From 5674853628b77a65a6d41d66809de865e79c98dc Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Fri, 13 Mar 2026 10:29:10 -0400
Subject: [PATCH] test: lock FileStore optimization boundaries

---
 .../FileStoreOptimizationGuardTests.cs        | 51 +++++++++++++++++++
 .../JetStream/Storage/StoreInterfaceTests.cs  | 18 +++++++
 .../JetStreamStoreIndexTests.cs               | 18 +++++++
 3 files changed, 87 insertions(+)
 create mode 100644 tests/NATS.Server.JetStream.Tests/JetStream/Storage/FileStoreOptimizationGuardTests.cs

diff --git a/tests/NATS.Server.JetStream.Tests/JetStream/Storage/FileStoreOptimizationGuardTests.cs b/tests/NATS.Server.JetStream.Tests/JetStream/Storage/FileStoreOptimizationGuardTests.cs
new file mode 100644
index 0000000..f04613e
--- /dev/null
+++ b/tests/NATS.Server.JetStream.Tests/JetStream/Storage/FileStoreOptimizationGuardTests.cs
@@ -0,0 +1,51 @@
+using NATS.Server.JetStream.Storage;
+
+namespace NATS.Server.JetStream.Tests.JetStream.Storage;
+
+public sealed class FileStoreOptimizationGuardTests
+{
+    [Fact]
+    public async Task Snapshot_round_trip_preserves_headers_and_payload_separately()
+    {
+        var srcDir = Directory.CreateTempSubdirectory();
+        var dstDir = Directory.CreateTempSubdirectory();
+
+        await using var src = new FileStore(new FileStoreOptions { Directory = srcDir.FullName });
+        var hdr = "NATS/1.0\r\nX-Test: two\r\n\r\n"u8.ToArray();
+        var msg = "payload-two"u8.ToArray();
+
+        var (seq, _) = src.StoreMsg("events.a", hdr, msg, 0L);
+        var snapshot = await src.CreateSnapshotAsync(default);
+
+        await using var dst = new FileStore(new FileStoreOptions { Directory = dstDir.FullName });
+        await dst.RestoreSnapshotAsync(snapshot, default);
+
+        var loaded = dst.LoadMsg(seq, null);
+        loaded.Header.ShouldNotBeNull();
+        loaded.Header.ShouldBe(hdr);
+        loaded.Data.ShouldNotBeNull();
+        loaded.Data.ShouldBe(msg);
+    }
+
+    [Fact]
+    public async Task PurgeEx_updates_last_by_subject_after_recovery()
+    {
+        var dir = Directory.CreateTempSubdirectory();
+
+        await using (var store = new FileStore(new FileStoreOptions { Directory = dir.FullName }))
+        {
+            store.StoreMsg("events.a", null, "one"u8.ToArray(), 0L);
+            store.StoreMsg("events.a", null, "two"u8.ToArray(), 0L);
+            store.StoreMsg("events.b", null, "other"u8.ToArray(), 0L);
+            store.PurgeEx("events.a", 0, 1);
+            await store.FlushAllPending();
+        }
+
+        await using var recovered = new FileStore(new FileStoreOptions { Directory = dir.FullName });
+        var last = await recovered.LoadLastBySubjectAsync("events.a", default);
+
+        last.ShouldNotBeNull();
+        last.Sequence.ShouldBe(2UL);
+        last.Payload.ToArray().ShouldBe("two"u8.ToArray());
+    }
+}
diff --git a/tests/NATS.Server.JetStream.Tests/JetStream/Storage/StoreInterfaceTests.cs b/tests/NATS.Server.JetStream.Tests/JetStream/Storage/StoreInterfaceTests.cs
index 8a0aa34..701bff9 100644
--- a/tests/NATS.Server.JetStream.Tests/JetStream/Storage/StoreInterfaceTests.cs
+++ b/tests/NATS.Server.JetStream.Tests/JetStream/Storage/StoreInterfaceTests.cs
@@ -532,4 +532,22 @@ public sealed class StoreInterfaceTests
         lastMsg = s.LoadLastMsg("foo", null);
         lastMsg.Sequence.ShouldBe(2UL);
     }
+
+    [Fact]
+    public void FileStore_LoadMsg_preserves_headers_separately_from_payload()
+    {
+        var dir = Directory.CreateTempSubdirectory();
+        using var store = new FileStore(new FileStoreOptions { Directory = dir.FullName });
+
+        var hdr = "NATS/1.0\r\nX-Test: one\r\n\r\n"u8.ToArray();
+        var msg = "payload"u8.ToArray();
+
+        var (seq, _) = store.StoreMsg("foo", hdr, msg, 0L);
+        var loaded = store.LoadMsg(seq, null);
+
+        loaded.Header.ShouldNotBeNull();
+        loaded.Header.ShouldBe(hdr);
+        loaded.Data.ShouldNotBeNull();
+        loaded.Data.ShouldBe(msg);
+    }
 }
diff --git a/tests/NATS.Server.JetStream.Tests/JetStreamStoreIndexTests.cs b/tests/NATS.Server.JetStream.Tests/JetStreamStoreIndexTests.cs
index 5c91d98..6cc12d0 100644
--- a/tests/NATS.Server.JetStream.Tests/JetStreamStoreIndexTests.cs
+++ b/tests/NATS.Server.JetStream.Tests/JetStreamStoreIndexTests.cs
@@ -15,4 +15,22 @@ public class JetStreamStoreIndexTests
         var last = await store.LoadLastBySubjectAsync("orders.created", default);
         last!.Payload.Span.SequenceEqual("3"u8).ShouldBeTrue();
     }
+
+    [Fact]
+    public async Task FileStore_trim_to_zero_preserves_high_water_mark_for_empty_state()
+    {
+        var dir = Directory.CreateTempSubdirectory();
+        await using var store = new FileStore(new FileStoreOptions { Directory = dir.FullName });
+
+        await store.AppendAsync("orders.created", "1"u8.ToArray(), default);
+        await store.AppendAsync("orders.updated", "2"u8.ToArray(), default);
+        await store.AppendAsync("orders.created", "3"u8.ToArray(), default);
+
+        store.TrimToMaxMessages(0);
+
+        var state = await store.GetStateAsync(default);
+        state.Messages.ShouldBe(0UL);
+        state.LastSeq.ShouldBe(3UL);
+        state.FirstSeq.ShouldBe(4UL);
+    }
 }