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From "James Burke (JIRA)" <>
Subject [jira] Created: (COUCHDB-431) Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
Date Thu, 23 Jul 2009 19:30:14 GMT
Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec

                 Key: COUCHDB-431
             Project: CouchDB
          Issue Type: New Feature
          Components: HTTP Interface
    Affects Versions: 0.9
            Reporter: James Burke
            Priority: Minor

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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