Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control
spec
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Key: COUCHDB-431
URL: https://issues.apache.org/jira/browse/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:
http://dev.w3.org/2006/waf/access-control/
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):
https://developer.mozilla.org/en/HTTP_access_control
And information on Safari/Webkit (functionality in latest WebKit and Safari 4):
http://developer.apple.com/safari/library/documentation/AppleApplications/Conceptual/SafariJSProgTopics/Articles/XHR.html
IE 8 also uses the Access Control spec, but the requests have to go through
their XDomainRequest object (XDR):
http://msdn.microsoft.com/en-us/library/cc288060%28VS.85%29.aspx
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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