Lib/test/test_nntplib.py

import io
import socket
import datetime
import textwrap
import unittest
import functools
import contextlib
import os.path
from test import support
from nntplib import NNTP, GroupInfo
import nntplib
from unittest.mock import patch
try:
    import ssl
except ImportError:
    ssl = None
try:
    import threading
except ImportError:
    threading = None

TIMEOUT = 30
certfile = os.path.join(os.path.dirname(__file__), 'keycert3.pem')

# TODO:
# - test the `file` arg to more commands
# - test error conditions
# - test auth and `usenetrc`


class NetworkedNNTPTestsMixin:

    def test_welcome(self):
        welcome = self.server.getwelcome()
        self.assertEqual(str, type(welcome))

    def test_help(self):
        resp, lines = self.server.help()
        self.assertTrue(resp.startswith("100 "), resp)
        for line in lines:
            self.assertEqual(str, type(line))

    def test_list(self):
        resp, groups = self.server.list()
        if len(groups) > 0:
            self.assertEqual(GroupInfo, type(groups[0]))
            self.assertEqual(str, type(groups[0].group))

    def test_list_active(self):
        resp, groups = self.server.list(self.GROUP_PAT)
        if len(groups) > 0:
            self.assertEqual(GroupInfo, type(groups[0]))
            self.assertEqual(str, type(groups[0].group))

    def test_unknown_command(self):
        with self.assertRaises(nntplib.NNTPPermanentError) as cm:
            self.server._shortcmd("XYZZY")
        resp = cm.exception.response
        self.assertTrue(resp.startswith("500 "), resp)

    def test_newgroups(self):
        # gmane gets a constant influx of new groups.  In order not to stress
        # the server too much, we choose a recent date in the past.
        dt = datetime.date.today() - datetime.timedelta(days=7)
        resp, groups = self.server.newgroups(dt)
        if len(groups) > 0:
            self.assertIsInstance(groups[0], GroupInfo)
            self.assertIsInstance(groups[0].group, str)

    def test_description(self):
        def _check_desc(desc):
            # Sanity checks
            self.assertIsInstance(desc, str)
            self.assertNotIn(self.GROUP_NAME, desc)
        desc = self.server.description(self.GROUP_NAME)
        _check_desc(desc)
        # Another sanity check
        self.assertIn("Python", desc)
        # With a pattern
        desc = self.server.description(self.GROUP_PAT)
        _check_desc(desc)
        # Shouldn't exist
        desc = self.server.description("zk.brrtt.baz")
        self.assertEqual(desc, '')

    def test_descriptions(self):
        resp, descs = self.server.descriptions(self.GROUP_PAT)
        # 215 for LIST NEWSGROUPS, 282 for XGTITLE
        self.assertTrue(
            resp.startswith("215 ") or resp.startswith("282 "), resp)
        self.assertIsInstance(descs, dict)
        desc = descs[self.GROUP_NAME]
        self.assertEqual(desc, self.server.description(self.GROUP_NAME))

    def test_group(self):
        result = self.server.group(self.GROUP_NAME)
        self.assertEqual(5, len(result))
        resp, count, first, last, group = result
        self.assertEqual(group, self.GROUP_NAME)
        self.assertIsInstance(count, int)
        self.assertIsInstance(first, int)
        self.assertIsInstance(last, int)
        self.assertLessEqual(first, last)
        self.assertTrue(resp.startswith("211 "), resp)

    def test_date(self):
        resp, date = self.server.date()
        self.assertIsInstance(date, datetime.datetime)
        # Sanity check
        self.assertGreaterEqual(date.year, 1995)
        self.assertLessEqual(date.year, 2030)

    def _check_art_dict(self, art_dict):
        # Some sanity checks for a field dictionary returned by OVER / XOVER
        self.assertIsInstance(art_dict, dict)
        # NNTP has 7 mandatory fields
        self.assertGreaterEqual(art_dict.keys(),
            {"subject", "from", "date", "message-id",
             "references", ":bytes", ":lines"}
            )
        for v in art_dict.values():
            self.assertIsInstance(v, (str, type(None)))

    def test_xover(self):
        resp, count, first, last, name = self.server.group(self.GROUP_NAME)
        resp, lines = self.server.xover(last - 5, last)
        if len(lines) == 0:
            self.skipTest("no articles retrieved")
        # The 'last' article is not necessarily part of the output (cancelled?)
        art_num, art_dict = lines[0]
        self.assertGreaterEqual(art_num, last - 5)
        self.assertLessEqual(art_num, last)
        self._check_art_dict(art_dict)

    @unittest.skipIf(True, 'temporarily skipped until a permanent solution'
                           ' is found for issue #28971')
    def test_over(self):
        resp, count, first, last, name = self.server.group(self.GROUP_NAME)
        start = last - 10
        # The "start-" article range form
        resp, lines = self.server.over((start, None))
        art_num, art_dict = lines[0]
        self._check_art_dict(art_dict)
        # The "start-end" article range form
        resp, lines = self.server.over((start, last))
        art_num, art_dict = lines[-1]
        # The 'last' article is not necessarily part of the output (cancelled?)
        self.assertGreaterEqual(art_num, start)
        self.assertLessEqual(art_num, last)
        self._check_art_dict(art_dict)
        # XXX The "message_id" form is unsupported by gmane
        # 503 Overview by message-ID unsupported

    def test_xhdr(self):
        resp, count, first, last, name = self.server.group(self.GROUP_NAME)
        resp, lines = self.server.xhdr('subject', last)
        for line in lines:
            self.assertEqual(str, type(line[1]))

    def check_article_resp(self, resp, article, art_num=None):
        self.assertIsInstance(article, nntplib.ArticleInfo)
        if art_num is not None:
            self.assertEqual(article.number, art_num)
        for line in article.lines:
            self.assertIsInstance(line, bytes)
        # XXX this could exceptionally happen...
        self.assertNotIn(article.lines[-1], (b".", b".\n", b".\r\n"))

    def test_article_head_body(self):
        resp, count, first, last, name = self.server.group(self.GROUP_NAME)
        # Try to find an available article
        for art_num in (last, first, last - 1):
            try:
                resp, head = self.server.head(art_num)
            except nntplib.NNTPTemporaryError as e:
                if not e.response.startswith("423 "):
                    raise
                # "423 No such article" => choose another one
                continue
            break
        else:
            self.skipTest("could not find a suitable article number")
        self.assertTrue(resp.startswith("221 "), resp)
        self.check_article_resp(resp, head, art_num)
        resp, body = self.server.body(art_num)
        self.assertTrue(resp.startswith("222 "), resp)
        self.check_article_resp(resp, body, art_num)
        resp, article = self.server.article(art_num)
        self.assertTrue(resp.startswith("220 "), resp)
        self.check_article_resp(resp, article, art_num)
        # Tolerate running the tests from behind a NNTP virus checker
        blacklist = lambda line: line.startswith(b'X-Antivirus')
        filtered_head_lines = [line for line in head.lines
                               if not blacklist(line)]
        filtered_lines = [line for line in article.lines
                          if not blacklist(line)]
        self.assertEqual(filtered_lines, filtered_head_lines + [b''] + body.lines)

    def test_capabilities(self):
        # The server under test implements NNTP version 2 and has a
        # couple of well-known capabilities. Just sanity check that we
        # got them.
        def _check_caps(caps):
            caps_list = caps['LIST']
            self.assertIsInstance(caps_list, (list, tuple))
            self.assertIn('OVERVIEW.FMT', caps_list)
        self.assertGreaterEqual(self.server.nntp_version, 2)
        _check_caps(self.server.getcapabilities())
        # This re-emits the command
        resp, caps = self.server.capabilities()
        _check_caps(caps)

    def test_zlogin(self):
        # This test must be the penultimate because further commands will be
        # refused.
        baduser = "notarealuser"
        badpw = "notarealpassword"
        # Check that bogus credentials cause failure
        self.assertRaises(nntplib.NNTPError, self.server.login,
                          user=baduser, password=badpw, usenetrc=False)
        # FIXME: We should check that correct credentials succeed, but that
        # would require valid details for some server somewhere to be in the
        # test suite, I think. Gmane is anonymous, at least as used for the
        # other tests.

