StreamUtil.cs

using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

public static class StreamUtil
{
    public static async Task<byte[]> ReadAsync(this Stream stream,
        int length, CancellationToken cancellationToken)
    {
        var ret = new byte[length];
        for (var count = 0; count < length;)
        {
            count += await stream.ReadAsync(
                ret, count, length - count, cancellationToken);
        }

        return ret;
    }

    public static Task WriteAsync(this Stream stream,
        byte[] buffer, CancellationToken cancellationToken)
    {
        return stream.WriteAsync(buffer, 0, buffer.Length, cancellationToken);
    }

    public static async Task<byte[]> ReadChunkAsync(this Stream stream,
        CancellationToken cancellationToken)
    {
        var length = BitConverter.ToInt32(
            await stream.ReadAsync(4, cancellationToken), 0);
        return await stream.ReadAsync(length, cancellationToken);
    }

    public static async Task WriteChunkAsync(this Stream stream,
        byte[] buffer, CancellationToken cancellationToken)
    {
        var length = BitConverter.GetBytes(buffer.Length);
        await stream.WriteAsync(length, cancellationToken);
        await stream.WriteAsync(buffer, cancellationToken);
    }
}