diff --git a/Lib/telnetlib.py b/Lib/telnetlib.py
new file mode 100644
index 0000000000..8ce053e881
--- /dev/null
+++ b/Lib/telnetlib.py
@@ -0,0 +1,677 @@
+r"""TELNET client class.
+
+Based on RFC 854: TELNET Protocol Specification, by J. Postel and
+J. Reynolds
+
+Example:
+
+>>> from telnetlib import Telnet
+>>> tn = Telnet('www.python.org', 79)   # connect to finger port
+>>> tn.write(b'guido\r\n')
+>>> print(tn.read_all())
+Login       Name               TTY         Idle    When    Where
+guido    Guido van Rossum      pts/2        <Dec  2 11:10> snag.cnri.reston..
+
+>>>
+
+Note that read_all() won't read until eof -- it just reads some data
+-- but it guarantees to read at least one byte unless EOF is hit.
+
+It is possible to pass a Telnet object to a selector in order to wait until
+more data is available.  Note that in this case, read_eager() may return b''
+even if there was data on the socket, because the protocol negotiation may have
+eaten the data.  This is why EOFError is needed in some cases to distinguish
+between "no data" and "connection closed" (since the socket also appears ready
+for reading when it is closed).
+
+To do:
+- option negotiation
+- timeout should be intrinsic to the connection object instead of an
+  option on one of the read calls only
+
+"""
+
+
+# Imported modules
+import sys
+import socket
+import selectors
+from time import monotonic as _time
+
+__all__ = ["Telnet"]
+
+# Tunable parameters
+DEBUGLEVEL = 0
+
+# Telnet protocol defaults
+TELNET_PORT = 23
+
+# Telnet protocol characters (don't change)
+IAC  = bytes([255]) # "Interpret As Command"
+DONT = bytes([254])
+DO   = bytes([253])
+WONT = bytes([252])
+WILL = bytes([251])
+theNULL = bytes([0])
+
+SE  = bytes([240])  # Subnegotiation End
+NOP = bytes([241])  # No Operation
+DM  = bytes([242])  # Data Mark
+BRK = bytes([243])  # Break
+IP  = bytes([244])  # Interrupt process
+AO  = bytes([245])  # Abort output
+AYT = bytes([246])  # Are You There
+EC  = bytes([247])  # Erase Character
+EL  = bytes([248])  # Erase Line
+GA  = bytes([249])  # Go Ahead
+SB =  bytes([250])  # Subnegotiation Begin
+
+
+# Telnet protocol options code (don't change)
+# These ones all come from arpa/telnet.h
+BINARY = bytes([0]) # 8-bit data path
+ECHO = bytes([1]) # echo
+RCP = bytes([2]) # prepare to reconnect
+SGA = bytes([3]) # suppress go ahead
+NAMS = bytes([4]) # approximate message size
+STATUS = bytes([5]) # give status
+TM = bytes([6]) # timing mark
+RCTE = bytes([7]) # remote controlled transmission and echo
+NAOL = bytes([8]) # negotiate about output line width
+NAOP = bytes([9]) # negotiate about output page size
+NAOCRD = bytes([10]) # negotiate about CR disposition
+NAOHTS = bytes([11]) # negotiate about horizontal tabstops
+NAOHTD = bytes([12]) # negotiate about horizontal tab disposition
+NAOFFD = bytes([13]) # negotiate about formfeed disposition
+NAOVTS = bytes([14]) # negotiate about vertical tab stops
+NAOVTD = bytes([15]) # negotiate about vertical tab disposition
+NAOLFD = bytes([16]) # negotiate about output LF disposition
+XASCII = bytes([17]) # extended ascii character set
+LOGOUT = bytes([18]) # force logout
+BM = bytes([19]) # byte macro
+DET = bytes([20]) # data entry terminal
+SUPDUP = bytes([21]) # supdup protocol
+SUPDUPOUTPUT = bytes([22]) # supdup output
+SNDLOC = bytes([23]) # send location
+TTYPE = bytes([24]) # terminal type
+EOR = bytes([25]) # end or record
+TUID = bytes([26]) # TACACS user identification
+OUTMRK = bytes([27]) # output marking
+TTYLOC = bytes([28]) # terminal location number
+VT3270REGIME = bytes([29]) # 3270 regime
+X3PAD = bytes([30]) # X.3 PAD
+NAWS = bytes([31]) # window size
+TSPEED = bytes([32]) # terminal speed
+LFLOW = bytes([33]) # remote flow control
+LINEMODE = bytes([34]) # Linemode option
+XDISPLOC = bytes([35]) # X Display Location
+OLD_ENVIRON = bytes([36]) # Old - Environment variables
+AUTHENTICATION = bytes([37]) # Authenticate
+ENCRYPT = bytes([38]) # Encryption option
+NEW_ENVIRON = bytes([39]) # New - Environment variables
+# the following ones come from
+# http://www.iana.org/assignments/telnet-options
+# Unfortunately, that document does not assign identifiers
+# to all of them, so we are making them up
