Lib/smtpd.py

   1 #! /usr/bin/env python
   2 """An RFC 2821 smtp proxy.
   3
   4 Usage: %(program)s [options] [localhost:localport [remotehost:remoteport]]
   5
   6 Options:
   7
   8     --nosetuid
   9     -n
  10         This program generally tries to setuid `nobody', unless this flag is
  11         set.  The setuid call will fail if this program is not run as root (in
  12         which case, use this flag).
  13
  14     --version
  15     -V
  16         Print the version number and exit.
  17
  18     --class classname
  19     -c classname
  20         Use `classname' as the concrete SMTP proxy class.  Uses `PureProxy' by
  21         default.
  22
  23     --debug
  24     -d
  25         Turn on debugging prints.
  26
  27     --help
  28     -h
  29         Print this message and exit.
  30
  31 Version: %(__version__)s
  32
  33 If localhost is not given then `localhost' is used, and if localport is not
  34 given then 8025 is used.  If remotehost is not given then `localhost' is used,
  35 and if remoteport is not given, then 25 is used.
  36 """
  37
  38 \f
  39 # Overview:
  40 #
  41 # This file implements the minimal SMTP protocol as defined in RFC 821.  It
  42 # has a hierarchy of classes which implement the backend functionality for the
  43 # smtpd.  A number of classes are provided:
  44 #
  45 #   SMTPServer - the base class for the backend.  Raises NotImplementedError
  46 #   if you try to use it.
  47 #
  48 #   DebuggingServer - simply prints each message it receives on stdout.
  49 #
  50 #   PureProxy - Proxies all messages to a real smtpd which does final
  51 #   delivery.  One known problem with this class is that it doesn't handle
  52 #   SMTP errors from the backend server at all.  This should be fixed
  53 #   (contributions are welcome!).
  54 #
  55 #   MailmanProxy - An experimental hack to work with GNU Mailman
  56 #   <www.list.org>.  Using this server as your real incoming smtpd, your
  57 #   mailhost will automatically recognize and accept mail destined to Mailman
  58 #   lists when those lists are created.  Every message not destined for a list
  59 #   gets forwarded to a real backend smtpd, as with PureProxy.  Again, errors
  60 #   are not handled correctly yet.
  61 #
  62 # Please note that this script requires Python 2.0
  63 #
  64 # Author: Barry Warsaw <barry@python.org>
  65 #
  66 # TODO:
  67 #
  68 # - support mailbox delivery
  69 # - alias files
  70 # - ESMTP
  71 # - handle error codes from the backend smtpd
  72
  73 import sys
  74 import os
  75 import errno
  76 import getopt
  77 import time
  78 import socket
  79 import asyncore
  80 import asynchat
  81
  82 __all__ = ["SMTPServer","DebuggingServer","PureProxy","MailmanProxy"]
  83
  84 program = sys.argv[0]
  85 __version__ = 'Python SMTP proxy version 0.2'
  86
  87
  88 class Devnull:
  89     def write(self, msg): pass
  90     def flush(self): pass
  91
  92
  93 DEBUGSTREAM = Devnull()
  94 NEWLINE = '\n'
  95 EMPTYSTRING = ''
  96 COMMASPACE = ', '
  97
  98
  99 \f
 100 def usage(code, msg=''):
 101     print >> sys.stderr, __doc__ % globals()
 102     if msg:
 103         print >> sys.stderr, msg
 104     sys.exit(code)
 105
 106
 107 \f
 108 class SMTPChannel(asynchat.async_chat):
 109     COMMAND = 0
 110     DATA = 1
 111
 112     def __init__(self, server, conn, addr):
 113         asynchat.async_chat.__init__(self, conn)
 114         self.__server = server
 115         self.__conn = conn
 116         self.__addr = addr
 117         self.__line = []
 118         self.__state = self.COMMAND
 119         self.__greeting = 0
 120         self.__mailfrom = None
 121         self.__rcpttos = []
 122         self.__data = ''
 123         self.__fqdn = socket.getfqdn()
 124         self.__peer = conn.getpeername()
 125         print >> DEBUGSTREAM, 'Peer:', repr(self.__peer)
 126         self.push('220 %s %s' % (self.__fqdn, __version__))
 127         self.set_terminator('\r\n')
 128
 129     # Overrides base class for convenience
 130     def push(self, msg):
 131         asynchat.async_chat.push(self, msg + '\r\n')
 132
 133     # Implementation of base class abstract method
