[Bug 77862] kio_imap processes hang when connection status changes

[Michael Kreitzer]

https://bugs.kde.org/show_bug.cgi?id=77862


Michael Kreitzer <mrgrim at gr1m.org> changed:

           What    |Removed                     |Added
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                 CC|                            |mrgrim at gr1m.org




--- Comment #88 from Michael Kreitzer <mrgrim gr1m org>  2010-11-11 17:57:30 ---
There are two main issues when it comes to dead connection detection, and both
place the burden of dealing with them on the client to some degree so this is a
bug for the client if it fails to handle them gracefully.

The first issue is detecting dead daemons. The symptoms will be that tcp
packets are sent and the proper ACKs returned indicating the connection is
fine, but the server does not respond. This is resolved via timeouts as you
mentioned. 

The second is detecting dead connections in protocols where traffic may not be
sent or received for long periods of time. This is generally resolved by
regular "pings" if the protocol supports it. IMAP has a NOOP command
specifically for this. In some cases the connection may be immediately reset by
a firewall, router, or the server tcp stack. In other cases a tcp timeout may
be required waiting for the ACK in which case a timeout may be issues by the
remote end firewall, router, server or the local tcp stack. Both error codes
are ICMP so if an ultra paranoid server admin is blocking these on either end
the client will may to rely on a client side timeout making this the same issue
as the former.

I've seen kmail/kio_imap4 not timeout indefinitely hanging on a dead
connection. This is one issue this bug has touched.

Another is kmail/kio_imap4 will not properly re-establish a connection even
when a connection is reset or it otherwise detects a failed connection. I'll
get the error dialog mentioning the connection was lost and it will try to
reconnect, but I'm never able to browse my mail again after that until I close
kmail and manually kill off the hung kio_imap4 processes.

Both related issues need to be addressed to correct the central issue this bug
report is about.

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