Restore Taiko FCU timestamp validation allowing equal timestamps

src/Nethermind/Nethermind.Merge.Plugin/Handlers/ForkchoiceUpdatedHandler.cs

@@ -288,7 +288,7 @@ protected virtual bool IsOnMainChainBehindHead(Block newHeadBlock, ForkchoiceSta
         return null;
     }
 
-    protected bool ArePayloadAttributesTimestampAndSlotNumberValid(Block newHeadBlock, ForkchoiceStateV1 forkchoiceState, PayloadAttributes payloadAttributes,
+    protected virtual bool ArePayloadAttributesTimestampAndSlotNumberValid(Block newHeadBlock, ForkchoiceStateV1 forkchoiceState, PayloadAttributes payloadAttributes,
         [NotNullWhen(false)] out ResultWrapper<ForkchoiceUpdatedV1Result>? errorResult)
     {
         if (newHeadBlock.Timestamp >= payloadAttributes.Timestamp)

src/Nethermind/Nethermind.Taiko.Test/TaikoEngineApiTests.cs

@@ -3,11 +3,13 @@
 
 using NUnit.Framework;
 using Nethermind.Core;
+using Nethermind.Consensus.Producers;
 using Nethermind.Merge.Plugin.Handlers;
 using System.Threading.Tasks;
 using Nethermind.Blockchain;
 using Nethermind.Consensus.Processing;
 using Nethermind.Consensus;
+using Nethermind.Core.Crypto;
 using Nethermind.Core.Specs;
 using Nethermind.Logging;
 using Nethermind.Merge.Plugin.BlockProduction;
@@ -68,4 +70,56 @@ static void AddBlock(IBlockTree blockTree, Block block)
             blockTree.HeadHash.Returns(block.Hash!);
         }
     }
+
+    [TestCase(100ul, 100ul, true, TestName = "Equal timestamps allowed for Pacaya")]
+    [TestCase(100ul, 101ul, true, TestName = "Greater timestamp allowed")]
+    [TestCase(100ul, 99ul, false, TestName = "Lesser timestamp rejected")]
+    public async Task Test_ForkchoiceUpdatedHandler_Allows_Equal_Timestamps(ulong headTimestamp, ulong payloadTimestamp, bool shouldSucceed)
+    {
+        IBlockTree blockTree = Substitute.For<IBlockTree>();
+
+        Block headBlock = Build.A.Block.WithNumber(1).WithTimestamp(headTimestamp).TestObject;
+
+        blockTree.FindBlock(headBlock.Hash!, BlockTreeLookupOptions.DoNotCreateLevelIfMissing).Returns(headBlock);
+        blockTree.GetInfo(headBlock.Number, headBlock.Hash!).Returns((new BlockInfo(headBlock.Hash!, 0) { WasProcessed = true }, new ChainLevelInfo(true)));
+        blockTree.Head.Returns(headBlock);
+        blockTree.HeadHash.Returns(headBlock.Hash!);
+        blockTree.IsMainChain(headBlock.Header).Returns(true);
+
+        TaikoForkchoiceUpdatedHandler handler = new(
+            blockTree,
+            Substitute.For<IManualBlockFinalizationManager>(),
+            Substitute.For<IPoSSwitcher>(),
+            Substitute.For<IPayloadPreparationService>(),
+            Substitute.For<IBlockProcessingQueue>(),
+            Substitute.For<IBlockCacheService>(),
+            Substitute.For<IInvalidChainTracker>(),
+            Substitute.For<IMergeSyncController>(),
+            Substitute.For<IBeaconPivot>(),
+            Substitute.For<IPeerRefresher>(),
+            Substitute.For<ISpecProvider>(),
+            Substitute.For<ISyncPeerPool>(),
+            new MergeConfig(),
+            Substitute.For<ILogManager>()
+        );
+
+        PayloadAttributes payloadAttributes = new()
+        {
+            Timestamp = payloadTimestamp,
+            PrevRandao = Keccak.Zero,
+            SuggestedFeeRecipient = Address.Zero
+        };
+
+        ForkchoiceStateV1 forkchoiceState = new(headBlock.Hash!, headBlock.Hash!, headBlock.Hash!);
+        ResultWrapper<ForkchoiceUpdatedV1Result> result = await handler.Handle(forkchoiceState, payloadAttributes, 1);
+
+        if (shouldSucceed)
+        {
+            Assert.That(result.Data.PayloadStatus.Status, Is.EqualTo(PayloadStatus.Valid));
+        }
+        else
+        {
+            Assert.That(result.Result.Error, Does.Contain("must be greater than or equal to"));
+        }
+    }
 }

src/Nethermind/Nethermind.Taiko/Rpc/TaikoForkchoiceUpdatedHandler.cs

@@ -77,6 +77,22 @@ protected override bool IsOnMainChainBehindHead(Block newHeadBlock, ForkchoiceSt
         return blockHeader;
     }
 
+    // Taiko Pacaya allows equal timestamps because multiple L2 blocks can be derived
+    // from a single L1 block, all sharing the same L1 anchor timestamp.
+    protected override bool ArePayloadAttributesTimestampAndSlotNumberValid(Block newHeadBlock, ForkchoiceStateV1 forkchoiceState, PayloadAttributes payloadAttributes,
+        [NotNullWhen(false)] out ResultWrapper<ForkchoiceUpdatedV1Result>? errorResult)
+    {
+        if (newHeadBlock.Timestamp > payloadAttributes.Timestamp)
+        {
+            string error = $"Payload timestamp {payloadAttributes.Timestamp} must be greater than or equal to block timestamp {newHeadBlock.Timestamp}.";
+            errorResult = ForkchoiceUpdatedV1Result.Error(error, MergeErrorCodes.InvalidPayloadAttributes);
+            return false;
+        }
+
+        errorResult = null;
+        return true;
+    }
+
     protected override bool TryGetBranch(Block newHeadBlock, out Block[] blocks)
     {
         // Allow resetting to any block already on the main chain (including genesis)