+TN3270E = bytes([40]) # TN3270E
+XAUTH = bytes([41]) # XAUTH
+CHARSET = bytes([42]) # CHARSET
+RSP = bytes([43]) # Telnet Remote Serial Port
+COM_PORT_OPTION = bytes([44]) # Com Port Control Option
+SUPPRESS_LOCAL_ECHO = bytes([45]) # Telnet Suppress Local Echo
+TLS = bytes([46]) # Telnet Start TLS
+KERMIT = bytes([47]) # KERMIT
+SEND_URL = bytes([48]) # SEND-URL
+FORWARD_X = bytes([49]) # FORWARD_X
+PRAGMA_LOGON = bytes([138]) # TELOPT PRAGMA LOGON
+SSPI_LOGON = bytes([139]) # TELOPT SSPI LOGON
+PRAGMA_HEARTBEAT = bytes([140]) # TELOPT PRAGMA HEARTBEAT
+EXOPL = bytes([255]) # Extended-Options-List
+NOOPT = bytes([0])
+
+
+# poll/select have the advantage of not requiring any extra file descriptor,
+# contrarily to epoll/kqueue (also, they require a single syscall).
+if hasattr(selectors, 'PollSelector'):
+    _TelnetSelector = selectors.PollSelector
+else:
+    _TelnetSelector = selectors.SelectSelector
+
+
+class Telnet:
+
+    """Telnet interface class.
+
+    An instance of this class represents a connection to a telnet
+    server.  The instance is initially not connected; the open()
+    method must be used to establish a connection.  Alternatively, the
+    host name and optional port number can be passed to the
+    constructor, too.
+
+    Don't try to reopen an already connected instance.
+
+    This class has many read_*() methods.  Note that some of them
+    raise EOFError when the end of the connection is read, because
+    they can return an empty string for other reasons.  See the
+    individual doc strings.
+
+    read_until(expected, [timeout])
+        Read until the expected string has been seen, or a timeout is
+        hit (default is no timeout); may block.
+
+    read_all()
+        Read all data until EOF; may block.
+
+    read_some()
+        Read at least one byte or EOF; may block.
+
+    read_very_eager()
+        Read all data available already queued or on the socket,
+        without blocking.
+
+    read_eager()
+        Read either data already queued or some data available on the
+        socket, without blocking.
+
+    read_lazy()
+        Read all data in the raw queue (processing it first), without
+        doing any socket I/O.
+
+    read_very_lazy()
+        Reads all data in the cooked queue, without doing any socket
+        I/O.
+
+    read_sb_data()
+        Reads available data between SB ... SE sequence. Don't block.
+
+    set_option_negotiation_callback(callback)
+        Each time a telnet option is read on the input flow, this callback
+        (if set) is called with the following parameters :
+        callback(telnet socket, command, option)
+            option will be chr(0) when there is no option.
+        No other action is done afterwards by telnetlib.
+
+    """
+
+    def __init__(self, host=None, port=0,
+                 timeout=socket._GLOBAL_DEFAULT_TIMEOUT):
+        """Constructor.
+
+        When called without arguments, create an unconnected instance.
+        With a hostname argument, it connects the instance; port number
+        and timeout are optional.
+        """
+        self.debuglevel = DEBUGLEVEL
+        self.host = host
+        self.port = port
+        self.timeout = timeout
+        self.sock = None
+        self.rawq = b''
+        self.irawq = 0
+        self.cookedq = b''
+        self.eof = 0
+        self.iacseq = b'' # Buffer for IAC sequence.
+        self.sb = 0 # flag for SB and SE sequence.
+        self.sbdataq = b''
+        self.option_callback = None
+        if host is not None:
+            self.open(host, port, timeout)
+
+    def open(self, host, port=0, timeout=socket._GLOBAL_DEFAULT_TIMEOUT):
+        """Connect to a host.
+
+        The optional second argument is the port number, which
+        defaults to the standard telnet port (23).
+
+        Don't try to reopen an already connected instance.
+        """
+        self.eof = 0
+        if not port:
+            port = TELNET_PORT
+        self.host = host
+        self.port = port
+        self.timeout = timeout
+        sys.audit("telnetlib.Telnet.open", self, host, port)
+        self.sock = socket.create_connection((host, port), timeout)
+
+    def __del__(self):
+        """Destructor -- close the connection."""
