Splitting stream & reading stuff inside

program.cs

using System;
using System.Threading;
using System.IO;
using System.Threading.Tasks;
using System.Text.Unicode;
using System.Text;
using SharpCompress.Readers;
using MicroKnights.IO.Streams;

class Program
{
    static void Main(string[] args)
    {
        AsyncMain(args[0], args[1]).Wait();
    }

    static async Task AsyncMain(string i, string o)
    {
        using var f = new FileStream(i, FileMode.Open);
        var buf = new byte[131072];
        using var fdest = new FileStream(o, FileMode.OpenOrCreate);
        Console.WriteLine("Opened");
        using var input = new ReadableSplitStream(f);
        using var input1 = input.GetForwardReadOnlyStream();
        using (var input2 = input.GetForwardReadOnlyStream())
        {
            await input.StartReadAHead();
            var task1 = Task.Run(async () =>
            {
                await input1.CopyToAsync(fdest);
            });
            var task2 = Task.Run(async () =>
            {
                await ReadArchive(input2);
            });
            await Task.WhenAll(task1, task2);
        }
    }

    static async Task ReadArchive(Stream underlying)
    {
        var opt = new ReaderOptions();
        opt.LeaveStreamOpen = true;
        var r = ReaderFactory.Open(underlying, opt);
        Console.WriteLine($"kind: {r.ArchiveType}");
        Console.WriteLine(underlying.Length);
        while (r.MoveToNextEntry())
        {
            var entry = r.Entry;
            Console.WriteLine($"Found entry: {entry.Key} with size {entry.Size}");
            if (entry.Key == "test.txt")
            {
                var len = entry.Size;
                var buf = new byte[4096];
                var s = r.OpenEntryStream();
                var n = await s.ReadAsync(buf);
                while (n > 0)
                {
                    Console.Write(UTF8Encoding.UTF8.GetString(buf));
                    n = await s.ReadAsync(buf);
                }
                Console.WriteLine();
            }
        }
        var end_buf = new byte[4096];
        int nx;
        do
            nx = await underlying.ReadAsync(end_buf);
        while (nx > 0);

        Console.WriteLine($"Read end");
    }
}

proj.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="MicroKnights.IO.SplitStream" Version="1.0.0" />
    <PackageReference Include="sharpcompress" Version="0.26.0" />
    <PackageReference Include="SharpZipLib" Version="1.2.0" />
    <PackageReference Include="System.IO.Compression" Version="4.3.0" />
  </ItemGroup>

</Project>