[Mimedefang] Please review: new Spamc feature

[Matthew.van.Eerde at hbinc.com]

I've broken down and coded a mimedefang-filter that calls spamc instead of use'ing Mail::SpamAssassin.

I'd ideally like to post this on the wiki for those who might find it useful... but I'm interested in feedback first. Can you glance over the code and tell me what you think?

The idea is to trim down the MIMEDefang threads to be lightweight, so I can make a whole lot of them.  I do all sorts of things w/ MIMEDefang besides spam-scan, and while the MIMEDefang threads are doing all these things, that SpamAssassin module is sitting there idle, but taking up space.  I do have a performance hit from spawning the spamc process, but I thought I'd experiment to see if the tradeoff is a net benefit or loss.

This requires a working spamd setup and a custom spamd report template.

Modifications to /etc/mail/spamassassin/local.cf:
# This changes the default report template to one which is easier to parse
# but not necessarily easier to read
# only the first five "report" lines are used by MIMEDefang...
# the rest can contain custom flavor text
# note the characters after each colon must be a TAB (\t)
clear_report_template
report Score:   _SCORE()_
report Required:        _REQD_
report Tests:   _TESTS(,)_
report
report _SUMMARY_

Modifications to mimedefang-filter:

# Outside of any function, but
# before detect_and_load_perl_modules();

$Features{"SpamAssassin"} = 0; # false but defined
$Features{"Spamc"} = 1; # new feature

# this function creates a spamc-scannable version of the message
# this is basically INPUTMSG with some extra headers
# the headers imitate what sendmail will eventually add anyway
sub create_spamc_scan_file()
{
	# code liberally stolen from
	# mimedefang.pl's spam_assassin_mail
	open(IN, "<./INPUTMSG") or return undef;
	my @msg = <IN>;
	close(IN);

	# Synthesize a "Return-Path" and "Received:" header
	my @sahdrs;
	push (@sahdrs, "Return-Path: $Sender\n");
	push (@sahdrs, split(/^/m, synthesize_received_header()));
	push (@sahdrs, gen_msgid_header()) if ($MessageID eq "NOQUEUE");

	unshift (@msg, @sahdrs);

	open(FORSPAMC, ">./FORSPAMC") or return undef;
	print FORSPAMC @msg;
	close(FORSPAMC);

	return 1;
}

# in filter_end, instead of the
# if ($Features{"SpamAssassin"}) block:
	if (
		$Features{"Spamc"} and # is there spamc?
		-s "./INPUTMSG" < 100 * 1024 and # don't scan messages over 100KB
		create_spamc_scan_file() # create a spamc-scannable file
	)
	{

		my $forcespamreport = 0;

		# this if() is another custom feature, unrelated to spamc
		# if this is to spam-check at example.com...
		# and ONLY to spam-check at example.com...
		# then force a spam report even if the message isn't spam
		if (
			@Recipients == 1 and
			$Recipients[0] =~ /^<?spam-check\@example\.com>?$/i
		)
		{
			$forcespamreport = 1;
		}

		# spamc options
		# -r shows a report only if it's spam
		# -R shows a report whether it's spam or not
		my $r = ($forcespamreport ? "-R" : "-r");

		my $report = `spamc $r < ./FORSPAMC`;
		unlink('./FORSPAMC'); 

		if ($report eq "")
		{
			# not spam! nothing to do.
		} elsif ( $report =~
			/^
			Score:		\t	([\d\.]+?)	\n
			Required:	\t	([\d\.]+?)	\n
			Tests:		\t	([\w,]+?)	\n
			\n
			/x
		)
		{
			my $score = $1;
			my $required = $2;
			my $tests = $3;
			my $stars = "*" x ($score < 40 ? int($score) : 40);


			if ($forcespamreport)
			{
				action_add_part(
					$entity,
					"text/plain",
					"-suggest",
					$report . "\n",
					"SpamAssassinReport.txt", "inline"
				);
			}

			if ($score >= $required)
			{
		                action_change_header(
					"X-Spam-Score",
					$stars . " (" . $score . ") " . $tests
				);

		                action_delete_all_headers("Subject");
				action_add_header(
					"Subject",
					"[Spam] $Subject"
				);
				md_graphdefang_log('spam', $score, $RelayAddr);
			} else
			{
		                # Delete any existing X-Spam-Score header
	        	        action_delete_header("X-Spam-Score");
			}
		} else
		{
			# malformed report!  Something's weird.
			md_syslog(
				'warning',
				"$QueueID: malformed spamc report"
			);
		}
	}


-- 
Matthew.van.Eerde (at) hbinc.com               805.964.4554 x902
Hispanic Business Inc./HireDiversity.com       Software Engineer