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.Xml;

using System.Xml.Linq;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

    // https://stackoverflow.com/questions/47881189/xml-entities-in-json-net

    class TestClass

    {

        public static void Test()

        {

            string xml = @"<?xml version='1.0' standalone='no'?>

    <!DOCTYPE notes [

        <!ENTITY ent 'Sample text'>

    ]>

    <notes>

        <note>&ent;</note>

    </notes>";

​

            var json2 = Test2(xml);

            var json1 = Test1(xml);

            Assert.IsTrue(json2 == json1);

            Console.WriteLine("\nXDocument and XmlDocument produce identical results.");

        }

​

        private static string Test2(string xml)

        {

            Console.WriteLine("\nTesting XDocument...");

            var doc = XDocument.Parse(xml);

            string json = JsonConvert.SerializeXNode(doc, Newtonsoft.Json.Formatting.Indented);

            Console.WriteLine(json);

            return json;

        }

​

        private static string Test1(string xml)

        {

            Console.WriteLine("\nTesting XmlDocument...");

​

​

            var settings = new XmlReaderSettings

            {

                // Allow processing of DTD

                DtdProcessing = DtdProcessing.Parse,

                // On older versions of .Net instead set 

                //ProhibitDtd = false,

                // But for security, prevent DOS attacks by limiting the total number of characters that can be expanded to something sane.

                MaxCharactersFromEntities = (long)1e7,

                // And for security, disable resolution of entities from external documents.

                XmlResolver = null,

            };

            XmlDocument doc = new XmlDocument();

            using (var textReader = new StringReader(xml))

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

            {

                doc.Load(xmlReader);

            }

            string json = JsonConvert.SerializeXmlNode(doc, Newtonsoft.Json.Formatting.Indented);

            Console.WriteLine(json);

            return json;

        }

    }

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine("Json.NET version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​

    public class AssertionFailedException : System.Exception

    {

        public AssertionFailedException() : base() { }

​

        public AssertionFailedException(string s) : base(s) { }

    }

​

    public static class Assert

    {

        public static void IsTrue(bool value)

        {

            IsTrue(value, "failed");

        }

​

        public static void IsTrue(bool value, string message)

        {

            if (value == false)

                throw new AssertionFailedException(message ?? "failed");

        }

    }

​