Added implementation of Modbus TCP Server

AMWD.Protocols.Modbus.Tcp/Extensions/StreamExtensions.cs

@@ -0,0 +1,26 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.IO
+{
+	internal static class StreamExtensions
+	{
+		public static async Task<byte[]> ReadExpectedBytesAsync(this Stream stream, int expectedBytes, CancellationToken cancellationToken = default)
+		{
+			byte[] buffer = new byte[expectedBytes];
+			int offset = 0;
+			do
+			{
+				int count = await stream.ReadAsync(buffer, offset, expectedBytes - offset, cancellationToken).ConfigureAwait(false);
+				if (count < 1)
+					throw new EndOfStreamException();
+
+				offset += count;
+			}
+			while (offset < expectedBytes && !cancellationToken.IsCancellationRequested);
+
+			cancellationToken.ThrowIfCancellationRequested();
+			return buffer;
+		}
+	}
+}