    def test_zzquit(self):
        # This test must be called last, hence the name
        cls = type(self)
        try:
            self.server.quit()
        finally:
            cls.server = None

    @classmethod
    def wrap_methods(cls):
        # Wrap all methods in a transient_internet() exception catcher
        # XXX put a generic version in test.support?
        def wrap_meth(meth):
            @functools.wraps(meth)
            def wrapped(self):
                with support.transient_internet(self.NNTP_HOST):
                    meth(self)
            return wrapped
        for name in dir(cls):
            if not name.startswith('test_'):
                continue
            meth = getattr(cls, name)
            if not callable(meth):
                continue
            # Need to use a closure so that meth remains bound to its current
            # value
            setattr(cls, name, wrap_meth(meth))

    def test_with_statement(self):
        def is_connected():
            if not hasattr(server, 'file'):
                return False
            try:
                server.help()
            except (OSError, EOFError):
                return False
            return True

        with self.NNTP_CLASS(self.NNTP_HOST, timeout=TIMEOUT, usenetrc=False) as server:
            self.assertTrue(is_connected())
            self.assertTrue(server.help())
        self.assertFalse(is_connected())

        with self.NNTP_CLASS(self.NNTP_HOST, timeout=TIMEOUT, usenetrc=False) as server:
            server.quit()
        self.assertFalse(is_connected())


NetworkedNNTPTestsMixin.wrap_methods()


class NetworkedNNTPTests(NetworkedNNTPTestsMixin, unittest.TestCase):
    # This server supports STARTTLS (gmane doesn't)
    NNTP_HOST = 'news.trigofacile.com'
    GROUP_NAME = 'fr.comp.lang.python'
    GROUP_PAT = 'fr.comp.lang.*'

    NNTP_CLASS = NNTP

    @classmethod
    def setUpClass(cls):
        support.requires("network")
        with support.transient_internet(cls.NNTP_HOST):
            cls.server = cls.NNTP_CLASS(cls.NNTP_HOST, timeout=TIMEOUT, usenetrc=False)

    @classmethod
    def tearDownClass(cls):
        if cls.server is not None:
            cls.server.quit()

@unittest.skipUnless(ssl, 'requires SSL support')
class NetworkedNNTP_SSLTests(NetworkedNNTPTests):

    # Technical limits for this public NNTP server (see http://www.aioe.org):
    # "Only two concurrent connections per IP address are allowed and
    # 400 connections per day are accepted from each IP address."

    NNTP_HOST = 'nntp.aioe.org'
    GROUP_NAME = 'comp.lang.python'
    GROUP_PAT = 'comp.lang.*'

    NNTP_CLASS = getattr(nntplib, 'NNTP_SSL', None)

    # Disabled as it produces too much data
    test_list = None

    # Disabled as the connection will already be encrypted.
    test_starttls = None


#
# Non-networked tests using a local server (or something mocking it).
#

class _NNTPServerIO(io.RawIOBase):
    """A raw IO object allowing NNTP commands to be received and processed
    by a handler.  The handler can push responses which can then be read
    from the IO object."""

    def __init__(self, handler):
        io.RawIOBase.__init__(self)
        # The channel from the client
        self.c2s = io.BytesIO()
        # The channel to the client
        self.s2c = io.BytesIO()
        self.handler = handler
        self.handler.start(self.c2s.readline, self.push_data)

    def readable(self):
        return True

    def writable(self):
        return True

    def push_data(self, data):
        """Push (buffer) some data to send to the client."""
        pos = self.s2c.tell()
        self.s2c.seek(0, 2)
        self.s2c.write(data)
        self.s2c.seek(pos)

    def write(self, b):
        """The client sends us some data"""
        pos = self.c2s.tell()
        self.c2s.write(b)
        self.c2s.seek(pos)
        self.handler.process_pending()
        return len(b)

    def readinto(self, buf):
        """The client wants to read a response"""
        self.handler.process_pending()
        b = self.s2c.read(len(buf))
        n = len(b)
        buf[:n] = b
        return n


def make_mock_file(handler):
    sio = _NNTPServerIO(handler)
    # Using BufferedRWPair instead of BufferedRandom ensures the file
    # isn't seekable.
    file = io.BufferedRWPair(sio, sio)
    return (sio, file)


class MockedNNTPTestsMixin:
    # Override in derived classes
    handler_class = None

    def setUp(self):
        super().setUp()
        self.make_server()

    def tearDown(self):
        super().tearDown()
        del self.server

    def make_server(self, *args, **kwargs):
        self.handler = self.handler_class()
        self.sio, file = make_mock_file(self.handler)
        self.server = nntplib._NNTPBase(file, 'test.server', *args, **kwargs)
        return self.server


class MockedNNTPWithReaderModeMixin(MockedNNTPTestsMixin):
    def setUp(self):
        super().setUp()
        self.make_server(readermode=True)


class NNTPv1Handler:
    """A handler for RFC 977"""

    welcome = "200 NNTP mock server"

    def start(self, readline, push_data):
        self.in_body = False
        self.allow_posting = True
        self._readline = readline
        self._push_data = push_data
        self._logged_in = False
        self._user_sent = False
        # Our welcome
        self.handle_welcome()

    def _decode(self, data):
        return str(data, "utf-8", "surrogateescape")

    def process_pending(self):
        if self.in_body:
            while True:
                line = self._readline()
                if not line:
                    return
                self.body.append(line)
                if line == b".\r\n":
                    break
            try:
                meth, tokens = self.body_callback
                meth(*tokens, body=self.body)
            finally:
                self.body_callback = None
                self.body = None
                self.in_body = False
        while True:
            line = self._decode(self._readline())
            if not line:
                return
            if not line.endswith("\r\n"):
                raise ValueError("line doesn't end with \\r\\n: {!r}".format(line))
            line = line[:-2]
            cmd, *tokens = line.split()
            #meth = getattr(self.handler, "handle_" + cmd.upper(), None)
            meth = getattr(self, "handle_" + cmd.upper(), None)
            if meth is None:
                self.handle_unknown()
            else:
                try:
                    meth(*tokens)
                except Exception as e:
                    raise ValueError("command failed: {!r}".format(line)) from e
                else:
                    if self.in_body:
                        self.body_callback = meth, tokens
                        self.body = []

    def expect_body(self):
        """Flag that the client is expected to post a request body"""
        self.in_body = True

    def push_data(self, data):
        """Push some binary data"""
        self._push_data(data)

    def push_lit(self, lit):
        """Push a string literal"""
        lit = textwrap.dedent(lit)
        lit = "\r\n".join(lit.splitlines()) + "\r\n"
        lit = lit.encode('utf-8')
        self.push_data(lit)

    def handle_unknown(self):
        self.push_lit("500 What?")

