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functions should produce 'raw' http responses, maybe you want a more generic http library for those?
Those features exist largely so you can navigate to them directly in the browser, or to support other client implementations that don't explicitly understand CouchDB (eg, jsonrpc/soap).
Im not a rubyist, so I can't reccomend any particular tool for this, but it looks like couchrest depends on rest-client, so using that wouldn't be an "additional dependency"