#19662: add decode_data to smtpd so you can get at DATA in bytes form.

Otherwise smtpd is restricted to 7bit clean data, since even if the
incoming data is actually utf-8, it will often break things to decode
it before parsing the message.

Patch by Maciej Szulik, with some adjustments (mostly the warning
support).

Doc/library/smtpd.rst

@@ -28,7 +28,7 @@ SMTPServer Objects
 
 
 .. class:: SMTPServer(localaddr, remoteaddr, data_size_limit=33554432,\
-                      map=None)
+                      map=None, decode_data=True)
 
    Create a new :class:`SMTPServer` object, which binds to local address
    *localaddr*.  It will treat *remoteaddr* as an upstream SMTP relayer.  It
@@ -41,6 +41,11 @@ SMTPServer Objects
 
    A dictionary can be specified in *map* to avoid using a global socket map.
 
+   *decode_data* specifies whether the data portion of the SMTP transaction
+   should be decoded using UTF-8.  The default is ``True`` for backward
+   compatibility reasons, but will change to ``False`` in Python 3.6.  Specify
+   the keyword value explicitly to avoid the :exc:`DeprecationWarning`.
+
    .. method:: process_message(peer, mailfrom, rcpttos, data)
 
       Raise :exc:`NotImplementedError` exception. Override this in subclasses to
@@ -51,6 +56,10 @@ SMTPServer Objects
       containing the contents of the e-mail (which should be in :rfc:`2822`
       format).
 
+      If the *decode_data* constructor keyword is set to ``True``, the *data*
+      argument will be a unicode string.  If it is set to ``False``, it
+      will be a bytes object.
+
    .. attribute:: channel_class
 
       Override this in subclasses to use a custom :class:`SMTPChannel` for
@@ -59,6 +68,9 @@ SMTPServer Objects
    .. versionchanged:: 3.4
       The *map* argument was added.
 
+   .. versionchanged:: 3.5
+      the *decode_data* argument was added.
+
 
 DebuggingServer Objects
 -----------------------
@@ -97,7 +109,7 @@ SMTPChannel Objects
 -------------------
 
 .. class:: SMTPChannel(server, conn, addr, data_size_limit=33554432,\
-                       map=None))
+                       map=None, decode_data=True)
 
    Create a new :class:`SMTPChannel` object which manages the communication
    between the server and a single SMTP client.
@@ -110,9 +122,17 @@ SMTPChannel Objects
 
    A dictionary can be specified in *map* to avoid using a global socket map.
 
+   *decode_data* specifies whether the data portion of the SMTP transaction
+   should be decoded using UTF-8.  The default is ``True`` for backward
+   compatibility reasons, but will change to ``False`` in Python 3.6.  Specify
+   the keyword value explicitly to avoid the :exc:`DeprecationWarning`.
+
    To use a custom SMTPChannel implementation you need to override the
    :attr:`SMTPServer.channel_class` of your :class:`SMTPServer`.
 
+   .. versionchanged:: 3.5
+      the *decode_data* argument was added.
+
    The :class:`SMTPChannel` has the following instance variables:
 
    .. attribute:: smtp_server

Doc/whatsnew/3.5.rst

@@ -184,6 +184,16 @@ signal
   debugging, instead of integer “magic numbers”. (contributed by Giampaolo
   Rodola' in :issue:`21076`)
 
+smtpd
+-----
+
+* Both :class:`~smtpd.SMTPServer` and :class:`smtpd.SMTPChannel` now accept a
+  *decode_data* keyword to determine if the DATA portion of the SMTP
+  transaction is decoded using the ``utf-8`` codec or is instead provided to
+  :meth:`~smtpd.SMTPServer.process_message` as a byte string.  The default
+  is ``True`` for backward compatibility reasons, but will change to ``False``
+  in Python 3.6.  (Contributed by Maciej Szulik in :issue:`19662`.)
+
 socket
 ------
 
@@ -245,6 +255,12 @@ Deprecated Python modules, functions and methods
 * The :mod:`formatter` module has now graduated to full deprecation and is still
   slated for removal in Python 3.6.
 
+* :mod:`smtpd` has in the past always decoded the DATA portion of email
+  messages using the ``utf-8`` codec.  This can now be controlled by the new
+  *decode_data* keyword to :class:`~smtpd.SMTPServer`.  The default value is
+  ``True``, but this default is deprecated.  Specify the *decode_data* keyword
+  with an appropriate value to avoid the deprecation warning.
+
 
 Deprecated functions and types of the C API
 -------------------------------------------

Lib/smtpd.py

@@ -98,7 +98,6 @@ class Devnull:
 
