#! /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 >> sys.stderr, __doc__ % globals()

    if msg:

        print >> sys.stderr, msg

    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 >> DEBUGSTREAM, 'Peer:', repr(self.__peer)

        self.push('220 %s %s' % (self.__fqdn, __version__))

        self.set_terminator('\r\n')

    # Overrides base class for convenience

    def push(self, msg):

        asynchat.async_chat.push(self, msg + '\r\n')

    # Implementation of base class abstract method

    def collect_incoming_data(self, data):

        self.__line.append(data)

    # Implementation of base class abstract method

    def found_terminator(self):

        line = EMPTYSTRING.join(self.__line)

        print >> DEBUGSTREAM, 'Data:', repr(line)

        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('\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 >> DEBUGSTREAM, '===> MAIL', arg

        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 >> DEBUGSTREAM, 'sender:', self.__mailfrom

        self.push('250 Ok')

    def smtp_RCPT(self, arg):

        print >> DEBUGSTREAM, '===> RCPT', arg

        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 >> DEBUGSTREAM, 'recips:', self.__rcpttos

        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('\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 >> DEBUGSTREAM, \

              '%s started at %s\n\tLocal addr: %s\n\tRemote addr:%s' % (

            self.__class__.__name__, time.ctime(time.time()),

            localaddr, remoteaddr)

    def handle_accept(self):

        conn, addr = self.accept()

        print >> DEBUGSTREAM, 'Incoming connection from %s' % repr(addr)

        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 >> DEBUGSTREAM, 'we got some refusals:', refused

    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, e:

            print >> DEBUGSTREAM, 'got SMTPRecipientsRefused'

            refused = e.recipients

        except (socket.error, smtplib.SMTPException), e:

            print >> DEBUGSTREAM, 'got', e.__class__

            # 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 cStringIO 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 >> DEBUGSTREAM, 'forwarding recips:', ' '.join(rcpttos)

        if rcpttos:

            refused = self._deliver(mailfrom, rcpttos, data)

            # TBD: what to do with refused addresses?

            print >> DEBUGSTREAM, 'we got refusals:', refused

        # 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 existance seem to add these if the original message doesn't

        # have them.

        if not msg.getheader('from'):

            msg['From'] = mailfrom

        if not msg.getheader('date'):

            msg['Date'] = time.ctime(time.time())

        for rcpt, listname, command in listnames:

            print >> DEBUGSTREAM, 'sending message to', rcpt

            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, e:

        usage(1, e)

    options = Options()

    for opt, arg in opts:

        if opt in ('-h', '--help'):

            usage(0)

        elif opt in ('-V', '--version'):

            print >> sys.stderr, __version__

            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 >> sys.stderr, \

                  'Cannot import module "pwd"; try running with -n option.'

            sys.exit(1)

        nobody = pwd.getpwnam('nobody')[2]