    def handle_welcome(self):
        self.push_lit(self.welcome)

    def handle_QUIT(self):
        self.push_lit("205 Bye!")

    def handle_DATE(self):
        self.push_lit("111 20100914001155")

    def handle_GROUP(self, group):
        if group == "fr.comp.lang.python":
            self.push_lit("211 486 761 1265 fr.comp.lang.python")
        else:
            self.push_lit("411 No such group {}".format(group))

    def handle_HELP(self):
        self.push_lit("""\
            100 Legal commands
              authinfo user Name|pass Password|generic <prog> <args>
              date
              help
            Report problems to <root@example.org>
            .""")

    def handle_STAT(self, message_spec=None):
        if message_spec is None:
            self.push_lit("412 No newsgroup selected")
        elif message_spec == "3000234":
            self.push_lit("223 3000234 <45223423@example.com>")
        elif message_spec == "<45223423@example.com>":
            self.push_lit("223 0 <45223423@example.com>")
        else:
            self.push_lit("430 No Such Article Found")

    def handle_NEXT(self):
        self.push_lit("223 3000237 <668929@example.org> retrieved")

    def handle_LAST(self):
        self.push_lit("223 3000234 <45223423@example.com> retrieved")

    def handle_LIST(self, action=None, param=None):
        if action is None:
            self.push_lit("""\
                215 Newsgroups in form "group high low flags".
                comp.lang.python 0000052340 0000002828 y
                comp.lang.python.announce 0000001153 0000000993 m
                free.it.comp.lang.python 0000000002 0000000002 y
                fr.comp.lang.python 0000001254 0000000760 y
                free.it.comp.lang.python.learner 0000000000 0000000001 y
                tw.bbs.comp.lang.python 0000000304 0000000304 y
                .""")
        elif action == "ACTIVE":
            if param == "*distutils*":
                self.push_lit("""\
                    215 Newsgroups in form "group high low flags"
                    gmane.comp.python.distutils.devel 0000014104 0000000001 m
                    gmane.comp.python.distutils.cvs 0000000000 0000000001 m
                    .""")
            else:
                self.push_lit("""\
                    215 Newsgroups in form "group high low flags"
                    .""")
        elif action == "OVERVIEW.FMT":
            self.push_lit("""\
                215 Order of fields in overview database.
                Subject:
                From:
                Date:
                Message-ID:
                References:
                Bytes:
                Lines:
                Xref:full
                .""")
        elif action == "NEWSGROUPS":
            assert param is not None
            if param == "comp.lang.python":
                self.push_lit("""\
                    215 Descriptions in form "group description".
                    comp.lang.python\tThe Python computer language.
                    .""")
            elif param == "comp.lang.python*":
                self.push_lit("""\
                    215 Descriptions in form "group description".
                    comp.lang.python.announce\tAnnouncements about the Python language. (Moderated)
                    comp.lang.python\tThe Python computer language.
                    .""")
            else:
                self.push_lit("""\
                    215 Descriptions in form "group description".
                    .""")
        else:
            self.push_lit('501 Unknown LIST keyword')

    def handle_NEWNEWS(self, group, date_str, time_str):
        # We hard code different return messages depending on passed
        # argument and date syntax.
        if (group == "comp.lang.python" and date_str == "20100913"
            and time_str == "082004"):
            # Date was passed in RFC 3977 format (NNTP "v2")
            self.push_lit("""\
                230 list of newsarticles (NNTP v2) created after Mon Sep 13 08:20:04 2010 follows
                <a4929a40-6328-491a-aaaf-cb79ed7309a2@q2g2000vbk.googlegroups.com>
                <f30c0419-f549-4218-848f-d7d0131da931@y3g2000vbm.googlegroups.com>
                .""")
        elif (group == "comp.lang.python" and date_str == "100913"
            and time_str == "082004"):
            # Date was passed in RFC 977 format (NNTP "v1")
            self.push_lit("""\
                230 list of newsarticles (NNTP v1) created after Mon Sep 13 08:20:04 2010 follows
                <a4929a40-6328-491a-aaaf-cb79ed7309a2@q2g2000vbk.googlegroups.com>
                <f30c0419-f549-4218-848f-d7d0131da931@y3g2000vbm.googlegroups.com>
                .""")
        elif (group == 'comp.lang.python' and
              date_str in ('20100101', '100101') and
              time_str == '090000'):
            self.push_lit('too long line' * 3000 +
                          '\n.')
        else:
            self.push_lit("""\
                230 An empty list of newsarticles follows
                .""")
        # (Note for experiments: many servers disable NEWNEWS.
        #  As of this writing, sicinfo3.epfl.ch doesn't.)

    def handle_XOVER(self, message_spec):
        if message_spec == "57-59":
            self.push_lit(
                "224 Overview information for 57-58 follows\n"
                "57\tRe: ANN: New Plone book with strong Python (and Zope) themes throughout"
                    "\tDoug Hellmann <doug.hellmann-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>"
                    "\tSat, 19 Jun 2010 18:04:08 -0400"
                    "\t<4FD05F05-F98B-44DC-8111-C6009C925F0C@gmail.com>"
                    "\t<hvalf7$ort$1@dough.gmane.org>\t7103\t16"
                    "\tXref: news.gmane.org gmane.comp.python.authors:57"
                    "\n"
                "58\tLooking for a few good bloggers"
                    "\tDoug Hellmann <doug.hellmann-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>"
                    "\tThu, 22 Jul 2010 09:14:14 -0400"
                    "\t<A29863FA-F388-40C3-AA25-0FD06B09B5BF@gmail.com>"
                    "\t\t6683\t16"
                    "\t"
                    "\n"
                # A UTF-8 overview line from fr.comp.lang.python
                "59\tRe: Message d'erreur incompréhensible (par moi)"
                    "\tEric Brunel <eric.brunel@pragmadev.nospam.com>"
                    "\tWed, 15 Sep 2010 18:09:15 +0200"
                    "\t<eric.brunel-2B8B56.18091515092010@news.wanadoo.fr>"
                    "\t<4c90ec87$0$32425$ba4acef3@reader.news.orange.fr>\t1641\t27"
                    "\tXref: saria.nerim.net fr.comp.lang.python:1265"
                    "\n"
                ".\n")
        else:
            self.push_lit("""\
                224 No articles
                .""")

    def handle_POST(self, *, body=None):
        if body is None:
            if self.allow_posting:
                self.push_lit("340 Input article; end with <CR-LF>.<CR-LF>")
                self.expect_body()
            else:
                self.push_lit("440 Posting not permitted")
        else:
            assert self.allow_posting
            self.push_lit("240 Article received OK")
            self.posted_body = body

    def handle_IHAVE(self, message_id, *, body=None):
        if body is None:
            if (self.allow_posting and
                message_id == "<i.am.an.article.you.will.want@example.com>"):
                self.push_lit("335 Send it; end with <CR-LF>.<CR-LF>")
                self.expect_body()
            else:
                self.push_lit("435 Article not wanted")
        else:
            assert self.allow_posting
            self.push_lit("235 Article transferred OK")
            self.posted_body = body

    sample_head = """\
        From: "Demo User" <nobody@example.net>
        Subject: I am just a test article
        Content-Type: text/plain; charset=UTF-8; format=flowed
        Message-ID: <i.am.an.article.you.will.want@example.com>"""

    sample_body = """\
        This is just a test article.
        ..Here is a dot-starting line.

