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

Remove the asyncore and asynchat modules, deprecated in Python
3.6: use the asyncio module instead.

Remove the smtpd module, deprecated in Python 3.6: the aiosmtpd
module can be used instead, it is based on asyncio.

* Remove asyncore, asynchat and smtpd documentation
* Remove test_asyncore, test_asynchat and test_smtpd
* Rename Lib/asynchat.py to Lib/test/support/_asynchat.py
* Rename Lib/asyncore.py to Lib/test/support/_asyncore.py
* Rename Lib/smtpd.py to Lib/test/support/_smtpd.py
* Remove DeprecationWarning from private _asyncore, _asynchat and
  _smtpd modules
* _smtpd: remove deprecated properties

3 files changed, 1704 insertions, 0 deletions

diff --git a/Lib/test/support/_asynchat.py b/Lib/test/support/_asynchat.py
new file mode 100644
index 0000000..941cc1d
--- /dev/null
+++ b/Lib/test/support/_asynchat.py
@@ -0,0 +1,307 @@
+# -*- Mode: Python; tab-width: 4 -*-
+#       Id: asynchat.py,v 2.26 2000/09/07 22:29:26 rushing Exp
+#       Author: Sam Rushing <rushing@nightmare.com>
+
+# ======================================================================
+# Copyright 1996 by Sam Rushing
+#
+#                         All Rights Reserved
+#
+# Permission to use, copy, modify, and distribute this software and
+# its documentation for any purpose and without fee is hereby
+# granted, provided that the above copyright notice appear in all
+# copies and that both that copyright notice and this permission
+# notice appear in supporting documentation, and that the name of Sam
+# Rushing not be used in advertising or publicity pertaining to
+# distribution of the software without specific, written prior
+# permission.
+#
+# SAM RUSHING DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+# INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
+# NO EVENT SHALL SAM RUSHING BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+# CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+# OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+# NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+# CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+# ======================================================================
+
+r"""A class supporting chat-style (command/response) protocols.
+
+This class adds support for 'chat' style protocols - where one side
+sends a 'command', and the other sends a response (examples would be
+the common internet protocols - smtp, nntp, ftp, etc..).
+
+The handle_read() method looks at the input stream for the current
+'terminator' (usually '\r\n' for single-line responses, '\r\n.\r\n'
+for multi-line output), calling self.found_terminator() on its
+receipt.
+
+for example:
+Say you build an async nntp client using this class.  At the start
+of the connection, you'll have self.terminator set to '\r\n', in
+order to process the single-line greeting.  Just before issuing a
+'LIST' command you'll set it to '\r\n.\r\n'.  The output of the LIST
+command will be accumulated (using your own 'collect_incoming_data'
+method) up to the terminator, and then control will be returned to
+you - by calling your self.found_terminator() method.
+"""
+from test.support import _asyncore as asyncore
+from collections import deque
+
+
+class async_chat(asyncore.dispatcher):
+    """This is an abstract class.  You must derive from this class, and add
+    the two methods collect_incoming_data() and found_terminator()"""
+
+    # these are overridable defaults
+
+    ac_in_buffer_size = 65536
+    ac_out_buffer_size = 65536
+
+    # we don't want to enable the use of encoding by default, because that is a
+    # sign of an application bug that we don't want to pass silently
+
+    use_encoding = 0
+    encoding = 'latin-1'
+
+    def __init__(self, sock=None, map=None):
+        # for string terminator matching
+        self.ac_in_buffer = b''
+
+        # we use a list here rather than io.BytesIO for a few reasons...
+        # del lst[:] is faster than bio.truncate(0)
+        # lst = [] is faster than bio.truncate(0)
+        self.incoming = []
+
+        # we toss the use of the "simple producer" and replace it with
+        # a pure deque, which the original fifo was a wrapping of
+        self.producer_fifo = deque()
+        asyncore.dispatcher.__init__(self, sock, map)
+
+    def collect_incoming_data(self, data):
+        raise NotImplementedError("must be implemented in subclass")
+
+    def _collect_incoming_data(self, data):
+        self.incoming.append(data)
+
+    def _get_data(self):
+        d = b''.join(self.incoming)
+        del self.incoming[:]
+        return d
+
+    def found_terminator(self):
+        raise NotImplementedError("must be implemented in subclass")
+
+    def set_terminator(self, term):
+        """Set the input delimiter.
