Web3j Writing operations on a contract always throw java lang ArrayIndexOutOfBoundsException

Question

Read operations are successfull. Writing returns the following error:

java.lang.ArrayIndexOutOfBoundsException
 at java.lang.System.arraycopy(Native Method)
 at org.bouncycastle.crypto.signers.HMacDSAKCalculator.init(Unknown Source)
 at org.bouncycastle.crypto.signers.ECDSASigner.generateSignature(Unknown Source)
 at org.web3j.crypto.ECKeyPair.sign(ECKeyPair.java:46)
 at org.web3j.crypto.Sign.signMessage(Sign.java:52)
 at org.web3j.crypto.Sign.signMessage(Sign.java:40)
 at org.web3j.crypto.TransactionEncoder.signMessage(TransactionEncoder.java:21)
 at org.web3j.tx.RawTransactionManager.signAndSend(RawTransactionManager.java:102)
 at org.web3j.tx.RawTransactionManager.sendTransaction(RawTransactionManager.java:91)
 at org.web3j.tx.TransactionManager.executeTransaction(TransactionManager.java:49)
 

I am using the following code:

String hexPrivateKey = String.format("%040x", new BigInteger(1, Config.privateKey.getBytes()));
String hexPublicKey = String.format("%040x", new BigInteger(1, Config.publicKey.getBytes()));
Credentials credentials = Credentials.create(hexPrivateKey, hexPublicKey);
DataSaver contract = DataSaver.load(
address, web3j, credentials, Contract.GAS_PRICE, Contract.GAS_LIMIT);

RemoteCall transaction2 = contract.updateDocumentPayload(
BigInteger.valueOf(1), "Test");
transaction2.send();

Can you tell me, what I am doing wrong?

Answer 1

That exception is thrown when you pass an invalid private key, with the wrong length, to web3j to sign the transaction. Take a look in the example below.

Working code (with valid private key):

BigInteger privateKey = new BigInteger("f9c8a5d689736d881cf9b4117bbae6d935b2368f8260a25677e35d4d1eea7231", 16);
BigInteger publicKey = new BigInteger("72445fcfdeb1fff79496d7ce66089d663ff90e26", 16);
ECKeyPair pair = new ECKeyPair(privateKey, publicKey);
pair.sign("".getBytes());

Same code using invalid private key (one more digit added) and throwing exactly the same exception as yours:

BigInteger privateKey = new BigInteger("f9c8a5d689736d881cf9b4117bbae6d935b2368f8260a25677e35d4d1eea7231a", 16);
BigInteger publicKey = new BigInteger("72445fcfdeb1fff79496d7ce66089d663ff90e26a", 16);
ECKeyPair pair = new ECKeyPair(privateKey, publicKey);
pair.sign("".getBytes());

Always check if the private key and address are valid using WalletUtils.isValidPrivateKey() and WalletUtils.isValidAddress()