+        self.close()
+
+    def msg(self, msg, *args):
+        """Print a debug message, when the debug level is > 0.
+
+        If extra arguments are present, they are substituted in the
+        message using the standard string formatting operator.
+
+        """
+        if self.debuglevel > 0:
+            print('Telnet(%s,%s):' % (self.host, self.port), end=' ')
+            if args:
+                print(msg % args)
+            else:
+                print(msg)
+
+    def set_debuglevel(self, debuglevel):
+        """Set the debug level.
+
+        The higher it is, the more debug output you get (on sys.stdout).
+
+        """
+        self.debuglevel = debuglevel
+
+    def close(self):
+        """Close the connection."""
+        sock = self.sock
+        self.sock = None
+        self.eof = True
+        self.iacseq = b''
+        self.sb = 0
+        if sock:
+            sock.close()
+
+    def get_socket(self):
+        """Return the socket object used internally."""
+        return self.sock
+
+    def fileno(self):
+        """Return the fileno() of the socket object used internally."""
+        return self.sock.fileno()
+
+    def write(self, buffer):
+        """Write a string to the socket, doubling any IAC characters.
+
+        Can block if the connection is blocked.  May raise
+        OSError if the connection is closed.
+
+        """
+        if IAC in buffer:
+            buffer = buffer.replace(IAC, IAC+IAC)
+        sys.audit("telnetlib.Telnet.write", self, buffer)
+        self.msg("send %r", buffer)
+        self.sock.sendall(buffer)
+
+    def read_until(self, match, timeout=None):
+        """Read until a given string is encountered or until timeout.
+
+        When no match is found, return whatever is available instead,
+        possibly the empty string.  Raise EOFError if the connection
+        is closed and no cooked data is available.
+
+        """
+        n = len(match)
+        self.process_rawq()
+        i = self.cookedq.find(match)
+        if i >= 0:
+            i = i+n
+            buf = self.cookedq[:i]
+            self.cookedq = self.cookedq[i:]
+            return buf
+        if timeout is not None:
+            deadline = _time() + timeout
+        with _TelnetSelector() as selector:
+            selector.register(self, selectors.EVENT_READ)
+            while not self.eof:
+                if selector.select(timeout):
+                    i = max(0, len(self.cookedq)-n)
+                    self.fill_rawq()
+                    self.process_rawq()
+                    i = self.cookedq.find(match, i)
+                    if i >= 0:
+                        i = i+n
+                        buf = self.cookedq[:i]
+                        self.cookedq = self.cookedq[i:]
+                        return buf
+                if timeout is not None:
+                    timeout = deadline - _time()
+                    if timeout < 0:
+                        break
+        return self.read_very_lazy()
+
+    def read_all(self):
+        """Read all data until EOF; block until connection closed."""
+        self.process_rawq()
+        while not self.eof:
+            self.fill_rawq()
+            self.process_rawq()
+        buf = self.cookedq
+        self.cookedq = b''
+        return buf
+
+    def read_some(self):
+        """Read at least one byte of cooked data unless EOF is hit.
+
+        Return b'' if EOF is hit.  Block if no data is immediately
+        available.
+
+        """
+        self.process_rawq()
+        while not self.cookedq and not self.eof:
+            self.fill_rawq()
+            self.process_rawq()
+        buf = self.cookedq
+        self.cookedq = b''
+        return buf
+
+    def read_very_eager(self):
+        """Read everything that's possible without blocking in I/O (eager).
+
+        Raise EOFError if connection closed and no cooked data
+        available.  Return b'' if no cooked data available otherwise.
+        Don't block unless in the midst of an IAC sequence.
+
+        """
+        self.process_rawq()
+        while not self.eof and self.sock_avail():
+            self.fill_rawq()
+            self.process_rawq()
+        return self.read_very_lazy()
+
+    def read_eager(self):
+        """Read readily available data.
+
+        Raise EOFError if connection closed and no cooked data
+        available.  Return b'' if no cooked data available otherwise.
+        Don't block unless in the midst of an IAC sequence.
+
+        """
+        self.process_rawq()
+        while not self.cookedq and not self.eof and self.sock_avail():
+            self.fill_rawq()
+            self.process_rawq()
+        return self.read_very_lazy()
+
+    def read_lazy(self):
+        """Process and return data that's already in the queues (lazy).
+
+        Raise EOFError if connection closed and no data available.
+        Return b'' if no cooked data available otherwise.  Don't block
+        unless in the midst of an IAC sequence.
+
+        """
+        self.process_rawq()
+        return self.read_very_lazy()
+
+    def read_very_lazy(self):
+        """Return any data available in the cooked queue (very lazy).
+
+        Raise EOFError if connection closed and no data available.
