Get The Parameter Values From A Web Service?

I have a web service (an ASP.NET .asmx page), and for debugging purposes I need to log all calls to the webservice, including values of all parameters passed into each call. So basically the first thing each WebMethod should do is log it's state with details of all the parameter values passed in to it.

So far so good. The complication is that I also want an automated way of getting the parameter values - there's quite a few webmethods with different signatures, and some of them have up to ~30 parameters, so manually coding against each specific parameter would likely be massively error-prone. I'd rather be able to call a method that looks at the current Http context and automatically uses that to grab and parse whatever has been passed in by the client.

But I hit a snag. When I look at HttpContext.Current.Request, it turns out that both the Form and QueryString collections are empty.