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/FragmentBuffer.cs

@@ -0,0 +1,29 @@
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace EmbedIO.WebSockets.Internal
+{
+    internal class FragmentBuffer : MemoryStream
+    {
+        private readonly bool _fragmentsCompressed;
+        private readonly Opcode _fragmentsOpcode;
+
+        public FragmentBuffer(Opcode frameOpcode, bool frameIsCompressed)
+        {
+            _fragmentsOpcode = frameOpcode;
+            _fragmentsCompressed = frameIsCompressed;
+        }
+
+        public void AddPayload(MemoryStream data) => data.CopyTo(this, 1024);
+
+        public async Task<MessageEventArgs> GetMessage(CompressionMethod compression)
+        {
+            var data = _fragmentsCompressed
+                ? await this.CompressAsync(compression, false, CancellationToken.None).ConfigureAwait(false)
+                : this;
+
+            return new MessageEventArgs(_fragmentsOpcode, data.ToArray());
+        }
+    }
+}