add batch size check in rollup contract

ethereum/contracts/Rollup.sol

@@ -8,10 +8,10 @@ contract Rollup is Availability {
     constructor(DAO dao) Availability(dao) {}
 
     struct BatchItem {
-        address worker;
+        address author;
         uint stakeAmount;
         uint fee;
-        string evidenceContentId;
+        string postId;
     }
 
     mapping(uint => BatchItem) items;
@@ -19,22 +19,29 @@ contract Rollup is Availability {
     address batchWorker;
     uint batchWorkerStakeIndex;
 
+    /// Instead of initiating a validation pool, call this method to include
+    /// the stakes and fee in the next batch validation pool
     function addItem(
-        address worker,
+        address author,
         uint stakeAmount,
-        string calldata evidenceContentId
+        string calldata postId
     ) public payable {
         BatchItem storage item = items[itemCount++];
-        item.worker = worker;
+        item.author = author;
         item.stakeAmount = stakeAmount;
         item.fee = msg.value;
-        item.evidenceContentId = evidenceContentId;
+        item.postId = postId;
     }
 
+    /// To be called by the currently assigned batch worker,
+    /// If no batch worker has been assigned this may be called by anybody,
+    /// but it will only succeed if it is able to assign a new worker.
     function submitBatch(
         string calldata batchPostId,
+        uint batchSize,
         uint poolDuration
-    ) public {
+    ) public returns (uint poolIndex) {
+        require(batchSize <= itemCount, "Batch size too large");
         if (batchWorker != address(0)) {
             require(
                 msg.sender == batchWorker,
@@ -46,7 +53,7 @@ contract Rollup is Availability {
         for (uint i = 0; i < itemCount; i++) {
             fee += items[i].fee;
         }
-        uint poolIndex = dao.initiateValidationPool{value: fee}(
+        poolIndex = dao.initiateValidationPool{value: fee}(
             batchPostId,
             poolDuration,
             [uint256(1), uint256(3)],
@@ -60,20 +67,31 @@ contract Rollup is Availability {
         for (uint i = 0; i < itemCount; i++) {
             dao.delegatedStakeOnValidationPool(
                 poolIndex,
-                items[i].worker,
+                items[i].author,
                 items[i].stakeAmount,
                 true
             );
         }
         // Include availability stakes from the batch worker
-        dao.delegatedStakeOnValidationPool(
-            poolIndex,
-            batchWorker,
-            stakes[batchWorkerStakeIndex].amount,
-            true
-        );
-        // Reset item count so we can start the next batch
-        itemCount = 0;
+        if (batchWorker != address(0)) {
+            dao.delegatedStakeOnValidationPool(
+                poolIndex,
+                batchWorker,
+                stakes[batchWorkerStakeIndex].amount,
+                true
+            );
+        }
+        if (batchSize < itemCount) {
+            // Some items were added after this batch was computed.
+            // Keep them in the queue to be included in the next batch.
+            for (uint i = 0; i < itemCount - batchSize; i++) {
+                items[i] = items[batchSize + i];
+            }
+            itemCount = itemCount - batchSize;
+        } else {
+            // Reset item count so we can start the next batch
+            itemCount = 0;
+        }
         // Select the next worker
         batchWorkerStakeIndex = assignWork();
         batchWorker = stakes[batchWorkerStakeIndex].worker;