        -- Signed by Andr\xe9."""

    sample_article = sample_head + "\n\n" + sample_body

    def handle_ARTICLE(self, message_spec=None):
        if message_spec is None:
            self.push_lit("220 3000237 <45223423@example.com>")
        elif message_spec == "<45223423@example.com>":
            self.push_lit("220 0 <45223423@example.com>")
        elif message_spec == "3000234":
            self.push_lit("220 3000234 <45223423@example.com>")
        else:
            self.push_lit("430 No Such Article Found")
            return
        self.push_lit(self.sample_article)
        self.push_lit(".")

    def handle_HEAD(self, message_spec=None):
        if message_spec is None:
            self.push_lit("221 3000237 <45223423@example.com>")
        elif message_spec == "<45223423@example.com>":
            self.push_lit("221 0 <45223423@example.com>")
        elif message_spec == "3000234":
            self.push_lit("221 3000234 <45223423@example.com>")
        else:
            self.push_lit("430 No Such Article Found")
            return
        self.push_lit(self.sample_head)
        self.push_lit(".")

    def handle_BODY(self, message_spec=None):
        if message_spec is None:
            self.push_lit("222 3000237 <45223423@example.com>")
        elif message_spec == "<45223423@example.com>":
            self.push_lit("222 0 <45223423@example.com>")
        elif message_spec == "3000234":
            self.push_lit("222 3000234 <45223423@example.com>")
        else:
            self.push_lit("430 No Such Article Found")
            return
        self.push_lit(self.sample_body)
        self.push_lit(".")

    def handle_AUTHINFO(self, cred_type, data):
        if self._logged_in:
            self.push_lit('502 Already Logged In')
        elif cred_type == 'user':
            if self._user_sent:
                self.push_lit('482 User Credential Already Sent')
            else:
                self.push_lit('381 Password Required')
                self._user_sent = True
        elif cred_type == 'pass':
            self.push_lit('281 Login Successful')
            self._logged_in = True
        else:
            raise Exception('Unknown cred type {}'.format(cred_type))


class NNTPv2Handler(NNTPv1Handler):
    """A handler for RFC 3977 (NNTP "v2")"""

    def handle_CAPABILITIES(self):
        fmt = """\
            101 Capability list:
            VERSION 2 3
            IMPLEMENTATION INN 2.5.1{}
            HDR
            LIST ACTIVE ACTIVE.TIMES DISTRIB.PATS HEADERS NEWSGROUPS OVERVIEW.FMT
            OVER
            POST
            READER
            ."""

        if not self._logged_in:
            self.push_lit(fmt.format('\n            AUTHINFO USER'))
        else:
            self.push_lit(fmt.format(''))

    def handle_MODE(self, _):
        raise Exception('MODE READER sent despite READER has been advertised')

    def handle_OVER(self, message_spec=None):
        return self.handle_XOVER(message_spec)


class CapsAfterLoginNNTPv2Handler(NNTPv2Handler):
    """A handler that allows CAPABILITIES only after login"""

    def handle_CAPABILITIES(self):
        if not self._logged_in:
            self.push_lit('480 You must log in.')
        else:
            super().handle_CAPABILITIES()


class ModeSwitchingNNTPv2Handler(NNTPv2Handler):
    """A server that starts in transit mode"""

    def __init__(self):
        self._switched = False

    def handle_CAPABILITIES(self):
        fmt = """\
            101 Capability list:
            VERSION 2 3
            IMPLEMENTATION INN 2.5.1
            HDR
            LIST ACTIVE ACTIVE.TIMES DISTRIB.PATS HEADERS NEWSGROUPS OVERVIEW.FMT
            OVER
            POST
            {}READER
            ."""
        if self._switched:
            self.push_lit(fmt.format(''))
        else:
            self.push_lit(fmt.format('MODE-'))

    def handle_MODE(self, what):
        assert not self._switched and what == 'reader'
        self._switched = True
        self.push_lit('200 Posting allowed')


class NNTPv1v2TestsMixin:

    def setUp(self):
        super().setUp()

    def test_welcome(self):
        self.assertEqual(self.server.welcome, self.handler.welcome)

    def test_authinfo(self):
        if self.nntp_version == 2:
            self.assertIn('AUTHINFO', self.server._caps)
        self.server.login('testuser', 'testpw')
        # if AUTHINFO is gone from _caps we also know that getcapabilities()
        # has been called after login as it should
        self.assertNotIn('AUTHINFO', self.server._caps)

    def test_date(self):
        resp, date = self.server.date()
        self.assertEqual(resp, "111 20100914001155")
        self.assertEqual(date, datetime.datetime(2010, 9, 14, 0, 11, 55))

    def test_quit(self):
        self.assertFalse(self.sio.closed)
        resp = self.server.quit()
        self.assertEqual(resp, "205 Bye!")
        self.assertTrue(self.sio.closed)

    def test_help(self):
        resp, help = self.server.help()
        self.assertEqual(resp, "100 Legal commands")
        self.assertEqual(help, [
            '  authinfo user Name|pass Password|generic <prog> <args>',
            '  date',
            '  help',
            'Report problems to <root@example.org>',
        ])

    def test_list(self):
        resp, groups = self.server.list()
        self.assertEqual(len(groups), 6)
        g = groups[1]
        self.assertEqual(g,
            GroupInfo("comp.lang.python.announce", "0000001153",
                      "0000000993", "m"))
        resp, groups = self.server.list("*distutils*")
        self.assertEqual(len(groups), 2)
        g = groups[0]
        self.assertEqual(g,
            GroupInfo("gmane.comp.python.distutils.devel", "0000014104",
                      "0000000001", "m"))

    def test_stat(self):
        resp, art_num, message_id = self.server.stat(3000234)
        self.assertEqual(resp, "223 3000234 <45223423@example.com>")
        self.assertEqual(art_num, 3000234)
        self.assertEqual(message_id, "<45223423@example.com>")
        resp, art_num, message_id = self.server.stat("<45223423@example.com>")
        self.assertEqual(resp, "223 0 <45223423@example.com>")
        self.assertEqual(art_num, 0)
        self.assertEqual(message_id, "<45223423@example.com>")
        with self.assertRaises(nntplib.NNTPTemporaryError) as cm:
            self.server.stat("<non.existent.id>")
        self.assertEqual(cm.exception.response, "430 No Such Article Found")
        with self.assertRaises(nntplib.NNTPTemporaryError) as cm:
            self.server.stat()
        self.assertEqual(cm.exception.response, "412 No newsgroup selected")

