From ae043136a1f29331f806e01db72e88aa99bd9885 Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Mon, 23 Feb 2026 04:30:36 -0500
Subject: [PATCH] fix: address lexer code review findings (newline handling,
 emit cleanup, null guard)

---
 .../Configuration/NatsConfLexer.cs            | 21 ++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/NATS.Server/Configuration/NatsConfLexer.cs b/src/NATS.Server/Configuration/NatsConfLexer.cs
index 8f878fb..2a17cab 100644
--- a/src/NATS.Server/Configuration/NatsConfLexer.cs
+++ b/src/NATS.Server/Configuration/NatsConfLexer.cs
@@ -61,6 +61,7 @@ public sealed class NatsConfLexer
 
     public static IReadOnlyList<Token> Tokenize(string input)
     {
+        ArgumentNullException.ThrowIfNull(input);
         var lx = new NatsConfLexer(input);
         LexState? state = LexTop;
         while (state is not null)
@@ -85,7 +86,17 @@ public sealed class NatsConfLexer
 
     private void Emit(TokenType type)
     {
-        var val = string.Concat(_stringParts) + _input[_start.._pos];
+        string val;
+        if (_stringParts.Count > 0)
+        {
+            val = string.Concat(_stringParts) + _input[_start.._pos];
+            _stringParts.Clear();
+        }
+        else
+        {
+            val = _input[_start.._pos];
+        }
+
         var pos = _pos - _ilstart - val.Length;
         _items.Add(new Token(type, val, _line, pos));
         _start = _pos;
@@ -660,7 +671,7 @@ public sealed class NatsConfLexer
     private static LexState? LexKeyEnd(NatsConfLexer lx)
     {
         var r = lx.Next();
-        if (char.IsWhiteSpace(r) && !IsNL(r))
+        if (char.IsWhiteSpace(r))
         {
             return LexSkip(lx, LexKeyEnd);
         }
@@ -961,7 +972,7 @@ public sealed class NatsConfLexer
     private static LexState? LexMapKeyEnd(NatsConfLexer lx)
     {
         var r = lx.Next();
-        if (char.IsWhiteSpace(r) && !IsNL(r))
+        if (char.IsWhiteSpace(r))
         {
             return LexSkip(lx, LexMapKeyEnd);
         }
@@ -1239,13 +1250,13 @@ public sealed class NatsConfLexer
     private static LexState? LexStringBinary(NatsConfLexer lx)
     {
         var r1 = lx.Next();
-        if (IsNL(r1))
+        if (IsNL(r1) || r1 == Eof)
         {
             return lx.Errorf("Expected two hexadecimal digits after '\\x', but hit end of line");
         }
 
         var r2 = lx.Next();
-        if (IsNL(r2))
+        if (IsNL(r2) || r2 == Eof)
         {
             return lx.Errorf("Expected two hexadecimal digits after '\\x', but hit end of line");
         }