Check if folder on web exists or not - vb.net

Question

I'm creating desktop aplication and when I write a username in TextBox1 and on Button1.Click event it should check does folder on web exists.
As far I've tried this:
username = Me.TextBox1.Text
password = Me.TextBox2.Text
Dim dir As Boolean = IO.Directory.Exists("http://www.mywebsite.com/" + username)
If dir = true Then
Dim response As String = web.DownloadString("http://www.mywebsite.com/" + username + "/Password.txt")
If response.Contains(password) Then
MsgBox("You've logged in succesfully", MsgBoxStyle.Information)
Exit Sub
Else
MsgBox("Password is incorect!")
End If
Else
MsgBox("Username is wrong, try again!")
End If
First problem is that my boolean is giving FALSE as answer (directory exists for sure and all permissions are granted to see folder). I tried to solve that with setting dir = false and after that I go into first IF (but that's not what I want, since it should be TRUE, not FALSE)
There we come to second problem, in this line: Dim response As String=web.DownloadString("http://www.mywebsite.com/" + username + "/Password.txt") I get this error message: The remote server returned an error: (404) Not Found.
Anyone more experienced with this kind of things who can help me?

Answer 1

IO.Directory.Exists will not work in this case. That method only works to check for a folder on a disk somewhere (locally or network) ; you can't use it to check for the existence of a resource over HTTP. (i.e a URI)
But even if it did work this way, it's actually pointless to call it before attempting to download - the method DownloadString will throw an exception if something goes wrong - as you have seen, in this case it's telling you 404 Not Found which means "This resource does not exist as far as you are concerned". **
So you should try/catch the operation, you need to catch exceptions of type WebException, cast its Response member to HttpWebException, and check the StatusCode property.
An good example (albeit in C#) is here
** I say "as far as you are concerned" because for all you know, the resource may very well exist on the server, but it has decided to hide it from you because you do not have access to it, etc, and the developer of that site decided to return 404 in this case instead of 401 Unauthorised. The point being that from your point of view, the resource is not available.
Update:
here is the code from the answer I linked to, translated via this online tool because my VB is dodgy enough :). This code runs just fine for me in LinqPad, and produces the output "testlozinka"
Sub Main
Try
Dim myString As String
Using wc As New WebClient()
myString = wc.DownloadString("http://dota2world.org/HDS/Klijenti/TestKlijent/password.txt")
Console.WriteLine(myString)
End Using
Catch ex As WebException
Console.WriteLine(ex.ToString())
If ex.Status = WebExceptionStatus.ProtocolError AndAlso ex.Response IsNot Nothing Then
Dim resp = DirectCast(ex.Response, HttpWebResponse)
If resp.StatusCode = HttpStatusCode.NotFound Then
' HTTP 404
'the page was not found, continue with next in the for loop
Console.WriteLine("Page not found")
End If
End If
'throw any other exception - this should not occur
Throw
End Try
End Sub
Hope that helps.