Re: Cyrus imap 3.4.8: synchronizing local mailbox list with MUPDATE server does not work

Hi,

On Thu, 13 Jun 2024, at 8:46 PM, Michael Menge wrote:
> but as "ctl_mboxlist" is acting as a client i find it more suspicious  
> that "pin->isclient" was 0 and
> therefore the "if (pin->isclient && c == '+') {" block was skipped

Since ctl_mboxlist is acting as a client here, its input ("pin") is from the server, so I think it's correct that pin->isclient is 0 -- the server is not a client.  The client side of this connection is its output ("pout"), so pout->isclient ought to be 1.  But getxstring doesn't consider pout->isclient at all.

There's clearly something not quite right here but I'm not sure what yet.  We only consider '+' when the input is a client.  Maybe that's incorrect?  Or maybe it's correct, and the server end of this is behaving badly by sending '+' to a client...

RFC7888 <https://www.rfc-editor.org/rfc/rfc7888#section-3> says: "The non-synchronizing literal form MUST NOT be sent from server to client."

So I think getxstring's new pin->isclient behaviour is correct here, but is more strict than it used to be.  The other end is behaving badly and ctl_mboxlist no longer tolerates it.  Interesting.

Ahh yep.  static int sendupdate(const mbentry_t *mbentry, void *rock) in imap/mupdate.c is what sends the LIST response, and it has hardcoded '+' in all its literal outputs.  Perhaps this function sometimes outputs to a server, and sometimes to a client.  In which case it ought to check and omit the '+' when pout->isclient is true, and it might need to check for the LITERAL+ capability (or whatever it's called) when talking to a server.  But if it never talks to a server, then we should just remove the '+'s.

What's been baffling me so far though, is that our tests don't detect any problem.  But!  That's because our tests only run ctl_mboxlist -m on startup, before any mailboxes have been created, and the LIST response is empty.  As part of fixing this, I think I'll probably add a ctl_mboxlist -m call on each backend as part of our post-test sanity checks.  That should catch this sort of thing coming back in the future.

> Kind regards
>
>     Michael Menge

Thanks heaps for your initial diagnosis, that was a big help!

Cheers,

ellie
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