Got at least one data fetching method working; turns out, we can't use a patched LogicStack to get the data

Vendor/EmbedIO-3.5.2/WebSockets/Internal/PayloadData.cs

@@ -0,0 +1,74 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using Swan;
+using EmbedIO.Net.Internal;
+
+namespace EmbedIO.WebSockets.Internal
+{
+    internal class PayloadData
+    {
+        public const ulong MaxLength = long.MaxValue;
+
+        private readonly byte[] _data;
+        private ushort? _code;
+
+        internal PayloadData(byte[] data)
+        {
+            _data = data;
+        }
+
+        internal PayloadData(ushort code = 1005, string? reason = null)
+        {
+            _code = code;
+            _data = code == 1005 ? Array.Empty<byte>() : Append(code, reason);
+        }
+
+        internal MemoryStream ApplicationData => new MemoryStream(_data);
+
+        internal ulong Length => (ulong)_data.Length;
+
+        internal ushort Code
+        {
+            get
+            {
+                if (!_code.HasValue)
+                {
+                    _code = _data.Length > 1
+                            ? BitConverter.ToUInt16(_data.Take(2).ToArray().ToHostOrder(Endianness.Big), 0)
+                            : (ushort)1005;
+                }
+
+                return _code.Value;
+            }
+        }
+
+        internal bool HasReservedCode => _data.Length > 1 && (Code == (ushort)CloseStatusCode.Undefined ||
+                   Code == (ushort)CloseStatusCode.NoStatus ||
+                   Code == (ushort)CloseStatusCode.Abnormal ||
+                   Code == (ushort)CloseStatusCode.TlsHandshakeFailure);
+
+        public override string ToString() => BitConverter.ToString(_data);
+
+        internal static byte[] Append(ushort code, string? reason)
+        {
+            var ret = code.ToByteArray(Endianness.Big);
+            if (string.IsNullOrEmpty(reason)) return ret;
+
+            var buff = new List<byte>(ret);
+            buff.AddRange(Encoding.UTF8.GetBytes(reason));
+
+            return buff.ToArray();
+        }
+
+        internal void Mask(byte[] key)
+        {
+            for (long i = 0; i < _data.Length; i++)
+                _data[i] = (byte)(_data[i] ^ key[i % 4]);
+        }
+
+        internal byte[] ToArray() => _data;
+    }
+}