#!/bin/ksh
# @(#) phost.ksh 1.3 96/06/13
# 96/05/17 john h. dubois iii (john@armory.com)
# 96/06/02 Allow mangling of list return address.
# 96/06/13 Do not require malias and /bin/env to exist.
# 97/06/09 Added u option.

# phost: convert user@host to user.host to implement per-hostname user aliases.
# This program is intended to be executed for the phost channel by the
# sendprog channel program.
#
# Portability notes:
# The sendprog channel program must be available for this to work.
#    sendprog is not shipped with SCO systems.  An archive containing
#    sendprog for SCO 3.2v5 is available at
#    ftp://ftp.armory.com/pub/scobins/progchan.tar.Z, and for SCO 3.2v4 at
#    ftp://ftp.armory.com/pub/scobins/3.2v4/progchan.tar.Z  The 'sendprog'
#    file in those archives should be put in the directory /usr/mmdf/chans
# This is a ksh program.  It should also work as a pd-ksh, bash, or zsh
#    program, but might require tweaking.
#
# Instructions for use:
# 1. Put this program in /usr/mmdf/bin/phost and make it readable and
#    executable.
# 2. Create a queue directory for phost.  cd to /usr/spool/mmdf/lock/home and
#    do:
#    mkdir q.phost; chown mmdf q.phost; chgrp mmdf q.phost; chmod 777 q.phost
#    Note: the queue directories will probably be somewhere other than
#    /usr/spool/mmdf/lock/home on non-SCO systems.
# 3. Add an mmdftailor entry like this:
# MCHN    phost, show="pseudo-host channel", ap=822, pgm=sendprog, mod=imm,
#	tbl=phost.chn,
#    confstr="/usr/mmdf/bin/phost [opts] $(from) $(to.user) $(to.host) $(local)"
#    where [opts] is any options you want to give to the phost program
#    (currently, only the -u option is defined).
#
# 4. Put any hostnames for which this mapping should be done into the phost.chn
# file.  No value needs to be associated with hostname in the table (just the
# name alone on a line will do).  If the hostnames were previously in any other
# channel table (e.g. local.chn if mail for a host was formerly accepted by
# the local host without mapping), take them out of those tables.
#
# 4.1. Before the channel table lookup is done, a hostname must be found in
# a domain table.  Therefore, if the hostnames you put in phost.chn are not
# yet in any domain table, put them in an appropriate domain table, for
# example, root.dom.  The right hand side of each entry in the domain table
# should exactly match the entry in phost.chn.  A typical entry would go in
# root.dom and simply map each name to itself.  If the MMDF system was
# previously configured to accept mail locally for the pseudo-hosts, they
# are already in a domain table, so this step is unneccessary.  Also, if the
# hostnames have appropriate DNS records and MMDF is configured to do DNS
# domain table lookups, that will suffice for the domain table lookup.
# 
# Once the table database is rebuilt, mail sent to a user at a host listed
# in the phost.chn table will be re-submitted into the mail system with its
# recipient address changed from user@host to user.host.  NOTE that due to the
# way the sendprog channel works, this will be done separately for each
# recipient address delivered via the phost channel, so a single submitted
# message is liable to result in multiple messages being re-submitted to the
# mail system.
#
# 5. An alias for any username that should be mailable at the alternate host
# should be created.  An alias must be created for every user; the default
# for recipient addresses that no alias exists for is to bounce the message,
# not to deliver it to the recipient username at the local hostname (this
# could be changed by modifying the script).
# Example:
# phost.chn contents:
# alt.domain
# alias table contents:
# user1.alt.domain	foo
# user2.alt.domain	bar@that.host
# This will cause mail to user1@alt.domain to be sent to local user foo,
# and mail to user2@alt.domain to be sent to bar@that.host.
#
# ALTERNATE steps 3 and 4, to allow for customized processing on a per-domain
# basis:
# 3. Add an mmdftailor entry like this:
# MCHN    phost, show="pseudo-host channel", ap=822, pgm=sendprog, mod=imm,
#	tbl=phost.chn
# 4. Put any hostnames for which this mapping should be done into the phost.chn
# file.  The righthand side of the table for each hostname should be:
# /usr/mmdf/bin/phost [options] $(from) $(to.user) $(to.host) $(local)
# Example: 
#
# alt.domain1 /usr/mmdf/bin/phost -u someone@somewhere $(from) $(to.user) $(to.host) $(local)
# alt.domain2 /usr/mmdf/bin/phost $(from) $(to.user) $(to.host) $(local)
#
# If the hostnames were previously in any other channel table (e.g. local.chn
# if mail for a host was formerly accepted by the local host without mapping),
# take them out of those tables.
#
# Options:
# phost has one option.  By default, mail sent to an unknown address is
# bounced back to the return address.  If you give "-u<address>", all mail to
# users who have no alias in the domain will be sent to <address>.  This option
# depends on the existance of the "malias" program, which is expected to be
# found in /usr/mmdf/bin/malias.  If it exists but is somewhere else, the
# program should be tweaked accordingly.

