1 #! /usr/bin/env python

     2 

     3 # Minimal interface to the Internet telnet protocol.

     4 #

     5 # It refuses all telnet options and does not recognize any of the other

     6 # telnet commands, but can still be used to connect in line-by-line mode.

     7 # It's also useful to play with a number of other services,

     8 # like time, finger, smtp and even ftp.

     9 #

    10 # Usage: telnet host [port]

    11 #

    12 # The port may be a service name or a decimal port number;

    13 # it defaults to 'telnet'.

    14 

    15 

    16 import sys, posix, time

    17 from socket import *

    18 

    19 BUFSIZE = 1024

    20 

    21 # Telnet protocol characters

    22 

    23 IAC  = chr(255) # Interpret as command

    24 DONT = chr(254)

    25 DO   = chr(253)

    26 WONT = chr(252)

    27 WILL = chr(251)

    28 

    29 def main():

    30     host = sys.argv[1]

    31     try:

    32         hostaddr = gethostbyname(host)

    33     except error:

    34         sys.stderr.write(sys.argv[1] + ': bad host name\n')

    35         sys.exit(2)

    36     #

    37     if len(sys.argv) > 2:

    38         servname = sys.argv[2]

    39     else:

    40         servname = 'telnet'

    41     #

    42     if '0' <= servname[:1] <= '9':

    43         port = eval(servname)

    44     else:

    45         try:

    46             port = getservbyname(servname, 'tcp')

    47         except error:

    48             sys.stderr.write(servname + ': bad tcp service name\n')

    49             sys.exit(2)

    50     #

    51     s = socket(AF_INET, SOCK_STREAM)

    52     #

    53     try:

    54         s.connect((host, port))

    55     except error, msg:

    56         sys.stderr.write('connect failed: ' + repr(msg) + '\n')

    57         sys.exit(1)

    58     #

    59     pid = posix.fork()

    60     #

    61     if pid == 0:

    62         # child -- read stdin, write socket

    63         while 1:

    64             line = sys.stdin.readline()

    65             s.send(line)

    66     else:

    67         # parent -- read socket, write stdout

    68         iac = 0         # Interpret next char as command

    69         opt = ''        # Interpret next char as option

    70         while 1:

    71             data = s.recv(BUFSIZE)

    72             if not data:

    73                 # EOF; kill child and exit

    74                 sys.stderr.write( '(Closed by remote host)\n')

    75                 posix.kill(pid, 9)

    76                 sys.exit(1)

    77             cleandata = ''

    78             for c in data:

    79                 if opt:

    80                     print ord(c)

    81                     s.send(opt + c)

    82                     opt = ''

    83                 elif iac:

    84                     iac = 0

    85                     if c == IAC:

    86                         cleandata = cleandata + c

    87                     elif c in (DO, DONT):

    88                         if c == DO: print '(DO)',

    89                         else: print '(DONT)',

    90                         opt = IAC + WONT

    91                     elif c in (WILL, WONT):

    92                         if c == WILL: print '(WILL)',

    93                         else: print '(WONT)',

    94                         opt = IAC + DONT

    95                     else:

    96                         print '(command)', ord(c)

    97                 elif c == IAC:

    98                     iac = 1

    99                     print '(IAC)',

   100                 else:

   101                     cleandata = cleandata + c

   102             sys.stdout.write(cleandata)

   103             sys.stdout.flush()

   104 

   105 

   106 try:

   107     main()

   108 except KeyboardInterrupt:

   109     pass