add csharp/dotnet devnull client to measure througput with different runtimes

test/compatibility/csharp/.gitignore

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+bin
+obj

test/compatibility/csharp/Main.cs

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+//
+// Main.cs
+// Author: Benjamin Sergeant
+// Copyright (c) 2020 Machine Zone, Inc. All rights reserved.
+//
+// In a different terminal, start a push server:
+// $ ws push_server -q
+//
+// $ dotnet run
+// messages received per second: 145157
+// messages received per second: 141405
+// messages received per second: 152202
+// messages received per second: 157149
+// messages received per second: 157673
+// messages received per second: 153594
+// messages received per second: 157830
+// messages received per second: 158422
+//
+
+using System;
+using System.Net.WebSockets;
+using System.Threading;
+using System.Threading.Tasks;
+
+public class DevNullClientCli
+{
+    private static int receivedMessage = 0;
+
+    public static async Task<byte[]> ReceiveAsync(ClientWebSocket ws, CancellationToken token)
+    {
+        int bufferSize = 8192; // 8K
+        var buffer = new byte[bufferSize];
+        var offset = 0;
+        var free = buffer.Length;
+
+        while (true)
+        {
+            var result = await ws.ReceiveAsync(new ArraySegment<byte>(buffer, offset, free), token).ConfigureAwait(false);
+
+            offset += result.Count;
+            free -= result.Count;
+            if (result.EndOfMessage) break;
+
+            if (free == 0)
+            {
+                // No free space
+                // Resize the outgoing buffer
+                var newSize = buffer.Length + bufferSize;
+
+                var newBuffer = new byte[newSize];
+                Array.Copy(buffer, 0, newBuffer, 0, offset);
+                buffer = newBuffer;
+                free = buffer.Length - offset;
+            }
+        }
+
+        return buffer;
+    }
+
+    private static void OnTimedEvent(object source, EventArgs e)
+    {
+        Console.WriteLine($"messages received per second: {receivedMessage}");
+        receivedMessage = 0;
+    }
+
+    public static async Task ReceiveMessagesAsync(string url)
+    {
+        var ws = new ClientWebSocket();
+
+        System.Uri uri = new System.Uri(url);
+        var cancellationToken = CancellationToken.None;
+
+        try 
+        {
+            await ws.ConnectAsync(uri, cancellationToken).ConfigureAwait(false);
+            while (true)
+            {
+                var data = await DevNullClientCli.ReceiveAsync(ws, cancellationToken);
+                receivedMessage += 1;
+            }
+        }
+        catch (System.Net.WebSockets.WebSocketException e)
+        {
+            Console.WriteLine($"WebSocket error: {e}");
+            return;
+        }
+    }
+
+    public static async Task Main()
+    {
+        var timer = new System.Timers.Timer(1000);
+        timer.Elapsed += OnTimedEvent;
+        timer.Enabled = true;
+        timer.Start();
+
+        var url = "ws://localhost:8008";
+        await ReceiveMessagesAsync(url);
+    }
+}

test/compatibility/csharp/devnull_client.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+  </PropertyGroup>
+</Project>