Re: Snapshot-date

Roy T. Fielding (fielding@simplon.ICS.UCI.EDU)
Tue, 19 Jul 1994 08:40:37 +0200

>>> snapshot-date: <date>
>> They already do -- it's called the "Date:" header. How the cache managers
>> interpret/use that information is what matters.
> That's what I thought at first. It turns out that the "Date:" header
> is very weakly defined in the RFCs and is likely to contain just about
> anything from the date the document was created to the date it is sent
> from the server. In other words, if "Date:" were used consistently, I
> would agree that what I have proposed is redundant.

Nonsense -- most of the HTTP2 spec is defined "weakly" and yet the
WWW seems to get along quite well. The "Date:" header ALWAYS represents
the timestamp when the rfc822-type message was generated.
If any software is using it to mean something else, then that software
is broken and must be fixed. Period.

All HTTP servers that I know of follow this behavior consistently.
As far as I know, all cache managers do the same -- if they don't,
it is likely because they are a simple hack (i.e. saving the entire
message in a file rather than separating the headers from the content)
and such are not likely to be protocol-compliant to begin with.

> I'm not sure that it would be safe to build on "Date:". That's why I am
> proposing a new header line with a very specific definition.

It is far easier to fix the non-compliant servers (if there are any) than
it is to add to them a new "feature" which is, by definition, completely
redundant. If the definition of "Date:" in the HTTP2 spec is weak, then
propose the specific wordage that will strengthen the definition. I am
sure that, if the definition is accurate, it will be added to the HTTP2
spec (the people at CERN are always willing to improve the WWW
documentation ... they just rarely have the time to do it themselves).

...Roy Fielding ICS Grad Student, University of California, Irvine USA
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