Fix/fastheader stackoverflow (#7908)

Author: asdacap

src/Nethermind/Nethermind.Synchronization.Test/FastBlocks/FastHeadersSyncTests.cs

@@ -72,6 +72,47 @@ public async Task Can_prepare_3_requests_in_a_row()
         await feed.PrepareRequest();
     }
 
+    [Test]
+    public async Task Can_handle_forks_with_persisted_headers()
+    {
+        IBlockTree remoteBlockTree = CachedBlockTreeBuilder.OfLength(1000);
+        IBlockTree forkedBlockTree = Build.A.BlockTree().WithStateRoot(Keccak.Compute("1245")).OfChainLength(1000).TestObject;
+        BlockHeader pivotBlock = remoteBlockTree.FindHeader(999)!;
+
+        IBlockTree blockTree = Build.A.BlockTree().TestObject;
+        for (int i = 500; i < 1000; i++)
+        {
+            blockTree.Insert(forkedBlockTree.FindHeader(i)!).Should().Be(AddBlockResult.Added);
+        }
+
+        ISyncReport syncReport = Substitute.For<ISyncReport>();
+        syncReport.FastBlocksHeaders.Returns(new MeasuredProgress());
+        syncReport.HeadersInQueue.Returns(new MeasuredProgress());
+        HeadersSyncFeed feed = new(
+            blockTree: blockTree,
+            syncPeerPool: Substitute.For<ISyncPeerPool>(),
+            syncConfig: new TestSyncConfig
+            {
+                FastSync = true,
+                PivotNumber = pivotBlock.Number.ToString(),
+                PivotHash = pivotBlock.Hash!.ToString(),
+                PivotTotalDifficulty = pivotBlock.TotalDifficulty.ToString()!,
+            },
+            syncReport: syncReport,
+            logManager: LimboLogs.Instance);
+
+        feed.InitializeFeed();
+        while (true)
+        {
+            var batch = await feed.PrepareRequest();
+            if (batch is null) break;
+            batch.Response = remoteBlockTree.FindHeaders(
+                remoteBlockTree.FindHeader(batch.StartNumber, BlockTreeLookupOptions.None)!.Hash!, batch.RequestSize, 0,
+                false)!;
+            feed.HandleResponse(batch);
+        }
+    }
+
     [Test]
     public async Task When_next_header_hash_update_is_delayed_do_not_drop_peer()
     {

src/Nethermind/Nethermind.Synchronization/FastBlocks/FastHeadersSyncFeed.cs

@@ -476,9 +476,9 @@ private static HeadersSyncBatch BuildDependentBatch(HeadersSyncBatch batch, long
             return dependentBatch;
         }
 
-        private void EnqueueBatch(HeadersSyncBatch batch)
+        private void EnqueueBatch(HeadersSyncBatch batch, bool skipPersisted = false)
         {
-            HeadersSyncBatch? left = ProcessPersistedPortion(batch);
+            HeadersSyncBatch? left = skipPersisted ? batch : ProcessPersistedPortion(batch);
             if (left is not null)
             {
                 _pending.Enqueue(batch);
@@ -638,7 +638,7 @@ protected virtual int InsertHeaders(HeadersSyncBatch batch)
                 {
                     batch.Response?.Dispose();
                     batch.Response = null;
-                    EnqueueBatch(batch);
+                    EnqueueBatch(batch, true);
                 }
                 else
                 {
@@ -733,7 +733,7 @@ bool ValidateFirstHeader(BlockHeader header)
 
                     if (_dependencies.ContainsKey(header.Number))
                     {
-                        EnqueueBatch(batch);
+                        EnqueueBatch(batch, true);
                         throw new InvalidOperationException($"Only one header dependency expected ({batch})");
                     }
                     long lastNumber = -1;