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[Custom Transactions] Define the
TxBuilder trait
This commit defines the `TxBuilder` trait to give users the ability to customize the build of the lightning commitment transactions. The `TxBuilder` trait has a single method, `build_commitment_transaction`, which builds the commitment transaction, and populates the output indices of the HTLCs passed in. Besides that, it is mostly a copy paste of chunks of code from `ChannelContext::build_commitment_transaction`.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,221 @@ | ||
| //! Defines the `TxBuilder` trait, and the `SpecTxBuilder` type | ||
| #![allow(dead_code)] | ||
| #![allow(unused_variables)] | ||
|
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||
| use core::ops::Deref; | ||
|
|
||
| use bitcoin::secp256k1::{self, PublicKey, Secp256k1}; | ||
|
|
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| use crate::ln::chan_utils::{ | ||
| self, ChannelTransactionParameters, CommitmentTransaction, HTLCOutputInCommitment, | ||
| }; | ||
| use crate::ln::channel::{self, CommitmentStats}; | ||
| use crate::prelude::*; | ||
| use crate::util::logger::Logger; | ||
|
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| /// A trait for types that can build commitment transactions, both for the holder, and the counterparty. | ||
| pub(crate) trait TxBuilder { | ||
| /// Build a commitment transaction, and populate the elements of `htlcs` with their output indices. | ||
| fn build_commitment_transaction<'a, L: Deref>( | ||
| &self, local: bool, commitment_number: u64, per_commitment_point: &PublicKey, | ||
| channel_transaction_parameters: &ChannelTransactionParameters, | ||
| secp_ctx: &Secp256k1<secp256k1::All>, channel_value_satoshis: u64, | ||
| value_to_self_with_offset_msat: u64, | ||
| htlcs_in_tx: impl Iterator<Item = &'a mut HTLCOutputInCommitment>, feerate_per_kw: u32, | ||
| broadcaster_dust_limit_satoshis: u64, logger: &L, | ||
| ) -> CommitmentStats | ||
| where | ||
| L::Target: Logger; | ||
| } | ||
|
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| /// A type that builds commitment transactions according to the Lightning Specification. | ||
| #[derive(Clone, Debug, Default)] | ||
| pub(crate) struct SpecTxBuilder {} | ||
|
|
||
| impl TxBuilder for SpecTxBuilder { | ||
| fn build_commitment_transaction<'a, L: Deref>( | ||
| &self, local: bool, commitment_number: u64, per_commitment_point: &PublicKey, | ||
| channel_transaction_parameters: &ChannelTransactionParameters, | ||
| secp_ctx: &Secp256k1<secp256k1::All>, channel_value_satoshis: u64, | ||
| value_to_self_with_offset_msat: u64, | ||
| htlcs_in_tx: impl Iterator<Item = &'a mut HTLCOutputInCommitment>, feerate_per_kw: u32, | ||
| broadcaster_dust_limit_satoshis: u64, logger: &L, | ||
| ) -> CommitmentStats | ||
| where | ||
| L::Target: Logger, | ||
| { | ||
| // We allocate this vector because we need to count the number of non-dust htlcs and calculate the total fee of the transaction | ||
| // before calling `CommitmentTransaction::new`. | ||
| // We could drop this vector and create two iterators: one to count the number of non-dust htlcs, and another to pass to `CommitmentTransaction::new` | ||
| let mut included_non_dust_htlcs: Vec<&mut HTLCOutputInCommitment> = Vec::with_capacity(htlcs_in_tx.size_hint().0); | ||
|
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||
| let mut remote_htlc_total_msat = 0; | ||
| let mut local_htlc_total_msat = 0; | ||
|
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| let channel_parameters = if local { | ||
| channel_transaction_parameters.as_holder_broadcastable() | ||
| } else { | ||
| channel_transaction_parameters.as_counterparty_broadcastable() | ||
| }; | ||
| let channel_type = channel_parameters.channel_type_features(); | ||
|
|
||
| // Trim dust htlcs | ||
| for htlc in htlcs_in_tx { | ||
| if htlc.offered { | ||
| let outbound = local; | ||
| if outbound { | ||
| local_htlc_total_msat += htlc.amount_msat; | ||
| } else { | ||
| remote_htlc_total_msat += htlc.amount_msat; | ||
| } | ||
| let htlc_tx_fee = if channel_type.supports_anchors_zero_fee_htlc_tx() { | ||
| 0 | ||
| } else { | ||
| feerate_per_kw as u64 * chan_utils::htlc_timeout_tx_weight(&channel_type) / 1000 | ||
| }; | ||
| if htlc.amount_msat / 1000 >= broadcaster_dust_limit_satoshis + htlc_tx_fee { | ||
| log_trace!( | ||
| logger, | ||
| " ...creating output for {} non-dust HTLC (hash {}) with value {}", | ||
| if outbound { "outbound" } else { "inbound" }, | ||
| htlc.payment_hash, | ||
| htlc.amount_msat | ||
| ); | ||