 DEBUGSTREAM = Devnull()
 NEWLINE = '\n'
-EMPTYSTRING = ''
 COMMASPACE = ', '
 DATA_SIZE_DEFAULT = 33554432
 
@@ -122,12 +121,28 @@ class SMTPChannel(asynchat.async_chat):
     max_command_size_limit = max(command_size_limits.values())
 
     def __init__(self, server, conn, addr, data_size_limit=DATA_SIZE_DEFAULT,
-                 map=None):
+                 map=None, decode_data=None):
         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
+        if decode_data is None:
+            warn("The decode_data default of True will change to False in 3.6;"
+                 " specify an explicit value for this keyword",
+                 DeprecationWarning, 2)
+            decode_data = True
+        self._decode_data = decode_data
+        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 = b'.'
+            self._newline = b'\n'
         self.received_lines = []
         self.smtp_state = self.COMMAND
         self.seen_greeting = ''
@@ -287,11 +302,14 @@ class SMTPChannel(asynchat.async_chat):
             return
         elif limit:
             self.num_bytes += len(data)
-        self.received_lines.append(str(data, "utf-8"))
+        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 = EMPTYSTRING.join(self.received_lines)
+        line = self._emptystring.join(self.received_lines)
         print('Data:', repr(line), file=DEBUGSTREAM)
         self.received_lines = []
         if self.smtp_state == self.COMMAND:
@@ -300,6 +318,8 @@ class SMTPChannel(asynchat.async_chat):
                 self.push('500 Error: bad syntax')
                 return
             method = None
+            if not self._decode_data:
+                line = str(line, 'utf-8')
             i = line.find(' ')
             if i < 0:
                 command = line.upper()
@@ -330,12 +350,12 @@ class SMTPChannel(asynchat.async_chat):
             # Remove extraneous carriage returns and de-transparency according
             # to RFC 5321, Section 4.5.2.
             data = []
-            for text in line.split('\r\n'):
-                if text and text[0] == '.':
+            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 = NEWLINE.join(data)
+            self.received_data = self._newline.join(data)
             status = self.smtp_server.process_message(self.peer,
                                                       self.mailfrom,
                                                       self.rcpttos,
@@ -577,10 +597,17 @@ class SMTPServer(asyncore.dispatcher):
     channel_class = SMTPChannel
 
     def __init__(self, localaddr, remoteaddr,
-                 data_size_limit=DATA_SIZE_DEFAULT, map=None):
+                 data_size_limit=DATA_SIZE_DEFAULT, map=None,
+                 decode_data=None):
         self._localaddr = localaddr
         self._remoteaddr = remoteaddr
         self.data_size_limit = data_size_limit
+        if decode_data is None:
+            warn("The decode_data default of True will change to False in 3.6;"
+                 " specify an explicit value for this keyword",
+                 DeprecationWarning, 2)
+            decode_data = True
+        self._decode_data = decode_data
         asyncore.dispatcher.__init__(self, map=map)
         try:
             self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
@@ -599,7 +626,7 @@ class SMTPServer(asyncore.dispatcher):
     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._map, self._decode_data)
 
     # API for "doing something useful with the message"
     def process_message(self, peer, mailfrom, rcpttos, data):

Lib/test/test_smtpd.py

@@ -7,13 +7,18 @@ import asyncore
 
 
 class DummyServer(smtpd.SMTPServer):
-    def __init__(self, localaddr, remoteaddr):
-        smtpd.SMTPServer.__init__(self, localaddr, remoteaddr)
+    def __init__(self, localaddr, remoteaddr, decode_data=True):
+        smtpd.SMTPServer.__init__(self, localaddr, remoteaddr,
+                                  decode_data=decode_data)
         self.messages = []
+        if decode_data:
+            self.return_status = 'return status'
+        else:
+            self.return_status = b'return status'
 
     def process_message(self, peer, mailfrom, rcpttos, data):
         self.messages.append((peer, mailfrom, rcpttos, data))
-        if data == 'return status':
+        if data == self.return_status:
             return '250 Okish'
 
 
@@ -31,9 +36,9 @@ class SMTPDServerTest(unittest.TestCase):
         smtpd.socket = asyncore.socket = mock_socket
 
     def test_process_message_unimplemented(self):
-        server = smtpd.SMTPServer('a', 'b')
+        server = smtpd.SMTPServer('a', 'b', decode_data=True)
         conn, addr = server.accept()
-        channel = smtpd.SMTPChannel(server, conn, addr)
+        channel = smtpd.SMTPChannel(server, conn, addr, decode_data=True)
 
         def write_line(line):
             channel.socket.queue_recv(line)
@@ -45,6 +50,10 @@ class SMTPDServerTest(unittest.TestCase):
         write_line(b'DATA')
         self.assertRaises(NotImplementedError, write_line, b'spam\r\n.\r\n')
 
+    def test_decode_data_default_warns(self):
+        with self.assertWarns(DeprecationWarning):
+            smtpd.SMTPServer('a', 'b')
+
     def tearDown(self):
         asyncore.close_all()
         asyncore.socket = smtpd.socket = socket
@@ -57,7 +66,8 @@ class SMTPDChannelTest(unittest.TestCase):
         self.debug = smtpd.DEBUGSTREAM = io.StringIO()
         self.server = DummyServer('a', 'b')
         conn, addr = self.server.accept()
-        self.channel = smtpd.SMTPChannel(self.server, conn, addr)
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr,
+                                         decode_data=True)
 
     def tearDown(self):
         asyncore.close_all()
@@ -502,6 +512,12 @@ class SMTPDChannelTest(unittest.TestCase):
         with support.check_warnings(('', DeprecationWarning)):
             self.channel._SMTPChannel__addr = 'spam'
 
