Editing: smtpd.py
#! /usr/bin/python2.7 """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() try: self.__peer = conn.getpeername() except socket.error, err: # a race condition may occur if the other end is closing # before we can get the peername self.close() if err[0] != errno.ENOTCONN: raise return 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) try: 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) except: # cleanup asyncore.socket_map before raising self.close() raise else: 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): pair = self.accept() if pair is not None: conn, addr = pair 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 existence 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 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)) 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] try: os.setuid(nobody) except OSError, e: if e.errno != errno.EPERM: raise print >> sys.stderr, \ 'Cannot setuid "nobody"; try running with -n option.' sys.exit(1) try: asyncore.loop() except KeyboardInterrupt: pass
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