Create telnetlib_receive_all.py

telnetlib_receive_all.py

@@ -0,0 +1,793 @@
+# This whole file is a copy of the 'telnetlib.py' that came with Python 2.7.9 distribution.
+# A patch was applied to this file, in order to stop dropping null (0x00) characters.
+
+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('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 select.select() in order to
+wait until more data is available.  Note that in this case,
+read_eager() may return '' 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 errno
+import sys
+import socket
+import select
+
+__all__ = ["Telnet"]
+
+# Tunable parameters
+DEBUGLEVEL = 0
+
+# Telnet protocol defaults
+TELNET_PORT = 23
+
+# Telnet protocol characters (don't change)
+IAC  = chr(255) # "Interpret As Command"
+DONT = chr(254)
+DO   = chr(253)
+WONT = chr(252)
+WILL = chr(251)
+theNULL = chr(0)
+
+SE  = chr(240)  # Subnegotiation End
+NOP = chr(241)  # No Operation
+DM  = chr(242)  # Data Mark
+BRK = chr(243)  # Break
+IP  = chr(244)  # Interrupt process
+AO  = chr(245)  # Abort output
+AYT = chr(246)  # Are You There
+EC  = chr(247)  # Erase Character
+EL  = chr(248)  # Erase Line
+GA  = chr(249)  # Go Ahead
+SB =  chr(250)  # Subnegotiation Begin
+
+
+# Telnet protocol options code (don't change)
+# These ones all come from arpa/telnet.h
+BINARY = chr(0) # 8-bit data path
+ECHO = chr(1) # echo
+RCP = chr(2) # prepare to reconnect
+SGA = chr(3) # suppress go ahead
+NAMS = chr(4) # approximate message size
+STATUS = chr(5) # give status
+TM = chr(6) # timing mark
+RCTE = chr(7) # remote controlled transmission and echo
+NAOL = chr(8) # negotiate about output line width
+NAOP = chr(9) # negotiate about output page size
+NAOCRD = chr(10) # negotiate about CR disposition
+NAOHTS = chr(11) # negotiate about horizontal tabstops
+NAOHTD = chr(12) # negotiate about horizontal tab disposition
+NAOFFD = chr(13) # negotiate about formfeed disposition
+NAOVTS = chr(14) # negotiate about vertical tab stops
+NAOVTD = chr(15) # negotiate about vertical tab disposition
+NAOLFD = chr(16) # negotiate about output LF disposition
+XASCII = chr(17) # extended ascii character set
+LOGOUT = chr(18) # force logout
+BM = chr(19) # byte macro
+DET = chr(20) # data entry terminal
+SUPDUP = chr(21) # supdup protocol
+SUPDUPOUTPUT = chr(22) # supdup output
+SNDLOC = chr(23) # send location
+TTYPE = chr(24) # terminal type
+EOR = chr(25) # end or record
+TUID = chr(26) # TACACS user identification
+OUTMRK = chr(27) # output marking
+TTYLOC = chr(28) # terminal location number
+VT3270REGIME = chr(29) # 3270 regime
+X3PAD = chr(30) # X.3 PAD
+NAWS = chr(31) # window size
+TSPEED = chr(32) # terminal speed
+LFLOW = chr(33) # remote flow control
+LINEMODE = chr(34) # Linemode option
+XDISPLOC = chr(35) # X Display Location
+OLD_ENVIRON = chr(36) # Old - Environment variables
+AUTHENTICATION = chr(37) # Authenticate
+ENCRYPT = chr(38) # Encryption option
+NEW_ENVIRON = chr(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 = chr(40) # TN3270E
+XAUTH = chr(41) # XAUTH
+CHARSET = chr(42) # CHARSET
+RSP = chr(43) # Telnet Remote Serial Port
+COM_PORT_OPTION = chr(44) # Com Port Control Option
+SUPPRESS_LOCAL_ECHO = chr(45) # Telnet Suppress Local Echo
+TLS = chr(46) # Telnet Start TLS
+KERMIT = chr(47) # KERMIT
+SEND_URL = chr(48) # SEND-URL
+FORWARD_X = chr(49) # FORWARD_X
+PRAGMA_LOGON = chr(138) # TELOPT PRAGMA LOGON
+SSPI_LOGON = chr(139) # TELOPT SSPI LOGON
+PRAGMA_HEARTBEAT = chr(140) # TELOPT PRAGMA HEARTBEAT
+EXOPL = chr(255) # Extended-Options-List
+NOOPT = chr(0)
+
+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 = ''
+        self.irawq = 0
+        self.cookedq = ''
+        self.eof = 0
+        self.iacseq = '' # Buffer for IAC sequence.
