fix(KlerosCore): drawing iterations don't repeat

Author: unknownunknown1

Diff for: contracts/src/arbitration/KlerosCore.sol

@@ -64,6 +64,7 @@ contract KlerosCore is IArbitratorV2 {
         uint256 sumFeeRewardPaid; // Total sum of arbitration fees paid to coherent jurors as a reward in this round.
         uint256 sumPnkRewardPaid; // Total sum of PNK paid to coherent jurors as a reward in this round.
         IERC20 feeToken; // The token used for paying fees in this round.
+        uint256 drawIterations; // The number of iterations passed drawing the jurors for this round.
     }
 
     struct Juror {
@@ -609,11 +610,10 @@ contract KlerosCore is IArbitratorV2 {
 
         IDisputeKit disputeKit = disputeKitNodes[round.disputeKitID].disputeKit;
 
-        uint256 startIndex = round.drawnJurors.length;
-        uint256 endIndex = startIndex + _iterations <= round.nbVotes ? startIndex + _iterations : round.nbVotes;
-
-        for (uint256 i = startIndex; i < endIndex; i++) {
-            address drawnAddress = disputeKit.draw(_disputeID);
+        uint256 startIndex = round.drawIterations;
+        // TODO: cap the iterations?
+        for (uint256 i = startIndex; i < startIndex + _iterations; i++) {
+            address drawnAddress = disputeKit.draw(_disputeID, i);
             if (drawnAddress != address(0)) {
                 jurors[drawnAddress].lockedPnk += round.pnkAtStakePerJuror;
                 emit Draw(drawnAddress, _disputeID, currentRound, round.drawnJurors.length);
@@ -624,6 +624,7 @@ contract KlerosCore is IArbitratorV2 {
                 }
             }
         }
+        round.drawIterations += _iterations;
     }
 
     /// @dev Appeals the ruling of a specified dispute.

Diff for: contracts/src/arbitration/SortitionModule.sol

@@ -268,15 +268,15 @@ contract SortitionModule is ISortitionModule {
     /// Note that this function reverts if the sum of all values in the tree is 0.
     /// @param _key The key of the tree.
     /// @param _coreDisputeID Index of the dispute in Kleros Core.
-    /// @param _voteID ID of the voter.
+    /// @param _nonce Nonce to hash with random number.
     /// @return drawnAddress The drawn address.
     /// `O(k * log_k(n))` where
     /// `k` is the maximum number of children per node in the tree,
     ///  and `n` is the maximum number of nodes ever appended.
     function draw(
         bytes32 _key,
         uint256 _coreDisputeID,
-        uint256 _voteID
+        uint256 _nonce
     ) public view override returns (address drawnAddress) {
         require(phase == Phase.drawing, "Wrong phase.");
         SortitionSumTree storage tree = sortitionSumTrees[_key];
@@ -285,7 +285,7 @@ contract SortitionModule is ISortitionModule {
             return address(0); // No jurors staked.
         }
 
-        uint256 currentDrawnNumber = uint256(keccak256(abi.encodePacked(randomNumber, _coreDisputeID, _voteID))) %
+        uint256 currentDrawnNumber = uint256(keccak256(abi.encodePacked(randomNumber, _coreDisputeID, _nonce))) %
             tree.nodes[0];
 
         // While it still has children

Diff for: contracts/src/arbitration/dispute-kits/DisputeKitClassic.sol

@@ -181,9 +181,11 @@ contract DisputeKitClassic is BaseDisputeKit, IEvidence {
     /// @dev Draws the juror from the sortition tree. The drawn address is picked up by Kleros Core.
     /// Note: Access restricted to Kleros Core only.
     /// @param _coreDisputeID The ID of the dispute in Kleros Core.
+    /// @param _nonce Nonce of the drawing iteration.
     /// @return drawnAddress The drawn address.
     function draw(
-        uint256 _coreDisputeID
+        uint256 _coreDisputeID,
+        uint256 _nonce
     ) external override onlyByCore notJumped(_coreDisputeID) returns (address drawnAddress) {
         Dispute storage dispute = disputes[coreDisputeIDToLocal[_coreDisputeID]];
         Round storage round = dispute.rounds[dispute.rounds.length - 1];
@@ -193,7 +195,7 @@ contract DisputeKitClassic is BaseDisputeKit, IEvidence {
         bytes32 key = bytes32(uint256(courtID)); // Get the ID of the tree.
 
