There appears to be no documentation of the _revs_diff API, which is a key component of the replication protocol, so I’ve just added a wiki page for it: http://wiki.apache.org/couchdb/HttpPostRevsDiff
This is based only on one or two archived list posts, a few remarks from Damien, and some experimentation with ‘curl’. The page would benefit from review by someone who actually knows how _revs_diff works :) Until then I’ve added a disclaimer saying it’s not authoritative. One thing I’m unsure of is whether it returns any information except which of the input revisions are not known. The structure of the output implies that it could use keys other than “missing” to return something else, maybe revisions in the database but not in the input? I’m also assuming that a revision is not classed as “missing” if it previously existed but was removed in a compaction; otherwise old revisions would keep getting resurrected during replication. —Jens
