On 30-Mar-09, at 7:12 PM, Peter Saint-Andre wrote:
As far as I can see, nothing in XEP-0237 (Roster Versioning)
prevents a
server from using timestamps (e.g., seconds in the Unix era) as
version/sequence numbers. Would that be a popular approach? If so, we
might want to add a note about it in the spec.
time makes a bad counter as it can go backwards and there are
resolution issues ;-)
Instead follow rfc4551 for version number,
An IMAP server that supports this extension MUST associate a
positive
unsigned 64-bit value called a modification sequence (mod-sequence)
with every IMAP message. This is an opaque value updated by the
server whenever a metadata item is modified. The server MUST
guarantee that each STORE command performed on the same mailbox
(including simultaneous stores to different metadata items from
different connections) will get a different mod-sequence value.
Also, for any two successful STORE operations performed in the same
session on the same mailbox, the mod-sequence of the second
completed
operation MUST be greater than the mod-sequence of the first
completed. Note that the latter rule disallows the use of the
system
clock as a mod-sequence, because if system time changes (e.g., an
NTP
[NTP] client adjusting the time), the next generated value might be
less than the previous one.
ck