         // TODO: Handle the situation when no one has staked yet.
-        drawnAddress = sortitionModule.draw(key, _coreDisputeID, round.votes.length);
+        drawnAddress = sortitionModule.draw(key, _coreDisputeID, _nonce);
 
         if (_postDrawCheck(_coreDisputeID, drawnAddress)) {
             round.votes.push(Vote({account: drawnAddress, commit: bytes32(0), choice: 0, voted: false}));

Diff for: contracts/src/arbitration/dispute-kits/DisputeKitSybilResistant.sol

@@ -200,9 +200,11 @@ contract DisputeKitSybilResistant is BaseDisputeKit, IEvidence {
     /// @dev Draws the juror from the sortition tree. The drawn address is picked up by Kleros Core.
     /// Note: Access restricted to Kleros Core only.
     /// @param _coreDisputeID The ID of the dispute in Kleros Core.
+    /// @param _nonce Nonce of the drawing iteration.
     /// @return drawnAddress The drawn address.
     function draw(
-        uint256 _coreDisputeID
+        uint256 _coreDisputeID,
+        uint256 _nonce
     ) external override onlyByCore notJumped(_coreDisputeID) returns (address drawnAddress) {
         Dispute storage dispute = disputes[coreDisputeIDToLocal[_coreDisputeID]];
         Round storage round = dispute.rounds[dispute.rounds.length - 1];
@@ -212,7 +214,7 @@ contract DisputeKitSybilResistant is BaseDisputeKit, IEvidence {
         bytes32 key = bytes32(uint256(courtID)); // Get the ID of the tree.
 
         // TODO: Handle the situation when no one has staked yet.
-        drawnAddress = sortitionModule.draw(key, _coreDisputeID, round.votes.length);
+        drawnAddress = sortitionModule.draw(key, _coreDisputeID, _nonce);
 
         if (_postDrawCheck(_coreDisputeID, drawnAddress) && !round.alreadyDrawn[drawnAddress]) {
             round.votes.push(Vote({account: drawnAddress, commit: bytes32(0), choice: 0, voted: false}));

Diff for: contracts/src/arbitration/interfaces/IDisputeKit.sol

@@ -51,8 +51,9 @@ interface IDisputeKit {
     /// @dev Draws the juror from the sortition tree. The drawn address is picked up by Kleros Core.
     /// Note: Access restricted to Kleros Core only.
     /// @param _coreDisputeID The ID of the dispute in Kleros Core, not in the Dispute Kit.
+    /// @param _nonce Nonce.
     /// @return drawnAddress The drawn address.
-    function draw(uint256 _coreDisputeID) external returns (address drawnAddress);
+    function draw(uint256 _coreDisputeID, uint256 _nonce) external returns (address drawnAddress);
 
     // ************************************* //
     // *           Public Views            * //

Diff for: contracts/src/arbitration/interfaces/ISortitionModule.sol

@@ -24,7 +24,7 @@ interface ISortitionModule {
 
     function notifyRandomNumber(uint256 _drawnNumber) external;
 
-    function draw(bytes32 _court, uint256 _coreDisputeID, uint256 _voteID) external view returns (address);
+    function draw(bytes32 _court, uint256 _coreDisputeID, uint256 _nonce) external view returns (address);
 
     function preStakeHook(address _account, uint96 _courtID, uint256 _stake) external returns (preStakeHookResult);