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[exim.git] / doc / doc-misc / LongTermIssues

Exim Long Term Issues
---------------------

I restarted this list from scratch for Exim 4. I amalgamated it with another
list when creating the CVS repository (October 2004). But it still probably
needs a substantial spring clean. Some of it is very old now.


AUTOCONF
--------

Somebody once tried to \(autoconf)\ Exim, but found it too big a job. I now
have some experience with using \(autoconf)\ for PCRE, and I think maybe some
use could be made of it. I don't, however, believe that \(all)\ Exim build-time
configuration should be done that way. The reason is that, unlike something
like PCRE, there is quite a lot of information that is "user choice". Giving it
all as options to a \(configure)\ command does not seem the best way of doing
things.

Whenever I build something that needs more than a couple of obvious options to
\(configure)\, I always save them in a file anyway, so I know what I did for
next time. Therefore, I think it is sensible to retain the current Local file
structure for all the user choice configuration.

However, it might be helpful to use \(autoconf)\ to dig out various bits of
information about the operating system. At present, the \(OS/Makefile-*)\ files
have hard-wired settings, and maybe this information could be figured out by
running \(autoconf)\, which would save having to keep maintaining these files.

I would arrange things so that \(configure)\ is run automatically the first
time that \(make)\ is run, but it would be possible to run it manually first,
to override defaults. (For example, if you have both \(cc)\ and \(gcc)\
installed on your system, as I do, you need to be able to specify which to
use.) I will need to do some experiments to see exactly how this would work.


EXIMON and other utilities
--------------------------

. Consider optionally making it possible to link with something other than
  Athena widgets - for example, gtk. Or indeed re-write the whole thing!


GENERAL
-------

. Convert os.c into a directory of separate functions, with the macro
  switches defined elsewhere. Then make it into a library.

. Use a pointer to an address structure for expanding $domain etc, to make it
  easier to save/restore this collection of variables. But note that $domain
  and $local_part aren't always in an address. Check out when these are set.
  Note also the new $address_data possibility.

. Spool_in and spool_out - speed up by using a table?

. Find a more compact way of encoding the options interpretation, and also of
  checking for incompatible options.

. Find a more compact way of passing an open SMTP channel without having
  to use options. What about the TLS state information? Could use a pipe to
  pass more data.

. Some people have suggested separately loadable modules. But do all systems
  have them? Is this going too far for just a few specialist users? In
  particular, people want to be able to replace the logging with his own code.
  Can we arrange this without going for the separately loaded modules? (cf the
  incoming checking code.)

. SIGHUP the daemon - don't close the sockets; instead pass a list of them
  somewhere for the new daemon to pick up. Iff started by exim or root, of
  course. There might be quite a long list of them - argv might not be the best
  idea. If this were done, then a non-setuid exim daemon could be SIGHUPped.

. Parallel deliveries. Currently dead host information doesn't get propagated
  between them very well. Is there anyway this could be improved?

. In some environments the use of gethostbyname() seems to cause problems.
  Check out its use, and see if having a "force DNS" option could be helpful.
  But people would have to know what they were doing.

. accept_max_per_host is a slow, linear search. If smtp_accept_max is large,
  this can be very slow. Is there some way we can speed this up? Some kind of
  index based on the IP address? Remember, this is in the daemon, so it must
  not consume store.

. Change the names of all the pcre_ stuff to, say, PCRE_ so that Exim can be
  linked with libraries or whatever that also use an external PCRE library.

. Look at code in pidentd for running Exim in wait mode from inetd and re-using
  the socket. This would allow it to run more tidily as non-root.

. Think up some scheme for checking for orphan files in the spool directories.
  Perhaps -bp should always do it, but it would be nice to have it done
  automatically now and again. Maybe we just leave this for a cron job? Perhaps
  a new -bx, e.g. -bpck or something. Better, perhaps, is a separate Perl
  script. Orphan = a file that is over 24h old (or 1s when test harness) and
  either doesn't end in -D or -H, or is a -D without a matching -H (or vice
  versa).

. Make set_process_info buffer bigger, and put the overflowed message at the
  end, thereby leaving the start.

. Swamping with delays in checking for reserved hosts - the connections are
  counted in the total allowed. Can we improve on this somehow? Maybe shared
  memory can help here. Think about different states and different limits.

. Lists that must use colons: can we check for other cases, and fix them up
  before passing them on? Is it worth it?

. Linux for S/390 - create configuration?

. Process receiving error message fails - can we get more info, such as the
  stdout/stderr?

. dbmbuild - if renaming one of .dir/.pag fails, reinstate the other. Should
  there be a lock?

. Write a script to check for format problems in the source - formats that are
  not fixed strings and are built from outside code.

. freeze_tell: Don't if message is a bounce message containing From: the local
  machine - even if the bounce comes from another host.

. Add additional data into the "frozen" log message at end of delivery, e.g. if
  remote host was the local host or whatever. At least some cross referencing.

. Someone had a requirement to install the Exim binary in a different place to
  the utilities, etc. Also, for different builds on the same host and
  architecture.

. Include (part of?) the ppid in the message id? Or a random number?

. Re-implement the code in readconf that reads error names for retry rules.
  Make it use a table for most of the error types. Then see if we can usefully
  add any additional error types.

. Should there be "exim -bP acls" etc? It would mean inventing some kind of
  "hide" facility within the ACL syntax.

. VERY LONG TERM: the message ID is too small now, with the recent changes to
  cram in the sub-second time. It would be a big project to extend it; Exim
  would have to recognize both forms for a while, and become stable, before
  generating the new form. Probably a runtime switch needed. The new form needs
  at least microsecond time (or more?) and should probably cope with 64-bit
  pids, just to be safe (or leave expansion space that could be used for that).
  It should also be able to hold big enough things in base 36.

. Take a look at libexec.

. Sort out the stcncpy/strlcpy issue once and for all. Time things.

. Error in transport filter. See test 407. All 3 processes see errors - which
  one should be noticed? Transport_filter_temp_errors may be needed.

. Think about 5xx thresholds -- too many and you're out. What about 4xx?

. autoreply - should it call /usr/sbin/sendmail? Provide a way of not passing
  -C and -D when creating the message ('cause it won't be privileged).

. Strings containing \000 - anything we can do?

. OpenSSL - can we pass an opened file for certificate? Repeatedly?
  Otherwise pre-initialize while root? There do seem to be functions for
  manipulating certificates, but documentation is scarce. Can we just load the
  certificate in as root in the server?

. Consider using poll() to close unwanted fds. Is this efficient? Perhaps it
  doesn't matter for the daemon.

. On a 64-bit system there are some cast warnings for casting addresses to
  ints. Either we must find a way of not warning, or we'll have to use unions
  to get round it.

. Run splint on the source?

. It has been suggested that rejection because not authenticated should use
  530 and not 550, but this is hard to detect because of the way ACLs work.

. When there is a sender verify failure, $acl_verify_message contains "sender
  verify failed", not the details of the failure. Should this change? Some of
  the waffly details are added later in smtp_in.c. In the ACL that text is in
  sender_verified_failed->user_message.

. An empty string for a transport filter currently causes an error. Should it
  ignore? Tricky because of special expansion rules for commands.

. GFDL for documentation (www.gnu.org/licenses/fdl.html)? The 1.2 version of
  this licence is still quite new (it is dated November 2002) so I think
  waiting for reaction/opinion is the best plan. There are Debian concerns
  about this licence. At very least, no Invariant Sections and no Cover Texts
  can be used.

. Allow $recipients in other places. Not clear what this value should be if,
  say, the system filter has overridden them. Default would be envelope
  recipients, as now.

End