Provisional fix of double spending/agreeing

Before it was possible that a wallet was able to spend more money than it has. The cause were two pending distributed commits in the system at the same time. Since the wallets only update their ledger when the supervisor sends the commit message, they also agreed to the second request because their ledger was not updated. However, the second request could exceed the rest amount of FUCs in the ledger

src/main/java/fucoin/Main.java

@@ -18,7 +18,7 @@ import java.util.List;
 public class Main {
 
     private static int numberOfWallets = 2;
-    private static boolean createGUI = false;
+    private static boolean createGUI = true;
 
     private static ActorSystem cSystem;
 

src/main/java/fucoin/actions/transaction/ActionCommitDistributedCommittedTransfer.java

@@ -42,11 +42,6 @@ public class ActionCommitDistributedCommittedTransfer extends ClientAction {
         wallet.addLogMsg("ActionCommitDistributedCommittedTransfer is granted? " + granted);
         if (granted) {
 
-            Integer sourceAmount = wallet.amounts.getOrDefault(source, 0);
-            Integer targetAmount = wallet.amounts.getOrDefault(target, 0);
-            wallet.amounts.put(source, sourceAmount - amount);
-            wallet.amounts.put(target, targetAmount + amount);
-
             if (source.compareTo(self) == 0) {
                 wallet.setAmount(wallet.getAmount() - amount);
                 wallet.addTransactionLogMessageSuccess("Sent " + amount + " FUC to " + target.path().name());
@@ -58,6 +53,12 @@ public class ActionCommitDistributedCommittedTransfer extends ClientAction {
         } else {
             wallet.addLogMsg("abort transaction with id" + id);
 
+            // rollback
+            Integer sourceAmount = wallet.amounts.getOrDefault(source, 0);
+            Integer targetAmount = wallet.amounts.getOrDefault(target, 0);
+            wallet.amounts.put(source, sourceAmount + amount);
+            wallet.amounts.put(target, targetAmount - amount);
+
             if (source.compareTo(self) == 0) {
                 wallet.addTransactionLogMessageFail("Failed to send " + amount + " FUC to " + target.path().name() + " (Commit has not been granted)");
             }

src/main/java/fucoin/actions/transaction/ActionPrepareDistributedCommittedTransfer.java

@@ -32,6 +32,13 @@ public class ActionPrepareDistributedCommittedTransfer extends Transaction {
                         //sender have enough money
                         && wallet.amounts.getOrDefault(source, 0) >= amount));
 
+        // precautionly update own ledger to prevent double spending (respectively agreeing)
+        Integer sourceAmount = wallet.amounts.getOrDefault(source, 0);
+        Integer targetAmount = wallet.amounts.getOrDefault(target, 0);
+        wallet.amounts.put(source, sourceAmount - amount);
+        wallet.amounts.put(target, targetAmount + amount);
+
+
         sender.tell(new ActionPrepareDistributedCommittedTransferAnswer(source, target, amount, timestamp, granted, id), self);
     }