>Postel's law states that one should be conservative in what one does, but liberal in what one accepts from others; this is great advice for life, but terrible

>Postel's law states that one should be conservative in what one does, but liberal in what one accepts from others; this is great advice for life, but terrible advice for writing software. This perfectly sums up what I've tried to say about this "robustness principle" for years. Fantastic. SIP inherits these status code ideas, plus adds super-neato whiz-bang headers, like "Retry-After", that allow comments. Their actual example is "Retry-After: 300 (in a meeting)". It's beyond delusional. Except.... someone read the spec. They see Retry-After. They then implement it in some big iron that connects to the PSTN. Little SIP VoIP provider comes along, passes along this dumb header, Retry-After. Suddenly, big switch guy is pissed, as Verizon has disabled all his lines as "Retry-After" gets translated into "shutdown trunk" or something. Awesome. Really a round of applause for the IETF there. (You have got to know that these headers came about just sitting around thinking shit up, vs actually trying to implement telephony. That's why SIP says it might be used "to run a chess game", but has a mandatory "Call-ID" field. Oops.)