# Copyright (c) 2001-2004 Twisted Matrix Laboratories.
# See LICENSE for details.

"""Telnet protocol implementation.

API Stability: Unstable

@author: U{Jp Calderone<mailto:exarkun@twistedmatrix.com>}
"""

import struct

from zope.interface import implements
from twisted.python.components import backwardsCompatImplements

from twisted.application import internet
from twisted.internet import protocol, interfaces as iinternet, defer
from twisted.python import log

MODE = chr(1)
EDIT = 1
TRAPSIG = 2
MODE_ACK = 4
SOFT_TAB = 8
LIT_ECHO = 16

# Characters gleaned from the various (and conflicting) RFCs.  Not all of these are correct.

NULL =           chr(0)   # No operation.
BEL =            chr(7)   # Produces an audible or
                          # visible signal (which does
                          # NOT move the print head).
BS =             chr(8)   # Moves the print head one
                          # character position towards
                          # the left margin.
HT =             chr(9)   # Moves the printer to the
                          # next horizontal tab stop.
                          # It remains unspecified how
                          # either party determines or
                          # establishes where such tab
                          # stops are located.
LF =             chr(10)  # Moves the printer to the
                          # next print line, keeping the
                          # same horizontal position.
VT =             chr(11)  # Moves the printer to the
                          # next vertical tab stop.  It
                          # remains unspecified how
                          # either party determines or
                          # establishes where such tab
                          # stops are located.
FF =             chr(12)  # Moves the printer to the top
                          # of the next page, keeping
                          # the same horizontal position.
CR =             chr(13)  # Moves the printer to the left
                          # margin of the current line.

ECHO  =          chr(1)   # User-to-Server:  Asks the server to send
                          # Echos of the transmitted data.
SGA =            chr(3)   # Suppress Go Ahead.  Go Ahead is silly
                          # and most modern servers should suppress
                          # it.
NAWS =           chr(31)  # Negotiate About Window Size.  Indicate that
                          # information about the size of the terminal
                          # can be communicated.
LINEMODE =       chr(34)  # Allow line buffering to be
                          # negotiated about.

SE =             chr(240) # End of subnegotiation parameters.
NOP =            chr(241) # No operation.
DM =             chr(242) # "Data Mark": The data stream portion
                          # of a Synch.  This should always be
                          # accompanied by a TCP Urgent
                          # notification.
BRK =            chr(243) # NVT character Break.
IP =             chr(244) # The function Interrupt Process.
AO =             chr(245) # The function Abort Output
AYT =            chr(246) # The function Are You There.
EC =             chr(247) # The function Erase Character.
EL =             chr(248) # The function Erase Line
GA =             chr(249) # The Go Ahead signal.
SB =             chr(250) # Indicates that what follows is
                          # subnegotiation of the indicated
                          # option.
WILL =           chr(251) # Indicates the desire to begin
                          # performing, or confirmation that
                          # you are now performing, the
                          # indicated option.
WONT =           chr(252) # Indicates the refusal to perform,
                          # or continue performing, the
                          # indicated option.
DO =             chr(253) # Indicates the request that the
                          # other party perform, or
                          # confirmation that you are expecting
                          # the other party to perform, the
                          # indicated option.
DONT =           chr(254) # Indicates the demand that the
                          # other party stop performing,
                          # or confirmation that you are no
                          # longer expecting the other party
                          # to perform, the indicated option.
IAC =            chr(255) # Data Byte 255.  Introduces a
                          # telnet command.

LINEMODE_MODE = chr(1)
LINEMODE_EDIT = chr(1)
LINEMODE_TRAPSIG = chr(2)
LINEMODE_MODE_ACK = chr(4)
LINEMODE_SOFT_TAB = chr(8)
LINEMODE_LIT_ECHO = chr(16)
LINEMODE_FORWARDMASK = chr(2)
LINEMODE_SLC = chr(3)
LINEMODE_SLC_SYNCH = chr(1)
LINEMODE_SLC_BRK = chr(2)
LINEMODE_SLC_IP = chr(3)
LINEMODE_SLC_AO = chr(4)
LINEMODE_SLC_AYT = chr(5)
LINEMODE_SLC_EOR = chr(6)
LINEMODE_SLC_ABORT = chr(7)
LINEMODE_SLC_EOF = chr(8)
LINEMODE_SLC_SUSP = chr(9)
LINEMODE_SLC_EC = chr(10)
LINEMODE_SLC_EL = chr(11)

