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From "Benoit Chesneau (JIRA)" <>
Subject [jira] [Commented] (COUCHDB-431) Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
Date Fri, 26 Aug 2011 07:41:29 GMT


Benoit Chesneau commented on COUCHDB-431:

Thanks for the review. Answers follow

1. session is working even if the db is protected by readers. like any preflight request.
I wrote the patch like that

2. Actually the patch works with a db protected against readers. If you are authenticated,
 a CORS request will works,. Allows-credentials is always True in couch, we always test credentials
and cookies internally anyway. You can test it with test_cors2 /../cors2.html

3. Security: The patch actually means that we accept from any connections on a db except you
filter origins in a db. If you filter origin a db will only be accessed by this origin. It
won't increase risks, since then an ajax client is just considered like any HTTP client. If
you already have some exploits then they are already feasible with any http client that doesn't
care about cross domain which is only a browser things. I don't see any other way to bypass
our small security. 

If you want a better protections, some modules can be added to couch, couch_throttle, filtering
users depending on the referrer or hosts, etc...I have some if you are interested ;)

4. Applications and multiples db. That's not how the system was designed until now (and you
will have other problem to handle before to go on origin sync). I can see that happen however,
but I don't see the real problem of keeping dbs origins synchronized. Also what if your db
is dispatched on multiple hosts. This isn't really a problem I think.

I would like to keep db origin filtering, it actually works well with the current couchdb
design. If we want more granularity we can discuss it and add it later imo. There are a lot
to do on that part, but that's another debate and ticket imo

> Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
> -----------------------------------------------------------------------------------
>                 Key: COUCHDB-431
>                 URL:
>             Project: CouchDB
>          Issue Type: New Feature
>          Components: HTTP Interface
>    Affects Versions: 0.9
>            Reporter: James Burke
>            Assignee: Benoit Chesneau
>            Priority: Minor
>             Fix For: 1.2
>         Attachments: 0001-cors-support.-should-fix-COUCHDB-431-2.patch, 0001-cors-support.-should-fix-COUCHDB-431.patch,
0001-cors-support.-should-fix-COUCHDB-431.patch, A_0001-Generalize-computing-the-appropriate-headers-for-any.patch,
A_0002-Send-server-headers-for-externals-responses.patch, A_0003-Usably-correct-w3c-CORS-headers-for-valid-requests.patch,
A_0004-Respond-to-CORS-preflight-checks-HTTP-OPTIONS.patch, cors.html, test_cors2-1.tgz, test_cors2.tgz
> Historically, browsers have been restricted to making XMLHttpRequests (XHRs) to the same
origin (domain) as the web page making the request. However, the latest browsers now support
cross-domain requests by implementing the Access Control spec from the W3C:
> In order to keep older servers safe that assume browsers only do same-domain requests,
the Access Control spec requires the server to opt-in to allow cross domain requests by the
use of special HTTP headers and supporting some "pre-flight" HTTP calls.
> Why should CouchDB support this: in larger, high traffic site, it is common to serve
the static UI files from a separate, differently scaled server complex than the data access/API
server layer. Also, there are some API services that are meant to be centrally hosted, but
allow API consumers to use the API from different domains. In these cases, the UI in the browser
would need to do cross domain requests to access CouchDB servers that act as the API/data
access server layer.
> JSONP is not enough in these cases since it is limited to GET requests, so no POSTing
or PUTing of documents.
> Some information from Firefox's perspective (functionality available as of Firefox 3.5):
> And information on Safari/Webkit (functionality in latest WebKit and Safari 4):
> IE 8 also uses the Access Control spec, but the requests have to go through their XDomainRequest
object (XDR):
> and I thought IE8 only allowed GET or POST requests through their XDR.
> But as far as CouchDB is concerned, implementing the Access Control headers should be
enough, and hopefully IE 9 will allow normal xdomain requests via XHR.

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