feat: add protocol tracing (<<- op arg) at LogLevel.Trace

src/NATS.Server/Protocol/NatsParser.cs

@@ -1,5 +1,6 @@
 using System.Buffers;
 using System.Text;
+using Microsoft.Extensions.Logging;
 
 namespace NATS.Server.Protocol;
 
@@ -35,6 +36,7 @@ public sealed class NatsParser
 {
     private static readonly byte[] CrLfBytes = "\r\n"u8.ToArray();
     private readonly int _maxPayload;
+    private readonly ILogger? _logger;
 
     // State for split-packet payload reading
     private bool _awaitingPayload;
@@ -44,9 +46,20 @@ public sealed class NatsParser
     private int _pendingHeaderSize;
     private CommandType _pendingType;
 
-    public NatsParser(int maxPayload = NatsProtocol.MaxPayloadSize)
+    public NatsParser(int maxPayload = NatsProtocol.MaxPayloadSize, ILogger? logger = null)
     {
         _maxPayload = maxPayload;
+        _logger = logger;
+    }
+
+    private void TraceInOp(string op, ReadOnlySpan<byte> arg = default)
+    {
+        if (_logger == null || !_logger.IsEnabled(LogLevel.Trace))
+            return;
+        if (arg.IsEmpty)
+            _logger.LogTrace("<<- {Op}", op);
+        else
+            _logger.LogTrace("<<- {Op} {Arg}", op, Encoding.ASCII.GetString(arg));
     }
 
     public bool TryParse(ref ReadOnlySequence<byte> buffer, out ParsedCommand command)
@@ -91,6 +104,7 @@ public sealed class NatsParser
                 {
                     command = ParsedCommand.Simple(CommandType.Ping);
                     buffer = buffer.Slice(reader.Position);
+                    TraceInOp("PING");
                     return true;
                 }
 
@@ -98,6 +112,7 @@ public sealed class NatsParser
                 {
                     command = ParsedCommand.Simple(CommandType.Pong);
                     buffer = buffer.Slice(reader.Position);
+                    TraceInOp("PONG");
                     return true;
                 }
 
@@ -121,6 +136,7 @@ public sealed class NatsParser
                 {
                     command = ParseSub(lineSpan);
                     buffer = buffer.Slice(reader.Position);
+                    TraceInOp("SUB", lineSpan[4..]);
                     return true;
                 }
 
@@ -131,6 +147,7 @@ public sealed class NatsParser
                 {
                     command = ParseUnsub(lineSpan);
                     buffer = buffer.Slice(reader.Position);
+                    TraceInOp("UNSUB", lineSpan[6..]);
                     return true;
                 }
 
@@ -141,6 +158,7 @@ public sealed class NatsParser
                 {
                     command = ParseConnect(lineSpan);
                     buffer = buffer.Slice(reader.Position);
+                    TraceInOp("CONNECT");
                     return true;
                 }
 
@@ -151,6 +169,7 @@ public sealed class NatsParser
                 {
                     command = ParseInfo(lineSpan);
                     buffer = buffer.Slice(reader.Position);
+                    TraceInOp("INFO");
                     return true;
                 }
 
@@ -159,11 +178,13 @@ public sealed class NatsParser
             case (byte)'+': // +OK
                 command = ParsedCommand.Simple(CommandType.Ok);
                 buffer = buffer.Slice(reader.Position);
+                TraceInOp("+OK");
                 return true;
 
             case (byte)'-': // -ERR
                 command = ParsedCommand.Simple(CommandType.Err);
                 buffer = buffer.Slice(reader.Position);
+                TraceInOp("-ERR");
                 return true;
         }
 
@@ -215,6 +236,7 @@ public sealed class NatsParser
         _pendingHeaderSize = -1;
         _pendingType = CommandType.Pub;
 
+        TraceInOp("PUB", argsSpan);
         return TryReadPayload(ref buffer, out command);
     }
 
@@ -264,6 +286,7 @@ public sealed class NatsParser
         _pendingHeaderSize = hdrSize;
         _pendingType = CommandType.HPub;
 
+        TraceInOp("HPUB", argsSpan);
         return TryReadPayload(ref buffer, out command);
     }