+    def test_decode_data_default_warning(self):
+        server = DummyServer('a', 'b')
+        conn, addr = self.server.accept()
+        with self.assertWarns(DeprecationWarning):
+            smtpd.SMTPChannel(server, conn, addr)
+
 
 class SMTPDChannelWithDataSizeLimitTest(unittest.TestCase):
 
@@ -512,7 +528,8 @@ class SMTPDChannelWithDataSizeLimitTest(unittest.TestCase):
         self.server = DummyServer('a', 'b')
         conn, addr = self.server.accept()
         # Set DATA size limit to 32 bytes for easy testing
-        self.channel = smtpd.SMTPChannel(self.server, conn, addr, 32)
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr, 32,
+                                         decode_data=True)
 
     def tearDown(self):
         asyncore.close_all()
@@ -553,5 +570,92 @@ class SMTPDChannelWithDataSizeLimitTest(unittest.TestCase):
                          b'552 Error: Too much mail data\r\n')
 
 
+class SMTPDChannelWithDecodeDataFalse(unittest.TestCase):
+
+    def setUp(self):
+        smtpd.socket = asyncore.socket = mock_socket
+        self.old_debugstream = smtpd.DEBUGSTREAM
+        self.debug = smtpd.DEBUGSTREAM = io.StringIO()
+        self.server = DummyServer('a', 'b', decode_data=False)
+        conn, addr = self.server.accept()
+        # Set decode_data to False
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr,
+                decode_data=False)
+
+    def tearDown(self):
+        asyncore.close_all()
+        asyncore.socket = smtpd.socket = socket
+        smtpd.DEBUGSTREAM = self.old_debugstream
+
+    def write_line(self, line):
+        self.channel.socket.queue_recv(line)
+        self.channel.handle_read()
+
+    def test_ascii_data(self):
+        self.write_line(b'HELO example')
+        self.write_line(b'MAIL From:eggs@example')
+        self.write_line(b'RCPT To:spam@example')
+        self.write_line(b'DATA')
+        self.write_line(b'plain ascii text')
+        self.write_line(b'.')
+        self.assertEqual(self.channel.received_data, b'plain ascii text')
+
+    def test_utf8_data(self):
+        self.write_line(b'HELO example')
+        self.write_line(b'MAIL From:eggs@example')
+        self.write_line(b'RCPT To:spam@example')
+        self.write_line(b'DATA')
+        self.write_line(b'utf8 enriched text: \xc5\xbc\xc5\xba\xc4\x87')
+        self.write_line(b'and some plain ascii')
+        self.write_line(b'.')
+        self.assertEqual(
+            self.channel.received_data,
+            b'utf8 enriched text: \xc5\xbc\xc5\xba\xc4\x87\n'
+                b'and some plain ascii')
+
+
+class SMTPDChannelWithDecodeDataTrue(unittest.TestCase):
+
+    def setUp(self):
+        smtpd.socket = asyncore.socket = mock_socket
+        self.old_debugstream = smtpd.DEBUGSTREAM
+        self.debug = smtpd.DEBUGSTREAM = io.StringIO()
+        self.server = DummyServer('a', 'b')
+        conn, addr = self.server.accept()
+        # Set decode_data to True
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr,
+                decode_data=True)
+
+    def tearDown(self):
+        asyncore.close_all()
+        asyncore.socket = smtpd.socket = socket
+        smtpd.DEBUGSTREAM = self.old_debugstream
+
+    def write_line(self, line):
+        self.channel.socket.queue_recv(line)
+        self.channel.handle_read()
+
+    def test_ascii_data(self):
+        self.write_line(b'HELO example')
+        self.write_line(b'MAIL From:eggs@example')
+        self.write_line(b'RCPT To:spam@example')
+        self.write_line(b'DATA')
+        self.write_line(b'plain ascii text')
+        self.write_line(b'.')
+        self.assertEqual(self.channel.received_data, 'plain ascii text')
+
+    def test_utf8_data(self):
+        self.write_line(b'HELO example')
+        self.write_line(b'MAIL From:eggs@example')
+        self.write_line(b'RCPT To:spam@example')
+        self.write_line(b'DATA')
+        self.write_line(b'utf8 enriched text: \xc5\xbc\xc5\xba\xc4\x87')
+        self.write_line(b'and some plain ascii')
+        self.write_line(b'.')
+        self.assertEqual(
+            self.channel.received_data,
+            'utf8 enriched text: żźć\nand some plain ascii')
+
+
 if __name__ == "__main__":
     unittest.main()