From c876aca3e85115d5e933fca0235ca4bdde0536b5 Mon Sep 17 00:00:00 2001
From: junderw <jonathan.underwood4649@gmail.com>
Date: Tue, 18 Oct 2022 11:52:19 +0900
Subject: [PATCH] Fix: Parse the inner witness_script properly for p2tr

---
 src/util/script.rs | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/util/script.rs b/src/util/script.rs
index 61be03e6..378bb00f 100644
--- a/src/util/script.rs
+++ b/src/util/script.rs
@@ -51,6 +51,7 @@ pub fn get_innerscripts(txin: &TxIn, prevout: &TxOut) -> InnerScripts {
 
     // Wrapped witnessScript for P2WSH or P2SH-P2WSH spends
     let witness_script = if prevout.script_pubkey.is_v0_p2wsh()
+        || prevout.script_pubkey.is_v1_p2tr()
         || redeem_script.as_ref().map_or(false, |s| s.is_v0_p2wsh())
     {
         let witness = &txin.witness;
@@ -63,7 +64,39 @@ pub fn get_innerscripts(txin: &TxIn, prevout: &TxOut) -> InnerScripts {
         #[cfg(feature = "liquid")]
         let wit_to_vec = Clone::clone;
 
-        witness.iter().last().map(wit_to_vec).map(Script::from)
+        let inner_script_slice = if prevout.script_pubkey.is_v1_p2tr() {
+            // Witness stack is potentially very large
+            // so we avoid to_vec() or iter().collect() for performance
+            let w_len = witness.len();
+            witness
+                .last()
+                // Get the position of the script spend script (if it exists)
+                .map(|last_elem| {
+                    // From BIP341:
+                    // If there are at least two witness elements, and the first byte of
+                    // the last element is 0x50, this last element is called annex a
+                    // and is removed from the witness stack.
+                    if w_len >= 2 && last_elem.get(0).filter(|&&v| v == 0x50).is_some() {
+                        // account for the extra item removed from the end
+                        3
+                    } else {
+                        // otherwise script is 2nd from last
+                        2
+                    }
+                })
+                // Convert to None if not script spend
+                // Note: Option doesn't have filter_map() method
+                .filter(|&script_pos_from_last| w_len >= script_pos_from_last)
+                .map(|script_pos_from_last| {
+                    // Can't use second_to_last() since it might be 3rd to last
+                    witness.iter().nth(w_len - script_pos_from_last)
+                })
+                .flatten()
+        } else {
+            witness.last()
+        };
+
+        inner_script_slice.map(wit_to_vec).map(Script::from)
     } else {
         None
     };