' Download the HTML source code at the specified URL' You can optionally specify the username/password credentials,'  in case the page uses Basic Authentication' Returns a null string if any error occursFunction GetHtmlPageSource(ByVal url As String, Optional ByVal username As _    String = Nothing, Optional ByVal password As String = Nothing) As String    Dim st As System.IO.Stream    Dim sr As System.IO.StreamReader    Try        ' make a Web request        Dim req As System.Net.WebRequest = System.Net.WebRequest.Create(url)        ' if the username/password are specified, use these credentials        If Not username Is Nothing AndAlso Not password Is Nothing Then            req.Credentials = New System.Net.NetworkCredential(username, _                password)        End If        ' get the response and read from the result stream        Dim resp As System.Net.WebResponse = req.GetResponse        st = resp.GetResponseStream        sr = New System.IO.StreamReader(st)        ' read all the text in it        Return sr.ReadToEnd    Catch ex As Exception        Return ""    Finally        ' always close readers and streams        sr.Close()        st.Close()    End TryEnd Function