Revert "bpo-28533: Remove asyncore, asynchat, smtpd modules (GH-29521)" (GH-29951)

This reverts commit 9bf2cbc4c498812e14f20d86acb61c53928a5a57.

1 files changed, 885 insertions, 0 deletions

diff --git a/Lib/smtpd.py b/Lib/smtpd.py
new file mode 100755
index 0000000..1cd004f
--- /dev/null
+++ b/Lib/smtpd.py
@@ -0,0 +1,885 @@
+#! /usr/bin/env python3
+"""An RFC 5321 smtp proxy with optional RFC 1870 and RFC 6531 extensions.
+
+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.
+
+    --size limit
+    -s limit
+        Restrict the total size of the incoming message to "limit" number of
+        bytes via the RFC 1870 SIZE extension.  Defaults to 33554432 bytes.
+
+    --smtputf8
+    -u
+        Enable the SMTPUTF8 extension and behave as an RFC 6531 smtp proxy.
+
+    --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 5321.  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!).
+#
+#
+# Author: Barry Warsaw <barry@python.org>
+#
+# TODO:
+#
+# - support mailbox delivery
+# - alias files
+# - Handle more ESMTP extensions
+# - handle error codes from the backend smtpd
+
+import sys
+import os
+import errno
+import getopt
+import time
+import socket
+import collections
+from warnings import warn
+from email._header_value_parser import get_addr_spec, get_angle_addr
+
+__all__ = [
+    "SMTPChannel", "SMTPServer", "DebuggingServer", "PureProxy",
+]
+
+warn(
+    'The smtpd module is deprecated and unmaintained.  Please see aiosmtpd '
+    '(https://aiosmtpd.readthedocs.io/) for the recommended replacement.',
+    DeprecationWarning,
+    stacklevel=2)
+
+
+# These are imported after the above warning so that users get the correct
+# deprecation warning.
+import asyncore
+import asynchat
+
+
+program = sys.argv[0]
+__version__ = 'Python SMTP proxy version 0.3'
+
+
+class Devnull:
+    def write(self, msg): pass
+    def flush(self): pass
+
+
+DEBUGSTREAM = Devnull()
+NEWLINE = '\n'
+COMMASPACE = ', '
+DATA_SIZE_DEFAULT = 33554432
+
+
+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
+
+    command_size_limit = 512
+    command_size_limits = collections.defaultdict(lambda x=command_size_limit: x)
+
+    @property
+    def max_command_size_limit(self):
+        try:
+            return max(self.command_size_limits.values())
+        except ValueError:
+            return self.command_size_limit
+
+    def __init__(self, server, conn, addr, data_size_limit=DATA_SIZE_DEFAULT,
+                 map=None, enable_SMTPUTF8=False, decode_data=False):
+        asynchat.async_chat.__init__(self, conn, map=map)
+        self.smtp_server = server
+        self.conn = conn
+        self.addr = addr
+        self.data_size_limit = data_size_limit
+        self.enable_SMTPUTF8 = enable_SMTPUTF8
+        self._decode_data = decode_data
+        if enable_SMTPUTF8 and decode_data:
+            raise ValueError("decode_data and enable_SMTPUTF8 cannot"
+                             " be set to True at the same time")
+        if decode_data:
+            self._emptystring = ''
+            self._linesep = '\r\n'
+            self._dotsep = '.'
+            self._newline = NEWLINE
+        else:
+            self._emptystring = b''
+            self._linesep = b'\r\n'
+            self._dotsep = ord(b'.')
+            self._newline = b'\n'
+        self._set_rset_state()
+        self.seen_greeting = ''
+        self.extended_smtp = False
+        self.command_size_limits.clear()
+        self.fqdn = socket.getfqdn()
+        try:
+            self.peer = conn.getpeername()
+        except OSError as err:
+            # a race condition  may occur if the other end is closing
+            # before we can get the peername
+            self.close()
+            if err.errno != errno.ENOTCONN:
+                raise
+            return
+        print('Peer:', repr(self.peer), file=DEBUGSTREAM)
+        self.push('220 %s %s' % (self.fqdn, __version__))
+
+    def _set_post_data_state(self):
+        """Reset state variables to their post-DATA state."""