+        self.sb = 0 # flag for SB and SE sequence.
+        self.sbdataq = ''
+        self.option_callback = None
+        self._has_poll = hasattr(select, 'poll')
+        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
+        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),
+            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."""
+        if self.sock:
+            self.sock.close()
+        self.sock = 0
+        self.eof = 1
+        self.iacseq = ''
+        self.sb = 0
+
+    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
+        socket.error if the connection is closed.
+
+        """
+        if IAC in buffer:
+            buffer = buffer.replace(IAC, IAC+IAC)
+        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.
+
+        """
+        if self._has_poll:
+            return self._read_until_with_poll(match, timeout)
+        else:
+            return self._read_until_with_select(match, timeout)
+
+    def _read_until_with_poll(self, match, timeout):
+        """Read until a given string is encountered or until timeout.
+
+        This method uses select.poll() to implement the timeout.
+        """
+        n = len(match)
+        call_timeout = timeout
+        if timeout is not None:
+            from time import time
+            time_start = time()
+        self.process_rawq()
+        i = self.cookedq.find(match)
+        if i < 0:
+            poller = select.poll()
+            poll_in_or_priority_flags = select.POLLIN | select.POLLPRI
+            poller.register(self, poll_in_or_priority_flags)
+            while i < 0 and not self.eof:
+                try:
+                    # Poll takes its timeout in milliseconds.
+                    ready = poller.poll(None if timeout is None
+                                        else 1000 * call_timeout)
+                except select.error as e:
+                    if e.errno == errno.EINTR:
+                        if timeout is not None:
+                            elapsed = time() - time_start
+                            call_timeout = timeout-elapsed
+                        continue
+                    raise
+                for fd, mode in ready:
+                    if mode & poll_in_or_priority_flags:
+                        i = max(0, len(self.cookedq)-n)
+                        self.fill_rawq()
+                        self.process_rawq()
+                        i = self.cookedq.find(match, i)
+                if timeout is not None:
+                    elapsed = time() - time_start
+                    if elapsed >= timeout:
+                        break
+                    call_timeout = timeout-elapsed
+            poller.unregister(self)
+        if i >= 0:
+            i = i + n
+            buf = self.cookedq[:i]
+            self.cookedq = self.cookedq[i:]
+            return buf
+        return self.read_very_lazy()
+
+    def _read_until_with_select(self, match, timeout=None):
+        """Read until a given string is encountered or until timeout.
+
+        The timeout is implemented using select.select().
+        """
+        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
+        s_reply = ([self], [], [])
+        s_args = s_reply
+        if timeout is not None:
+            s_args = s_args + (timeout,)
+            from time import time
+            time_start = time()
+        while not self.eof and select.select(*s_args) == s_reply:
+            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:
+                elapsed = time() - time_start
+                if elapsed >= timeout:
+                    break
+                s_args = s_reply + (timeout-elapsed,)
+        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 = ''
+        return buf
+
+    def read_some(self):
+        """Read at least one byte of cooked data unless EOF is hit.
+
+        Return '' 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 = ''
+        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 '' 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 '' 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 '' 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 '' if no cooked data available otherwise.  Don't block.
+
+        """
+        buf = self.cookedq
+        self.cookedq = ''
+        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 '' 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 = ''
+        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 = ['', '']
+        try:
+            while self.rawq:
+                c = self.rawq_getchar()
+                if not self.iacseq:
+                    #if c == theNULL:
+                    #    continue
+                    #if c == "\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 = ''
+                    if c == IAC:
+                        buf[self.sb] = buf[self.sb] + c
+                    else:
+                        if c == SB: # SB ... SE start.
