Fix: zero-valued BigInt tx fields encode as non-canonical RLP (0x00)

lib/ethereum/src/transaction/eth_transaction.dart

@@ -55,7 +55,10 @@ enum ETHTransactionType {
 /// Utility class for Ethereum transaction-related operations.
 class ETHTransactionUtils {
   /// Converts a [BigInt] to a byte list with a maximum length of 32 bytes.
+  /// Returns an empty list if the value is 0, so that RLP encodes it as the
+  /// canonical empty byte string (0x80) rather than a non-canonical 0x00.
   static List<int> bigintToBytes(BigInt value) {
+    if (value == BigInt.zero) return [];
     final toBytes = BigintUtils.toBytes(
       value,
       length: BigintUtils.bitlengthInBytes(value),

test/etherum/transaction_test.dart

@@ -1,30 +1,80 @@
-import 'package:on_chain/ethereum/ethereum.dart';
 import 'package:blockchain_utils/blockchain_utils.dart';
+import 'package:on_chain/ethereum/ethereum.dart';
 import 'package:test/test.dart';
 
 void main() {
   /// transaction with leading zero s bytes.
   test('transaction leading zero s', () {
     final addr = ETHAddress('0x084937B3f86ea7BbCA86F2809809A65ED8A7ADa9');
-    final signer = ETHSigner.fromKeyBytes(BytesUtils.fromHexString(
-        'e9f4fe38ffc54abd156dd4b8a39611fce696af62841ee6422ee36ba7b26c53f5'));
+    final signer = ETHSigner.fromKeyBytes(
+      BytesUtils.fromHexString(
+        'e9f4fe38ffc54abd156dd4b8a39611fce696af62841ee6422ee36ba7b26c53f5',
+      ),
+    );
 
     final receiver = ETHAddress('0x4fAfB33f0e492FD10e91b55ED88872104fFd94ee');
     final transaction = ETHTransaction(
-        nonce: 0,
-        from: addr,
-        type: ETHTransactionType.legacy,
-        to: receiver,
-        gasLimit: BigInt.from(21000),
-        data: const [],
-        value: ETHHelper.toWei('0.01'),
-        chainId: BigInt.from(97),
-        gasPrice: BigInt.from(5000000000));
+      nonce: 0,
+      from: addr,
+      type: ETHTransactionType.legacy,
+      to: receiver,
+      gasLimit: BigInt.from(21000),
+      data: const [],
+      value: ETHHelper.toWei('0.01'),
+      chainId: BigInt.from(97),
+      gasPrice: BigInt.from(5000000000),
+    );
     final serialize = transaction.serialized;
     final sign = signer.signConst(serialize);
     final signedSerialize = transaction.signedSerialized(sign);
 
     final decode = ETHTransaction.fromSerialized(signedSerialize);
     expect(decode.signedSerialized(), signedSerialize);
   });
+
+  /// A zero-valued BigInt field must be RLP-encoded as the canonical empty byte
+  /// string, not a non-canonical single 0x00 byte. Otherwise nodes reject the tx
+  /// with "rlp: non-canonical integer (leading zero bytes)".
+  test('bigintToBytes encodes zero as canonical empty bytes', () {
+    expect(ETHTransactionUtils.bigintToBytes(BigInt.zero), <int>[]);
+    // sanity: non-zero values are unaffected.
+    expect(ETHTransactionUtils.bigintToBytes(BigInt.one), [0x01]);
+    expect(ETHTransactionUtils.bigintToBytes(BigInt.from(0x2673c00)), [
+      0x02,
+      0x67,
+      0x3c,
+      0x00,
+    ]);
+  });
+
+  /// Reproduces the Arbitrum failure: an EIP-1559 transaction with
+  /// maxPriorityFeePerGas == 0 (the norm on L2s). The zero tip (GasTipCap) must
+  /// serialize as an empty RLP item, not 0x00.
+  test('EIP-1559 zero maxPriorityFeePerGas serializes canonically', () {
+    final transaction = ETHTransaction(
+      nonce: 17,
+      from: ETHAddress('0xb90630D3108A368b5a7603A854bF24D6c9376d01'),
+      type: ETHTransactionType.eip1559,
+      to: ETHAddress('0x618d99A2F3412A2185246614D30bE233011Ee250'),
+      gasLimit: BigInt.from(26606),
+      data: const [],
+      value: ETHHelper.toWei('0.01'),
+      chainId: BigInt.from(421614), // Arbitrum Sepolia
+      maxPriorityFeePerGas: BigInt.zero,
+      maxFeePerGas: BigInt.from(40320000),
+    );
+
+    final serialized = transaction.serialized;
+    // strip the EIP-1559 type prefix (0x02) before RLP-decoding the payload.
+    expect(serialized.first, ETHTransactionType.eip1559.prefix);
+    final fields = RLPDecoder.decode(serialized.sublist(1));
+
+    // field[2] is maxPriorityFeePerGas (GasTipCap): must be empty, not [0].
+    expect(fields[2], <int>[]);
+
+    // round-trip still holds.
+    final decode = ETHTransaction.fromSerialized(serialized);
+    expect(decode.serialized, serialized);
+    expect(decode.maxPriorityFeePerGas, BigInt.zero);
+  });
 }