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From "Jason Smith (JIRA)" <>
Subject [jira] [Commented] (COUCHDB-431) Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
Date Sun, 15 May 2011 12:15:47 GMT


Jason Smith commented on COUCHDB-431:

I made a patchset to enable Cross-Origin Resource Sharing from CouchDB. I will attach them
to JIRA.

The point of CORS is, instead of the classic same-origin security policy, browsers will ask
the "foreign" server's permission first. The foreign server can indicate whether the browser's
origin is trusted and what if any HTTP stuff is allowed. With permission granted, XHR requests
to the foreign resource work just like normal.

My implementation uses the couch config. To enable CORS, set /_config/httpd/cors = "true".
Then the "cors" section is just like the "vhosts" section. To have trust code
from and also, you would set /_config/cors/ = "" (mnemonic: same format as the w3c Origin header).

The upshot is you can $.couch all day long, from any web page to any number of couches. But
the couches have to whitelist you first. Also, a validate_doc_update() function can check
req.headers.Origin to act on local vs. cross-origin queries.

> 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
>            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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