Just for what it's worth: you are presuming China is backing Iran for the long term, when they could be using it as a bargaining chip against a different conflict with the US / western powers. E.g. Tibet, Xinjiang, Taiwan, the Koreas, to name the ones just bordering / within China. That said, I agree Iran has acted rational to their means, but as the country tends dangerously close to provoking an Israeli attack, one might alter that viewpoint.