smtpd.py
#! /usr/bin/env python
"""An RFC 2821 smtp proxy.
Usage: %(program)s [options] [localhost:localport [remotehost:remoteport]]
Options:
--nosetuid
-n
This program generally tries to setuid `nobody', unless this flag is
set. The setuid call will fail if this program is not run as root (in
which case, use this flag).
--version
-V
Print the version number and exit.
--class classname
-c classname
Use `classname' as the concrete SMTP proxy class. Uses `PureProxy' by
default.
--debug
-d
Turn on debugging prints.
--help
-h
Print this message and exit.
Version: %(__version__)s
If localhost is not given then `localhost' is used, and if localport is not
given then 8025 is used. If remotehost is not given then `localhost' is used,
and if remoteport is not given, then 25 is used.
"""
# Overview:
#
# This file implements the minimal SMTP protocol as defined in RFC 821. It
# has a hierarchy of classes which implement the backend functionality for the
# smtpd. A number of classes are provided:
#
# SMTPServer - the base class for the backend. Raises NotImplementedError
# if you try to use it.
#
# DebuggingServer - simply prints each message it receives on stdout.
#
# PureProxy - Proxies all messages to a real smtpd which does final
# delivery. One known problem with this class is that it doesn't handle
# SMTP errors from the backend server at all. This should be fixed
# (contributions are welcome!).
#
# MailmanProxy - An experimental hack to work with GNU Mailman
# <www.list.org>. Using this server as your real incoming smtpd, your
# mailhost will automatically recognize and accept mail destined to Mailman
# lists when those lists are created. Every message not destined for a list
# gets forwarded to a real backend smtpd, as with PureProxy. Again, errors
# are not handled correctly yet.
#
# Please note that this script requires Python 2.0
#
# Author: Barry Warsaw <barry@python.org>
#
# TODO:
#
# - support mailbox delivery
# - alias files
# - ESMTP
# - handle error codes from the backend smtpd
import sys
import os
import errno
import getopt
import time
import socket
import asyncore
import asynchat
__all__ = ["SMTPServer","DebuggingServer","PureProxy","MailmanProxy"]
program = sys.argv[0]
__version__ = 'Python SMTP proxy version 0.2'
class Devnull:
def write(self, msg): pass
def flush(self): pass
DEBUGSTREAM = Devnull()
NEWLINE = '\n'
EMPTYSTRING = ''
COMMASPACE = ', '
def usage(code, msg=''):
print(__doc__ % globals(), file=sys.stderr)
if msg:
print(msg, file=sys.stderr)
sys.exit(code)
class SMTPChannel(asynchat.async_chat):
COMMAND = 0
DATA = 1
def __init__(self, server, conn, addr):
asynchat.async_chat.__init__(self, conn)
self.__server = server
self.__conn = conn
self.__addr = addr
self.__line = []
self.__state = self.COMMAND
self.__greeting = 0
self.__mailfrom = None
self.__rcpttos = []
self.__data = ''
self.__fqdn = socket.getfqdn()
self.__peer = conn.getpeername()
print('Peer:', repr(self.__peer), file=DEBUGSTREAM)
self.push('220 %s %s' % (self.__fqdn, __version__))
self.set_terminator(b'\r\n')
# Overrides base class for convenience
def push(self, msg):
asynchat.async_chat.push(self, bytes(msg + '\r\n', 'ascii'))
# Implementation of base class abstract method
def collect_incoming_data(self, data):
self.__line.append(str(data, "utf8"))
# Implementation of base class abstract method
def found_terminator(self):
line = EMPTYSTRING.join(self.__line)
print('Data:', repr(line), file=DEBUGSTREAM)
self.__line = []
if self.__state == self.COMMAND:
if not line:
self.push('500 Error: bad syntax')
return
method = None
i = line.find(' ')
if i < 0:
command = line.upper()
arg = None
else:
command = line[:i].upper()
arg = line[i+1:].strip()
method = getattr(self, 'smtp_' + command, None)
if not method:
self.push('502 Error: command "%s" not implemented' % command)
return
method(arg)
return
else:
if self.__state != self.DATA:
self.push('451 Internal confusion')