# NOTE: there is a problem using this channel to create a mailing list name
# within a domain if the mailing list is handled by the list channel.  The
# list channel will always make the return address be listname-request, without
# the alternate domain attached to it.
# Short of modifying the list channel, about the best that can be done in this
# situation is to simply implement the listname-request alias in the local
# domain rather than the alternate domain.  If this would collide with another
# list name, the outbound name passed to the list processor (e.g.
# foo-outbound@list-processor) can be changed.  If the list-request alias 
# should also exist in the alternate domain, as an administrative alias to be
# mailed to, it should be separately aliased.
# Example alias file entries to use this method:
# foo.nonesuch.org:            foo-outbound@list-processor
# foo-request:                 spcecdt
# foo-request.nonesuch.org:    spcecdt
# foo-outbound:                recipient1 recipient2 recipient3

# The alternative to all of this is to have this program itself handle
# conversion of the list outbound address to a different name and set the
# return address itself.  This program therefore recognizes a name ending
# in '-mangle' and translates it in the same way as it does other messages,
# but also sets the return address by replacing -mangle with
# -request@alternate-host.
# Example alias file entries to use this method:
# foo.nonesuch.org:             foo-mangle@nonesuch.org
# foo-request.nonesuch.org:     spcecdt
# foo-mangle.nonesuch.org:      recipient1 recipient2 recipient3

##############################

# If mail is e.g. sent from johnd@sco.com to root@nonesuch.org,
# and the local machine name (MLNAME.MLDOMAIN) is armory.com,
# these vars would be set as follows:
# From: johnd@sco.com
# ToUser: root
# ToHost: nonesuch.org
# Local: armory.com


name=${0##*/}
Usage=\
"Usage: $name [-u<unknown-address>] from-address to-user to-host local-host"

while getopts u: opt; do
    case $opt in
    u)
	unknownAddr=$OPTARG
	;;
    esac
done

# remove args that were options
let OPTIND=OPTIND-1
shift $OPTIND

if [ $# -ne 4 ]; then
    print -r -u2 -- "$name: Wrong number of arguments (expected 4, got $#).
$Usage"
    exit 1
fi

From=$1
ToUser=$2
ToHost=$3
Local=$4

OrigDest="$ToUser@$ToHost"
NewDest="$ToUser.$ToHost"
admin=mmdf@$Local

if [[ "$ToUser" = *-mangle ]]; then
    Return="${ToUser%mangle}request@$ToHost"
else
    Return=$From
fi


# If env is available, use it to hide any local user environment variables
# from execmail, just in case
if [ -x /bin/env ]; then
    alias env=/bin/env
else
    function env {
	# If there are actually specific env. vars found to cause problems,
	# they could be unset here.
	shift 2
	"$@"
    }
fi

function bounce {
    {
    # Let execmail generate all of header except From: line
    print -r -- \
"From: $admin (MMDF Mail System)

Trouble sending mail on $Local:

============ Transcript follows ============

Unknown user name: \"$OrigDest\"
(\"$ToUser\" is not a user in the domain \"$ToHost\")

============== Message follows =============
"
	/bin/cat
    } | env - "TZ=$TZ" /usr/lib/mail/execmail -f "$admin" "$From"
    exit 0
}

# If the the malias program is available, use it to check whether the recipient
# address is aliased in the given domain.  If not, bounce it here, because if
# bounced by execmail it will tell the originator that there is no such user
# "user.host" which is liable to be confusing.

malias=/usr/mmdf/bin/malias
if [ -x $malias ]; then
    set -- `/usr/mmdf/bin/malias "$NewDest"`
    if [ "$1 $2" = "no aliases" ]; then
	[ -n "$unknownAddr" ] && NewDest=$unknownAddr || bounce
    fi
fi

env - "TZ=$TZ" /usr/lib/mail/execmail -f "$Return" "$NewDest"

exit 0