FileValidating runs server-side on the postback, before FileUploaded.
Set e.Cancel = True and the file never reaches your save logic - regardless of what
the client claimed.
What you should see: normal files are accepted and saved; an empty file or a .tmp file is listed as REJECTED with the reason, and no save occurs for it.
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Protected Sub Uploader1_FileValidating(ByVal sender As Object,
ByVal e As AjaxUploader.Events.FileValidatingEventArgs)
If e.FileSize <= 0 Then
e.Cancel = True
e.CancelReason = "Empty files are not allowed."
ElseIf String.Equals(System.IO.Path.GetExtension(If(e.FileName, "")),
".tmp", StringComparison.OrdinalIgnoreCase) Then
e.Cancel = True
e.CancelReason = ".tmp files are blocked by server policy."
End If
End Sub