#!/bin/sh
#
# check-attachments — check that referenced attachments are actually attached
#
# This is based on the idea behind
# http://www.vim.org/scripts/download_script.php?src_id=3165: if the mail body
# matches a given regular expression, then check whether there are also
# non-PGP MIME parts in the message, or else refuse to send the message.
#
# You can override the checking by adding the X-No-Attachments header to the
# message.
#
# Copyright © 2010 martin f. krafft <madduck@madduck.net>
# Released under the terms of the Artistic Licence 2.0
#
set -eu

RE_ENGLISH='attach(ing|ed|ment)?|included\W+(with|in)\W+th(is|e\W+(curr|pres)ent)\W+mail'
RE_GERMAN='an(gehängt|hängsel|bei)|bei(gefügt|lage)|(im|siehe)\W+(anhang|beilage)'
RE_FRENCH='attach(e|er|ée?s?|ement|ant)'
OVERRIDE_HEADER=X-No-Attachments

if ! grep -q "^${OVERRIDE_HEADER}:" "$1" \
     && egrep -ziq "($RE_ENGLISH|$RE_GERMAN|$RE_FRENCH)" "$1"; then

  nr_attach=$(sed -rne 's/^Content-Type:[[:space:]]+//p' "$1" |
              egrep -cv '^(multipart/|application/pgp-signature)')

  if [ $nr_attach -lt 2 ]; then
    echo >&2 "E: the mail message references an attachment,"
    echo >&2 "E: but there seems to be no non-PGP MIME part."
    echo >&2 "E: (add the $OVERRIDE_HEADER header to override the check)."
    exit 1
  fi
fi

sed -i -e "/^${OVERRIDE_HEADER}:/d" "$1"