+
+        Can be a fixed string of any length, an integer, or None.
+        """
+        if isinstance(term, str) and self.use_encoding:
+            term = bytes(term, self.encoding)
+        elif isinstance(term, int) and term < 0:
+            raise ValueError('the number of received bytes must be positive')
+        self.terminator = term
+
+    def get_terminator(self):
+        return self.terminator
+
+    # grab some more data from the socket,
+    # throw it to the collector method,
+    # check for the terminator,
+    # if found, transition to the next state.
+
+    def handle_read(self):
+
+        try:
+            data = self.recv(self.ac_in_buffer_size)
+        except BlockingIOError:
+            return
+        except OSError:
+            self.handle_error()
+            return
+
+        if isinstance(data, str) and self.use_encoding:
+            data = bytes(str, self.encoding)
+        self.ac_in_buffer = self.ac_in_buffer + data
+
+        # Continue to search for self.terminator in self.ac_in_buffer,
+        # while calling self.collect_incoming_data.  The while loop
+        # is necessary because we might read several data+terminator
+        # combos with a single recv(4096).
+
+        while self.ac_in_buffer:
+            lb = len(self.ac_in_buffer)
+            terminator = self.get_terminator()
+            if not terminator:
+                # no terminator, collect it all
+                self.collect_incoming_data(self.ac_in_buffer)
+                self.ac_in_buffer = b''
+            elif isinstance(terminator, int):
+                # numeric terminator
+                n = terminator
+                if lb < n:
+                    self.collect_incoming_data(self.ac_in_buffer)
+                    self.ac_in_buffer = b''
+                    self.terminator = self.terminator - lb
+                else:
+                    self.collect_incoming_data(self.ac_in_buffer[:n])
+                    self.ac_in_buffer = self.ac_in_buffer[n:]
+                    self.terminator = 0
+                    self.found_terminator()
+            else:
+                # 3 cases:
+                # 1) end of buffer matches terminator exactly:
+                #    collect data, transition
+                # 2) end of buffer matches some prefix:
+                #    collect data to the prefix
+                # 3) end of buffer does not match any prefix:
+                #    collect data
+                terminator_len = len(terminator)
+                index = self.ac_in_buffer.find(terminator)
+                if index != -1:
+                    # we found the terminator
+                    if index > 0:
+                        # don't bother reporting the empty string
+                        # (source of subtle bugs)
+                        self.collect_incoming_data(self.ac_in_buffer[:index])
+                    self.ac_in_buffer = self.ac_in_buffer[index+terminator_len:]
+                    # This does the Right Thing if the terminator
+                    # is changed here.
+                    self.found_terminator()
+                else:
+                    # check for a prefix of the terminator
+                    index = find_prefix_at_end(self.ac_in_buffer, terminator)
+                    if index:
+                        if index != lb:
+                            # we found a prefix, collect up to the prefix
+                            self.collect_incoming_data(self.ac_in_buffer[:-index])
+                            self.ac_in_buffer = self.ac_in_buffer[-index:]
+                        break
+                    else:
+                        # no prefix, collect it all
+                        self.collect_incoming_data(self.ac_in_buffer)
+                        self.ac_in_buffer = b''
+
+    def handle_write(self):
+        self.initiate_send()
+
+    def handle_close(self):
+        self.close()
+
+    def push(self, data):
+        if not isinstance(data, (bytes, bytearray, memoryview)):
+            raise TypeError('data argument must be byte-ish (%r)',
+                            type(data))
+        sabs = self.ac_out_buffer_size
+        if len(data) > sabs:
+            for i in range(0, len(data), sabs):
+                self.producer_fifo.append(data[i:i+sabs])
+        else:
+            self.producer_fifo.append(data)
+        self.initiate_send()
+
+    def push_with_producer(self, producer):
+        self.producer_fifo.append(producer)
+        self.initiate_send()
+
+    def readable(self):
+        "predicate for inclusion in the readable for select()"
+        # cannot use the old predicate, it violates the claim of the
+        # set_terminator method.