+        Return b'' if no cooked data available otherwise.  Don't block.
+
+        """
+        buf = self.cookedq
+        self.cookedq = b''
+        if not buf and self.eof and not self.rawq:
+            raise EOFError('telnet connection closed')
+        return buf
+
+    def read_sb_data(self):
+        """Return any data available in the SB ... SE queue.
+
+        Return b'' if no SB ... SE available. Should only be called
+        after seeing a SB or SE command. When a new SB command is
+        found, old unread SB data will be discarded. Don't block.
+
+        """
+        buf = self.sbdataq
+        self.sbdataq = b''
+        return buf
+
+    def set_option_negotiation_callback(self, callback):
+        """Provide a callback function called after each receipt of a telnet option."""
+        self.option_callback = callback
+
+    def process_rawq(self):
+        """Transfer from raw queue to cooked queue.
+
+        Set self.eof when connection is closed.  Don't block unless in
+        the midst of an IAC sequence.
+
+        """
+        buf = [b'', b'']
+        try:
+            while self.rawq:
+                c = self.rawq_getchar()
+                if not self.iacseq:
+                    if c == theNULL:
+                        continue
+                    if c == b"\021":
+                        continue
+                    if c != IAC:
+                        buf[self.sb] = buf[self.sb] + c
+                        continue
+                    else:
+                        self.iacseq += c
+                elif len(self.iacseq) == 1:
+                    # 'IAC: IAC CMD [OPTION only for WILL/WONT/DO/DONT]'
+                    if c in (DO, DONT, WILL, WONT):
+                        self.iacseq += c
+                        continue
+
+                    self.iacseq = b''
+                    if c == IAC:
+                        buf[self.sb] = buf[self.sb] + c
+                    else:
+                        if c == SB: # SB ... SE start.
+                            self.sb = 1
+                            self.sbdataq = b''
+                        elif c == SE:
+                            self.sb = 0
+                            self.sbdataq = self.sbdataq + buf[1]
+                            buf[1] = b''
+                        if self.option_callback:
+                            # Callback is supposed to look into
+                            # the sbdataq
+                            self.option_callback(self.sock, c, NOOPT)
+                        else:
+                            # We can't offer automatic processing of
+                            # suboptions. Alas, we should not get any
+                            # unless we did a WILL/DO before.
+                            self.msg('IAC %d not recognized' % ord(c))
+                elif len(self.iacseq) == 2:
+                    cmd = self.iacseq[1:2]
+                    self.iacseq = b''
+                    opt = c
+                    if cmd in (DO, DONT):
+                        self.msg('IAC %s %d',
+                            cmd == DO and 'DO' or 'DONT', ord(opt))
+                        if self.option_callback:
+                            self.option_callback(self.sock, cmd, opt)
+                        else:
+                            self.sock.sendall(IAC + WONT + opt)
+                    elif cmd in (WILL, WONT):
+                        self.msg('IAC %s %d',
+                            cmd == WILL and 'WILL' or 'WONT', ord(opt))
+                        if self.option_callback:
+                            self.option_callback(self.sock, cmd, opt)
+                        else:
+                            self.sock.sendall(IAC + DONT + opt)
+        except EOFError: # raised by self.rawq_getchar()
+            self.iacseq = b'' # Reset on EOF
+            self.sb = 0
+            pass
+        self.cookedq = self.cookedq + buf[0]
+        self.sbdataq = self.sbdataq + buf[1]
+
+    def rawq_getchar(self):
+        """Get next char from raw queue.
+
+        Block if no data is immediately available.  Raise EOFError
+        when connection is closed.
+
+        """
+        if not self.rawq:
+            self.fill_rawq()
+            if self.eof:
+                raise EOFError
+        c = self.rawq[self.irawq:self.irawq+1]
+        self.irawq = self.irawq + 1
+        if self.irawq >= len(self.rawq):
+            self.rawq = b''
+            self.irawq = 0
+        return c
+
+    def fill_rawq(self):
+        """Fill raw queue from exactly one recv() system call.
+
+        Block if no data is immediately available.  Set self.eof when
+        connection is closed.
+
+        """
+        if self.irawq >= len(self.rawq):
+            self.rawq = b''
+            self.irawq = 0
+        # The buffer size should be fairly small so as to avoid quadratic
+        # behavior in process_rawq() above
+        buf = self.sock.recv(50)
+        self.msg("recv %r", buf)
+        self.eof = (not buf)
+        self.rawq = self.rawq + buf
+
+    def sock_avail(self):
+        """Test whether data is available on the socket."""
+        with _TelnetSelector() as selector:
+            selector.register(self, selectors.EVENT_READ)
+            return bool(selector.select(0))
+
+    def interact(self):
+        """Interaction function, emulates a very dumb telnet client."""