    def test_next(self):
        resp, art_num, message_id = self.server.next()
        self.assertEqual(resp, "223 3000237 <668929@example.org> retrieved")
        self.assertEqual(art_num, 3000237)
        self.assertEqual(message_id, "<668929@example.org>")

    def test_last(self):
        resp, art_num, message_id = self.server.last()
        self.assertEqual(resp, "223 3000234 <45223423@example.com> retrieved")
        self.assertEqual(art_num, 3000234)
        self.assertEqual(message_id, "<45223423@example.com>")

    def test_description(self):
        desc = self.server.description("comp.lang.python")
        self.assertEqual(desc, "The Python computer language.")
        desc = self.server.description("comp.lang.pythonx")
        self.assertEqual(desc, "")

    def test_descriptions(self):
        resp, groups = self.server.descriptions("comp.lang.python")
        self.assertEqual(resp, '215 Descriptions in form "group description".')
        self.assertEqual(groups, {
            "comp.lang.python": "The Python computer language.",
            })
        resp, groups = self.server.descriptions("comp.lang.python*")
        self.assertEqual(groups, {
            "comp.lang.python": "The Python computer language.",
            "comp.lang.python.announce": "Announcements about the Python language. (Moderated)",
            })
        resp, groups = self.server.descriptions("comp.lang.pythonx")
        self.assertEqual(groups, {})

    def test_group(self):
        resp, count, first, last, group = self.server.group("fr.comp.lang.python")
        self.assertTrue(resp.startswith("211 "), resp)
        self.assertEqual(first, 761)
        self.assertEqual(last, 1265)
        self.assertEqual(count, 486)
        self.assertEqual(group, "fr.comp.lang.python")
        with self.assertRaises(nntplib.NNTPTemporaryError) as cm:
            self.server.group("comp.lang.python.devel")
        exc = cm.exception
        self.assertTrue(exc.response.startswith("411 No such group"),
                        exc.response)

    def test_newnews(self):
        # NEWNEWS comp.lang.python [20]100913 082004
        dt = datetime.datetime(2010, 9, 13, 8, 20, 4)
        resp, ids = self.server.newnews("comp.lang.python", dt)
        expected = (
            "230 list of newsarticles (NNTP v{0}) "
            "created after Mon Sep 13 08:20:04 2010 follows"
            ).format(self.nntp_version)
        self.assertEqual(resp, expected)
        self.assertEqual(ids, [
            "<a4929a40-6328-491a-aaaf-cb79ed7309a2@q2g2000vbk.googlegroups.com>",
            "<f30c0419-f549-4218-848f-d7d0131da931@y3g2000vbm.googlegroups.com>",
            ])
        # NEWNEWS fr.comp.lang.python [20]100913 082004
        dt = datetime.datetime(2010, 9, 13, 8, 20, 4)
        resp, ids = self.server.newnews("fr.comp.lang.python", dt)
        self.assertEqual(resp, "230 An empty list of newsarticles follows")
        self.assertEqual(ids, [])

    def _check_article_body(self, lines):
        self.assertEqual(len(lines), 4)
        self.assertEqual(lines[-1].decode('utf-8'), "-- Signed by André.")
        self.assertEqual(lines[-2], b"")
        self.assertEqual(lines[-3], b".Here is a dot-starting line.")
        self.assertEqual(lines[-4], b"This is just a test article.")

    def _check_article_head(self, lines):
        self.assertEqual(len(lines), 4)
        self.assertEqual(lines[0], b'From: "Demo User" <nobody@example.net>')
        self.assertEqual(lines[3], b"Message-ID: <i.am.an.article.you.will.want@example.com>")

    def _check_article_data(self, lines):
        self.assertEqual(len(lines), 9)
        self._check_article_head(lines[:4])
        self._check_article_body(lines[-4:])
        self.assertEqual(lines[4], b"")

    def test_article(self):
        # ARTICLE
        resp, info = self.server.article()
        self.assertEqual(resp, "220 3000237 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000237)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_data(lines)
        # ARTICLE num
        resp, info = self.server.article(3000234)
        self.assertEqual(resp, "220 3000234 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000234)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_data(lines)
        # ARTICLE id
        resp, info = self.server.article("<45223423@example.com>")
        self.assertEqual(resp, "220 0 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 0)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_data(lines)
        # Non-existent id
        with self.assertRaises(nntplib.NNTPTemporaryError) as cm:
            self.server.article("<non-existent@example.com>")
        self.assertEqual(cm.exception.response, "430 No Such Article Found")

    def test_article_file(self):
        # With a "file" argument
        f = io.BytesIO()
        resp, info = self.server.article(file=f)
        self.assertEqual(resp, "220 3000237 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000237)
        self.assertEqual(message_id, "<45223423@example.com>")
        self.assertEqual(lines, [])
        data = f.getvalue()
        self.assertTrue(data.startswith(
            b'From: "Demo User" <nobody@example.net>\r\n'
            b'Subject: I am just a test article\r\n'
            ), ascii(data))
        self.assertTrue(data.endswith(
            b'This is just a test article.\r\n'
            b'.Here is a dot-starting line.\r\n'
            b'\r\n'
            b'-- Signed by Andr\xc3\xa9.\r\n'
            ), ascii(data))

    def test_head(self):
        # HEAD
        resp, info = self.server.head()
        self.assertEqual(resp, "221 3000237 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000237)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_head(lines)
        # HEAD num
        resp, info = self.server.head(3000234)
        self.assertEqual(resp, "221 3000234 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000234)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_head(lines)
        # HEAD id
        resp, info = self.server.head("<45223423@example.com>")
        self.assertEqual(resp, "221 0 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 0)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_head(lines)
        # Non-existent id
        with self.assertRaises(nntplib.NNTPTemporaryError) as cm:
            self.server.head("<non-existent@example.com>")
        self.assertEqual(cm.exception.response, "430 No Such Article Found")

    def test_head_file(self):
        f = io.BytesIO()
        resp, info = self.server.head(file=f)
        self.assertEqual(resp, "221 3000237 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000237)
        self.assertEqual(message_id, "<45223423@example.com>")
        self.assertEqual(lines, [])
        data = f.getvalue()
        self.assertTrue(data.startswith(
            b'From: "Demo User" <nobody@example.net>\r\n'
            b'Subject: I am just a test article\r\n'
            ), ascii(data))
        self.assertFalse(data.endswith(
            b'This is just a test article.\r\n'
            b'.Here is a dot-starting line.\r\n'
            b'\r\n'
            b'-- Signed by Andr\xc3\xa9.\r\n'
            ), ascii(data))

    def test_body(self):
        # BODY
        resp, info = self.server.body()
        self.assertEqual(resp, "222 3000237 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000237)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_body(lines)
        # BODY num
        resp, info = self.server.body(3000234)
        self.assertEqual(resp, "222 3000234 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000234)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_body(lines)
        # BODY id
        resp, info = self.server.body("<45223423@example.com>")
        self.assertEqual(resp, "222 0 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 0)
        self.assertEqual(message_id, "<45223423@example.com>")
        self._check_article_body(lines)
        # Non-existent id
        with self.assertRaises(nntplib.NNTPTemporaryError) as cm:
            self.server.body("<non-existent@example.com>")
        self.assertEqual(cm.exception.response, "430 No Such Article Found")