 134     def collect_incoming_data(self, data):
 135         self.__line.append(data)
 136
 137     # Implementation of base class abstract method
 138     def found_terminator(self):
 139         line = EMPTYSTRING.join(self.__line)
 140         print >> DEBUGSTREAM, 'Data:', repr(line)
 141         self.__line = []
 142         if self.__state == self.COMMAND:
 143             if not line:
 144                 self.push('500 Error: bad syntax')
 145                 return
 146             method = None
 147             i = line.find(' ')
 148             if i < 0:
 149                 command = line.upper()
 150                 arg = None
 151             else:
 152                 command = line[:i].upper()
 153                 arg = line[i+1:].strip()
 154             method = getattr(self, 'smtp_' + command, None)
 155             if not method:
 156                 self.push('502 Error: command "%s" not implemented' % command)
 157                 return
 158             method(arg)
 159             return
 160         else:
 161             if self.__state != self.DATA:
 162                 self.push('451 Internal confusion')
 163                 return
 164             # Remove extraneous carriage returns and de-transparency according
 165             # to RFC 821, Section 4.5.2.
 166             data = []
 167             for text in line.split('\r\n'):
 168                 if text and text[0] == '.':
 169                     data.append(text[1:])
 170                 else:
 171                     data.append(text)
 172             self.__data = NEWLINE.join(data)
 173             status = self.__server.process_message(self.__peer,
 174                                                    self.__mailfrom,
 175                                                    self.__rcpttos,
 176                                                    self.__data)
 177             self.__rcpttos = []
 178             self.__mailfrom = None
 179             self.__state = self.COMMAND
 180             self.set_terminator('\r\n')
 181             if not status:
 182                 self.push('250 Ok')
 183             else:
 184                 self.push(status)
 185
 186     # SMTP and ESMTP commands
 187     def smtp_HELO(self, arg):
 188         if not arg:
 189             self.push('501 Syntax: HELO hostname')
 190             return
 191         if self.__greeting:
 192             self.push('503 Duplicate HELO/EHLO')
 193         else:
 194             self.__greeting = arg
 195             self.push('250 %s' % self.__fqdn)
 196
 197     def smtp_NOOP(self, arg):
 198         if arg:
 199             self.push('501 Syntax: NOOP')
 200         else:
 201             self.push('250 Ok')
 202
 203     def smtp_QUIT(self, arg):
 204         # args is ignored
 205         self.push('221 Bye')
 206         self.close_when_done()
 207
 208     # factored
 209     def __getaddr(self, keyword, arg):
 210         address = None
 211         keylen = len(keyword)
 212         if arg[:keylen].upper() == keyword:
 213             address = arg[keylen:].strip()
 214             if not address:
 215                 pass
 216             elif address[0] == '<' and address[-1] == '>' and address != '<>':
 217                 # Addresses can be in the form <person@dom.com> but watch out
 218                 # for null address, e.g. <>
 219                 address = address[1:-1]
 220         return address
 221
 222     def smtp_MAIL(self, arg):
 223         print >> DEBUGSTREAM, '===> MAIL', arg
 224         address = self.__getaddr('FROM:', arg) if arg else None
 225         if not address:
 226             self.push('501 Syntax: MAIL FROM:<address>')
 227             return
 228         if self.__mailfrom:
 229             self.push('503 Error: nested MAIL command')
 230             return
 231         self.__mailfrom = address
 232         print >> DEBUGSTREAM, 'sender:', self.__mailfrom
 233         self.push('250 Ok')
 234
 235     def smtp_RCPT(self, arg):
 236         print >> DEBUGSTREAM, '===> RCPT', arg
 237         if not self.__mailfrom:
 238             self.push('503 Error: need MAIL command')
 239             return
 240         address = self.__getaddr('TO:', arg) if arg else None
