invokes callback that should return a (request,response) tuple.
        representing the SOAP request and response respectively.
        ps -- ParsedSoap instance representing HTTP Body.
        request -- twisted.web.server.Request

def processRequest(cls, ps, **kw):
        """invokes callback that should return a (request,response) tuple.
        representing the SOAP request and response respectively.
        ps -- ParsedSoap instance representing HTTP Body.
        request -- twisted.web.server.Request
        """
        resource = kw['resource']
        method = resource.getOperation(ps, None) # This getOperation method is valid for ServiceSOAPBinding subclass
        rsp = method(ps, **kw)[1] # return (request, response) but we only need response
        return rsp