Trigger to execute just before closing the span

        :param opentracing.span.Span  span: the SpanContext instance
        :param Any obj: Object to use as context
        :param dict kwargs: additional data

def _postrun(cls, span, obj, **kwargs):
        """ Trigger to execute just before closing the span

        :param opentracing.span.Span  span: the SpanContext instance
        :param Any obj: Object to use as context
        :param dict kwargs: additional data
        """
        span.set_tag("response.status_code", obj.status_code)
        span.set_tag(
            "response.content_lenght", len(getattr(obj, 'content', ""))
        )