    def test_body_file(self):
        f = io.BytesIO()
        resp, info = self.server.body(file=f)
        self.assertEqual(resp, "222 3000237 <45223423@example.com>")
        art_num, message_id, lines = info
        self.assertEqual(art_num, 3000237)
        self.assertEqual(message_id, "<45223423@example.com>")
        self.assertEqual(lines, [])
        data = f.getvalue()
        self.assertFalse(data.startswith(
            b'From: "Demo User" <nobody@example.net>\r\n'
            b'Subject: I am just a test article\r\n'
            ), ascii(data))
        self.assertTrue(data.endswith(
            b'This is just a test article.\r\n'
            b'.Here is a dot-starting line.\r\n'
            b'\r\n'
            b'-- Signed by Andr\xc3\xa9.\r\n'
            ), ascii(data))

    def check_over_xover_resp(self, resp, overviews):
        self.assertTrue(resp.startswith("224 "), resp)
        self.assertEqual(len(overviews), 3)
        art_num, over = overviews[0]
        self.assertEqual(art_num, 57)
        self.assertEqual(over, {
            "from": "Doug Hellmann <doug.hellmann-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>",
            "subject": "Re: ANN: New Plone book with strong Python (and Zope) themes throughout",
            "date": "Sat, 19 Jun 2010 18:04:08 -0400",
            "message-id": "<4FD05F05-F98B-44DC-8111-C6009C925F0C@gmail.com>",
            "references": "<hvalf7$ort$1@dough.gmane.org>",
            ":bytes": "7103",
            ":lines": "16",
            "xref": "news.gmane.org gmane.comp.python.authors:57"
            })
        art_num, over = overviews[1]
        self.assertEqual(over["xref"], None)
        art_num, over = overviews[2]
        self.assertEqual(over["subject"],
                         "Re: Message d'erreur incompréhensible (par moi)")

    def test_xover(self):
        resp, overviews = self.server.xover(57, 59)
        self.check_over_xover_resp(resp, overviews)

    def test_over(self):
        # In NNTP "v1", this will fallback on XOVER
        resp, overviews = self.server.over((57, 59))
        self.check_over_xover_resp(resp, overviews)

    sample_post = (
        b'From: "Demo User" <nobody@example.net>\r\n'
        b'Subject: I am just a test article\r\n'
        b'Content-Type: text/plain; charset=UTF-8; format=flowed\r\n'
        b'Message-ID: <i.am.an.article.you.will.want@example.com>\r\n'
        b'\r\n'
        b'This is just a test article.\r\n'
        b'.Here is a dot-starting line.\r\n'
        b'\r\n'
        b'-- Signed by Andr\xc3\xa9.\r\n'
    )

    def _check_posted_body(self):
        # Check the raw body as received by the server
        lines = self.handler.posted_body
        # One additional line for the "." terminator
        self.assertEqual(len(lines), 10)
        self.assertEqual(lines[-1], b'.\r\n')
        self.assertEqual(lines[-2], b'-- Signed by Andr\xc3\xa9.\r\n')
        self.assertEqual(lines[-3], b'\r\n')
        self.assertEqual(lines[-4], b'..Here is a dot-starting line.\r\n')
        self.assertEqual(lines[0], b'From: "Demo User" <nobody@example.net>\r\n')

    def _check_post_ihave_sub(self, func, *args, file_factory):
        # First the prepared post with CRLF endings
        post = self.sample_post
        func_args = args + (file_factory(post),)
        self.handler.posted_body = None
        resp = func(*func_args)
        self._check_posted_body()
        # Then the same post with "normal" line endings - they should be
        # converted by NNTP.post and NNTP.ihave.
        post = self.sample_post.replace(b"\r\n", b"\n")
        func_args = args + (file_factory(post),)
        self.handler.posted_body = None
        resp = func(*func_args)
        self._check_posted_body()
        return resp

    def check_post_ihave(self, func, success_resp, *args):
        # With a bytes object
        resp = self._check_post_ihave_sub(func, *args, file_factory=bytes)
        self.assertEqual(resp, success_resp)
        # With a bytearray object
        resp = self._check_post_ihave_sub(func, *args, file_factory=bytearray)
        self.assertEqual(resp, success_resp)
        # With a file object
        resp = self._check_post_ihave_sub(func, *args, file_factory=io.BytesIO)
        self.assertEqual(resp, success_resp)
        # With an iterable of terminated lines
        def iterlines(b):
            return iter(b.splitlines(keepends=True))
        resp = self._check_post_ihave_sub(func, *args, file_factory=iterlines)
        self.assertEqual(resp, success_resp)
        # With an iterable of non-terminated lines
        def iterlines(b):
            return iter(b.splitlines(keepends=False))
        resp = self._check_post_ihave_sub(func, *args, file_factory=iterlines)
        self.assertEqual(resp, success_resp)

    def test_post(self):
        self.check_post_ihave(self.server.post, "240 Article received OK")
        self.handler.allow_posting = False
        with self.assertRaises(nntplib.NNTPTemporaryError) as cm:
            self.server.post(self.sample_post)
        self.assertEqual(cm.exception.response,
                         "440 Posting not permitted")

    def test_ihave(self):
        self.check_post_ihave(self.server.ihave, "235 Article transferred OK",
                              "<i.am.an.article.you.will.want@example.com>")
        with self.assertRaises(nntplib.NNTPTemporaryError) as cm:
            self.server.ihave("<another.message.id>", self.sample_post)
        self.assertEqual(cm.exception.response,
                         "435 Article not wanted")

    def test_too_long_lines(self):
        dt = datetime.datetime(2010, 1, 1, 9, 0, 0)
        self.assertRaises(nntplib.NNTPDataError,
                          self.server.newnews, "comp.lang.python", dt)


class NNTPv1Tests(NNTPv1v2TestsMixin, MockedNNTPTestsMixin, unittest.TestCase):
    """Tests an NNTP v1 server (no capabilities)."""

    nntp_version = 1
    handler_class = NNTPv1Handler

    def test_caps(self):
        caps = self.server.getcapabilities()
        self.assertEqual(caps, {})
        self.assertEqual(self.server.nntp_version, 1)
        self.assertEqual(self.server.nntp_implementation, None)


class NNTPv2Tests(NNTPv1v2TestsMixin, MockedNNTPTestsMixin, unittest.TestCase):
    """Tests an NNTP v2 server (with capabilities)."""

    nntp_version = 2
    handler_class = NNTPv2Handler

    def test_caps(self):
        caps = self.server.getcapabilities()
        self.assertEqual(caps, {
            'VERSION': ['2', '3'],
            'IMPLEMENTATION': ['INN', '2.5.1'],
            'AUTHINFO': ['USER'],
            'HDR': [],
            'LIST': ['ACTIVE', 'ACTIVE.TIMES', 'DISTRIB.PATS',
                     'HEADERS', 'NEWSGROUPS', 'OVERVIEW.FMT'],
            'OVER': [],
            'POST': [],
            'READER': [],
            })
        self.assertEqual(self.server.nntp_version, 3)
        self.assertEqual(self.server.nntp_implementation, 'INN 2.5.1')


class CapsAfterLoginNNTPv2Tests(MockedNNTPTestsMixin, unittest.TestCase):
    """Tests a probably NNTP v2 server with capabilities only after login."""

