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      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
    110