Expose previous UTXO for anchor and HTLC inputs

This may be required by some wallets that rely on PSBTs internally to
create/sign transactions.

diff --git a/lightning/src/events/bump_transaction.rs b/lightning/src/events/bump_transaction.rs
index 9d086a26d274749d9589aa2a4e814a3d71c7cc04..1f28bcfb9389d82040237fd3b3807166116c234d 100644 (file)
--- a/lightning/src/events/bump_transaction.rs
+++ b/lightning/src/events/bump_transaction.rs
@@ -18,6 +18,7 @@ use core::ops::Deref;
 use crate::chain::chaininterface::BroadcasterInterface;
 use crate::chain::ClaimId;
 use crate::io_extras::sink;
+use crate::ln::channel::ANCHOR_OUTPUT_VALUE_SATOSHI;
 use crate::ln::chan_utils;
 use crate::ln::chan_utils::{
        ANCHOR_INPUT_WITNESS_WEIGHT, HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT,
@@ -76,6 +77,15 @@ pub struct AnchorDescriptor {
 }
 
 impl AnchorDescriptor {
+       /// Returns the UTXO to be spent by the anchor input, which can be obtained via
+       /// [`Self::unsigned_tx_input`].
+       pub fn previous_utxo(&self) -> TxOut {
+               TxOut {
+                       script_pubkey: self.witness_script().to_v0_p2wsh(),
+                       value: ANCHOR_OUTPUT_VALUE_SATOSHI,
+               }
+       }
+
        /// Returns the unsigned transaction input spending the anchor output in the commitment
        /// transaction.
        pub fn unsigned_tx_input(&self) -> TxIn {
@@ -139,6 +149,15 @@ pub struct HTLCDescriptor {
 }
 
 impl HTLCDescriptor {
+       /// 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 {
@@ -325,6 +344,8 @@ pub enum BumpTransactionEvent {
 pub struct Input {
        /// The unique identifier of the input.
        pub outpoint: OutPoint,
+       /// The UTXO being spent by the input.
+       pub previous_utxo: 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.
@@ -664,6 +685,7 @@ where
        ) -> Result<Transaction, ()> {
                let must_spend = vec![Input {
                        outpoint: anchor_descriptor.outpoint,
+                       previous_utxo: anchor_descriptor.previous_utxo(),
                        satisfaction_weight: commitment_tx.weight() as u64 + ANCHOR_INPUT_WITNESS_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT,
                }];
                let coin_selection = self.utxo_source.select_confirmed_utxos(
@@ -730,6 +752,7 @@ where
                        let htlc_input = htlc_descriptor.unsigned_tx_input();
                        must_spend.push(Input {
                                outpoint: htlc_input.previous_output.clone(),
+                               previous_utxo: htlc_descriptor.previous_utxo(&self.secp),
                                satisfaction_weight: EMPTY_SCRIPT_SIG_WEIGHT + if htlc_descriptor.preimage.is_some() {
                                        HTLC_SUCCESS_INPUT_ANCHOR_WITNESS_WEIGHT
                                } else {