Implement "application/xcap-error+xml" (and use 409 for errors)

[ibc]

According to  http://tools.ietf.org/html/rfc4825#section-11, if a node selection is "invalid" the server should reply 409 with Content-Type "application/xcap-error+xml" and a body following the according XML schema.

But OpenXCAP returns 404 with a description in "text/plain" (for other errors is uses "text/html").

For example:

HTTP/1.1 404 Not Found
Content-Type: text/plain

The requested node selector
/a:ruleset/a:rule[@id='pres_whitelist']/a:conditions/a:identity/a:one
matches more than one element

The easier issue to handle is to reply 409 in these cases. A more complex task is returing a XML according to section 11 of RFC 4825.

[ibc]

Ops, I've realized that OpenXCAP does implement the request feature in some cases:

HTTP/1.1 409 Conflict
Date: Tue, 21 Jul 2009 23:18:58 GMT
Content-Length: 175
Content-Type: application/xcap-error+xml;charset=utf-8
Server: OpenXCAP/1.1.0
Connection: close

<?xml version="1.0" encoding="UTF-8"?>
<xcap-error xmlns="urn:ietf:params:xml:ns:xcap-error"><cannot-insert phrase="PUT request failed GET(PUT(x))==x invariant"/></xcap-error>

However, I expect that in the case I wrote in the initial report, 409 with Content-Type "application/xcap-error+xml" should also be returned.