+        if sys.platform == "win32":
+            self.mt_interact()
+            return
+        with _TelnetSelector() as selector:
+            selector.register(self, selectors.EVENT_READ)
+            selector.register(sys.stdin, selectors.EVENT_READ)
+
+            while True:
+                for key, events in selector.select():
+                    if key.fileobj is self:
+                        try:
+                            text = self.read_eager()
+                        except EOFError:
+                            print('*** Connection closed by remote host ***')
+                            return
+                        if text:
+                            sys.stdout.write(text.decode('ascii'))
+                            sys.stdout.flush()
+                    elif key.fileobj is sys.stdin:
+                        line = sys.stdin.readline().encode('ascii')
+                        if not line:
+                            return
+                        self.write(line)
+
+    def mt_interact(self):
+        """Multithreaded version of interact()."""
+        import _thread
+        _thread.start_new_thread(self.listener, ())
+        while 1:
+            line = sys.stdin.readline()
+            if not line:
+                break
+            self.write(line.encode('ascii'))
+
+    def listener(self):
+        """Helper for mt_interact() -- this executes in the other thread."""
+        while 1:
+            try:
+                data = self.read_eager()
+            except EOFError:
+                print('*** Connection closed by remote host ***')
+                return
+            if data:
+                sys.stdout.write(data.decode('ascii'))
+            else:
+                sys.stdout.flush()
+
+    def expect(self, list, timeout=None):
+        """Read until one from a list of a regular expressions matches.
+
+        The first argument is a list of regular expressions, either
+        compiled (re.Pattern instances) or uncompiled (strings).
+        The optional second argument is a timeout, in seconds; default
+        is no timeout.
+
+        Return a tuple of three items: the index in the list of the
+        first regular expression that matches; the re.Match object
+        returned; and the text read up till and including the match.
+
+        If EOF is read and no text was read, raise EOFError.
+        Otherwise, when nothing matches, return (-1, None, text) where
+        text is the text received so far (may be the empty string if a
+        timeout happened).
+
+        If a regular expression ends with a greedy match (e.g. '.*')
+        or if more than one expression can match the same input, the
+        results are undeterministic, and may depend on the I/O timing.
+
+        """
+        re = None
+        list = list[:]
+        indices = range(len(list))
+        for i in indices:
+            if not hasattr(list[i], "search"):
+                if not re: import re
+                list[i] = re.compile(list[i])
+        if timeout is not None:
+            deadline = _time() + timeout
+        with _TelnetSelector() as selector:
+            selector.register(self, selectors.EVENT_READ)
+            while not self.eof:
+                self.process_rawq()
+                for i in indices:
+                    m = list[i].search(self.cookedq)
+                    if m:
+                        e = m.end()
+                        text = self.cookedq[:e]
+                        self.cookedq = self.cookedq[e:]
+                        return (i, m, text)
+                if timeout is not None:
+                    ready = selector.select(timeout)
+                    timeout = deadline - _time()
+                    if not ready:
+                        if timeout < 0:
+                            break
+                        else:
+                            continue
+                self.fill_rawq()
+        text = self.read_very_lazy()
+        if not text and self.eof:
+            raise EOFError
+        return (-1, None, text)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self.close()
+
+
+def test():
+    """Test program for telnetlib.
+
+    Usage: python telnetlib.py [-d] ... [host [port]]
+
+    Default host is localhost; default port is 23.
+
+    """
+    debuglevel = 0
+    while sys.argv[1:] and sys.argv[1] == '-d':
+        debuglevel = debuglevel+1
+        del sys.argv[1]
+    host = 'localhost'
+    if sys.argv[1:]:
+        host = sys.argv[1]
+    port = 0
+    if sys.argv[2:]:
+        portstr = sys.argv[2]
+        try:
+            port = int(portstr)
+        except ValueError:
+            port = socket.getservbyname(portstr, 'tcp')
+    with Telnet() as tn:
+        tn.set_debuglevel(debuglevel)
+        tn.open(host, port, timeout=0.5)
+        tn.interact()
+
+if __name__ == '__main__':
+    test()
diff --git a/Lib/test/test_telnetlib.py b/Lib/test/test_telnetlib.py
new file mode 100644
index 0000000000..414c328b79
--- /dev/null
+++ b/Lib/test/test_telnetlib.py
@@ -0,0 +1,401 @@
+import socket
+import selectors
+import telnetlib
+import threading
+import contextlib
+
+from test import support
+import unittest
+
+HOST = support.HOST
+
+def server(evt, serv):
+    serv.listen()
+    evt.set()
+    try:
+        conn, addr = serv.accept()
+        conn.close()
+    except socket.timeout:
+        pass
+    finally:
+        serv.close()
+
+class GeneralTests(unittest.TestCase):
+
+    def setUp(self):
+        self.evt = threading.Event()
+        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        self.sock.settimeout(60)  # Safety net. Look issue 11812
+        self.port = support.bind_port(self.sock)
+        self.thread = threading.Thread(target=server, args=(self.evt,self.sock))
+        self.thread.setDaemon(True)
+        self.thread.start()
+        self.evt.wait()
+
+    def tearDown(self):
+        self.thread.join()
+        del self.thread  # Clear out any dangling Thread objects.
