Flow control when posting "application / x-www-form-urlencoded" in WCF

Am I sending data to WCF using the method suggested in the Best way to support "application / x-www-form-urlencoded" send data using WCF?

I follow the example http://blogs.southworks.net/erossetto/2007/09/03/raw-http-post-with-wcf/ and everything looks fine. However, one problem is with the flow control in the request. I created a helper method like

    public static NameValueCollection ParsePOSTRequest(Stream input)
    {
        StreamReader sr = new StreamReader(input);
        string s = sr.ReadToEnd();
        sr.Dispose();

        return HttpUtility.ParseQueryString(s);
    }

I call this in all my methods, so I can more easily find the parameters. Now I noticed a problem when trying to access request information through WebOperationContext.Current. Any property or method simply throws an exception, for example The System.ServiceModel.Channels.MessageProperties object has been disposed., which, apparently, is due to the fact that the stream reader is in front of my business logic.