Quoting Timo Sirainen <t...@iki.fi>:
On 13.2.2012, at 23.32, Timo Sirainen wrote:
Perhaps a way for (trusted) clients to be able to do this? :)
a logout save
* OK [SAVEDSTATE 1234567890]
* BYE logged out
a OK
Actually, this could probably be safely implemented by sending all
of the state to the client as a string:
* OK [SAVEDSTATE base64-encoded-state]
There isn't a whole lot of state to be saved really. Mailbox GUID,
UIDVALIDITY, HIGHESTMODSEQ gives the mailbox state. Then you have
the language/etc. states. Clients could restore their earlier state
from days ago, as long as Dovecot still has the necessary .log
records available (similar to how QRESYNC works).
Given that it is not *that* expensive to re-create the state, I don't
think the ability to recreate state from several days ago would be
worth the effort of storing in the log/index files. For a
disconnected client (e.g. webmail), there's going to necessarily need
to be startup costs of initializing the session anyway so re-creating
the state can be buried in this other work.
Re-creating becomes more important when users are doing actions they
expect immediate (or at least very fast) responses for. Things like
listing messages in a mailbox, viewing a message, or polling
mailboxes. Saving 50ms per request becomes important in these
situations since re-creating state now takes 10% of the total request
time.
So I don't think states don't need a terribly long lifetime. I almost
think of something like an internal Dovecot IDLE queue - after a
logout is received, state is stored for 30 minutes after which it is
discarded. (Although not knowing anything about internal Dovecot
state, don't know if this is overly resource intensive.)
As for base-64-encoded state: if other IMAP servers ever wanted to
implement a similar protocol trying to coordinate the data structure
would be a nightmare. Keeping it to something like a MODSEQ value
would hide the state ID -> data abstraction entirely within dovecot.
And would allow you to change your mind in the future if
you come up with a better way to represent state.
michael
