draft-miller-ssh-agent-02: extensions and success messages

[Alex Wilson]

Hi,

I've been reading the RFC draft for the OpenSSH agent protocol and
trying to understand the extension mechanism. It seems like a client,
after sending an extension message, will have to then interpret any
following success (0x6) message differently according to the extension
request just sent. The example with the "query" extension returning a
success message with extra data appended would seem to imply that, too.
Is that correct?

If so, I would love to get some insight into why this was chosen over
having an "extension reply" message number or something like that. It
seems to me that the protocol up until now has always been stateless --
you didn't have to know what you sent last in order to parse and
validate received data -- which generally makes implementations nice and
simple. After this change, client impls will have to change their
parsing of the success message dramatically after sending each extension
request message (and will have to track which ext they last sent etc),
since it doesn't include enough information in the message itself any
more to figure out what it should contain.

Sorry if I'm retreading on a discussion that's already been had (I did
search this list but couldn't find anything)

Thanks!