#!/usr/pkg/bin/perl -I/usr/pkg/lib
#
# This file is part of DKIMproxy, an SMTP-proxy implementing DKIM.
# Copyright (c) 2005-2008 Messiah College.
# Written by Jason Long <jlong@messiah.edu>.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor,
# Boston, MA  02110-1301, USA.
#
# This file incorporates work covered by the following copyright and
# permission notice. See the top-level AUTHORS file for more details.
#
#     This code is Copyright (C) 2001 Morgan Stanley Dean Witter, and
#     is distributed according to the terms of the GNU Public License
#     as found at <URL:http://www.fsf.org/copyleft/gpl.html>.
#
#     Written by Bennett Todd <bet@rahul.net>.
#
#
#
#

use warnings;
use strict;

use Getopt::Long;
use Pod::Usage;
use IO::File;
use Sys::Syslog;

use Mail::DKIM 0.17;
use Mail::DKIM::Verifier;
use MySmtpServer;

use constant DEFAULT_RELAY_PORT => 25;

my $hostname;
my $reject_fail = 0;
my $reject_error = 0;
my $debugtrace;

use base "MySmtpProxyServer";
main->run(
		server_type => "PreFork",
	);

sub options
{
	my $self = shift;
	my ($template) = @_;

	$self->SUPER::options(@_);

	# compatibility arguments (older versions of dkimproxy)
	$template->{daemonize} = \$self->{server}->{setsid};
	$template->{pidfile} = \$self->{server}->{pid_file};

	$template->{reject_error} = \$reject_error;
	$template->{reject_fail} = \$reject_fail;
	$template->{hostname} = \$hostname;
	$template->{debugtrace} = \$debugtrace;

	$template->{listen} = \$self->{server}->{listen};
	$template->{relay} = \$self->{server}->{relay};
	$template->{relay_host} = \$self->{server}->{relay_host};
	$template->{relay_port} = \$self->{server}->{relay_port};
}

sub configure
{
	my $self = shift;

	if ($self->isa("Net::Server::MultiType")
		&& !$self->{server}->{server_type})
	{
		# Net::Server::MultiType hasn't done its thing yet,
		# so let it continue. It will call configure() again
		# after it has processed the server_type parameter.
		return $self->SUPER::configure(@_);
	}

	$self->SUPER::configure(@_);

	#
	# At this point, Net::Server should have removed from @ARGV
	# any arguments that it recognized. So any remaining
	# arguments in @ARGV should be for us.
	#
	my $help;
	GetOptions(
			"reject-error" => \$reject_error, #Net::Server doesn't like hyphens
			"reject-fail" => \$reject_fail,
			"help|?" => \$help)
		or pod2usage(2);
	pod2usage(1) if $help;

	if (@ARGV == 2)
	{
		$self->{server}->{listen} = shift @ARGV;
		$self->{server}->{relay} = shift @ARGV;
	}
	pod2usage("Error: wrong number of arguments")
		unless @ARGV == 0;

	if (my $tmp = $self->{server}->{listen})
	{
		my ($host, $port) = split_host_port($tmp);
		$self->{server}->{host} = $host;
		$self->{server}->{port} = [ $port ] if defined $port;
	}
	if (my $tmp = $self->{server}->{relay})
	{
		my ($host, $port) = split_host_port($tmp);
		$self->{server}->{relay_host} = $host;
		$self->{server}->{relay_port} = $port if defined $port
	}

	if (not defined $self->{server}->{port})
	{
		pod2usage("Error: listening port was not specified");
	}
	if (not defined $self->{server}->{relay_host})
	{
		pod2usage("Error: relay host was not specified");
	}

	if (not defined $hostname)
	{
		use Sys::Hostname;
		$hostname = hostname;
	}
}

sub setup_client_socket
{
	my $self = shift;

	$self->{server}->{relay_port} ||= DEFAULT_RELAY_PORT;

	# create an object for sending the outgoing SMTP commands
	#  (and the verified message)
    my $client = eval { MSDW::SMTP::Client->new(
			interface => $self->{server}->{relay_host},
			port => $self->{server}->{relay_port}) };
	if (my $E = $@)
	{
		chomp $E;
		print "421 Internal error (Next hop is down)\n";
		die "$E\n";
	}

	return $client;
}

sub process_request
{
	my $self = shift;

	# try to determine peer's address
	use Socket;
	my $peersockaddr = getpeername(STDOUT);
	my ($port, $iaddr) = sockaddr_in($peersockaddr);
	$ENV{REMOTE_ADDR} = inet_ntoa($iaddr);

	# initialize syslog
	eval
	{
		openlog("dkimproxy.in", "perror,pid,ndelay", "mail");
		syslog("debug", '%s', "connect from $ENV{REMOTE_ADDR}");
	};
	if (my $E = $@)
	{
		chomp $E;
		print "421 Internal error (Syslog is down)\n";
		die "$E\n";
	}

	$self->{debug} = $debugtrace;

	$self->SUPER::process_request;
}

sub handle_end_of_data
{
	my $self = shift;
	my $server = $self->{smtp_server};
	my $client = $self->{smtp_client};

	my $fh = $server->{data};
	my $dkim;
	my $verify_result;
	my $verify_detail;
	eval
	{
		$dkim = Mail::DKIM::Verifier->new(
				Hostname => $hostname,
			);
		$dkim->load($fh);

