check uploaded file in vb.net

I need a snippet to check fi开发者_开发问答le for validity (I'm allowing users to upload xml files). So I need to check whether uploaded file is XML. The best I can think of is just check if extension is ".xml". What if its replaced?

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You can try loading it like this and catch the exception:

XDocument xdoc = XDocument.Load("data.xml"));

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Presumably, if they're uploading XML, then you're going to use it for something afterwards. In this case you should validate the XML against a Schema (XSD etc) so that you know you aren't going to hit unexpected values/layouts etc.

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In Urlmon.dll, there's a function called FindMimeFromData.

From the documentation

MIME type detection, or "data sniffing," refers to the process of determining an appropriate MIME type from binary data. The final result depends on a combination of server-supplied MIME type headers, file extension, and/or the data itself. Usually, only the first 256 bytes of data are significant.

So, read the first (up to) 256 bytes from the file and pass it to FindMimeFromData.

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If you must validate the xml (assuming you want to validate the entire thing) you can use the XmlDocument class and catch an exception if it's not XML.