+
+    def testBasic(self):
+        # connects
+        telnet = telnetlib.Telnet(HOST, self.port)
+        telnet.sock.close()
+
+    def testContextManager(self):
+        with telnetlib.Telnet(HOST, self.port) as tn:
+            self.assertIsNotNone(tn.get_socket())
+        self.assertIsNone(tn.get_socket())
+
+    def testTimeoutDefault(self):
+        self.assertTrue(socket.getdefaulttimeout() is None)
+        socket.setdefaulttimeout(30)
+        try:
+            telnet = telnetlib.Telnet(HOST, self.port)
+        finally:
+            socket.setdefaulttimeout(None)
+        self.assertEqual(telnet.sock.gettimeout(), 30)
+        telnet.sock.close()
+
+    def testTimeoutNone(self):
+        # None, having other default
+        self.assertTrue(socket.getdefaulttimeout() is None)
+        socket.setdefaulttimeout(30)
+        try:
+            telnet = telnetlib.Telnet(HOST, self.port, timeout=None)
+        finally:
+            socket.setdefaulttimeout(None)
+        self.assertTrue(telnet.sock.gettimeout() is None)
+        telnet.sock.close()
+
+    def testTimeoutValue(self):
+        telnet = telnetlib.Telnet(HOST, self.port, timeout=30)
+        self.assertEqual(telnet.sock.gettimeout(), 30)
+        telnet.sock.close()
+
+    def testTimeoutOpen(self):
+        telnet = telnetlib.Telnet()
+        telnet.open(HOST, self.port, timeout=30)
+        self.assertEqual(telnet.sock.gettimeout(), 30)
+        telnet.sock.close()
+
+    def testGetters(self):
+        # Test telnet getter methods
+        telnet = telnetlib.Telnet(HOST, self.port, timeout=30)
+        t_sock = telnet.sock
+        self.assertEqual(telnet.get_socket(), t_sock)
+        self.assertEqual(telnet.fileno(), t_sock.fileno())
+        telnet.sock.close()
+
+class SocketStub(object):
+    ''' a socket proxy that re-defines sendall() '''
+    def __init__(self, reads=()):
+        self.reads = list(reads)  # Intentionally make a copy.
+        self.writes = []
+        self.block = False
+    def sendall(self, data):
+        self.writes.append(data)
+    def recv(self, size):
+        out = b''
+        while self.reads and len(out) < size:
+            out += self.reads.pop(0)
+        if len(out) > size:
+            self.reads.insert(0, out[size:])
+            out = out[:size]
+        return out
+
+class TelnetAlike(telnetlib.Telnet):
+    def fileno(self):
+        raise NotImplementedError()
+    def close(self): pass
+    def sock_avail(self):
+        return (not self.sock.block)
+    def msg(self, msg, *args):
+        with support.captured_stdout() as out:
+            telnetlib.Telnet.msg(self, msg, *args)
+        self._messages += out.getvalue()
+        return
+
+class MockSelector(selectors.BaseSelector):
+
+    def __init__(self):
+        self.keys = {}
+
+    @property
+    def resolution(self):
+        return 1e-3
+
+    def register(self, fileobj, events, data=None):
+        key = selectors.SelectorKey(fileobj, 0, events, data)
+        self.keys[fileobj] = key
+        return key
+
+    def unregister(self, fileobj):
+        return self.keys.pop(fileobj)
+
+    def select(self, timeout=None):
+        block = False
+        for fileobj in self.keys:
+            if isinstance(fileobj, TelnetAlike):
+                block = fileobj.sock.block
+                break
+        if block:
+            return []
+        else:
+            return [(key, key.events) for key in self.keys.values()]
+
+    def get_map(self):
+        return self.keys
+
+
+@contextlib.contextmanager
+def test_socket(reads):
+    def new_conn(*ignored):
+        return SocketStub(reads)
+    try:
+        old_conn = socket.create_connection
+        socket.create_connection = new_conn
+        yield None
+    finally:
+        socket.create_connection = old_conn
+    return
+
+def test_telnet(reads=(), cls=TelnetAlike):
+    ''' return a telnetlib.Telnet object that uses a SocketStub with
+        reads queued up to be read '''
+    for x in reads:
+        assert type(x) is bytes, x
+    with test_socket(reads):
+        telnet = cls('dummy', 0)
+        telnet._messages = '' # debuglevel output
+    return telnet
+
+class ExpectAndReadTestCase(unittest.TestCase):
+    def setUp(self):
+        self.old_selector = telnetlib._TelnetSelector
+        telnetlib._TelnetSelector = MockSelector
+    def tearDown(self):
+        telnetlib._TelnetSelector = self.old_selector
+
+class ReadTests(ExpectAndReadTestCase):
+    def test_read_until(self):
+        """
+        read_until(expected, timeout=None)
+        test the blocking version of read_util
+        """
+        want = [b'xxxmatchyyy']
+        telnet = test_telnet(want)
+        data = telnet.read_until(b'match')
+        self.assertEqual(data, b'xxxmatch', msg=(telnet.cookedq, telnet.rawq, telnet.sock.reads))
+
+        reads = [b'x' * 50, b'match', b'y' * 50]
+        expect = b''.join(reads[:-1])
+        telnet = test_telnet(reads)
+        data = telnet.read_until(b'match')
+        self.assertEqual(data, expect)
+
+
+    def test_read_all(self):
+        """
+        read_all()
+          Read all data until EOF; may block.