LINEMODE_SLC_EW = chr(12)
LINEMODE_SLC_RP = chr(13)
LINEMODE_SLC_LNEXT = chr(14)
LINEMODE_SLC_XON = chr(15)
LINEMODE_SLC_XOFF = chr(16)
LINEMODE_SLC_FORW1 = chr(17)
LINEMODE_SLC_FORW2 = chr(18)
LINEMODE_SLC_MCL = chr(19)
LINEMODE_SLC_MCR = chr(20)
LINEMODE_SLC_MCWL = chr(21)
LINEMODE_SLC_MCWR = chr(22)
LINEMODE_SLC_MCBOL = chr(23)
LINEMODE_SLC_MCEOL = chr(24)
LINEMODE_SLC_INSRT = chr(25)
LINEMODE_SLC_OVER = chr(26)
LINEMODE_SLC_ECR = chr(27)
LINEMODE_SLC_EWR = chr(28)
LINEMODE_SLC_EBOL = chr(29)
LINEMODE_SLC_EEOL = chr(30)

LINEMODE_SLC_DEFAULT = chr(3)
LINEMODE_SLC_VALUE = chr(2)
LINEMODE_SLC_CANTCHANGE = chr(1)
LINEMODE_SLC_NOSUPPORT = chr(0)
LINEMODE_SLC_LEVELBITS = chr(3)

LINEMODE_SLC_ACK = chr(128)
LINEMODE_SLC_FLUSHIN = chr(64)
LINEMODE_SLC_FLUSHOUT = chr(32)
LINEMODE_EOF = chr(236)
LINEMODE_SUSP = chr(237)
LINEMODE_ABORT = chr(238)

class ITelnetProtocol(iinternet.IProtocol):
    def unhandledCommand(self, command, argument):
        """A command was received but not understood.
        """

    def unhandledSubnegotiation(self, bytes):
        """A subnegotiation command was received but not understood.
        """

    def enableLocal(self, option):
        """Enable the given option locally.

        This should enable the given option on this side of the
        telnet connection and return True.  If False is returned,
        the option will be treated as still disabled and the peer
        will be notified.
        """

    def enableRemote(self, option):
        """Indicate whether the peer should be allowed to enable this option.

        Returns True if the peer should be allowed to enable this option,
        False otherwise.
        """

    def disableLocal(self, option):
        """Disable the given option locally.

        Unlike enableLocal, this method cannot fail.  The option must be
        disabled.
        """

    def disableRemote(self, option):
        """Indicate that the peer has disabled this option.
        """

class ITelnetTransport(iinternet.ITransport):
    def do(self, option):
        """Indicate a desire for the peer to begin performing the given option.

        Returns a Deferred that fires with True when the peer begins performing
        the option, or False when the peer refuses to perform it.  If the peer
        is already performing the given option, the Deferred will fail with
        C{AlreadyEnabled}.  If a negotiation regarding this option is already
        in progress, the Deferred will fail with C{AlreadyNegotiating}.

        Note: It is currently possible that this Deferred will never fire,
        if the peer never responds, or if the peer believes the option to
        already be enabled.
        """

    def dont(self, option):
        """Indicate a desire for the peer to cease performing the given option.

        Returns a Deferred that fires with True when the peer ceases performing
        the option.  If the peer is not performing the given option, the
        Deferred will fail with C{AlreadyDisabled}.  If negotiation regarding
        this option is already in progress, the Deferred will fail with
        C{AlreadyNegotiating}.

        Note: It is currently possible that this Deferred will never fire,
        if the peer never responds, or if the peer believes the option to
        already be disabled.
        """

    def will(self, option):
        """Indicate our willingness to begin performing this option locally.

        Returns a Deferred that fires with True when the peer agrees to allow
        us to begin performing this option, or False if the peer refuses to
        allow us to begin performing it.  If the option is already enabled
        locally, the Deferred will fail with C{AlreadyEnabled}.  If negotiation
        regarding this option is already in progress, the Deferred will fail with
        C{AlreadyNegotiating}.

        Note: It is currently possible that this Deferred will never fire,
        if the peer never responds, or if the peer believes the option to
        already be enabled.
        """

    def wont(self, option):
        """Indicate that we will stop performing the given option.

