Compression Http

I have a question, this code that do when is running.
protected void Application_BeginRequest(object sender, EventArgs e)
{
HttpCompress(sender);
}
private void HttpCompress(object sender) { HttpApplication app = (HttpApplication)sender;
string acceptEncoding = app.Request.Headers["Accept-Encoding"]; Stream prevUncompressedStream = app.Response.Filter;
if (!(app.Context.CurrentHandler is Page) || app.Request["HTTP_X_MICROSOFTAJAX"] != null) return;
if (string.IsNullOrEmpty(acceptEncoding)) return; if (CompressScript(Request.ServerVariables["SCRIPT_NAME"])) { acceptEncoding = acceptEncoding.ToLower();
if (acceptEncoding.Contains("gzip") || acceptEncoding.Contains("*")) { // gzip app.Response.Filter = new GZipStream(prevUncompressedStream, CompressionMode.Compress); app.Response.AppendHeader("Conten ...