+                            self.sb = 1
+                            self.sbdataq = ''
+                        elif c == SE:
+                            self.sb = 0
+                            self.sbdataq = self.sbdataq + buf[1]
+                            buf[1] = ''
+                        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]
+                    self.iacseq = ''
+                    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 = '' # 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 = self.irawq + 1
+        if self.irawq >= len(self.rawq):
+            self.rawq = ''
+            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 = ''
+            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."""
+        return select.select([self], [], [], 0) == ([self], [], [])
+
+    def interact(self):
+        """Interaction function, emulates a very dumb telnet client."""
+        if sys.platform == "win32":
+            self.mt_interact()
+            return
+        while 1:
+            rfd, wfd, xfd = select.select([self, sys.stdin], [], [])
+            if self in rfd:
+                try:
+                    text = self.read_eager()
+                except EOFError:
+                    print '*** Connection closed by remote host ***'
+                    break
+                if text:
+                    sys.stdout.write(text)
+                    sys.stdout.flush()
+            if sys.stdin in rfd:
+                line = sys.stdin.readline()
+                if not line:
+                    break
+                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)
+
+    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)
+            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.RegexObject 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 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.
+
+        """
+        if self._has_poll:
+            return self._expect_with_poll(list, timeout)
+        else:
+            return self._expect_with_select(list, timeout)
+
+    def _expect_with_poll(self, expect_list, timeout=None):
+        """Read until one from a list of a regular expressions matches.
+
+        This method uses select.poll() to implement the timeout.
+        """
+        re = None
+        expect_list = expect_list[:]
+        indices = range(len(expect_list))
+        for i in indices:
+            if not hasattr(expect_list[i], "search"):
+                if not re: import re
+                expect_list[i] = re.compile(expect_list[i])
+        call_timeout = timeout
+        if timeout is not None:
+            from time import time
+            time_start = time()
+        self.process_rawq()
+        m = None
+        for i in indices:
+            m = expect_list[i].search(self.cookedq)
+            if m:
+                e = m.end()
+                text = self.cookedq[:e]
+                self.cookedq = self.cookedq[e:]
+                break
+        if not m:
+            poller = select.poll()
+            poll_in_or_priority_flags = select.POLLIN | select.POLLPRI
+            poller.register(self, poll_in_or_priority_flags)
+            while not m and not self.eof:
+                try:
+                    ready = poller.poll(None if timeout is None
+                                        else 1000 * call_timeout)
+                except select.error as e:
+                    if e.errno == errno.EINTR:
+                        if timeout is not None:
+                            elapsed = time() - time_start
+                            call_timeout = timeout-elapsed
+                        continue
+                    raise
+                for fd, mode in ready:
+                    if mode & poll_in_or_priority_flags:
+                        self.fill_rawq()
+                        self.process_rawq()
+                        for i in indices:
+                            m = expect_list[i].search(self.cookedq)
+                            if m:
+                                e = m.end()
+                                text = self.cookedq[:e]
+                                self.cookedq = self.cookedq[e:]
+                                break
+                if timeout is not None:
+                    elapsed = time() - time_start
+                    if elapsed >= timeout:
+                        break
+                    call_timeout = timeout-elapsed
+            poller.unregister(self)
+        if m:
+            return (i, m, text)
+        text = self.read_very_lazy()
+        if not text and self.eof:
+            raise EOFError
+        return (-1, None, text)
+
+    def _expect_with_select(self, list, timeout=None):
+        """Read until one from a list of a regular expressions matches.
+
+        The timeout is implemented using select.select().
+        """
+        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:
+            from time import time
+            time_start = time()
+        while 1:
+            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 self.eof:
+                break
+            if timeout is not None:
+                elapsed = time() - time_start
+                if elapsed >= timeout:
+                    break
+                s_args = ([self.fileno()], [], [], timeout-elapsed)
+                r, w, x = select.select(*s_args)
+                if not r:
+                    break
+            self.fill_rawq()
+        text = self.read_very_lazy()
+        if not text and self.eof:
+            raise EOFError
+        return (-1, None, text)
+
+
+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')
+    tn = Telnet()
+    tn.set_debuglevel(debuglevel)
+    tn.open(host, port, timeout=0.5)
+    tn.interact()
+    tn.close()
+
+if __name__ == '__main__':
+    test()