+        """
+        reads = [b'x' * 500, b'y' * 500, b'z' * 500]
+        expect = b''.join(reads)
+        telnet = test_telnet(reads)
+        data = telnet.read_all()
+        self.assertEqual(data, expect)
+        return
+
+    def test_read_some(self):
+        """
+        read_some()
+          Read at least one byte or EOF; may block.
+        """
+        # test 'at least one byte'
+        telnet = test_telnet([b'x' * 500])
+        data = telnet.read_some()
+        self.assertTrue(len(data) >= 1)
+        # test EOF
+        telnet = test_telnet()
+        data = telnet.read_some()
+        self.assertEqual(b'', data)
+
+    def _read_eager(self, func_name):
+        """
+        read_*_eager()
+          Read all data available already queued or on the socket,
+          without blocking.
+        """
+        want = b'x' * 100
+        telnet = test_telnet([want])
+        func = getattr(telnet, func_name)
+        telnet.sock.block = True
+        self.assertEqual(b'', func())
+        telnet.sock.block = False
+        data = b''
+        while True:
+            try:
+                data += func()
+            except EOFError:
+                break
+        self.assertEqual(data, want)
+
+    def test_read_eager(self):
+        # read_eager and read_very_eager make the same guarantees
+        # (they behave differently but we only test the guarantees)
+        self._read_eager('read_eager')
+        self._read_eager('read_very_eager')
+        # NB -- we need to test the IAC block which is mentioned in the
+        # docstring but not in the module docs
+
+    def read_very_lazy(self):
+        want = b'x' * 100
+        telnet = test_telnet([want])
+        self.assertEqual(b'', telnet.read_very_lazy())
+        while telnet.sock.reads:
+            telnet.fill_rawq()
+        data = telnet.read_very_lazy()
+        self.assertEqual(want, data)
+        self.assertRaises(EOFError, telnet.read_very_lazy)
+
+    def test_read_lazy(self):
+        want = b'x' * 100
+        telnet = test_telnet([want])
+        self.assertEqual(b'', telnet.read_lazy())
+        data = b''
+        while True:
+            try:
+                read_data = telnet.read_lazy()
+                data += read_data
+                if not read_data:
+                    telnet.fill_rawq()
+            except EOFError:
+                break
+            self.assertTrue(want.startswith(data))
+        self.assertEqual(data, want)
+
+class nego_collector(object):
+    def __init__(self, sb_getter=None):
+        self.seen = b''
+        self.sb_getter = sb_getter
+        self.sb_seen = b''
+
+    def do_nego(self, sock, cmd, opt):
+        self.seen += cmd + opt
+        if cmd == tl.SE and self.sb_getter:
+            sb_data = self.sb_getter()
+            self.sb_seen += sb_data
+
+tl = telnetlib
+
+class WriteTests(unittest.TestCase):
+    '''The only thing that write does is replace each tl.IAC for
+    tl.IAC+tl.IAC'''
+
+    def test_write(self):
+        data_sample = [b'data sample without IAC',
+                       b'data sample with' + tl.IAC + b' one IAC',
+                       b'a few' + tl.IAC + tl.IAC + b' iacs' + tl.IAC,
+                       tl.IAC,
+                       b'']
+        for data in data_sample:
+            telnet = test_telnet()
+            telnet.write(data)
+            written = b''.join(telnet.sock.writes)
+            self.assertEqual(data.replace(tl.IAC,tl.IAC+tl.IAC), written)
+
+class OptionTests(unittest.TestCase):
+    # RFC 854 commands
+    cmds = [tl.AO, tl.AYT, tl.BRK, tl.EC, tl.EL, tl.GA, tl.IP, tl.NOP]
+
+    def _test_command(self, data):
