[RFC PATCH v2] imapd.c: imapoptions: implement idle timeout

[Carson Gaspar]

On 9/19/2016 10:02 PM, ellie timoney via Cyrus-devel wrote:
> I've been looking at tcp_keepalive a bit lately and I'm wondering how it
> interacts with this?
>
> It's my understanding that, in most cases, tcp_keepalive will do the job
> of detecting clients that have dropped out, and allow us to close the
> connection on our end.  Since we're generally either waiting for a
> command from the client, or producing and about to send output to the
> client, this works -- because if tcp_keepalive detects that the client
> isn't there, reads and writes to the socket will start failing.
This is why KEEPALIVE is affectionately known as MAKEDEAD ;-)
> But during the IDLE state, we only read from the client socket if select
> reports it as having data ready for reading (presumably containing
> "DONE"), and we only write to the client socket if there is activity on
> the selected mailbox.
>
> If the client's connection has dropped out, no data will ever appear on
> the socket, so select will never flag it as readable, so we will never
> try to read from it, so we will never receive the read error even though
> tcp_keepalive detected the dropout.  And if this client was idling with
>
Not true on any flavour of UNIX of which I'm aware. select() marks a fd 
as readable on EOF. poll() marks the fd as either POLLIN, POLLHUP, or 
both (sadly implementation specific).

-- 
Carson