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From "Curt Arnold (JIRA)" <j...@apache.org>
Subject [jira] Commented: (COUCHDB-257) HTTP caching headers don't provide expected behaviour
Date Fri, 28 Aug 2009 20:43:32 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12748972#action_12748972
] 

Curt Arnold commented on COUCHDB-257:
-------------------------------------

Spent a few hours testing this today.

max_age still has a problem with rapid requests   The test case below fails when CouchDB returns
max-age=0, but works with a Expires date in the past.  Specifying Expires in the past does
appear to be effective.  That approach is currently used in couch_httpd_misc_handlers.erl.

Default headers are generated in two locations in couch_httpd.erl and once in couch_httpd_misc_handlers.erl.
 Should try to combine those so the default headers are only specified in one location.

Making CacheControl and Expires configurable would probably be the best solution with a default
like:

[httpd]
CacheControl = must-revalidate
Expires = 0

The following test will fail on IE 6 when Tools/Options/General/Temporary Internet Files/Check
for newer is set to automatic.


couchTests.basics = function(debug) {
  var result = JSON.parse(CouchDB.request("GET", "/").responseText);
  T(result.couchdb == "Welcome");

  var db = new CouchDB("test_suite_db", {"X-Couch-Full-Commit":"false"});
  db.deleteDb();

  db.createDb();

  // create a document and save it to the database
  var doc = {_id:"0",a:1,b:1};
  var result = db.save(doc);

  T(result.ok==true); // return object has an ok member with a value true
  var id = result.id;
  // reopen document we saved earlier
  var existingDoc = db.open(id);

  T(existingDoc.a==1);

  //modify and save
  existingDoc.a=4;
  db.save(existingDoc);

  var modifiedDoc = db.open(id);
  T(modifiedDoc.a == 4);


};


I'll work up a patch tonight.

> 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
>
>
> 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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