25 December, 2008

Converting a Html News Page to RSS

This have been my little weekend project this weekend (ok, some Christmas preparations to).


As some of you know I play underwater rugby. The communication from the Swedish Underwater Rugby Association to it’s members is mainly through the news page on their site’s news page: http://www.ssdf.se/t3.aspx?p=51459 (in Swedish). This page is only exposing HTML and does not expose an rss-feed (they should have used SharePoint). My problem is that I never remember to visit the site with regular intervals, so I miss out on stuff.


As I truly am a RSS junkie, that’s what I wanted. To be able to get these news (together with all other news I’m interested in) in my feed reader. So the approach I took outlined:

  1. Get HTML from newspage
  2. Make sense out of and parse HTML
  3. Generate RSS XML and save to file
  4. Expose the RSS on my own web server

Doing all the parsing by hand didn’t sound very tempting so I Lived around a little and found the HtmlAgilityPack on CodePlex, which is a framework that let’s you query a HTML document in the same way you would query a XML document using XSLT or XPath. The release on codeplex was compiled against the 2.0 framework, I simply changed target framework for the project an recompiled, worked like a charm.

Let’s Get Going

Getting the HTML

The HtmlAgilityPack supports getting the HTML itself by using something like:

HtmlWeb hw = new HtmlWeb();
HtmlDocument newsDoc = hw.Load(url);

The problem I had with that (and it’s probably due to incompetence on my part) is that I could not get the right encoding (very important in Swedish due to our extended alphabet). So what I ended up doing was getting the HTML myself and load it into a HtmlAgilityPack HtmlDocument object:

// Did not manage to solve the encoding bit so I retrive the data myself first ...
HttpWebRequest webRequest = (HttpWebRequest) WebRequest.Create(urlToFetch);
HttpWebResponse webResponse = (HttpWebResponse) webRequest.GetResponse();

// ... and then apply the encoding while reading in the stream into HtmlAgilityPack object
HtmlDocument htmlDocument = new HtmlDocument();
htmlDocument.Load(webResponse.GetResponseStream(), Encoding.Default);

Parsing the HTML

Now it’s time to leverage the power of the HtmlAgilityPack, but first I did a manual analysis of the HTML using View Source and the IE Developer Toolbar. I found that I could identify each a news item by looking for a DIV-tag with the class attribute set to clMainnewsEntries.


So, let’s get cracking and find those nodes:

HtmlNodeCollection htmlNodeCollection = htmlDocument.DocumentNode.SelectNodes("//div[@class='clMainnewsEntries']");

foreach (HtmlNode newsNode in htmlNodeCollection)
    // ... generate rss items ...

That was easy, now the HTML stars working against me. A few issues are

No Author

The news have no author, that I easily can get to programmatically. But it aint really important either so I’m just setting it to “N/A”.

No Links

Not all news have links and if they do it’s hard to tell if it’s a link to the news item or something else. So to fill the link-element in the rss I try to find a link that has title tag (which seems to be the way this cms system handles read more links.

string link = string.Empty;

if (newsNode.SelectSingleNode(".//a[@title!='']") != null)
    link = newsNode.SelectSingleNode(".//a[@title!='']").Attributes["href"].Value;
    if (!link.StartsWith("http"))
        link = String.Format("{0}{1}", "http://www.ssdf.se/", link);

No Publishing Date

This one is trickier. To add on the confusion I learned the editors update a news item when they want to push it to the top of the list. So what I do here is simply put the date and time when I retrieve it the first time, keeping track of them with a hash (see next paragraph). This should work fine when it runs with a steady intervall, tough the first time it will give all news the same date.


To keep track of the items I calcluate a hash for each item and store that in a separate XML file.

public string ComputeHash(string Value)
    System.Security.Cryptography.MD5CryptoServiceProvider x =
        new System.Security.Cryptography.MD5CryptoServiceProvider();
    byte[] data = System.Text.Encoding.ASCII.GetBytes(Value);
    data = x.ComputeHash(data);
    string ret = "";
    for (int i = 0; i < data.Length; i++)
        ret += data[i].ToString("x2").ToLower();
    return ret;

I put this hash in the guid-tag of the RSS. So if the news is updated I hope they change something in it so it renders a different hash.

Building the RSS

It’s time to start building the RSS. I start creating the document using LinqToXml (which by the way is pure love to use and deserves a blog post all of it’s own):

// Creating XDocument
XDocument xDocument = new XDocument(
    new XDeclaration("1.0", "windows-1252", "true"),
    new XProcessingInstruction("xml-stylesheet", "type=\"text/xsl\" href=\"EvelntLog.xsl\"" ),
    new XElement("rss", new XAttribute("version", "2.0"),
         new XElement("channel",
                      new XElement("title", "UV-rugbynyheter"),
                      new XElement("link", HtmlDocument.HtmlEncode( "http://www.ssdf.se/t3.aspx?p=51459") ),
                      new XElement("description", "Undervattensrugbynyheter från SSDF"),
                      new XElement("language", "sv-se")

And then I add each item to item to the feed:

root.Add(new XElement("item", "",
      new XElement("title", newsNode.SelectSingleNode("h1").InnerHtml),
      new XElement("description", newsNode.OuterHtml),
      new XElement("link", link),
      new XElement("author", "N/A"),
      new XElement("pubDate", pubDate.ToString("r")),
      new XElement("guid", postHash)



I put this little program on my web server and used the windows scheduler to run it every 2 hours. And the final piece of code pushes the generated file out to the right directory.

    File.Copy(".\\" + ConfigurationManager.AppSettings["Filename"],
        ConfigurationManager.AppSettings["Filename"]), true);

You can grab the source code for the first working version here. Now it’s refactor time!

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