Dates vs. Deltas [was: An alternative to explicit revocation? ]

As far as I can tell, it's possible to get the same effect using
relative times as absolute times, though it's certainly far simpler to
use the relative times.

It's interesting to note that there is a now-deprecated format for the
Expires header that consists of an integer -- the number of seconds
till expiration.

When using absolute times, each intermediate needs to adjust the
expiration time to its own clock, and use the current time when
generating Date headers.  This is fairly clearly prohibited by the
current 1.1 spec, but earlier 1.0 specs were not so clear what date
the Date header corresponded to. (the origin server's date of sending,
or the intermediate server's).

So, if we stick with absolute dates, we need to adjust things so that
each proxy can do its own crude deskewing using the received Date
header vs. the local clock (which is actually pretty easy if you don't
get carried away).  We also need to define that Date means "time sent"
according to the server that generates it, so the deskewing can happen
at all (as Jeff points out).

If we switch to a relative time for Expires, this is all much simpler
to manage.  The only reason I can think of not to is to try to make
backwards compatibility with 1.0 servers work better.  Whether this is
relevant at all depends on what the common practice is for Date
headers in 1.0.  Are they the passed through as stamped by the
origin-server?  Or are they usually generated on the fly by each
intermediate?

--Shel

Received on Wednesday, 3 January 1996 23:42:43 UTC