using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

using System.Collections.ObjectModel;

using System.Threading.Tasks;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/60915876/jtoken-writetoasync-does-not-write-to-jsonwriter

​

    public class User

    {

        public string Name { get; set; }

    }

​

    public class Program

    {

        static async Task Main()

        {

            Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , GetNetCoreVersion());

            Console.WriteLine("{0} version: {1}", typeof(JsonSerializer).Assembly.GetName().Name,  typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                var token = JToken.FromObject(new User { Name = "Bob" });

​

                var memoryStream = new MemoryStream();

                // StreamWriter implements IAsyncDisposable

                // Leave the underlying stream open

                await using (var requestWriter = new StreamWriter(memoryStream, leaveOpen: true)) 

                {

                    var jsonWriter = new JsonTextWriter(requestWriter); // But JsonTextWriter does not implement IAsyncDisposable, only IDisposable!

                    try

                    {

                        await token.WriteToAsync(jsonWriter); 

                    }

                    finally

                    {

                        await jsonWriter.CloseAsync();

                    }

                }

                memoryStream.Length.Dump(); // <-- MemoryStream.Length = 0

                Assert.AreNotEqual(0L, memoryStream.Length);

                Assert.AreEqual(token.ToString(Formatting.None), Encoding.UTF8.GetString(memoryStream.GetBuffer(), 0, checked((int)memoryStream.Length)));

                Console.WriteLine(Encoding.UTF8.GetString(memoryStream.GetBuffer(), 0, checked((int)memoryStream.Length)));

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.Location.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return null;

        }

    }

​