Adding some basic fucntions

contracts/ExitHandler.sol

@@ -181,6 +181,64 @@ contract ExitHandler is DepositHandler {
     exitDuration = _exitDuration;
   }
 
+  function startLimboExit(
+    bytes memory limboTxData, bytes32 signature, uint8 _outputIndex,
+    bytes memory depositTxData, bytes memory depositProof
+  ) public payable {
+    // Transaction is from A to B
+    // B will have to pay exitStake 
+    require(msg.value >= exitStake, "Not enough ether sent to pay for exit stake");
+    TxLib.Tx memory transferTx = TxLib.parseTx(limboTxData);
+    TxLib.Output memory out = transferTx.outs[_outputIndex];
+
+    // check if B has the right to do the exit for A or not
+    bytes32 sigHash = TxLib.getSigHash(limboTxData);
+    require(sigHash == signature);
+
+
+    // isWellDecodedTransaction();
+    bytes32 limboTxHash = keccak256(limboTxData);
+
+    bytes32 utxoId = bytes32(uint256(_outputIndex) << 120 | uint120(uint256(limboTxHash)));
+    uint256 priority;
+
+    require(depositProof.length > 0, "Not a limbo exit");
+
+    // check youngest input tx inclusion in the root chain block
+    bytes32 depositTxHash;
+    (txPos, depositTxHash,) = TxLib.validateProof(96, depositProof);
+    require(
+      depositTxHash == transferTx.ins[*].outpoint.hash, 
+      "Input from the proof is not referenced in transfer tx"
+    );
+
+    if (isNft(out.color)) {
+      priority = (nftExitCounter << 128) | uint128(uint256(utxoId));
+      nftExitCounter++;
+    } else {      
+      priority = getERC20ExitPriority(*, utxoId, txPos);
+    }
+
+    exits[utxoId] = Exit({
+      owner: out.owner,
+      color: out.color,
+      amount: out.value,
+      finalized: false,
+      stake: exitStake,
+      priorityTimestamp: timestamp
+    });
+    emit ExitStarted(
+      limboTxHash, 
+      _outputIndex, 
+      out.color, 
+      out.owner, 
+      out.value
+    );
+
+    tokens[out.color].insert(priority);
+
+  }
+
   function startExit(
     bytes32[] memory _youngestInputProof, bytes32[] memory _proof,
     uint8 _outputIndex, uint8 _inputIndex
@@ -320,6 +378,46 @@ contract ExitHandler is DepositHandler {
     exits[utxoId].finalized = true;
   }
 
+  function challengeLimboExit(
+    bytes32 utxoId,
+    bytes  spendTxData
+  ) public payable {
+    require(msg.value >= exitStake, "Not enough ether sent to pay for exit stake");
+    TxLib.Tx memory spendTx = TxLib.parseTx(spendTxData);
+    TxLib.Output memory out = spendTx.outs[0];
+    // uint256 offset = 32 * (spendProof.length + 2);
+    // bytes32 txHash0;
+    // bytes memory txData0;
+    // (, txHash0, txData0) = TxLib.validateProof(offset + 64, transferProof);
+    // bytes32 utxoId = bytes32(uint256(_outputIndex) << 120 | uint120(uint256(txHash0)));
+
+    Exit memory limboExit = exits[utxoId]
+    require(limboExit.isLimbo == true);
+
+    // require(testProof.length > 0, "Challenger failed to provide validated txn");
+
+    // bytes32 txHash;
+    // (, txHash, txData) = TxLib.validateProof(96, testProof);
+    // txn = TxLib.parseTx(txData);
+
+    // // check if A is trying to use the coin again
+    // // check if B is sending that coin to someone else
+
+    // // make sure one is spending the other one
+    // require(txHash0 == txn.ins[_inputIndex].outpoint.hash);
+    // require(0 == spendTx.ins[0].outpoint.pos);
+
+    // //If transfer then make sure signature is correct
+    // bytes32 sigHash = TxLib.getSigHash(txData);
+    // address signer = ecrecover(
+    //   sigHash, 
+    //   txn.ins[_inputIndex].v, 
+    //   txn.ins[_inputIndex].r, 
+    //   txn.ins[_inputIndex].s
+    // );
+    //   require(exits[utxoId].owner == signer);
+  }
+
   function challengeExit(
     bytes32[] memory _proof, 
     bytes32[] memory _prevProof, 

