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(__doc__ % globals(), file=sys.stderr)
 102     if msg:
 103         print(msg, file=sys.stderr)
 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('Peer:', repr(self.__peer), file=DEBUGSTREAM)
 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(str(data, "utf8"))
 136
 137     # Implementation of base class abstract method
 138     def found_terminator(self):
 139         line = EMPTYSTRING.join(self.__line)
 140         print('Data:', repr(line), file=DEBUGSTREAM)
 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('===> MAIL', arg, file=DEBUGSTREAM)
 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('sender:', self.__mailfrom, file=DEBUGSTREAM)
 233         self.push('250 Ok')
 234
 235     def smtp_RCPT(self, arg):
 236         print('===> RCPT', arg, file=DEBUGSTREAM)
 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('recips:', self.__rcpttos, file=DEBUGSTREAM)
 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('%s started at %s\n\tLocal addr: %s\n\tRemote addr:%s' % (
 283             self.__class__.__name__, time.ctime(time.time()),
 284             localaddr, remoteaddr), file=DEBUGSTREAM)
 285
 286     def handle_accept(self):
 287         conn, addr = self.accept()
 288         print('Incoming connection from %s' % repr(addr), file=DEBUGSTREAM)
 289         channel = SMTPChannel(self, conn, addr)
 290
 291     # API for "doing something useful with the message"
 292     def process_message(self, peer, mailfrom, rcpttos, data):
 293         """Override this abstract method to handle messages from the client.
 294
 295         peer is a tuple containing (ipaddr, port) of the client that made the
 296         socket connection to our smtp port.
 297
 298         mailfrom is the raw address the client claims the message is coming
 299         from.
 300
 301         rcpttos is a list of raw addresses the client wishes to deliver the
 302         message to.
 303
 304         data is a string containing the entire full text of the message,
 305         headers (if supplied) and all.  It has been `de-transparencied'
 306         according to RFC 821, Section 4.5.2.  In other words, a line
 307         containing a `.' followed by other text has had the leading dot
 308         removed.
 309
 310         This function should return None, for a normal `250 Ok' response;
 311         otherwise it returns the desired response string in RFC 821 format.
 312
 313         """
 314         raise NotImplementedError
 315
 316
 317 \f
 318 class DebuggingServer(SMTPServer):
 319     # Do something with the gathered message
 320     def process_message(self, peer, mailfrom, rcpttos, data):
 321         inheaders = 1
 322         lines = data.split('\n')
 323         print('---------- MESSAGE FOLLOWS ----------')
 324         for line in lines:
 325             # headers first
 326             if inheaders and not line:
 327                 print('X-Peer:', peer[0])
 328                 inheaders = 0
 329             print(line)
 330         print('------------ END MESSAGE ------------')
 331
 332
 333 \f
 334 class PureProxy(SMTPServer):
 335     def process_message(self, peer, mailfrom, rcpttos, data):
 336         lines = data.split('\n')
 337         # Look for the last header
 338         i = 0
 339         for line in lines:
 340             if not line:
 341                 break
 342             i += 1
 343         lines.insert(i, 'X-Peer: %s' % peer[0])
 344         data = NEWLINE.join(lines)
 345         refused = self._deliver(mailfrom, rcpttos, data)
 346         # TBD: what to do with refused addresses?
 347         print('we got some refusals:', refused, file=DEBUGSTREAM)
 348
 349     def _deliver(self, mailfrom, rcpttos, data):
 350         import smtplib
 351         refused = {}
 352         try:
 353             s = smtplib.SMTP()
 354             s.connect(self._remoteaddr[0], self._remoteaddr[1])
 355             try:
 356                 refused = s.sendmail(mailfrom, rcpttos, data)
 357             finally:
 358                 s.quit()
 359         except smtplib.SMTPRecipientsRefused as e:
 360             print('got SMTPRecipientsRefused', file=DEBUGSTREAM)
 361             refused = e.recipients
 362         except (socket.error, smtplib.SMTPException) as e:
 363             print('got', e.__class__, file=DEBUGSTREAM)
 364             # All recipients were refused.  If the exception had an associated
 365             # error code, use it.  Otherwise,fake it with a non-triggering
 366             # exception code.
 367             errcode = getattr(e, 'smtp_code', -1)
 368             errmsg = getattr(e, 'smtp_error', 'ignore')
 369             for r in rcpttos:
 370                 refused[r] = (errcode, errmsg)
 371         return refused
 372
 373
 374 \f
 375 class MailmanProxy(PureProxy):
 376     def process_message(self, peer, mailfrom, rcpttos, data):
 377         from io import StringIO
 378         from Mailman import Utils
 379         from Mailman import Message
 380         from Mailman import MailList
 381         # If the message is to a Mailman mailing list, then we'll invoke the
 382         # Mailman script directly, without going through the real smtpd.
 383         # Otherwise we'll forward it to the local proxy for disposition.
 384         listnames = []
 385         for rcpt in rcpttos:
 386             local = rcpt.lower().split('@')[0]
 387             # We allow the following variations on the theme
 388             #   listname
 389             #   listname-admin
 390             #   listname-owner
 391             #   listname-request
 392             #   listname-join
 393             #   listname-leave
 394             parts = local.split('-')
 395             if len(parts) > 2:
 396                 continue
 397             listname = parts[0]
 398             if len(parts) == 2:
 399                 command = parts[1]
 400             else:
 401                 command = ''
 402             if not Utils.list_exists(listname) or command not in (
 403                     '', 'admin', 'owner', 'request', 'join', 'leave'):
 404                 continue
 405             listnames.append((rcpt, listname, command))
 406         # Remove all list recipients from rcpttos and forward what we're not
 407         # going to take care of ourselves.  Linear removal should be fine
 408         # since we don't expect a large number of recipients.
