Send BTCACCT refunds to first unused received address instead of address derived from tradePrivateKey.

Added BTC.getUnusedReceiveAddress() to support above.

src/main/java/org/qortal/api/model/CrossChainBitcoinRefundRequest.java

@@ -22,6 +22,9 @@ public class CrossChainBitcoinRefundRequest {
 	@Schema(description = "Bitcoin miner fee", example = "0.00001000")
 	public BigDecimal bitcoinMinerFee;
 
+	@Schema(description = "Bitcoin HASH160(public key) for receiving funds, or omit to derive from private key", example = "u17kBVKkKSp12oUzaxFwNnq1JZf")
+	public byte[] receivingAccountInfo;
+
 	public CrossChainBitcoinRefundRequest() {
 	}
 

src/main/java/org/qortal/api/resource/CrossChainResource.java

@@ -719,6 +719,13 @@ public class CrossChainResource {
 		if (refundRequest.atAddress == null || !Crypto.isValidAtAddress(refundRequest.atAddress))
 			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_ADDRESS);
 
+		if (refundRequest.receivingAccountInfo == null)
+			refundRequest.receivingAccountInfo = refundKey.getPubKeyHash();
+
+		if (refundRequest.receivingAccountInfo.length != 20)
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_PUBLIC_KEY);
+
+
 		// Extract data from cross-chain trading AT
 		try (final Repository repository = RepositoryManager.getRepository()) {
 			ATData atData = fetchAtDataWithChecking(repository, refundRequest.atAddress);
@@ -756,7 +763,7 @@ public class CrossChainResource {
 
 			Coin refundAmount = Coin.valueOf(p2shBalance - refundRequest.bitcoinMinerFee.unscaledValue().longValue());
 
-			org.bitcoinj.core.Transaction refundTransaction = BTCP2SH.buildRefundTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, lockTime);
+			org.bitcoinj.core.Transaction refundTransaction = BTCP2SH.buildRefundTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, lockTime, refundRequest.receivingAccountInfo);
 			boolean wasBroadcast = BTC.getInstance().broadcastTransaction(refundTransaction);
 
 			if (!wasBroadcast)

src/main/java/org/qortal/controller/TradeBot.java

@@ -980,7 +980,17 @@ public class TradeBot {
 		ECKey refundKey = ECKey.fromPrivate(tradeBotData.getTradePrivateKey());
 		List<TransactionOutput> fundingOutputs = BTC.getInstance().getUnspentOutputs(p2shAddress);
 
-		Transaction p2shRefundTransaction = BTCP2SH.buildRefundTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, crossChainTradeData.lockTimeB);
+
+		// Determine receive address for refund
+		String receiveAddress = BTC.getInstance().getUnusedReceiveAddress(tradeBotData.getXprv58());
+		if (receiveAddress == null) {
+			LOGGER.debug(() -> String.format("Couldn't determine a receive address for P2SH-B refund?"));
+			return;
+		}
+
+		Address receiving = Address.fromString(BTC.getInstance().getNetworkParameters(), receiveAddress);
+
+		Transaction p2shRefundTransaction = BTCP2SH.buildRefundTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, crossChainTradeData.lockTimeB, receiving.getHash());
 		if (!BTC.getInstance().broadcastTransaction(p2shRefundTransaction)) {
 			// We couldn't refund P2SH-B at this time
 			LOGGER.debug(() -> String.format("Couldn't broadcast P2SH-B refund transaction?"));
@@ -1025,7 +1035,16 @@ public class TradeBot {
 			return;
 		}
 