test/exitHandler.js

@@ -147,6 +147,33 @@ contract('ExitHandler', (accounts) => {
         assert(aliceBalanceBefore.add(new BN(50)).eq(aliceBalanceAfter));
       });
 
+      it('Should allow to limbo exit', async () => {
+        const period = await submitNewPeriod(depositTx);
+        const depositProof = period.proof(depositTx);
+        const outputIndex = 1;
+        const exitStake = exitHandler.exitStake;
+
+        // transaction hash + constant signed by alice
+        const signature = (transferTx + c).sign(alicePriv);
+
+        const inTxData = Tx.parseToParams(transferTx);
+
+        // Bob will start the exit for Alice
+        await exitHandler.startLimboExit(inTxData, signature, outputIndex, 
+          depositTx, depositProof, {from: bob, value: exitStake});
+
+        const aliceBalanceBefore = await nativeToken.balanceOf(alice);
+
+        const exitTime = (await time.latest()) + (2 * time.duration.seconds(exitDuration));
+        await time.increaseTo(exitTime);
+
+        await exitHandler.finalizeTopExit(nativeTokenColor);
+
+        const aliceBalanceAfter = await nativeToken.balanceOf(alice);
+
+        assert(aliceBalanceBefore.add(new BN(50)).eq(aliceBalanceAfter));
+      });
+
       it('Should allow to exit deposit utxo', async () => {
         const period = await submitNewPeriod([depositTx]);
 
@@ -303,6 +330,51 @@ contract('ExitHandler', (accounts) => {
 
       });
 
+      it('Should allow to challenge limbo exit and prevent it', async () => {
+        // utxo that will have spend exit utxo
+        const period = await submitNewPeriod(depositTx);
+        const spendTx = Tx.transfer(
+          [new Input(new Outpoint(transferTx.hash(), 0))],
+          [new Output(50, charlie)]
+        ).sign([bobPriv]);
+
+        const depositProof = period.proof(depositTx);
+        const outputIndex = 1;
+        const exitStake = exitHandler.exitStake;
+
+        const signature = (transferTx + c).sign(alicePriv);
+        const inTxData = Tx.parseToParams(transferTx);
+        const spendTxData = Tx.parseToParams(spendTx);
+
+        // withdraw output
+        const event = await exitHandler.startLimboExit(inTxData, signature, outputIndex, 
+          depositTx, depositProof, {from: bob, value: exitStake});
+
+        const utxoId = exitUtxoId(event);
+
+        // challenge exit and make sure exit is removed
+        assert.equal((await exitHandler.exits(utxoId))[2], bob);
+        await exitHandler.challengeLimboExit(utxoId, spendTxData);
+
+        const bal1 = await nativeToken.balanceOf(bob);
+        const bal3 = await nativeToken.balanceOf(alice);
+
+        const exitTime = (await time.latest()) + (2 * time.duration.seconds(exitDuration));
+        await time.increaseTo(exitTime);
+
+        await exitHandler.finalizeTopExit(0);
+
+        const bal2 = await nativeToken.balanceOf(bob);
+        const bal4 = await nativeToken.balanceOf(alice);
+        // check transfer didn't happen
+        assert.equal(bal1.toNumber(), bal2.toNumber());
+        assert.equal(bal3.toNumber(), bal4.toNumber());
+
+        // check exit was evicted from PriorityQueue
+        assert.equal((await exitHandler.tokens(0))[1], 0);
+
+      });
+
       it('Should allow to challenge exit by verified tx', async () => {
         transferTx = Tx.transfer(
           [new Input(new Outpoint(depositTx.hash(), 0))],