Add a test for type 4 transaction, refactoring

Signed-off-by: dan437 <80175477+dan437@users.noreply.github.com>

Author: dan437

src/utils.test.ts

@@ -1,3 +1,5 @@
+import { arrayify, hexlify } from '@ethersproject/bytes';
+import { keccak256 } from '@ethersproject/keccak256';
 import { ChainId, NetworkType } from '@metamask/controller-utils';
 import {
   type TransactionMeta,
@@ -374,6 +376,13 @@ describe('src/utils.js', () => {
         utils.getTxHash('0x0302b75dfb9fd9eb34056af0');
       }).toThrow('unsupported transaction type: 3');
     });
+
+    it('computes hash for type 4 transaction', () => {
+      const type4TxHex = '0x04deadbeef';
+      const expectedHash = hexlify(keccak256(arrayify(type4TxHex)));
+      const txHash = utils.getTxHash(type4TxHex);
+      expect(txHash).toBe(expectedHash);
+    });
   });
 
   describe('getReturnTxHashAsap', () => {

src/utils.ts

@@ -224,6 +224,10 @@ export const incrementNonceInHex = (nonceInHex: string): string => {
   return hexlify(Number(nonceInDec) + 1);
 };
 
+const isType4Transaction = (signedTxHex: string) => {
+  return typeof signedTxHex === 'string' && signedTxHex.startsWith('0x04');
+};
+
 export const getTxHash = (signedTxHex: any) => {
   if (!signedTxHex) {
     return '';
@@ -232,7 +236,7 @@ export const getTxHash = (signedTxHex: any) => {
     const parsed = parse(signedTxHex);
     return parsed?.hash ?? '';
   } catch (error) {
-    if (typeof signedTxHex === 'string' && signedTxHex.startsWith('0x04')) {
+    if (isType4Transaction(signedTxHex)) {
       return hexlify(keccak256(arrayify(signedTxHex)));
     }
     throw error;