Detect if file is html

Question

Detect if file is html

StewartBW 1,765

Hello

I need to detect if a file is html (any version ie 4 or 5), not by extension, but contents.

No need full html validation, just to find if it's html, specially distinguished with xml.

Can I use WebBrowser to load the file?

If file is not html, WebBrowser will report back?

If no easy way, the minimum validation which is opening and closing html tags would be enough, how to check their existance, because they can be in lower/upper case and different forms, html start tag can have additional info.

Thanks all :)

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Answer 1

Hi @StewartBW ,

You can attempt to read the first few bytes of the file and check for text patterns like <!DOCTYPE html> (for HTML5) or <html> (for older HTML versions).

Dim filePath As String = "yourfile.html"
Dim bufferSize As Integer = 4096 ' Read first 4KB of the file

Using fs As New System.IO.FileStream(filePath, System.IO.FileMode.Open, System.IO.FileAccess.Read)
    Dim buffer(bufferSize - 1) As Byte
    fs.Read(buffer, 0, bufferSize)

    Dim content As String = System.Text.Encoding.UTF8.GetString(buffer)

    ' Check for <!DOCTYPE html> or <html> tags in the initial bytes
    If content.IndexOf("<!DOCTYPE html", StringComparison.OrdinalIgnoreCase) >= 0 OrElse 
       content.IndexOf("<html", StringComparison.OrdinalIgnoreCase) >= 0 Then
        MessageBox.Show("This is an HTML file.")
    Else
        MessageBox.Show("This is not an HTML file.")
    End If
End Using

Best Regards.

Jiachen Li

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Detect if file is html

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