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[Splicing] Tx negotiation during splicing #3736

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[Splicing] Tx negotiation during splicing #3736

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0b89a36
Rename DualFundingContext
optout21 Jun 3, 2025
299c643
Extend begin_interactive_...() with splicing-specific parameters
optout21 Jun 17, 2025
5df8c8c
Introduce NegotiatingChannelView to bridge Funded and PendingV2
optout21 Jun 17, 2025
c3ec314
Implement transaction negotiation during splicing
optout21 Jun 17, 2025
3577418
Formatting, remove rustfmt skips
optout21 Jun 17, 2025
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50 changes: 30 additions & 20 deletions lightning/src/ln/channel.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2703,20 +2703,25 @@ where
/// default destination address is used.
/// If error occurs, it is caused by our side, not the counterparty.
#[allow(dead_code)] // TODO(dual_funding): Remove once contribution to V2 channels is enabled
#[rustfmt::skip]
fn begin_interactive_funding_tx_construction<ES: Deref>(
&mut self, signer_provider: &SP, entropy_source: &ES, holder_node_id: PublicKey,
change_destination_opt: Option<ScriptBuf>,
is_initiator: bool, change_destination_opt: Option<ScriptBuf>,
prev_funding_input: Option<(TxIn, TransactionU16LenLimited)>,
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Should we just drop this commit and revisit once #3842 lands? Or we can just drop the prev_funding_input part for now.

) -> Result<Option<InteractiveTxMessageSend>, AbortReason>
where ES::Target: EntropySource
where
ES::Target: EntropySource,
{
debug_assert!(matches!(self.context.channel_state, ChannelState::NegotiatingFunding(_)));
debug_assert!(self.interactive_tx_constructor.is_none());

let mut funding_inputs = Vec::new();
mem::swap(&mut self.funding_negotiation_context.our_funding_inputs, &mut funding_inputs);

// TODO(splicing): Add prev funding tx as input, must be provided as a parameter
if is_initiator {
if let Some(prev_funding_input) = prev_funding_input {
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Reminder we still need to track this in the constructor somehow when we're not the initiator, similar to expected_remote_shared_funding_output

funding_inputs.push(prev_funding_input);
}
}

// Add output for funding tx
// Note: For the error case when the inputs are insufficient, it will be handled after
Expand All @@ -2729,12 +2734,11 @@ where
script_pubkey: self.funding.get_funding_redeemscript().to_p2wsh(),
};

if self.funding.is_outbound() {
funding_outputs.push(
OutputOwned::Shared(SharedOwnedOutput::new(
shared_funding_output, self.funding_negotiation_context.our_funding_satoshis,
))
);
if is_initiator {
funding_outputs.push(OutputOwned::Shared(SharedOwnedOutput::new(
shared_funding_output,
self.funding_negotiation_context.our_funding_satoshis,
)));
} else {
let TxOut { value, script_pubkey } = shared_funding_output;
expected_remote_shared_funding_output = Some((script_pubkey, value.to_sat()));
Expand All @@ -2744,22 +2748,26 @@ where
let change_script = if let Some(script) = change_destination_opt {
script
} else {
signer_provider.get_destination_script(self.context.channel_keys_id)
signer_provider
.get_destination_script(self.context.channel_keys_id)
.map_err(|_err| AbortReason::InternalError("Error getting destination script"))?
};
let change_value_opt = calculate_change_output_value(
self.funding.is_outbound(), self.funding_negotiation_context.our_funding_satoshis,
&funding_inputs, &funding_outputs,
is_initiator,
self.funding_negotiation_context.our_funding_satoshis,
&funding_inputs,
&funding_outputs,
self.funding_negotiation_context.funding_feerate_sat_per_1000_weight,
change_script.minimal_non_dust().to_sat(),
)?;
if let Some(change_value) = change_value_opt {
let mut change_output = TxOut {
value: Amount::from_sat(change_value),
script_pubkey: change_script,
};
let mut change_output =
TxOut { value: Amount::from_sat(change_value), script_pubkey: change_script };
let change_output_weight = get_output_weight(&change_output.script_pubkey).to_wu();
let change_output_fee = fee_for_weight(self.funding_negotiation_context.funding_feerate_sat_per_1000_weight, change_output_weight);
let change_output_fee = fee_for_weight(
self.funding_negotiation_context.funding_feerate_sat_per_1000_weight,
change_output_weight,
);
let change_value_decreased_with_fee = change_value.saturating_sub(change_output_fee);
// Check dust limit again
if change_value_decreased_with_fee > self.context.holder_dust_limit_satoshis {
Expand All @@ -2773,8 +2781,10 @@ where
holder_node_id,
counterparty_node_id: self.context.counterparty_node_id,
channel_id: self.context.channel_id(),
feerate_sat_per_kw: self.funding_negotiation_context.funding_feerate_sat_per_1000_weight,
is_initiator: self.funding.is_outbound(),
feerate_sat_per_kw: self
.funding_negotiation_context
.funding_feerate_sat_per_1000_weight,
is_initiator,
funding_tx_locktime: self.funding_negotiation_context.funding_tx_locktime,
inputs_to_contribute: funding_inputs,
outputs_to_contribute: funding_outputs,
Expand Down