Podcast (RSS) to Playlist

<%@ Page Language="C#" %>
<%@ OutputCache Duration="240" VaryByParam="*" %>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="System.Linq"%>
<%@ Import Namespace="System.Xml.Linq"%>
<script language="C#" runat="server">
      	
        void Page_Load(object sender, EventArgs e)
        {
            string sAsxFileName;
            string sRssUrl;
            //set the default xslt flename extension/type
            string sXslFileType = "ASX";
            //prepend the full path of the current directory
            string sXslFile = Path.GetDirectoryName(Request.PhysicalPath) + Path.DirectorySeparatorChar;

            //if they provided the OutType QueryString param, lets use this transform file
            if (Request.QueryString["OutType"] != null)
            {
                sXslFileType = Request.QueryString["OutType"];
            }

            //format the xslt filename to use based on the out type
            sXslFile += String.Format("RssTo{0}.xslt", sXslFileType);
            
            //check to make sure they provided the RssUrl QueryString param
            if (Request.QueryString["RssUrl"] != null)
            {
                sRssUrl = Request.QueryString["RssUrl"];
                
                //we'll try to use a formatted title of the feed for the asx filename
                sAsxFileName = FormatFileName(GetRssTitle(sRssUrl)) + "." + sXslFileType;
            }
            else
            {
                throw new ApplicationException("No RSS Feed URL (RssUrl) QueryString parameter provided.");
            }
         
            Response.Buffer = true;
            Response.ClearContent();
            Response.ClearHeaders();
            Response.Clear();
            Response.ContentEncoding = Encoding.UTF8;

            //if they provided the "inline" QueryString param, use it to determine how to send the asx file
            //inline sends the asx xml to the browser, attachment prompts the user to download the file
            //attachment is the defalut
            if ((Request.QueryString["Inline"] != null) && (Request.QueryString["Inline"].ToLower() == "true"))
            {
                //set Response.ContentType based on output method in xsl (this lets us switch between xml or text)
                Response.ContentType = GetXslOutputMethod(sXslFile);
                Response.AppendHeader("content-disposition", "inline;filename=" + sAsxFileName);
            }
            else
            {
                //we just use "text/x-unknown-content-type" because if we set to "text/plain" or "text/xml"
                //some browsers sometimes change the file extension to .txt or .xml respectively.
                Response.ContentType = "text/x-unknown-content-type";
                Response.AppendHeader("content-disposition", "attachment;filename=" + sAsxFileName);
            }

            //send transformed xml
            Response.Write(TransformXML(sRssUrl, sXslFile));
            Response.End();
        }
        

        /// <summary>
        /// removed unwanted characters from filename
        /// </summary>
        /// <param name="fileName">unformated filename</param>
        /// <returns>formated filename</returns>
        private string FormatFileName(string fileName)
        {
            string sReturn = fileName;

            sReturn = sReturn.Replace(" ", "");
            sReturn = sReturn.Replace(":", "");
            sReturn = sReturn.Replace("\\", "");
            sReturn = sReturn.Replace("/", "");
            sReturn = sReturn.Replace("@", "");
            sReturn = sReturn.Replace("$", "");
            sReturn = sReturn.Replace("+", "");
            sReturn = sReturn.Replace("%", "");
            sReturn = sReturn.Replace(">", "");
            sReturn = sReturn.Replace("<", "");
            sReturn = sReturn.Replace("?", "");
            sReturn = sReturn.Replace("\"", "");
            sReturn = sReturn.Replace("'", "");
            sReturn = sReturn.Replace(",", "");
            sReturn = sReturn.Replace("`", "");

            return sReturn;
        }


        /// <summary>
        /// Transforms xml from url using an xslt file.
        /// In this case, it will take a rss feed url and return the the playlist file
        /// </summary>
        /// <param name="xmlUrl">rss feed url</param>
        /// <param name="xslUrl">xslt filename</param>
        /// <returns>asx xml</returns>
        private string TransformXML(string xmlUrl, string xslUrl)
        {
            MemoryStream ms = new MemoryStream();
            string sOutput;
            try
            {
                System.Xml.XPath.XPathDocument oXPath = new System.Xml.XPath.XPathDocument(xmlUrl);
                System.Xml.Xsl.XslTransform oXSLT = new System.Xml.Xsl.XslTransform();
                oXSLT.Load(xslUrl);
                oXSLT.Transform(oXPath, null, ms);
                ms.Position = 0;
                StreamReader sr = new StreamReader(ms, Encoding.UTF8);
                sOutput = sr.ReadToEnd().ToString();
            }
            catch (Exception ex)
            {
                //Put in custom error handler here...
                sOutput = ex.ToString();
            }

            return sOutput;
        }

    
        /// <summary>
        /// Gets the title from an rss feed url
        /// </summary>
        /// <param name="xmlUrl">rss feed url</param>
        /// <returns>return the title from an rss feed url</returns>
        private string GetRssTitle(string xmlUrl)
        {
            string sReturn;

            try
            {
                XDocument xmlDoc = XDocument.Load(xmlUrl);

                var qry = from r in xmlDoc.Descendants("channel")
                          select (string)r.Element("title");

                sReturn = qry.First();
            }
            catch (Exception ex)
            {
                // there was a problem trying to get the title
                // we'll just use "rss"
                sReturn = "rss";
            }
            
            return sReturn;
        }
    

        /// <summary>
        /// Gets the output method (xsl:output method="xml" ...) from the given xsl file
        /// </summary>
        /// <param name="xslUrl">xsl url/filename</param>
        /// <returns>returns "text/xml" or "text/plain"</returns>
        private string GetXslOutputMethod(string xslUrl)
        {
            string sReturn = "xml";  //default to xml

            try
            {
                XNamespace xsl = "http://www.w3.org/1999/XSL/Transform";
                XDocument xmlDoc = XDocument.Load(xslUrl);

                var qry = from r in xmlDoc.Descendants(xsl + "stylesheet")
                          select r.Element(xsl + "output");
                
                XElement xslOutput = qry.First();
                if (xslOutput != null) { sReturn = xslOutput.Attribute("method").Value; }
            }
            catch (Exception ex)
            {
                // there was a problem trying to get the output method
                // we'll just use "xml"
            }

            sReturn = sReturn == "text" ? "text/plain" : "text/xml";
            return sReturn;
        }
    
</script>