 241         if not address:
 242             self.push('501 Syntax: RCPT TO: <address>')
 243             return
 244         self.__rcpttos.append(address)
 245         print >> DEBUGSTREAM, 'recips:', self.__rcpttos
 246         self.push('250 Ok')
 247
 248     def smtp_RSET(self, arg):
 249         if arg:
 250             self.push('501 Syntax: RSET')
 251             return
 252         # Resets the sender, recipients, and data, but not the greeting
 253         self.__mailfrom = None
 254         self.__rcpttos = []
 255         self.__data = ''
 256         self.__state = self.COMMAND
 257         self.push('250 Ok')
 258
 259     def smtp_DATA(self, arg):
 260         if not self.__rcpttos:
 261             self.push('503 Error: need RCPT command')
 262             return
 263         if arg:
 264             self.push('501 Syntax: DATA')
 265             return
 266         self.__state = self.DATA
 267         self.set_terminator('\r\n.\r\n')
 268         self.push('354 End data with <CR><LF>.<CR><LF>')
 269
 270
 271 \f
 272 class SMTPServer(asyncore.dispatcher):
 273     def __init__(self, localaddr, remoteaddr):
 274         self._localaddr = localaddr
 275         self._remoteaddr = remoteaddr
 276         asyncore.dispatcher.__init__(self)
 277         self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
 278         # try to re-use a server port if possible
 279         self.set_reuse_addr()
 280         self.bind(localaddr)
 281         self.listen(5)
 282         print >> DEBUGSTREAM, \
 283               '%s started at %s\n\tLocal addr: %s\n\tRemote addr:%s' % (
 284             self.__class__.__name__, time.ctime(time.time()),
 285             localaddr, remoteaddr)
 286
 287     def handle_accept(self):
 288         conn, addr = self.accept()
 289         print >> DEBUGSTREAM, 'Incoming connection from %s' % repr(addr)
 290         channel = SMTPChannel(self, conn, addr)
 291
 292     # API for "doing something useful with the message"
 293     def process_message(self, peer, mailfrom, rcpttos, data):
 294         """Override this abstract method to handle messages from the client.
 295
 296         peer is a tuple containing (ipaddr, port) of the client that made the
 297         socket connection to our smtp port.
 298
 299         mailfrom is the raw address the client claims the message is coming
 300         from.
 301
 302         rcpttos is a list of raw addresses the client wishes to deliver the
 303         message to.
 304
 305         data is a string containing the entire full text of the message,
 306         headers (if supplied) and all.  It has been `de-transparencied'
 307         according to RFC 821, Section 4.5.2.  In other words, a line
 308         containing a `.' followed by other text has had the leading dot
 309         removed.
 310
 311         This function should return None, for a normal `250 Ok' response;
 312         otherwise it returns the desired response string in RFC 821 format.
 313
 314         """
 315         raise NotImplementedError
 316
 317
 318 \f
 319 class DebuggingServer(SMTPServer):
 320     # Do something with the gathered message
 321     def process_message(self, peer, mailfrom, rcpttos, data):
 322         inheaders = 1
 323         lines = data.split('\n')
 324         print '---------- MESSAGE FOLLOWS ----------'
 325         for line in lines:
 326             # headers first
 327             if inheaders and not line:
 328                 print 'X-Peer:', peer[0]
 329                 inheaders = 0
 330             print line
 331         print '------------ END MESSAGE ------------'
 332
 333
 334 \f
 335 class PureProxy(SMTPServer):
 336     def process_message(self, peer, mailfrom, rcpttos, data):
 337         lines = data.split('\n')
 338         # Look for the last header
 339         i = 0
 340         for line in lines:
 341             if not line:
 342                 break
 343             i += 1
 344         lines.insert(i, 'X-Peer: %s' % peer[0])
 345         data = NEWLINE.join(lines)
 346         refused = self._deliver(mailfrom, rcpttos, data)
 347         # TBD: what to do with refused addresses?
