I
believe that HTTP switched to using an integer based expiry (i.e. max-age)
mechanism (rather than date) to get around the problem of unsynchronized
clocks. If you send an absolute time (in an absolute time zone), you are
depending on the clocks on the client and server being in sync. A lot of
applications want to cache content for just a few minutes, which is well within
the possible error of clock synchronicity.
If for
some reason we really want to use an absolute date for expiry, the server would
have to send back its current date so that the client can calculate how long the
content should remain fresh. We would also have to be explicit that the
expiry date was to be calculated relative to the server's returned current
date.
Cheers,
Sasha.
-----Original Message-----
From: Michael Freedman
[mailto:]
Sent: Monday, September 23,
2002 4:51 PM
To:
Subject:
Re: [wsrp-wsia] [I#97] Caching Mechanism
If I recall
correctly, "expires" refers to the refHandle not the content. I.e. it
defines the length of time the refHandle will be valid for between
requests. As such it is a duration -- which is reset per request.
Hence its definition as an "int". Content expiration isn't affected by
access, hence using an absolute time can be considered. Using a
duration, however, would also be valid. We need to decide which is more
common/convenient for our developers. I.e. Is it more common/easier to
say this content expires in 30 minutes or to dynamically compute when 30
minutes from now is (in some absolute timezone form)?
-Mike-
"Tamari, Yossi" wrote:
Hi
Gil,I must be misreading the spec, because it seems to me that expires
is an int number of seconds currently in the spec (which may not be the the
right way, but that's what was decided).As for scoping to the Producer,
can you please explain how that works around the need for other scopes
(unless they are coded into the
validationTag)? Yossi.
-----Original Message-----
From: Gil Tayar [mailto:]
Sent: Monday, September 23,
2002 7:23 AM
To:
Subject: RE: [wsrp-wsia] [I#97] Caching
Mechanism
Good
questions.On the scope
question, I would scope it to the Producer. This is the easiest and
works around problems with the other
scopes.On the type of time
- the validUntil is a "date-time" field just like Expires is, and I
suggest we use the xsd:dateTime type for it (or whatever its exact name
is). This means that the time is an absolute
time.
-----Original Message-----
From: Tamari, Yossi [mailto:]
Sent: Thu, September 19, 2002
17:56
To: 'Gil
Tayar';
Subject: RE: [wsrp-wsia] [I#97] Caching
Mechanism
What is the scope of the cached fragments? user? session?
entity? Should this be explicitly returned in the markupResponse or in
the metadata of the entity, or does the entity encode it into the
validationTag if it wants to?Should we return the
(absolute) expiration time or the (relative) amount of time until
expiration? on the "expires" field I was for expiration time but I was
out-voted. Yossi.
-----Original Message-----
From: Gil Tayar [mailto:]
Sent: Thursday, September
19, 2002 9:03 AM
To:
Subject: [wsrp-wsia] [I#97]
Caching Mechanism
Topic:
interfaceClass: TechnicalTitle: Caching MechanismDocument Section: Interfaces/6.1Description:I am
submitting the following proposition to the committee as a proposition
for dealing with caching of the markup. This proposition deals with
"Expires"-like methods of caching, along with
"If-Modified-Since/ETags" type of caching. I believe it is simple
enough to be included in the v1.0 spec.Caching Proposal[The
proposal is described as edits to the spec]6.1
Operations [getMarkup][instead of expires in
markupResponse, add the following]cacheControl: A
data structure, defined in Section 11, which includes information
which CAN be used by the Consumer to cache the markup. This structure
includes: validUntil: The
time at which the markup is valid. Until that time the Consumer CAN use
its cache entry instead of calling getMarkup. After
this time passes, the Consumer MAY continue to use this cache entry,
but only after validating it with a getMarkup
operation, using the validationTag
below, if given. validationTag: The Consumer MUST store this tag along with the
markup while the markup is valid.
This enables the Producer to use this tag to invalidate the cache
entry by sending an invalidationTagPrefix in the performInteraction operation. After the markup expires,
the Consumer CAN send the validationTag in
the markupResponse to indicate that it still has the markup but
would like to validate it. The Producer returns a fault response [TBD]
to indicate that the markup is still valid, otherwise if it returns
markup , the Consumer MUST invalidate the old
markup.[add to markupContext the
following field] validationTag:
This field CAN be sent to indicate that the Consumer has cached markup
(which was tagged by the Producer with this value) and wishes to check
whether it is still valid. See validationTag in
markupResponse for more
information. 6.1 Operations
[performInteraction][add
the following field to interactionResponse] invalidationTagPrefix: If the Producer returned this value, the
Consumer MUST expire all markup-s who's
validationTag begins with this value. The Consumer MUST not call
getMarkup with these invalidationTag-s
to validate these expired markup-s. [add
these fields to the relevant places in section
11]%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Discussion:
