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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 Mon, 29 Aug 2011 19:09:37 GMT


Benoit Chesneau commented on COUCHDB-431:

Hi Adam, thanks for the review, 

You're correct, the process is :

1) set default cors headers 
2) on OPTION check asked capabilities and eventually return preflight headers. At this steps
CORS headers can be [] (capability not handled or the list preflight headers like the spec
3) on db , we check origin header in a list of origin. Eventually we reset cors headers to
null if the origin isn't supported

I will remove my custom headers, sorry for that. Maybe at some point we could allow people
to add their own header via the settings.

About Simple and Couch that's mostly to distinct them, simple headers are defined by the spec.
But I could join them. I don't know what's the best for that. I will push the patch later
tonight with above fixes and doc.

- benoit

> 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, 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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