How to resolve XSL includes in a Transformation that loads XSL from a String?

Question

.NET 2.0/VS2005

I am trying to use the XslCompiledTransform class to perform a XSL Transformation. I have two XSL files, the first of which includes a reference to the other in the form of an <xsl:include> statement :

Main.xsl:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"&gt;
  <xsl:include href="Included.xsl" />
  ...
  ...
</xsl:stylesheet>

Now, If I could load the "Main.xsl" file itself as a URI, my transformation code would be as simple as :

// This is a function that works. For demo only.
private string Transform(string xslFileURI)
{
  XslCompiledTransform xslt = new XslCompiledTransform();

  // This load works just fine, if I provide the path to "Main.xsl".
  // The xsl:include is automatically resolved.
  xslTransform.Load(xslFileURI);

  StringWriter sw = new StringWriter();
  xslt.Transform(Server.MapPath("~/XML/input.xml"), null, sw);
  return sw.ToString();
}

The problem is that I receive the contents of the Main.xsl file as a string and need to load the string as an XmlReader/IXpathNavigable. This is a necessary restriction at this time. When I try to do the same using an XmlReader/XpathDocument, it fails because the code looks for "Included.xsl" in the C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\ folder! Obviously, the XmlResolver is not able to resolve the relative URL because it only receives a string as input XSL.

My efforts in this direction look like:

// This doesn't work! Halp!
private string Transform(string xslContents)
{
  XslCompiledTransform xslt = new XslCompiledTransform();
  XmlUrlResolver resolver = new XmlUrlResolver();
  resolver.Credentials = CredentialCache.DefaultCredentials;

  //METHOD 1: This method does not work.
  XmlReaderSettings settings = new XmlReaderSettings();
  settings.XmlResolver = resolver;
  XmlReader xR = XmlReader.Create(new StringReader(xslContents), settings);
  xslt.Load(xR);    // fails

  // METHOD 2: Does not work either.
  XPathDocument xpDoc = new XPathDocument(new StringReader(xslContents));
  xslt.Load(xpDoc, new XsltSettings(true, true), resolver);  //fails.

  StringWriter sw = new StringWriter();
  xslt.Transform(Server.MapPath("~/XML/input.xml"), null, sw);
  return sw.ToString();
}

I have tried to use the ResolveUri method of the XmlUrlResolver to obtain a Stream referencing the XSL file to be included, but am confused as to how to use this Stream. IOW, how do I tell the XslCompiledTransform object to use this stream in addition to the Main.xsl XmlReader:

Uri mainURI = new Uri(Request.PhysicalApplicationPath + "Main.xsl");
Uri uri = resolver.ResolveUri(mainURI, "Included.xsl");

// I can verify that the Included.xsl file loads in the Stream below.
Stream s = resolver.GetEntity(uri, null, typeof(Stream)) as Stream;

// How do I use this Stream in the function above??

Any help is greatly appreciated. Sorry for the long post!

For your reference, the Exception StackTrace looks like this:

[FileNotFoundException: Could not find file 'C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\Included.xsl'.]
   System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) +328
   System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy) +1038
   System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize) +113
   System.Xml.XmlDownloadManager.GetStream(Uri uri, ICredentials credentials) +78
   System.Xml.XmlUrlResolver.GetEntity(Uri absoluteUri, String role, Type ofObjectToReturn) +51
   System.Xml.Xsl.Xslt.XsltLoader.CreateReader(Uri uri, XmlResolver xmlResolver) +22
   System.Xml.Xsl.Xslt.XsltLoader.LoadStylesheet(Uri uri, Boolean include) +33
   System.Xml.Xsl.Xslt.XsltLoader.LoadInclude() +349
   System.Xml.Xsl.Xslt.XsltLoader.LoadRealStylesheet() +704
   System.Xml.Xsl.Xslt.XsltLoader.LoadDocument() +293
   System.Xml.Xsl.Xslt.XsltLoader.LoadStylesheet(XmlReader reader, Boolean include) +173

Answer 1

Hi Cerberus,

I am probably missing the obvious but is there a reason you don't just change the URI of Included.xsl to be a true URL? This could either be done in the XSL doc if you have access or using string manipulation otherwise?

Answer 2

Hey Cerberus, Use a custom XmlUrlResolver

class MyXmlUrlResolver : XmlUrlResolver
    {
        public override Uri ResolveUri(Uri baseUri, string relativeUri)
        {
            if (baseUri != null)
                return base.ResolveUri(baseUri, relativeUri);
            else
                return base.ResolveUri(new Uri("http://mypath/"), relativeUri);
        }
    }

And use it in load function of XslCompiledTransform,

resolver=new MyXmlUrlResolver();
xslt.Load(xR,null,resolver);