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I'm writing xml with XmlWriter. My code has lots of sections like this:

xml.WriteStartElement("payload");
ThirdPartyLibrary.Serialise(results, xml);
xml.WriteEndElement(); // </payload>

The problem is that the ThirdPartyLibrary.Serialise method is unreliable. It can happen (depending on the variable results) that it doesn't close all the tags it opens. As a consequence, my WriteEndElement line is perverted, consumed closing the library's hanging tags, rather than writing </payload>.

Thus I'd like to make a checked call to WriteEndElement that checks the element name, and throws an exception unless the cursor is at the expected element. 

xml.WriteEndElement("payload");

You can think of this like XmlReader.ReadStartElement(name) which throws unless the cursor is at the expected place in the document.

How can I achieve this?

Edit: A second use case for this extension method would be to make my own code more readable and reliable.

Colonel Panic
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  • Can you send a new `XmlWriter` to `ThirdPartyLibrary.Serialise` and check that explicity before adding it to your `xml` object? – zimdanen Apr 04 '13 at 14:02
  • Can you validate `results` somehow before passing it to `Serialise`? (i.e. can you repro the breaking of the serialise method when you pass in certain types of results) – keyboardP Apr 04 '13 at 14:29
  • @KeyboardP — the third party library is actually a user-supplied plug-in implementing an interface, so it's not to be trusted. – Colonel Panic Apr 04 '13 at 14:51

2 Answers2

1

XMLWriter is just writes the given xml information in the stream with out any validation. If it does any validation while writing the xml tags, the performance problem will arise while creating the big xml file.

Creating the XML file using XMLWriter is up to developer risk. If you want to do any such kind of validation, you can use XMLDocument.

If you really want to do this validation in XMLWriter, you have to create the writer by using String or StringBuilder. Because, if you use Stream or TextWriter you can't read the information which is written into the stream in the middle of writing. In Every update of the XML you have to read the string and write your own method to validate the written information.

I Suggest you to use XMLDocument for creating these type of xml.

petchirajan
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0

In the end, I wrote an extention method WriteSubtree that gives this usable API:

using (var resultsXml = xml.WriteSubtree("Results"))
{
    ThirdPartyLibrary.Serialise(results, resultsXml);
}

The extension method XmlWriter.WriteSubtree is analogous to .NET's XmlReader.ReadSubtree. It returns a special XmlWriter that checks against funny business. Its dispose method closes any tags left open.

Colonel Panic
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