Validates that the given params match the expected length and types for this 
        interface and function.  

        Returns two element tuple: (bool, string)

        - `bool` - True if valid, False if not
        - `string` - Description of validation error, or None if valid

        :Parameters:
          iface_name
            Name of interface
          func_name
            Name of function
          params
            List of params to validate against this function

def validate_request(self, iface_name, func_name, params):
        """
        Validates that the given params match the expected length and types for this 
        interface and function.  

        Returns two element tuple: (bool, string)

        - `bool` - True if valid, False if not
        - `string` - Description of validation error, or None if valid

        :Parameters:
          iface_name
            Name of interface
          func_name
            Name of function
          params
            List of params to validate against this function
        """
        self.interface(iface_name).function(func_name).validate_params(params)