-		Transaction p2shRefundTransaction = BTCP2SH.buildRefundTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, tradeBotData.getLockTimeA());
+		// Determine receive address for refund
+		String receiveAddress = BTC.getInstance().getUnusedReceiveAddress(tradeBotData.getXprv58());
+		if (receiveAddress == null) {
+			LOGGER.debug(() -> String.format("Couldn't determine a receive address for P2SH-A refund?"));
+			return;
+		}
+
+		Address receiving = Address.fromString(BTC.getInstance().getNetworkParameters(), receiveAddress);
+
+		Transaction p2shRefundTransaction = BTCP2SH.buildRefundTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, tradeBotData.getLockTimeA(), receiving.getHash());
 		if (!BTC.getInstance().broadcastTransaction(p2shRefundTransaction)) {
 			// We couldn't refund P2SH-A at this time
 			LOGGER.debug(() -> String.format("Couldn't broadcast P2SH-A refund transaction?"));

src/main/java/org/qortal/crosschain/BTC.java

@@ -20,6 +20,7 @@ import org.bitcoinj.core.TransactionOutput;
 import org.bitcoinj.core.UTXO;
 import org.bitcoinj.core.UTXOProvider;
 import org.bitcoinj.core.UTXOProviderException;
+import org.bitcoinj.crypto.ChildNumber;
 import org.bitcoinj.crypto.DeterministicHierarchy;
 import org.bitcoinj.crypto.DeterministicKey;
 import org.bitcoinj.params.MainNetParams;
@@ -240,6 +241,89 @@ public class BTC {
 		return balance.value;
 	}
 
+	/**
+	 * Returns first unused receive address given 'm' BIP32 key.
+	 *
+	 * @param xprv58 BIP32 extended Bitcoin private key
+	 * @return Bitcoin P2PKH address, or null if something went wrong
+	 */
+	public String getUnusedReceiveAddress(String xprv58) {
+		Wallet wallet = Wallet.fromSpendingKeyB58(this.params, xprv58, DeterministicHierarchy.BIP32_STANDARDISATION_TIME_SECS);
+		DeterministicKeyChain keyChain = wallet.getActiveKeyChain();
+
+		keyChain.setLookaheadSize(WalletAwareUTXOProvider.LOOKAHEAD_INCREMENT);
+		keyChain.maybeLookAhead();
+
+		final int keyChainPathSize = keyChain.getAccountPath().size();
+		List<DeterministicKey> keys = new ArrayList<>(keyChain.getLeafKeys());
+
+		int ki = 0;
+		do {
+			for (; ki < keys.size(); ++ki) {
+				DeterministicKey dKey = keys.get(ki);
+				List<ChildNumber> dKeyPath = dKey.getPath();
+
+				// If keyChain is based on 'm', then make sure dKey is m/0/ki
+				if (dKeyPath.size() != keyChainPathSize + 2 || dKeyPath.get(dKeyPath.size() - 2) != ChildNumber.ZERO)
+					continue;
+
+				// Check unspent
+				Address address = Address.fromKey(this.params, dKey, ScriptType.P2PKH);
+				byte[] script = ScriptBuilder.createOutputScript(address).getProgram();
+
+				List<UnspentOutput> unspentOutputs = this.electrumX.getUnspentOutputs(script);
+				if (unspentOutputs == null)
+					return null;
+
+				/*
+				 * If there are no unspent outputs then either:
+				 * a) all the outputs have been spent
+				 * b) address has never been used
+				 * 
+				 * For case (a) we want to remember not to check this address (key) again.
+				 */
+
+				if (unspentOutputs.isEmpty()) {
+					// If this is a known key that has been spent before, then we can skip asking for transaction history
+					if (this.spentKeys.contains(dKey)) {
+						wallet.getActiveKeyChain().markKeyAsUsed((DeterministicKey) dKey);
+						continue;
+					}
+
+					// Ask for transaction history - if it's empty then key has never been used
+					List<byte[]> historicTransactionHashes = this.electrumX.getAddressTransactions(script);
+					if (historicTransactionHashes == null)
+						return null;
+
+					if (!historicTransactionHashes.isEmpty()) {
+						// Fully spent key - case (a)
+						this.spentKeys.add(dKey);
+						wallet.getActiveKeyChain().markKeyAsUsed(dKey);
+					} else {
+						// Key never been used - case (b)
+						return address.toString();
+					}
+				}
+
+				// Key has unspent outputs, hence used, so no good to us
+				this.spentKeys.remove(dKey);
+			}
+
+			// Generate some more keys
+			keyChain.setLookaheadSize(keyChain.getLookaheadSize() + WalletAwareUTXOProvider.LOOKAHEAD_INCREMENT);
+			keyChain.maybeLookAhead();
+
+			// This returns all keys, including those already in 'keys'
+			List<DeterministicKey> allLeafKeys = keyChain.getLeafKeys();
+			// Add only new keys onto our list of keys to search
+			List<DeterministicKey> newKeys = allLeafKeys.subList(ki, allLeafKeys.size());
+			keys.addAll(newKeys);
+			// Fall-through to checking more keys as now 'ki' is smaller than 'keys.size()' again
+
+			// Process new keys
+		} while (true);
+	}
+
 	// UTXOProvider support
 