+        self.smtp_state = self.COMMAND
+        self.mailfrom = None
+        self.rcpttos = []
+        self.require_SMTPUTF8 = False
+        self.num_bytes = 0
+        self.set_terminator(b'\r\n')
+
+    def _set_rset_state(self):
+        """Reset all state variables except the greeting."""
+        self._set_post_data_state()
+        self.received_data = ''
+        self.received_lines = []
+
+
+    # properties for backwards-compatibility
+    @property
+    def __server(self):
+        warn("Access to __server attribute on SMTPChannel is deprecated, "
+            "use 'smtp_server' instead", DeprecationWarning, 2)
+        return self.smtp_server
+    @__server.setter
+    def __server(self, value):
+        warn("Setting __server attribute on SMTPChannel is deprecated, "
+            "set 'smtp_server' instead", DeprecationWarning, 2)
+        self.smtp_server = value
+
+    @property
+    def __line(self):
+        warn("Access to __line attribute on SMTPChannel is deprecated, "
+            "use 'received_lines' instead", DeprecationWarning, 2)
+        return self.received_lines
+    @__line.setter
+    def __line(self, value):
+        warn("Setting __line attribute on SMTPChannel is deprecated, "
+            "set 'received_lines' instead", DeprecationWarning, 2)
+        self.received_lines = value
+
+    @property
+    def __state(self):
+        warn("Access to __state attribute on SMTPChannel is deprecated, "
+            "use 'smtp_state' instead", DeprecationWarning, 2)
+        return self.smtp_state
+    @__state.setter
+    def __state(self, value):
+        warn("Setting __state attribute on SMTPChannel is deprecated, "
+            "set 'smtp_state' instead", DeprecationWarning, 2)
+        self.smtp_state = value
+
+    @property
+    def __greeting(self):
+        warn("Access to __greeting attribute on SMTPChannel is deprecated, "
+            "use 'seen_greeting' instead", DeprecationWarning, 2)
+        return self.seen_greeting
+    @__greeting.setter
+    def __greeting(self, value):
+        warn("Setting __greeting attribute on SMTPChannel is deprecated, "
+            "set 'seen_greeting' instead", DeprecationWarning, 2)
+        self.seen_greeting = value
+
+    @property
+    def __mailfrom(self):
+        warn("Access to __mailfrom attribute on SMTPChannel is deprecated, "
+            "use 'mailfrom' instead", DeprecationWarning, 2)
+        return self.mailfrom
+    @__mailfrom.setter
+    def __mailfrom(self, value):
+        warn("Setting __mailfrom attribute on SMTPChannel is deprecated, "
+            "set 'mailfrom' instead", DeprecationWarning, 2)
+        self.mailfrom = value
+
+    @property
+    def __rcpttos(self):
+        warn("Access to __rcpttos attribute on SMTPChannel is deprecated, "
+            "use 'rcpttos' instead", DeprecationWarning, 2)
+        return self.rcpttos
+    @__rcpttos.setter
+    def __rcpttos(self, value):
+        warn("Setting __rcpttos attribute on SMTPChannel is deprecated, "
+            "set 'rcpttos' instead", DeprecationWarning, 2)
+        self.rcpttos = value
+
+    @property
+    def __data(self):
+        warn("Access to __data attribute on SMTPChannel is deprecated, "
+            "use 'received_data' instead", DeprecationWarning, 2)
+        return self.received_data
+    @__data.setter
+    def __data(self, value):
+        warn("Setting __data attribute on SMTPChannel is deprecated, "
+            "set 'received_data' instead", DeprecationWarning, 2)
+        self.received_data = value
+
+    @property
+    def __fqdn(self):
+        warn("Access to __fqdn attribute on SMTPChannel is deprecated, "
+            "use 'fqdn' instead", DeprecationWarning, 2)
+        return self.fqdn
+    @__fqdn.setter
+    def __fqdn(self, value):
+        warn("Setting __fqdn attribute on SMTPChannel is deprecated, "
+            "set 'fqdn' instead", DeprecationWarning, 2)
+        self.fqdn = value
+
+    @property
+    def __peer(self):
+        warn("Access to __peer attribute on SMTPChannel is deprecated, "
+            "use 'peer' instead", DeprecationWarning, 2)
+        return self.peer
+    @__peer.setter
+    def __peer(self, value):
+        warn("Setting __peer attribute on SMTPChannel is deprecated, "
+            "set 'peer' instead", DeprecationWarning, 2)
+        self.peer = value
+
+    @property
+    def __conn(self):
+        warn("Access to __conn attribute on SMTPChannel is deprecated, "
+            "use 'conn' instead", DeprecationWarning, 2)
+        return self.conn
+    @__conn.setter
+    def __conn(self, value):
+        warn("Setting __conn attribute on SMTPChannel is deprecated, "
+            "set 'conn' instead", DeprecationWarning, 2)
+        self.conn = value
+
+    @property
+    def __addr(self):
+        warn("Access to __addr attribute on SMTPChannel is deprecated, "
+            "use 'addr' instead", DeprecationWarning, 2)
+        return self.addr
+    @__addr.setter
+    def __addr(self, value):
+        warn("Setting __addr attribute on SMTPChannel is deprecated, "
+            "set 'addr' instead", DeprecationWarning, 2)
+        self.addr = value
+
+    # Overrides base class for convenience.
