#!/bin/bash

###################
# a simple mail delivery and transmission system
# Copyright Andrew Tridgell <tridge@samba.org> 1997-2002
# released under the GNU General Public License version 2 or later

VERSION="1.2"

# setup the default configuration
MAIL_SSH="ssh"
MAIL_DIR="Mail"
MAIL_INBOX="$HOME/InBox"
MAIL_RUNNER="mail.runner"
SENDMAIL="/usr/lib/sendmail"
SENDMAIL_OPTS="-t -i"
RSYNC_OPTS="-Pavz"
MAIL_TIMEOUT=300
PROCMAIL_COMMAND="formail -s procmail"
MAIL_VERBOSE=2
MAIL_NO_PIDOF=0

# sensible paths are often not setup when invoking commands remotely
export PATH=$PATH:$HOME/bin:/usr/local/bin:/usr/bin:/bin:/sbin:/usr/sbin


# define an empty sendmail hook - replace this in .mail.runner for 
# interesting multi-host tricks
mail_sendmail_hook() {
 msg="$1"
}


# load the user specific config
if [ -f $HOME/.mail.runner ]; then
    HAVE_MAIL_RUNNER_CONFIG=1
    . $HOME/.mail.runner
else 
    echo "YOU MUST HAVE A .mail.runner config!" 1>&2
    HAVE_MAIL_RUNNER_CONFIG=0
fi

if [ ! -z "$MAIL_RUNNER_CONF" -a -r "$MAIL_RUNNER_CONF" ]; then
 . $MAIL_RUNNER_CONF
fi

if [ -z "$MAIL_OUT_DIR" ]; then
    MAIL_OUT_DIR="$MAIL_DIR"
fi



# processing now continues in MAIN SCRIPT section at bottom of file


##############################################################
# print a message if the level <= $MAIL_VERBOSE
debug_msg() {
    level=$1;
    if [ $level -le $MAIL_VERBOSE ]; then
	message="$2";
	echo "$message";
    fi
}

##################################
# print an error message to stderr
error_msg() {
    echo "$1" 1>&2;
}


##############################################################
# try to make sure two copies of this script don't run at once
exit_if_running() {
    if [ "$MAIL_NO_PIDOF" == 1 ]; then
	return;
    fi
    pids=`pidof -x -o $$ mail.runner`;
    myid=`id -u`;
    for p in $pids; do
	pid_owner=`stat -c"%u" /proc/$p/stat`
	if [ x$pid_owner = x$myid ]; then
	    echo "mail.runner is already running - pid $p"
	    exit 1
        fi
    done
}




###############################################################################
# send all pending mail, invoking mail.deliver at the other end
mail_send() {
    exit_if_running

    list=`echo $HOME/$MAIL_OUT_DIR/mail.out.*.*[0-9]`
    debug_msg 2 "";
    if [ "$list" = "" ]; then
	debug_msg 2 "No messages to send";
	return 0;
    fi
    debug_msg 1 "Sending `echo $list | wc -w` messages";

    if rsync --rsync-path="$MAIL_RUNNER remote_deliver" \
	--timeout=$MAIL_TIMEOUT $RSYNC_OPTS -e "$MAIL_SSH" \
	$list $MAIL_HOST:$MAIL_DIR/; then
         rm -f $list
    fi
    return 0;
}

###############################################################################
# fetch mail from the remote host and deliver it via procmail
mail_fetch() {
    exit_if_running

    if ! rsync --timeout=$MAIL_TIMEOUT $RSYNC_OPTS -e "$MAIL_SSH" \
	    --rsync-path="$MAIL_RUNNER remote_send" \
	    $MAIL_HOST:$MAIL_DIR/EMPTY_FILE $HOME/$MAIL_DIR/; then
	error_msg "transfer failed";
	return 1;
    fi

    if [ "`echo $HOME/$MAIL_DIR/mail.in.*.*`" = "" ]; then 
	debug_msg 1 "";
	debug_msg 1 "No mail to retrieve";
	return 1
    fi

    for f in $HOME/$MAIL_DIR/mail.in.*.*; do
	if cat $f | $PROCMAIL_COMMAND; then
	    # it is useful seeing what mail is being processed
	    if [ "$MAIL_FRM" = "1" ]; then
		frm $f
	    fi
	    rm -f $f
	fi
    done

    # this is useful for seeing where procmail has put things ...
    if [ "$MAIL_PROCMAIL_TAIL" = "1" ]; then
	debug_msg 2 "";
	debug_msg 2 "";
	debug_msg 2 `tail $HOME/$MAIL_DIR/procmail.log`;
    fi

    return 0;
}


###############################################################################
# a sendmail-like call. This just places the mail in a known location for 
# mail_send to find
mail_sendmail() {
    msg=$HOME/$MAIL_DIR/mail.out.$RANDOM.$$
    tmp=$msg.tmp
    cat > $tmp
    /bin/mv $tmp $msg
    mail_sendmail_hook $msg
    exit 0
}


##############################################################################
# a rsync wrapper function that delivers mail on the remote host
mail_remote_deliver() {
    exit_if_running

    rsync $*
    status=$?

    if [ $status != 0 ]; then
	return $status;
    fi

    for f in $HOME/$MAIL_DIR/mail.out.*.*[0-9]; do
	    if $SENDMAIL $SENDMAIL_OPTS < $f; then
		rm -f $f
	    else
		error_msg "Mail of $f failed $status";
	    fi
    done
    return 0
}

###############################################################################
# a rsync wrapper function for fetching mail from the remote host
mail_remote_send() {
    exit_if_running

