Question

I’ve been trying to implement server-side XSLT transformations as an IIS HttpModule. My basic approach is to install a new filter at BeginRequest that diverts writes into a MemoryStream, and then at PreSendRequestContent to transform the document using XSLT and write it to the original output stream. However, even without performing the transformation I’m clearly doing something wrong as the HttpModule appears to work for the first page load and then I get no response from the server at all until I restart the application pool. With the transformation in place I get an empty page the first time and then no response. I’m clearly doing something stupid but this is the first C# code I’d written in years (and my first attempt at an HttpModule) and I have no idea what the problem might be. What mistakes am I making? (I’ve commented out the XSLT part in the code below and uncommented a line that writes the contents of the cache to the response.)

using System;
using System.IO;
using System.Text;
using System.Web;
using System.Xml;
using System.Xml.Xsl;

namespace Onyx {

    public class OnyxModule : IHttpModule {

        public String ModuleName {
            get { return "OnyxModule"; }
        }

        public void Dispose() {
        }

        public void Init(HttpApplication application) {

            application.BeginRequest += (sender, e) => {
                HttpResponse response = HttpContext.Current.Response;
                response.Filter = new CacheFilter(response.Filter);
                response.Buffer = true;
            };

            application.PreSendRequestContent += (sender, e) => {

                HttpResponse response = HttpContext.Current.Response;
                CacheFilter cache = (CacheFilter)response.Filter;

                response.Filter = cache.originalStream;
                response.Clear();

 /*               XmlReader xml = XmlReader.Create(new StreamReader(cache), new XmlReaderSettings() {
                    ProhibitDtd = false,
                    ConformanceLevel = ConformanceLevel.Auto
                });

                XmlWriter html = XmlWriter.Create(response.OutputStream, new XmlWriterSettings() {
                    ConformanceLevel = ConformanceLevel.Auto
                });

                XslCompiledTransform xslt = new XslCompiledTransform();
                xslt.Load("http://localhost/transformations/test_college.xsl", new XsltSettings() {
                    EnableDocumentFunction = true
                }, new XmlUrlResolver());
                xslt.Transform(xml, html); */

                response.Write(cache.ToString());

                response.Flush();

            };

        }


    }

    public class CacheFilter : MemoryStream {

        public Stream originalStream;
        private MemoryStream cacheStream;

        public CacheFilter(Stream stream) {
            originalStream = stream;
            cacheStream = new MemoryStream();
        }

        public override int Read(byte[] buffer, int offset, int count) {
            return cacheStream.Read(buffer, offset, count);
        }

        public override void Write(byte[] buffer, int offset, int count) {
            cacheStream.Write(buffer, offset, count);
        }

        public override bool CanRead {
            get { return cacheStream.CanRead; }
        }

        public override string ToString() {
            return Encoding.UTF8.GetString(cacheStream.ToArray());
        }

    }

}

Answer 1

When you are done reading the data into your MemoryStream the position is at the end of the stream. Before sending the stream to the StreamReader/XmlReader you need to reset the position to 0.

stream.Position = 0;
/* or */
stream.Seek(0, SeekOrigin.Begin);