        Returns a Deferred that fires with True when the peer acknowledges
        we have stopped performing this option.  If the option is already
        disabled locally, the Deferred will fail with C{AlreadyDisabled}.
        If negotiation regarding this option is already in progress,
        the Deferred will fail with C{AlreadyNegotiation}.

        Note: It is currently possible that this Deferred will never fire,
        if the peer never responds, or if the peer believes the option to
        already be disabled.
        """

    def requestNegotiation(self, about, bytes):
        """Send a subnegotiation request.

        @param about: A byte indicating the feature being negotiated.
        @param bytes: Any number of bytes containing specific information
        about the negotiation being requested.  No values in this string
        need to be escaped, as this function will escape any value which
        requires it.
        """

class TelnetError(Exception):
    pass

class NegotiationError(TelnetError):
    def __str__(self):
        return self.__class__.__module__ + '.' + self.__class__.__name__ + ':' + repr(self.args[0])

class OptionRefused(NegotiationError):
    pass

class AlreadyEnabled(NegotiationError):
    pass

class AlreadyDisabled(NegotiationError):
    pass

class AlreadyNegotiating(NegotiationError):
    pass

class TelnetProtocol(protocol.Protocol):
    implements(ITelnetProtocol)

    def unhandledCommand(self, command, argument):
        pass

    def unhandledSubnegotiation(self, command, bytes):
        pass

    def enableLocal(self, option):
        pass

    def enableRemote(self, option):
        pass

    def disableLocal(self, option):
        pass

    def disableRemote(self, option):
        pass
backwardsCompatImplements(TelnetProtocol)


class Telnet(protocol.Protocol):
    """
    @ivar commandMap: A mapping of bytes to callables.  When a
    telnet command is received, the command byte (the first byte
    after IAC) is looked up in this dictionary.  If a callable is
    found, it is invoked with the argument of the command, or None
    if the command takes no argument.  Values should be added to
    this dictionary if commands wish to be handled.  By default,
    only WILL, WONT, DO, and DONT are handled.  These should not
    be overridden, as this class handles them correctly and
    provides an API for interacting with them.

    @ivar negotiationMap: A mapping of bytes to callables.  When
    a subnegotiation command is received, the command byte (the
    first byte after SB) is looked up in this dictionary.  If
    a callable is found, it is invoked with the argument of the
    subnegotiation.  Values should be added to this dictionary if
    subnegotiations are to be handled.  By default, no values are
    handled.

    @ivar options: A mapping of option bytes to their current
    state.  This state is likely of little use to user code.
    Changes should not be made to it.

    @ivar state: A string indicating the current parse state.  It
    can take on the values "data", "escaped", "command", "newline",
    "subnegotiation", and "subnegotiation-escaped".  Changes
    should not be made to it.

    @ivar transport: This protocol's transport object.
    """

    # One of a lot of things
    state = 'data'

    def __init__(self):
        self.options = {}
        self.negotiationMap = {}
        self.commandMap = {
            WILL: self.telnet_WILL,
            WONT: self.telnet_WONT,
            DO: self.telnet_DO,
            DONT: self.telnet_DONT}

    def _write(self, bytes):
        self.transport.write(bytes)

    class _OptionState:
        class _Perspective:
            state = 'no'
            negotiating = False
            onResult = None

            def __str__(self):
                return self.state + ('*' * self.negotiating)

        def __init__(self):
            self.us = self._Perspective()
            self.him = self._Perspective()

        def __repr__(self):
            return '<_OptionState us=%s him=%s>' % (self.us, self.him)

    def getOptionState(self, opt):
        return self.options.setdefault(opt, self._OptionState())

    def _do(self, option):
        self._write(IAC + DO + option)

    def _dont(self, option):
        self._write(IAC + DONT + option)

    def _will(self, option):
        self._write(IAC + WILL + option)

    def _wont(self, option):
        self._write(IAC + WONT + option)

    def will(self, option):
        """Indicate our willingness to enable an option.
        """
        s = self.getOptionState(option)
        if s.us.negotiating or s.him.negotiating:
            return defer.fail(AlreadyNegotiating(option))
        elif s.us.state == 'yes':
            return defer.fail(AlreadyEnabled(option))
        else:
            s.us.negotiating = True
            s.us.onResult = d = defer.Deferred()
            self._will(option)
            return d