 	static class WalletAwareUTXOProvider implements UTXOProvider {
@@ -320,6 +404,7 @@ public class BTC {
 					}
 
 					// If we reach here, then there's definitely at least one unspent key
+					btc.spentKeys.remove(key);
 					areAllKeysSpent = false;
 
 					for (UnspentOutput unspentOutput : unspentOutputs) {

src/main/java/org/qortal/crosschain/BTCP2SH.java

@@ -131,9 +131,10 @@ public class BTCP2SH {
 	 * @param fundingOutput output from transaction that funded P2SH address
 	 * @param redeemScriptBytes the redeemScript itself, in byte[] form
 	 * @param lockTime transaction nLockTime - must be at least locktime used in redeemScript
+	 * @param receivingAccountInfo Bitcoin PKH used for output
 	 * @return Signed Bitcoin transaction for refunding P2SH
 	 */
-	public static Transaction buildRefundTransaction(Coin refundAmount, ECKey refundKey, List<TransactionOutput> fundingOutputs, byte[] redeemScriptBytes, long lockTime) {
+	public static Transaction buildRefundTransaction(Coin refundAmount, ECKey refundKey, List<TransactionOutput> fundingOutputs, byte[] redeemScriptBytes, long lockTime, byte[] receivingAccountInfo) {
 		Function<byte[], Script> refundSigScriptBuilder = (txSigBytes) -> {
 			// Build scriptSig with...
 			ScriptBuilder scriptBuilder = new ScriptBuilder();
@@ -152,7 +153,7 @@ public class BTCP2SH {
 		};
 
 		// Send funds back to funding address
-		return buildP2shTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, lockTime, refundSigScriptBuilder, refundKey.getPubKeyHash());
+		return buildP2shTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, lockTime, refundSigScriptBuilder, receivingAccountInfo);
 	}
 
 	/**

src/test/java/org/qortal/test/btcacct/BtcTests.java

@@ -104,4 +104,17 @@ public class BtcTests extends Common {
 		assertEquals(balance, repeatBalance);
 	}
 
+	@Test
+	public void testGetUnusedReceiveAddress() {
+		BTC btc = BTC.getInstance();
+
+		String xprv58 = "tprv8ZgxMBicQKsPdahhFSrCdvC1bsWyzHHZfTneTVqUXN6s1wEtZLwAkZXzFP6TYLg2aQMecZLXLre5bTVGajEB55L1HYJcawpdFG66STVAWPJ";
+
+		String address = btc.getUnusedReceiveAddress(xprv58);
+
+		assertNotNull(address);
+
+		System.out.println(address);
+	}
+
 }

src/test/java/org/qortal/test/btcacct/Refund.java

@@ -186,7 +186,7 @@ public class Refund {
 			Coin refundAmount = Coin.valueOf(p2shBalance).subtract(bitcoinFee);
 			System.out.println(String.format("Spending %s of output, with %s as mining fee", BTC.format(refundAmount), BTC.format(bitcoinFee)));
 
-			Transaction redeemTransaction = BTCP2SH.buildRefundTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, lockTime);
+			Transaction redeemTransaction = BTCP2SH.buildRefundTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, lockTime, refundKey.getPubKeyHash());
 
 			byte[] redeemBytes = redeemTransaction.bitcoinSerialize();