#!/usr/bin/ruby
# filter-dspam.rb: Qmail + DSPAM glue script
# This script takes a piece of mail on STDIN and sends it through DSPAM for
# filtering.  It then delivers to the appropriate mailbox depending on the
# results of the DSPAM check.
#
# Copyright 2008 Alkaloid Networks LLC
# Released under the terms of the GNU Public License version 2
# http://projects.alkaloid.net
# Author: Ben Klang <ben@alkaloid.net>
# $Id$
#
require 'rubygems'
require 'tmail'
require 'logger'
require 'pp'

## Customize these variables as required
# Configure the path to DSPAM and the program arguments here
$dspambin = "/opt/dspam/bin/dspam"
$dspamargs = "--mode=teft --stdout --deliver=innocent,spam"

# Path to qmail/control
$qmailbase = "/opt/qmail"

# Only check messages smaller than 256KiB
$maxchecksize = 256 * 1024

# Level of information sent to STDERR
$verbose = Logger::DEBUG

# Folder to hold quarantined messages
$spamfolder = "SPAM"

# Path to per-user log files area.  Must be writeable by the UID doing the
# filtering.  If multiple user IDs will be filtering, try either logging
# directly into each user's home directory (ENV['HOME']) or into /tmp
# Valid replacements:
# %u - Delivery username
# %e - Destination email address
# %l - "Local" (user) portion of destination email address
# %d - Destination domain name
$logpath = "/opt/qmail/log/filter-dspam/%u"

EXIT_HARD = 100
EXIT_SOFT = 111

# Sanity check:  make sure we have a required environment variables
if (!ENV.key?('USER') || !ENV.key?('RECIPIENT') || !ENV.key?('LOCAL') ||
    !ENV.key?('HOST') || !ENV.key?('HOME'))
    $stderr.puts("Missing required environment variable.\nMust have $USER, $RECIPIENT, $LOCAL, $HOME and $HOST set.\nBailing out!")
    exit EXIT_HARD
end

# Create a log instance
begin
    # While email addresses and domain names are not case sensitive, the
    # username may be.
    # Downcase the email components.
    user = ENV['USER']
    recipient = ENV['RECIPIENT'].downcase
    local = ENV['LOCAL'].downcase
    host = ENV['HOST'].downcase
    $logpath.gsub!(/%u/, user)
    $logpath.gsub!(/%e/, recipient)
    $logpath.gsub!(/%l/, local)
    $logpath.gsub!(/%d/, host)
    log = Logger.new(File.open($logpath, File::WRONLY | File::APPEND | File::CREAT, 0600))
    log.level = $verbose
    log.info("Processing new mail message to #{ENV['RECIPIENT']}")
rescue Exception => e
    $stderr.puts("Unable to open logger instance: #{e.to_s}")
    exit EXIT_SOFT
end

# Parse the incoming message
msg = TMail::Mail.parse(STDIN.read)

# Bail out if the message is too large
if (msg.body.length < $maxchecksize)
    # Load the message for processing
    begin
        agentstr = `#{$dspambin} --version`.grep(/DSPAM Anti-Spam Suite/).pop.chop
        msg['X-AntiSpam-Agent'] = agentstr
        dspam = IO.popen("#{$dspambin} #{$dspamargs} --user #{user}", "w+")
        dspam.puts(msg.to_s)
        dspam.close_write
        msg = TMail::Mail.parse(dspam.read)
        dspam.close
    rescue Exception => e
        log.error("Error while scanning message for spam: #{e.to_s}")
        exit EXIT_SOFT
    end
end

# Try to determine the default delivery path
if File.readable?("#{$qmailbase}/control/defaultdelivery")
    defaultdelivery = File.open("#{$qmailbase}/control/defaultdelivery").read.chop
else
    defaultdelivery = "./Maildir/"
end

# FIXME: If using qmail-ldap, how does mailMessageStore get propagated?
mbpath = "#{ENV['HOME']}/#{defaultdelivery}"

# Try to deliver the message
if (msg.key?('X-DSPAM-Result'))
    if (msg['X-DSPAM-Result'].to_s.downcase == 'spam')
        log.info("SPAM detected.  Quarantining message to #{$spamfolder}")
        mailbox = TMail::Maildir.new("#{mbpath}/.#{spamfolder}")
    elsif (msg['X-DSPAM-Result'].to_s.downcase == 'innocent')
        log.info("DSPAM result clean; delivering to INBOX")
        mailbox = TMail::Maildir.new(mbpath)
    else
        log.error("Unknown DSPAM return code: #{msg['X-DSPAM-Result']}")
        exit EXIT_HARD
    end
else
    log.info("DSPAM return empty or message filtering skipped.  Delivering to INBOX.")
    mailbox = TMail::Maildir.new(mbpath)
end

mailbox.new_port{|filehandle| filehandle.puts(msg.to_s)}.move_to_new