		$verify_result = $dkim->result;
		$verify_detail = $dkim->result_detail;

		syslog("info", '%s',
			"DKIM verify - $verify_detail; "
			. join(", ", $dkim->message_attributes));
		print STDERR "DKIM verify - $verify_detail; "
			. join(", ", $dkim->message_attributes) . "\n";
	};
	if ($@)
	{
		my $E = $@;
		chomp $E;
		$E =~ s/\n/ /gs;
		eval { syslog("warning", '%s', "verify error: $E") };
		print STDERR "verify error: $E\n";
		$verify_result = "temperror";
		$verify_detail = "$verify_result ($E)";
	}

	# check signing result
	if ($verify_result =~ /error$/ && $reject_error)
	{
		# temporary or permanent error
		$server->fail(
			($verify_result eq "permerror" ? "550" : "450")
			. " DKIM - $verify_detail");
		return 0;
	}

	my $policy_result = "none";
	my $found_reject;
	eval
	{
		foreach my $policy ($dkim->policies())
		{
			$policy_result = $policy->apply($dkim);
			if ($policy_result eq "reject")
			{
				$found_reject = "rejected by " . $policy->name . " policy";
			}
		}
	};
	if ($@)
	{
		$policy_result = "error";
	}
	if ($found_reject && $reject_fail)
	{
		# failed
		$server->fail("550 5.7.1 DKIM - $verify_detail");
		return 0;
	}

	$fh->seek(0,0);

	if ($dkim)
	{
		# output authentication results header
		my $auth_results = join("; ",
			map { make_auth_result($_) }
			$dkim->signatures);
		$client->write_data_line("Authentication-Results: $hostname; "
			. $auth_results . "\015\012");

		# output a psuedo authentication results header
		$client->write_data_line("X-DKIM-Authentication-Results: "
			. $dkim->result_detail . "\015\012");

		# send the original message as is
		$client->yammer($fh);
	}
	else
	{
		# send the message unaltered
		$client->yammer($fh);
	}
	return 1;
}

sub make_auth_result
{
	my $signature = shift;

	my $type = $signature->isa("Mail::DKIM::DkSignature")
		? "domainkeys" : "dkim";
	my $tag = $signature->can("identity_source")
		? $signature->identity_source : "header.i";

	return "$type=" . $signature->result_detail
		. " $tag=" . $signature->identity;
}

sub split_host_port
{
	my $str = shift;
	if ($str =~ /^\[(.*)\](?::(\d+))?$/)
	{
		return ($1, $2);
	}
	elsif ($str =~ /^([^:]+):(\d+)$/)
	{
		return ($1, $2);
	}
	return $str;
}

__END__

=head1 NAME

dkimproxy.in - SMTP proxy for verifying DKIM signatures

=head1 SYNOPSIS

  dkimproxy.in [options] LISTENADDR:PORT RELAYADDR:PORT
    smtp options:
      --conf_file=FILENAME
      --listen=LISTENADDR:PORT
      --relay=RELAYADDR:PORT
      --reject-error

    verification options:
      --reject-fail
      --hostname=HOSTNAME

    daemon options:
      --daemonize
      --user=USER
      --group=GROUP
      --pidfile=PIDFILE

  dkimproxy.in --help
    to see a full description of the various options

=head1 OPTIONS

=over

=item B<--daemonize>

If specified, the server will run in the background.

=item B<--group=GROUP>

If specified, the daemonized process will setgid() to the specified
GROUP.

=item B<--hostname=HOSTNAME>

Overrides the hostname used in the Authentication-Results header.
This header gets added to every verified message.
Use this option if the hostname that appears is not fully qualified
or you want to use an alternate name.

=item B<--pidfile=PIDFILE>

Creates a PID file (a file containing the PID of the process) for
the daemonized process. This makes it possible to check the status
of the process, and to cleanly shut it down.

=item B<--reject-error>

This option specifies what to do if an error occurs during verification
of a message. If this option is specified, the message will be rejected
with an SMTP error code. This will result in the MTA sending the message
to try again later, or bounce it back to the sender (depending on the
exact error code used). If this option is not specified, the message
will be passed through with an error listed in the Authentication-Results
header instead of the verification results.

The most common cause of an error when verifying a message is a
DNS error when trying to retrieve a public key or sender policy.

=item B<--reject-fail>

This option specifies what to do if verification fails and the sender
signing policy says to reject the message. If this option is specified,
the message will be rejected with an SMTP error code.
This will result in the sending MTA to
bounce the message back to the sender. If this option is not specified,
the message will pass through as normal.

=item B<--user=USER>

If specified, the daemonized process will setuid() to USER after
completing any necessary privileged operations, but before accepting
connections.

=back

=head1 DESCRIPTION

dkimproxy.in listens on the IP address and TCP port specified by its
first argument (the "listen" port), and sends the traffic it receives
onto the second argument (the "relay" port), with messages getting
verified and having an "Authentication-Results" header added to them.

=head1 EXAMPLE

For example, if dkimproxy.in is started with:

  dkimproxy.in --reject-fail --reject-error 127.0.0.1:10025 127.0.0.1:10026

the proxy will listen on port 10025 and send the verified messages to
some other SMTP service on port 10026.

=head1 CONFIGURATION FILE

Parameters can be stored in a separate file instead of specifying
them all on the command-line. Use the conf_file option to specify
the path to the configuration file, e.g.

  dkimproxy.in --conf_file=/etc/dkimproxy_in.conf

The format of the configuration file is one option per line:
name of the option, space, then the value of the option. E.g.

  # this is an example config file
  listen      127.0.0.1:10025
  relay       127.0.0.1:10026
  hostname    myhost.example.com
  reject_fail

is equivalent to

  dkimproxy.out --hostname=myhost.example.com --reject-fail \
                  127.0.0.1:10025 127.0.0.1:10026

=head1 AUTHOR

Jason Long

=cut