    nntp_version = 2
    handler_class = CapsAfterLoginNNTPv2Handler

    def test_caps_only_after_login(self):
        self.assertEqual(self.server._caps, {})
        self.server.login('testuser', 'testpw')
        self.assertIn('VERSION', self.server._caps)


class SendReaderNNTPv2Tests(MockedNNTPWithReaderModeMixin,
        unittest.TestCase):
    """Same tests as for v2 but we tell NTTP to send MODE READER to a server
    that isn't in READER mode by default."""

    nntp_version = 2
    handler_class = ModeSwitchingNNTPv2Handler

    def test_we_are_in_reader_mode_after_connect(self):
        self.assertIn('READER', self.server._caps)


class MiscTests(unittest.TestCase):

    def test_decode_header(self):
        def gives(a, b):
            self.assertEqual(nntplib.decode_header(a), b)
        gives("" , "")
        gives("a plain header", "a plain header")
        gives(" with extra  spaces ", " with extra  spaces ")
        gives("=?ISO-8859-15?Q?D=E9buter_en_Python?=", "Débuter en Python")
        gives("=?utf-8?q?Re=3A_=5Bsqlite=5D_probl=C3=A8me_avec_ORDER_BY_sur_des_cha?="
              " =?utf-8?q?=C3=AEnes_de_caract=C3=A8res_accentu=C3=A9es?=",
              "Re: [sqlite] problème avec ORDER BY sur des chaînes de caractères accentuées")
        gives("Re: =?UTF-8?B?cHJvYmzDqG1lIGRlIG1hdHJpY2U=?=",
              "Re: problème de matrice")
        # A natively utf-8 header (found in the real world!)
        gives("Re: Message d'erreur incompréhensible (par moi)",
              "Re: Message d'erreur incompréhensible (par moi)")

    def test_parse_overview_fmt(self):
        # The minimal (default) response
        lines = ["Subject:", "From:", "Date:", "Message-ID:",
                 "References:", ":bytes", ":lines"]
        self.assertEqual(nntplib._parse_overview_fmt(lines),
            ["subject", "from", "date", "message-id", "references",
             ":bytes", ":lines"])
        # The minimal response using alternative names
        lines = ["Subject:", "From:", "Date:", "Message-ID:",
                 "References:", "Bytes:", "Lines:"]
        self.assertEqual(nntplib._parse_overview_fmt(lines),
            ["subject", "from", "date", "message-id", "references",
             ":bytes", ":lines"])
        # Variations in casing
        lines = ["subject:", "FROM:", "DaTe:", "message-ID:",
                 "References:", "BYTES:", "Lines:"]
        self.assertEqual(nntplib._parse_overview_fmt(lines),
            ["subject", "from", "date", "message-id", "references",
             ":bytes", ":lines"])
        # First example from RFC 3977
        lines = ["Subject:", "From:", "Date:", "Message-ID:",
                 "References:", ":bytes", ":lines", "Xref:full",
                 "Distribution:full"]
        self.assertEqual(nntplib._parse_overview_fmt(lines),
            ["subject", "from", "date", "message-id", "references",
             ":bytes", ":lines", "xref", "distribution"])
        # Second example from RFC 3977
        lines = ["Subject:", "From:", "Date:", "Message-ID:",
                 "References:", "Bytes:", "Lines:", "Xref:FULL",
                 "Distribution:FULL"]
        self.assertEqual(nntplib._parse_overview_fmt(lines),
            ["subject", "from", "date", "message-id", "references",
             ":bytes", ":lines", "xref", "distribution"])
        # A classic response from INN
        lines = ["Subject:", "From:", "Date:", "Message-ID:",
                 "References:", "Bytes:", "Lines:", "Xref:full"]
        self.assertEqual(nntplib._parse_overview_fmt(lines),
            ["subject", "from", "date", "message-id", "references",
             ":bytes", ":lines", "xref"])

    def test_parse_overview(self):
        fmt = nntplib._DEFAULT_OVERVIEW_FMT + ["xref"]
        # First example from RFC 3977
        lines = [
            '3000234\tI am just a test article\t"Demo User" '
            '<nobody@example.com>\t6 Oct 1998 04:38:40 -0500\t'
            '<45223423@example.com>\t<45454@example.net>\t1234\t'
            '17\tXref: news.example.com misc.test:3000363',
        ]
        overview = nntplib._parse_overview(lines, fmt)
        (art_num, fields), = overview
        self.assertEqual(art_num, 3000234)
        self.assertEqual(fields, {
            'subject': 'I am just a test article',
            'from': '"Demo User" <nobody@example.com>',
            'date': '6 Oct 1998 04:38:40 -0500',
            'message-id': '<45223423@example.com>',
            'references': '<45454@example.net>',
            ':bytes': '1234',
            ':lines': '17',
            'xref': 'news.example.com misc.test:3000363',
        })
        # Second example; here the "Xref" field is totally absent (including
        # the header name) and comes out as None
        lines = [
            '3000234\tI am just a test article\t"Demo User" '
            '<nobody@example.com>\t6 Oct 1998 04:38:40 -0500\t'
            '<45223423@example.com>\t<45454@example.net>\t1234\t'
            '17\t\t',
        ]
        overview = nntplib._parse_overview(lines, fmt)
        (art_num, fields), = overview
        self.assertEqual(fields['xref'], None)
        # Third example; the "Xref" is an empty string, while "references"
        # is a single space.
        lines = [
            '3000234\tI am just a test article\t"Demo User" '
            '<nobody@example.com>\t6 Oct 1998 04:38:40 -0500\t'
            '<45223423@example.com>\t \t1234\t'
            '17\tXref: \t',
        ]
        overview = nntplib._parse_overview(lines, fmt)
        (art_num, fields), = overview
        self.assertEqual(fields['references'], ' ')
        self.assertEqual(fields['xref'], '')

    def test_parse_datetime(self):
        def gives(a, b, *c):
            self.assertEqual(nntplib._parse_datetime(a, b),
                             datetime.datetime(*c))
        # Output of DATE command
        gives("19990623135624", None, 1999, 6, 23, 13, 56, 24)
        # Variations
        gives("19990623", "135624", 1999, 6, 23, 13, 56, 24)
        gives("990623", "135624", 1999, 6, 23, 13, 56, 24)
        gives("090623", "135624", 2009, 6, 23, 13, 56, 24)

    def test_unparse_datetime(self):
        # Test non-legacy mode
        # 1) with a datetime
        def gives(y, M, d, h, m, s, date_str, time_str):
            dt = datetime.datetime(y, M, d, h, m, s)
            self.assertEqual(nntplib._unparse_datetime(dt),
                             (date_str, time_str))
            self.assertEqual(nntplib._unparse_datetime(dt, False),
                             (date_str, time_str))
        gives(1999, 6, 23, 13, 56, 24, "19990623", "135624")
        gives(2000, 6, 23, 13, 56, 24, "20000623", "135624")
        gives(2010, 6, 5, 1, 2, 3, "20100605", "010203")
        # 2) with a date
        def gives(y, M, d, date_str, time_str):
            dt = datetime.date(y, M, d)
            self.assertEqual(nntplib._unparse_datetime(dt),
                             (date_str, time_str))
            self.assertEqual(nntplib._unparse_datetime(dt, False),
                             (date_str, time_str))
        gives(1999, 6, 23, "19990623", "000000")
        gives(2000, 6, 23, "20000623", "000000")
        gives(2010, 6, 5, "20100605", "000000")

