tracing.go
func (s *injectableSpan) initFromOpenTracing(span opentracing.Span) error {
	return span.Tracer().Inject(span.Context(), zipkinSpanFormat, s)
}
func (s *injectableSpan) initFromOpenTracing(span opentracing.Span) error {
	return span.Tracer().Inject(span.Context(), zipkinSpanFormat, s)
}
// initFromOpenTracing initializes injectableSpan fields from an OpenTracing Span,
// assuming the tracing implementation supports Zipkin-style span IDs.