Asp – Grade D on Compress components with gzip

asp.netdeflategziphttpiis

I used the YSlow Firefox add-on and it return the follow result:

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Grade D on Compress components with gzip

There are 3 plain text components that should be sent compressed

* http://localhost:63808/WebSite/BemVindo/
* http://localhost:63808/WebSite/css/Global.css?...
* http://localhost:63808/WebSite/js/Global.js?...

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So I started to search and got this piece of code:

Global.asax

Private Sub Application_PreRequestHandlerExecute(ByVal sender As Object, ByVal e As EventArgs)

    Dim Response As HttpResponse = HttpContext.Current.Response
    Dim AcceptEncoding As String = HttpContext.Current.Request.Headers("Accept-Encoding")

    If Not String.IsNullOrEmpty(AcceptEncoding) AndAlso AcceptEncoding.Contains("gzip") OrElse AcceptEncoding.Contains("deflate") Then
        If AcceptEncoding.Contains("deflate") Then
            Response.Filter = New System.IO.Compression.DeflateStream(Response.Filter, System.IO.Compression.CompressionMode.Compress)
            Response.AppendHeader("Content-Encoding", "deflate")
        Else
            Response.Filter = New System.IO.Compression.GZipStream(Response.Filter, System.IO.Compression.CompressionMode.Compress)
            Response.AppendHeader("Content-Encoding", "gzip")
        End If
    End If

    Response.AppendHeader("Vary", "Content-Encoding")

End Sub

And now I have:

Grade A on Compress components with gzip

Fine, hum? The question is: Is the Application_PreRequestHandlerExecute event the best place to gzip/deflate the requests?

Best Answer

Not sure but your code might cause problem in pages using Ajax. The following page shows a similar code but cancel the compression if Ajax is detected: Enabling Gzip and Deflate HTTP Compression in ASP.NET pages. I translated the code in VB but didn't tried it.

Eric

  Private Sub Application_PreRequestHandlerExecute(ByVal sender As Object, ByVal e As EventArgs)
Dim app As HttpApplication = TryCast(sender, HttpApplication)
Dim acceptEncoding As String = app.Request.Headers("Accept-Encoding")
Dim prevUncompressedStream As Stream = app.Response.Filter

If Not (TypeOf app.Context.CurrentHandler Is Page OrElse app.Context.CurrentHandler.[GetType]().Name = "SyncSessionlessHandler") OrElse app.Request("HTTP_X_MICROSOFTAJAX") IsNot Nothing Then
  Return
End If

If acceptEncoding Is Nothing OrElse acceptEncoding.Length = 0 Then
  Return
End If

acceptEncoding = acceptEncoding.ToLower()

If acceptEncoding.Contains("deflate") OrElse acceptEncoding = "*" Then
  ' defalte
  app.Response.Filter = New DeflateStream(prevUncompressedStream, CompressionMode.Compress)
  app.Response.AppendHeader("Content-Encoding", "deflate")
ElseIf acceptEncoding.Contains("gzip") Then
  ' gzip
  app.Response.Filter = New GZipStream(prevUncompressedStream, CompressionMode.Compress)
  app.Response.AppendHeader("Content-Encoding", "gzip")
End If

End Sub

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