feat: add per-client trace mode flag with dynamic parser logger

src/NATS.Server/ClientFlags.cs

@@ -15,6 +15,7 @@ public enum ClientFlags
     WriteLoopStarted = 1 << 4,
     IsSlowConsumer = 1 << 5,
     ConnectProcessFinished = 1 << 6,
+    TraceMode = 1 << 7,
 }
 
 /// <summary>

src/NATS.Server/NatsClient.cs

@@ -54,6 +54,20 @@ public sealed class NatsClient : IDisposable
     public bool ConnectReceived => _flags.HasFlag(ClientFlags.ConnectReceived);
     public ClientClosedReason CloseReason { get; private set; }
 
+    public void SetTraceMode(bool enabled)
+    {
+        if (enabled)
+        {
+            _flags.SetFlag(ClientFlags.TraceMode);
+            _parser.Logger = _logger;
+        }
+        else
+        {
+            _flags.ClearFlag(ClientFlags.TraceMode);
+            _parser.Logger = _options.Trace ? _logger : null;
+        }
+    }
+
     public DateTime StartTime { get; }
     private long _lastActivityTicks;
     public DateTime LastActivity => new(Interlocked.Read(ref _lastActivityTicks), DateTimeKind.Utc);

src/NATS.Server/Protocol/NatsParser.cs

@@ -36,7 +36,8 @@ public sealed class NatsParser
 {
     private static readonly byte[] CrLfBytes = "\r\n"u8.ToArray();
     private readonly int _maxPayload;
-    private readonly ILogger? _logger;
+    private ILogger? _logger;
+    public ILogger? Logger { set => _logger = value; }
 
     // State for split-packet payload reading
     private bool _awaitingPayload;

tests/NATS.Server.Tests/ClientTraceModeTests.cs

@@ -0,0 +1,15 @@
+namespace NATS.Server.Tests;
+
+public class ClientTraceModeTests
+{
+    [Fact]
+    public void TraceMode_flag_can_be_set_and_cleared()
+    {
+        var holder = new ClientFlagHolder();
+        holder.HasFlag(ClientFlags.TraceMode).ShouldBeFalse();
+        holder.SetFlag(ClientFlags.TraceMode);
+        holder.HasFlag(ClientFlags.TraceMode).ShouldBeTrue();
+        holder.ClearFlag(ClientFlags.TraceMode);
+        holder.HasFlag(ClientFlags.TraceMode).ShouldBeFalse();
+    }
+}