postfix, integrating memcache as a lookup table using tcp_table

I have not had time to do the test “postfix memcached patch” because there are no idle servers that can be used for the experiment. instead, I’ve made a tutorial how to integrate memcached as a “postfix lookup table” with the help of tcp_table and a simple perl script.

Indeed, tcp_table “table lookup protocol” is one of the most powerful tools as well as the regexp and pcre, in my opinion. although client-server connection is not protected and and the server is not authenticated.

yes, I did a lot of experiments using tcp_table and perl scripts. it made me realize that I can do almost everything I need and make postfix as my favorite MTA.

Things required:

• perl Cache::Memcached module
• memcached
• postfix with tcp_table support

OK, first we create a simple perl script that allows you to handle the protocols of tcp_table. let’s call it memc.pl

#!/usr/bin/perl
use strict;
use warnings;
use Sys::Syslog qw(:DEFAULT setlogsock);
use Cache::Memcached;

# Configure the memcached server
my $memd = new Cache::Memcached {
            'servers' => [ '127.0.0.1:11211' ],
};

#
# Initalize and open syslog.
#
openlog('postfix/memcached','pid','mail');

sub qrymemc {
        return unless /^get\s+(.+)/i;
        my $kmemc = lc($1);
        chomp($kmemc);
        trim($kmemc);
        my $vmemc = $memd->get($kmemc);
        if (defined $vmemc) {
                return ($kmemc,$vmemc);
        }
        return;
}

sub trim{
        $_[0]=~s/^\s+//;
        $_[0]=~s/\s+$//;
        return;
}

#
# Autoflush standard output.
#
select STDOUT; $|++;

while (<>) {
        chomp;
        if (/^get\s+(.+)/i) {
                my $data = lc($1);
                my @res = qrymemc($data);
                syslog("info","data: %s", $data);
                if (@res) {
                        chomp(@res);
                        print "200 $res[1]\n";
                        syslog("info","Found: key = %s, value = %s", $res[0], $res[1]);
                        next;
                }
        }
        print "200 DUNNO\n";
}

Create an entry like this in master.cf

127.0.0.1:2552 inet  n       n       n       -       0      spawn
    user=nobody argv=/etc/postfix/memc.pl

Make memc.pl executable and don’t forget to reload postfix

# chmod 755 memc.pl
# postfix reload

To perform the entry/deletion “key, value” to the memcache I wrote a perl script called postmemc.pl

#!/usr/bin/perl
use strict;
use warnings;
use Cache::Memcached;
use Getopt::Long;

my $memd = new Cache::Memcached {
    'servers' => [ "localhost:11211" ],
  };

my ($k, $v, $help, $delk);

usage() if ( @ARGV < 1 or
           ! GetOptions ('help|?' => \$help, "k=s" => \$k, "v=s" => \$v, "del=s" => \$delk)
           or defined $help );

sub usage
{
        print "Unknown option: @_\n" if ( @_ );
        print "Usage: postmemc.pl --k=key --v='value'\n";
        print "       postmemc.pl --k key --v 'value'\n";
        print "       postmemc.pl --del=key\n";
        print "       postmemc.pl --del key\n";
        exit;
}

if (defined($k) && defined($v) && !defined($delk)) {
        my $val = $memd->get($k);

        if ($val)
        {
                print "Key: $k with Value: '$val' exist\n";
        } else {
                $memd->set($k, $v);
        }
} elsif (!defined($k) && !defined($v) && defined($delk)) {
        my $val = $memd->get($delk);

        if ($val)
        {
                $memd->delete($delk);
        } else {
                print "Key: $delk not' exist\n";
        }
} else {
        usage();
}

$memd->disconnect_all();

Now, let’s try to enter some data using postmemc.pl

$ ./postmemc.pl --k='spam@example.com' --v='REJECT not allowed'

And, for example we want to use it in smtpd_recipient_restrictions as check_recipient_access in main.cf

smtpd_recipient_restrictions =
   ...
   check_recipient_access tcp:[127.0.0.1]:2552,
   ...

Don’t forget to reload postfix. let’s try using postmap to query entries that we have input into memcached.

$ postmap -q spam@example.com tcp:[127.0.0.1]:2552
REJECT not allowed

yeah, another tcp_table’s greatness has been created.