| included_non_dust_htlcs.push(htlc); | ||
| } else { | ||
| log_trace!( | ||
| logger, | ||
| " ...trimming {} HTLC (hash {}) with value {} due to dust limit", | ||
| if outbound { "outbound" } else { "inbound" }, | ||
| htlc.payment_hash, | ||
| htlc.amount_msat | ||
| ); | ||
| } | ||
| } else { | ||
| let outbound = !local; | ||
| if outbound { | ||
| local_htlc_total_msat += htlc.amount_msat; | ||
| } else { | ||
| remote_htlc_total_msat += htlc.amount_msat; | ||
| } | ||
| let htlc_tx_fee = if channel_type.supports_anchors_zero_fee_htlc_tx() { | ||
| 0 | ||
| } else { | ||
| feerate_per_kw as u64 * chan_utils::htlc_success_tx_weight(&channel_type) / 1000 | ||
| }; | ||
| if htlc.amount_msat / 1000 >= broadcaster_dust_limit_satoshis + htlc_tx_fee { | ||
| log_trace!( | ||
| logger, | ||
| " ...creating output for {} non-dust HTLC (hash {}) with value {}", | ||
| if outbound { "outbound" } else { "inbound" }, | ||
| htlc.payment_hash, | ||
| htlc.amount_msat | ||
| ); | ||
| included_non_dust_htlcs.push(htlc); | ||
| } else { | ||
| log_trace!( | ||
| logger, | ||
| " ...trimming {} HTLC (hash {}) with value {} due to dust limit", | ||
| if outbound { "outbound" } else { "inbound" }, | ||
| htlc.payment_hash, | ||
| htlc.amount_msat | ||
| ); | ||
| } | ||
| } | ||
| } | ||
|
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||
| // Note that in case they have several just-awaiting-last-RAA fulfills in-progress (ie | ||
| // AwaitingRemoteRevokeToRemove or AwaitingRemovedRemoteRevoke) we may have allowed them to | ||
| // "violate" their reserve value by couting those against it. Thus, we have to do checked subtraction | ||
| // as otherwise we can overflow. | ||
| let mut value_to_remote_msat = | ||
| u64::checked_sub(channel_value_satoshis * 1000, value_to_self_with_offset_msat) | ||
| .unwrap(); | ||
| let value_to_self_msat = | ||
| u64::checked_sub(value_to_self_with_offset_msat, local_htlc_total_msat).unwrap(); | ||
| value_to_remote_msat = | ||
| u64::checked_sub(value_to_remote_msat, remote_htlc_total_msat).unwrap(); | ||
|
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||
| let total_fee_sat = chan_utils::commit_tx_fee_sat( | ||
| feerate_per_kw, | ||
| included_non_dust_htlcs.len(), | ||
| &channel_type, | ||
| ); | ||
| let anchors_val = if channel_type.supports_anchors_zero_fee_htlc_tx() { | ||
| channel::ANCHOR_OUTPUT_VALUE_SATOSHI * 2 | ||
| } else { | ||
| 0 | ||
| }; | ||
| let (value_to_self, value_to_remote) = | ||
| if channel_transaction_parameters.is_outbound_from_holder { | ||
| ( | ||
| (value_to_self_msat / 1000) | ||
| .saturating_sub(anchors_val) | ||
| .saturating_sub(total_fee_sat), | ||
| value_to_remote_msat / 1000, | ||
| ) | ||
| } else { | ||
| ( | ||
| value_to_self_msat / 1000, | ||
| (value_to_remote_msat / 1000) | ||
| .saturating_sub(anchors_val) | ||
| .saturating_sub(total_fee_sat), | ||
| ) | ||
| }; | ||
|
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||
| let mut value_to_a = if local { value_to_self } else { value_to_remote }; | ||
| let mut value_to_b = if local { value_to_remote } else { value_to_self }; | ||
|
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||
| if value_to_a >= broadcaster_dust_limit_satoshis { | ||
| log_trace!( | ||
| logger, | ||
| " ...creating {} output with value {}", | ||
| if local { "to_local" } else { "to_remote" }, | ||
| value_to_a | ||
| ); | ||
| } else { | ||
| log_trace!( | ||
| logger, | ||
| " ...trimming {} output with value {} due to dust limit", | ||
| if local { "to_local" } else { "to_remote" }, | ||
| value_to_a | ||
| ); | ||
| value_to_a = 0; | ||
| } | ||
|
|
||
| if value_to_b >= broadcaster_dust_limit_satoshis { | ||
| log_trace!( | ||
| logger, | ||
| " ...creating {} output with value {}", | ||
| if local { "to_remote" } else { "to_local" }, | ||
| value_to_b | ||
| ); | ||
| } else { | ||
| log_trace!( | ||
| logger, | ||
| " ...trimming {} output with value {} due to dust limit", | ||
| if local { "to_remote" } else { "to_local" }, | ||
| value_to_b | ||
| ); | ||
| value_to_b = 0; | ||
| } | ||
|
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||
| let tx = CommitmentTransaction::new( | ||
| commitment_number, | ||
| &per_commitment_point, | ||
| value_to_a, | ||
| value_to_b, | ||
| feerate_per_kw, | ||
| included_non_dust_htlcs.into_iter(), | ||
| &channel_parameters, | ||
| &secp_ctx, | ||
| ); | ||
|
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||
| CommitmentStats { | ||
| tx, | ||
| total_fee_sat, | ||
| local_balance_msat: value_to_self_msat, | ||
| remote_balance_msat: value_to_remote_msat, | ||
| } | ||
| } | ||
| } |