 348         print >> DEBUGSTREAM, 'we got some refusals:', refused
 349
 350     def _deliver(self, mailfrom, rcpttos, data):
 351         import smtplib
 352         refused = {}
 353         try:
 354             s = smtplib.SMTP()
 355             s.connect(self._remoteaddr[0], self._remoteaddr[1])
 356             try:
 357                 refused = s.sendmail(mailfrom, rcpttos, data)
 358             finally:
 359                 s.quit()
 360         except smtplib.SMTPRecipientsRefused, e:
 361             print >> DEBUGSTREAM, 'got SMTPRecipientsRefused'
 362             refused = e.recipients
 363         except (socket.error, smtplib.SMTPException), e:
 364             print >> DEBUGSTREAM, 'got', e.__class__
 365             # All recipients were refused.  If the exception had an associated
 366             # error code, use it.  Otherwise,fake it with a non-triggering
 367             # exception code.
 368             errcode = getattr(e, 'smtp_code', -1)
 369             errmsg = getattr(e, 'smtp_error', 'ignore')
 370             for r in rcpttos:
 371                 refused[r] = (errcode, errmsg)
 372         return refused
 373
 374
 375 \f
 376 class MailmanProxy(PureProxy):
 377     def process_message(self, peer, mailfrom, rcpttos, data):
 378         from cStringIO import StringIO
 379         from Mailman import Utils
 380         from Mailman import Message
 381         from Mailman import MailList
 382         # If the message is to a Mailman mailing list, then we'll invoke the
 383         # Mailman script directly, without going through the real smtpd.
 384         # Otherwise we'll forward it to the local proxy for disposition.
 385         listnames = []
 386         for rcpt in rcpttos:
 387             local = rcpt.lower().split('@')[0]
 388             # We allow the following variations on the theme
 389             #   listname
 390             #   listname-admin
 391             #   listname-owner
 392             #   listname-request
 393             #   listname-join
 394             #   listname-leave
 395             parts = local.split('-')
 396             if len(parts) > 2:
 397                 continue
 398             listname = parts[0]
 399             if len(parts) == 2:
 400                 command = parts[1]
 401             else:
 402                 command = ''
 403             if not Utils.list_exists(listname) or command not in (
 404                     '', 'admin', 'owner', 'request', 'join', 'leave'):
 405                 continue
 406             listnames.append((rcpt, listname, command))
 407         # Remove all list recipients from rcpttos and forward what we're not
 408         # going to take care of ourselves.  Linear removal should be fine
 409         # since we don't expect a large number of recipients.
 410         for rcpt, listname, command in listnames:
 411             rcpttos.remove(rcpt)
 412         # If there's any non-list destined recipients left,
 413         print >> DEBUGSTREAM, 'forwarding recips:', ' '.join(rcpttos)
 414         if rcpttos:
 415             refused = self._deliver(mailfrom, rcpttos, data)
 416             # TBD: what to do with refused addresses?
 417             print >> DEBUGSTREAM, 'we got refusals:', refused
 418         # Now deliver directly to the list commands
 419         mlists = {}
 420         s = StringIO(data)
 421         msg = Message.Message(s)
 422         # These headers are required for the proper execution of Mailman.  All
 423         # MTAs in existance seem to add these if the original message doesn't
 424         # have them.
 425         if not msg.getheader('from'):
 426             msg['From'] = mailfrom
 427         if not msg.getheader('date'):
 428             msg['Date'] = time.ctime(time.time())
 429         for rcpt, listname, command in listnames:
 430             print >> DEBUGSTREAM, 'sending message to', rcpt
 431             mlist = mlists.get(listname)
 432             if not mlist:
 433                 mlist = MailList.MailList(listname, lock=0)
 434                 mlists[listname] = mlist
 435             # dispatch on the type of command
 436             if command == '':
 437                 # post
 438                 msg.Enqueue(mlist, tolist=1)
 439             elif command == 'admin':
 440                 msg.Enqueue(mlist, toadmin=1)
 441             elif command == 'owner':
 442                 msg.Enqueue(mlist, toowner=1)
 443             elif command == 'request':
 444                 msg.Enqueue(mlist, torequest=1)
 445             elif command in ('join', 'leave'):
 446                 # TBD: this is a hack!
