fix: wrong signature index at EVMWalletConnector (#112)

Co-authored-by: LuizAsFight <felipebolsonigomes@gmail.com>

.changeset/old-eyes-worry.md

@@ -0,0 +1,5 @@
+---
+"@fuel-connectors/evm-connector": patch
+---
+
+fix: wrong signature index at `EVMWalletConnector`

packages/evm-connector/src/EvmWalletConnector.ts

@@ -28,6 +28,7 @@ import {
 } from './types';
 import type { EIP1193Provider } from './utils/eip-1193';
 import { METAMASK_ICON } from './utils/metamask-icon';
+import { getSignatureIndex } from './utils/predicate';
 
 export class EVMWalletConnector extends FuelConnector {
   name = 'Metamask';
@@ -351,11 +352,13 @@ export class EVMWalletConnector extends FuelConnector {
     }
     const transactionRequest = transactionRequestify(transaction);
 
+    const signatureIndex = getSignatureIndex(transactionRequest.witnesses);
+
     // Create a predicate and set the witness index to call in predicate`
     const predicate = this.predicateAccount.createPredicate(
       evmAccount,
       fuelProvider,
-      [transactionRequest.witnesses.length],
+      [signatureIndex],
     );
     predicate.connect(fuelProvider);
 

packages/evm-connector/src/utils/predicate.ts

@@ -54,3 +54,24 @@ export const createPredicate = memoize(function createPredicate<
 
   return predicate;
 });
+
+/**
+ * Since the predicate resources were fetched and added to the TransactionRequest before the predicate
+ * was instantiated, it is very likely that they were fetched and added as normal account resources,
+ * resulting in a witness placeholder being added to the witnesses of the TransactionRequest to
+ * later be replaced with an actual signature. Since predicate resources do not require a signature,
+ * this placeholder witness will be removed when calling `Predicate.populateTransactionPredicateData`.
+ * However, we need to validate if this placeholder witness was added here in order to instantiate the
+ * predicate with the correct witness index argument.
+ */
+export const getSignatureIndex = (witnesses: BytesLike[]) => {
+  const hasPlaceholderWitness = witnesses.some(
+    (item) =>
+      item instanceof Uint8Array &&
+      item.length === 64 &&
+      item.every((value) => value === 0),
+  );
+
+  // if it is a placeholder witness, we can safely replace it, otherwise we will consider a new element.
+  return hasPlaceholderWitness ? witnesses.length - 1 : witnesses.length;
+};

packages/walletconnect-connector/src/WalletConnectConnector.ts

@@ -31,6 +31,7 @@ import { ETHEREUM_ICON, TESTNET_URL } from './constants';
 import type { Predicate, PredicateConfig, WalletConnectConfig } from './types';
 import { PredicateAccount } from './utils/Predicate';
 import { createModalConfig } from './utils/wagmiConfig';
+import { getSignatureIndex } from './utils/witness';
 
 export class WalletConnectConnector extends FuelConnector {
   name = 'Ethereum Wallets';
@@ -306,7 +307,9 @@ export class WalletConnectConnector extends FuelConnector {
     const transactionRequest = transactionRequestify(transaction);
     const transactionFee = transactionRequest.maxFee.toNumber();
 
-    const predicateSignatureIndex = transactionRequest.witnesses.length - 1;
+    const predicateSignatureIndex = getSignatureIndex(
+      transactionRequest.witnesses,
+    );
 
     // Create a predicate and set the witness index to call in predicate`
     const predicate = this.predicateAccount.createPredicate(

packages/walletconnect-connector/src/utils/witness.ts

@@ -0,0 +1,22 @@
+import type { BytesLike } from 'fuels';
+
+/**
+ * Since the predicate resources were fetched and added to the TransactionRequest before the predicate
+ * was instantiated, it is very likely that they were fetched and added as normal account resources,
+ * resulting in a witness placeholder being added to the witnesses of the TransactionRequest to
+ * later be replaced with an actual signature. Since predicate resources do not require a signature,
+ * this placeholder witness will be removed when calling `Predicate.populateTransactionPredicateData`.
+ * However, we need to validate if this placeholder witness was added here in order to instantiate the
+ * predicate with the correct witness index argument.
+ */
+export const getSignatureIndex = (witnesses: BytesLike[]) => {
+  const hasPlaceholderWitness = witnesses.some(
+    (item) =>
+      item instanceof Uint8Array &&
+      item.length === 64 &&
+      item.every((value) => value === 0),
+  );
+
+  // if it is a placeholder witness, we can safely replace it, otherwise we will consider a new element.
+  return hasPlaceholderWitness ? witnesses.length - 1 : witnesses.length;
+};