using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

using System.Data;

using System.Globalization;

using System.IO.MemoryMappedFiles;

using System.Runtime.Serialization;

using System.Runtime.Versioning;

using System.Runtime.InteropServices;

​

using System.Xml;

using System.Xml.Serialization;

using System.Xml.Linq;

​

using Debug = System.Console;

​

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

​

//https://stackoverflow.com/questions/79005457/system-runtime-serialization-serializationexception-the-data-at-the-root-level

​

#nullable enable

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    public static partial class MemoryMappedFileExtensions

    {

        static readonly int LongSize = Marshal.SizeOf<long>();

​

        public static long WriteAndFrame<T>(this MemoryMappedFile mmf, T value, long offset = 0, DataContractSerializer? serializer = null)

        {

            long actualSize;

            serializer ??= new DataContractSerializer(typeof(T));

            // Write the data contract data at offset 8.

            using (var stream = mmf.CreateViewStream(checked(offset + LongSize), 0, MemoryMappedFileAccess.Write))

            {

                var startPosition = stream.Position;

                serializer.WriteObject(stream, value);

                stream.Flush();

                actualSize = stream.Position - startPosition;

            }

            // Write the message frame size at offset 0.

            using (var accessor = mmf.CreateViewAccessor(offset, LongSize))

            {

                accessor.Write(0, actualSize);

            }

            return checked(actualSize + LongSize);

        }

        public static (T? Value, long SizeRead) ReadFromFrame<T>(this MemoryMappedFile mmf, long offset = 0, DataContractSerializer? serializer = null)

        {

            long actualSize;

            serializer ??= new DataContractSerializer(typeof(T));

​

            // Read the message frame size from offset zero.

            using (var accessor = mmf.CreateViewAccessor(offset, LongSize))

            {

                accessor.Read(0, out actualSize);

            }

​

            // Read the XML starting at offset 8 with the specified message frame size.

            using (var stream = mmf.CreateViewStream(offset + LongSize, actualSize, MemoryMappedFileAccess.Read))

            {

                return ((T?)serializer.ReadObject(stream), checked(actualSize + LongSize));

            }

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            // Fix for Unix taken from this answer https://stackoverflow.com/a/77149446

            // by https://stackoverflow.com/users/1576055/user1576055

            // To https://stackoverflow.com/questions/66308340/how-to-use-net-memory-mapped-file-in-linux-without-persisted-file

            using (var mmf = MemoryMappedFile.CreateFromFile("/dev/shm/test", System.IO.FileMode.OpenOrCreate, null, 10240, MemoryMappedFileAccess.ReadWrite))

            //using (MemoryMappedFile.CreateNew("TempName", 10240, MemoryMappedFileAccess.ReadWrite))

            {

                WriteToMemoryMappedFile(mmf);

​

                var infoObj = ReadFromMemoryMappedFile(mmf);

​

                Console.WriteLine(infoObj?.Name);

                Assert.That(infoObj?.Name == "TestApp");

            }

        }   

        private static void WriteToMemoryMappedFile(MemoryMappedFile mmf)

        {

            var infoObj = new SampleClass { Name = "TestApp" };

            mmf.WriteAndFrame(infoObj);

        }

​

        private static SampleClass? ReadFromMemoryMappedFile(MemoryMappedFile mmf) =>

            mmf.ReadFromFrame<SampleClass>().Value;

    }

​

    [DataContract]

    public class SampleClass

    {

        [DataMember]

        public string? Name { get; set; }

    }

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    public static partial class DataContractSerializerHelper

    {

        public static string ToContractXml<T>(this T obj, DataContractSerializer? serializer = null, XmlWriterSettings? settings = null)

        {

            serializer = serializer ?? new DataContractSerializer(obj == null ? typeof(T) : obj.GetType());

            using (var textWriter = new StringWriter())

            {

                settings = settings ?? new XmlWriterSettings { Indent = true };

                using (var xmlWriter = XmlWriter.Create(textWriter, settings))

                {

                    serializer.WriteObject(xmlWriter, obj);

                }

                return textWriter.ToString();

            }

        }

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        public static T? FromContractXml<T>(string xml, DataContractSerializer? serializer = null)

        {

            using (var textReader = new StringReader(xml ?? ""))

            using (var xmlReader = XmlReader.Create(textReader))

            {

                return (T?)(serializer ?? new DataContractSerializer(typeof(T))).ReadObject(xmlReader);

            }

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}), {2}", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine();

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            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​