Improved WebSocket receive performance and reduced allocations

src/Discord.Net/Net/WebSockets/DefaultWebsocketClient.cs

@@ -1,5 +1,4 @@
-using Discord.Extensions;
-using System;
+using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.IO;
@@ -12,7 +11,7 @@ namespace Discord.Net.WebSockets
 {
     public class DefaultWebSocketClient : IWebSocketClient
     {
-        public const int ReceiveChunkSize = 12 * 1024; //12KB
+        public const int ReceiveChunkSize = 16 * 1024; //16KB
         public const int SendChunkSize = 4 * 1024; //4KB
         private const int HR_TIMEOUT = -2147012894;
 
@@ -137,50 +136,64 @@ namespace Discord.Net.WebSockets
         private async Task RunAsync(CancellationToken cancelToken)
         {
             var buffer = new ArraySegment<byte>(new byte[ReceiveChunkSize]);
-            var stream = new MemoryStream();
 
             try
             {
                 while (!cancelToken.IsCancellationRequested)
                 {
-                    WebSocketReceiveResult result = null;
-                    do
+                    WebSocketReceiveResult socketResult = await _client.ReceiveAsync(buffer, cancelToken).ConfigureAwait(false);
+                    byte[] result;
+                    int resultCount;
+                        
+                    if (socketResult.MessageType == WebSocketMessageType.Close)
                     {
-                        if (cancelToken.IsCancellationRequested) return;
+                        var _ = Closed(new WebSocketClosedException((int)socketResult.CloseStatus, socketResult.CloseStatusDescription));
+                        return;
+                    }
 
-                        try
-                        {
-                            result = await _client.ReceiveAsync(buffer, cancelToken).ConfigureAwait(false);
-                        }
-                        catch (Win32Exception ex) when (ex.HResult == HR_TIMEOUT)
+                    if (!socketResult.EndOfMessage)
+                    {
+                        //This is a large message (likely just READY), lets create a temporary expandable stream
+                        using (var stream = new MemoryStream())
                         {
-                            throw new Exception("Connection timed out.");
+                            stream.Write(buffer.Array, 0, socketResult.Count);
+                            do
+                            {
+                                if (cancelToken.IsCancellationRequested) return;
+                                socketResult = await _client.ReceiveAsync(buffer, cancelToken).ConfigureAwait(false);
+                                stream.Write(buffer.Array, 0, socketResult.Count);
+                            }
+                            while (socketResult == null || !socketResult.EndOfMessage);
+
+                            //Use the internal buffer if we can get it
+                            resultCount = (int)stream.Length;
+                            ArraySegment<byte> streamBuffer;
+                            if (stream.TryGetBuffer(out streamBuffer))
+                                result = streamBuffer.Array;
+                            else
+                                result = stream.ToArray();
                         }
-
-                        if (result.Count > 0)
-                            stream.Write(buffer.Array, 0, result.Count);
                     }
-                    while (result == null || !result.EndOfMessage);
-
-                    var array = stream.ToArray();
-                    stream.Position = 0;
-                    stream.SetLength(0);
+                    else
+                    {
+                        //Small message
+                        resultCount = socketResult.Count;
+                        result = buffer.Array;
+                    }
 
-                    switch (result.MessageType)
+                    if (socketResult.MessageType == WebSocketMessageType.Text)
                     {
-                        case WebSocketMessageType.Binary:
-                            await BinaryMessage(array, 0, array.Length).ConfigureAwait(false);
-                            break;
-                        case WebSocketMessageType.Text:
-                            string text = Encoding.UTF8.GetString(array, 0, array.Length);
-                            await TextMessage(text).ConfigureAwait(false);
-                            break;
-                        case WebSocketMessageType.Close:
-                            var _ = Closed(new WebSocketClosedException((int)result.CloseStatus, result.CloseStatusDescription));
-                            return;
+                        string text = Encoding.UTF8.GetString(result, 0, resultCount);
+                        await TextMessage(text).ConfigureAwait(false);
                     }
+                    else
+                        await BinaryMessage(result, 0, resultCount).ConfigureAwait(false);
                 }
             }
+            catch (Win32Exception ex) when (ex.HResult == HR_TIMEOUT)
+            {
+                var _ = Closed(new Exception("Connection timed out.", ex));
+            }
             catch (OperationCanceledException) { }
             catch (Exception ex)
             {