+    def push(self, msg):
+        asynchat.async_chat.push(self, bytes(
+            msg + '\r\n', 'utf-8' if self.require_SMTPUTF8 else 'ascii'))
+
+    # Implementation of base class abstract method
+    def collect_incoming_data(self, data):
+        limit = None
+        if self.smtp_state == self.COMMAND:
+            limit = self.max_command_size_limit
+        elif self.smtp_state == self.DATA:
+            limit = self.data_size_limit
+        if limit and self.num_bytes > limit:
+            return
+        elif limit:
+            self.num_bytes += len(data)
+        if self._decode_data:
+            self.received_lines.append(str(data, 'utf-8'))
+        else:
+            self.received_lines.append(data)
+
+    # Implementation of base class abstract method
+    def found_terminator(self):
+        line = self._emptystring.join(self.received_lines)
+        print('Data:', repr(line), file=DEBUGSTREAM)
+        self.received_lines = []
+        if self.smtp_state == self.COMMAND:
+            sz, self.num_bytes = self.num_bytes, 0
+            if not line:
+                self.push('500 Error: bad syntax')
+                return
+            if not self._decode_data:
+                line = str(line, 'utf-8')
+            i = line.find(' ')
+            if i < 0:
+                command = line.upper()
+                arg = None
+            else:
+                command = line[:i].upper()
+                arg = line[i+1:].strip()
+            max_sz = (self.command_size_limits[command]
+                        if self.extended_smtp else self.command_size_limit)
+            if sz > max_sz:
+                self.push('500 Error: line too long')
+                return
+            method = getattr(self, 'smtp_' + command, None)
+            if not method:
+                self.push('500 Error: command "%s" not recognized' % command)
+                return
+            method(arg)
+            return
+        else:
+            if self.smtp_state != self.DATA:
+                self.push('451 Internal confusion')
+                self.num_bytes = 0
+                return
+            if self.data_size_limit and self.num_bytes > self.data_size_limit:
+                self.push('552 Error: Too much mail data')
+                self.num_bytes = 0
+                return
+            # Remove extraneous carriage returns and de-transparency according
+            # to RFC 5321, Section 4.5.2.
+            data = []
+            for text in line.split(self._linesep):
+                if text and text[0] == self._dotsep:
+                    data.append(text[1:])
+                else:
+                    data.append(text)
+            self.received_data = self._newline.join(data)
+            args = (self.peer, self.mailfrom, self.rcpttos, self.received_data)
+            kwargs = {}
+            if not self._decode_data:
+                kwargs = {
+                    'mail_options': self.mail_options,
+                    'rcpt_options': self.rcpt_options,
+                }
+            status = self.smtp_server.process_message(*args, **kwargs)
+            self._set_post_data_state()
+            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
+        # See issue #21783 for a discussion of this behavior.