    def wont(self, option):
        """Indicate we are not willing to enable an option.
        """
        s = self.getOptionState(option)
        if s.us.negotiating or s.him.negotiating:
            return defer.fail(AlreadyNegotiating(option))
        elif s.us.state == 'no':
            return defer.fail(AlreadyDisabled(option))
        else:
            s.us.negotiating = True
            s.us.onResult = d = defer.Deferred()
            self._wont(option)
            return d

    def do(self, option):
        s = self.getOptionState(option)
        if s.us.negotiating or s.him.negotiating:
            return defer.fail(AlreadyNegotiating(option))
        elif s.him.state == 'yes':
            return defer.fail(AlreadyEnabled(option))
        else:
            s.him.negotiating = True
            s.him.onResult = d = defer.Deferred()
            self._do(option)
            return d

    def dont(self, option):
        s = self.getOptionState(option)
        if s.us.negotiating or s.him.negotiating:
            return defer.fail(AlreadyNegotiating(option))
        elif s.him.state == 'no':
            return defer.fail(AlreadyDisabled(option))
        else:
            s.him.negotiating = True
            s.him.onResult = d = defer.Deferred()
            self._dont(option)
            return d

    def requestNegotiation(self, about, bytes):
        bytes = bytes.replace(IAC, IAC * 2)
        self._write(IAC + SB + bytes + IAC + SE)

    def dataReceived(self, data):
        # Most grossly inefficient implementation ever
        for b in data:
            if self.state == 'data':
                if b == IAC:
                    self.state = 'escaped'
                elif b == '\r':
                    self.state = 'newline'
                else:
                    self.applicationDataReceived(b)
            elif self.state == 'escaped':
                if b == IAC:
                    self.applicationDataReceived(b)
                    self.state = 'data'
                elif b == SB:
                    self.state = 'subnegotiation'
                    self.commands = []
                elif b in (NOP, DM, BRK, IP, AO, AYT, EC, EL, GA):
                    self.state = 'data'
                    self.commandReceived(b, None)
                elif b in (WILL, WONT, DO, DONT):
                    self.state = 'command'
                    self.command = b
                else:
                    raise ValueError("Stumped", b)
            elif self.state == 'command':
                self.state = 'data'
                command = self.command
                del self.command
                self.commandReceived(command, b)
            elif self.state == 'newline':
                if b == '\n':
                    self.applicationDataReceived('\n')
                elif b == '\0':
                    self.applicationDataReceived('\r')
                else:
                    self.applicationDataReceived('\r' + b)
                self.state = 'data'
            elif self.state == 'subnegotiation':
                if b == IAC:
                    self.state = 'subnegotiation-escaped'
                else:
                    self.commands.append(b)
            elif self.state == 'subnegotiation-escaped':
                if b == SE:
                    self.state = 'data'
                    commands = self.commands
                    del self.commands
                    self.negotiate(commands)
                else:
                    self.state = 'subnegotiation'
                    self.commands.append(b)
            else:
                raise ValueError("How'd you do this?")

    def connectionLost(self, reason):
        for state in self.options.values():
            if state.us.onResult is not None:
                d = state.us.onResult
                state.us.onResult = None
                d.errback(reason)
            if state.him.onResult is not None:
                d = state.him.onResult
                state.him.onResult = None
                d.errback(reason)

    def applicationDataReceived(self, bytes):
        """Called with application-level data.
        """

    def unhandledCommand(self, command, argument):
        """Called for commands for which no handler is installed.
        """

    def commandReceived(self, command, argument):
        cmdFunc = self.commandMap.get(command)
        if cmdFunc is None:
            self.unhandledCommand(command, argument)
        else:
            cmdFunc(argument)

    def unhandledSubnegotiation(self, command, bytes):
        """Called for subnegotiations for which no handler is installed.
        """

    def negotiate(self, bytes):
        command, bytes = bytes[0], bytes[1:]
        cmdFunc = self.negotiationMap.get(command)
        if cmdFunc is None:
            self.unhandledSubnegotiation(command, bytes)
        else:
            cmdFunc(bytes)

    def telnet_WILL(self, option):
        s = self.getOptionState(option)
        self.willMap[s.him.state, s.him.negotiating](self, s, option)

