code: def _GetRequestClass(self, method_descriptor):
      
      if method_descriptor.containing_service != self.descriptor:
        raise RuntimeError(
            'GetRequestClass() given method descriptor for wrong service type.')
      return method_descriptor.input_type._concrete_class
docs: Returns the class of the request protocol message.
  
      Args:
        method_descriptor: Descriptor of the method for which to return the
          request protocol message class.
  
      Returns:
        A class that represents the input protocol message of the specified
        method.