[bisq-network/bisq] Apply rule to not allow BSQ outputs after BTC output for regular txs (#3413)

[sqrrm]

sqrrm commented on this pull request.



>          daoKillSwitch.assertDaoIsNotDisabled();
-        final Transaction tx = new Transaction(params);
-        addInputsAndChangeOutputForTx(tx, fee, bsqCoinSelector, requireChangeOutput);
-        // printTx("getPreparedFeeTx", tx);
-        return tx;
+
+        Transaction tx = new Transaction(params);
+        // We look for inputs covering out BSQ fee we want to pay.
+        CoinSelection coinSelection = bsqCoinSelector.select(fee, wallet.calculateAllSpendCandidates());

It would be better to include the dust here in the initial coin selection since it is a requirement that it's included. Then there is no need to do a double take when this initial selection wasn't enough.

> +                            return false;
+                        }
+
+                        // Burned BSQ output is last output before opReturn.
+                        // We could have also a BSQ change output as last output before opReturn but that will
+                        // be detected at blindVoteFee check.
+                        // We always have the BSQ change before the burned BSQ output if both are present.
+                        checkArgument(optionalOpReturnIndex.isPresent());
+                        if (index != optionalOpReturnIndex.get() - 1) {
+                            return false;
+                        }
+
+                        // Without checking the fee we would not be able to distinguish between 2 structurally same transactions, one
+                        // where the output is burned BSQ and one where it is a BSQ change output.
+                        long blindVoteFee = daoStateService.getParamValueAsCoin(Param.BLIND_VOTE_FEE, tempTxOutput.getBlockHeight()).value;
+                        return availableInputValue == blindVoteFee;

What happens with a vote that's using the wrong fee. It would set this output to BSQ, but would it fail to register as a valid vote?

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