Function dry_run_taproot_input

bitvm/src/lib.rs:182–241

Dry-runs a specific taproot input

(
    tx: &Transaction,
    input_index: usize,
    prevouts: &[TxOut],
)

/// Dry-runs a specific taproot input
pub fn dry_run_taproot_input(
    tx: &Transaction,
    input_index: usize,
    prevouts: &[TxOut],
) -> ExecuteInfo {
    let script = tx.input[input_index].witness.tapscript().unwrap();
    let stack = {
        let witness_items = tx.input[input_index].witness.to_vec();
        let last = witness_items.last().unwrap();

        // 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.
        let script_index =
            if witness_items.len() >= 3 && last.first() == Some(&TAPROOT_ANNEX_PREFIX) {
                witness_items.len() - 3
            } else {
                witness_items.len() - 2
            };

        witness_items[0..script_index].to_vec()
    };

    let leaf_hash = TapLeafHash::from_script(
        Script::from_bytes(script.as_bytes()),
        LeafVersion::TapScript,
    );

    let mut exec = Exec::new(
        ExecCtx::Tapscript,
        Options::default(),
        TxTemplate {
            tx: tx.clone(),
            prevouts: prevouts.into(),
            input_idx: input_index,
            taproot_annex_scriptleaf: Some((leaf_hash, None)),
        },
        ScriptBuf::from_bytes(script.to_bytes()),
        stack,
    )
    .expect("error creating exec");

    loop {
        if exec.exec_next().is_err() {
            break;
        }
    }
    let res = exec.result().unwrap();
    let info = ExecuteInfo {
        success: res.success,
        error: res.error.clone(),
        last_opcode: res.opcode,
        final_stack: FmtStack(exec.stack().clone()),
        remaining_script: exec.remaining_script().to_asm_string(),
        stats: exec.stats().clone(),
    };