Improve logging for malformed packet diagnosis

The existing exception handling in SocketIOCompleted already catches
all exceptions from message handlers and disconnects the client, so
the server does not crash on malformed packets. However, the log
output was unhelpful (e.g. "ArgumentOutOfRangeException error
encountered!" with no packet context).

Add try/catch in Invoke() that logs the message ID, size, and hex
dump before disconnecting. Fix BinaryReader.ReadByteString() to throw
a descriptive GameProtocolViolationException on missing null
terminators instead of an opaque ArgumentOutOfRangeException. Fix
GetNextNull() to restore stream position on failure.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: wjlafrance

src/Atlasd/Battlenet/BinaryReader.cs

@@ -1,4 +1,5 @@
-using System.IO;
+using Atlasd.Battlenet.Exceptions;
+using System.IO;
 using System.Text;
 
 namespace Atlasd.Battlenet
@@ -17,7 +18,7 @@ public long GetNextNull()
             {
                 long lastPosition = BaseStream.Position;
 
-                while (BaseStream.CanRead)
+                while (BaseStream.Position < BaseStream.Length)
                 {
                     if (ReadByte() == 0)
                     {
@@ -27,6 +28,7 @@ public long GetNextNull()
                     }
                 }
 
+                BaseStream.Position = lastPosition;
                 return -1;
             }
         }
@@ -35,7 +37,13 @@ public byte[] ReadByteString()
         {
             lock (_lock)
             {
-                var size = GetNextNull() - BaseStream.Position;
+                var nullPos = GetNextNull();
+                if (nullPos < 0)
+                {
+                    throw new GameProtocolViolationException(null,
+                        $"Truncated string field at stream position {BaseStream.Position}: missing null terminator");
+                }
+                var size = nullPos - BaseStream.Position;
                 return ReadBytes((int)size)[..^1];
             }
         }
@@ -46,7 +54,7 @@ public override string ReadString()
             {
                 string str = "";
                 char chr;
-                while ((int)(chr = ReadChar()) != 0)
+                while (BaseStream.Position < BaseStream.Length && (int)(chr = ReadChar()) != 0)
                     str += chr;
                 return str;
             }

src/Atlasd/Battlenet/ClientState.cs

@@ -139,8 +139,20 @@ private void Invoke(SocketAsyncEventArgs e)
 
             while (BattlenetGameFrame.Messages.TryDequeue(out var msg))
             {
-                if (!msg.Invoke(context))
+                try
+                {
+                    if (!msg.Invoke(context))
+                    {
+                        Disconnect();
+                        return;
+                    }
+                }
+                catch (Exception ex)
                 {
+                    var hexDump = msg.Buffer != null ? BitConverter.ToString(msg.Buffer) : "(null)";
+                    Logging.WriteLine(Logging.LogLevel.Error, Logging.LogType.Client, RemoteEndPoint,
+                        $"Exception processing {Message.MessageName(msg.Id)} (0x{msg.Id:X2}, {msg.Buffer?.Length ?? 0} bytes): " +
+                        $"{ex.GetType().Name}: {ex.Message}; packet dump: {hexDump}");
                     Disconnect();
                     return;
                 }