    def will_no_false(self, state, option):
        # He is unilaterally offering to enable an option.
        if self.enableRemote(option):
            state.him.state = 'yes'
            self._do(option)
        else:
            self._dont(option)

    def will_no_true(self, state, option):
        # Peer agreed to enable an option in response to our request.
        state.him.state = 'yes'
        state.him.negotiating = False
        d = state.him.onResult
        state.him.onResult = None
        d.callback(True)
        assert self.enableRemote(option), "enableRemote must return True in this context (for option %r)" % (option,)

    def will_yes_false(self, state, option):
        # He is unilaterally offering to enable an already-enabled option.
        # Ignore this.
        pass

    def will_yes_true(self, state, option):
        # This is a bogus state.  It is here for completeness.  It will
        # never be entered.
        assert False, "will_yes_true can never be entered, but was called with %r, %r" % (state, option)

    willMap = {('no', False): will_no_false,   ('no', True): will_no_true,
               ('yes', False): will_yes_false, ('yes', True): will_yes_true}

    def telnet_WONT(self, option):
        s = self.getOptionState(option)
        self.wontMap[s.him.state, s.him.negotiating](self, s, option)

    def wont_no_false(self, state, option):
        # He is unilaterally demanding that an already-disabled option be/remain disabled.
        # Ignore this (although we could record it and refuse subsequent enable attempts
        # from our side - he can always refuse them again though, so we won't)
        pass

    def wont_no_true(self, state, option):
        # Peer refused to enable an option in response to our request.
        state.him.negotiating = False
        d = state.him.onResult
        state.him.onResult = None
        d.errback(OptionRefused(option))

    def wont_yes_false(self, state, option):
        # Peer is unilaterally demanding that an option be disabled.
        state.him.state = 'no'
        self.disableRemote(option)
        self._dont(option)

    def wont_yes_true(self, state, option):
        # Peer agreed to disable an option at our request.
        state.him.state = 'no'
        state.him.negotiating = False
        d = state.him.onResult
        state.him.onResult = None
        d.callback(True)
        self.disableRemote(option)

    wontMap = {('no', False): wont_no_false,   ('no', True): wont_no_true,
               ('yes', False): wont_yes_false, ('yes', True): wont_yes_true}

    def telnet_DO(self, option):
        s = self.getOptionState(option)
        self.doMap[s.us.state, s.us.negotiating](self, s, option)

    def do_no_false(self, state, option):
        # Peer is unilaterally requesting that we enable an option.
        if self.enableLocal(option):
            state.us.state = 'yes'
            self._will(option)
        else:
            self._wont(option)

    def do_no_true(self, state, option):
        # Peer agreed to allow us to enable an option at our request.
        state.us.state = 'yes'
        state.us.negotiating = False
        d = state.us.onResult
        state.us.onResult = None
        d.callback(True)
        self.enableLocal(option)

    def do_yes_false(self, state, option):
        # Peer is unilaterally requesting us to enable an already-enabled option.
        # Ignore this.
        pass

    def do_yes_true(self, state, option):
        # This is a bogus state.  It is here for completeness.  It will never be
        # entered.
        assert False, "do_yes_true can never be entered, but was called with %r, %r" % (state, option)

    doMap = {('no', False): do_no_false,   ('no', True): do_no_true,
             ('yes', False): do_yes_false, ('yes', True): do_yes_true}

    def telnet_DONT(self, option):
        s = self.getOptionState(option)
        self.dontMap[s.us.state, s.us.negotiating](self, s, option)

    def dont_no_false(self, state, option):
        # Peer is unilaterally demanding us to disable an already-disabled option.
        # Ignore this.
        pass

    def dont_no_true(self, state, option):
        # This is a bogus state.  It is here for completeness.  It will never be
        # entered.
        assert False, "dont_no_true can never be entered, but was called with %r, %r" % (state, option)


    def dont_yes_false(self, state, option):
        # Peer is unilaterally demanding we disable an option.
        state.us.state = 'no'
        self.disableLocal(option)
        self._wont(option)

    def dont_yes_true(self, state, option):
        # Peer acknowledged our notice that we will disable an option.
        state.us.state = 'no'
        state.us.negotiating = False
        d = state.us.onResult
        state.us.onResult = None
        d.callback(True)
        self.disableLocal(option)

