transaction_parameters.channel_type_features
+ )
+ }
+
+ /// Derives the channel signer required to sign the HTLC input.
+ pub fn derive_channel_signer<S: WriteableEcdsaChannelSigner, 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
+ }
+}
+