Prefix socketServerScreenShot blob with length too (resolves #3461)

fixes b1602da

src/BizHawk.Client.Common/Api/SocketServer.cs

@@ -1,12 +1,21 @@
 using System;
+using System.Linq;
 using System.Net;
 using System.Net.Sockets;
 using System.Text;
 
+using BizHawk.Common.CollectionExtensions;
+
 namespace BizHawk.Client.Common
 {
 	public sealed class SocketServer
 	{
+		public static readonly byte[] LENGTH_PREFIX_SEPARATOR = { (byte) ' ' };
+
+		public static byte[] PrefixWithLength(byte[] payload)
+			=> Encoding.ASCII.GetBytes(payload.Length.ToString()).Concat(LENGTH_PREFIX_SEPARATOR).ToArray()
+				.ConcatArray(payload);
+
 		private IPEndPoint _remoteEp;
 
 		private Socket _soc = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
@@ -134,7 +143,7 @@ public int SendBytes(byte[] sendBytes)
 
 		public string SendScreenshot(int waitingTime = 0)
 		{
-			var bmpBytes = _takeScreenshotCallback();
+			var bmpBytes = PrefixWithLength(_takeScreenshotCallback());
 			var sentBytes = 0;
 			var tries = 0;
 			while (sentBytes <= 0 && tries < Retries)
@@ -166,17 +175,7 @@ public string SendScreenshot(int waitingTime = 0)
 
 		public int SendString(string sendString, Encoding encoding = null)
 		{
-			var payloadBytes = (encoding ?? Encoding.UTF8).GetBytes(sendString);
-			var strLenOfPayloadBytes = payloadBytes.Length.ToString();
-			var strLenOfPayloadBytesAsBytes = Encoding.ASCII.GetBytes(strLenOfPayloadBytes);
-
-			System.IO.MemoryStream ms = new System.IO.MemoryStream();
-			ms.Write(strLenOfPayloadBytesAsBytes, 0, strLenOfPayloadBytesAsBytes.Length);
-			ms.WriteByte((byte)' ');
-			ms.Write(payloadBytes,0,payloadBytes.Length);
-
-			int sentBytes = SendBytes(ms.ToArray());
-
+			var sentBytes = SendBytes(PrefixWithLength((encoding ?? Encoding.UTF8).GetBytes(sendString)));
 			Successful = sentBytes > 0;
 			return sentBytes;
 		}