return
# Remove extraneous carriage returns and de-transparency according
# to RFC 821, Section 4.5.2.
data = []
for text in line.split('\r\n'):
if text and text[0] == '.':
data.append(text[1:])
else:
data.append(text)
self.__data = NEWLINE.join(data)
status = self.__server.process_message(self.__peer,
self.__mailfrom,
self.__rcpttos,
self.__data)
self.__rcpttos = []
self.__mailfrom = None
self.__state = self.COMMAND
self.set_terminator(b'\r\n')
if not status:
self.push('250 Ok')
else:
self.push(status)
# SMTP and ESMTP commands
def smtp_HELO(self, arg):
if not arg:
self.push('501 Syntax: HELO hostname')
return
if self.__greeting:
self.push('503 Duplicate HELO/EHLO')
else:
self.__greeting = arg
self.push('250 %s' % self.__fqdn)
def smtp_NOOP(self, arg):
if arg:
self.push('501 Syntax: NOOP')
else:
self.push('250 Ok')
def smtp_QUIT(self, arg):
# args is ignored
self.push('221 Bye')
self.close_when_done()
# factored
def __getaddr(self, keyword, arg):
address = None
keylen = len(keyword)
if arg[:keylen].upper() == keyword:
address = arg[keylen:].strip()
if not address:
pass
elif address[0] == '<' and address[-1] == '>' and address != '<>':
# Addresses can be in the form <person@dom.com> but watch out
# for null address, e.g. <>
address = address[1:-1]
return address
def smtp_MAIL(self, arg):
print('===> MAIL', arg, file=DEBUGSTREAM)
address = self.__getaddr('FROM:', arg) if arg else None
if not address:
self.push('501 Syntax: MAIL FROM:<address>')
return
if self.__mailfrom:
self.push('503 Error: nested MAIL command')
return
self.__mailfrom = address
print('sender:', self.__mailfrom, file=DEBUGSTREAM)
self.push('250 Ok')
def smtp_RCPT(self, arg):
print('===> RCPT', arg, file=DEBUGSTREAM)
if not self.__mailfrom:
self.push('503 Error: need MAIL command')
return
address = self.__getaddr('TO:', arg) if arg else None
if not address:
self.push('501 Syntax: RCPT TO: <address>')
return
self.__rcpttos.append(address)
print('recips:', self.__rcpttos, file=DEBUGSTREAM)
self.push('250 Ok')
def smtp_RSET(self, arg):
if arg:
self.push('501 Syntax: RSET')
return
# Resets the sender, recipients, and data, but not the greeting
self.__mailfrom = None
self.__rcpttos = []
self.__data = ''
self.__state = self.COMMAND
self.push('250 Ok')
def smtp_DATA(self, arg):
if not self.__rcpttos:
self.push('503 Error: need RCPT command')
return
if arg:
self.push('501 Syntax: DATA')
return
self.__state = self.DATA
self.set_terminator(b'\r\n.\r\n')
self.push('354 End data with <CR><LF>.<CR><LF>')
class SMTPServer(asyncore.dispatcher):
def __init__(self, localaddr, remoteaddr):
self._localaddr = localaddr
self._remoteaddr = remoteaddr
asyncore.dispatcher.__init__(self)
self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
# try to re-use a server port if possible
self.set_reuse_addr()
self.bind(localaddr)
self.listen(5)
print('%s started at %s\n\tLocal addr: %s\n\tRemote addr:%s' % (
self.__class__.__name__, time.ctime(time.time()),
localaddr, remoteaddr), file=DEBUGSTREAM)
def handle_accept(self):
conn, addr = self.accept()
print('Incoming connection from %s' % repr(addr), file=DEBUGSTREAM)
channel = SMTPChannel(self, conn, addr)
# API for "doing something useful with the message"
def process_message(self, peer, mailfrom, rcpttos, data):
"""Override this abstract method to handle messages from the client.
