CODEWITHSUNDEEP
c#svg
JSarwer
JSarwer

Reputation: 313

How to properly validate a svg string in C#?

I'm trying to verify that a given string is valid svg using this little util method I made:

public static bool IsValidSvg(string str) {
    try {
        var svg = XDocument.Load(new StringReader(str));
        return svg.Root.Name.LocalName.Equals("svg");
    } catch {
        return false;
    }
}

This works for 90% of the cases, but, for instance, I have an svg which has an opening tag as follows:

<svg version="1.1" id="Layer_2" xmlns:x="&ns_extend;" xmlns:i="&ns_ai;" xmlns:graph="&ns_graphs;"
 xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:a="http://ns.adobe.com/AdobeSVGViewerExtensions/3.0/"
 x="0px" y="0px" width="599.33398px" height="490.66748px" viewBox="0 0 599.33398 490.66748"
 enable-background="new 0 0 599.33398 490.66748" xml:space="preserve">

Then the validation fails because it doesn't know what ns_extend is... It throws:

System.Xml.XmlException: Referenced entity 'ns_extend' does not exist. Line 1, position 53.

How can I get around this? The svg renders properly, so it should be a valid svg...

Upvotes: 2

Views: 1977

Answers (1)

a-ctor
a-ctor

Reputation: 3733

A quick and dirty fix for your method:

private static bool IsSvg(string input)
{
    try
    {
        using (var file = new FileStream(input, FileMode.Open, FileAccess.Read))
        using (var reader = new XmlTextReader(file) {XmlResolver = null})
            return reader.Read() && reader.Name.Equals("svg", StringComparison.InvariantCultureIgnoreCase);
    }
    catch
    {
        return false;
    }
}

By setting the XmlResolver property to null the reader will ignore DTD reference.

Upvotes: 3

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