Idempotency in EPP

[Robert Burbidge <robert.burbidge@poptel.coop>]

Can I just get confirmation of a small point regarding idempotency?

My understanding of idempotency is that if the server received two identical
commands from a registrar then it should produce the same results for each
identical command. This is to ensure, for example, that if the server is
hanging off a session-less protocol that cannot guarantee unique delivery of
datagrams it's OK to action the same command twice. There seems to be two
aspects to this - that both commands have the same effect, and that both
commands return the same results to the client.

First question: Is that a correct interpretation?

So for example, if registrar X creates domain Y with an appropriate
<domain:create> command and follows that with an identical epp command, both
commands have the same effect (either both succeed or both fail) and with
exactly the same result epp response.

Second question: Is that example correct?

If the above are true, it follows for example that the EPP server needs to
keep a certain degree of history. For example if registrar X deletes domain
Y, and actions the same command again, the server needs to remember that
domain Y used to belong to registrar X in order have the same effect and
return identical responses each time. This is not necessarily a problem; we
do that kind of thing anyway.

If all the above are correct interpretations of idempotency in EPP, it
follows that it also applies to changing passwords, so for example if
registrar X changes its password from Y to Z, the server needs to store not
only the current password but also the previous password for each registrar.

Can someone confirm or deny this interpretation for me? Thanks.

Rob Burbidge