test_postfix.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
'''
Check that postfix listen correctly the port 25.
Postfix is the service which handles email sendings.
'''
import os
import re
import subprocess
import sys


if not os.path.exists('/etc/postfix'):
    print('Postfix dir does not exists, test skipped.')
else:
    out = subprocess.check_output('netstat -pant | grep \':25\'', shell=True)
    out = out.decode('utf-8') if out else ''

    # netstat -pant output columns are:
    # Proto | Recv-Q | Send-Q | Local address | Foreign address | State | PID/Program name

    expected = r'tcp +\d +\d +127\.0\.0\.1:25 +0\.0\.0\.0:\* +LISTEN +[\d]+/master'
    found = False
    if out:
        for line in out.split('\n'):
            line = re.sub(r' +', ' ', line)
            if line:
                if not re.match(expected, line):
                    print('Unexpected result for postfix listening ports:\n%s' % line)
                    sys.exit(1)
                else:
                    found = True

    if not found:
        print('The port 25 is not listened by any process.')
        sys.exit(1)
    print('Postfix listening port: OK.')