Hi Scott,
Right, the download.taf generates the complete HTTP response -- header
plus data.
The problem is that the browser (or proxy) has cached the request,
following its own guidelines (or mine if I added the Expires property).
When a user changes the resource on the origin server, the browser
cache doesn't know that the cached entity no long matches the server.
The application in question has both content-management and
content-delivery aspects. Caching is important for the delivery, but
fresh content is needed for the management interface. One wants long
expiry, the other short.
You may be right that "selectively expiring" content is a good
compromise. I'm curious about ETags, but I'm not sure I really
understand them from reading the RFC.
bill
On Thursday, August 4, 2005, at 02:13 PM, Scott Cadillac wrote:
Hi Bill,
Using the local$HttpHeader variable you can dictate any HTTP response
command you like.
Generally when it comes to controlling client-side caching I just
manipulate
the "Expires" property or sometimes set a custom cookie to manage the
"Last
Modified" logic.
I've looked at the eTag thing, but find it overly complex for
something that
can usually be managed easier by selectively expiring your content in
timed
intervals.
If that's not helping, I guess I don't understand what you're after.
Remember, when it comes to client-side caching - the User's browser
will
sometimes make decisions beyond your control.
Good luck.
~ Scott Cadillac
~ 403-254-5002
~ [EMAIL PROTECTED]
~ Custom Software for Business
http://custom.softwarefor.net
~ The XML-Extranet Partnership
~ P.O. Box 69006
RPO Bridlewood SW
Calgary, Alberta
Canada T2Y 4T9
-----Original Message-----
From: Bill Conlon [mailto:[EMAIL PROTECTED]
Sent: Thursday, August 04, 2005 2:56 PM
To: [email protected]
Subject: Re: Witango-Talk: HTTP file cache
What about entity tags
(http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.3.3)?
I would have an auto increment column associated with the
thumbnail (or
the source document for that matter) to use an E-Tag instead of
last-modified in the response header of download.taf.
I presume if you provide an entity tag, the User-Agent will have to
re-validate every file, but in most cases would use the cached
resource. Anyone have any experience with this?
On Thursday, August 4, 2005, at 01:45 PM, Bill Conlon wrote:
Thx Scott & Roland. Using &<@RANDOM> will indeed cause the
freshly updated image to be displayed for the admin user
that updated
the content.
But I really want the cached items refreshed, so that other
users will
get the new thumbnail. I hate the idea of losing the
ability to cache,
but I need to think about this.
bill
On Thursday, August 4, 2005, at 01:26 PM, Scott Cadillac wrote:
Hi Bill,
Have you tried:
<img src="download.taf?_uid1=<@COLUMN
"thumb_id">&random=<@RANDOM>">
Just have your server-side code ignore the "random" argument.
Works for me.
~ Scott Cadillac
~ 403-254-5002
~ [EMAIL PROTECTED]
~ Custom Software for Business
http://custom.softwarefor.net
~ The XML-Extranet Partnership
~ P.O. Box 69006
RPO Bridlewood SW
Calgary, Alberta
Canada T2Y 4T9
-----Original Message-----
From: Bill Conlon [mailto:[EMAIL PROTECTED]
Sent: Thursday, August 04, 2005 2:21 PM
To: Witango-Talk
Subject: Witango-Talk: HTTP file cache
I know a few people on this list have addressed the issue
of dealing
with cached files. Here's my scenario:
I go to an admin page, and get some info on a file stored
in the db.
The page includes a thumbnail (also stored in the db), such as:
<img src="download.taf?_uid1=<@COLUMN "thumb_id">
the browser requests and caches the thumbnail image.
Response header
for this download is:
http://ccmh3.tothept.com/download.taf?_uID=165
Date: Thu, 04 Aug 2005 19:13:17 GMT
Server: Apache/2.0.54 (Unix) mod_perl/1.99_16 Perl/v5.8.5 DAV/2
PHP/4.3.10
Accept-Ranges: bytes
content-disposition: inline;
filename=spiritofcaring_gray_thumb.jpg
Last-Modified: Monday, 22-Sep-2003 10:48:26 GMT
Content-Length: 5448
Content-Type: image/jpeg
I then upload a replacement file, and in the process, the
application
invokes ImageMagick to generate a new thumbnail, and then
displays the
same page with updated information. Again the thumbnail is
referenced
as
<img src="download.taf?_uid1=<@COLUMN "thumb_id">
but the previous, cached, version appears.
If I force a cache refresh, my new response header looks like:
http://ccmh3.tothept.com/download.taf?_uID=165
Date: Thu, 04 Aug 2005 19:42:50 GMT
Server: Apache/2.0.54 (Unix) mod_perl/1.99_16 Perl/v5.8.5 DAV/2
PHP/4.3.10
Accept-Ranges: bytes
content-disposition: inline;
filename=thumb_spiritofcaring_logo_gray_sm.png
Last-Modified: Thursday, 04-Aug-2005 12:42:05 GMT
Content-Length: 6681
Content-Type: image/png
The thumbnail info is generally static, and should therefore be
cacheable, but in this case I'm displaying the stale info.
Does anyone
know any tricks, or must I instead create an entirely new
URI, giving
the thumbnail a new ID?
thanks.
Bill
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