Question

I have a asp.net mvc route that is taking a url and doing a simple get and return the status code from the request.

<AcceptVerbs(HttpVerbs.Post)> _
Public Function ValidateUrlStatusCode(ByVal url As String) As ActionResult
   Dim code As Integer = 0

   Try
      Dim request As HttpWebRequest = CType(WebRequest.Create(url), HttpWebRequest)
      request.Method = "GET"
      request.AllowAutoRedirect = True
      Using response As HttpWebResponse = request.GetResponse
         response.Close()
         code = response.StatusCode
      End Using
   Catch ex As Exception
      code = HttpStatusCode.InternalServerError
   End Try
   Return Content(code, "text/plain")
End Function

Now if I use firefox (using Firebug) and go to the url http://www.facebook.com/blah.html, I get the expected 404 returned. However if I use my application to call the mvc route via an ajax call, I get 200. If I set the request object’s AllowAutoRedirect to false, I get 302. I never get a 404. I am verifying this once again through Firebug. Can anyone point out what I am doing wrong?

Thanks!

Answer 1

If you use FaceBook make sure you set the user agent or the site will redirect you to a standard HTML page explaining you to do so (thus the 200 status code):

request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0";

Also when a status code different than 200 is returned from the HttpWebRequest an exception will be thrown, and more specifically a WebException. So you need to trap this WebException and inside the Response property containing the HttpWebResponse you will find the 404 StatusCode.

Also I would probably use a WebClient to simplify the code:

Public Function ValidateUrlStatusCode(url As String) As ActionResult
    Dim code = 0
    Try
        Using client = New WebClient()
            client.Headers(HttpRequestHeader.UserAgent) = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0"
            Dim response = client.DownloadString(url)
        End Using
    Catch ex As WebException
        Dim httpResponse = TryCast(ex.Response, HttpWebResponse)
        If httpResponse IsNot Nothing Then
            code = CInt(httpResponse.StatusCode)
        End If
    End Try

    Return Content(code.ToString(), "text/plain")
End Function

And on the client:

<script type="text/javascript">
    $.ajax({
        url: '@Url.Action("ValidateUrlStatusCode")',
        type: 'POST',
        data: { url: 'http://www.facebook.com/blah.html' },
        success: function (result) {
            alert(result);
        }
    });
</script>