    dontMap = {('no', False): dont_no_false,   ('no', True): dont_no_true,
               ('yes', False): dont_yes_false, ('yes', True): dont_yes_true}

    def enableLocal(self, option):
        return self.protocol.enableLocal(option)

    def enableRemote(self, option):
        return self.protocol.enableRemote(option)

    def disableLocal(self, option):
        return self.protocol.disableLocal(option)

    def disableRemote(self, option):
        return self.protocol.disableRemote(option)

class ProtocolTransportMixin:
    def write(self, bytes):
        self.transport.write(bytes.replace('\n', '\r\n'))

    def writeSequence(self, seq):
        self.transport.writeSequence(seq)

    def loseConnection(self):
        self.transport.loseConnection()

    def getHost(self):
        return self.transport.getHost()

    def getPeer(self):
        return self.transport.getPeer()

class TelnetTransport(Telnet, ProtocolTransportMixin):
    """
    @ivar protocol: An instance of the protocol to which this
    transport is connected, or None before the connection is
    established and after it is lost.

    @ivar protocolFactory: A callable which returns protocol instances
    which provide ITelnetProtocol.  This will be invoked when a
    connection is established.  It is passed *protocolArgs and
    **protocolKwArgs.

    @ivar protocolArgs: A tuple of additional arguments to
    pass to protocolFactory.

    @ivar protocolKwArgs: A dictionary of additional arguments
    to pass to protocolFactory.
    """

    disconnecting = False

    protocolFactory = None
    protocol = None

    def __init__(self, protocolFactory=None, *a, **kw):
        Telnet.__init__(self)
        if protocolFactory is not None:
            self.protocolFactory = protocolFactory
            self.protocolArgs = a
            self.protocolKwArgs = kw

    def connectionMade(self):
        if self.protocolFactory is not None:
            self.protocol = self.protocolFactory(*self.protocolArgs, **self.protocolKwArgs)
            assert ITelnetProtocol.providedBy(self.protocol)
            try:
                factory = self.factory
            except AttributeError:
                pass
            else:
                self.protocol.factory = factory
            self.protocol.makeConnection(self)

    def connectionLost(self, reason):
        Telnet.connectionLost(self, reason)
        if self.protocol is not None:
            try:
                self.protocol.connectionLost(reason)
            finally:
                del self.protocol

    def enableLocal(self, option):
        return self.protocol.enableLocal(option)

    def enableRemote(self, option):
        return self.protocol.enableRemote(option)

    def disableLocal(self, option):
        return self.protocol.disableLocal(option)

    def disableRemote(self, option):
        return self.protocol.disableRemote(option)

    def unhandledSubnegotiation(self, command, bytes):
        self.protocol.unhandledSubnegotiation(command, bytes)

    def unhandledCommand(self, command, argument):
        self.protocol.unhandledCommand(command, argument)

    def applicationDataReceived(self, bytes):
        self.protocol.dataReceived(bytes)

    def write(self, data):
        ProtocolTransportMixin.write(self, data.replace('\xff','\xff\xff'))


class TelnetBootstrapProtocol(TelnetProtocol, ProtocolTransportMixin):
    implements()

    protocol = None

    def __init__(self, protocolFactory, *args, **kw):
        self.protocolFactory = protocolFactory
        self.protocolArgs = args
        self.protocolKwArgs = kw

    def connectionMade(self):
        self.transport.negotiationMap[NAWS] = self.telnet_NAWS
        self.transport.negotiationMap[LINEMODE] = self.telnet_LINEMODE

        for opt in (LINEMODE, NAWS, SGA):
            self.transport.do(opt).addErrback(log.err)
        for opt in (ECHO,):
            self.transport.will(opt).addErrback(log.err)

        self.protocol = self.protocolFactory(*self.protocolArgs, **self.protocolKwArgs)

        try:
            factory = self.factory
        except AttributeError:
            pass
        else:
            self.protocol.factory = factory

        self.protocol.makeConnection(self)

    def connectionLost(self, reason):
        if self.protocol is not None:
            try:
                self.protocol.connectionLost(reason)
            finally:
                del self.protocol

    def dataReceived(self, data):
        self.protocol.dataReceived(data)

    def enableLocal(self, opt):
        if opt == ECHO:
            return True
        elif opt == SGA:
            return True
        else:
            return False

