c# - Dealing with invalid XML hexadecimal characters

Question

I'm trying to send an XML document over the wire but receiving the following exception:

"MY LONG EMAIL STRING" was specified for the 'Body' element. ---> System.ArgumentException: '', hexadecimal value 0x02, is an invalid character.
   at System.Xml.XmlUtf8RawTextWriter.InvalidXmlChar(Int32 ch, Byte* pDst, Boolean entitize)
   at System.Xml.XmlUtf8RawTextWriter.WriteElementTextBlock(Char* pSrc, Char* pSrcEnd)
   at System.Xml.XmlUtf8RawTextWriter.WriteString(String text)
   at System.Xml.XmlUtf8RawTextWriterIndent.WriteString(String text)
   at System.Xml.XmlRawWriter.WriteValue(String value)
   at System.Xml.XmlWellFormedWriter.WriteValue(String value)
   at Microsoft.Exchange.WebServices.Data.EwsServiceXmlWriter.WriteValue(String value, String name)
   --- End of inner exception stack trace ---

I don't have any control over what I attempt to send because the string is gathered from an email. How can I encode my string so it's valid XML while keeping the illegal characters?

I'd like to keep the original characters one way or another.

Answer 1

The following code removes XML invalid characters from a string and returns a new string without them:

public static string CleanInvalidXmlChars(string text) 
{ 
     // From xml spec valid chars: 
     // #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]     
     // any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. 
     string re = @"[^x09x0Ax0Dx20-xD7FFxE000-xFFFDx10000-x10FFFF]"; 
     return Regex.Replace(text, re, ""); 
}