peer is a tuple containing (ipaddr, port) of the client that made the
socket connection to our smtp port.
mailfrom is the raw address the client claims the message is coming
from.
rcpttos is a list of raw addresses the client wishes to deliver the
message to.
data is a string containing the entire full text of the message,
headers (if supplied) and all. It has been `de-transparencied'
according to RFC 821, Section 4.5.2. In other words, a line
containing a `.' followed by other text has had the leading dot
removed.
This function should return None, for a normal `250 Ok' response;
otherwise it returns the desired response string in RFC 821 format.
"""
raise NotImplementedError
class DebuggingServer(SMTPServer):
# Do something with the gathered message
def process_message(self, peer, mailfrom, rcpttos, data):
inheaders = 1
lines = data.split('\n')
print('---------- MESSAGE FOLLOWS ----------')
for line in lines:
# headers first
if inheaders and not line:
print('X-Peer:', peer[0])
inheaders = 0
print(line)
print('------------ END MESSAGE ------------')
class PureProxy(SMTPServer):
def process_message(self, peer, mailfrom, rcpttos, data):
lines = data.split('\n')
# Look for the last header
i = 0
for line in lines:
if not line:
break
i += 1
lines.insert(i, 'X-Peer: %s' % peer[0])
data = NEWLINE.join(lines)
refused = self._deliver(mailfrom, rcpttos, data)
# TBD: what to do with refused addresses?
print('we got some refusals:', refused, file=DEBUGSTREAM)
def _deliver(self, mailfrom, rcpttos, data):
import smtplib
refused = {}
try:
s = smtplib.SMTP()
s.connect(self._remoteaddr[0], self._remoteaddr[1])
try:
refused = s.sendmail(mailfrom, rcpttos, data)
finally:
s.quit()
except smtplib.SMTPRecipientsRefused as e:
print('got SMTPRecipientsRefused', file=DEBUGSTREAM)
refused = e.recipients
except (socket.error, smtplib.SMTPException) as e:
print('got', e.__class__, file=DEBUGSTREAM)
# All recipients were refused. If the exception had an associated
# error code, use it. Otherwise,fake it with a non-triggering
# exception code.
errcode = getattr(e, 'smtp_code', -1)
errmsg = getattr(e, 'smtp_error', 'ignore')
for r in rcpttos:
refused[r] = (errcode, errmsg)
return refused
class MailmanProxy(PureProxy):
def process_message(self, peer, mailfrom, rcpttos, data):
from io import StringIO
from Mailman import Utils
from Mailman import Message
from Mailman import MailList
# If the message is to a Mailman mailing list, then we'll invoke the
# Mailman script directly, without going through the real smtpd.
# Otherwise we'll forward it to the local proxy for disposition.
listnames = []
for rcpt in rcpttos:
local = rcpt.lower().split('@')[0]
# We allow the following variations on the theme
# listname
# listname-admin
# listname-owner
# listname-request
# listname-join
# listname-leave
parts = local.split('-')
if len(parts) > 2:
continue
listname = parts[0]
if len(parts) == 2:
command = parts[1]
else:
command = ''
if not Utils.list_exists(listname) or command not in (
'', 'admin', 'owner', 'request', 'join', 'leave'):
continue
listnames.append((rcpt, listname, command))
# Remove all list recipients from rcpttos and forward what we're not
# going to take care of ourselves. Linear removal should be fine
# since we don't expect a large number of recipients.
for rcpt, listname, command in listnames:
rcpttos.remove(rcpt)
# If there's any non-list destined recipients left,
print('forwarding recips:', ' '.join(rcpttos), file=DEBUGSTREAM)
if rcpttos:
refused = self._deliver(mailfrom, rcpttos, data)