+
+        # return (len(self.ac_in_buffer) <= self.ac_in_buffer_size)
+        return 1
+
+    def writable(self):
+        "predicate for inclusion in the writable for select()"
+        return self.producer_fifo or (not self.connected)
+
+    def close_when_done(self):
+        "automatically close this channel once the outgoing queue is empty"
+        self.producer_fifo.append(None)
+
+    def initiate_send(self):
+        while self.producer_fifo and self.connected:
+            first = self.producer_fifo[0]
+            # handle empty string/buffer or None entry
+            if not first:
+                del self.producer_fifo[0]
+                if first is None:
+                    self.handle_close()
+                    return
+
+            # handle classic producer behavior
+            obs = self.ac_out_buffer_size
+            try:
+                data = first[:obs]
+            except TypeError:
+                data = first.more()
+                if data:
+                    self.producer_fifo.appendleft(data)
+                else:
+                    del self.producer_fifo[0]
+                continue
+
+            if isinstance(data, str) and self.use_encoding:
+                data = bytes(data, self.encoding)
+
+            # send the data
+            try:
+                num_sent = self.send(data)
+            except OSError:
+                self.handle_error()
+                return
+
+            if num_sent:
+                if num_sent < len(data) or obs < len(first):
+                    self.producer_fifo[0] = first[num_sent:]
+                else:
+                    del self.producer_fifo[0]
+            # we tried to send some actual data
+            return
+
+    def discard_buffers(self):
+        # Emergencies only!
+        self.ac_in_buffer = b''
+        del self.incoming[:]
+        self.producer_fifo.clear()
+
+
+class simple_producer:
+
+    def __init__(self, data, buffer_size=512):
+        self.data = data
+        self.buffer_size = buffer_size
+
+    def more(self):
+        if len(self.data) > self.buffer_size:
+            result = self.data[:self.buffer_size]
+            self.data = self.data[self.buffer_size:]
+            return result
+        else:
+            result = self.data
+            self.data = b''
+            return result
+
+
+# Given 'haystack', see if any prefix of 'needle' is at its end.  This
+# assumes an exact match has already been checked.  Return the number of
+# characters matched.
+# for example:
+# f_p_a_e("qwerty\r", "\r\n") => 1
+# f_p_a_e("qwertydkjf", "\r\n") => 0
+# f_p_a_e("qwerty\r\n", "\r\n") => <undefined>
+
+# this could maybe be made faster with a computed regex?
+# [answer: no; circa Python-2.0, Jan 2001]
+# new python:   28961/s
+# old python:   18307/s
+# re:        12820/s
+# regex:     14035/s
+
+def find_prefix_at_end(haystack, needle):
+    l = len(needle) - 1
+    while l and not haystack.endswith(needle[:l]):
+        l -= 1
+    return l
diff --git a/Lib/test/support/_asyncore.py b/Lib/test/support/_asyncore.py
new file mode 100644
index 0000000..7863efa
--- /dev/null
+++ b/Lib/test/support/_asyncore.py
@@ -0,0 +1,643 @@
+# -*- Mode: Python -*-
+#   Id: asyncore.py,v 2.51 2000/09/07 22:29:26 rushing Exp
+#   Author: Sam Rushing <rushing@nightmare.com>
+
+# ======================================================================
+# Copyright 1996 by Sam Rushing
+#
+#                         All Rights Reserved
+#
+# Permission to use, copy, modify, and distribute this software and
+# its documentation for any purpose and without fee is hereby
+# granted, provided that the above copyright notice appear in all
+# copies and that both that copyright notice and this permission
+# notice appear in supporting documentation, and that the name of Sam
+# Rushing not be used in advertising or publicity pertaining to
+# distribution of the software without specific, written prior
+# permission.
+#
+# SAM RUSHING DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+# INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
+# NO EVENT SHALL SAM RUSHING BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+# CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+# OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+# NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+# CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+# ======================================================================
+
+"""Basic infrastructure for asynchronous socket service clients and servers.
+
+There are only two ways to have a program on a single processor do "more
+than one thing at a time".  Multi-threaded programming is the simplest and
+most popular way to do it, but there is another very different technique,
+that lets you have nearly all the advantages of multi-threading, without
+actually using multiple threads. it's really only practical if your program
+is largely I/O bound. If your program is CPU bound, then pre-emptive
+scheduled threads are probably what you really need. Network servers are
+rarely CPU-bound, however.
+
+If your operating system supports the select() system call in its I/O
+library (and nearly all do), then you can use it to juggle multiple
+communication channels at once; doing other work while your I/O is taking
+place in the "background."  Although this strategy can seem strange and
+complex, especially at first, it is in many ways easier to understand and
+control than multi-threaded programming. The module documented here solves
+many of the difficult problems for you, making the task of building
+sophisticated high-performance network servers and clients a snap.
