how to capture the HTTPResponseBody data in ASP.Net?

I have written a HTTPModule after deriving from IHttpModule as follows.

public void Init(HttpApplication httpApplication)
{
    EventHandlerTaskAsyncHelper taskAsyncHelper = new EventHandlerTaskAsyncHelper(LogMessage);
    httpApplication.AddOnBeginRequestAsync(taskAsyncHelper.BeginEventHandler, taskAsyncHelper.EndEventHandler);
}

private async Task LogMessage(object sender, EventArgs e)
{
           var app = (HttpApplication)sender;
            var ctx = app.Context;
           string myURL = ((HttpApplication)sender).Context.Request.Url.ToString();

          StreamReader reader = new StreamReader(((HttpApplication)sender).Context.Request.InputStream);

            try
            {
                string body = reader.ReadToEnd();
            }
            finally
            {
                reader.BaseStream.Position = 0;
            }

            StreamReader ResponseStreamReader = new StreamReader(((HttpApplication)sender).Context.Response.OutputStream);

}

The StreamReader code is throwing error(the exact error message is: System.ArgumentException: Stream was not readable).

How can I read the ResponseBody of a HTTP request. I am using .Net 4.5. Thank you, John

The OutputStream represents the output as it is being written, so you may need to set the reader position to 0 before attempting to read from it.