Fix taker use all BSQ for fee payment

core/src/main/java/bisq/core/btc/wallet/BsqWalletService.java

@@ -694,6 +694,7 @@ private void addInputsAndChangeOutputForTx(Transaction tx,
         coinSelection.gathered.forEach(tx::addInput);
         try {
             Coin change = bsqCoinSelector.getChange(fee, coinSelection);
+            // Change can be ZERO, then no change output is created so don't rely on a BSQ change output
             if (change.isPositive()) {
                 checkArgument(Restrictions.isAboveDust(change),
                         "The change output of " + change.value / 100d + " BSQ is below the min. dust value of "

core/src/main/java/bisq/core/btc/wallet/TradeWalletService.java

@@ -58,6 +58,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
 import java.util.stream.Collectors;
 
 import org.slf4j.Logger;
@@ -219,25 +220,31 @@ public Transaction completeBsqTradingFeeTx(Transaction preparedBsqTx,
         // outputs [0-1] BTC change output
         // mining fee: BTC mining fee + burned BSQ fee
 
-        // In case of txs for burned BSQ fees we have no receiver output and it might be that there are no change outputs
+        // In case all BSQ were burnt as fees we have no receiver output and it might be that there are no change outputs
         // We need to guarantee that min. 1 valid output is added (OP_RETURN does not count). So we use a higher input
         // for BTC to force an additional change output.
 
         final int preparedBsqTxInputsSize = preparedBsqTx.getInputs().size();
-
-
+        final boolean hasBsqOutputs = !preparedBsqTx.getOutputs().isEmpty();
+
+        // If there are no BSQ change outputs an output larger than the burnt BSQ amount has to be added as the first
+        // output to make sure the reserved funds are in output 1, deposit tx input creation depends on the reserve
+        // being output 1. The amount has to be larger than the BSQ input to make sure the inputs get burnt.
+        // The BTC changeAddress is used, so it might get used for both output 0 and output 2.
+        if (!hasBsqOutputs) {
+            var bsqInputValue = preparedBsqTx.getInputs().stream()
+                    .map(TransactionInput::getValue)
+                    .reduce(Coin.valueOf(0), Coin::add);
+
+            preparedBsqTx.addOutput(bsqInputValue.add(Coin.valueOf(1)), changeAddress);
+        }
         // the reserved amount we need for the trade we send to our trade reservedForTradeAddress
         preparedBsqTx.addOutput(reservedFundsForOffer, reservedForTradeAddress);
 
         // we allow spending of unconfirmed tx (double spend risk is low and usability would suffer if we need to
         // wait for 1 confirmation)
         // In case of double spend we will detect later in the trade process and use a ban score to penalize bad behaviour (not impl. yet)
 
-        // If BSQ trade fee > reservedFundsForOffer we would create a BSQ output instead of a BTC output.
-        // As the min. reservedFundsForOffer is 0.001 BTC which is 1000 BSQ this is an unrealistic scenario and not
-        // handled atm (if BTC price is 1M USD and BSQ price is 0.1 USD, then fee would be 10% which still is unrealistic).
-
-        // WalletService.printTx("preparedBsqTx", preparedBsqTx);
         SendRequest sendRequest = SendRequest.forTx(preparedBsqTx);
         sendRequest.shuffleOutputs = false;
         sendRequest.aesKey = aesKey;
@@ -335,6 +342,8 @@ OUT[0] dummyOutputAmount (inputAmount - tx fee)
 
         // We created the take offer fee tx in the structure that the second output is for the funds for the deposit tx.
         TransactionOutput reservedForTradeOutput = takeOfferFeeTx.getOutputs().get(1);
+        checkArgument(reservedForTradeOutput.getValue().equals(inputAmount),
+                "Reserve amount does not equal input amount");
         dummyTX.addInput(reservedForTradeOutput);
 
         WalletService.removeSignatures(dummyTX);

core/src/main/java/bisq/core/trade/protocol/tasks/buyer_as_taker/BuyerAsTakerCreatesDepositTxInputs.java

@@ -42,19 +42,14 @@ protected void run() {
         try {
             runInterceptHook();
 
-            // In case we pay the taker fee in bsq we reduce tx fee by that as the burned bsq satoshis goes to miners.
-            Coin bsqTakerFee = trade.isCurrencyForTakerFeeBtc() ? Coin.ZERO : trade.getTakerFee();
-
             Coin txFee = trade.getTxFee();
             Coin takerInputAmount = checkNotNull(trade.getOffer()).getBuyerSecurityDeposit()
                     .add(txFee)
-                    .add(txFee)
-                    .subtract(bsqTakerFee);
-            Coin fee = txFee.subtract(bsqTakerFee);
+                    .add(txFee);
             InputsAndChangeOutput result = processModel.getTradeWalletService().takerCreatesDepositTxInputs(
                     processModel.getTakeOfferFeeTx(),
                     takerInputAmount,
-                    fee);
+                    txFee);
             processModel.setRawTransactionInputs(result.rawTransactionInputs);
             processModel.setChangeOutputValue(result.changeOutputValue);
             processModel.setChangeOutputAddress(result.changeOutputAddress);