+"""
+
+import select
+import socket
+import sys
+import time
+import warnings
+
+import os
+from errno import EALREADY, EINPROGRESS, EWOULDBLOCK, ECONNRESET, EINVAL, \
+     ENOTCONN, ESHUTDOWN, EISCONN, EBADF, ECONNABORTED, EPIPE, EAGAIN, \
+     errorcode
+
+
+_DISCONNECTED = frozenset({ECONNRESET, ENOTCONN, ESHUTDOWN, ECONNABORTED, EPIPE,
+                           EBADF})
+
+try:
+    socket_map
+except NameError:
+    socket_map = {}
+
+def _strerror(err):
+    try:
+        return os.strerror(err)
+    except (ValueError, OverflowError, NameError):
+        if err in errorcode:
+            return errorcode[err]
+        return "Unknown error %s" %err
+
+class ExitNow(Exception):
+    pass
+
+_reraised_exceptions = (ExitNow, KeyboardInterrupt, SystemExit)
+
+def read(obj):
+    try:
+        obj.handle_read_event()
+    except _reraised_exceptions:
+        raise
+    except:
+        obj.handle_error()
+
+def write(obj):
+    try:
+        obj.handle_write_event()
+    except _reraised_exceptions:
+        raise
+    except:
+        obj.handle_error()
+
+def _exception(obj):
+    try:
+        obj.handle_expt_event()
+    except _reraised_exceptions:
+        raise
+    except:
+        obj.handle_error()
+
+def readwrite(obj, flags):
+    try:
+        if flags & select.POLLIN:
+            obj.handle_read_event()
+        if flags & select.POLLOUT:
+            obj.handle_write_event()
+        if flags & select.POLLPRI:
+            obj.handle_expt_event()
+        if flags & (select.POLLHUP | select.POLLERR | select.POLLNVAL):
+            obj.handle_close()
+    except OSError as e:
+        if e.errno not in _DISCONNECTED:
+            obj.handle_error()
+        else:
+            obj.handle_close()
+    except _reraised_exceptions:
+        raise
+    except:
+        obj.handle_error()
+
+def poll(timeout=0.0, map=None):
+    if map is None:
+        map = socket_map
+    if map:
+        r = []; w = []; e = []
+        for fd, obj in list(map.items()):
+            is_r = obj.readable()
+            is_w = obj.writable()
+            if is_r:
+                r.append(fd)
+            # accepting sockets should not be writable
+            if is_w and not obj.accepting:
+                w.append(fd)
+            if is_r or is_w:
+                e.append(fd)
+        if [] == r == w == e:
+            time.sleep(timeout)
+            return
+
+        r, w, e = select.select(r, w, e, timeout)
+
+        for fd in r:
+            obj = map.get(fd)
+            if obj is None:
+                continue
+            read(obj)
+
+        for fd in w:
+            obj = map.get(fd)
+            if obj is None:
+                continue
+            write(obj)
+
+        for fd in e:
+            obj = map.get(fd)
+            if obj is None:
+                continue
+            _exception(obj)
+
+def poll2(timeout=0.0, map=None):
+    # Use the poll() support added to the select module in Python 2.0
+    if map is None:
+        map = socket_map
+    if timeout is not None:
+        # timeout is in milliseconds
+        timeout = int(timeout*1000)
+    pollster = select.poll()
+    if map:
+        for fd, obj in list(map.items()):
+            flags = 0
+            if obj.readable():
+                flags |= select.POLLIN | select.POLLPRI
+            # accepting sockets should not be writable
+            if obj.writable() and not obj.accepting:
+                flags |= select.POLLOUT
+            if flags:
+                pollster.register(fd, flags)
+
+        r = pollster.poll(timeout)
+        for fd, flags in r:
+            obj = map.get(fd)
+            if obj is None:
+                continue
+            readwrite(obj, flags)
+
+poll3 = poll2                           # Alias for backward compatibility
+
+def loop(timeout=30.0, use_poll=False, map=None, count=None):
+    if map is None:
+        map = socket_map
+
+    if use_poll and hasattr(select, 'poll'):
+        poll_fun = poll2
+    else:
+        poll_fun = poll
+
+    if count is None:
+        while map:
+            poll_fun(timeout, map)
+
+    else:
+        while map and count > 0:
+            poll_fun(timeout, map)
+            count = count - 1
+
+class dispatcher:
+
+    debug = False
+    connected = False
+    accepting = False
+    connecting = False
+    closing = False
+    addr = None
+    ignore_log_types = frozenset({'warning'})
+
+    def __init__(self, sock=None, map=None):
+        if map is None:
+            self._map = socket_map
+        else:
+            self._map = map
+
+        self._fileno = None
+
+        if sock:
+            # Set to nonblocking just to make sure for cases where we
+            # get a socket from a blocking source.