# TBD: what to do with refused addresses?
print('we got refusals:', refused, file=DEBUGSTREAM)
# Now deliver directly to the list commands
mlists = {}
s = StringIO(data)
msg = Message.Message(s)
# These headers are required for the proper execution of Mailman. All
# MTAs in existence seem to add these if the original message doesn't
# have them.
if not msg.get('from'):
msg['From'] = mailfrom
if not msg.get('date'):
msg['Date'] = time.ctime(time.time())
for rcpt, listname, command in listnames:
print('sending message to', rcpt, file=DEBUGSTREAM)
mlist = mlists.get(listname)
if not mlist:
mlist = MailList.MailList(listname, lock=0)
mlists[listname] = mlist
# dispatch on the type of command
if command == '':
# post
msg.Enqueue(mlist, tolist=1)
elif command == 'admin':
msg.Enqueue(mlist, toadmin=1)
elif command == 'owner':
msg.Enqueue(mlist, toowner=1)
elif command == 'request':
msg.Enqueue(mlist, torequest=1)
elif command in ('join', 'leave'):
# TBD: this is a hack!
if command == 'join':
msg['Subject'] = 'subscribe'
else:
msg['Subject'] = 'unsubscribe'
msg.Enqueue(mlist, torequest=1)
class Options:
setuid = 1
classname = 'PureProxy'
def parseargs():
global DEBUGSTREAM
try:
opts, args = getopt.getopt(
sys.argv[1:], 'nVhc:d',
['class=', 'nosetuid', 'version', 'help', 'debug'])
except getopt.error as e:
usage(1, e)
options = Options()
for opt, arg in opts:
if opt in ('-h', '--help'):
usage(0)
elif opt in ('-V', '--version'):
print(__version__, file=sys.stderr)
sys.exit(0)
elif opt in ('-n', '--nosetuid'):
options.setuid = 0
elif opt in ('-c', '--class'):
options.classname = arg
elif opt in ('-d', '--debug'):
DEBUGSTREAM = sys.stderr
# parse the rest of the arguments
if len(args) < 1:
localspec = 'localhost:8025'
remotespec = 'localhost:25'
elif len(args) < 2:
localspec = args[0]
remotespec = 'localhost:25'
elif len(args) < 3:
localspec = args[0]
remotespec = args[1]
else:
usage(1, 'Invalid arguments: %s' % COMMASPACE.join(args))
# split into host/port pairs
i = localspec.find(':')
if i < 0:
usage(1, 'Bad local spec: %s' % localspec)
options.localhost = localspec[:i]
try:
options.localport = int(localspec[i+1:])
except ValueError:
usage(1, 'Bad local port: %s' % localspec)
i = remotespec.find(':')
if i < 0:
usage(1, 'Bad remote spec: %s' % remotespec)
options.remotehost = remotespec[:i]
try:
options.remoteport = int(remotespec[i+1:])
except ValueError:
usage(1, 'Bad remote port: %s' % remotespec)
return options
if __name__ == '__main__':
options = parseargs()
# Become nobody
if options.setuid:
try:
import pwd
except ImportError:
print('Cannot import module "pwd"; try running with -n option.', file=sys.stderr)
sys.exit(1)
nobody = pwd.getpwnam('nobody')[2]
try:
os.setuid(nobody)
except OSError as e:
if e.errno != errno.EPERM: raise
print('Cannot setuid "nobody"; try running with -n option.', file=sys.stderr)
sys.exit(1)
classname = options.classname
if "." in classname:
lastdot = classname.rfind(".")
mod = __import__(classname[:lastdot], globals(), locals(), [""])
classname = classname[lastdot+1:]
else:
import __main__ as mod
class_ = getattr(mod, classname)
proxy = class_((options.localhost, options.localport),
(options.remotehost, options.remoteport))
try:
asyncore.loop()
except KeyboardInterrupt:
pass
