From 41f34a33269153c4b05d623842b371fab47822a0 Mon Sep 17 00:00:00 2001
From: Lucas Soriano del Pino <lucas_soriano@fastmail.com>
Date: Wed, 23 Oct 2024 12:20:21 +1100
Subject: [PATCH] Use correct input in settle claim transaction

Relying on the `is_offer` heuristic caused problems in production.
---
 dlc-manager/src/channel_updater.rs |  2 --
 dlc-manager/src/manager.rs         |  8 ++------
 dlc/src/channel/mod.rs             | 18 +++++++++++-------
 3 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/dlc-manager/src/channel_updater.rs b/dlc-manager/src/channel_updater.rs
index 8cf2cc1b..204c2d88 100644
--- a/dlc-manager/src/channel_updater.rs
+++ b/dlc-manager/src/channel_updater.rs
@@ -2855,7 +2855,6 @@ pub fn finalize_unilateral_close_settled_channel<S: Deref>(
     destination_address: &Address,
     fee_rate_per_vb: u64,
     signer: &S,
-    is_offer: bool,
     is_initiator: bool,
 ) -> Result<(Transaction, Channel), Error>
 where
@@ -2892,7 +2891,6 @@ where
         CET_NSEQUENCE,
         0,
         fee_rate_per_vb,
-        is_offer,
     )?;
 
     let closing_channel = SettledClosingChannel {
diff --git a/dlc-manager/src/manager.rs b/dlc-manager/src/manager.rs
index 23de11a3..dd2f5c1d 100644
--- a/dlc-manager/src/manager.rs
+++ b/dlc-manager/src/manager.rs
@@ -1298,11 +1298,10 @@ where
         &self,
         signed_channel: SignedChannel,
     ) -> Result<(), Error> {
-        let (settle_tx, &is_offer, &is_initiator) = get_signed_channel_state!(
+        let (settle_tx, &is_initiator) = get_signed_channel_state!(
             signed_channel,
             SettledClosing,
             settle_transaction,
-            is_offer,
             is_initiator
         )?;
 
@@ -1312,11 +1311,9 @@ where
             >= CET_NSEQUENCE
         {
             log::info!(
-                "Settle transaction {} for channel {} has enough confirmations to spend from it. is_offer={}, is_initiator={}",
+                "Settle transaction {} for channel {} has enough confirmations to spend from it",
                 settle_tx.txid(),
                 serialize_hex(&signed_channel.channel_id),
-                is_offer,
-                is_initiator
             );
 
             let fee_rate_per_vb: u64 = {
@@ -1338,7 +1335,6 @@ where
                     &self.wallet.get_new_address()?,
                     fee_rate_per_vb,
                     &self.wallet,
-                    is_offer,
                     is_initiator,
                 )?;
 
diff --git a/dlc/src/channel/mod.rs b/dlc/src/channel/mod.rs
index 3e9fe5e0..559edac3 100644
--- a/dlc/src/channel/mod.rs
+++ b/dlc/src/channel/mod.rs
@@ -415,27 +415,31 @@ pub fn create_and_sign_claim_settle_transaction<C: Signing>(
     csv_timelock: u32,
     lock_time: u32,
     fee_rate_per_vb: u64,
-    is_offer: bool,
 ) -> Result<Transaction, Error> {
     let own_descriptor = settle_descriptor(own_params, &counter_params.own_pk, csv_timelock);
 
-    let vout = if is_offer {
-        0
-    } else {
-        1
+    let output = settle_tx.output.iter().enumerate().find(|(_, output)| {
+        output.script_pubkey == own_descriptor.script_pubkey()
+    });
+
+    let (vout, output) = match output {
+        Some((vout, output)) => (vout, output),
+        None => {
+            return Err(Error::InvalidArgument("No claimable output found on settle transaction".to_string()));
+        },
     };
 
     let tx_in = TxIn {
         previous_output: OutPoint {
             txid: settle_tx.txid(),
-            vout,
+            vout: vout as u32,
         },
         sequence: Sequence::from_height(csv_timelock as u16),
         script_sig: Script::default(),
         witness: Witness::default(),
     };
 
-    let input_value = settle_tx.output[vout as usize].value;
+    let input_value = output.value;
 
     let dest_script_pk_len = dest_address.script_pubkey().len();
     let var_int_prefix_len = crate::util::compute_var_int_prefix_size(dest_script_pk_len);