    def test_unparse_datetime_legacy(self):
        # Test legacy mode (RFC 977)
        # 1) with a datetime
        def gives(y, M, d, h, m, s, date_str, time_str):
            dt = datetime.datetime(y, M, d, h, m, s)
            self.assertEqual(nntplib._unparse_datetime(dt, True),
                             (date_str, time_str))
        gives(1999, 6, 23, 13, 56, 24, "990623", "135624")
        gives(2000, 6, 23, 13, 56, 24, "000623", "135624")
        gives(2010, 6, 5, 1, 2, 3, "100605", "010203")
        # 2) with a date
        def gives(y, M, d, date_str, time_str):
            dt = datetime.date(y, M, d)
            self.assertEqual(nntplib._unparse_datetime(dt, True),
                             (date_str, time_str))
        gives(1999, 6, 23, "990623", "000000")
        gives(2000, 6, 23, "000623", "000000")
        gives(2010, 6, 5, "100605", "000000")

    @unittest.skipUnless(ssl, 'requires SSL support')
    def test_ssl_support(self):
        self.assertTrue(hasattr(nntplib, 'NNTP_SSL'))


class PublicAPITests(unittest.TestCase):
    """Ensures that the correct values are exposed in the public API."""

    def test_module_all_attribute(self):
        self.assertTrue(hasattr(nntplib, '__all__'))
        target_api = ['NNTP', 'NNTPError', 'NNTPReplyError',
                      'NNTPTemporaryError', 'NNTPPermanentError',
                      'NNTPProtocolError', 'NNTPDataError', 'decode_header']
        if ssl is not None:
            target_api.append('NNTP_SSL')
        self.assertEqual(set(nntplib.__all__), set(target_api))

class MockSocketTests(unittest.TestCase):
    """Tests involving a mock socket object

    Used where the _NNTPServerIO file object is not enough."""

    nntp_class = nntplib.NNTP

    def check_constructor_error_conditions(
            self, handler_class,
            expected_error_type, expected_error_msg,
            login=None, password=None):

        class mock_socket_module:
            def create_connection(address, timeout):
                return MockSocket()

        class MockSocket:
            def close(self):
                nonlocal socket_closed
                socket_closed = True

            def makefile(socket, mode):
                handler = handler_class()
                _, file = make_mock_file(handler)
                files.append(file)
                return file

        socket_closed = False
        files = []
        with patch('nntplib.socket', mock_socket_module), \
             self.assertRaisesRegex(expected_error_type, expected_error_msg):
            self.nntp_class('dummy', user=login, password=password)
        self.assertTrue(socket_closed)
        for f in files:
            self.assertTrue(f.closed)

    def test_bad_welcome(self):
        #Test a bad welcome message
        class Handler(NNTPv1Handler):
            welcome = 'Bad Welcome'
        self.check_constructor_error_conditions(
            Handler, nntplib.NNTPProtocolError, Handler.welcome)

    def test_service_temporarily_unavailable(self):
        #Test service temporarily unavailable
        class Handler(NNTPv1Handler):
            welcome = '400 Service temporarily unavailable'
        self.check_constructor_error_conditions(
            Handler, nntplib.NNTPTemporaryError, Handler.welcome)

    def test_service_permanently_unavailable(self):
        #Test service permanently unavailable
        class Handler(NNTPv1Handler):
            welcome = '502 Service permanently unavailable'
        self.check_constructor_error_conditions(
            Handler, nntplib.NNTPPermanentError, Handler.welcome)

    def test_bad_capabilities(self):
        #Test a bad capabilities response
        class Handler(NNTPv1Handler):
            def handle_CAPABILITIES(self):
                self.push_lit(capabilities_response)
        capabilities_response = '201 bad capability'
        self.check_constructor_error_conditions(
            Handler, nntplib.NNTPReplyError, capabilities_response)

    def test_login_aborted(self):
        #Test a bad authinfo response
        login = 't@e.com'
        password = 'python'
        class Handler(NNTPv1Handler):
            def handle_AUTHINFO(self, *args):
                self.push_lit(authinfo_response)
        authinfo_response = '503 Mechanism not recognized'
        self.check_constructor_error_conditions(
            Handler, nntplib.NNTPPermanentError, authinfo_response,
            login, password)

class bypass_context:
    """Bypass encryption and actual SSL module"""
    def wrap_socket(sock, **args):
        return sock

@unittest.skipUnless(ssl, 'requires SSL support')
class MockSslTests(MockSocketTests):
    @staticmethod
    def nntp_class(*pos, **kw):
        return nntplib.NNTP_SSL(*pos, ssl_context=bypass_context, **kw)

@unittest.skipUnless(threading, 'requires multithreading')
class LocalServerTests(unittest.TestCase):
    def setUp(self):
        sock = socket.socket()
        port = support.bind_port(sock)
        sock.listen()
        self.background = threading.Thread(
            target=self.run_server, args=(sock,))
        self.background.start()
        self.addCleanup(self.background.join)

        self.nntp = NNTP(support.HOST, port, usenetrc=False).__enter__()
        self.addCleanup(self.nntp.__exit__, None, None, None)

    def run_server(self, sock):
        # Could be generalized to handle more commands in separate methods
        with sock:
            [client, _] = sock.accept()
        with contextlib.ExitStack() as cleanup:
            cleanup.enter_context(client)
            reader = cleanup.enter_context(client.makefile('rb'))
            client.sendall(b'200 Server ready\r\n')
            while True:
                cmd = reader.readline()
                if cmd == b'CAPABILITIES\r\n':
                    client.sendall(
                        b'101 Capability list:\r\n'
                        b'VERSION 2\r\n'
                        b'STARTTLS\r\n'
                        b'.\r\n'
                    )
                elif cmd == b'STARTTLS\r\n':
                    reader.close()
                    client.sendall(b'382 Begin TLS negotiation now\r\n')
                    context = ssl.SSLContext()
                    context.load_cert_chain(certfile)
                    client = context.wrap_socket(
                        client, server_side=True)
                    cleanup.enter_context(client)
                    reader = cleanup.enter_context(client.makefile('rb'))
                elif cmd == b'QUIT\r\n':
                    client.sendall(b'205 Bye!\r\n')
                    break
                else:
                    raise ValueError('Unexpected command {!r}'.format(cmd))

    @unittest.skipUnless(ssl, 'requires SSL support')
    def test_starttls(self):
        file = self.nntp.file
        sock = self.nntp.sock
        self.nntp.starttls()
        # Check that the socket and internal pseudo-file really were
        # changed.
        self.assertNotEqual(file, self.nntp.file)
        self.assertNotEqual(sock, self.nntp.sock)
        # Check that the new socket really is an SSL one
        self.assertIsInstance(self.nntp.sock, ssl.SSLSocket)
        # Check that trying starttls when it's already active fails.
        self.assertRaises(ValueError, self.nntp.starttls)


if __name__ == "__main__":
    unittest.main()