telnet.py   [plain text]

# Twisted, the Framework of Your Internet
# Copyright (C) 2001 Matthew W. Lefkowitz
# 
# This library is free software; you can redistribute it and/or
# modify it under the terms of version 2.1 of the GNU Lesser General Public
# License as published by the Free Software Foundation.
# 
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
# 
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""TELNET implementation, with line-oriented command handling.
"""


# System Imports
try:
    from cStringIO import StringIO
except ImportError:
    from StringIO import StringIO

# Twisted Imports
from twisted import copyright
from twisted.python import log, failure
from twisted.internet import protocol

# Some utility chars.
ESC =            chr(27) # ESC for doing fanciness
BOLD_MODE_ON =   ESC+"[1m" # turn bold on
BOLD_MODE_OFF=   ESC+"[m"  # no char attributes


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

NULL =            chr(0)  # No operation.
LF   =           chr(10)  # Moves the printer to the
                          # next print line, keeping the
                          # same horizontal position.
CR =             chr(13)  # Moves the printer to the left
                          # margin of the current line.
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.
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.
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.

# features

ECHO  =           chr(1)  # User-to-Server:  Asks the server to send
                          # Echos of the transmitted data.

                          # Server-to User:  States that the server is
                          # sending echos of the transmitted data.
                          # Sent only as a reply to ECHO or NO ECHO.

SUPGA =           chr(3)  # Supress Go Ahead...? "Modern" telnet servers
                          # are supposed to do this.

LINEMODE =       chr(34)  # I don't care that Jon Postel is dead.

HIDE  =         chr(133)  # The intention is that a server will send
                          # this signal to a user system which is
                          # echoing locally (to the user) when the user
                          # is about to type something secret (e.g. a
                          # password).  In this case, the user system
                          # is to suppress local echoing or overprint
                          # the input (or something) until the server
                          # sends a NOECHO signal.  In situations where
                          # the user system is not echoing locally,
                          # this signal must not be sent by the server.


NOECHO=         chr(131)  # User-to-Server:  Asks the server not to
                          # return Echos of the transmitted data.
                          # 
                          # Server-to-User:  States that the server is
                          # not sending echos of the transmitted data.
                          # Sent only as a reply to ECHO or NO ECHO,
                          # or to end the hide your input.



iacBytes = {
    DO:   'DO',
    DONT: 'DONT',
    WILL: 'WILL',
    WONT: 'WONT',
    IP:   'IP'
    }

def multireplace(st, dct):
    for k, v in dct.items():
        st = st.replace(k, v)
    return st

class Telnet(protocol.Protocol):
    """I am a Protocol for handling Telnet connections. I have two
    sets of special methods, telnet_* and iac_*.

    telnet_* methods get called on every line sent to me. The method
    to call is decided by the current mode. The initial mode is 'User';
    this means that telnet_User is the first telnet_* method to be called.
    All telnet_* methods should return a string which specifies the mode
    to go into next; thus dictating which telnet_* method to call next.
    For example, the default telnet_User method returns 'Password' to go
    into Password mode, and the default telnet_Password method returns
    'Command' to go into Command mode.

    The iac_* methods are less-used; they are called when an IAC telnet
    byte is received. You can define iac_DO, iac_DONT, iac_WILL, iac_WONT,
    and iac_IP methods to do what you want when one of these bytes is
    received."""


    gotIAC = 0
    iacByte = None
    lastLine = None
    buffer = ''
    echo = 0
    delimiters = ['\r\n', '\r\000']
    mode = "User"

    def write(self, data):
        """Send the given data over my transport."""
        self.transport.write(data)


    def connectionMade(self):
        """I will write a welcomeMessage and loginPrompt to the client."""
        self.write(self.welcomeMessage() + self.loginPrompt())

    def welcomeMessage(self):
        """Override me to return a string which will be sent to the client
        before login."""
        x = self.factory.__class__
        return ("\r\n" + x.__module__ + '.' + x.__name__ +
                '\r\nTwisted %s\r\n' % copyright.version
                )

    def loginPrompt(self):
        """Override me to return a 'login:'-type prompt."""
        return "username: "

    def iacSBchunk(self, chunk):
        pass

    def iac_DO(self, feature):
        pass

    def iac_DONT(self, feature):
        pass

    def iac_WILL(self, feature):
        pass

    def iac_WONT(self, feature):
        pass

    def iac_IP(self, feature):
        pass

    def processLine(self, line):
        """I call a method that looks like 'telnet_*' where '*' is filled
        in by the current mode. telnet_* methods should return a string which
        will become the new mode.  If None is returned, the mode will not change.
        """
        mode = getattr(self, "telnet_"+self.mode)(line)
        if mode is not None:
            self.mode = mode

    def telnet_User(self, user):
        """I take a username, set it to the 'self.username' attribute,
        print out a password prompt, and switch to 'Password' mode. If
        you want to do something else when the username is received (ie,
        create a new user if the user doesn't exist), override me."""
        self.username = user
        self.write(IAC+WILL+ECHO+"password: ")
        return "Password"

    def telnet_Password(self, paswd):
        """I accept a password as an argument, and check it with the
        checkUserAndPass method. If the login is successful, I call
        loggedIn()."""
        self.write(IAC+WONT+ECHO+"*****\r\n")
        try:
            checked = self.checkUserAndPass(self.username, paswd)
        except:
            return "Done"
        if not checked:
            return "Done"
        self.loggedIn()
        return "Command"

    def telnet_Command(self, cmd):
        """The default 'command processing' mode. You probably want to
        override me."""
        return "Command"

    def processChunk(self, chunk):
        """I take a chunk of data and delegate out to telnet_* methods
        by way of processLine. If the current mode is 'Done', I'll close
        the connection. """
        self.buffer = self.buffer + chunk

        #yech.
        for delim in self.delimiters:
            idx = self.buffer.find(delim)
            if idx != -1:
                break
            
        while idx != -1:
            buf, self.buffer = self.buffer[:idx], self.buffer[idx+2:]
            self.processLine(buf)
            if self.mode == 'Done':
                self.transport.loseConnection()

            for delim in self.delimiters:
                idx = self.buffer.find(delim)
                if idx != -1:
                    break

    def dataReceived(self, data):
        chunk = StringIO()
        # silly little IAC state-machine
        for char in data:
            if self.gotIAC:
                # working on an IAC request state
                if self.iacByte:
                    # we're in SB mode, getting a chunk
                    if self.iacByte == SB:
                        if char == SE:
                            self.iacSBchunk(chunk.getvalue())
                            chunk = StringIO()
                            del self.iacByte
                            del self.gotIAC
                        else:
                            chunk.write(char)
                    else:
                        # got all I need to know state
                        try:
                            getattr(self, 'iac_%s' % iacBytes[self.iacByte])(char)
                        except KeyError:
                            pass
                        del self.iacByte
                        del self.gotIAC
                else:
                    # got IAC, this is my W/W/D/D (or perhaps sb)
                    self.iacByte = char
            elif char == IAC:
                # Process what I've got so far before going into
                # the IAC state; don't want to process characters
                # in an inconsistent state with what they were
                # received in.
                c = chunk.getvalue()
                if c:
                    why = self.processChunk(c)
                    if why:
                        return why
                    chunk = StringIO()
                self.gotIAC = 1
            else:
                chunk.write(char)
        # chunks are of a relatively indeterminate size.
        c = chunk.getvalue()
        if c:
            why = self.processChunk(c)
            if why:
                return why

    def loggedIn(self):
        """Called after the user succesfully logged in.
        
        Override in subclasses.
        """
        pass