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From "Robert Newson (JIRA)" <>
Subject [jira] [Commented] (COUCHDB-2052) Add API for discovering feature availability
Date Fri, 07 Feb 2014 16:54:23 GMT


Robert Newson commented on COUCHDB-2052:

The three examples are useful but each appears to be "what if the the server/client doesn't
implement HTTP 1.1 correctly" to me.

1) is the client sending an Upgrade header, and the server either doing the 101 switching
dance or not.
2) If you send a well-formed request, with gzipped body and Content-Encoding:gzip, the server
should return a 415 rather than "barfing on it or (worse) storing it without any indication
that it's zipped."
3) That's an ugly wrinkle of couchdb, true. The multipart/related format was added for the
replicator's consumption and made that no-shuffle assumption. It no longer does, though, and
you can tell based on the published version.

There's a lot of negotiation things in HTTP itself, as indicated. There must be examples fully
outside of that?

I struggle to think of an item to go in this proposed blob that isn't a new endpoint (e.g,
Cloudant could advertise the various _search endpoints)

> Add API for discovering feature availability
> --------------------------------------------
>                 Key: COUCHDB-2052
>                 URL:
>             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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