improved popminpoll handling

[Brian K. Becknell]

Phil,
   I ran into the same problem when migrating to cyrus. I turned off
polling due to it's harshness. Please send me the patch!!!

thanks
-brian

> On my old UW POP server I added a patch to limit the polling frequency.
> Rather than  just apply a fixed minimum time interval I made it give
> some flexibility.  The patch  allows users to do a few checks in quick
> succession but would fail if the longer  term rate was too high.  This
> is something which our POP users found to be a major  improvement.
>
> On moving to cyrus, the rigid limit has caused many complaints.
>
> I have worked the same algorithm into cyrus's popminpoll handling.
> However, since I  have not had time to really get to grips with the
> cyrus code, I have had to limit  the possible impact my code would have.
>  Perhaps someone with more knowledge of  cyrus would like to improve
> matters for me.
>
> The algorithm needs to store an integer value between connections.
> Since the time  of the last pop connection is stored in the inbox's
> cyrus.index file, that seemed  the sensible place to store the new
> value.  However, I did not want to extend the  size of the data stored
> and create unforseen problems!  My solution was to pack the  new value
> in with "minor_version", using the top 16 of the 32 bits allocated in
> cyrus.index.
>
> My patch involves making imap/mailbox.c pack and unpack the new variable
> with  "minor_version" in mailbox_write_index_header() and
> mailbox_read_index_header().   Also, to add a function which does the
> checking to imap/pop3d.c, which is called  from openinbox() where
> openinbox() normally compares the elapsed time with  pipminpoll.
>
> If there is sufficient interest, perhaps the cyrus team might consider
> rolling it  in.
>
> My patch is currently to 2.1.13, but I am about to apply it to 2.1.15
> too. I will be  happy to to pass the patch to anyone who is interested
> (particularly anyone who can  do a proper job of storing an extra
> integer in cyrus.index).
>
> Phil.
> ---------------------------------------
> Phil Chambers (postmaster at exeter.ac.uk)
> University of Exeter