c# - Ignore DOCTYPE .dtd, but .dtd file must still exist

Question

I have a web service that processes an HTTP request. The document it receives has an embeded DOCTYPE that specifies a .dtd file. I wish to use a newer XML schema validation file made for when newer devices connect to my service.

I can successfully ignore the validation that goes on in the .dtd file, but the .dtd file must exist on my local hard drive. I want to remove these obsolete files, and have not found a way.

Sample XML document I am processing:

<?xml version="1.0" encoding="us-ascii" standalone="no"?>
<!DOCTYPE SomeMessage SYSTEM "SomeMessage.dtd">
<SomeMessage>data</SomeMessage>

The function that I am using to open the document:

private void LoadXmlDoc(XmlTextReader myXmlTextReader)
{
    XmlReaderSettings readerSettings = new XmlReaderSettings();
    readerSettings.ValidationType = ValidationType.Schema;
    readerSettings.Schemas.Add(null, MyGoodSchemaFile);
    readerSettings.DtdProcessing = DtdProcessing.Ignore;
    readerSettings.XmlResolver = null; // Added as a test.

    readerSettings.ValidationEventHandler += ValidationEventHandle;
    XmlReader myXmlReader = XmlReader.Create(myXmlTextReader, readerSettings);

    XmlDocument myXmlDocument = new XmlDocument();
    myXmlDocument.XmlResolver = null; // Added as a test.
    myXmlDocument.Load(myXmlReader); // Exception thrown here!
}

The exception that is caught:

System.IO.FileNotFoundException: Could not find file 'c:windowssystem32inetsrvSomeMessage.dtd'.
File name: 'c:windowssystem32inetsrvSomeMessage.dtd'
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)

The content of the SomeMessage.dtd file is not used--it is ignored as I desire. However, the dummy file "c:windowssystem32inetsrvSomeMessage.dtd" must exist, otherwise the exception is thrown.

I am running on Windows 7, using Visual Studio 2010 and .Net 4.0

How can I ignore the embeded .dtd and also not require a dummy .dtd file to be installed on my computer?

Answer 1

The solution is to set the underlying XmlTextReader's XmlResolver to null. Changing the XmlReaderSettings.XmlResolver=null did not help, nor did setting the XmlDocument.XmlResolver=null

Here is the corrected function:

private void LoadXmlDoc(XmlTextReader myXmlTextReader)
{
    // The next line is the fix!!!
    myXmlTextReader.XmlResolver = null;  // Don't require file in system32inetsrv

    XmlReaderSettings readerSettings = new XmlReaderSettings();
    readerSettings.ValidationType = ValidationType.Schema;
    readerSettings.Schemas.Add(null, MyGoodSchemaFile);
    readerSettings.DtdProcessing = DtdProcessing.Ignore;
    readerSettings.XmlResolver = null; // Doesn't help

    readerSettings.ValidationEventHandler += ValidationEventHandle;
    XmlReader myXmlReader = XmlReader.Create(myXmlTextReader, readerSettings);

    XmlDocument myXmlDocument = new XmlDocument();
    myXmlDocument.XmlResolver = null; // Doesn't help
    myXmlDocument.Load(myXmlReader); // Load doc, no .dtd required on local disk
}