 447                 if command == 'join':
 448                     msg['Subject'] = 'subscribe'
 449                 else:
 450                     msg['Subject'] = 'unsubscribe'
 451                 msg.Enqueue(mlist, torequest=1)
 452
 453
 454 \f
 455 class Options:
 456     setuid = 1
 457     classname = 'PureProxy'
 458
 459
 460 \f
 461 def parseargs():
 462     global DEBUGSTREAM
 463     try:
 464         opts, args = getopt.getopt(
 465             sys.argv[1:], 'nVhc:d',
 466             ['class=', 'nosetuid', 'version', 'help', 'debug'])
 467     except getopt.error, e:
 468         usage(1, e)
 469
 470     options = Options()
 471     for opt, arg in opts:
 472         if opt in ('-h', '--help'):
 473             usage(0)
 474         elif opt in ('-V', '--version'):
 475             print >> sys.stderr, __version__
 476             sys.exit(0)
 477         elif opt in ('-n', '--nosetuid'):
 478             options.setuid = 0
 479         elif opt in ('-c', '--class'):
 480             options.classname = arg
 481         elif opt in ('-d', '--debug'):
 482             DEBUGSTREAM = sys.stderr
 483
 484     # parse the rest of the arguments
 485     if len(args) < 1:
 486         localspec = 'localhost:8025'
 487         remotespec = 'localhost:25'
 488     elif len(args) < 2:
 489         localspec = args[0]
 490         remotespec = 'localhost:25'
 491     elif len(args) < 3:
 492         localspec = args[0]
 493         remotespec = args[1]
 494     else:
 495         usage(1, 'Invalid arguments: %s' % COMMASPACE.join(args))
 496
 497     # split into host/port pairs
 498     i = localspec.find(':')
 499     if i < 0:
 500         usage(1, 'Bad local spec: %s' % localspec)
 501     options.localhost = localspec[:i]
 502     try:
 503         options.localport = int(localspec[i+1:])
 504     except ValueError:
 505         usage(1, 'Bad local port: %s' % localspec)
 506     i = remotespec.find(':')
 507     if i < 0:
 508         usage(1, 'Bad remote spec: %s' % remotespec)
 509     options.remotehost = remotespec[:i]
 510     try:
 511         options.remoteport = int(remotespec[i+1:])
 512     except ValueError:
 513         usage(1, 'Bad remote port: %s' % remotespec)
 514     return options
 515
 516
 517 \f
 518 if __name__ == '__main__':
 519     options = parseargs()
 520     # Become nobody
 521     if options.setuid:
 522         try:
 523             import pwd
 524         except ImportError:
 525             print >> sys.stderr, \
 526                   'Cannot import module "pwd"; try running with -n option.'
 527             sys.exit(1)
 528         nobody = pwd.getpwnam('nobody')[2]
 529         try:
 530             os.setuid(nobody)
 531         except OSError, e:
 532             if e.errno != errno.EPERM: raise
 533             print >> sys.stderr, \
 534                   'Cannot setuid "nobody"; try running with -n option.'
 535             sys.exit(1)
 536     classname = options.classname
 537     if "." in classname:
 538         lastdot = classname.rfind(".")
 539         mod = __import__(classname[:lastdot], globals(), locals(), [""])
 540         classname = classname[lastdot+1:]
 541     else:
 542         import __main__ as mod
 543     class_ = getattr(mod, classname)
 544     proxy = class_((options.localhost, options.localport),
 545                    (options.remotehost, options.remoteport))
 546     try:
 547         asyncore.loop()
 548     except KeyboardInterrupt:
 549         pass