+        if self.seen_greeting:
+            self.push('503 Duplicate HELO/EHLO')
+            return
+        self._set_rset_state()
+        self.seen_greeting = arg
+        self.push('250 %s' % self.fqdn)
+
+    def smtp_EHLO(self, arg):
+        if not arg:
+            self.push('501 Syntax: EHLO hostname')
+            return
+        # See issue #21783 for a discussion of this behavior.
+        if self.seen_greeting:
+            self.push('503 Duplicate HELO/EHLO')
+            return
+        self._set_rset_state()
+        self.seen_greeting = arg
+        self.extended_smtp = True
+        self.push('250-%s' % self.fqdn)
+        if self.data_size_limit:
+            self.push('250-SIZE %s' % self.data_size_limit)
+            self.command_size_limits['MAIL'] += 26
+        if not self._decode_data:
+            self.push('250-8BITMIME')
+        if self.enable_SMTPUTF8:
+            self.push('250-SMTPUTF8')
+            self.command_size_limits['MAIL'] += 10
+        self.push('250 HELP')
+
+    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()
+
+    def _strip_command_keyword(self, keyword, arg):
+        keylen = len(keyword)
+        if arg[:keylen].upper() == keyword:
+            return arg[keylen:].strip()
+        return ''
+
+    def _getaddr(self, arg):
+        if not arg:
+            return '', ''
+        if arg.lstrip().startswith('<'):
+            address, rest = get_angle_addr(arg)
+        else:
+            address, rest = get_addr_spec(arg)
+        if not address:
+            return address, rest
+        return address.addr_spec, rest
+
+    def _getparams(self, params):
+        # Return params as dictionary. Return None if not all parameters
+        # appear to be syntactically valid according to RFC 1869.
+        result = {}
+        for param in params:
+            param, eq, value = param.partition('=')
+            if not param.isalnum() or eq and not value:
+                return None
+            result[param] = value if eq else True
+        return result
+
+    def smtp_HELP(self, arg):
+        if arg:
+            extended = ' [SP <mail-parameters>]'
+            lc_arg = arg.upper()
+            if lc_arg == 'EHLO':
+                self.push('250 Syntax: EHLO hostname')
+            elif lc_arg == 'HELO':
+                self.push('250 Syntax: HELO hostname')
+            elif lc_arg == 'MAIL':
+                msg = '250 Syntax: MAIL FROM: <address>'
+                if self.extended_smtp:
+                    msg += extended
+                self.push(msg)
+            elif lc_arg == 'RCPT':
+                msg = '250 Syntax: RCPT TO: <address>'
+                if self.extended_smtp:
+                    msg += extended
+                self.push(msg)
+            elif lc_arg == 'DATA':
+                self.push('250 Syntax: DATA')
+            elif lc_arg == 'RSET':
+                self.push('250 Syntax: RSET')
+            elif lc_arg == 'NOOP':
+                self.push('250 Syntax: NOOP')
+            elif lc_arg == 'QUIT':
+                self.push('250 Syntax: QUIT')
+            elif lc_arg == 'VRFY':
+                self.push('250 Syntax: VRFY <address>')
+            else:
+                self.push('501 Supported commands: EHLO HELO MAIL RCPT '
+                          'DATA RSET NOOP QUIT VRFY')
+        else:
+            self.push('250 Supported commands: EHLO HELO MAIL RCPT DATA '
+                      'RSET NOOP QUIT VRFY')
+
+    def smtp_VRFY(self, arg):
+        if arg:
+            address, params = self._getaddr(arg)
+            if address:
+                self.push('252 Cannot VRFY user, but will accept message '
+                          'and attempt delivery')
+            else:
+                self.push('502 Could not VRFY %s' % arg)
+        else:
+            self.push('501 Syntax: VRFY <address>')
+
+    def smtp_MAIL(self, arg):
+        if not self.seen_greeting:
+            self.push('503 Error: send HELO first')
+            return
+        print('===> MAIL', arg, file=DEBUGSTREAM)
+        syntaxerr = '501 Syntax: MAIL FROM: <address>'
+        if self.extended_smtp:
+            syntaxerr += ' [SP <mail-parameters>]'
+        if arg is None:
+            self.push(syntaxerr)
+            return
+        arg = self._strip_command_keyword('FROM:', arg)
+        address, params = self._getaddr(arg)
+        if not address:
+            self.push(syntaxerr)
+            return
+        if not self.extended_smtp and params:
+            self.push(syntaxerr)
+            return
+        if self.mailfrom:
+            self.push('503 Error: nested MAIL command')
+            return
+        self.mail_options = params.upper().split()
+        params = self._getparams(self.mail_options)
+        if params is None:
+            self.push(syntaxerr)
+            return
+        if not self._decode_data:
+            body = params.pop('BODY', '7BIT')
+            if body not in ['7BIT', '8BITMIME']:
+                self.push('501 Error: BODY can only be one of 7BIT, 8BITMIME')
+                return
+        if self.enable_SMTPUTF8:
+            smtputf8 = params.pop('SMTPUTF8', False)
+            if smtputf8 is True:
+                self.require_SMTPUTF8 = True
+            elif smtputf8 is not False:
+                self.push('501 Error: SMTPUTF8 takes no arguments')
+                return
+        size = params.pop('SIZE', None)
+        if size:
+            if not size.isdigit():
+                self.push(syntaxerr)
+                return
+            elif self.data_size_limit and int(size) > self.data_size_limit:
+                self.push('552 Error: message size exceeds fixed maximum message size')
+                return
+        if len(params.keys()) > 0:
+            self.push('555 MAIL FROM parameters not recognized or not implemented')
+            return
+        self.mailfrom = address
+        print('sender:', self.mailfrom, file=DEBUGSTREAM)
+        self.push('250 OK')
+
+    def smtp_RCPT(self, arg):
+        if not self.seen_greeting:
+            self.push('503 Error: send HELO first');
+            return
+        print('===> RCPT', arg, file=DEBUGSTREAM)
+        if not self.mailfrom:
+            self.push('503 Error: need MAIL command')
+            return
+        syntaxerr = '501 Syntax: RCPT TO: <address>'
+        if self.extended_smtp:
+            syntaxerr += ' [SP <mail-parameters>]'
+        if arg is None:
+            self.push(syntaxerr)
+            return
+        arg = self._strip_command_keyword('TO:', arg)
+        address, params = self._getaddr(arg)
+        if not address:
+            self.push(syntaxerr)
+            return
+        if not self.extended_smtp and params:
+            self.push(syntaxerr)
+            return
+        self.rcpt_options = params.upper().split()
+        params = self._getparams(self.rcpt_options)
+        if params is None:
+            self.push(syntaxerr)
+            return
+        # XXX currently there are no options we recognize.
+        if len(params.keys()) > 0:
+            self.push('555 RCPT TO parameters not recognized or not implemented')
+            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
+        self._set_rset_state()
+        self.push('250 OK')
+
+    def smtp_DATA(self, arg):
+        if not self.seen_greeting:
+            self.push('503 Error: send HELO first');
+            return
+        if not self.rcpttos:
+            self.push('503 Error: need RCPT command')
+            return
+        if arg:
+            self.push('501 Syntax: DATA')
+            return
+        self.smtp_state = self.DATA
+        self.set_terminator(b'\r\n.\r\n')
+        self.push('354 End data with <CR><LF>.<CR><LF>')
+
+    # Commands that have not been implemented
+    def smtp_EXPN(self, arg):
+        self.push('502 EXPN not implemented')
+
+
+class SMTPServer(asyncore.dispatcher):
+    # SMTPChannel class to use for managing client connections
+    channel_class = SMTPChannel
+
+    def __init__(self, localaddr, remoteaddr,
+                 data_size_limit=DATA_SIZE_DEFAULT, map=None,
+                 enable_SMTPUTF8=False, decode_data=False):
+        self._localaddr = localaddr
+        self._remoteaddr = remoteaddr
+        self.data_size_limit = data_size_limit
+        self.enable_SMTPUTF8 = enable_SMTPUTF8
+        self._decode_data = decode_data
+        if enable_SMTPUTF8 and decode_data:
+            raise ValueError("decode_data and enable_SMTPUTF8 cannot"
+                             " be set to True at the same time")
+        asyncore.dispatcher.__init__(self, map=map)
+        try:
+            gai_results = socket.getaddrinfo(*localaddr,
+                                             type=socket.SOCK_STREAM)
+            self.create_socket(gai_results[0][0], gai_results[0][1])
+            # try to re-use a server port if possible
+            self.set_reuse_addr()
+            self.bind(localaddr)
+            self.listen(5)
+        except:
+            self.close()
+            raise
+        else:
+            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_accepted(self, conn, addr):
+        print('Incoming connection from %s' % repr(addr), file=DEBUGSTREAM)
+        channel = self.channel_class(self,
+                                     conn,
+                                     addr,
+                                     self.data_size_limit,
+                                     self._map,
+                                     self.enable_SMTPUTF8,
+                                     self._decode_data)
+
+    # API for "doing something useful with the message"
+    def process_message(self, peer, mailfrom, rcpttos, data, **kwargs):
+        """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.
