wse chainstream override

[simon taylor]

Dear all,
I'm wanting to write a wse filter to intercept the incoming stream to
a webservice.
According to the wse help you can do.....

public override Stream ChainStream( Stream stream )
{
...............
}

However, I'm writing an input filter to do this and as far as I know
they must (?) inherit from SoapInputFilter thus

public class InputFilter : SoapInputFilter
{
public override void ProcessMessage(SoapEnvelope envelope)
{
.................
}
}

which overrides ProcessMessage nicely. However SoapInputFilter does
not have a ChainStream to override ? - ChainStream is a member of
WebServicesExtension (I believe).

So I guess my question has two possible answers - Is it possible to
get at the stream from within SoapInputFilter ?
Or is it possible to inherit from WebServicesExtension as an input
filter ?

Ive tried
public class InputFilter : WebServicesExtension
and I get an error message....
"..... is not derived from Microsoft.Web.Services.SoapInputFilter"


Any answers would be much appreciated as the wse help is a little
cryptic to my fragile mind
If you can help please try and explain your solution as you would to a
three year old
cheers
simon