Initial Client/Server Communication

#1
Followed the MagicOnion quickstart guide, borrowing code from the chat sample app to get something working

Assets/Scripts/MagicOnion/Utils/ArrayPoolBufferWriter.cs

@@ -0,0 +1,100 @@
+using System;
+using System.Buffers;
+
+namespace MagicOnion.Utils
+{
+    internal sealed class ArrayPoolBufferWriter : IBufferWriter<byte>, IDisposable
+    {
+        [ThreadStatic]
+        static ArrayPoolBufferWriter staticInstance;
+
+        public static ArrayPoolBufferWriter RentThreadStaticWriter()
+        {
+            if (staticInstance == null)
+            {
+                staticInstance = new ArrayPoolBufferWriter();
+            }
+            staticInstance.Prepare();
+            return staticInstance;
+        }
+
+        const int MinimumBufferSize = 32767; // use 32k buffer.
+
+        byte[] buffer;
+        int index;
+
+        void Prepare()
+        {
+            if (buffer == null)
+            {
+                buffer = ArrayPool<byte>.Shared.Rent(MinimumBufferSize);
+            }
+            index = 0;
+        }
+
+        public ReadOnlyMemory<byte> WrittenMemory => buffer.AsMemory(0, index);
+        public ReadOnlySpan<byte> WrittenSpan => buffer.AsSpan(0, index);
+
+        public int WrittenCount => index;
+
+        public int Capacity => buffer.Length;
+
+        public int FreeCapacity => buffer.Length - index;
+
+        public void Advance(int count)
+        {
+            if (count < 0) throw new ArgumentException(nameof(count));
+            index += count;
+        }
+
+        public Memory<byte> GetMemory(int sizeHint = 0)
+        {
+            CheckAndResizeBuffer(sizeHint);
+            return buffer.AsMemory(index);
+        }
+
+        public Span<byte> GetSpan(int sizeHint = 0)
+        {
+            CheckAndResizeBuffer(sizeHint);
+            return buffer.AsSpan(index);
+        }
+
+        void CheckAndResizeBuffer(int sizeHint)
+        {
+            if (sizeHint < 0) throw new ArgumentException(nameof(sizeHint));
+
+            if (sizeHint == 0)
+            {
+                sizeHint = MinimumBufferSize;
+            }
+
+            int availableSpace = buffer.Length - index;
+
+            if (sizeHint > availableSpace)
+            {
+                int growBy = Math.Max(sizeHint, buffer.Length);
+
+                int newSize = checked(buffer.Length + growBy);
+
+                byte[] oldBuffer = buffer;
+
+                buffer = ArrayPool<byte>.Shared.Rent(newSize);
+
+                Span<byte> previousBuffer = oldBuffer.AsSpan(0, index);
+                previousBuffer.CopyTo(buffer);
+                ArrayPool<byte>.Shared.Return(oldBuffer);
+            }
+        }
+
+        public void Dispose()
+        {
+            if (buffer == null)
+            {
+                return;
+            }
+
+            ArrayPool<byte>.Shared.Return(buffer);
+            buffer = null;
+        }
+    }
+}