Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!hal!ncoast!allbery
From: allbery@NCoast.ORG (Brandon S. Allbery)
Newsgroups: news.software.b
Subject: Re: Format of "Expires: " header?
Message-ID: <1989Oct13.005537.17579@NCoast.ORG>
Date: 13 Oct 89 00:55:37 GMT
References: <4036@phri.UUCP>
Reply-To: allbery@ncoast.ORG (Brandon S. Allbery)
Followup-To: news.software.b
Organization: North Coast Public Access UN*X, Cleveland, OH
Lines: 48

As quoted from <4036@phri.UUCP> by roy@phri.UUCP (Roy Smith):
+---------------
| 	Perusing my news spool directory tree, I noticed two different
| formats for Expires: headers.  All the articles in news.announce.conferences
| have headers which look like the following (some header lines deleted):
| 
| |Expires: 11/10/89
| 
| while the articles in  news.newusers.questions have headers like this:
| 
| |Expires: 10 Oct 89 00:00:00 GMT
| 
| 	It was always my understanding that the proper "Expires: " format is
| as in the second example.  Is the first (mm/dd/yy) also legal?
+---------------

The "Expires:" line can, in practice, take almost any date format.  The smarts
are hidden in a YACC parser, "getdate.y", which can construct dates from
absolute or relative date specifications in a subset of English as well as in
various digital formats.  (Example:  my Welcome! postings in comp.sources.misc
get an Expires: of "6 weeks"; getdate.y has no trouble with this, it expires 6
weeks after arriving on a system.)

There *are* things it cannot or will not handle.  Example:  occasional
postings come in with "31 Dec 1969 21:00:00" expiration dates, which are the
usual result of passing 0 to the ctime() function.  Second example:  someone
in rec.motorcycles put "Expires: never" in his posting.  (The latter, BTW,
contained other header irregularities which convinced me that the poster
simply wasn't aware of the intended meaning of the headers.  I can define a
meaning for Expires: which does what the poster apparently intended, but it
isn't the official meaning (and would be less useful as well, since the
current meaning includes the restricted one):  the date is the date after
which the article is no longer applicable, as with e.g. a posting about
something to happen on a given date, which is less than useful the day *after*
the event.)  (How did I notice this?  Expire does the date conversion in C
news, and send mail to the news administrator if it can't understand the date.)

Anyway, while the relevant RFC's may define a specific date format, in
practice one can use almost anything.  I wouldn't worry about it unless Rick
Adams, Henry Spencer, Geoff Collyer, or some other news program architect
(Eric?) decides not to support the current date-handling mechanism.

++Brandon
-- 
Brandon S. Allbery, moderator of comp.sources.misc	     allbery@NCoast.ORG
uunet!hal.cwru.edu!ncoast!allbery		    ncoast!allbery@hal.cwru.edu
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