Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!evax!texas!ylee
From: ylee@csl.dl.nec.com (Ying-Da Lee)
Newsgroups: comp.mail.sendmail
Subject: Re: Idempotence of S3
Message-ID: <1991Apr16.165044.21308@csl.dl.nec.com>
Date: 16 Apr 91 16:50:44 GMT
References: <1991Apr12.192026.11296@csl.dl.nec.com> <1991Apr12.213421.22457@decuac.dec.com> <1991Apr16.065813.24921@pa.dec.com>
Organization: NEC America, C & C Software Development Lab
Lines: 41

In article <1991Apr16.065813.24921@pa.dec.com> vixie@pa.dec.com (Paul Vixie) writes:
>I have rarely encountered S3's that hurt you if you ran them N>1 times.

Neither Sun's, nor UCB's, Ultrix's, Neils's, or mine for that matter,
has idempotent S3.

>Where I have encountered them, I have changed them.  I'm not sure where
>I read that S3 was supposed to be idempotent, but I did read it somewhere
>and it seems intuitively correct that it should work that way.  

What is the particular nature of S3 that would make it intuitively
correct to be idempotent?

Essentially S3 takes an address and puts <> around the portion of
focus to aid other rulesets in further processing.  I can't see
how any part of this would philosophically require it to be
idempotent.  From a practical point of view, since S3 is applied
at least once on each and every address in the header, it should
be particularly important to make it lean and clean.  Adding rule
or rules to it for the sole purpose of making it idempotent is a
bad idea bacause

1) it introduces unnecessary processing in S3, and
2) it encourages unnecessary invocation of S3 ("just to be safe",
   or "it won't hurt").

I suspect the practice of spurious invocation of S3 near the top
of S0 started out as a mistake and, once it was in, it stays in
because of the peculiar mystique of sendmail.cf.  The idempotence
requirement, if it exists, seems more likely a rationalization for
such practice after the fact.

Why don't the basic principles of good programming
apply in sendmail.cf?  It IS programming, isn't it?

	Ying-Da Lee			(214)518-3490
	C&C Software Development Lab
	NEC America			(214)518-3990 (FAX)
	ylee@csl.dl.nec.com
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