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From "Benjamin Young (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COUCHDB-2052) Add API for discovering feature availability
Date Sat, 10 May 2014 21:58:29 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-2052?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13993880#comment-13993880
] 

Benjamin Young commented on COUCHDB-2052:
-----------------------------------------

Strangely (to me) I've only just found [RFC2295|http://tools.ietf.org/html/rfc2295]. [Section
8|http://tools.ietf.org/html/rfc2295#section-8] introduces a set of HTTP headers that would
(have...) made feature and content-type discovery by agents (in this case, CouchDB clients)
much simpler.

Of the headers, {{Accept-Features}} and {{Alternates}} would be of particular interest to
this discussion.

> Add API for discovering feature availability
> --------------------------------------------
>
>                 Key: COUCHDB-2052
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-2052
>             Project: CouchDB
>          Issue Type: Improvement
>      Security Level: public(Regular issues) 
>          Components: HTTP Interface
>            Reporter: Jens Alfke
>
> I propose adding to the response of "GET /" a property called "features" or "extensions"
whose value is an array of strings, each string being an agreed-upon identifier of a specific
optional feature. For example:
> 	{"couchdb": "welcome", "features": ["_bulk_get", "persona"]}, "vendor": …
> Rationale:
> Features are being added to CouchDB over time, plug-ins may add features, and there are
compatible servers that may have nonstandard features (like _bulk_get). But there isn't a
clear way for a client (which might be another server's replicator) to determine what features
a server has. Currently a client looking at the response of a GET / has to figure out what
server and version thereof it's talking to, and then has to consult hardcoded knowledge that
version X of server Y supports feature Z.
> (True, you can often get away without needing to check, by assuming a feature exists
but falling back to standard behavior if you get an error. But not all features may be so
easy to detect — the behavior of an unaware server might be to ignore the feature and do
the wrong thing, rather than returning an error — and anyway this adds extra round-trips
that slow down the operation.)



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