[Kde-pim] Making offline/online handling sane

[Andras Mantia]

Hi,

 I've been sturggling a lot whenever I travel with the fact that I cannot 
read my *offline* imap mail. Friday I run into it again and spent almost all 
my flight time to identify and fix the problem. What I discovered is not 
good.

The problem
-----------
  The visible problem is that if a resource is offline, and there is a 
request to it to deliver an item, you get an error:
"Cannot fetch item in offline mode." 

The cause
---------
  For the above, the cause is pretty simple:
   if ( !isOnline() ) {
     const QString errorMsg = i18nc( "@info", "Cannot fetch item in offline 
mode." );
     emit error( errorMsg );
     return errorMsg;
   }
in ResourceBase::requestItemDeliveryV2. 
Sounds simple and reasonable at the first read, but here is a question: why 
do we have it in the ResourceBase? 

The real problem
----------------

The answer to the above question is: because we don't know what "isOnline" 
means for a resource. There is a weird mix of its meaning in the Akonadi 
libraries and resources. Does it mean that the resource is turned off? Does 
it mean that the resource is not allowed to do network operations? Does it 
mean a mix of the two or something else?
Well, the problem is that right now it is a mix. From the above it means 
that Akonadi should not even *try* to get anything from a resoruce that is 
offline, as it will get an error, so it means "offline resource is turned 
off resource". But a resoruce is automatically turned offline if there is no 
network. That means a resource is offline when there is no network. And this 
is *generic*, the code is in AgentBase that turns them offline.

What the above means: no network, resource goes offline, if akonadi wants to 
get something from it, you get the error.

Even more: if a resource is offline, the task scheduler inside the resource 
does nothing. Task processing is shut down (see  void 
ResourceScheduler::scheduleNext() ). This means not even a local resource 
works on offline mode: no task are processed.

The suggested solution
----------------------
Hereby I suggest to bound the "online" state to the network operations. 
Online means a resource is *allowed* to perform network operations. Offline 
means a resource is *not allowed* to perform network operations. The Akonadi 
libraries (and here I mean AgentBase and ResourceBase) don't deal with 
online/offline state, the most they do is to signal the network state, 
although this would just replicate a Solid signal, so no real need for that 
either. Akonadi *should not* care about what the resources do or allowed to 
do.
Online/Offline handling will be moved to the resources. If a resource 
doesn't work on the network, it just ignores it: it cannot be set offline. 
If it works on a network, if setOnline(false) is called, it must shut down 
all network connections and should not perform any network operation until 
setOnline(true) is called.
 POP3 seems to do the right things, IMAP doesn't.
If it wants, it can give back items in another way (think of local cache per 
resource).

The questionmarks
-----------------

I couldn't do a complete analysis of the whole code yet, I run out of flight 
time. :) And there are some questionmarks in my mind:
- why can you read offline imap content if you set KMail to offline (but you 
cannot if you have no network): here I just have a guess: if the IMAP 
resource cannot connect to the server, it sets itself to offline mode 
(another confusion, as offline in this context might mean "broken"). If it 
is in that state, it starts to report errors back to the Akonadi server. 
My suspition is that "KMail in Offline mode", but with working connection 
doesn't set the imap resource completely offline and it performs some 
operations instead of reporting back errors (like cannot connect to the imap 
server).
- why does Akonadi asks at all for items on a disconnected IMAP account, 
when everything should be in cache? Note that my wondering is only for the 
items. There is anyway the problem I said above, as IMAP sync folders on 
click, while it can't do it in offline mode. You end up with some sync task 
scheduled...
- how many resources would be affected, who relied on the current offline 
interpration?

Anyway, I'd not mind if somebody would try to reproduce what I see to 
confirm it. How to do it?
- set up a maildir and a disconnected IMAP account
- sync them, especially the disconnected IMAP so you are sure mail content 
is downloaded
- File>Work Offline in KMail: everything should work fine, you can switch 
between folder and read mail content
- in akonadiconsole set the maildir resource offline and try to read mails 
(read those that you haven't read lately, so they are not in the cache)
- unplug any network cable, shut down any wireless acount, if possible 
disable the wireless completely. Now try to read mail on the IMAP account 
and switch folders. Alternatively restart Akonadi/KMail after you disabled 
the network.

Tell me how it works.

If you agree with the above approach, I volunteer to come up a solution 
inside the akonadi libs (which will be easy, like removing code mangling 
offline and leave there only the interfaces to set a resource 
offline/online) and check the imap/pop3/mail dispatcher resources that they 
perform well and do what you should.

The above suggestion removes the feature of turning off a resource. In order 
to have that, we would need to introduce a new state for resources, but I'm 
not sure we need it at all.

Andras
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