+            sock.setblocking(False)
+            self.set_socket(sock, map)
+            self.connected = True
+            # The constructor no longer requires that the socket
+            # passed be connected.
+            try:
+                self.addr = sock.getpeername()
+            except OSError as err:
+                if err.errno in (ENOTCONN, EINVAL):
+                    # To handle the case where we got an unconnected
+                    # socket.
+                    self.connected = False
+                else:
+                    # The socket is broken in some unknown way, alert
+                    # the user and remove it from the map (to prevent
+                    # polling of broken sockets).
+                    self.del_channel(map)
+                    raise
+        else:
+            self.socket = None
+
+    def __repr__(self):
+        status = [self.__class__.__module__+"."+self.__class__.__qualname__]
+        if self.accepting and self.addr:
+            status.append('listening')
+        elif self.connected:
+            status.append('connected')
+        if self.addr is not None:
+            try:
+                status.append('%s:%d' % self.addr)
+            except TypeError:
+                status.append(repr(self.addr))
+        return '<%s at %#x>' % (' '.join(status), id(self))
+
+    def add_channel(self, map=None):
+        #self.log_info('adding channel %s' % self)
+        if map is None:
+            map = self._map
+        map[self._fileno] = self
+
+    def del_channel(self, map=None):
+        fd = self._fileno
+        if map is None:
+            map = self._map
+        if fd in map:
+            #self.log_info('closing channel %d:%s' % (fd, self))
+            del map[fd]
+        self._fileno = None
+
+    def create_socket(self, family=socket.AF_INET, type=socket.SOCK_STREAM):
+        self.family_and_type = family, type
+        sock = socket.socket(family, type)
+        sock.setblocking(False)
+        self.set_socket(sock)
+
+    def set_socket(self, sock, map=None):
+        self.socket = sock
+        self._fileno = sock.fileno()
+        self.add_channel(map)
+
+    def set_reuse_addr(self):
+        # try to re-use a server port if possible
+        try:
+            self.socket.setsockopt(
+                socket.SOL_SOCKET, socket.SO_REUSEADDR,
+                self.socket.getsockopt(socket.SOL_SOCKET,
+                                       socket.SO_REUSEADDR) | 1
+                )
+        except OSError:
+            pass
+
+    # ==================================================
+    # predicates for select()
+    # these are used as filters for the lists of sockets
+    # to pass to select().
+    # ==================================================
+
+    def readable(self):
+        return True
+
+    def writable(self):
+        return True
+
+    # ==================================================
+    # socket object methods.
+    # ==================================================
+
+    def listen(self, num):
+        self.accepting = True
+        if os.name == 'nt' and num > 5:
+            num = 5
+        return self.socket.listen(num)
+
+    def bind(self, addr):
+        self.addr = addr
+        return self.socket.bind(addr)
+
+    def connect(self, address):
+        self.connected = False
+        self.connecting = True
+        err = self.socket.connect_ex(address)
+        if err in (EINPROGRESS, EALREADY, EWOULDBLOCK) \
+        or err == EINVAL and os.name == 'nt':
+            self.addr = address
+            return
+        if err in (0, EISCONN):
+            self.addr = address
+            self.handle_connect_event()
+        else:
+            raise OSError(err, errorcode[err])
+
+    def accept(self):
+        # XXX can return either an address pair or None
+        try:
+            conn, addr = self.socket.accept()
+        except TypeError:
+            return None
+        except OSError as why:
+            if why.errno in (EWOULDBLOCK, ECONNABORTED, EAGAIN):
+                return None
+            else:
+                raise
+        else:
+            return conn, addr
+
+    def send(self, data):
+        try:
+            result = self.socket.send(data)
+            return result
+        except OSError as why:
+            if why.errno == EWOULDBLOCK:
+                return 0
+            elif why.errno in _DISCONNECTED:
+                self.handle_close()
+                return 0
+            else:
+                raise
+
+    def recv(self, buffer_size):
+        try:
+            data = self.socket.recv(buffer_size)
+            if not data:
+                # a closed connection is indicated by signaling
+                # a read condition, and having recv() return 0.
