Adds protection against DApps with same id

contracts/DAppStore.sol

@@ -41,6 +41,7 @@ contract DAppStore is ApproveAndCallFallBack, BancorFormula {
     
     Data[] public dapps;
     mapping(bytes32 => uint) public id2index;
+    mapping(bytes32 => bool) existingIDs;
     
     event DAppCreated(bytes32 indexed id, uint votesMint, uint amount);
     event Upvote(bytes32 indexed id, uint newEffectiveBalance);
@@ -231,6 +232,8 @@ contract DAppStore is ApproveAndCallFallBack, BancorFormula {
     }
 
     function _createDApp(address _from, bytes32 _id, uint _amount) internal {
+        require(!existingIDs[_id], "You must submit a unique ID");
+        
         require(_amount > 0, "You must spend some SNT to submit a ranking in order to avoid spam");
         require (_amount < safeMax, "You cannot stake more SNT than the ceiling dictates");
         
@@ -260,6 +263,7 @@ contract DAppStore is ApproveAndCallFallBack, BancorFormula {
         d.effectiveBalance = _amount;
 
         id2index[_id] = dappIdx;
+        existingIDs[_id] = true;
 
         require(SNT.allowance(_from, address(this)) >= _amount, "Not enough SNT allowance");
         require(SNT.transferFrom(_from, address(this), _amount), "Transfer failed");

test/dappstore_spec.js

@@ -87,6 +87,21 @@ contract("DAppStore", function () {
     assert.strictEqual(amount, parseInt(receipt.effectiveBalance, 10));
   })
 
+  it("should not create a new DApp with the same ID", async function () {
+    let id = "0x7465737400000000000000000000000000000000000000000000000000000000";
+    let amount = 1000;
+
+    await SNT.methods.generateTokens(accounts[0], amount).send();
+    const encodedCall = DAppStore.methods.createDApp(id,amount).encodeABI();
+
+    try {
+      await SNT.methods.approveAndCall(DAppStore.options.address, amount, encodedCall).send({from: accounts[0]});
+      assert.fail('should have reverted before');
+    } catch (error) {
+      TestUtils.assertJump(error);
+    }
+  })
+
   it("should not create a new DApp when exceeding the ceiling or staking nothing", async function () {
     let id = "0x7465737400000000000000000000000000000000000000000000000000000000";
     let initial = await DAppStore.methods.max().call();