System.ServiceModel.Syndication.SyndicationFeed throws when the RSS document includes a <script> block embedded in an element

Question

The code:

using (XmlReader xmlr = XmlReader.Create(new StringReader(allXml)))
{
    var items = from item in SyndicationFeed.Load(xmlr).Items
        select item;
}

The exception:

Exception: System.Xml.XmlException: Unexpected node type Element. 
   ReadElementString method can only be called on elements with simple or empty content. Line 11, position 25.
   at System.Xml.XmlReader.ReadElementString()
   at System.ServiceModel.Syndication.Rss20FeedFormatter.ReadXml(XmlReader reader, SyndicationFeed result)
   at System.ServiceModel.Syndication.Rss20FeedFormatter.ReadFeed(XmlReader reader)
   at System.ServiceModel.Syndication.Rss20FeedFormatter.ReadFrom(XmlReader reader)
   at System.ServiceModel.Syndication.SyndicationFeed.Load[TSyndicationFeed](XmlReader reader)
   at System.ServiceModel.Syndication.SyndicationFeed.Load(XmlReader reader)
   at Ionic.ToolsAndTests.ReadRss.Run() in c:\dev\dotnet\ReadRss.cs:line 90

The XML content:

<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet type="text/xsl" href="https://www.ibm.com/developerworks/mydeveloperworks/blogs/roller-ui/styles/rss.xsl" media="screen"?><rss version="2.0" 
  xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:atom="http://www.w3.org/2005/Atom" >
<channel>
  <title>Software architecture, software engineering, and Renaissance Jazz</title>
  <link>https://www.ibm.com/developerworks/mydeveloperworks/blogs/gradybooch&lt;/link&gt;
  <atom:link rel="self" type="application/rss+xml" href="https://www.ibm.com/developerworks/mydeveloperworks/blogs/gradybooch/feed/entries/rss?lang=en" />
  <description>Software architecture, software engineering, and Renaissance Jazz</description>
  <language>en-us</language>
  <copyright>Copyright <script type='text/javascript'> document.write(blogsDate.date.localize (1273534889181));</script></copyright>
  <lastBuildDate>Mon, 10 May 2010 19:41:29 -0400</lastBuildDate>

As you can see, on line 11, at position 25, there's a script block inside the <copyright> element.

Other people have reported similar errors with other XML documents.

The way I worked around this was to do a StreamReader.ReadToEnd, then do Regex.Replace on the result of that to yank out the script block, before passing the modified string to XmlReader.Create(). Feels like a hack.

---

1. Has anyone got a better approach? I don't like this because I have to read in a 125k string into memory.

2. Is it valid rss to include "complex content" like that - a script block inside an element?

Answer 1

No, noone has a better approach.

No, it sure doesn't look like valid RSS. at the very least it's bad manners.

Answer 2

You can subclass XmlTextReader and override ReadElementString to skip or modify the offending element as it's being read. Still feels like a hack but at least avoids the pre-processing with regex.

Here's a simple implementation that gets the job done:

class BrokenFeedXmlReader : XmlTextReader 
{
    // Additional XmlTextReader constructors can be added in 
    // similar fashion as needed
    public BrokenFeedXmlReader(TextReader input)
        : base(input)
    {
    }

    public override string ReadElementString()
    {
        if ("copyright" == Name)
        {
            base.Skip();
            return String.Empty; 
        }

        return base.ReadElementString();
    }            
}

Your example code would then look something like this:

using (XmlReader xmlr = new BrokenFeedXmlReader(new StringReader(allXml)))
{
    var items = from item in SyndicationFeed.Load(xmlr).Items
                select item;
}