[Kde-pim] [PATCH] imap resource: Support multiple IDLE folders.

[Rüdiger Sonderfeld]

On Friday 19 October 2012 14:57:18 Kevin Ottens wrote:

> That's correct, but this limitation somewhat comes from the protocol
> itself... IDLE is fairly limited, there's been work to overcome those
> limitations in the form of the NOTIFY extention:
> http://www.faqs.org/rfcs/rfc5465.html
> 
> I'm not sure which IMAP servers implement that extension though.

As far as I know Dovecot will add support for it in version 2.2. But it will 
be a while until this is widely available and I don't know if any other imap 
implementation or mail service has shown any interest in NOTIFY.

> And that's exactly the problem I have with the proposed patch... It opens
> one connection per monitored box, and I'd expect quite a few sysadmins to
> hate us for allowing such consumption of resources...

This certainly is a problem. But I think it's a problem the users and 
sysadmins have to solve. Imap server software such as dovecot or courier has 
max connections settings for each user and this should prevent users from 
watching too many folders. We are not putting servers at risk here and 
sysadmins already have the tools to protect themselves. And other imap clients 
such as Offlineimap already support watching several folders.

We certainly should keep the settings in the Advanced-part of KMail and warn 
users that opening too many connections might cause problems.

> I see two ways to walk toward an acceptable solution:
>  1) Modify your patch in a way that only one connection is used to the
> server for IDLE, it could be done by rotating between several boxes
> (SELECT, IDLE, SELECT, IDLE, etc.). The trick being to find out how long to
> IDLE on each box while still having an acceptable behavior for the user.
> It'll also generate somewhat more traffic but that should still be OK if
> done well.

I don't think that this is a good solution. If the rotation is too quick then 
this results in a lot of traffic and action on the server side. If it is too 
slow then it offers no advantage over the current interval checking. It's 
simply not what the user would expect or want.

>  2) Implement the support for NOTIFY instead. It's definitely the better
> option to me, but it's clearly getting further away from your existing
> patch. It also requires investigating which servers support it of course.

I hope that NOTIFY will replace IDLE in the future. But it is not available at 
the moment and so far I only know about Dovecot planning to support it. That's 
why I don't think it's an option for now.

Regards,
Rüdiger
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