+                self.handle_close()
+                return b''
+            else:
+                return data
+        except OSError as why:
+            # winsock sometimes raises ENOTCONN
+            if why.errno in _DISCONNECTED:
+                self.handle_close()
+                return b''
+            else:
+                raise
+
+    def close(self):
+        self.connected = False
+        self.accepting = False
+        self.connecting = False
+        self.del_channel()
+        if self.socket is not None:
+            try:
+                self.socket.close()
+            except OSError as why:
+                if why.errno not in (ENOTCONN, EBADF):
+                    raise
+
+    # log and log_info may be overridden to provide more sophisticated
+    # logging and warning methods. In general, log is for 'hit' logging
+    # and 'log_info' is for informational, warning and error logging.
+
+    def log(self, message):
+        sys.stderr.write('log: %s\n' % str(message))
+
+    def log_info(self, message, type='info'):
+        if type not in self.ignore_log_types:
+            print('%s: %s' % (type, message))
+
+    def handle_read_event(self):
+        if self.accepting:
+            # accepting sockets are never connected, they "spawn" new
+            # sockets that are connected
+            self.handle_accept()
+        elif not self.connected:
+            if self.connecting:
+                self.handle_connect_event()
+            self.handle_read()
+        else:
+            self.handle_read()
+
+    def handle_connect_event(self):
+        err = self.socket.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
+        if err != 0:
+            raise OSError(err, _strerror(err))
+        self.handle_connect()
+        self.connected = True
+        self.connecting = False
+
+    def handle_write_event(self):
+        if self.accepting:
+            # Accepting sockets shouldn't get a write event.
+            # We will pretend it didn't happen.
+            return
+
+        if not self.connected:
+            if self.connecting:
+                self.handle_connect_event()
+        self.handle_write()
+
+    def handle_expt_event(self):
+        # handle_expt_event() is called if there might be an error on the
+        # socket, or if there is OOB data
+        # check for the error condition first
+        err = self.socket.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
+        if err != 0:
+            # we can get here when select.select() says that there is an
+            # exceptional condition on the socket
+            # since there is an error, we'll go ahead and close the socket
+            # like we would in a subclassed handle_read() that received no
+            # data
+            self.handle_close()
+        else:
+            self.handle_expt()
+
+    def handle_error(self):
+        nil, t, v, tbinfo = compact_traceback()
+
+        # sometimes a user repr method will crash.
+        try:
+            self_repr = repr(self)
+        except:
+            self_repr = '<__repr__(self) failed for object at %0x>' % id(self)
+
+        self.log_info(
+            'uncaptured python exception, closing channel %s (%s:%s %s)' % (
+                self_repr,
+                t,
+                v,
+                tbinfo
+                ),
+            'error'
+            )
+        self.handle_close()
+
+    def handle_expt(self):
+        self.log_info('unhandled incoming priority event', 'warning')
+
+    def handle_read(self):
+        self.log_info('unhandled read event', 'warning')
+
+    def handle_write(self):
+        self.log_info('unhandled write event', 'warning')
+
+    def handle_connect(self):
+        self.log_info('unhandled connect event', 'warning')
+
+    def handle_accept(self):
+        pair = self.accept()
+        if pair is not None:
+            self.handle_accepted(*pair)
+
+    def handle_accepted(self, sock, addr):
+        sock.close()
+        self.log_info('unhandled accepted event', 'warning')
+
+    def handle_close(self):
+        self.log_info('unhandled close event', 'warning')
+        self.close()
+
+# ---------------------------------------------------------------------------
+# adds simple buffered output capability, useful for simple clients.