 409         for rcpt, listname, command in listnames:
 410             rcpttos.remove(rcpt)
 411         # If there's any non-list destined recipients left,
 412         print('forwarding recips:', ' '.join(rcpttos), file=DEBUGSTREAM)
 413         if rcpttos:
 414             refused = self._deliver(mailfrom, rcpttos, data)
 415             # TBD: what to do with refused addresses?
 416             print('we got refusals:', refused, file=DEBUGSTREAM)
 417         # Now deliver directly to the list commands
 418         mlists = {}
 419         s = StringIO(data)
 420         msg = Message.Message(s)
 421         # These headers are required for the proper execution of Mailman.  All
 422         # MTAs in existance seem to add these if the original message doesn't
 423         # have them.
 424         if not msg.getheader('from'):
 425             msg['From'] = mailfrom
 426         if not msg.getheader('date'):
 427             msg['Date'] = time.ctime(time.time())
 428         for rcpt, listname, command in listnames:
 429             print('sending message to', rcpt, file=DEBUGSTREAM)
 430             mlist = mlists.get(listname)
 431             if not mlist:
 432                 mlist = MailList.MailList(listname, lock=0)
 433                 mlists[listname] = mlist
 434             # dispatch on the type of command
 435             if command == '':
 436                 # post
 437                 msg.Enqueue(mlist, tolist=1)
 438             elif command == 'admin':
 439                 msg.Enqueue(mlist, toadmin=1)
 440             elif command == 'owner':
 441                 msg.Enqueue(mlist, toowner=1)
 442             elif command == 'request':
 443                 msg.Enqueue(mlist, torequest=1)
 444             elif command in ('join', 'leave'):
 445                 # TBD: this is a hack!
 446                 if command == 'join':
 447                     msg['Subject'] = 'subscribe'
 448                 else:
 449                     msg['Subject'] = 'unsubscribe'
 450                 msg.Enqueue(mlist, torequest=1)
 451
 452
 453 \f
 454 class Options:
 455     setuid = 1
 456     classname = 'PureProxy'
 457
 458
 459 \f
 460 def parseargs():
 461     global DEBUGSTREAM
 462     try:
 463         opts, args = getopt.getopt(
 464             sys.argv[1:], 'nVhc:d',
 465             ['class=', 'nosetuid', 'version', 'help', 'debug'])
 466     except getopt.error as e:
 467         usage(1, e)
 468
 469     options = Options()
 470     for opt, arg in opts:
 471         if opt in ('-h', '--help'):
 472             usage(0)
 473         elif opt in ('-V', '--version'):
 474             print(__version__, file=sys.stderr)
 475             sys.exit(0)
 476         elif opt in ('-n', '--nosetuid'):
 477             options.setuid = 0
 478         elif opt in ('-c', '--class'):
 479             options.classname = arg
 480         elif opt in ('-d', '--debug'):
 481             DEBUGSTREAM = sys.stderr
 482
 483     # parse the rest of the arguments
 484     if len(args) < 1:
 485         localspec = 'localhost:8025'
 486         remotespec = 'localhost:25'
 487     elif len(args) < 2:
 488         localspec = args[0]
 489         remotespec = 'localhost:25'
 490     elif len(args) < 3:
 491         localspec = args[0]
 492         remotespec = args[1]
 493     else:
 494         usage(1, 'Invalid arguments: %s' % COMMASPACE.join(args))
 495
 496     # split into host/port pairs
 497     i = localspec.find(':')
 498     if i < 0:
 499         usage(1, 'Bad local spec: %s' % localspec)
 500     options.localhost = localspec[:i]
 501     try:
 502         options.localport = int(localspec[i+1:])
 503     except ValueError:
 504         usage(1, 'Bad local port: %s' % localspec)
 505     i = remotespec.find(':')
 506     if i < 0:
 507         usage(1, 'Bad remote spec: %s' % remotespec)
 508     options.remotehost = remotespec[:i]
 509     try:
 510         options.remoteport = int(remotespec[i+1:])
 511     except ValueError:
 512         usage(1, 'Bad remote port: %s' % remotespec)
 513     return options
 514
 515
 516 \f
 517 if __name__ == '__main__':
 518     options = parseargs()
 519     # Become nobody
 520     if options.setuid:
 521         try:
 522             import pwd
 523         except ImportError:
 524             print('Cannot import module "pwd"; try running with -n option.', file=sys.stderr)
 525             sys.exit(1)
 526         nobody = pwd.getpwnam('nobody')[2]
 527         try:
 528             os.setuid(nobody)
 529         except OSError as e:
 530             if e.errno != errno.EPERM: raise
 531             print('Cannot setuid "nobody"; try running with -n option.', file=sys.stderr)
 532             sys.exit(1)
 533     classname = options.classname
 534     if "." in classname:
 535         lastdot = classname.rfind(".")
 536         mod = __import__(classname[:lastdot], globals(), locals(), [""])
 537         classname = classname[lastdot+1:]
 538     else:
 539         import __main__ as mod
 540     class_ = getattr(mod, classname)
 541     proxy = class_((options.localhost, options.localport),
 542                    (options.remotehost, options.remoteport))
 543     try:
 544         asyncore.loop()
 545     except KeyboardInterrupt:
 546         pass