feat(abstract-utxo): add transaction decoding utils

Refactor transaction decoding logic into separate helper functions to support
both utxolib and wasm-utxo backends. Extract string-to-buffer conversion
into a reusable utility function.

Issue: BTC-2806

Co-authored-by: llm-git <llm-git@ttll.de>

Author: OttoAllmendinger

modules/abstract-utxo/src/abstractUtxoCoin.ts

@@ -77,6 +77,7 @@ import { assertDescriptorWalletAddress, getDescriptorMapFromWallet, isDescriptor
 import { getChainFromNetwork, getFamilyFromNetwork, getFullNameFromNetwork } from './names';
 import { assertFixedScriptWalletAddress } from './address/fixedScript';
 import { ParsedTransaction } from './transaction/types';
+import { decodePsbtWith, stringToBufferTryFormats } from './transaction/decode';
 import { toBip32Triple, UtxoKeychain } from './keychains';
 import { verifyKeySignature, verifyUserPublicKey } from './verifyKey';
 import { getPolicyForEnv } from './descriptor/validatePolicy';
@@ -527,22 +528,12 @@ export abstract class AbstractUtxoCoin extends BaseCoin {
 
   decodeTransaction<TNumber extends number | bigint>(input: Buffer | string): DecodedTransaction<TNumber> {
     if (typeof input === 'string') {
-      for (const format of ['hex', 'base64'] as const) {
-        const buffer = Buffer.from(input, format);
-        const bufferToString = buffer.toString(format);
-        if (
-          (format === 'base64' && bufferToString === input) ||
-          (format === 'hex' && bufferToString === input.toLowerCase())
-        ) {
-          return this.decodeTransaction(buffer);
-        }
-      }
-
-      throw new Error('input must be a valid hex or base64 string');
+      const buffer = stringToBufferTryFormats(input, ['hex', 'base64']);
+      return this.decodeTransaction(buffer);
     }
 
     if (utxolib.bitgo.isPsbt(input)) {
-      return utxolib.bitgo.createPsbtFromBuffer(input, this.network);
+      return decodePsbtWith(input, this.network, 'utxolib');
     } else {
       return utxolib.bitgo.createTransactionFromBuffer(input, this.network, {
         amountType: this.amountType,

modules/abstract-utxo/src/transaction/decode.ts

@@ -0,0 +1,59 @@
+import * as utxolib from '@bitgo/utxo-lib';
+import { fixedScriptWallet, utxolibCompat } from '@bitgo/wasm-utxo';
+
+import { SdkBackend } from './types';
+
+type BufferEncoding = 'hex' | 'base64';
+
+export function stringToBufferTryFormats(input: string, formats: BufferEncoding[] = ['hex', 'base64']): Buffer {
+  for (const format of formats) {
+    const buffer = Buffer.from(input, format);
+    const bufferToString = buffer.toString(format);
+    if (
+      (format === 'base64' && bufferToString === input) ||
+      (format === 'hex' && bufferToString === input.toLowerCase())
+    ) {
+      return buffer;
+    }
+  }
+
+  throw new Error('input must be a valid hex or base64 string');
+}
+
+function toNetworkName(network: utxolib.Network): utxolibCompat.UtxolibName {
+  const networkName = utxolib.getNetworkName(network);
+  if (!networkName) {
+    throw new Error(`Invalid network: ${network}`);
+  }
+  return networkName;
+}
+
+export function decodePsbtWith(
+  psbt: string | Buffer,
+  network: utxolib.Network,
+  backend: 'utxolib'
+): utxolib.bitgo.UtxoPsbt;
+export function decodePsbtWith(
+  psbt: string | Buffer,
+  network: utxolib.Network,
+  backend: 'wasm-utxo'
+): fixedScriptWallet.BitGoPsbt;
+export function decodePsbtWith(
+  psbt: string | Buffer,
+  network: utxolib.Network,
+  backend: SdkBackend
+): utxolib.bitgo.UtxoPsbt | fixedScriptWallet.BitGoPsbt;
+export function decodePsbtWith(
+  psbt: string | Buffer,
+  network: utxolib.Network,
+  backend: SdkBackend
+): utxolib.bitgo.UtxoPsbt | fixedScriptWallet.BitGoPsbt {
+  if (typeof psbt === 'string') {
+    psbt = Buffer.from(psbt, 'hex');
+  }
+  if (backend === 'utxolib') {
+    return utxolib.bitgo.createPsbtFromBuffer(psbt, network);
+  } else {
+    return fixedScriptWallet.BitGoPsbt.fromBytes(psbt, toNetworkName(network));
+  }
+}

modules/abstract-utxo/src/transaction/types.ts

@@ -4,6 +4,8 @@ import type { UtxoNamedKeychains } from '../keychains';
 
 import type { CustomChangeOptions } from './fixedScript';
 
+export type SdkBackend = 'utxolib' | 'wasm-utxo';
+
 export type DecodedTransaction<TNumber extends number | bigint> =
   | utxolib.bitgo.UtxoTransaction<TNumber>
   | utxolib.bitgo.UtxoPsbt;