+        """ helper for testing IAC + cmd """
+        telnet = test_telnet(data)
+        data_len = len(b''.join(data))
+        nego = nego_collector()
+        telnet.set_option_negotiation_callback(nego.do_nego)
+        txt = telnet.read_all()
+        cmd = nego.seen
+        self.assertTrue(len(cmd) > 0) # we expect at least one command
+        self.assertIn(cmd[:1], self.cmds)
+        self.assertEqual(cmd[1:2], tl.NOOPT)
+        self.assertEqual(data_len, len(txt + cmd))
+        nego.sb_getter = None # break the nego => telnet cycle
+
+    def test_IAC_commands(self):
+        for cmd in self.cmds:
+            self._test_command([tl.IAC, cmd])
+            self._test_command([b'x' * 100, tl.IAC, cmd, b'y'*100])
+            self._test_command([b'x' * 10, tl.IAC, cmd, b'y'*10])
+        # all at once
+        self._test_command([tl.IAC + cmd for (cmd) in self.cmds])
+
+    def test_SB_commands(self):
+        # RFC 855, subnegotiations portion
+        send = [tl.IAC + tl.SB + tl.IAC + tl.SE,
+                tl.IAC + tl.SB + tl.IAC + tl.IAC + tl.IAC + tl.SE,
+                tl.IAC + tl.SB + tl.IAC + tl.IAC + b'aa' + tl.IAC + tl.SE,
+                tl.IAC + tl.SB + b'bb' + tl.IAC + tl.IAC + tl.IAC + tl.SE,
+                tl.IAC + tl.SB + b'cc' + tl.IAC + tl.IAC + b'dd' + tl.IAC + tl.SE,
+               ]
+        telnet = test_telnet(send)
+        nego = nego_collector(telnet.read_sb_data)
+        telnet.set_option_negotiation_callback(nego.do_nego)
+        txt = telnet.read_all()
+        self.assertEqual(txt, b'')
+        want_sb_data = tl.IAC + tl.IAC + b'aabb' + tl.IAC + b'cc' + tl.IAC + b'dd'
+        self.assertEqual(nego.sb_seen, want_sb_data)
+        self.assertEqual(b'', telnet.read_sb_data())
+        nego.sb_getter = None # break the nego => telnet cycle
+
+    def test_debuglevel_reads(self):
+        # test all the various places that self.msg(...) is called
+        given_a_expect_b = [
+            # Telnet.fill_rawq
+            (b'a', ": recv b''\n"),
+            # Telnet.process_rawq
+            (tl.IAC + bytes([88]), ": IAC 88 not recognized\n"),
+            (tl.IAC + tl.DO + bytes([1]), ": IAC DO 1\n"),
+            (tl.IAC + tl.DONT + bytes([1]), ": IAC DONT 1\n"),
+            (tl.IAC + tl.WILL + bytes([1]), ": IAC WILL 1\n"),
+            (tl.IAC + tl.WONT + bytes([1]), ": IAC WONT 1\n"),
+           ]
+        for a, b in given_a_expect_b:
+            telnet = test_telnet([a])
+            telnet.set_debuglevel(1)
+            txt = telnet.read_all()
+            self.assertIn(b, telnet._messages)
+        return
+
+    def test_debuglevel_write(self):
+        telnet = test_telnet()
+        telnet.set_debuglevel(1)
+        telnet.write(b'xxx')
+        expected = "send b'xxx'\n"
+        self.assertIn(expected, telnet._messages)
+
+    def test_debug_accepts_str_port(self):
+        # Issue 10695
+        with test_socket([]):
+            telnet = TelnetAlike('dummy', '0')
+            telnet._messages = ''
+        telnet.set_debuglevel(1)
+        telnet.msg('test')
+        self.assertRegex(telnet._messages, r'0.*test')
+
+
+class ExpectTests(ExpectAndReadTestCase):
+    def test_expect(self):
+        """
+        expect(expected, [timeout])
+          Read until the expected string has been seen, or a timeout is
+          hit (default is no timeout); may block.
+        """
+        want = [b'x' * 10, b'match', b'y' * 10]
+        telnet = test_telnet(want)
+        (_,_,data) = telnet.expect([b'match'])
+        self.assertEqual(data, b''.join(want[:-1]))
+
+
+if __name__ == '__main__':
+    unittest.main()