    def enableRemote(self, opt):
        if opt == LINEMODE:
            self.transport.requestNegotiation(LINEMODE, MODE + chr(TRAPSIG))
            return True
        elif opt == NAWS:
            return True
        elif opt == SGA:
            return True
        else:
            return False

    def telnet_NAWS(self, bytes):
        # NAWS is client -> server *only*.  self.protocol will
        # therefore be an ITerminalTransport, the `.protocol'
        # attribute of which will be an ITerminalProtocol.  Maybe.
        # You know what, XXX TODO clean this up.
        if len(bytes) == 4:
            width, height = struct.unpack('!HH', ''.join(bytes))
            self.protocol.terminalProtocol.terminalSize(width, height)
        else:
            log.msg("Wrong number of NAWS bytes")


    linemodeSubcommands = {
        LINEMODE_SLC: 'SLC'}
    def telnet_LINEMODE(self, bytes):
        revmap = {}
        linemodeSubcommand = bytes[0]
        if 0:
            # XXX TODO: This should be enabled to parse linemode subnegotiation.
            getattr(self, 'linemode_' + self.linemodeSubcommands[linemodeSubcommand])(bytes[1:])

    def linemode_SLC(self, bytes):
        chunks = zip(*[iter(bytes)]*3)
        for slcFunction, slcValue, slcWhat in chunks:
            # Later, we should parse stuff.
            'SLC', ord(slcFunction), ord(slcValue), ord(slcWhat)
backwardsCompatImplements(TelnetBootstrapProtocol)

from twisted.protocols import basic

class StatefulTelnetProtocol(basic.LineReceiver, TelnetProtocol):
    delimiter = '\n'

    state = 'Discard'

    def connectionLost(self, reason):
        basic.LineReceiver.connectionLost(self, reason)
        TelnetProtocol.connectionLost(self, reason)

    def lineReceived(self, line):
        oldState = self.state
        newState = getattr(self, "telnet_" + oldState)(line)
        if newState is not None:
            if self.state == oldState:
                self.state = newState
            else:
                log.msg("Warning: state changed and new state returned")

    def telnet_Discard(self, line):
        pass

from twisted.cred import credentials

class AuthenticatingTelnetProtocol(StatefulTelnetProtocol):
    """A protocol which prompts for credentials and attempts to authenticate them.

    Username and password prompts are given (the password is obscured).  When the
    information is collected, it is passed to a portal and an avatar implementing
    ITelnetProtocol is requested.  If an avatar is returned, it connected to this
    protocol's transport, and this protocol's transport is connected to it.
    Otherwise, the user is re-prompted for credentials.
    """

    state = "User"
    protocol = None

    def __init__(self, portal):
        self.portal = portal

    def connectionMade(self):
        self.transport.write("Username: ")

    def connectionLost(self, reason):
        StatefulTelnetProtocol.connectionLost(self, reason)
        if self.protocol is not None:
            try:
                self.protocol.connectionLost(reason)
                self.logout()
            finally:
                del self.protocol, self.logout

    def telnet_User(self, line):
        self.username = line
        self.transport.will(ECHO)
        self.transport.write("Password: ")
        return 'Password'

    def telnet_Password(self, line):
        username, password = self.username, line
        del self.username
        def login(ignored):
            creds = credentials.UsernamePassword(username, password)
            d = self.portal.login(creds, None, ITelnetProtocol)
            d.addCallback(self._cbLogin)
            d.addErrback(self._ebLogin)
        self.transport.wont(ECHO).addCallback(login)
        return 'Discard'

    def _cbLogin(self, ial):
        interface, protocol, logout = ial
        assert interface is ITelnetProtocol
        self.protocol = protocol
        self.logout = logout
        self.state = 'Command'

        protocol.makeConnection(self.transport)
        self.transport.protocol = protocol

    def _ebLogin(self, failure):
        self.transport.write("\nAuthentication failed\n")
        self.transport.write("Username: ")
        self.state = "User"

__all__ = [
    # Exceptions
    'TelnetError', 'NegotiationError', 'OptionRefused',
    'AlreadyNegotiating', 'AlreadyEnabled', 'AlreadyDisabled',

    # Interfaces
    'ITelnetProtocol', 'ITelnetTransport',

    # Other stuff, protocols, etc.
    'Telnet', 'TelnetProtocol', 'TelnetTransport',
    'TelnetBootstrapProtocol',

    ]
