Converting RSS Feed through URL to XPathNavigator

In one of my project, i was required to read RSS Feed from a website, cache it and then output the RSS feed onto website that i am working on using XSLT.

To accomplish this, I have used open source library or code, they are RSS.Net and CacheHelper

It took me sometime to accomplish these as i run into some problems. They are:

1. XML Document root element missing

2. XML Document element not closed properly which cause memory leakage

After several trials and error, i found out that RssWriter in RSS.Net works fine if you output the xml into a document, however it is not the same case if you were to output it onto a Stream.

So the following code that output RSS onto a file works fine:

var writer = new RssWriter(@"c:\\test.ml");

writer.Write(feed.Channels[0]);

writer.Close();

However the following code that deal with memory stream doesnt work

var rssXmlDoc = new XmlDocument();

var memStream = new MemoryStream();

var writer = new RssWriter(memStream, Encoding.UTF8);

writer.Write(feed.Channels[0]);

writer.Close();

rssXmlDoc.Load(memStream);

-- This will not work, since the stream is already closed

so because of that i thought it should be

rssXmlDoc.Load(memStream)

writer.Close();

-- But this doesnt work as well, because without writer.Close(), the last element is not closed properly.

so I modify the RSS.Net and create a method CloseDocument() that close the element without first closing the writer.

so the code becomes

var rssXmlDoc = new XmlDocument();

var memStream = new MemoryStream();

var writer = new RssWriter(memStream, Encoding.UTF8);

writer.Write(feed.Channels[0]);

writer.CloseDocument();

rssXmlDoc.Load(memStream);

writer.Close();

-- We are almost there. This will still throw an error and the error will be XML Root document element missing

we need to add the following line in red

var rssXmlDoc = new XmlDocument();

var memStream = new MemoryStream();

var writer = new RssWriter(memStream, Encoding.UTF8);

writer.Write(feed.Channels[0]);

writer.CloseDocument();

memStream.Position = 0;

rssXmlDoc.Load(memStream);

writer.Close();

this will move the read/write location back to the start of the stream.

Finally the method that i came out with to get FeedUrl to XPathNavigator is

public class ExternalFeed

{

//Default cache time will be 1 minute

public const int DefaultCacheTime = 60;

public string FeedUrl { get; private set; }

public int CacheTimeInSeconds { get; private set; }

public ExternalFeed(BaseItem definitionItem)

{

if (definitionItem == null)

{

Log.Error("ExternalFeed: definition item is null", this);

return;

}

FeedUrl = definitionItem[Constants.MeltwaterFields.FeedUrl];

var secondString = definitionItem[Constants.MeltwaterFields.CacheTime];

int second;

CacheTimeInSeconds = int.TryParse(secondString, out second) ? second : DefaultCacheTime;

}

///

/// Load data from the external source. to be called after construction

///

/// True if loaded successfully, otherwise false

public bool Load()

{

//Ensure that the URL is valid

if (string.IsNullOrEmpty(FeedUrl))

{

Log.Error("ExternalFeed: Feed Url is empty", this);

return false;

}

var feed = RssFeed.Read(FeedUrl);

CacheHelper.Add(feed, FeedUrl, CacheTimeInSeconds);

return true;

}

///

/// Get the data of the feed

///

/// The feed data

public XPathNavigator GetData()

{

RssFeed feed;

if (!CacheHelper.Get(FeedUrl, out feed)) {

Load();

CacheHelper.Get(FeedUrl, out feed);

}

var rssXmlDoc = new XmlDocument();

var memStream = new MemoryStream();

var writer = new RssWriter(memStream, Encoding.UTF8);

writer.Write(feed.Channels[0]);

writer.CloseDocument();

//This will move the read/write location back to the start of the Stream and allow the XMLDocument to read in the entire contents

memStream.Position = 0;

rssXmlDoc.Load(memStream);

writer.Close();

return rssXmlDoc.CreateNavigator();

}

}

Here is the other code for Closing Document in RSS.NET. The code below is from "RssWriter.cs" class

///

Closes instance of RssWriter.

/// Writes end elements, and releases connections

/// Occurs if the RssWriter is already closed or the caller is attempting to close before writing a channel.

public void Close()

{

writer.Close();

writer = null;

}

///

///

///

public void CloseDocument()

{

if (writer == null)

throw new InvalidOperationException("RssWriter has been closed, and can not be closed again.");

if (!wroteChannel)

throw new InvalidOperationException("Can't close RssWriter without first writing a channel.");

writer.WriteEndElement(); //

writer.WriteEndElement(); // or

writer.Flush();

}