using System;

using System.Collections.Generic;

using System.Text;

using System.Linq;

using System.Xml;

using System.Xml.Linq;

using System.IO;

​

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

​

//https://stackoverflow.com/questions/79421216/c-sharp-xmldocument-vs-xdocument-behaviour-on-invalid-hexadecimal-character

// MCVE here: https://dotnetfiddle.net/KEPEFA

​

    public static class XDocumentExtensions

    {

        static readonly XmlReaderSettings noCheckedCharacterParseSettings = new() { CheckCharacters = false, };

        static readonly XmlReaderSettings checkedCharacterParseSettings = new() { CheckCharacters = true, };

​

        public static XDocument Parse(string xml, bool checkCharacters) =>

            Parse(xml, checkCharacters ? checkedCharacterParseSettings : noCheckedCharacterParseSettings);

        public static XDocument Parse(string xml, XmlReaderSettings settings)

        {

            using var reader = new StringReader(xml);

            using var xmlReader = XmlReader.Create(reader, settings);

            return XDocument.Load(xmlReader);

        }

​

        static readonly XmlWriterSettings noCheckedCharacterToStringSettings = new() { CheckCharacters = false, Indent = true, OmitXmlDeclaration = true, };

        static readonly XmlWriterSettings checkedCharacterToStringSettings = new() { CheckCharacters = true, Indent = true, OmitXmlDeclaration = true, };

        public static string ToString(this XNode node, bool checkCharacters) =>

            node.ToString(checkCharacters ? checkedCharacterToStringSettings : noCheckedCharacterToStringSettings);

        public static string ToString(this XNode node, XmlWriterSettings settings)

        {

            using var writer = new StringWriter();

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

            {

                node.WriteTo(xmlWriter);

            }

            return writer.ToString();

        }

    }

​

    public class TestClass

    {

        public static void Test()

        {

            Console.WriteLine("Testing XmlDocument:");

            string message = "Hello, \x01\x1EWorld!"; // string with control code 1E encoded.

​

            // This block completes - create an xml document incorporating the message string

            XmlDocument xmlDoc = new XmlDocument();

            XmlElement root = xmlDoc.CreateElement("greeting");

            xmlDoc.AppendChild(root);

            root.InnerText = message;

            Console.WriteLine(xmlDoc.OuterXml);

            var xmlDoc2 = new XmlDocument();

            xmlDoc2.LoadXml(xmlDoc.OuterXml);

            Console.WriteLine(xmlDoc2.OuterXml);

            // This block completes - XmlDocument load document containing an  entity expression

            string xmlWithEscapedHexEntity = xmlDoc.OuterXml; // <greeting>Hello, &x1E;World!</greeting>";

            xmlDoc = new XmlDocument();

            xmlDoc.LoadXml(xmlWithEscapedHexEntity);

            Console.WriteLine(xmlDoc.OuterXml);

​

​

            // Outputs: <greeting>Hello, &#x1E;World!</greeting>

​

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

            // This block fails - XDocument creation of document containing control-code character x1E

            try

            {

                XDocument xdoc = new XDocument(

                    new XElement("greeting", message)

                );

                Console.WriteLine(xdoc.ToString(checkCharacters : false));

            }

            catch (Exception ex)

            {

                Console.WriteLine($"XDocument creation error: {ex}");

            }

​

            // This block fails - XDocument parse document containing an  entity expression

            try

            {

                XDocument xDoc = XDocumentExtensions.Parse(xmlWithEscapedHexEntity, checkCharacters : false);

                Console.WriteLine(xDoc.ToString(checkCharacters : false));

            }

            catch (Exception ex)

            {

                Console.WriteLine($"XDocument parse failure: {ex}");

            }

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}, {2}, NewLine: {3}).", 

                              System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion,

                              System.Text.Json.JsonSerializer.Serialize(Environment.NewLine));

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​