+
+        kwargs is a dictionary containing additional information.  It is
+        empty if decode_data=True was given as init parameter, otherwise
+        it will contain the following keys:
+            'mail_options': list of parameters to the mail command.  All
+                            elements are uppercase strings.  Example:
+                            ['BODY=8BITMIME', 'SMTPUTF8'].
+            'rcpt_options': same, for the rcpt command.
+
+        This function should return None for a normal `250 Ok' response;
+        otherwise, it should return the desired response string in RFC 821
+        format.
+
+        """
+        raise NotImplementedError
+
+
+class DebuggingServer(SMTPServer):
+
+    def _print_message_content(self, peer, data):
+        inheaders = 1
+        lines = data.splitlines()
+        for line in lines:
+            # headers first
+            if inheaders and not line:
+                peerheader = 'X-Peer: ' + peer[0]
+                if not isinstance(data, str):
+                    # decoded_data=false; make header match other binary output
+                    peerheader = repr(peerheader.encode('utf-8'))
+                print(peerheader)
+                inheaders = 0
+            if not isinstance(data, str):
+                # Avoid spurious 'str on bytes instance' warning.
+                line = repr(line)
+            print(line)
+
+    def process_message(self, peer, mailfrom, rcpttos, data, **kwargs):
+        print('---------- MESSAGE FOLLOWS ----------')
+        if kwargs:
+            if kwargs.get('mail_options'):
+                print('mail options: %s' % kwargs['mail_options'])
+            if kwargs.get('rcpt_options'):
+                print('rcpt options: %s\n' % kwargs['rcpt_options'])
+        self._print_message_content(peer, data)
+        print('------------ END MESSAGE ------------')
+
+
+class PureProxy(SMTPServer):
+    def __init__(self, *args, **kwargs):
+        if 'enable_SMTPUTF8' in kwargs and kwargs['enable_SMTPUTF8']:
+            raise ValueError("PureProxy does not support SMTPUTF8.")
+        super(PureProxy, self).__init__(*args, **kwargs)
+
+    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 (OSError, 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 Options:
+    setuid = True
+    classname = 'PureProxy'
+    size_limit = None
+    enable_SMTPUTF8 = False
+
+
+def parseargs():
+    global DEBUGSTREAM
+    try:
+        opts, args = getopt.getopt(
+            sys.argv[1:], 'nVhc:s:du',
+            ['class=', 'nosetuid', 'version', 'help', 'size=', 'debug',
+             'smtputf8'])
+    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__)
+            sys.exit(0)
+        elif opt in ('-n', '--nosetuid'):
+            options.setuid = False
+        elif opt in ('-c', '--class'):
+            options.classname = arg
+        elif opt in ('-d', '--debug'):
+            DEBUGSTREAM = sys.stderr
+        elif opt in ('-u', '--smtputf8'):
+            options.enable_SMTPUTF8 = True
+        elif opt in ('-s', '--size'):
+            try:
+                int_size = int(arg)
+                options.size_limit = int_size
+            except:
+                print('Invalid size: ' + arg, file=sys.stderr)
+                sys.exit(1)
+
+    # 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),
+                   options.size_limit, enable_SMTPUTF8=options.enable_SMTPUTF8)
+    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 PermissionError:
+            print('Cannot setuid "nobody"; try running with -n option.', file=sys.stderr)
+            sys.exit(1)
+    try:
+        asyncore.loop()
+    except KeyboardInterrupt:
+        pass