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https://issues.apache.org/jira/browse/COUCHDB-257?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jan Lehnardt closed COUCHDB-257.
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Resolution: Won't Fix
>From dev@:
Christopher Lenz:
This is a somewhat misleading description; it's not the lack of an Expires
header on CouchDB responses that results in incorrect caching, it's a (really
ugly) bug in the XMLHttpRequest implementation of IE6 that does this. As far as
I know, the cache control headers sent by CouchDB are absolutely correct
according to the HTTP specification. Unconditionally adding an Expires header
(with a date in the past) just to workaround the XHR bug in IE6 *completely
disables* any caching by any user agent!
Note also that IE6 gets cache invalidation right when you don't go through
XMLHttpRequest (that is, request CouchDB documents/views directly).
A CouchDB-based application that runs on the client (CouchApp-style), and that
needs to work on IE6, has the option to force all XHR requests to invalidate
the cache (for example by using jQuery's "cache=false" option to AJAX requests,
which simply adds an extra timestamp-valued query string parameter). In
addition, it can choose to do so if, and only if, it detects to be running on
IE6. And of course, applications accessing CouchDB only through server-side
code do not need to care about this issue at all.
Presumably we *could* add the browser detection and the conditional addition of
an Expires header to the CouchDB HTTP server, but browser detection is a really
slippery slope that I think we should avoid, and IE6 is likely (or so I hope)
to be pretty much extinct by the time CouchDB reaches the 1.0 mark. In any
case, I'm -1 on any patch that does this unconditionally, and -0.5 on any patch
that does the Expires header dance conditionally. I'd be okay with adding the
cache busting trick to Futon (but again, only conditionally), and documenting
the issue and workaround for CouchApps.
> HTTP caching headers don't provide expected behaviour
> -----------------------------------------------------
>
> Key: COUCHDB-257
> URL: https://issues.apache.org/jira/browse/COUCHDB-257
> Project: CouchDB
> Issue Type: Bug
> Components: HTTP Interface
> Affects Versions: 0.8.1, 0.9
> Environment: Server: Ubuntu Hardy on x86. Client: Windows XP (32-bit).
> Reporter: Vinay Sajip
> Priority: Minor
> Attachments: caching-header-patch.diff, expires.patch
>
>
> The HTTP caching headers currently put out cause IE (for example) to not
> display information correctly in Futon. It's easy to reproduce: I open
> windows in Firefox and IE simultaneously, do an update using Firefox (e.g.
> add a new document) and refresh the IE window. The updated document count is
> not shown. If I clear the browser cache and try again, the updated
> information is displayed. The HTTP header put out is
> Cache-Control: must-revalidate
> which seems to me insufficient - for IE, at least. Is there way of
> configuring these headers, to for example
> Cache-Control: no-cache
> Pragma: no-cache
> Expires: some date in the past, or the same value as the Date: header
> Christopher Lenz has said about this that "This is due to extra-aggressive
> (and against the HTTP spec) caching that IE does on XMLHTTPRequests. A
> patch would need to do user agent sniffing to conditionally add the "cache:
> false" parameter to the jQuery ajax() invocations in jquery.couch.js (and
> maybe elsewhere). I wouldn't want to add this for all user agents, as it
> basically circumvents any caching for AJAX requests (even for
> not-craptastically-broken implementations), and thus would add quite a bit
> of unnecessary overhead."
> To this, I would comment that I don't believe a patch to the client-side code
> in Futon would be sufficient. There are other clients out there, some of
> which will be on Windows and so by default use the (acknowledgely broken)
> Microsoft stack. In my view it is more important to err on the side of
> correctness than performance - so I believe the headers generated server-side
> need to change, as well as perhaps Futon client-side changes.
> I note that handle_uuids_req in couch_httpd_misc_handlers.erl uses the
> no-cache/Expires scheme I mention.
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