Merge #260: fix spend change detection

a56cab73c5c0193a90732f3ba0c2c5be7b993928 fix spend change detection (edouard)

Pull request description:

  Use the presence of bip32_derivation
  in the spend outputs to detect the
  change outputs.

ACKs for top commit:
  edouardparis:
    Self-ACK a56cab73c5c0193a90732f3ba0c2c5be7b993928

Tree-SHA512: 092f8929ebed4ff4c80d8425a1c83831d165a5d31d0c80bc9aac26edf3dffb0241d547fe4fc5208e0dcb4caa39c09f85f3898af56cd0cd03136e5404b503d02e

gui/src/app/state/spend/step.rs

@@ -5,9 +5,7 @@ use std::sync::Arc;
 use iced::{Command, Element};
 use liana::{
     config::Config as DaemonConfig,
-    miniscript::bitcoin::{
-        self, util::psbt::Psbt, Address, Amount, Denomination, OutPoint, Script,
-    },
+    miniscript::bitcoin::{self, util::psbt::Psbt, Address, Amount, Denomination, OutPoint},
 };
 
 use crate::{
@@ -416,26 +414,9 @@ impl SaveSpend {
 
 impl Step for SaveSpend {
     fn load(&mut self, draft: &TransactionDraft) {
-        let outputs_script_pubkeys: Vec<Script> = draft
-            .outputs
-            .keys()
-            .map(|addr| addr.script_pubkey())
-            .collect();
-        let index = if let Some(psbt) = &draft.generated {
-            psbt.unsigned_tx
-                .output
-                .iter()
-                .position(|output| !outputs_script_pubkeys.contains(&output.script_pubkey))
-        } else {
-            None
-        };
         self.spend = Some(detail::SpendTxState::new(
             self.config.clone(),
-            SpendTx::new(
-                draft.generated.clone().unwrap(),
-                index,
-                draft.inputs.clone(),
-            ),
+            SpendTx::new(draft.generated.clone().unwrap(), draft.inputs.clone()),
             false,
         ));
     }

gui/src/app/view/spend/detail.rs

@@ -44,7 +44,7 @@ pub fn spend_view<'a, T: Into<Element<'a, Message>>>(
                 &tx.coins,
                 &tx.psbt.unsigned_tx,
                 network,
-                tx.change_index.map(|i| vec![i]),
+                Some(tx.change_indexes.clone()),
                 None,
             )),
     )

gui/src/daemon/mod.rs

@@ -88,7 +88,7 @@ pub trait Daemon: Debug {
                     })
                     .copied()
                     .collect();
-                model::SpendTx::new(tx.psbt, tx.change_index.map(|i| i as usize), coins)
+                model::SpendTx::new(tx.psbt, coins)
             })
             .collect())
     }

gui/src/daemon/model.rs

@@ -24,7 +24,7 @@ pub fn remaining_sequence(coin: &Coin, blockheight: u32, timelock: u32) -> u32 {
 pub struct SpendTx {
     pub coins: Vec<Coin>,
     pub psbt: Psbt,
-    pub change_index: Option<usize>,
+    pub change_indexes: Vec<usize>,
     pub spend_amount: Amount,
     pub fee_amount: Amount,
     pub status: SpendStatus,
@@ -38,11 +38,13 @@ pub enum SpendStatus {
 }
 
 impl SpendTx {
-    pub fn new(psbt: Psbt, change_index: Option<usize>, coins: Vec<Coin>) -> Self {
+    pub fn new(psbt: Psbt, coins: Vec<Coin>) -> Self {
+        let mut change_indexes = Vec::new();
         let (change_amount, spend_amount) = psbt.unsigned_tx.output.iter().enumerate().fold(
             (Amount::from_sat(0), Amount::from_sat(0)),
             |(change, spend), (i, output)| {
-                if Some(i) == change_index {
+                if !psbt.outputs[i].bip32_derivation.is_empty() {
+                    change_indexes.push(i);
                     (change + Amount::from_sat(output.value), spend)
                 } else {
                     (change, spend + Amount::from_sat(output.value))
@@ -66,7 +68,7 @@ impl SpendTx {
         Self {
             coins,
             psbt,
-            change_index,
+            change_indexes,
             spend_amount,
             fee_amount: inputs_amount - spend_amount - change_amount,
             status,