+# [for more sophisticated usage use asynchat.async_chat]
+# ---------------------------------------------------------------------------
+
+class dispatcher_with_send(dispatcher):
+
+    def __init__(self, sock=None, map=None):
+        dispatcher.__init__(self, sock, map)
+        self.out_buffer = b''
+
+    def initiate_send(self):
+        num_sent = 0
+        num_sent = dispatcher.send(self, self.out_buffer[:65536])
+        self.out_buffer = self.out_buffer[num_sent:]
+
+    def handle_write(self):
+        self.initiate_send()
+
+    def writable(self):
+        return (not self.connected) or len(self.out_buffer)
+
+    def send(self, data):
+        if self.debug:
+            self.log_info('sending %s' % repr(data))
+        self.out_buffer = self.out_buffer + data
+        self.initiate_send()
+
+# ---------------------------------------------------------------------------
+# used for debugging.
+# ---------------------------------------------------------------------------
+
+def compact_traceback():
+    t, v, tb = sys.exc_info()
+    tbinfo = []
+    if not tb: # Must have a traceback
+        raise AssertionError("traceback does not exist")
+    while tb:
+        tbinfo.append((
+            tb.tb_frame.f_code.co_filename,
+            tb.tb_frame.f_code.co_name,
+            str(tb.tb_lineno)
+            ))
+        tb = tb.tb_next
+
+    # just to be safe
+    del tb
+
+    file, function, line = tbinfo[-1]
+    info = ' '.join(['[%s|%s|%s]' % x for x in tbinfo])
+    return (file, function, line), t, v, info
+
+def close_all(map=None, ignore_all=False):
+    if map is None:
+        map = socket_map
+    for x in list(map.values()):
+        try:
+            x.close()
+        except OSError as x:
+            if x.errno == EBADF:
+                pass
+            elif not ignore_all:
+                raise
+        except _reraised_exceptions:
+            raise
+        except:
+            if not ignore_all:
+                raise
+    map.clear()
+
+# Asynchronous File I/O:
+#
+# After a little research (reading man pages on various unixen, and
+# digging through the linux kernel), I've determined that select()
+# isn't meant for doing asynchronous file i/o.
+# Heartening, though - reading linux/mm/filemap.c shows that linux
+# supports asynchronous read-ahead.  So _MOST_ of the time, the data
+# will be sitting in memory for us already when we go to read it.
+#
+# What other OS's (besides NT) support async file i/o?  [VMS?]
+#
+# Regardless, this is useful for pipes, and stdin/stdout...
+
+if os.name == 'posix':
+    class file_wrapper:
+        # Here we override just enough to make a file
+        # look like a socket for the purposes of asyncore.
+        # The passed fd is automatically os.dup()'d
+
+        def __init__(self, fd):
+            self.fd = os.dup(fd)
+
+        def __del__(self):
+            if self.fd >= 0:
+                warnings.warn("unclosed file %r" % self, ResourceWarning,
+                              source=self)
+            self.close()
+
+        def recv(self, *args):
+            return os.read(self.fd, *args)
+
+        def send(self, *args):
+            return os.write(self.fd, *args)
+
+        def getsockopt(self, level, optname, buflen=None):
+            if (level == socket.SOL_SOCKET and
+                optname == socket.SO_ERROR and
+                not buflen):
+                return 0
+            raise NotImplementedError("Only asyncore specific behaviour "
+                                      "implemented.")
+
+        read = recv
+        write = send
+
+        def close(self):
+            if self.fd < 0:
+                return
+            fd = self.fd
+            self.fd = -1
+            os.close(fd)
+
+        def fileno(self):
+            return self.fd
+
+    class file_dispatcher(dispatcher):
+
+        def __init__(self, fd, map=None):
+            dispatcher.__init__(self, None, map)
+            self.connected = True
+            try:
+                fd = fd.fileno()
+            except AttributeError:
+                pass
+            self.set_file(fd)
+            # set it to non-blocking mode
+            os.set_blocking(fd, False)
+
+        def set_file(self, fd):
+            self.socket = file_wrapper(fd)
+            self._fileno = self.socket.fileno()
+            self.add_channel()
diff --git a/Lib/test/support/_smtpd.py b/Lib/test/support/_smtpd.py
new file mode 100755
index 0000000..0e37d08
--- /dev/null
+++ b/Lib/test/support/_smtpd.py
@@ -0,0 +1,754 @@
+#! /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
+
+from test.support import _asyncore as asyncore
+from test.support import _asynchat as asynchat
+
+__all__ = [
+    "SMTPChannel", "SMTPServer", "DebuggingServer", "PureProxy",
+]
+
+
+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 = []
+
+
+    # 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