Testing whether or not something is parseable XML in C# [duplicate]

Question

Does anyone know of a quick way to check if a string is parseable as XML in C#? Preferably something quick, low resource, which returns a boolean whether or not it will parse.

I'm working on a database app which deals with errors that are sometimes stored as XML, and sometimes not. Hence, I'd like to just be able to test the string I grab from the database (contained in a DataTable) very quickly...and not have to resort to any try / catch {} statements or other kludges...unless those are the only way to make it happen.

Answer 1

It sounds like that you sometimes get back XML and sometimes you get back "plain" (non-XML) text.

If that's the case you could just check that the text starts with <:

if (!string.IsNullOrEmpty(str) && str.TrimStart().StartsWith("<"))
    var doc = XDocument.Parse(str);

Since "plain" messages seem unlikely to start with < this may be reasonable. The only thing you need to decide is what to do in the edge case that you have non-XML text that starts with a <?

If it were me I would default to trying to parse it and catching the exception:

if (!string.IsNullOrEmpty(str) && str.TrimStart().StartsWith("<"))
{
    try
    {
        var doc = XDocument.Parse(str);
        return //???
    }   
    catch(Exception ex)
        return str;
}
else
{
    return str;   
}

That way the only time you have the overhead of a thrown exception is when you have a message that starts with < but is not valid XML.

Answer 2

You could try to parse the string into an XDocument. If it fails to parse, then you know that it is not valid.

string xml = "";
XDocument document = XDocument.Parse(xml);

And if you don't want to have the ugly try/catch visible, you can throw it into an extension method on the string class...

public static bool IsValidXml(this string xml)
{
    try
    {
        XDocument.Parse(xml);
        return true;
    }
    catch
    {
        return false;
    }
}

Then your code simply looks like if (mystring.IsValidXml()) {