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From Jens Alfke <j...@couchbase.com>
Subject What's the exact definition of 'oldDoc' in a validation function?
Date Sun, 23 Feb 2014 00:45:03 GMT
What’s the exact definition of the ‘oldDoc’ parameter that’s passed to a validation
function? The current CouchDB docs just say it’s "the current document stored in the database”.
This is unambiguous during a normal PUT operation, but I’ve just realized I’m unsure what
the exact behavior is during replication or with new_edits=false.

Situation 1: There are no revisions of document “foo” in the database. A replication pulls
in revision 3-zzzz of “foo”, along with a revision history giving the ancestry as 2-yyyy
and 1-xxxx.
—> Is the validation function called with oldDoc=null, or with oldDoc={“_rev”:”2-yyyy”}?

Situation 2: The database contains revision 1-xxxx of “foo”. A replication pulls in the
same revision 3 as described above.
—> Is the validation function called with oldDoc={“_rev”:”1-xxxx”}, or with oldDoc={“_rev”:”2-yyyy”}?

This has an impact on fancy validation functions that want to check for invariants between
a new revision and its parent. For example, in the document-signing spec I’m working on,
a document’s signature data needs to include the revision ID of the parent, to avoid certain
types of replay attacks. But if the validation function isn’t called with the exact parent
revision, there isn’t a way for it to determine the parent rev ID to verify the signature.

—Jens
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