feat(utxo-core): improve bip322 transaction handling

Change buildToSignPsbt to directly accept a Transaction object instead of hex
string, and return a Psbt object instead of hex. Similarly update
buildToSpendTransaction to return a Transaction object.

Issue: BTC-2362

Co-authored-by: llm-git <[email protected]>

Author: davidkaplanbitgo

modules/utxo-core/src/bip322/toSign.ts

@@ -14,13 +14,11 @@ export type AddressDetails = {
  * @param {AddressDetails} addressDetails - The details of the address, including redeemScript and/or witnessScript.
  * @returns {string} - The hex representation of the constructed PSBT.
  */
-export function buildToSignPsbt(toSpendTxHex: string, addressDetails: AddressDetails): string {
+export function buildToSignPsbt(toSpendTx: Transaction<bigint>, addressDetails: AddressDetails): Psbt {
   if (!addressDetails.redeemScript && !addressDetails.witnessScript) {
     throw new Error('redeemScript and/or witnessScript must be provided');
   }
 
-  const toSpendTx = Transaction.fromHex(toSpendTxHex);
-
   // Create PSBT object for constructing the transaction
   const psbt = new Psbt();
   // Set default value for nVersion and nLockTime
@@ -37,13 +35,15 @@ export function buildToSignPsbt(toSpendTxHex: string, addressDetails: AddressDet
     psbt.updateInput(0, { redeemScript: addressDetails.redeemScript });
   }
   if (addressDetails.witnessScript) {
-    psbt.updateInput(0, { witnessUtxo: { value: BigInt(0), script: addressDetails.witnessScript } });
+    psbt.updateInput(0, {
+      witnessUtxo: { value: BigInt(0), script: addressDetails.witnessScript },
+    });
   }
 
   // Set the output
   psbt.addOutput({
     value: BigInt(0), // vout[0].nValue = 0
     script: Buffer.from([0x6a]), // vout[0].scriptPubKey = OP_RETURN
   });
-  return psbt.toHex();
+  return psbt;
 }

modules/utxo-core/src/bip322/toSpend.ts

@@ -1,5 +1,5 @@
 import { Hash } from 'fast-sha256';
-import { Psbt } from '@bitgo/utxo-lib';
+import { Psbt, Transaction } from '@bitgo/utxo-lib';
 
 export const BIP322_TAG = 'BIP0322-signed-message';
 
@@ -31,9 +31,13 @@ export function hashMessageWithTag(message: string | Buffer, tag = BIP322_TAG):
  * @param {Buffer} scriptPubKey - The scriptPubKey to use for the output
  * @param {string | Buffer} message - The message to include in the transaction
  * @param {Buffer} [tag=BIP322_TAG] - The tag to use for hashing, defaults to BIP322_TAG.
- * @returns {string} - The hex representation of the constructed transaction
+ * @returns {Transaction} - The constructed transaction
  */
-export function buildToSpendTransaction(scriptPubKey: Buffer, message: string | Buffer, tag = BIP322_TAG): string {
+export function buildToSpendTransaction(
+  scriptPubKey: Buffer,
+  message: string | Buffer,
+  tag = BIP322_TAG
+): Transaction<bigint> {
   // Create PSBT object for constructing the transaction
   const psbt = new Psbt();
   // Set default value for nVersion and nLockTime
@@ -60,5 +64,5 @@ export function buildToSpendTransaction(scriptPubKey: Buffer, message: string |
     script: scriptPubKey, // vout[0].scriptPubKey = message_challenge
   });
   // Return transaction
-  return psbt.extractTransaction().toHex();
+  return psbt.extractTransaction();
 }

modules/utxo-core/test/bip322/toSign.ts

@@ -1,6 +1,6 @@
 import assert from 'assert';
 
-import { payments, Psbt, ECPair, Transaction } from '@bitgo/utxo-lib';
+import { payments, ECPair, Transaction } from '@bitgo/utxo-lib';
 
 import * as bip322 from '../../src/bip322';
 
@@ -26,12 +26,12 @@ describe('BIP322 toSign', function () {
 
     fixtures.forEach(({ message, txid }) => {
       it(`should build a to_sign PSBT for message "${message}"`, function () {
-        const toSpendTxHex = bip322.buildToSpendTransaction(scriptPubKey, Buffer.from(message));
+        const toSpendTx = bip322.buildToSpendTransaction(scriptPubKey, Buffer.from(message));
         const addressDetails = {
           witnessScript: scriptPubKey,
         };
-        const result = bip322.buildToSignPsbt(toSpendTxHex, addressDetails);
-        const computedTxid = Psbt.fromHex(result)
+        const result = bip322.buildToSignPsbt(toSpendTx, addressDetails);
+        const computedTxid = result
           .signAllInputs(prv, [Transaction.SIGHASH_ALL])
           .finalizeAllInputs()
           .extractTransaction()

modules/utxo-core/test/bip322/toSpend.ts

@@ -1,6 +1,6 @@
 import assert from 'assert';
 
-import { payments, Transaction } from '@bitgo/utxo-lib';
+import { payments } from '@bitgo/utxo-lib';
 
 import { buildToSpendTransaction, hashMessageWithTag } from '../../src/bip322';
 
@@ -50,7 +50,7 @@ describe('to_spend', function () {
     fixtures.forEach(({ message, txid }) => {
       it(`should build a to_spend transaction for message "${message}"`, function () {
         const result = buildToSpendTransaction(scriptPubKey, Buffer.from(message));
-        const computedTxid = Transaction.fromHex(result).getId();
+        const computedTxid = result.getId();
         assert.strictEqual(computedTxid, txid, `Transaction ID for message "${message}" does not match expected value`);
       });
     });