Brennan’s Blog

I read HTTP compression in ASP.NET 2.0 by Mads Kristensen the other day and tried it out on a website that is using ASP.NET AJAX. I found that while the development web server run by Visual Studio handles it all just fine, IIS 6 on the server does not. Somehow the process is corrupting the page state. So while I want to use the compression to get what I can for bandwidth savings I had to work around this problem.

What I did was check for the ViewState data on a request and if it was there I would not add the compression filter to the request. The initial page load will still be compressed but any PostBacks or AJAX callbacks will not. I can live with that for now. Below is the code snippet. You can get the full source on Kristensen's website.

On my website I was able to take a 50KB page down to 13KB.

void context_BeginRequest(object sender, EventArgs e)
{
    HttpApplication app = sender as HttpApplication;

    // do not compress PostBack requests (AJAX friendly)
    if (app.Context.Request.Params["__ViewState"] != null)
    {
        return;
    }

    if (app.Context.Request.FilePath.EndsWith(".aspx") ||
        app.Context.Request.FilePath.EndsWith(".ashx"))
    {
        if (IsEncodingAccepted(GZIP))
        {
            app.Response.Filter = new GZipStream(app.Response.Filter, CompressionMode.Compress);
            SetEncoding(GZIP);
        }
        else if (IsEncodingAccepted(DEFLATE))
        {
            app.Response.Filter = new DeflateStream(app.Response.Filter, CompressionMode.Compress);
            SetEncoding(DEFLATE);
        }
    }
}