    # atomically move mail from InBox to a temporary file
    if test -s $MAIL_INBOX; then
	movemail $MAIL_INBOX $HOME/$MAIL_DIR/mail.in.$RANDOM.$$ > /dev/null
    fi

    # by using an empty file we avoid error messages from rsync about not
    # having any files to transfer
    if [ ! -f $HOME/$MAIL_DIR/EMPTY_FILE ]; then
	touch $HOME/$MAIL_DIR/EMPTY_FILE
    fi

    rsync $* $HOME/$MAIL_DIR/mail.in.*.*
    status=$?
    if [ $status != 0 ]; then
	return $status;
    fi

    rm -f $HOME/$MAIL_DIR/mail.in.*.*
    return 0
}


###############################################################################
# display help text
mail_help() {
cat <<EOF
mail.runner version $VERSION
-----------------------

mail.runner is a script for sending and receiving email. 

FEATURES
--------

The main features of mail.runner are

- good performance over very slow links
- secure mail transfer via rsync and ssh
- incremental transfer in case the link is lost
- no mta installation needed on the client


REQUIREMENTS
------------

To use mail.runner you need the following:

- a working 'rsync' and 'ssh' installation
- the 'bash' shell
- the 'movemail' utility
- the 'formail' utility
- the Linux 'pidof' utility
- a working 'procmail' installation for mail delivery on the client
- a working 'sendmail' (or equivalent) installation on the server for sending 
  email
- optionally you may use the 'frm' utility


INSTALLATION
------------

To install mail.runner you need to do the following:

- install the mail.runner script on both the server and client 
- create a .mail.runner configuration file on the server and client (see
  the CONFIGURATION section of this help for details)
- tell your email program to use "mail.runner sendmail" as the local
  program to send email with

How you do the last step depends on your email program. I use RMAIL in
emacs to read and send email, so I used the following in my .emacs:
  (setq sendmail-program "~/bin/mail.sendmail")
and then I created a one line script called 'mail.sendmail' that runs
'mail.runner sendmail'.


RUNNING
-------

Once installed, you should just run 'mail.runner' to fetch any
outstanding emails from the server and send any pending messages. You
can also ask mail.runner to just send or fetch by using:
    mail.runner send
or
    mail.runner fetch

Any diagnostics messages should be self explanatory.

CONFIGURATION
-------------

You should configure mail.runner using a file called .mail.runner in
your home directory on both the client and the server. The minimal
configuration would contain the single option MAIL_HOST like this:

  MAIL_HOST="your.mail.server"

Other options are:

  MAIL_SSH
    This specifies the remote shell to use for rsync. Defaults to "ssh"

  MAIL_DIR
    This specifies the name of the directory where you store mail on
    both the client and the server. This should be a relative path,
    relative to your home directory.  The default is "Mail".

  MAIL_INBOX
    This specifies the location of your mail inbox on your mail server.
    The default is '\$HOME/InBox'

  MAIL_RUNNER 
    This specifies the location of the mail.runner script on the
    server, relative to your home directory. The default is "mail.runner".

  MAIL_TIMEOUT
    This specifies the number of seconds to wait for transfers. It is
    passed as a timeout parameter to rsync. The default is 300.

  SENDMAIL
    This specifies the name of your sendmail program on the
    server. This program should accept raw emails on stdin and send
    them. The default is "/usr/lib/sendmail"

  SENDMAIL_OPTS
    This specifies additional command line options to be passed to
    sendmail. The default is no additional options.

  MAIL_FRM
    If this is set to "1" then mail.runner will use the 'frm' utility
    to display the subject and sender of incoming emails as they are
    processed.

  MAIL_PROCMAIL_TAIL
    If this is set to "1" then mail.runner will display the last 10
    lines of your '\$MAIL_DIR/procmail.log' after processing incoming
    emails.

  RSYNC_OPTS 
    This defaults to "$RSYNC_OPTS", you may wish to remove the
    -v and add -q for quieter operation

  PROCMAIL_COMMAND
    This sets the command used to deliver mail locally. 
    It defaults to "$PROCMAIL_COMMAND"

  MAIL_VERBOSE
    Verbosity level:
      1 - Summary of messages sent and received.
      2 - Additional whitespace and output when no mail to send.

  MAIL_NO_PIDOF
    If this is set to "1" no "pidof" checking is done.  You should set
    this to "1" if you don't have pidof or your pidof is broken in 
    some way.


LICENSE
-------

mail.runner is released under the GNU General Public License, version
2 or later. Please see http://www.gnu.org/ for a full copy of the license.


AUTHOR
------

mail.runner was written by Andrew Tridgell <tridge@samba.org>

EOF
}


###############################################################################
# START OF MAIN SCRIPT
###############################################################################

# See if user is just after help, if so display and exit
if [ "$1" = "-h" -o "$1" = "--help" -o $HAVE_MAIL_RUNNER_CONFIG == 0 ]; then
    mail_help
    exit 0
fi

# we rely on expansion to a null list
shopt -s nullglob

# make sure the necessary variables are defined
if [ "$MAIL_HOST" = "" ]; then
    error_msg "You must define a MAIL_HOST in $HOME/.mail.runner";
    error_msg "Use -h for more help";
    exit 1
fi

# when an argument is passed then call the corresponding mail_* function 
# with the remaining arguments. This is used to invoke the right function
# remotely, but can also be used to do things like "mail.runner send" from
# the command line
if [ $# != 0 ]; then

    cmd=$1
    shift
    mail_$cmd $*
    exit $?
fi

# the default is to fetch then send
mail_fetch
mail_send