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witness: Improve Witness::tapscript

This commit is contained in:
Steven Roose 2023-10-12 13:45:44 +01:00
parent e48a2e4225
commit ef336e1387
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GPG Key ID: 2F2A88D7F8D68E87
1 changed files with 15 additions and 28 deletions
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43
bitcoin/src/blockdata/witness.rs
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@ -394,24 +394,19 @@ impl Witness {
/// [Script::is_p2tr](crate::blockdata::script::Script::is_p2tr) to
/// check whether this is actually a Taproot witness.
pub fn tapscript(&self) -> Option<&Script> {
let len = self.len();
self.last()
.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 len >= 2 && last_elem.first() == Some(&TAPROOT_ANNEX_PREFIX) {
// account for the extra item removed from the end
3
} else {
// otherwise script is 2nd from last
2
}
})
.filter(|&script_pos_from_last| len >= script_pos_from_last)
.and_then(|script_pos_from_last| self.nth(len - script_pos_from_last))
.map(Script::from_bytes)
self.last().and_then(|last| {
// 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 self.len() >= 3 && last.first() == Some(&TAPROOT_ANNEX_PREFIX) {
self.nth(self.len() - 3).map(Script::from_bytes)
} else if self.len() >= 2 {
self.nth(self.len() - 2).map(Script::from_bytes)
} else {
None
}
})
}
}
@ -702,16 +697,8 @@ mod test {
let witness_serialized: Vec<u8> = serialize(&witness_vec);
let witness_serialized_annex: Vec<u8> = serialize(&witness_vec_annex);
let witness = Witness {
content: append_u32_vec(witness_serialized[1..].to_vec(), &[0, 5]),
witness_elements: 2,
indices_start: 7,
};
let witness_annex = Witness {
content: append_u32_vec(witness_serialized_annex[1..].to_vec(), &[0, 5, 7]),
witness_elements: 3,
indices_start: 9,
};
let witness = deserialize::<Witness>(&witness_serialized[..]).unwrap();
let witness_annex = deserialize::<Witness>(&witness_serialized_annex[..]).unwrap();
// With or without annex, the tapscript should be returned.
assert_eq!(witness.tapscript(), Some(Script::from_bytes(&tapscript[..])));