sos-milter/app/sos-milter.py

import Milter
import sys
import traceback
import os
import logging
import string
import random
import re
import dns.resolver
from timeit import default_timer as timer

# Globals with mostly senseless defaults ;)
g_milter_name = 'sos-milter'
g_milter_socket = '/socket/' + g_milter_name
g_milter_reject_message = 'Security policy violation!'
g_milter_tmpfail_message = 'Service temporarily not available! Please try again later.'
g_re_domain = re.compile(r'^\S*@(\S+)$')
g_loglevel = logging.INFO
g_milter_mode = 'test'
g_milter_default_policy = 'reject'

class SOSMilter(Milter.Base):
  # Each new connection is handled in an own thread
  def __init__(self):
    self.time_start = timer()
    self.env_from = None
    self.env_from_domain = None
    # https://stackoverflow.com/a/2257449
    self.mconn_id = g_milter_name + ': ' + ''.join(
      random.choice(string.ascii_lowercase + string.digits) for _ in range(8)
    )
  # Not registered/used callbacks
  @Milter.nocallback
  def connect(self, IPname, family, hostaddr):
    return Milter.CONTINUE
  @Milter.nocallback
  def hello(self, heloname)
    return Milter.CONTINUE
  @Milter.nocallback
  def envrcpt(self, to, *str):
    return Milter.CONTINUE
  @Milter.nocallback
  def data(self):
    return Milter.CONTINUE
  @Milter.nocallback
  def header(self, name, hval):
    return Milter.CONTINUE
  @Milter.nocallback
  def eoh(self):
    return Milter.CONTINUE
  @Milter.nocallback
  def body(self, chunk):
    return Milter.CONTINUE

  def envfrom(self, mailfrom, *str):
    mailfrom = mailfrom.replace("<","")
    mailfrom = mailfrom.replace(">","")
    self.env_from = mailfrom
    m = g_re_domain.match(self.env_from)
    if m == None:
      logging.error(self.mconn_id + "/FROM " +
        "Could not determine domain of 5321.from=" + self.env_from
      )
      self.setreply('450','4.7.1', g_milter_tmpfail_message)
      return Milter.TEMPFAIL
    self.env_from_domain = m.group(1)
    logging.debug(self.mconn_id +
      "/FROM env_from_domain=" + self.env_from_domain
    )
    # Get SPF record of sender domain
    dns_response = dns.resolver.query(self.env_from_domain, 'TXT')
    for rdata in dns_response:
      logging.debug(self.mconn_id +
        "RDATA: " + str(rdata)
      )
    return Milter.CONTINUE

  def eom(self):
    # EOM is not optional and thus, always called by MTA
    return Milter.CONTINUE

  def abort(self):
    # Client disconnected prematurely
    return Milter.CONTINUE

  def close(self):
    # Always called, even when abort is called.
    # Clean up any external resources here.
    return Milter.CONTINUE

if __name__ == "__main__":
    if 'LOG_LEVEL' in os.environ:
      if re.match(r'^info$', os.environ['LOG_LEVEL'], re.IGNORECASE):
        g_loglevel = logging.INFO
      elif re.match(r'^warn|warning$', os.environ['LOG_LEVEL'], re.IGNORECASE):
        g_loglevel = logging.WARN
      elif re.match(r'^error$', os.environ['LOG_LEVEL'], re.IGNORECASE):
        g_loglevel = logging.ERROR
      elif re.match(r'debug', os.environ['LOG_LEVEL'], re.IGNORECASE):
        g_loglevel = logging.DEBUG
    logging.basicConfig(
      filename=None, # log to stdout
      format='%(asctime)s: %(levelname)s %(message)s',
      level=g_loglevel
    )
    if 'MILTER_MODE' in os.environ:
      if re.match(r'^test|reject$',os.environ['MILTER_MODE'], re.IGNORECASE):
        g_milter_mode = os.environ['MILTER_MODE']
    if 'MILTER_DEFAULT_POLICY' in os.environ:
      if re.match(r'^reject|permit$',os.environ['MILTER_DEFAULT_POLICY'], re.IGNORECASE):
        g_milter_default_policy = str(os.environ['MILTER_DEFAULT_POLICY']).lower()
      else:
        logging.warn("MILTER_DEFAULT_POLICY invalid value: " +
          os.environ['MILTER_DEFAULT_POLICY']
        )
    if 'MILTER_NAME' in os.environ:
      g_milter_name = os.environ['MILTER_NAME']
    if 'MILTER_SOCKET' in os.environ:
      g_milter_socket = os.environ['MILTER_SOCKET']
    if 'MILTER_REJECT_MESSAGE' in os.environ:
      g_milter_reject_message = os.environ['MILTER_REJECT_MESSAGE']
    if 'MILTER_TMPFAIL_MESSAGE' in os.environ:
      g_milter_tmpfail_message = os.environ['MILTER_TMPFAIL_MESSAGE']
  try:
    timeout = 600
    # Register to have the Milter factory create instances of your class:
    Milter.factory = SOSMilter
    # Tell the MTA which features we use
    flags = Milter.ADDHDRS
    Milter.set_flags(flags)
    logging.info("Startup " + g_milter_name +
      "@socket: " + g_milter_socket +
      " in mode: " + g_milter_mode
    )
    Milter.runmilter(g_milter_name,g_milter_socket,timeout,True)
    logging.info("Shutdown " + g_milter_name)
  except:
    logging.error("MAIN-EXCEPTION: " + traceback.format_exc())