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From Adam Kocoloski <kocol...@apache.org>
Subject Re: [PROPOSAL] Capability identification
Date Wed, 05 Jun 2013 00:21:26 GMT
As the author of one of those replicator UA-sniffing compatibility hacks I definitely think
a system for advertising capabilities is a Good Idea :)

Adam

On Jun 4, 2013, at 6:40 PM, Joan Touzet <wohali@apache.org> wrote:

> Today, if I GET http://localhost:5984/ , I get:
> 
>  {"couchdb":"Welcome","uuid":"b1b1dbe964914a9cb1467bfd4f297fed","version":"1.3.0","vendor":{"version":"1.3.0","name":"The
> Apache Software Foundation"}}
> 
> If I GET from http://mozauto.iriscouch.com/ , I get:
> 
>  {"couchdb":"Welcome","uuid":"bac168113808f7ed357fb53f3a7a68bc","version":"1.3.0","vendor":{"version":"1.3.0r1","name":"Iris
> Couch"}}
> 
> And if I GET http://wohali.cloudant.com/ , I get:
> 
>  {"couchdb":"Welcome","version":"1.0.2","cloudant_build":"1202"}
> 
> I believe I get further still different responses from Pouch and Touch
> and other CouchDB-alikes, provided they even have an equivalent of
> GET /.
> 
> Long ago, in a galaxy far far away, the developers of Internet Relay
> Chat daemons faced a similar problem. While they were bound by a single
> RFC (and later, its twin), each developer wanted to extend the program
> in interesting and unique ways. Some of those features became
> commonplace and built a shared understanding, others were unique
> capabilities of specific implementations, and yet others indicated
> specific incompatibilities introduced for nefarious purposes.
> 
> While the sordid history of the IRC protocol is a topic for drinks after
> a meetup some night, one lesson learned has proved exceedingly useful:
> the CAPAB string. Documented in the TS6 specification[1] but universally
> adopted, server-to-server CAPAB/PROTOCTL provided a negotiation of both
> implemented functionality as well as services offered. A further
> extension was created for client-to-server capabiliity negotiation
> as a draft RFC[2][4] and is also widely implemented.
> 
> To make this more tangible, reference this list[3] of IRC server
> CAPABilities. If you've ever used IRC, and especially different IRC
> networks, you should be able to intuitively understand how this up-front
> negotiation helps simplify server-to-server connection negotiation.
> 
> ---
> 
> I think CouchDB should extend its identification in the root-level
> document with a capability advertisement. This would help prevent the
> current anti-patterns in production use of CouchDB:
> 
>  1. Client library negotiation based exclusively on "compatibility
>     with >= version of Apache CouchDB," which is nebulously documented
>     at best.
> 
>  2. Provide a clear means by which CouchDB plugins and CouchDB-alike
>     services can advertise their availability.
> 
>  3. Provide a way for alternate implementations of similar
>     functionality to indicate interoperability.
> 
>  4. Possibly simplify the replicator (though this is a special case of
>     1 and 2 above).
> 
> I've gotten no further than this in my thinking yet; I didn't want to
> start implementation before folks had a chance to say whether they
> thought it'd be a good idea or not.
> 
> [1]:
> https://github.com/grawity/irc-docs/blob/master/server/ts6.txt#L205-L216
> [2]: https://tools.ietf.org/html/draft-mitchell-irc-capabilities-01
> [3]: https://github.com/grawity/irc-docs/blob/master/server/ts-capab.txt
> [4]: https://github.com/grawity/irc-docs/tree/master/client/CAP-drafts
> 
> -- 
> Joan Touzet | joant@atypical.net | wohali everywhere else


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